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Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section I-Introduction SECOND EDITION, MAY 1998 This material is electronically reproduced by CSSinfo, (734) 930-9277, www.cssinfo.com. No part of the printed publication, nor any part of this electronic file may be reproduced or transmitted in any form, including transmittal by e-mail, by file transfer protocol (FTP), or by being made part of a network-accessible system, without the prior written permission of the Publisher, American Petroleum Institute, 1220 L Street, NW, Washington, D.C. 20005.

American Petroleum Institute Helping You Get The Job Done RightSM

Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 1-Introduction Measurement Coordination SECOND EDITION, MAY 1998

American Petroleum Institute Helping You Get The Job Dona Right?

SPECIAL NOTES

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panicAH pub]icalions nmsari]y address problems of a general nature. With E ~ P ~ u f ~ c i ~ u m s ~ local, a n c slate, ~ , and federal laws and regulations should be " API is no, undertaking to meet the duties of efnp10yerS, manufacture*, Or warn and property train and equip their employees, and ochers exposed, and safety risks and precautions, nor undertaking their ob1igations under local, state*Or federal laws. Information concerning safety and health risks and proper precautions with lCspect to Particular materials and conditions should be obtained from the employer, the manufacturer Or supplier of that material, or the material safety data sheet. granting any right, by Nothing contained in any API publication is to be construed i~nplicationor otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered hy letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letlers paleat. Generally,API standards are reviewed and revised, reaffirmed, or withdrawn at least every five yews. Sometimes a one-time extension d up 1.0two years will be added to this review cycle. This publication will no longer be in effect five years after its publication date as an operative API standard or, where an extension has been granted, upon republication. Status of the publication can be ascertained from the API Measurement Coordination Department [telephone (202) 682-8000]. A catalog of API publications and materials is published annually and updated qualzerly by API, 1220L Street, N.W., Washington, D.C. 20005. This document was produced under API sfnndardization procedures bat ensure appropriate notification and participation in the dcvelopmenial process and is designated as an API standard. Questions concerning the interpretation of the content of this standard or comments and questions concerning the procedures under which this standard was developed should be directed in writing to the director of the Measurement Coordination Department (shown on the title page of this document), American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published hcrein should also be addressed to the director. API standards are published to facilitate the broad availability of proven, sound engineering and operating p~actices.These standards are not intended to obvinte the need for applying sound engineering judgment regarding when and where these standards should be utilized. The formulation and publication of API standards is not intended in any way to inhibit anyone from using any other practices. Any manufacturer markhg equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not rcprasent, warrant, or guarantee that such products do in fact conform to the applicableAPI standard.

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FOREWORD Chapler 4 of the Manual of Petf~leutnMewurenle,lt Sra~tdatziswas prepared as a guide for the design, installalion, calibration, and operation of lneter proving systems co~nmonly used by the majorily of pctroleuin operators. The devices and practices covered in this chaptcr may not be applicable to all liquid hydrocarbons under all operating conditions. Other types d proving devices that are not covered in this chapter inay be appropriate for use if agreed on by the parties involved. The infor~nationcontained in this edition of Chapter 4 supersedes the information containcd in the previous edition (First Edition, May 39783, which is no longer in print. It also supersedes the information on proving systems contained in API Standard 1 101, Meusurenzetllr of Petroleum Liquid Hydrocarbotu by I'ositive Displucenlent Meter (First Edition, 1960); API Standard 253 1, Mecl~aniculDisplacement Meter Provers; API Standard 2533, Metering Viscous Nj~drocarbons;and API Standard 2534, Measuretneni of Liquid Hydmcarbons by 7itrbir1e-MeterSystems, which na no longer in print. This publico~ioiijs primarily intended for use in thc Unitcd States and is rclated to the standards, specifications, aiid procedures of the National Institute of Standards and Technology (NIST). When the information provided herein is used in other countries, the specifications and praccdures of the appropriate national standards organizatio~lsmay apply. Wherc appropriate, other test codes and procedures far chccking pressure and electrical equipment may be used. are For the purposes of business traasactions, limits on e-r or measurement tolcra~~ce usually set by law, regulation, or mutual agreement between contracling parties. This publication is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved. Chapter 4 now contains the following sections: Section 3-"Introduction" Section 2-"Conventional Pipe Provers" Scction 3-"Smdl Volume Provers" Section W ' T a n k Provers" Section 5-"Master-Meter Provers" Section t+"Pulse Inte~polation" Scction 7-"Field-Standard Test Measures" Section 8-"Operation of Proving Systems"

API publjcati,onsmay be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy nnd reliability of the data contained in them; however, the 'Institute inakes r1o represenlalion, warranty, or guaranlcc in connection with this publication and hereby expressly.disclaimsany liability or responsibility for loss or damage resulting f~umits use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted to the director of the Measurement Coordination Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C.20005.

CONTENTS Page

SECTION 1-INTRODUCTION 1

SCOPE ............................................................... 1

2

REFERENCED PUBLICATIONS......................................... 1

3

DEFINITION OF TERMS ............................................... 1

4

LIQUID METERING HIERARCHIES .....................................1 4.1 Overview of Hierarchy .............................................1 4.2 Uncc~rajntyLimits Within the Hierarchy ...............................2

5

PROVING AND METER FACTOR 3 5.1 General Considerations 3 . 5.2 Objectives 3 5.3 Procedures .......................................................3 5.4 Proving Technique .................................................3 ;........ 4 5.5 Accuracy ............................................... 5.6 Multiple Meters 4

6

7

....................................... .............................................. ........................................................

................................................... TYPES OF PROVERS ..................................................4 6.1 Conventional Pipe Provers........................................... 4 6 3 Small Volume Provers .............................................. 4 6.3 Tank Provers.....................................................; 4 6.4 Master-MeterProvers .............................................. 4 FIELD-STANDARDTEST MEASURE ....................................4

IIhbles General Liquid Metering Hierarchy Levels 1 2 Uncertainty 111dicesfor General Liquid Metering Hierarchy Hypothetical Annual Uncertainty Limits in General 3 Liquid Metering Hierarchy

...............................I ..................2 ........................................... 2 ;

Chapter 4-Proving

Systems

Section I-Introduction 1 Scope

3.7 prover round trip: The forward and.reversepasses in a bi-directional prover.

Chapter 1 is a general introduction to the subject of proving. The rcquircments in Chapter 4 are based on customary pmctices thit evolved for the-crude oils covered by Table 6~ and the products covered by Table 6B in Chapter 1 1.1, The prover and meter uncertainties sl~ouldbe appropriate for the measured -fluidsand should be agreeable to the parties involvd.

3.8 shall: Uscd throughout Chaptw 4 for situations in which a deviation kern the recommended practice is likely to adversely affect measulcment. 3.9 standard conditions: 6OoF(15"C) and atmospheric pressure.

2 Referenced Publications

4 Liquid Merer~ngnlerilrcnies

Scvcral documents sewed as references and as a resource of information in the revision of this standard. Manual of PerroIeum Measurement Stanhnis Chapter 1-"Vocabularyy' Chapter 4--"Provjng Syste~ns" Chapter 5-'Metering" Chapter 7-'Temperature Determination" Chapter 11.1-"Physical Properties Data" Chapter 12-"Calculation of Pclroleum Quantities" Chapter 13-"Statistical Aspects of Measuring and Sampling"

4.1 OVERVIEW OF HIERARCHY Liquid mctcring systems for custody lransfer and other measurement activities pcrfmed in conformance of API's Manual ofPet~oleum. Measurement Standards typically have at least the following levels in its hierarchy as shown in Table 1. Table 1-General Liquid Meterjng Hierarchy Levels

Levels 1

2 3 4 5 6 7

3 Definition of Terms Terms used in this chapter are defined in 3.1 through 3.9. 3.1 calibration: The procedure used to determine the volume of a pmver.

Level I. Primary Standards involve mass, volume, andlor density standards developed and/or maintained by National Institute of Standards and Tecl~nology(NIST)andlor other national laboratories to calibrate secondary working standards. Level 2. Secondary Working Standards include mass, volume, density, andlor weighing systems maintained by NIST and/or other national laboratories to calibrate field transfer standards conforming to Chapter 4.7. Secondary Working Standards may also be maintained by state and other certified metrology laboratories to calibrate field transfer standards. These additional secondary working standards, however, increase uncertainty in the final custody transfer quantities. Level 3. Field Transfer Standards conforming to Chapter 4.7 are devices used to calibrate meter provers conforming to Chapters 4.2,4.3, and 4.4. Level 4. Meter provers conforming to Chapter 4 are used to determine meter factors that correct the indicated volumes d meters L v e l s 5,6, dl 7. Compositional anaiyses. where appropriate, together with the meter factor, is used to make cotrections in the quality andlor quantity of the indicated volume of the

3.2 meter proof: The multiple passes or round trips of the displacer in a prover for purposes of determining a meter factor.

3.3 meter prover: An open or closed vesscl of known volume that is used as a volumetrjc reference standard for the calibration of meters in liquid petrdoum service. Such provers arc designed, fabl'icated, and operated within the recommendations of Chapter 4. . 3.4

~escriptionof Hierarchy Level Primary Standards SecondaryWorking Standards Field Standard Test Measures Meter Prover Meter Assembly (indicated volume) Corrections for Quality andlor Quantity Custody Transfer Ticket (net standard volume)

meter pulse: A single electrical pulse generated by

flow induced effects in the meter. The flow induced effects are normally caused by rnove~nentof physical elements within the meter's primary now element but may be caused by other flow induced effects that are proportional to flow rate. The pulses produced by the meter shall not be multiplied to increase the number of pulses to confor~nlo the require~nents of Chapter 4.

3.5 proving: The procedure used to determine a meter factor.

3.6 prover pass: One movenlcnt of the displacer between the detectors in a prover. I

meter, to determine the net standad volume being inetered for custody transfer purposes. Whcti practical, the number of levels in a hicmrchy should be kept to a mini~nu~n to keep uncertainty low. Each level in the hierarchy will incitasc the uncertainty of subsequent levels and eventually the final custody transfer quantity. 4.2 UNCERTAINTY LIMITS WITHIN THE HIERARCHY Each level within a hierarchy will include all the errors and ul~ccrtaintiesfrom the p~eviousor higher levels of the hierarchy. Therefore, uncertainties will always incease throughout each level of thc hierarchy. Exact, defined, and rigorous proccdures must be developed imd followed exactly through each level of a hierarchy so that the uncertainty in thc final level of the hierarchy is not higher than specified and still tolerable for commercial purposes. For levels in the hierarchy that exhibit randomness because of the intrinsic random nature of the activity or equipment, error or uncertainty limits mav be limited to twice or slightly less of the unccrtainty in previous level in the hierarchy. For levels that are perlbrrned infrequently in the hierarchy, such as primary standards, the next level in the hierarchy, such as secondary working standards, may have uncertainty limits that are up to four times the previous level in the hierarchy. In the general hicrarchy shown in Table 2, unccrtainty indices are used to indicate the ratio of uncertainty of one level co~~ipared to the primary standard.

The effects of time should also be included in establishing limits wjthin a hierarchy. Most custody transfer contracts or arrangements are in cffcct for years between two or more parties; therefom, the effects of random uncertainties to propagate to lower average values with time should be considered. Frequently, repeated activities may have uncertainty limits that are closer to the adjacent level in the hierarchy if rigorous procedures are developed and implemented that minimize additional uncertainties. In the hierarchy of Table 2, the uncertainty index for meter indicated volume and corrections for quantity, such as the meter factors, can be lower than indicated in Table 2. Alr unccrtainty index of 16 to 24 or lower can be obtainable over the period of a year or longer. A lower unccrtaitity index over time for the custody transfer ticket of 32 to 48 is also obtainable from rigorous and frequently performed activities. If the uncertainty limit for the average of a custody transfer over one year is prescribed as 0.10%, the corresponding uncertainty limits for each of the levels in the hierarchy would be found in Table 3. Within each of the hierarchy there are other activities that are sources of error that must be identified and limited so that they do not disrupt the integrity of the hierarchy. These activities include procedures for calibrating the secondary working standards, field transfer standards, and meter provers. Rigorous procedures must be developed and followed so that these additional sources of uncertainties do not disrupt the uncertainty control within the hierarchy.

*

Table 2-Uncertainty Indices for General Liquid Metering Hierarchy Uncertainty Indices Level

I 2 3

4 5 6 7

Description of Hierarchy Level Primary Standards Secondaq Working Standards PiddTransfer Standards Meter Prover Base Volume Meter IndicatedVolurne

Correction for Quality andlor Quantity Custody Transfer Ticket

Table 3-Hypothetical hml 1

2 3 4 5

6 7

Per Event

Average with Time

1

1 2 to 4

2 to4

4to16 8 to 32 16 to 64 32t0 128

64to 256

4to8 8 to 16 16 1064 24 10 32 32 to 48

Annual Uncertainty Limits in General Liquid Mstering Hierarchy

Description of Hierarchy Level Priinary Standards Secondary Working Standards Field Transfer Standards Meter Prover Base Volume Meter Indicated Volume Correctiotl for Quality ~ n d l oQuantity r Custody 'IkansfcrlEcket

Uncertainty Limit, + or- % Per Event Per Year Ob002

0.002 0.005 0.015 0.03 0.05

0.005 0.01 5 0.03 0.10 0.15

0.07

0.20

0.10

5 Proving and Meter Factor purpasc of provinga meter is lo determine its m

r

fact^ which is the numbor obtained by dividing the actual volume of liquid passed through a meter during proving by the volume registered by the nleter The purpose of a meter factor is to correct a meter's indicated volume. Obtaining a meter factor is an essential step in calculating the net standard volu~neof a receipt or delivery of petroleum liquids. Because all cdculations involve one or more corrections, and because the computation of numerous correction factors can lead to small differences if the computations are not carried out in a standard way, the calculations of petroleum quantities in dynamic measurement is covered in API MPMS Chapter 12.2. Refer to Chapter 12.2 whenever one or more of the following items must be calculated: a. Volumes in the provers. b. Meter factors.

c. Measurement tickets. 5.1

GENERAL CONSIDERATIONS

A meter that requires flow conditioning should be proved with its normal flow-conditioning sections. A11 meters should be proved with the liquid to be measured and at the operating flowlate, pressure, and temperature. If the meter cannol be proved with the liquid to be measured, it should be proved with a liquid that has a density (API gravity) and viscosity as close as possible to that of the liquid to be measured and is known to give comparable results. A meter that is used to rncasun: several different liquids should be proved with each liquid. Meter proving must be pcrforrned with a high degree of accuracy.'The many details of the meter, its auxiliary equip ment, and the plmovjngsystem can contribute to measurement uncertainty. Likewise, there are difficulties in determining the physical properties of the measured Iiquid, pressure, temperature, and the presence of trapped air. Thorough inspections of provers and their appurtenances should be made frequently to cnsure the reproducibility of proving results. Meter-proving data must be observed, recorded, and studied, and calculations must be correct. See API MPMSChapters 12 and 13 for applicable methods.

5.2 OBJECTIVES Meter proving has two general objectives depending on the type of service. A meter may bc proved to adjust its registration, if necessary, to give a meter factor as close to 1.0000 (unity) as practical. The meter's indicated volume will be the volume of liquid actually delivered (gross volume) within allowable tolerances. Tliis is the normal practice for meters that operate on intermittent deliveries, such as tank-tntck meters or loading-rack meters at terminals or bulk plants.

Alternatively, a meter may be proved to dcter~nineits meter factor (an expression of meter performance).The meter faclor is applied to the indicated volume to compute the volume that is delivaed *rough tile meter, m i s is normal practice operations. pipe,ine and oil

far

5.3 ~ROCEDURES

Meter proving can be classified according to the following procedu~s:

a. The standing stan-and-stop procedure uses the meter register, or counter, from which the opening and closing readings are obtained at no-flow conditions. If the flow is started too rapidly, pressure in the piping may momentarily fall below the vapor pressure of the liquid, causing some vapor to pass through the meter. Thc result may be damage to the meter and over-registration of indicated flow. Too rapid a change of liquid velocity may cause hydraulic shock. b. The running start-and-stop procedure requires that the opening and closing meter readings of the proof be obtained while the meter is in operation. This is accomplished by using an auxiliary or a secondary register or counter of high discrimination that may be started and stopped while the meter and primary register continue to operate. If the line meter proving registration is derived from something other than the meter register, steps shall bhc taken to ensure that all volumcs indicated by the proving counter are also reflected in the meter register. 5.4

PROVING TECHNIQUE

Meter proofs should be made with the same read-out equipment that is used in regular operation or with additional auxiliary readouts, or counters, that meet the requirements in API MPMS Chapter 4.8. If it is used, auxiliary equipment such as gravity selectors, temperature compensators, pressure and temperature instrumcnlation, and quantity-predetermining registers or computers should be set and operative while meter proofs are being made. T i e intervals between prover passes should be kept to a practical minimum.

5.4.1 Prellmlnary Proof Runs Before a meter is proved, a preliminary unrecorded pass or passes should be made to stabilize temperatures, pressures, and flowratc; displace vapors or gases; and wet the interior of the prover. Tempera1ui-e and pressure measuring instruments should be checked periodically against appropriate standards and calibrated, or replaced, as applicable. 5.4.2

Provtng for Meter Adjustments

The tneter registration may be adjusted after each proving to carrect the indicated volume. Proving and required adjustincnts should be conthlued until consecutive results demon-

,

4

CHAPTER 4--PRO

strate that the meter register is indicaling a dclivercd volume that is within the desired accuracy tolerance. 5.4.3

Proving to Determine Meter Factor

When a meter is provcd to determine the meter factor, no adjustments are madc to the meter's registration. Meter proofs are made and recorcled until thc required nu~liberrepeats within a pre-established allowable variation. The average factor from these meter proofs is accepted as the nlcter factor. If mutually agreed on by the interested parties, the allowable repeatability deviation inay be relaxed in spccid situations (c.g., when small througllput meters are used). 5.5 ACCURACY

The accuracy of any calculated meter factor or the averagc of two or inore m e ~factors ' is linlitcd by at least the following considerations: a. Prover calibration uncertainty. b. Meter proving procedural uncertainties. c. Equipment performance, d. Errors that arise from observation. e. Errors that are implicit in the computation used to corrcct a measurement to standard conditions. Abbrevialecl tables, nonstandardized rounding of conversion factors, or intermediate calculations (see API MPMS Chapter 12.2 for standardized calculwtions) can adversely affect the consistency of caIculations. The observcd and con]pulcd data for all meter proofs that are made to obtain a meter factor or another expression of meter perfoanance shall be reported on a suitable meter-proving report form; examples are provided in API MPMS Chapter 12.2. 5.6

MULTIPLE METERS

Most of the procedures described apply to the proving of a single mcter. If the meter to be proved is part of a battery of nleters that handles a common stream, the stream must be diverted from thc sdcctcd nlctcr to be proved through the prover. The flow tht*oughthe meter being provcd must be lnaintained at its normal operating rate.

pass of the dispiacer. This results in a proving resolution of a1 Icast one part in a n thousand (0.0001). For more detailed information on conventional pipe provers see API MPMS, Chaptcr 4, Section 2. 6.2 SMALLVOLUME PROVERS

Small volume provers have a volume between detectors that does not permit a minimum accumulalion of 10,000 dircct (unaltered) pulses from tllc mcter. Small volume provers 1.equi1-epulse interpolation to increase the resolution to a minimum of one part in ten thousand parts (0.0001). For nlore dctailed information on small volu~neprovers scc API MPMS Chapter 4, Section 3, and Chapter 4, Section 6.

6.3 TANK PROVERS A tank prover is a volumetric vessel that has a reduced cross section or neck located at both the top and bottom or, in some cases, at the top only. Thcsc necks arc cquipped with gauge glasses and graduated scales. Thnk provers may be open to the at~nosphcrc,or they may be closed pressurized vcsscls. Proving by a tank provcr c~nploysthe stallding start-and-stop method (that is, the flow through the meter must come to a complete' stop at the beginning and end of each proving run). For more detailed inforniation on tank provers see API MPMS Chapter 4, Section 4. 6.4

MASTER-METER PROVERS

The master-mcter is an indirect prover that uses the concept of transfer proving. A flow meter, with exceptional linearity and repeatability is selected to serve as a master-meter (Intermediate Standard) between a meter or prover operating in thc field and a master-meter prover, %o separate stages arc required in master-~neterproving: first, the master-meter must be proved using a meter prover (master prover) that has been calibrated by the water-draw method, with test measures traceable to NIST; and second, this provcd master-meter is then used to dctcnni~~e the meter factor of the field operating meter or Lo calibrate other field provers. For more detailed infor~nntionon master-n~cierprovers see API MPMS Chapter 4, Section 5.

6 vpesof Provers 6.1

CONVENTIONAL PIPE PROVERS

A pipe prover includes a calibrated section in which the displacer travels with the How, activating detection d~vices

and finally stopping as the stream is diverted or bypassed. A convc~ltionalpipe prover is defined as a prover with a SUBciorlt volume to accumulate a minimum of 10,000 whole unaltered meter pulses between detector switches for each

7 Field-StandardTest Measure A field-standard test measure is a volumetric container that is calibrated by NIST or by any other NIST-certified laboratory that can provide traceability to NIST and is acceptable to all parties involved. The field standard test measure is the standard used to calibrate most proving systems and is dcscribcd in detail in API MPMS Chapter 4.

Invoice To

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Ll Check hecc if same as "Ship To"

Company:

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will not deliver to a P.0. Box)

Company:

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Address:

Address:

city:

Stale/Pmvlnce:

City:

State/Prwince:

Zip:

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Zip:

Counrry:

Custarner Daytlme Telephone No.:

Customcr Daytime Telephone No.:

Fax No.:

Fax No.: (Erren~lallw FNgn Ddm)

D Please Bill Me P.D. No.:

0 Payment Enclosed $ CL Payment By Charge Account: O MasterCard O h

C1 Amcrican Express

Account NO.:

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Slate Sales Tax The Anwrican Peuoleunl lnnl~u~e hrepuirtd ~ o c o lsalts l ~ ~taxan publica~lonr mailed !a lhefallolvin~staler:Al. AR. CE DC. FL. G4 IL.18 1.4 W.XY ME. MD. M.MI. MN. MO, NE. NI. NY HC,ND.OH, Ph R1,SCTN.TX, W, IklR and WI. P~epapnc~ dadersshipped~olhesestalesshould lnclsde

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applicable sales tax unless a purchaser Is exempl. If wmpl, plmse print your stale exwnpllon numbw and enclosea copyollt~eruuen~ exemybncefUfimle .

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Title

Quantity Order Number

-

----..--

lele:

Unit Pfice

H30082

MPMS Ch. 4.2, Conventional Pipe Provers

$40.00

H30083

MPMS Ch. 4.3,Small Volume Provers

$40.00

H30084

MPMS Ch. 4.4, Tank Provers

$40.00

H30086

M P M S Ch. 4.5, Master-Meter Provers

$80.00

H30086

MPMS Ch. 4.6, Pulse Interpolation

$30.00

H30087

MPMS Ch. 4.7, field-Standard Test Measures

$30.00

H04081

MPMS Ch. 4.8, Operalion of Proving Systems

$60.00

I

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Order No. H04012

Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Pipe Provers

Section 2-Conventional

FIRST EDITION, OCTOBER 1988 REAFFIRMED, OCTOBER 1993

American Petroleum Institute 1220 t Street, Northwest Washington, D.C. 20005 Copfight Amerlcan Peboleum InstlWk. This reproduction made by CSSfnlo, (800) 694-9271, (313) under Ucenae from API.

Q

Manual of Petroleum Measurement Standards Chapter &Proving Systems Section 2-Conventional

Pipe Provers

Measurement Coordination Department FIRST EDITION, OCTOBER 1988


SPECIAL NOTES 1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTlCULAR CIRCVMSTANCES,LOCAL, STATE,AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED.

2. APl IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANUFACI'LJRERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL, STATE, OR

FEDERAL LAWS. CONCERNING SAFETY AND HEALTH RISKS AND PROPER PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDJTlONS SHOULD BE OBTAINEDFROM THE EMPLOYER, THE MANUFACTURER OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

3 . INFORMATION

4. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED AS GRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANUFACIZIRE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCTCOVERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LlABlLlTY FOR INFRINGEMENT OF LETTERS PATENT.

5. GENERALLY, API STANDARDS ARE REVIEWD AND REVISED, REAFFIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS. SOMETIMES A ONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW CYCLE. THIS PUBLICATION WILL NO LONGER BE IN EFFECTFIVE YEARS AFTER ITS PUBLICATlONDATE AS AN OPERATIVE Afl STANDARD OR, WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. STATUS OF Tf-IE PUBLICATION CAN BE ASCERTAINED FROM THE API AUTHORING DEPARTMENT [TELEPHONE (202) 682-8000]. A CATALOG OF API PUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L STREET,N.W., WASHINGTON, D.C. 20005.

Copyright Q 1988 American Petroleum Institute

FOREWORD Chapter 4 of the Manual @Petroleum Memrement S~andardswas prepared as a guide for the design, instaIlation,caIibration, and operation of meter proving systems commonly used by the majority ofpetroleum operators. The devices and practices covered in this chapter may not be applicable to all liquid hydrocarbons under all operating conditions. Other types of proving devices that are not covered in this chapter may be appropriate for use if agreed upon by the parties involved. The information contained in this edition of Chapter 4 supersedes the information contained in the previous edition (First Edition, May 1978), which is no longer in print. It also supersedes the information on proving systems contained in API Standard 1101, Mensuremenr of Petroleum Liquid Hydrocarbons by Positive Dhplacement Merer (First Edition, 1960); API Standard 2531, Mechanical Dkplacemenr Meter Provers; API Standard 2533, Metering Viscous Hydrocarbons; and API Standard 2534, Measurement of Liquid Hydrocarbons by Turbine-Meter Systems, which are no longer in print. This publication is primarily intended for use in the United Stares and is related to the standards, specifications and procedures of the National Bureau of Standards (NBS).W h e n the information provided herein is used in other countries, the specifications and procedures of the appropriate national standards organizations may apply. Where appropriate, other test codes and procedures for checking pressure and electrical equipment may be used. For the purposes of business transactions, limits on error or measurement tolerance are usually set by law, regulation, or mutual agreement between contracting parties. Tbis publication is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved. Chapter 4 now contains tbe following sections: Section 1, "Introduction" Section 2, "Conventional Pipe Provers" Section 3, "Small Volume Provers" Section 4, 'LTankFrovers" Section 5, "Master-Meter Rovers" Section 6, "Pulse Interpolation" Section 7, "Field-Standard Test Measures" API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, ?he Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for lass or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted t o the director of the Measurement Coordination Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

lli

CONTENTS SECTION 24ONVENTIONAL PIPE PROVERS ~ P C

................................................... ..................................................... ......................................... ............................................

4.2.1 3ntroduction 4.2.1.1 Scope 4.2.1.2 Definition of Terms 4.2.1.3 Referenced Publications ..................................... 4.2.2 Pipe Prover Systems 4.2.2.1 Unidirectional Provers ....................................... 4.2.2.2 Bidirectional Provers ........................................ 4.2.3 Performance Requirements ...................................... 4.2.3.1 Calibration Repeatability for Prover Volume ................... 4.2.3.2 Valve Seating 4.2.3.3 Freedom From Shock 4.2.4 Equipment 4.2.4.1 Materials and Fabrication .................................... 4.2.4.2 Temperature Stability ....................................... 4.2.4.3 Temperature Measurement................................... 4.2.4.4 Pressure Measurement 4.2.4.5 Diplacing Devices 4.2.4.6 Valves 4.2.4.7 Connections 4.2.4.8 Detectors 4.2.4.9. Peripheral Equipment ....................................... 4.2.4.10 Roving Counter ........................................... 4.2.5 Equipment for Automatic-Return Unidirectional Pipe Provers 4.2.5.1 Sphere lnterchmge 4.2.5.2 Separator Tees 4.2.5.3 Launching Tees 4.2.6 Equipment for Bidirectional Pipe Provers 4.2.6.1 Outlets and Inlets 4 2.6.2 Flow Reversal 4.2.7 Design of Pipe Provers 4.2.7.1 Initial Considerations 4.2.7.2 Pressure Drop Across the Rover 4.2.7.3 Volume 4.2.7.4 Displaper Velocity 4.2.7.5 Repeaiability and Accuracy 4.2.8 Ihnensions of Provers 4.2.9 Sample Calculations for the Design of a Pipe Rover 4.2.9.1 Basis of Calculation 4.2.9.2 Minimum-Volume Calculation 4.2.9.3 Minimum-Length Calculation 4.2.9.4 Rover Diameter 4.2.9.5 Summary of Calculations 4.2.10 Installation 4.2.10.1 General Considerations.. 4.2.10.2 hover Location 4.2.11 Calibrating Pipe Provers........................................ 4.2.11.1 Calibrating Pipe Rovers by the Waterdraw Method 4.2.11.2 Calibrating Bidirectional Provers by the Waterdraw Method

............................................... ....................................... ....................................................

....................................... ........................................... ..................................................... ................................................ ..................................................

1

1 1 1

1 2 2 2

2 2 2 6

6 6 6

6 6 6 7 7 7 7

....... 7 ......................................... 7 ............................................. 7 ............................................. 7 .......................... 7 ........................................... 7 .............................................. 7 .......................................... 7 ........................................ 7 ............................. 8 .................................................... 8

.......................................... 8 .................................. 8 .......................................... 9 ................ 9

......................................... 9 ................................ 9 ................................ 9 ............................................ 10 .................................... 10 ................................................... 10 ................................... 10 ........................................... 10 11 ............ 11 .... 14

4.2.11.3 4.211.4

Calibrating Unidirectional Provers by the Waterdraw Method ~aljbratingPipe Rovers by the ~ a G e r - ~ e t Method er

... 15

.........

Fimres . I-Typical ~uidirectional Return-Type Prover System 2-Tjq~ ical Bidirectional U-Type Sphere Rover System .................. 3.. Typical Bidirectional Straight-Type Piston Prover System ............. 4. Waterdraw Calibration of Unidirectional Provers >Waterdraw Calibration of Bidirectional Rovers

...................

..................... ......................

15 3 4

5 12

13

.

Systems

Chapter &Proving SECTION 2-CONVENTIONAL 42.1

Introduction

Conventional pipe provers are used as volume standards for proving liquid meters that generate at least 10,000 unaltered pulses during a prover pass. Pipe provers may be straight or folded in the form of a loop. Both mobile and stationary provers may be constructed in accordance with the principles described in this chapter. Pipe provers are also used for pipelines in which a calibrated portion of the pipeline (either straight, U-shaped, or folded) serves as the reference volume. Some provers are arranged so that liquid can be displaced in either direction. A pipe prover's main advantage over a tank prover is that its flow of liquid is not interrupted during proving. This unintermpted flow permits the meter to be proved under specific operating conditions and at a uniform rate of flow without having to start and stop. The reference volume (the volume needed between detectors) required of a pipe prover depends on such factors as the discrimination of the proving register, the repeatability of the detectors, and the repeatability required of the provingsystem as a whole. The relationship between the flow range of the meter and the reference volume must also be taken into account. Provers that have a smaller volume than was once considered necessary can now be used as a result af pulse-interpolation techniques and precision displacer detectors (see Chapter 4.3). 4.2.1.1

SCOPE

Tbis chapter outlines the essential elements of unidirectional and bidirectional conventional pipe provers and provides design, installation, and calibration details for tbe types of pipe provers that are currently in use. The pipe provers discussed in this chapter are designed for the running start-and-stop procedures described in Chapter 4.1. These provers consist of a pipe section through which a displacer travels and activates detection &vices before stopping at the end of the run as the stream is divened or bypassed. 4.2.1 P DEFINITION OF TERMS

PIPE PROVERS

A prover round trip refers to the forward and reverse passes in a bidirectional prover.

4.2.4.2.2

Meter proof refers to the multiple passes or round trips of the displacer in a prover for purposes of deterniining a meter factor. 4.2.1.2.3

4.2.1.2.4 A meter prover is an open or closed vessel of

known volume utilized as a volumetric reference standard for the calibration of meters in liquid petroleum service. Such provers are designed, fabricated, and operated within the recommendations of Chapter 4. 4.2.1.3

REFERENCED PUBICAT1ONS

The current editions of the following standards, codes, and specifications are cited in this chapter: API Manual of Perroleurn Measurement Standards Chapter 4, "Proving Systems," Section 1, Yntroduction," Section 3, "Small Volume Provers," Section 5, "Master-Meter Provers," Section 6, "Pulse Interpolation," and Section 7, "Field-Standard Test Measures" Chapter 5.4, "Accessory Equipment for Liquid Meters" Chapter 7.2, "Dynamic Temperature Detennination" Chapter 1I, "Physical Properties Data" Chapter 12.2, "Calculation of Liquid Petroleum Quantities Measured by Turbine or Displacement Meters" DOTI

49 Code of Federal Regulations Parts 171-177 (Subchapter C, "Hazardous Materials Regulations") and 390-397 (Subchapter B, "Federal Motor Carrier Safety Regulations")

4.2.2

Pipe Prover Systems

All types of pipe prover systems operate on the common principle of the repeatable displacement of a known volume of liquid from a calibrated section of pipe be-

Terms used in this chapter are defined in 4.2.1.2.1 through 4.2.1.2.4. 4.2.1.2.1

A prover pass is one movement of the dis-

placer between the detectors in a prover.

'U.S. Dcprrtrncnt of Transportation. Thc Code of Federal &plariom is available fmm the U.S. Government hinting Office,Washing. ton, D.C. 20402.

tween two signalling detectors. Displacement is achieved by means of a slightly oversized sphere or piston that is driven dong the pipe by the liquid stream being metered. The corresponding metered volume is simultaneously determined. A meter that is being proved on a continuous-flow basis must be connected at the time of proof to a counter that can be instantly started or stopped by the signalling detectors. The counter is usually an electronic pulse counter. The counter is started and stopped when the displacing device actuates the two detectors at the ends of the calibrated section. The two types of continuous-flow pipe provers are unidirectional and bidirectional. The unidirectional prover allows the displacer to travel in only one direction through the provjng section and has an arrangement for returning the displacer to its starting position. The bjdirectional prover allows the displacer to travel first in one direction and then in the other and incorporates a means of reversing the flow through the pipe prover. Both unidirectional and bidirectional provers must be constructed so that the full flow of the stream through a meter being proved will pass through the prover. Pipe provers may be manually or automaticdly operated. 4.2.2.1

UNlDlRECTlONAL PROVERS

Unidirectional provers may be subdivided into the foUowing two categories depending on the manner in wbich the displacer is banded: a. The manual-return unidirectionalprover, prover, sometimes

referred to as the measured distance, is an elementary form of an in-line prover that uses a section of pipeline as the prover section. Detectors that d e h e the calibrated volume of the prover sectjon are placed at selected points. A displacer launching device is placed upstream from the prover section, and receivingfacilities are installed at same point downstream from the prwer section. Conventional:launchingand receiving scraper traps are usually used for this purpose. To make a proving m, a displacer (a sphere or specially designed piston) is launched and allowed to displace the reference volume before being received downstream and manually trmsported back to the launching site. b. The circhring-rerum unidirectiona/prover (see Figure 11, often referred to as the endless loop, has evolved from the Drover described in Item a. In the endless loop, is arranged so that the downstream end of the the 100b crosses over and above the upstream end of the ldbcd sextion. The interchange is ;he means by which the displacer is transferred from the downstream to the upstream end of the loop without being removed from the prover. The displacer detectors are located inside the looped portion at a suitable distance from the inter-

change. Continuous or endless prover loops may be automated or manually operated.

The base volume of a unidirectional prover is the calibrated volume between detectors corrected to stan: dard temperature and pressure conditions. 4.2.2.2

BlDIRECTlONAL PROVERS

Bidirectional provers (see Figures 2 and 3) have a length of pipe through which the displacer travels back and forth, actuating a detector at each end of the calibrated section and stopping at the end of each prover pass when the displacer enters a region where the flow can bypass it or when valve action diverts the flow. Suitable supplementary pipework and a reversing valve or valve assembly that is either manually or automatically operated make possible the reversal of the flow through the prover. The main body of the prover is often a straight piece of pipe, but ir may be contoured or folded to fit in alimited space or to make it more readily mobile. A sphere is used as the displacer in the folded or coatoured type; a piston or sphere may be used in the straight-pipe type. The base volume in a bidirectional prover is expressed as the sum of the calibrated volumes between detectors in two consecutive one-way passes in opposite directions, each corrected to standard temperature and pressure conditions.

4.2.3

Performance Requfrements

4.2.3.1

CALIBRATION REPEATABILITY FOR PROVER VOLUME

When the prover volume is calibrated, the results, after correction, of two or more consecutive runs as agreed upan by the interested parties shall lie within 0.02 percent ( a 0.01 percent of the average) to determine the prover volume (see 4.2.11). 4.2.39 VALVE SEAllNG

The sphere interchange in a unidirectional prover or the flow-diverter valve or valves in a bidirectional prover shall be fully seated and sealed before the displacer actuates the first detector. These and any other valves whose leakage can affect the accuracy of proving shall be provided with some means of demonstrating during the proving run that they are leak free. 4.2.3.3

FREEDOM FROM SHOCK

When the prover is operating at its maximum design flow rate, the displacer shall decelerate and come to rest safely at the end of its travel wjthout shock or damage.

(rexr cohtinued on page 6)

a-

4.2.4

Equipment

4.2.4.4

42.4.1

MATERIALS AND FAB RICATlON

Pressure-measurement devices of suitable range and accuracy are used at appropriate locations to measure pressure at the meter and the prover. The pressure devices should reflect the pressures within the meter and the calibrated section of the prover. See Chapter 12.2 for further information.

The materials selected for a prover shall conform to applicable codes, pressure and temperature ratings, corrosion resistance, and area classifications. Pipe, fittings, and bends shouId be selected for roundness and smoothness to ensure consistent sealing of the displacer during a prover pass. The calibrated section of the prover between the displacer position sensors must be designed to exclude any appurtenances such as vents or drains. Flanges or other provisions should be provided for access to the inside surfaces of the calibrated and prerun sections. Care shall be exercised to ensure and maintain proper alignment and concentricity of pipe joints. Ranges in the calibrated volume shall be match bored and uniquely doweled or otherwise designed to maintain tbe match-bored position of the flanges. Gaskets used in the calibrated section shall be designed to seal on a flange-face metal-to-metal makeup, with the seding being obtained froman 0-ring-type seal. All internal welds and metal surfaces shall be ground smooth to precIude damage to and leakage around the displacer. internally coating the prover section with a coating material that will provide a hard, smooth, long-lasting finish will reduce corrosion and prolong the life of the displacer and the prover. Experience has shown that internal coatings are particularly useful when the prover is used with liquids that have poor lubricatingproperties, such as gasoline or liquefied petroleum gas; however, in certain cases, satisfactory results and displacer longevity may be achieved when uncoated pipe is used.

4.2.4.2

TEMPERATURE STABILITY

Temperature stability is necessary to achieve acceptable proving results. Temperature stabilization is normally accomplished by conthiuously circulating liquid through the prover section with or without insulation. When provers are installed aboveground, the appIicatioo of thermal insulation will contribute to better temperature stabilization. 4.2.4.3

TEMPERATURE MEASUREMENT

Temperature-measurement sensors shall be of suitable range and accuracy and shall be installed at the inlet and outlet of the prover (see Chapter 7.2 for detail requirements). Caution must be exercised to ensure that the temperature sensors are located where they will not be shut off horn the liquid path.

4.2.4.5

PRESSURE MEASUREMENT

.DISPLACING DEVICES

One type of displacing device commonly used in pipe provers is the elastomer sphere hydrostatically filled with liquid under pressure. The displacer is expanded to provide a seal without excessive friction to a diameter greater (normally 2-4 percent) than that of the inside diameter of the prover pipe. In general, the larger the sphere, the greater the percentage of inflation required. Insufficient expansion of the sphere can lead to leakage past the sphere and consequently to measurement error. Excessive expansion of the sphere may not improve sealing ability and will generally cause it to wear more r a p idly and move erratically. Care must be exercised to ensure that no air remains inside the sphere. The displacer shall be as impervious as possible to the operating liquids. The liquid used to fill the sphere shall have a freezing pojnt below any expected temperatures. Water or water-glycol mixtuxes are commonly used. Anothex commonly used displacer is the cylindrical piston with suitable seals. 4.2.4.6

VALVES

All valves used in pipe prover systems that can provide or cantribute to a bypass of liquid around the prover or meter or to leakage between the prover and meter shall be of the block-and-bleed type or an equivalent with a provision for seal verification. FuU positioning of the flow-reversing valve or valves in a bidirectional prover or the interchange valve in a unidirectional prover must be accomplished before the displacer is allowed to actuate the fist detsctor. This design ensures that no liquid is allowed to bypass the prover during the displacer's travel through the calibrated volume. The distance before the first detector, commonly called prerun, depends on valve operation time and the velocity of the displacer. Methods used to shorten this prerun, such as faster operation of the valve or delay of the displacer launching, require that caution be exercised in the design so that hydraulic shock or additional undesired pressure drop is not introduced. If more than one flow-directing valve is used, all valves should be arranged by linkage or another means to prevent shock caused by an incorrect sequence of operations.

4.2.4.7

CONNECTIONS

Connections shall be provided on the prover or cannecting piping to allow for calibration, venting, and draining. 4.2.4.8

DETECTORS

Detection devices must indicate the position of the djsplacer within close tolerance. Various types of detectors are currently used. The mast common is the mechanically actuated electrical switch. Other types include the electronic proximity switch and the induction pickup; these types may be used if they provide satisfactory repeatability. The repeatability with which the detector in a prover can signal the position of the displacer, which is one of the governing factors in determining the length of the prover section, must be ascertained as accurately as possible. Openings through the pipe wall for detectors must be smaller than the longitudinal sealing area of the displacer. 4.2.4.9

@

PERIPHERAL EQUIPMENT

A meter pulse generator shall be provided for transmission of flow data and must provide electrical pulses with satisfactory characteristics for the type of proving mbnter used. The device should generate a suflicient number of pulses per unit volume to provide the required discrimination (see Chapter 5.4). 4.2.4.1 0 PROVING COUNTER

An electronic pulse counter is usually used in meter proving because of the ease and accuracy with which it can count higb-frequency pulses and its ability to transmit this count to remote locations. The pulse-wunring devices are equipped with an electronic startlstop switching circuit that is actuated by the pipe prover's detectors (see Chapter 5.4).

4.2.5

Equipment lor Automatic-Return Unid~rectionalPipe Provers

4.2.5.1

SPHERE INTERCHANGE

The sphere interchange provides a means for transferring the sphere from the downstream end of the proving section to the upstream end. Sphere interchange may be accomplished with several different combinations of valves or other devices to minimize bypass flow through the interchange during the sphere-transfer process. A verifiable leaktight valve seal is essential before the sphere reaches the first detector switch of the proving section.

4.2.5.2

SEPARATOR TEES

Separator tees are at least one pipe size larger than the nominal size of the sphere or loop. Sizing is best determined by experience. The design of the separator lee shall ensure dependable separation of the sphere from the stream for all rates within the flow range of the prover. For practical purposes, the mean liquid velocity through the tee should not exceed 5 feet (1.5 meters) per second; a considerably lower liquid velocity is often desirable. The tee must sometimes be sized several sizes larger. Smooth-flow transition fittings on both ends of the tee are important. A means of directing the sphere into the interchange shall be provided at the downstream end. Care should be taken in designing this device to prevent damage to a sphere. 4.2.5.3

LAUNCHING TEES

Launching tees are generally only one pipe size larger than the sphere displacer. They shall have smooth transition fittings leading into the prover. The launching tee should have a slight inclination downwards toward the prover section, or another means should be provided to ensure that the sphere moves into the prover during periods of low flow,-whichmight occur duringcalibration by the waterdraw method.

4.2.6

Equipment for Bidltectional Pipe Provers

4.2.6.1

OUTLETS AND INLETS

The outlets and inlets on the pipe prover end chambers of bidirectional provers are designed to pass liquids and restrain the displacer. The openings shall be deburred and shall have an area sufficient to avoid excessive pressure loss. 43.69

FLOW REVERSAL

A single multipart valve is commonly used for reversing the direction of the displacer. Other means of flow reversal may also be used. All valves must be leak free and allow continuous flow through the meter during proving. A method of checking for seal leakage during a proving pass shall be provided for all valves. The valve size and actuator shall be selected to minimize hydraulic shock.

4.2.7

Design of Pipe Provers

Before a pipe prover is designed or selected, it is necessary to establish the type of prover required for the application and the manner in which it will be connected

with the meter piping. From a study of the application, intended use, and space limitations, the following should be established: a. Whether the prover is to be stationary or mobile. 1. If the prover is stationary, whether it will be dedicated (on line) or used as part of a central system. 2. If the prover is stationary and dedicated, whether it will be kept in service continuously or isolated from the mete~edstream when it is not being used to prove a meter. 3. If the prover is stationary, what portions, if any, are desired below ground. b. The ranges of temperature and pressure that will be encountered. c. The maximum and minimum flow rates expected and the flow-rate stability. d. The maximum pressure drop allowable across the prover. e. The physical properties of the fluids to be handled. f. The degree of automation t o be incorporated in the proving operation. g. Available utilities. 4.2.7.2

PRESSURE DROP ACROSS THE PROVER

In determining the size of the piping and openings to be used in the manifolding and the prover, the pIessure loss through the pipe prover system should be cornpatible with the pressure loss considered tolerable in the metering inst allation. 4.2.7.3

VOLUME

In determining the volume of a prover between detectors, the designer must consider the following items: a. The overall repeatability required of the proving system. b. The repeatabiiity of the detectors. c. The accumulation of 10,000 unaltered pulses or the use of pulse interpolation (see Chapter 4.6). d. The resolution of the meter pulse generator (that is, the number of pulses per unit volume). e. The maximum and minimum flow rates of the system. '

4.2.7.4

DISPLACER VELOCITY

The velocity of the displacer can be determined by the internal diameter of the prover pipe and the maximum and minimum flow rates of the meters to be proved. Some practical limit to the maximum velocity of a displacer must be established to prevent damage to the displacer and the delectors, Nevertheless, the dweloping slate of the art advises against setting a firm limit to

displacer velocity as a criterion for design. Demonstrated results are better to use as a criterion. The results are manifested in the repeatability, accuracy, and reproducibility of meter factors using the prover in question. Most operators and designers agree that 10 feet (3 meters) per second is a typical design specification for unidirectional provers, whereas velocities up to 5 feet (1.5 meters) per second are typical in bidirectional provers, Higher velocities may be possible if the design incorporates a means of reducing surges and displacer velocity before the prover completes its pass. Minimum displacer velocity must also be considered, especially for proving meters in a liquid that has little or no lubricating ability, such as gasoline that contains high proportions of aromatics or liquefied petroleum gas. When lubricating ability is poor or nonexistent and the displacer is operating at low velocities, the displacer may move, hesitate, and move again. Velocities, as the term is used in this publication, refers to uniform velocities between detecton. This standard is not intended to limit the velocity of displacers. Provided that acceptable performance can be assured, no arbitrary limit is imposed on velocity. 4.2.7.5 4.2.7.5.1

REPEATABILITY AND ACCURACY

General Considerations

The ultimate requirement for a prover is that it prove meters accurately; however, accuracy cannot be established directly because it depends on the repeatability of the meters, the accuracy of the instrumentation, and the uncertainty of the prover's base volume. The repeatability of any proverlmeter combination can be determined by carrying out a series of repeated rneasurements under carefully controlled conditions and analyzing the results statistically. Repeatability is usually adopted as the primary criterion for a prover's acceptability. Whereas poor repeatability is an immediate indication that a prover is not performing satisfactorily, good repeatability does not necessarily indicate good accuracy because of the possibility of unknown systematic errors. Operators must always guard against such errors. The minimum distance between detector switches depends on the detector's ability to repeatedly locate the displacer. The total e n o r of the displacer during a proving pass shall be limited to 0.02 percent of the volume between the detectors. 4.2.7.5.2

Replacing the Detectors

When the worn or damaged parts of a detector are replaced, care must be taken to ensure that neither the detector's actuating depth nor its electrical switch cornponents are altered t o the extent that the prover volume

i ,

9

6

is changed. This is especially true for unidirectional provers because changes in detector actuation are not compensated for round trip sphere travel as they are in bidirectional provers. Recalibration of unidirectional provers is in order as soon as practical. 4.2.7.5.3

Counter Resolution

The resolution of a digital counter is unity; that is, a counter can indicateonly a whole number ofpulses. The indicated pulse count therefore has a 2 1 pulse uncertainty for a pass between detectors. For example, to limit the pulse uncertainty to 1 pulse during a prover pass without using pulse interpolation (see Chapter 4.6), at least 10,000 pulses wouId have to be collected during a single pass. This degree of uncertainty is represented mathematicalIy as follows:

U=

-c 1 pulse

N

Where:

U = degree of uncertain1y of the recorded pulse count during a prover pass, commonly called the resolution. N = minimum number of pulses to be collected during a prover pass.

@

42.7.5.4

Pulse Generation

The preceding considerations suggest that prover volumes can be reduced by increasing the pulse-generation rate of the meters to be proved. Caution must be exercised when gear-driven pulse generators are used on displacement meters to obtain very high pulse-generation rates, since mechanical problems such as backlash, drive-shaft torsion, and cyclic variations can cause irregular pulse generation. An electronic means of pulse interpolation can also be used to increase the resolution for both small volume and conventiohd volume provers (see Chapter 4.6).

4.2.8

Dimensions of Provers

The dimensions selected for provers have to be based on a cornp~ornise.Decreasing the diameter of the prover pipe increases the length between detectors for a given volume and reduces the sensitivity to detector resolution. Decreasing the pipe diameter also increases displacer velocity; this increase may become a limiting factor. Increasing the diameter of the prover pipe has the opposite effect; the velocity of the displacer is reduced, but the resulting decrease in length increases the sensitivity to detector resolution and thus may become a limiting factor. .

Sample Calculations for the

4.2.9

Design of a Pipe Prover

A typical approach to the design of unidirectional or bidirectional pipe provers is described in 4.2.9.1 through 4.2.9.5. The examples given are for a 6-inch (150-millimeter) meter operating ar 1200 barrels per hour and generating a nominal 2000 pulses per barrel.

BASIS OF CALCULATION

4.2.9.1

. . A

..

s

.:

,

.. .

...

The repeatability obtained during calibration runs must be within the range stated in 4.2.3.1. For the purpose of this example, the following conditions are assumed:

a. The acceptable counter resolution error, U (see 4.2.7.5.3), is kl pulse during a prover pass. b. T h e meter to be proved generates 2000 pulses per barrel. c. The repeatability for each of the detectors to the sphere js assumed to be .+- 0.030 inch. d, The maximum displacer velocity is provisionally set at 10 feet (3 meters) per second.

MINIMUM-VOLUME CALCULATION

4.2.9.2

After the degree of uncertainty during a prover pass (see4.2.7.5.3) is established, the minimum volume during a pass is determined using Equation 1 as follows:

Where: V = minimum volume between prover detectors

21 - (1110,000)(2000) = 5 barrels.

U =degree of uncertainty of the recorded pulse count during a prover pass. K = minimum number of counts per consistent unit volume of any meter that will be proved. N = minimum number of pulses to be collected dur-

.

ing a prover pass. 4.2.9.3

MINIMUM-LENGTH CALCULATION

The minimum length between detector switches depends on the accuracy with which the detector switch can repeatedly determine the position of the displacer and the desired discrimination of the prover system during calibration. Item b in 4.2.9.1 indicates that the desired discrimination of the prover system during calibration is

. -. ..,

0.02 percent ( 20.01 percent of the average). Item c in 4.2.9.1 states that the repeatability of response to the sphere for each of the detector switches is rt0.030 inch (20.75 milljmeters). If L represents the nominal indicated length of the prover, one pass could displace a maximum volume represented by L plus 0.060 inch (1.5 millimeters); another pass could displace a minimum volume represented by L minus 0.060 inch (1 -5 millimeters). When the minimum is subtracted from the maximum, the diffe~encein the indicated length cannot exceed 0.12 inch ( % 3 millimeters). The caJculation for the minimum length would then be 0.12 inch ( 4 3 millimeters) divided by0.02 percent (0.0002), which results in a 50-foot (15-meter) minimum length. If the repeatability of response for each of the detector switches is better than -r- 0.030 inch ( 20.75 millimeters), the lengths between the detector switches can be decreased. 4.2.9.4

PROVER DIAMETER

Item d in4.2.9.1 sets a provisional maximum displacer velocity of 10 feet (3 meters) per second for use in this example. The smallest appliEab1e prover diameter would therefore be 6 inches (150 millimeters); however, the length necessary to obtain the 5-barrel (0.795 -CU b'ICmerer) volume would have to be in excess of the 50 feet (15 meters) previously calculated. 4.2.9.5

SUMMARY

OF CALCULATlONS

Based on the stated assumption of a 6-inch (150-millimeter) meter operating at 1200 barrels per hour, the calculations indicate that a prover with a minimum length of 50 feet (15 meters) between detectors that would displace a minimum volume of 5 barrels (0.795 cubic meter) and has a minimum diameter of 6 inches (150 millimeters) is required,

4.2.10

lnsta flation

4.2.10.1


All components of the prover installation, including electrical piping, valves, and manifolds, shall be in accordance with applicable codes. Once the prover is onstream, it becomes a part of the pressure system. The proving section and related components shall have suitable Pulse Variation GrapW4-Percent Adjustment ...................

.................... ................................

5

6 13 19

20 21

Chapter &Proving Systems SECTION S S M A L L VOLUME PROVERS 4.3.1 Introduction The use of small volume provers has been made possible by the availability of high-precision displacerposition detectors used in conjunction with pulseinterpolation techniques (see Chapter 4.6). The smaU volume prover normally has a smaller base volume than that of conventional pipe provers (see Chapter 4.2) and is usually capabte of fast provjng passes over a wide range of flow rates. Smallvolume provers have a volume between deteo tors that does not pennit a minimum accumulation of 10,000direct (unaItered) pulses from the meter. Small volume provers require meter pulse discrimination using a pulse-interpolation counter or another technique that increases the resolution (see Chapter 4.6). This may include using provers with both large and small base volumes, depending on the pulse rates of the meters to be proved. The small volume prover may be used in many applications in which pipe provers or tank provers are commonly used. Sm11 volume provers may be stationary or portable. The volume required of a small volume prover can be less than that ofa conventionti1pipe prover when highprecision detectors are used in conjunction with pulseinterpolation techniques. Pulse-interpolation methods of counting a series of pulses to fractional parts of a pulse are used to achieve high resolution without counting 10,000 whole meter pulses for a single pass of the displacer between detectors (see Chapter 4.6.) . To achieve the required proving accuracy and repeatability, the minimum volume berween detector switches depends on the discrimination of a combination of pulse-interpolation electronics, detectors, and uniform meter pulses, as well as flow rate, pressure, temperature, and meter characteristics. 4.3.1 ,I SCOPE This chapter outlines tbe essential elements of a small volume prover and provides descriptions of and operating detaiIs for the various types of small volume provers that meet acceptable standards of repeatability and accuracy.

DEFINITION OF TERMS Terms used in this chapter are defined in 4.3.1.2.1 through 4.3.1.2.6.

4.9.1.2

4,3.1.2.1 Interpulse spacing refers to variations ,inthe meter pulse width or space, normally expressed in percent. 4.3.1 2.2 Meter proof refers to the multiple passes or

round trjps of the displacer in a prover for purposes of determining a meter factor. 4.3.1.2.3 A meter prover is an open or closed vessel of known volume utilized as a volumetric reference standard for the calibration of meters in liquid petroleum

senice. Such provers are designed, fabricated, and operated within the recommendations of Chapter 4. A prover pass is one movement of the displacer betwee? the detectors in a prover. 4.3.1.2.4

A prbver round rrip is the result of the forward and reverse passes in a~bidirectiofialprover.

4.3.t.2.5

4.3.1.2.6 A proving timerlcoun&eris a high-speed counter used in double chronometry to measure time with a pulsed sigiral of known frequency. 4.3.1.3

REFERENCED PUBLICATIONS

The current editions of the following standards, codes, and specifications are cited in this chapter:

WI

Munaral of Petroleum Mectruremeni Standards Chapter 4, "Proving Systems," Section 2, "Conventional Pipe Provers," Section 6, "Pulse Interpolation," and Section 7, "Field-Standard Test Measures" Chapter 5, "Metering," Section 2, "Measurement of Liquid Hydrocarbons by Displacement Meters," Section 3, "Measurement of Liquid Hydrocarbons by Thbine Metm," and Section 4, "Accessory Equipment for Liquid Meters" Chapter 7.2, "Dynamic Temperature Determination'* Chapter 12.2, "Calculation of Liquid Petroleum Quantities Measured by Turbine or Displacement Meters"

NFPA1 70 N&nal'Elecbical

Code

'National R n ProteCtio~Assacistion, Battcrymarcb Park, Q b e y , Msacbusetts 02269.

4.3.2

Small Volume Prover Systems

The small volume prover is available in several different configurations that aUow a continuous and uniform rate of Bow. AU types operate on the common principle of the repeatable displacement of a known volume of liquid in the calibrated section of a pipe or tube. A displacer travels through a calibrated section with its limits defined by one or more highly repeatable detectors. The corresponding metered volume sirnuitaneously passes through the meter, and the whole number of pulses is counted. Precise calculations are made using a pulse-interpolation technique (see Chapter 4.6). The.two types of continuous-flow small volume provers are unidirectional and bidirectional. The unidirectional prover allows the displacer to travel and measure in only one direction through the proving section and has a means of returning the displacer to its starting position, The'bidirectional prover allows the displacer to travel and measure first in one direction and then in the other and is capable of reversing the flow through the prover section. Both unidirectional and bidirectional smalI volume provers must be constructed so that the full flow of the stream passing through the meter being proved will pass' through the prover.

4.3.3

Equipment

The small volume prover must be suitable for the intended fluids, pressures, temperatuxes, and type of installation. The materials used must be compatible with the fluid stream and the location where the prover will be installed. A small volume prover will normally consist of the following ebments: a. A precision cylinder.

b. A displacer piston, spheroid, or other fluidseparation device. c. A means of positioning and launching the displacer upstream of the calibrated section, d. A displacer detector or detectors. e. A valve arrangement that allows fluid flow while the displacer is traveling from one position to the opposite position. f, Pressure-measurement devices. g. Temperat~lre-measuremtnt devices. h. instrumentation timema ~unters,and P&* interpolation capability. 4.3.3.1

MATERIALS AND FABRICATION

The materials selected for a prover shall conform to applicable codes, pressure ratings, corrosion resistance, .

md area classifications.

The calibrated volume-measurement section of the prover, located between the displacer-position sensors, must be designed to excIude any appurtenances such as vents or drains. Flanges or other provisions should be included for access to the inside surfaces of the calibrated and prerun sections. Care should be exercised to ensure and maintain proper alignment and concentrjcity of pipe joints. Internally coating the prover section with a coating or plating material that will provide a hard, smooth, longlasting finish will reduce corrosion and prolong the life of.the displacer o r displacer seals and the prover. 4.3.3.2

TEMPERATURE STABILITY

Temperature stability is necessary to achieve acceptable proving results. Temperature stabitition is normaUy achieved by continuously circulating liquid through the prover section, with or without insulation. When provers are installed aboveground, the appIication of thermal insulation will contribute to better temperature stabilization. 4.3.3.3

TEMPERATURE MEASUREMENT

Temperature-measurement sensors should be of suitable range and accuracy and should be graduated by temperature discrimination in fractional degrees to at least 0.5"F (0.25'C). See Chapters 7.2 and 12.2. Temperature-measuremeMdevicesshall be installed at appropriate locations to measure temperature at the meter and the prover. Caution must be exercised to ensure that the temperature sensors are located in a position in which they will not be shut off from the liquid path. 4.3.3.4


Pressure-measurement devices of suitable range and accuracy, calibrated to an accuracy of 2 percent full scale or better, shall be instailed at appropriate bcations to measure pressure at the meter and the prover. (See Figures 1-4 and Chapter 12.2 for further information). 4.3.3.5

DISPLACING DEVICES

One type of displacer is a piston, with seals, connected to a central shaft. A second type of displacer is a free piston that uses 1816 between the precision cylbder and the piston. A third type is the elastomer sphere filed with tiquid under pressure. To provide a sealwithout excessive friction, the s p h is expanded to a diameter greater than the pr&er pipe's &side diameter, which is nomally 2-4 percent. insufficient expansion of the sphere can lead to leakage past the sphere and

consequently to measurement error. Excessive expansion of the sphere may not improve sealing abiIity and will generally cattse the sphere to wear more rapidly and move erratically. Care must be exercised to ensure that no air remains inside the sphere. The elastomer should be impervious to the operating liquids. A means for inspecting or monitoring displacer-seal integrity must be included in the design and operation of all smaU volume provers. Displacer-seal integrity may be either statically or dynamically verified under conditions of low-pressure differential that are consistent with norma1 operations. Other types of displacers will be acceptable if they provide accuracy and repeatability that is equal to or better than the three types described above. 4.3.3.6 VALVES

I

~

AU valves used in smalI volume prover systems that can provide or contribute to a bypass of liquid around the prover or meter or to leakage between the prover and meter shall be of the block-and-bleed type. Full positioning of the flow-reversing valve or valves in a bidirectional prover or the interchange valve in a unidirectional prover must be established before rhe displacer is allowed to 'actuate the firse detector. This design ensures that no liquid is allowed to bypass the prover during the displacer's travel rhrough the calibrated volume. The distance before the firs1 detector, commonly calIed prerun, depends on valve operation time and the velocity of the displacer. Methods used to shorten this prerun, such as faster operation of the valve or delay of the displacer launching, require that caution be exercised in the design so that hydraulic shock or additional undesired pressure drop is not introduced.

Vent and drain lines shall be provided on the prover or the connecting piping and must have a means of checking for leaks. Provisions should be made to allow field waterdraw calibration of the small volume prover. 4.3.3.8

DETECTORS

Detectors must indicate the position of the displacer within 20.01 percent. The repeatability with which a prover's detector can signal the position of the displacer (which is one of the governing factors in determining the length of the calibrated prover section) must be ascertained as accurately as possible. Care must bti taken to correct detector positions that are subject to temperature changes throughout the proving operation.

4.3.3.9

METER PULSE GENERATOR

A meter pulse generator shall be provided for t r k mittinn flow data. The generator.must provide electrical pulsesthat have satisfactory characteristicsfor the type of electronic instrumentation employed. 4.3.3.10

PULSE-INTERPOLATION SYSTEM

The prover timerlcounter for small volume provers is an electronic device that utilizes pulse interpolation and double chronometry (see Chapter 4.6). 4.3.3.1 1 CONTROLLER The controller is used to process all signals both to and from the prover. It receives the stadstop sighals from'the detector or detectors that gate the timers, receives the pulses generated by the test meter, performs tbe calculations, and displays all data. The proving controller may be equipped t o provide remote operation, alarms, printing, logic sequences, and other desired functions.

4.3.4

Design of Small Volume Provers

4.3.4.1

INITIAL CONSlDERATlONS

Before a srnal~'vo1ume prover is designed or selected, it is necessary to establish the type of prover required for the application and the manner in which it will be connected to the meter piping. The following items should be established from a study of the application, intended use, and space limitations of the prover:

a. Whether the prover will be stationary or mobile. 1. Whether a stationary prover will be dedicated (on line) or used as part of a central system. 2. Whether a stationary and dedicated prover will be kept in service continuously or isolated from the metered stream when it is not being used to prove a meter. b. The temperature and pressure ranges that will be encountered. c. The expected maximum and minimum flow rates and the flowrate stability. d. The maximurn pressure drop allowable across the prover. e. The physical properties df the fluids to be bandled. f. The degree of automation to be incorporated hto the proving operation. g. The availabifity of electric power and other tltilities. h. The size and types of meten to be proved. . i. The applicable oodes.

45.4.2

PRESSURE DROP ACROSS THE PROVER.

In determining the size of the piping and the openings to be used in the manifolding and the prover, the pressure loss through the prover system should be compatible with the pressure loss considered tolerable in the metering installation. Flow rate should not vary significantly during movement of the displacer. 4.3.4.3

DISPLACER VELOCITY

The velocity of the displacer a n be determined by the diameter of the prover cylinder and the maximum and minimum flow rates of the meters to be proved. A practical Limit to the maximum velocity of a displacer must be established to prevent damage to the displacer and the detectors. Typical maximum displacer velocities are close to but not limited to 5 feet per second (1.5 meters per second). The developing state of the art advises against setting a firm limit on displacer velocity as a criterion for design. Demonstrated results are better to use as a criterion. The results are manifested in repeatability, accuracy, and reproducibility of meter factors using the prover in question. Establishing guidelines for minimum velocities is difficult because of the many factors that must be considered, such as the following: '

a. The smoothness of the cyIinder's internal surface. b. The type a£ displacer used. c. The asplacer's launching capability. d. The lubricity of the liquid being measured.

Piston-type displacers can generally operate at lower veIocities than can sphere types. The intention of this standard is not to limit the velocity of the displacer. Provided that acceptable performance is guaranteed, there is no arbitrary limit imposed on velocity. 4.3.4.4

VOLUME

' In determining the volume of a prover between detectors, the designer must consider the folIowing items:

a. The overall repeatability required of the proving system. b. The repeatability of the detectors. c. The ability of the electronic counter to indicate whole pulses, unless pulse interpolation is employed. d. The resolution of the meter pulse generator (the number of pulses per unit volume). e. The maximum and minimum flow rates of the system,

f. The uniformityof the meter signal, or pulse, relative

to time (interpulse spacing). g. The meter's displaced volume per revolution. 4.3.4.5

.

CRITICAL PARTS

When a detector's worn or damaged parts are replaced, c&e must be taken to ensure that neither the detector's actuating depth nor its electrical switch components are altered.to the extent that the prover volume is changed. This is especially important in the case of unidirectional provers because changes in detector actuation are not compensated for by round trip sphere travel, as they are in bidirectional provers. When unidirectional provers are used, recalibration is needed as soon as practical. 4.3.4.6

COUNTERS

The small volume prover requires using a meter pulse-interpolation-type system (see Chapter 4.6) to provide a resolution of at least one part in 10,000of the indicated meter volume for each pass of the displacer between the detectors. 4.3.4.7

METER PROVING GUIDELINES

Different types of ineters produce pulse trains that have different characteristics. At a steady flow, the rotation of a turbine meter and its pulse train is uniform. Under comparable flow, the rotation of some displacement-meter elements is also uniform; however, mechanical gears, couplings, adj u s t ~ ~counters, ~, temperature-correction devices, and other accessories reduce the uniformity of the displacement-meter pulses. Demonstrations have shown that the closer the pulse generator is to the meter rotor, the more uniform the pulse train will be. The further the pulse is moved from the meter rotor, the more erratic the pulse train becomes (see Appendix A). For example, a displacement meter that has a closecoupled pulser will require only a minimal number of prover passes performed by a relatively-low-volume prover to establish a merer factor. (See Figure A-2 for pulse train characteristics.) A displacement meter with a full assortment of accessories will usually require more passes or the use of a larger prover to qstablish a meter factor. (See Figure A-3 for pulse train characteristics.)

4.3.5

Sample Calculations for the Design of Small Volume Provers

A typical approach to the design and application of small volume provers is provided in 4.3.5.1 and 4.3.5.2.

Note: Test-run observation indicates that the calculation method used in 4.3.5.1 and 4.3.5.2 should provide a minimum volume for proving a meter with a uniform pulse train (for example, a turbine meter or a displacement meter thet has a uniform pulse output), A proving method that consists of five prover passes, or round trips, with a repeatability range of 0.05 percent is achievable. Proving methods br use on nonunifo~mpulse output meters are discussed in Appendix B. The examples used in this section are not intended to impiy that the meter and prover data will be appropriate for a11 equipment or that other methods of prover design analysis are inappropriate.

PROBLEM

4.3.5.1

The maximum flow rate of the meter to be proved is 1715 barrels per hour (1200 gallons per minute, 272.66 cubic meters per hour). The minimum flow rate is 343 barrels per hour (240 gallons pet 'minute, 54.49 cubic meters per hour). The meter is a 6-inch displacement meter with a pulse rate of 8400 pulses per barrel (52,834.4 pulses per cubic meter). The maximum interpulse spacing is equal to 210 prcent of the average. The meter puke output is approximately uniform with the rotation of the meter element. The puke interpolation is performed by the doublechronometry method using one clock with a frequency of 100,000hem. The prover displacer-position detectors have a repeatability range of 0.001 inch (0.0254 millimeter) and a position stability range of 0.001 inch (0.0254 millimeter)The meter output resolution at the start and end of one prover pass is k0.01 percent (t0.0001 percent of the average). The prover displacer-position error at the start and end of a prover pass has an uncertainty of 20.01 percent. The maximum displacer ve1ocity.i~3.5 feet per second (1.067 meters per sewnd). The rninimum displacer velocity is 1.2 inches per second (3.048 centimeters per second), The required design adata is the minimum vdlume, minimum diameter, and minimum length of the prover.

The number of clock pulses accumulated during a prover pass is calculated as follows:

N, T2Fc

T2= clock operating time during a prover pass, in seconds. 17, = clock frequency, in hertz.

The clock operating time during a prover pass is calculated as follows: Tz=Nm/Fm

Where:

The potential error due to the resplution of doublechronometry timers during a prover pass can be caIculated as follows:

pulses.

Fm = meter pulse frequency, in hertz. Equations 1,2,and 3 can be combined to express the error of the timers in terms of meter output and timer frequency:

u,= +2F,/N,Fe

(4) The meter pulse frequency is calculated as follows: Fm

2 = number of timers. N,= number of clock pukes accumulated during a

prover pass.

Qm Pt/36M

Where:

Q,= meter flow rate, in barrels per hour (cubic meters per hour).

P,= meter pulse rate, in pulses per barrel (pulses per cubic meter). 3600 = number of seconds per hour.

In this exmpIe the maximum pulse frequency is calcdated as follows: F~@w = (1715)(8400) 13600 = 4002 hertz In SI units,

FTm, = (272.66)(56,834.4) 13600 =: 4002 hertz The potential error of the double-chronometry time can be caIculated from Equation 4 as follows:

U,= ( 22)(.4002)1 (N,)(IOO,~ = 20.080 / N,

Where:

U,= potential error in time accumuIated by two timers (one that times meter puke output and one that times prover displacement), expressed as a plusiminus fraction of a pulse.

(3)

N, = number of meter pulses during a prover pass, in

SOLUTION

4.3.5.2

(2)

Where:

The error due to nonuniform meter interpulse-spacing at the start and end of a prover pass is calculated as f0Uows: Umf(2)(*PJlNm Where:

(5)

U, = potential error due to nonuniform meter inter-

pulse spacing during a prover pass, expressed as a plus !minus fraction. 2 = number of displacer detections during a prover pass. P,= meter interpulse spacing expressed as a pluslminus fraction of a pulse.

meter flow rate, in cubic inches per second (cubic centimeters per second). = displacer velocity, in inches per-second (centi-meters per second).

Qm=

In this example the minimum prover diameter for the velocity limit is caIculated as follows:

In this example the error due to nonuniform metex interpulse spacing is as follows: Um~2(*0.10)/Nm = 20.20 IN,,,

The combined meter output error at the start and end of a prover pass can be estimated by combining Equations 4 and 5 as folIows:

Ut-t-Um=+2F~/NmFc+(2)(~P~)lN~ (6)

Dma,= (46201[(0.7854)(42)]}0.5 = 11.83 inches

In ST units,

D,,.,

= (75,708.2 / [(0.78M)(106.68)]}05 = 30.06.centimeters

The velocity of the displacer at the rninimurn flow rate, with the inside diameter given above, is calculated as follows: .

Note: Equation 6 sums the errors U, and Urninstead of taking the root mean square, the usual rntrhod of calculation. This approach results in a slightly larger prover than might otherwise be calculated.

V m q = Qm1 [0.7854(0,2)]

= 924 / [(0.7854)(11.832)] = 8.4 inches per second = 0.7 foot per second

In this example the combined meter pulse uncertainty during a prover pass is as follows:

U,+Urn=('-0.0801- -t0.20)/Nm

In SI units,

= -t.0.280/Nm

Vq,, = Qm / [(30-05)(0,2)] = 15,141.61[(0.7854)(30.053] = 21.35 centimeters per second = 0.213 meter per second

The maximum meter output error at the start and end of a prover pass is limited to the following:

U,+ Urn= +.0.0001(40.01 percent) In this example the minimum number of meter pulses that limits meter error to &0.0001 is as follows:

-C0.280/Nm= ~ 0 . 0 0 0 1

-

Since the minimum calculated displacer velocity of 0.7 foot per second (0.213 meter per second) is more than the design limit of 0.1 foot per second (0.03 meter per second), the diameter of 11.83 inches (30.05 centimeters) is satisfactory. The prover's calibrated section is calculated as follows: '

Therefore,

N,,, = 2800 meter pulses The minimum pxaver volume is calculated as follows:

v,,,==NmIP,

= 2800/8400

= 0.33333 barrel (0.05299 cubic meter) = 14.000 gaUons (52.996 liters) = 3234.Ocubic inches (52,996 cubic centimeters) The minimum diameter of st prover's calibrated chamber at the maximum flow rate is calculared as follow: Dp= [Q,/ (0.7854&)]0-5

In SI units,

In %isexample the minimum prover length, based on the minimum volume and diameter of the prover section, is as follows:

L,,, In St units,

Lp,m,= 52,996 / [(0.7854)(30.052)] = 74.72 centimeters

The error in the displacer's position during a prover pass can be estimated as follows:

Dp= [Q, 1(0.7854'&)]0.5 Where:

Where:

D,= internal diameter of the prover's calibrated chamber, in inches (centimeters).

= 3234 / [(0.7854)(11 .832)] = 29.42 inches

u d = [2(rrl$ sd))

Lp

Ud= range of error in the displacer's position during a prover pass, expressed as a fraction.

-

-

2 = number of displacer positions during a prover pass. rd=-range-of-rep3atabilityof the displacer detector or detectors, in inches (centimeters). sd= range of stability in the mounting position of the displacer detector or detectors, in inches (centimeters).

.

In this example the minimum Iength of the prover's calibrated section for a maximum error range of 0.0002 (0.02 percent) in displacer positions during a prover pass would be is follows:

L,,, = 2(rd4 sd)/ Ud = [2(0.00140.001)J10.0002 = 20 inches

In SI units, LPlmh) = 2(rd + sd) f u d = [2(0.00254 -t O.OW4)I 10.0002 = 50.8 centimeters

Since the minimum prwer length corresponding to the minimum diameter 129.42 inches (74.72 centimeters)] is longer than the minimum prover length based on displacer detector error [20 inches (50.8 centi- . meters)J, the former prover length. is satisfactory. 495.3 SUMMARY OF PROVER DESIGN CALCULATlONS

he minimum volume equals 14.000 gallons (52.996 liters); The minimum diameter equals 11.83 inches. (30.05 centimeters). The minimum kngth equals 29.42 inches (74.72 centimeters). 4.3.5.4

OTHER CdNSlDERATlONS

When operating at its maximum design flow rate, the small volume prover shall allow the displacer to wme to rest safely without shock at the end of its travel. When the prover is operating at its maximum flow race with liquids for which it was designed, there shall be no sign of cavitation in the prover, the valves, or any other apparatus within the specified temperature and pressure ranges.

All jnstallation components of the small volume prover, including connecting piping, valves, manifolds, and so forth, shall be in accordance with the applicable piping codes. Once the prover is onstream, it becomes a part of the pressure system. 3f the proving section and related components are installed aboveground, they shall have suitable hangers and supports prescribed by the applicable codes and in

accordance with sound engineering principles. Adequate provisions should be made for expansion and contraction, vibration, reaction to pressure surges, and other conditions. Suitable valves shall be installed to isolate the prover unit from line pressure during maintenance, removal of the displacer, replacement of seals, cleaning, and recalibration. Likewise, connections on the prover or in the lines should be considered for subsequent recalibrations. All units shall be equipped with vent and drain connections, and provision should be made for the disposal of liquids or vapors that are drained or vented from the small volume prover section. This may be accompiished by pumping liquids or vapors back into the system or by diverting them to a collecting point. Temperature and pressure devices shall be installed in suitable locations near the meter and the prover so that they can be used to determine the temperature and pressure of each.. Blinded valves or valve connections should probably be provided on either side of a bubbletigbt block valve in the carrier stream to serve as a permanent connection for proving portable meters. Installations in hazardous locations must be recognized as such, and all wiring and controls in these locations shall conform to the requirements of NFPA 70 and any other applicable electrical standards. Provisions shall be made for proper grounding and electrical installation of portable small volume provers. Components shall come from the class and group that are most appropriate for the location and operation. AI1 electrical controls and components should be ptaced in a location that is convenient for operation and mainte nance. Manufacturers' instructions should be strictly followed during the installation and grounding of such items as eIectronic counters, pulse-interpolation equip ment, and signal cables (see Chapter 5.4). Pressure relief valves and leak-detection facilities shall be installed with discharge piping to control thermal expmsion of the liquid in the small volume prover while it is isolated from the main stream. Power controls and remote controls should be suitably protected with lockout switches between remote and adjacent panel locations to prevent accidental remote operation while a unit is being controlled locally. Suitable safety devices and bcks should be installed to prevent inadvertent operation of or unauthorized tampering with equipment. Automated or power-operated meter proving systems may be equipped with emergency manual operators for use during a power failure. Small volume provers may require straining or filtering equipment,

-.

4.3.7

Calibration

ing the prover, field standards, and test liquid in a stable temperature environment shaded from direct sunshine 4.3.7.1 GENERAL CONSlDERATlONS to allow the equipment and liquid to reach an equilibrium temperature. A small volume prover must be calibrated before it is Water is the ideal calibrating medium because of its placed in senice to determine its base volume (the calihigh heat capacity, low compressibility, and low coeffibrated volume corrected to standard conditions). Pecient of thermal expansion compared to petroleum riodic recalibration of the prover is aIso required. Chapliquids. The use of any other medium in these measures ter 12.2 gives details for determining dl the correction changes the surface tension; consequently, the measure factors and calculating the base volume. Some of the is no longer calibrated. To prevent contamination of the differences in calcolating the base volume of a small water, the prover and fill lines must be void of foreign volume prover are discussed in the following paramaterials. graphs. The displacers should be moved through the small The accuracy of the base volume (documented on a volume prover enough times to flush the prover and calibration certificate), as determined, cannot be better eliminate air that may have been caught in parts of the than the accuracy of the field standard used in detersmall volume prover system and to allow both the metal . mining it (see Chapter 12.2). and liquid of the prover system to reach a common and It should be clearly understood that the base volume steady temperature. Uninsulated small volume provers of a unidirectional prover is the calibrated volume corthat are calibrated outdoors under hot or cold condirected to standard conditions and displaced between tions should be temporarily insulated and sheltered to detectors for a single pass. The base volume of a bireduce variations in temperature. In addition to stabidirectional prover is the sum of the volumes displaced lizing the prover, it is necessary to verify that the valves, between detectors for a round trip of the displacer and seals, and displacer are secure and that there is no leakcorrected to standard conditions. age from or around the prover. Some unidirectional small volume provers have one The temperature and pressure of the water at the or more shafts attached to the displacer. The shaft may . prover, between the displacer and the standard meabe continuous or may be on only one side of the dissures, s h a then ~ be observed and recorded as the templacer. If the shaft is continuous and uniform, the effecperature and pressure in the prover at the start of calitive upstream volume may be equal to the effective bration. downstream voIume; however, if the shafl is on only Test measures for the calibration of small volume one side of the displacer, the effectiveupstream volume provers shall comply with the requirements given in will differ from the effective downstream volume. For Chapter 4.7. High-sensitivity field standards with a further clarification, if the shaft is on the upstream side resolution of 0.02 percent or better are recommended of the displacer, the effective volume when a meter is for use in calibrating smaIl volume provers. Only a sinproved upstream of the prover will be less than the gle field standard or as few field standards as possible effective volume when a meter-is proved downstream of should be used during a waterdraw calibration of a small the prover. Conversely, if the shaft is on the downvolume prover. stream side of the displacer, the effective volume when The prover may be calibrated using small-diameter a meter is proved upstream of the prover will be greater water lines and temporary valves. Automated fastthan the effectivevolume when a meter is proved downresponding valves actuated by the detector switches, stream of the prover. The difference in volumes is called solenoid valves, shall be used. (See commonly equivalent to the volume displaced by the shaft. Both Figure 5.) Provjsions shall be made to ensure that no volumes shall therefore be stated on the calibration cerwater bypasses the field standard. The data recording tificate. If only one volume is determined, the ceM1sheets should be checked and signed by all parties that cate shall clearly state and identify the side of the prover witness the calibration. that is calibrated to ensure that it is the side used t o prove a meter. 4.3.7.3 CALIBRATING BlDlRECTlONAL The methods of calibrating a small volume prover PROVERS include the waterdraw method, the gravirnetricmethod, After completion of the preparatory steps for flush- . and the master-meter method. The waterdraw method, ing air out of the prover and stabiiizing the temperature, described in 4.3.7.2, is by far the most common. at least one trial calibration run should be made to 4.3.7.2 WATERDRAW METHOD determine the approximate voIume of the smaIi volume prover between its detectors so that the appropriate The calibration of smallvolume provers by the waternumber and sizes of 6eld standards can be estimated. A draw method may be simplifiedwhere possible by phc-

minimum number of field standards should be used (see Chapter 4.7). Bidirectional calibration runs should now be started. The displacer should be driven past one of the switches into the space just outside the calibrated volume at either end of the small volume prover. The valves should be reversed so that the displacer travels toward the section to be calibrated while wasting the effluent water. Before reaching the detector, the water should be wasted slowly through a fast-acting automated valve. The waste should be stopped by using'the fast-acting automated valve at the .instant the switch indication shows "ON." The temperature and pressure of the water in the prover should be recorded. .Next, all additional effluent water should be directed into the selected field standards. The withdrawals should be continued until the last field standard is .being filIed. The withdrawal should be reduced to a controllable slowbleed rate through the fast-acting automated valve until the "OW' switch indication is observed at the second detector point; the withdrawal should be stopped at the instant the switch shows "ON." The total of the fieldstandard voIumes indicates the observed displaced volume between detectors in that direction of travel under conditions of pressure and temperature that exist at the start of calibration. The fill condition of the drain hose and other withdrawal equipment shall be the same at the end of the withdrawal as it was at the start; --Asimilar-displacer-trip should now be made in the opposite direction, repeating the procedure. These two Mps do not necessarily have to agree in observed displaced volume because the action of the detectors may be different for each direction of travel. The calibrating procedure should be repeated until satisfactoryrepeatabzty is achieved. The average of at least two consecutive round trip corrected volumes within 0.02 percent (+0.01 percent of the average) is required. The corrected volume for the' consecutive trips in any given direction shall also agree within 0.02 percent (20.01 percent of the average). The base volume is the average of two or more consecutive round trips of the displacer within the tolerances after correcting to the standard temperature'and pressureFailure to repeat may be caused by leaking values, air in the system, varying pressure, improper condition of the displacer or detectors, or poor calibration technique. 4.3.7.4

CALIBRATING UN1DlRECTlONAL PROVERS

The bask volume of a unidirectional prover is the volume that is displaced as the displacer moves from

one detector switch point to a second detector switch point. The described one-way trip procedure should be repeated until satisfactoryrepeatability is achieved. The average value for a minimum of two such one-way corrected volumes is considered the base volume for the prover at standard conditions. This pubbeation does not restrict the determination of the base volume to two consecutive runs. More runs may be used if agreed to by the parties involved. The procedure for calibrating a unidirectional prover by the waterdraw method is substantially the same as the procedure described for a single one-way trip of the displacer in a bidirectional prover. The results of two or more consecutive runs (as agreed upon by the interested parties) shall agree within 0.02 percent (k0.01. percent of the average) or better to determine the base volume. For waterdraw calibration of the upstream section with the displacer moving in the opposite direction, the procedures are exactly the same .except that care must be taken to use the same edge of the detector trigger that is used in calibrating the downstream section, and the displacer and valve seals must be confirmed in this direction. In effect, the difference between upstream and downstream volumes is equivalent .to the area of the shaft or shafts times the length between detector trigger points. 4.3.75

REPEATABILITY

Repeatability is only one component of'caIibration accuracy. By filling the same field standards with the test runs made at an equal rate, an operator can complete a series of erroneous calibrations as the result of a consistent leak. This hazard can be reduced or eiirninated by making an additional run at a rate change of at least 25 percent. With a changed flow rate, a different volume (after correction) that is outside 0.02 percent (-t0.01percent of the average) of the initial runs (after correction) indicates the possibility of a leak in the proving circuit, which must be corrected before cafibration can be achieved. All corrected volumes at both now rates shall fall within 0.02 percent (+.O.Of percent of the average). This is true of both unidirectional and bidirectional provers. 4.3.7.6

CERTIFICATE OF CALIBRATION

After a small volume prover is calibrated, the data sheets shall be used to prepare a certification of calibration. The certificate shall state the calibration method used, the base volume or volumes, the reference conditions, the serial numbers, and the date. For unidirectional small volume provers that have a shaft attached to the piston, the certificate shall clearly

pulse-interpolation or other types of counters used in conjunction with small volume provers shall be verified for correct operation before proof runs are conducted. (See Chapter 4.6 for descriptions of calibration tests and functional checks.) Automated small volume provers that incorporate microprocessor computer sequencecontrol, pulse interpolation, data acquisition, and data reduction shall be tested for functional operation before meter proofs are conducted. Such systems should contain self-test features to verify the operation of computer software and hardware. Manufaciurers'procedures and recommendations should be followed in accordance with the appropriate sections of the Manual of Petroletun Measurement Sraniiiards. In unidirectional smaIl volume provers, a proving m consists of one trip of the dispIacex through the calibrated section.

state and identify the side of the prover that is calibrated to ensure that it is the side used to prove a meter, .- -

1

4.3.8

Operation

Proving with small volume provers requires the same good practices commonly associated with pipe provers. All valves in the flow path between the meter and the small volume prover must be positioned so that fluid cannot be diverted from or added to the stream. All valves associated with the proving system must include a method for detecting leaks and must be free from leaks. The proving systern shall include at least one temperature indicator in the flow line adjacent to the meter and at least one indicator adjacent to the prover (see 4.3.5.3). Pressure indicators shall be installed at appropriate locations to measure pressure at the meter and the prover (see 4.3.5.4). Venting should be performed on the smdl volume prover and at other appropriate Iocations to ensure that air or gas is not trapped in the flow system before proving. Steady flow shouId be established in the system to ensure stable temperature and pressure before proving. The need for maintaining back pressure on the meter/ prover system depends on various factors such as fluid velocity, fluid vapor pressure, and operating pressure and temperature. (See Chapters 5.2 and 5.3 for recommendations.) Meter pulse output should be checked to ensure pulse integrity. Mechanical or electrical meter register tests should be conducted before proving. The displacer seals of small volume provers should be checked for sealing integrity in accordance with the manufacturer's recommended procedure.

Note: Care must be exercised during the use of displacers that inmrporate a rod or rods, since the volumes upstream and downstream of the displacer will &edifferent.

In bidirectional small volume provers, a proving run consists of a round trip of the displacer (that is, the sum of two consecutive trips in apposite directions through the calibrated section). ,

.

4.3.9

- . -

-Nonuniform

Pulses

Caution is. recommended when gear-driven pulse generators are used on displacement meters to ensure that backlash, drive-shaft torsion, and cyclic effects do not cause irregular pulse generation. If these problems occur, an evaluation of the gearing and pulsegeneration systems should be made to ensure that proper equipment is selected to provide optimum performance, Problems should be referred to the manufacturer of the meter and the small volume prover.

APPENDIX A-EVALUATION OF DISPLACEMENT METER PULSE VARIATIONS A.1 General During the development of Chapter 4.3, a question was raised about the magnitude of the pulse variations in conventional displacement metex systems. No experience or data were known, and two manufacturers volunteered to test several meters to define the range of pulse variations that could reasonably be expected. variations Some ofthe terms used to describe include interpulse linearity and pulse interspace variations. In fact, the concern is with pulse frequency variations within one cycle or rotation of a meter-measuring element or the gear train that provides the output motion for the proving pickup or counter. Gear systems, ul-&enal joints, and clutch-type adjustment devices are known to impart acceIerationswithin a single revolution of a meter. The same variations may occur in &erndriven turbine-meter outputs and turbine-meter rotors where the magnetic plugs are not uniformly spaced Qn the perimeter of the rotor* These are probably minor variations compared with those that would be expected from displacement meters. NO tests were performed on turbine meters. Forty-four tests consisting of 1 0 4 5 provings with a small volume prover and 11 tests consisting of five pass provings with a 54-barrel unidirectional displacement pr&er were completed and recorded. The results are summarized in A.2 through A.4.

A.2 A2.1

i I I

I

Equipment METERS AND PROVERS

The displacement meters were connected in series in flowing-Iiquid test loops with nominal 15-gallon small volume provers for the tests. A conventional 54-barrel displacement prover was in the loop in one series of tests. The meters were new production units available at the manufacturer's test facility. Each had limited pretest operation. The pulses were generated in tbe conventional manner from commercial displacement meters. Two 3-inch meters, two 4-inch meters, and one 6-inch meter were used. In additian, a 3-inch and a Binch meter were equipped with special close-coupled pickup arrange-

to the pe*omance of measuring element only,without the influenceof gears and shafts.

merits

A.2.2

RECORDER

A precision bigh-frequency recording system was used for the tests at both locations. The &pen recorder

with a chart speed of 50 millimetersper second was used to display the pulse trains generated by the meters.

A.3

Analysis of Results

The chart records of the test were analyzed manually if^ the pulse variations. following method was used: 10 Want

a. Pulses generated by several rotations of the meter system were recorded. b. he n m b e r of pulses representing 0.25 pDon of squid passing through the meter was and marked. This resulted in 25- and 50-pu1se segments for the mete, that were tested. E. ]en@ of represented 4,me pulses from 0.25 was md iecorded. d. The series of chart lengths was plotted in bar-gaph style. ,. m e maximum chart length (that is, h e lowest frequency segment) and the minimum chart length (that is, the highest frequency segment) a meter rotation ,re identified. g. The pulse variation was calculated as follows: -C

Percent pulse range = (maximum chart length minimum chart length) x 100 2 x mean chart length

-

A.4

Results

A.4,1

GENERAL

Figures A-I, A-2, and A-3 illustrate the typical bargraph analysis and results. The plots represent typical results obtained for the three meter sizes and the accessory equipment noted on the respective figures. The graphs are typical and cannot be considered specific for any given manufacturer's equipment. The charts do, however, illustrate the quality of the pulse output for various accessory arrangements and indicate the trend in pulse quality that may be expected from more or less equipment on a meter stack. A.4.2

EXPLANATION OF BAR CHART

A displacement meter equipped with a pulse generator produces a series of electrical pulses separated by sPaCa. Fm simPMeation, a puls bo cornidend have a length'of % inch, which is then followed by a space of Y1 inch. This is termed a SO-percent-on/ 50-percent-off p d s train. This is predicated on the meter operating at a constant flow rate.

may

Even though the meter be running at a constant flow rate, krehlarities in the meter's drive mechanism may cause the pulse train to be alternately compressed and expanded.

Each of the bar charts has a horizontal and vertical axis. The hoxizontal axis represents the total number of pulses accumulated over a given period of time, and the numbers shown represent pulses counted on a linear chart. The vertical axis represents the number of inches

between the pulses counted on the horizontal axis. Thus, on Figure A-1 the first six pulseslspaces account for 15.9 inches, whereas the second six pulses and accompanying spaces account for 16.0 inches, and so forth. The shortest and the longest lengths in the barchart group are 15.85 and 16.1 inches, respectively. Thus, 16.1minus 35.85 divided by the mean length of 16 inches is equal to 1.5 percent interspace variation.

SECTION 3-SW

VWME PROVERS

18

APPENDIX &METER

FACTOR DETERMINATION WITH SMALL VOLUME PROVERS I

B.l

General

The contributors t o the initial Chapter 4.3 perceived a need to provide guidance for the development of acceptable meter factors with small volume provers. The methods described in the following paragraphs have been demonstrated to yield meter factors either comparable to those obtained from conventional displacement provers or considered to be accurate within usual tolerances by virtue of the repeatability of individual passes or prover round trips or groups of passes or prover round trips from properly operated systems. Calculation details shall be in accordance wirh the usual practices and as documented in Chapter 12.2. The meter factors obtained from two sepatate provers for a specific meter and operating condition will rarely agree exactly because of the differences in the equipment, base-volume calibration tolerances, meter repeatability, and other factors. Agreement within 0.04 percent (+0.02 percent of the average) is generally considered acceptable for normal industry practice if no other agreement has been defined. The following methods, based oa observations and experience, were compiled by the working group before 1986. The methods are for guidance only; they are not a final recommendation, nor are they all-inclusive. Other methods, some of which were arrived at by various statistical techniques, exist but have not been sufficiently demonstrated to be listed here. The methods will ultimately be replaced by mature techniques to be documented in a future section of Chapter 4 that wiU address operational aspects of proving and will supersede this appendix.

8.2 Method 1 Turbine meters and displacement meters whose pulse generation is directly from, or very close to, the measuring elements can be proved with the samemethods used for conventional displacement provers. This normally consists of five consecutive passes or round trips that repeat within 0.05 percent (20.025 pexcent of the average). The berage of the results from these passes or prover round trips then becomes the meter factor to be used in subsequent operations.

6.3 Method 2 Meters that have a nonuniform pulse output [that is, turbine and dispIacement meters with gear trains, shaft couplings, and shaft-driven accessories) may be proved by ,increasing the number of passes or prover round trips or by increasing the repeatability tolerance. For example, 10 passes or prover round i;ips that repeat within 0.10 percent.(*0.05 percent of the average). The average of the prover-pass r e d t s becomes the meter factor to be used in subsequent operations. Additional passes or prover round trips may be added as required to accommodate meters that repeat beyond 0.10 percent (50.05 percent of the average) because of the nonuniform pulse characteristics. For example, 15 prover passes or prover round trips that repeat within 0.15 percent (st0.075 percent of the average) would be the next level of consideration. The rationale for this procedure is that as the number of passes or prover round trips is increased, the repeatability performance of the meter usually increases and at the same time the quality of the average improves. '

B.4

Method 3

A meter that has more severe nonuniform pulse output or a prover that is minimal in size may necessitate using the following method. The concept is to accumulate individual prover passes or prover round trips to form groups and then to average each group, The ranges of these groups should fall within tolerances that are consistent with the first and second methods, The average of the group averages then becomes the meter factor to be used in subsequent operations. Increasing the number of passes or prover round trips in each group will improve the quality of the intergroup repeatability. Twenty passes or prover round trips per goup is considered a practical limit; more will not improve the quality. If an acceptable repeatability is not obtained in 20 or fewer passes or prover round trips, the meter manufacturer should be ~ ~ m u l t e d ,

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Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section &Tank

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SECOND EDITION, MAY 1998

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'

Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 4-Tank

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FOREWORD Chapter 4 of the Manual of Petroleum Measurement Standards was prepared as a guide for the design, instaIlation, calibration, and operation of meter proving systems cmmonly used by the ~najorityof petroleum operators. The devices and pracljces covered in this chapter may not be applicable to all liquid hydrocarbons under all operating conditions. Oher types of proving devices that are not covered in this chapter may be appropriate for use if agreed upon by the parties involved. The informalion contained in this edition of Chapter 4 supersedes rhe information contained in the previous edition (First Edition, May l978), which is no longer in print. It also supersedes the information on proving systems contained in API Standard 1101, Measurement of Petroleum Quid Hyrlucurbons by Positive Displacement Meter (First Edition, 1960); API Standard 2531, Mechanical Displacenrent Meter Provers; API Standard 2533, Metering Viscous Hj~drucarbons; and API Standard 2534, Measurement of Liquid Hydrocarbons by Turbine-Meter Systems, which are no longer in print. This publication is prirnariIy intended for use in the United States and is related to the standards, specifications, and procedures of the National Institute of Standards and Technology (NIST). When the information provided herein is used in other countries, the specifications and procedures of the appropriate national standards organizations may apply. Where appropriate, other test codes and procedures for checking pressure and electrical equipment may be used. For the purposes of business transactions, limits on error or measurement tolerance are, usually set by law, regulation, or mutual agreement between contracting parties. This publication is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved. Chapter4 now contains the following sections: Section 1, "Introduction" Section 2, "Conventional Pipe Provers" Section 3, "Small Volume Provers" Section 4, "Bnk Provers" Section 5, "Master-Meter Provers" Section 6, "Pulse Interpolation" Section 7, "Field-Standard Test Measures" Section 8, "Operation of Proving Systems" API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should bc submitted to the Measurement Coordinator, American Petroleum Institute, 1220L Street, N.W.,Washington, D.C. 20005.

iii

Chapter 4--Proving Systems Section 4--Tank Provers

1 Introduction

4 Equipment

Throughout this chapter a prover tank shall be considered an open or closed volumetric measure that generally has a graduated top neck and may have a graduated bottom neck. The volume is established between a shut-off valve or bottom-neck graduation and an upper-neck graduation. The requirements in this chapter are intended for crude oiI and refined petroleum products. Meter proving requirements for other fluids should be appropriate for the overall custodytransfer accuracy and should be agreeable to the parties involved.

4.1 GENERALCONSIDERATIONS All components of the tank prover installation, including connecting piping, valves, and manifolds, shall be in accordance with applicable pressure codes. Once a closed tank prover is on stream, it becomes part of the pressure system. Provisions should be made for expansion and contraction, vibration, reaction lo pressure surges, and other process conditions. Consideration should be given to the installation of valving to isolate the tank prover from line pressure when the system is not in use or during maintenance. All closed tank provers should be equipped with vent and drain connections. Provisions should be made for the disposal of liquids andfor vapors that are drained or vented from the tank prover. The disposal may be accomplished by pumping liquids or vapors back into the system or by diverting them to a collecting point. Blind flanges or valve connections should be provided on either side of a double block-and-bleed valve in the tank prover piping system. These connections can serve as locations for proving portable meters or as a means of calibrating the tank prover by the master-meter or waterdraw method.

2 Scope This chapter specifies the characteristics of stationary (fixed) or portable tank provers that are h general use and the procedures for their calibration. Guidelines are provided for the design, manufacture, calibration and use of new andor replacement tank provers, and are not intended to make any existing tank provers obsolete. More specific design criteria are available in NET'Handbook 105-3, SpeciJScarions and Tolerances for Graduated Neck-Type Volumetric Field Standards (includes Provers, per Section I. 1 of MST 105-3).Consideration musl also be given to the requirements of any weights and measures authorjty that may be involved.

4.2 VALVES All valves used in a tank prover system that can provide or contribule to a bypass of liquid around the tank prover or the meter or to leakage between the tank prover and the meter shall be double block-and-bleed valves, or the system shall be provided with valves and piping that are the equivalent. A method for checking leakage in the valve system is required.

3 Referenced Publications The current editions of the following standards, codes, and specificationsare cited in this chapter:

API Manual ofPetmleum Measurement Standards Chapter 1 . Vocabulary Chapter 4 Pmving Systems Chapter 5 Metering Chapter 7 Temperature Determination Chapter 11 Phystcal Properties Data Chapter 12 Cu~culationofPetroleurn Quantities Chapter 13 SfuiisticalAspects ofMeasuring and Sampling

4.3 WIRING AND CONTROLS All wiring devices and controls shall conform to the applicable codes, Electrical controls and components should be.located in a convenient place for operation and maintenance. 4.4 SAFETY DEVICES Safely relief valves, with discharge piping and leak detection facilities, shall be installed to control thermal expansion of the liquid in the tank prover and its connecting piping while they are isolated from the main stream. Automatic and remote controls should be protected with lockout switches or circuits or both between remote and local panel locations to prevent accidental remote operation while a unit is being conb;olledlocally.

MST1 Handbook 105-3 Specifrcazions and To~eruncesforGraduated Neck-Type Volumetric Field

Standards 'National Institute of Standards and Technology, Gaithersburg, Maryland 20899. 1

'

CHAPTER 4-PROVING SYSTEMS

2

depend on the maximum pressure to which the prover may be subjected and the characteris~icsof the liquid to be metered. The construction of a tank prover shall be strong and rugged enough to prevent distortion of the vessel that would significantly influence measurement when the rank prover is full of liquid at the proving pressure. Tank provers shall be constructed to ensure complete drainage of all liquid to the lower reference level without trapping pockets of liquid or sediment. Changes of cross-sections should be gradual and sufficiently sloped so that gas bubbles will not be trapped, but will travel to the top of the tank prover. As the tank prover is e m p lied, the liquid will quickly drain. The tank prover should be as self-cleaning as possible so that corrosive products, valve grease, and other foreign matter will not collect inside. Arrangements should be made for periodic internal inspection of the tank prover. Lining a tank prover to prevent rust can, in some cases, greatly extend the intervals between calibrations. Gauge glasses should he capable of being cleaned, or swabbed out, without being removed from the tank prover. Appurtenances should be installed in locations that are convenient for quick and practical operation and precise readability.

Safety devices and locks -should be installed to prevent inadvertent operation of, or unauthorized tampering with, equipment. All automated or power-operated meter proving systems should have emergency manual operators for use during an accident or power failure. Grounding devices should be provided to protect against electrical shock or static discharge in both tank prover and electrical instrumentation. 4.5

CLOSED SYSTEMS

If the liquid to be measured by meter has a high vapor pressure, a closed tank provjng system should be used. Open tank provers (with or without evaporation control) or closed tank provers may be used for liquids that have low vapor pressure. The distinction between low-vapo~pressureliquid and highvapor-pressure liquid depends on whether its equilibrium vapor pressure is less or greater than atmospheric pressure at the operating temperature. 4.6

NECKS

Tank.provers may have top and hottom graduated necks (see Figures 1, 2, and 3) or a top graduated neck only (see Figures 4 and 5). The top and bottom graduated-neck scale tank prover is a vessel that has a redu&d cross-section neck so that a more accurate determination of incremental volume can be made. It may he used as either an open or closed tank prover and js suitable for most liquids. Both top and bottom 'necks should have graduated scales and gauge gIasses or other suitable means for indicating the liquid level. Each neck may have one or more gauge scales. The top graduated-neck tank prover is a vessel lhat has a reduced cross-section neck at the top only and may be either open tx closed. The neck should have gauge glasses or another suitable means for indicating the liquid level. The neck may have one or more gauge scales.

During meter proving operations there are occasions when the meter registration, used in meter-factorcalculations, is derived from an auxiliary proving counter rather than from the meter regisler. In such'cases, steps shall be taken to ensure that all volumes indicated by the proving counter are also reflected in the meter regisler.

5 Design and Construction 5.1 GENERAL CONSIDEFIATIONS

The design of a tank ,proving system should include the piping, instruments, and auxiliaries as well as the tank prover. The design and materials used jn construction and the codes applicable to a closed pressure-type tank prover will

5.2 TEMPERATURE MEASUREMENT .

Temperature measurement of the test liquid in both the meter and the tank prover is essential. All temperature devices should be checked with an N1ST-cerlified thermometer, or a precision thermometer that is traceable to a NIST-certified thermometer. Temperature devices should be checked frequently to ensure continued accurate indication (see API MPMS Chapter 7-Temperature Determination). Temperature devices of suitable range should be graduated in fractional degrees and should be accurate within '12'~ ('14'C) or better. The location of remperature sensors in the tank prover is important. The use of one sensor in tank provers that hold up to 100 gallons (380 liters) is acceptable. The use of two sensors is recommended in tank prbvers that have a capacity of at least 100 gallons (380 liters) but not more than 500 gallons (1900 liters). Three sensors should be used in tank provers that have a capacity of 500 gallons (1900 liters) or more. If one sensor is used, it should be placed in the center of the tank prover vertical height. If two sensors are used, one should be located in the upper third of the vertical-tank height and the other in the lower third. If three sensors are used, one should be located within each third of the tank prover shell height. When more than one sensor is used, sensors should be equally spaced around the tank circumference. Where tank prover operating pressure allows, temperature sensors should be installed directly through the tank prover shell without using a themowell. A stem immersion depth of one third of the tank radius is recommended; however, a min-

Spray line and nozzle (optional)

7

-

Vapor recovery system connection {optional)

Pressure gauge must be above

glass

0.5 percent prover VOIUme

Sealing wire and seal Calibrated vol~mE?

Gauge glass

0.5 percent prover volume

Gauge scale

Temperature sensor

Temperature sensor c-z , = .3

Overlapping gauge glasses Swirl plate (optional)

Cone bottom, dish bollorn (optional) Flanged tw cleanout (optional)

0.5 percent of tank bottom

Sealing wire and seal

L Inlet or discharge Figure I-Closed imum depth of 12 inches (30 centimeters) is desirable, provided that the sensor does not extend past the tank prover centet If temperature sensor wells must be used in a tank prover (for example, when pressure is great enough to require them), the sensor well shduld be constructed so that it has the smallest possible diameter and metallic section consistent with the necessary strength. 5.3


A pressure gauge is required on dosed tank provers. The gauge shall be of suitable range and calibrated to an accuracy of2 percent of full-scale reading. Gauge connections shall be above the uppermost liquid level and sloped to avoid trapping vapors or liquids.

5.4

PROVER CAPACITY

The capacity of a tank prover shall not be less than the vol-. ume delivered in 1 minute at the normal operating flow rate through the meter lo be proved. The capacity will preferably be 1lh times the volume delivered in I minute.

Stationary Tank Prover

The inside diameter of the necks on tank provers shall be such that the smallest graduation represents no more than 0.02 percent of the total volume of the tank prover. The inside diameter of the neck shall not be less than 3% inches (10 centimeters). The capacity of the upper neck h i n g within the gaugeglass length shall be at least 1.0 percent of the tank prow volume, and the capacity of the lower neck falling within the gauge-glass length shall be it least 0.5 percent of the tank prover volume. When large-capacity meters are to be proved, a longer reading range (larger neck capacity) may be required to provide observation of the liquid level during the time required for manipulating the valves. 5.5 CONNECTIONS

Tank prover inlet and outlet connections will depend on the particular application involved. If a submerged fill pipe is used, it shall be permanently installed and equipped with a vapor bleed vaIve. The pipe shall be sized to accommodate the maximum flow rate of the meter being proved (see Figure 4) and so minimize splash and turbulence. The tank

Sealing wire and seal 0.5 percent of prover volume

Gauge glass and scale

Calibrated volume 0.5 percent of prover volume

Overlapping gauge glasses

Temperature sensor

Cone bottom, dish bottom (optional)

Swirl plate (optional)

Boltom inlet (optional)

Bottom valve must be In vert[cal line

0.5 percent of prover volume

.

Drain for calibration ~urpases and for zeroing liquid l&l

Inlet or discharge

Figure 2-Open

Stationary Prover Tank (Drain-to-Zeroor Bottom Gauge-GlassType)

prover outlet conneclions should be sized to permit rapid emptying of the tank prover, and provisions made for indicating the drawdown level. All inlet and outlet valves shall be of the double block-and-bleed type. A vent should be provided at the highest point of the tank prover to remove any gas that may accumulate.

An upper gauge glass and scale shall cover at least 1.0 percent of the nominal volume of the tank prover, while a lower gauge glass and scale shall cover at leas1 0.5 percent.

5.6 GAUGE GLASSES

Tank provers are normally calibrated at atmospheric pressure using water. When tank provers are calibrated and owated at almospheric pressure, no pressure-volume corrections are needed; however, when a tank prover is to be operated at pressures above aunospheric,a correction must be made for the resulting increase in the tank prover volume over the volume determined in the calibration at atmospheric pressure. This correction should be experimentally determined during the calibration (see6.7).

Gauge glasses shall have a minimum inside diameter of % inch (16 millimeters), preferably {arger. Shown in Table 1 is the capillary rise for several sizes of gauge glasses and water. Gauge glass fittings on rank provers should be installed directly into the walls of the neck or the body of the tank prover. Additional gauge glasses may be provided to cover the main body of the tank prover. The suggested maximum length for any single gauge glass is 24 inches (60centimeters). This length minimizes errors that result from temperature differences between the liquid in the gauge glass and in the tank prover. The gauge-glass scales shall be subdivided into !he desired increments. Scales shall be securely mounted behind or immediately adjacent to the gauge glasses. Tbey shall have pravisions for vertical adjustment and scaling into a pennanent position. Scales should be made of cornsion-resistant metal with a coefficient of thermal expansion similar to that of the tank plover material.

6 Tank Prover Calibration 6.1


Table I--Capillary Rise in Glass Tubes with Varying Water Quallty Capillarv Rise. Inches

Tube Diameter. Inches 518

314 1

.

Pure Water

Aerated Water

Dirty Water

0.025 0.015 0,005

0.0060

0.016

0.0035

0.012

0.0011

0.005

Bleed valve Submerged fill pipe

,Temperature

sensor

Temperature

'Leveling

jacks

\ arsvity outlet

Figure $--Portable Prover (Drain-to-Zero or Bottom Gauge-Glass Type) Water is considered the best medium for calibration. There are two industry-accepted methods of calibrating tank provers: a. Calibration by means of field standard test measures; or b, Calibration by means of a master meter. The preferred method, using field standard test measures, involves either the determination of the volume of water withdrawn from the full tank prover into field standard test measures; or the determination of the volume of water taken from field standard test measures to fill the tank prover. The recommendation of this standard is that it is preferable to calibrate a tank prover by withdrawing water into test measures, however, in certain installations it may be expedient to reverse the procedure, In either case, the appropriate water-volume corrections shall be applied, to compensate for the temperature differences between the $water in the tank prover and the water in the field standard test measures. The second calibrating method involves wing a master meter, previously proved by a Master Prover, where tank provers are large enough that the use of field standard test measures is impractical, or when cjrcumstances, such as those found in the desert or the arctic, are not physically wmpatible with water calibration using test measures.With this method, water or a stable low viscosity petroleum liquid may be metered into or out of the tank prover, and correction factots applied as necessary. The following general procedures apply to the calibration of both permatlently installed and portable tank provers:

a, The cank prover shall be internally cleaned and shall be plumb and level, b. All devices and instruments that affect the inlemal volume of the prover, such as spray lines, temperature sensors, and gauge glasses, shall be in place.

c. Tank provers, including all valves, fittings, and blinds that hold the test liquid, shall be checked for leaks. d. Provisions should be made for convenient filling and withdrawal of the test liquid. I

6.2 PROCEDURAL UNCERTAINTY IN PROVER CALIBRATION

MPMS Chapter 13 contains procedures to estimate the standard devia~ionand uncertainty of meter prover calibration procedures. Range limits of 0.02% between high and low runs are normally used to prescribe tank prover calibration acceptance requirements. The estimated standard devialion of the average of the two to five calibration runs that agree within a range of 0.02% are shown in Table 2. The uncertainty of the average at the 95% confidence level of two to five calibration runs that agree within a range of 0.02% are shown in Table 3. Table 2-Estimated Standard Deviation of Average Tank Prover Calibration Sets Estimated Standard Deviation Number of Cal. Runs 2

(Percent)

0.018

Table 3-Uncertainty of the Average at the 95% Confidence Level of Prover Calibration Sds Number of Cai. Runs 2 3 4

5

Uncertainty i0.159 d.029 10.016 10.011

SECTION4-TANK

PROVERS

7


Temparature sensor Flexible connection

Cone Alternate bottom inlet

, hose

Drain-to-zero valve . . .

Figure !?--Open Portable ProverTank With Pump Assembly

6.3 TEMPERATURE STABILITY

The calibration of tank provers may be sirnpIified, when possible, by placing the tank prover, field standard test measures, and the liquid in a constant temperature enclosure for enough time to allow the equipment and test liquid to reach an equilibrium temperature. The calibration should preferably be conducted under these conditions to minimize the temperature changes of the equipment and test liquid during the calibraljon. Coriection factors for the effects of temperature on water and steel must be applied (see 6.6 and MPMS Chapter 12Calcubtion of ~etiwieurnQuantifies).

To prevent accumulation of air bubbles on the inside of the tank prover walls, the tank prover should not be allowed to stand full of water any longer than necessary to stabilize the lernperature before the calibration is started. 6.4 CALIBRATION BY THE WATERDRAW METHOD 6.4.1

Tank Provers WlthTop and Bottom Necks

In tank provers that have top and bottom necks, either of two methods may be used to calibrate the lower and upper necks. The first method, described in this section, consists of determining and marking the actual capacity of the tank prover on the scaie. The second method consists of installing previously marked scales and preparing tank tables in appropriate units of measurement. Each melhod has both advantages and disadvantages, and either method may be used if agreeable to all the parties concerned.

The followingprocedure describes a method of calibrating a lank prover with top and bottom necks at standard conditions and at atmospheric pressure using water as a calibrating liquid:

a. To remove any floating debris, the tank prover should be filled to overflowingwith water and allowed to stand for several minutes; then the debris should be flushed off the top. All drain valves should be checked for leaks. The withdrawal line must be free from air. After filling, the water source shall be disconnected at Ihe inlet valve. b. The upper neck shall be calibrated. The water drawoff shall be opened slightly until the water level appears at the extreme top of the upper gauge glass; the valve shall then be closed. This point should be temporarily marked on the gauge scale, and the water withdrawals should be started. Decrements should be marked on the gauge scale as the water is withdrawn one test measure at a time from the tank prover into the chosen test measure. When the level approaches the midpoint of the upper gauge glass at the completion of a whole decrement, a mark should be made on the scale and identified as the assumed upper reference level. Withdrawals should be continued, and the scale should be marked,as before, as long as the liquid level remains in sight in the upper gauge glass. These measured divisions may be subdivided as desired to complete the calibration of the upper neck. The upper and lower necks may be calibrated as a separate exercise. c. Withdrawal of the water from the main body of the tank prover should be continued, one test measure at a time, using a conveniently sized field standard test measure until the water level is approximately at the top of the lower gauge glass.

8

CHAPTER ~-PAO

Withdrawals should be contimed from this point with the test measure used in the upper-scale operation, and the lower gauge scale should be marked in the same decrements. The lower reference level for the uncorrected nominal volume of the tank prover should be set on a whole decrement mark midpoint on the lower gauge scale. The volumes withdrawn between the upper and lower reference levels should be corrected for any water temperature variations that may have occurred during the calibration run, as described in 6.6. This corrected total should be recorded as the corrected volume for the run. d. Finally, the lower neck below the lower reference level should be calibrated. Withdrawal should be continued one field standard test measure at a time below the lower reference level until the liquid level reaches the lower end of the gauge scale, which is marked at each measured interval. This calibration should be repeated until two or more consecutive runs, after correction, agree within a range of 0.02 percent. The average of the consecutive tank prover volumes shall be used as the calibrated volume of the tank prover. The final operation is to permanently mark the upper and lower reference levels,.and all graduations, on both the upper and lower scales, and to attach the scales securely and permanently to the rank prover necks, sealing lhem to preventunattended or unauthorized movement.

6.4.2

Tank Provers WithTop Neck and Bottom DralnValve

The following procedure describes the method of performing a "to-deliver" calibration of a tank prover with a top neck and a bottom drain valve as the lower reference level at standard conditions, using water as the calibrating liquid a. Water should be withdrawn into the test measure by one of the following methods: 1. Gravity method. The piping should first be disconnected below the bottom valve. Water shall be withdrawn through the bottom valve of the tank prover into test measures using a hose or pipe sloped for free and complete drainage. The bottom valve and any other drain valves should be,closed to perform a leak check. Tests for leaks shall be made by pouring a small volume of water into the rank prover. After the leak check is made, the bottom valve shall be opened to drain the water through the drain hose. The prover and drain hose must be emptied, but the hose should be left wet. The bottom valve shall then be closed, and the tank prover filled with water. to the extreme top of the upper gauge glass. This liquid level should be temporarily marked on the scale. 2. Pump metirod If elevating the tank prover above the test measures is not practical, a pump may bo used, If a pump is used, the hoses and pump should be purged of air,

and with this pump running (pumping against a blocked vaIve at the test measure filling line), the bottom valve on the tank prover shall be closed. The liquid level should then be temporarily marked on the scale. 6. The upper neck shall be calibrated. Withdrawals should be made using a suitable test measure. Decrements should be markg on the gauge scale as the water is withdrawn. Withdrawals should be continued one at a time as long as the liquid level remains in sight in the upper gauge glass. c. The body of the tank prover shall be calibrated using one of the following methods: 1. Gravity method. Withdrawals shall be made through the bottom valve with a conveniently sized test measure until all the water has been withdrawn. The last withdrawal may be a partial test measure volume, which must be determined to the nearest 1 cubic inch (10 cubic centimeters). This partial volume should be converted into linear inches (centimeters)of the upper neck. A temporary upper reference level should be established near the center of the scale, to bring the volume of the tank prover, below the upper reference level, to a whole unit of volume. The gauge scale should be marked at this temporary upper reference level. Throughout this operation, temperature corrections should be made as described in 6.6. 2. Pump merhod. If a pump is used, the bottom valve must be closed when the liquid level nears the bottom "zero" before the pump is turned off. The pump and hoses may then be disconnected, and a final withdrawal should be made directly into a small test measure or transfer container. d. The calibration should be repeated, starting with the tank prover, filled to the new temporary reference level, until two or more consecutive runs, after correction, agree within a range of 0.02 percent. The average of the tank prover volumes shall be used as the calibrated volume. The upper reference level should be temporarily marked on the gauge glass or on a part of the tank prover, immediately adjacent to the scale, so that the scale may be removed for permanent marking. e. All required graduations shall be permanently marked on the upper gauge-glass scale and adjusted to the corrected upper reference level; the scale shall be securely and permanently attached to the prover neck and sealed to prevent unintended or unauthorized movement.

6.4.3

Small Tank Provers With Top Neck and Closed Bottom

Small tank provers with top necks and closed bottoms are used to prove small meters and calibrate provers. The best practice js to send small provers to the NIST, or another approved competent laboratory, for calibration. It is possible and permissible to calibrate small tank provers by using field standard test measures and suitable glass graduates. If drying the prover after each emptying is convenient, the prover may be calibrated to contain; when the prover is calibrated and

used in this manner, it will be most accurate for measuring liquid hydrocarbons. If the prover is intended to calibrate large provers using water, fhencal&r&pg the prover to deliver is more suitabIe. The following procedure should be used to calibrate small lank provers as described in this section: a. The inside of the prover should be thoroughly dried if the prover is to be calibrated to contain. To calibrate the tank prover 'Yo deliver:' it must first be filled with water and then emptied, allowing the water to drain for the prescribed draining time. b. The tank prover should be placed in a level position and checked with a leveling insirument. c. Water should be poured into the tank prover, one test measure at a time, from certified field standard test measures. The temperature of the water in each test measure should be recorded. The tank prover should be filled to a whole unit volume le,vel near the center of the neck. This level should he marked on the gauge glass or tank prover shell as the temporary reference level. The temperature of the water in the tank prover shouId now be determined; after any necessary temperature corrections are made, the corrected volume should be recorded for the run. d. The calibration shall be repeated until two or more consec-. utive runs, after correction, agree within a range of 0.02 percent. The average of the volume shall be used as the calibrated volume. e. Having started with the tank prover filled to the established reference level, the upper neck, above and below the established reference level, should be calibrated by adding or extracting water and measuring it in a glass graduate. This may be done conveniently by using a syringe. The tank prover reference level and scale graduations should be permanently marked on the gauge scale, and the scale should be fastened and sealed. 6 5 CALIBRATION 8~THE MASTER-METER

METHOD In calibrating some tank provers, particularly large ones, using a master meter may be more expedient than filling individual field standard test measures. The following general procedure shall be used for mastermeter calibration: a. A non-lemperatore compensated direct-drive master meter shall be proved, and its meter factor shall be determined at the intended flow rate, pressure, and temperature, using a calibrated master prover or field standard test measure, and the same liquid with which the master meter is intended to calibrate the tank prover, The preferred test liquid is water; however, a stable, low viscosity petroleum liquid may be used, if Ihe necessary temperature and pressure corrections are available and accepted by all parties.

b. The tank prover shall be calibrated in accordance with the appropriate methd, except that volumes should be indicated by the master meter rather than by counting test measures. If the tank prover being calibmted is equipped with a neck or necks, it is often more practical to calibrate the neck or necks using test measures, and the body of the tank prover calibrated using the master meter. c. Sufficient temperature readings shall betaken to compute the average temperature of the metered liquid. Volume corrections necessitated by temperature differences between the metered x made. liquid and the liquid in the filled tank prover must l

The following procedure describes the use of a master meter in a ''todeliver" calibration of the body of a tank prover, with top and bottom necks, using water, at standard conditions:

a. The top and bottom necks shall be calibrated using field standard test measures. b. The master meter shall be connecfed so that water may be removed from the tank prover through the meter at the required rate of flow. A pump may be required. The tank prover should then be filled with water to the reference mark in the upper neck, and the master meter should be sufficiently purged during the filling operation to ensure that the master meter and all the piping are full of water. c. The tank prover body should be calibrated by withdrawing water from the tank prover through the master meter. The master meter reading, and water temperature, shall be recorded. Water should be withdrawn until the level appears at the top of the lower gauge-glass scale. During this withdrawal the master meter must be operated at the rate at which it was proved. The meter factor should be applied to the observed meter volume, and temperature corrections should be made to bring the metered volume to reference conditions.A temperature correction for the steel in the tank prover must: also be made to the volume metered to determine the calibrated volume of the tank prover at standard conditions. See MPMS Chapter 12-Culculadon of Petroleum Quantities. If the master meter is stopped when water reaches the top of the lower gauge-glass scale, the volume from there, to the lower reference, must be determined from the calibration in Item (a) to obtain total tank prover volume to the lower reference level. d. The calibration shall be repeated until two or more consecutive runs, after correction, agree within a range of 0.02 percent. The average of the tank prover volumes shall be used as the calibrated volume. e. The required graduations shall be marked on the gaugeglass scales, which shall then bbe attached and sealed.

6.6 TEMPERATURE CORRECTIONS Correction factors for the effects of temperature on water and steel must be applied (see MPMS Chapter 12-Calcrrhtion of Petroieum Quantities). The following procedure is

10

CHAPTER 4-PROVING

for the withdrawal of water from a tank prover into test measures. If the tank prover is filled from the test measures, appropriate changes in the procedure must be made. Tfie following is the volume correction procedure, for a change in the water ternperdure, during the calibration of a prover:

a. The starting tank prover temperature shall be recorded. If there is more than one thermometer in the tank prover, then the average temperature shall be determined and recorded, as the starting tank prover temperature. b. The volume of each test measure withdrawal shall be recorded. c. The temperature of the water in each test measure withdrawn shall be recorded. The temperature shall be measured immediately after the volume is filled and read. d. The difference between the water temperature in each test measure withdrawal and the average starting temperature in the full tank prover shall be recorded as a temperature rise, or a temperature drop, with respect to the average tank prover starting temperature. e. The temperature-correction factor for each test measure volume shall be determined (see MPMS Chapter 11-Physical Properties Data), and multiplied by the volume of the test measure. The sum of these corrected volumes is the tank prover volume at reference candilions for this run (see MPMS Chapter 12-Calculation ofPetmroleum Quantities).

SYSTEMS

spheric pressure shall be recorded. While the water temperature is kept as constant as possible, gas or air should be introduced into the top of the tank prover, in pressure increments, until the maximum operating pressure has been reached. With each increment of pressure, the indicated volumes of water at the pressure shall be recorded. The next step is to reduce the pressure, in the same increments as above, until atmospheric pressure is reached. The volume change in the water, between each increment of pressure, shall be measured and recorded, along with the pressure increment. The average that results from the first and second steps, for each pressure increment, is used to calculate the pressure-correction factor. From the above data, a table or graph of volume-correction factors versus pressure js prepared for the tank prover operating range. The formula for finding the factor is given as follows:

Factor = 1 +

decrease in liquid observed increase in tank volume caused - volume caused by by increase in pressure increase in pressure beginning tank volume

6.7 DETERMlNlMG ATANK PROVER VOLUME UNDER PRESSURE If a tank prover is to be used at a pressure above atmospheric, a correction must be made for the resulting increase in the tank prover volume over the volume that was determined in calibrating the tank prover at atmospheric pressure. This correction shall be experimentally determined, for each tank prover, during the calibration procedure, and after the tank prover has been calibrated at nunospheric pressure. For a tank prover that is used at a single operating pressure, a corntion factor should be determined at that pressure. If the tank prover is u&d at varying pressures, correction factors shaU be determined throughout the range of operating prek sures. A table or graph of pressurecocrection factors should be prepared to provide the necessary correction data during operation of the tank prover. Facilities are required to pressurize the tank prover to its maximum operating pressure. Tank provers [hat have top gauge glasses must first be filled with water, to a mark near the top of the upper gauge glass. This gauged volume of the water in the tank prover at atmo-

where

P = observed pressure, in pounds per square inch gauge (kilopascals).

Y, = observed volume in the prover at 0pounds per square inch gauge (atmospheric pressure).

Vp = observed volume in the p r o y at pressure increment.

Q = calculated or measured volume of water between the bottom reference mark and the drain valve used to control withdrawal (if applicable).

F = compressibility factor for water, 0.0000032per pound per square inch gauge (O.OOW0847 kPa) above atmospheric pressure.

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MPMS Ch. 4.1, Introduction

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MPMS Ch. 4.2, Conventional Pipe Provers

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Total

--

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MPMS Ch. 4.6, Pulse interpolation I404081

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MPMS Ch. 4.8, Operation of Proving Systems

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SPECIAL NOTES AA publications n & d y address problems of a generalnamh With respect to particular ~ t a n c e s , . l o c a lstate, , and federal law^ and ~gdationsshould be reviewed. API is not undertaking to meet the duties of eqIoyem, manuor suppliers to warn and properly train and equip their employees, and others a p e d , concerniug health and safely risb and pnxautim, aor undertaking W obligations uuder local, state, mfeddlaws. . Infomationconcerningsafety and health risks and proper ptxautions with respect to particular materials and conditions should be obtained from the employer, the m.auufactmror supplier of that ngerjai, or the d a l safety data sheet. Nothing contained in any API publication is to be construed as granting any right, by implicationor otherwise,for the manufacture,sale, or use of any method, apparatus, or product covered by letters patent. Neither should an-g contained in the publication be owstrued as inswing anyone aga+st liability for Mrhgement of Ietters patent. Genaally,Am staodards are reviewed and revised, ~d3bnec4or withdrap at least wery five years. Sometimes a one-time externion af lop to two years will be added to this review cycle. This publication will no longer be in effect five years after its publication date as an operathe Am standard or, where an extension has been granted, upon republication. Status of the publication can be ascatabed h m the APlUpstream Segment [kkphone (202) 68280001. A catalog ofAP1publications and materials is published mually and updated qaarterly by Am, 1220 L Street, N.W., W d g t m . D.C.20005. This document was produced under API standar-on procedures t?mt ensum appropiate notilication and participation in the developmntal p r a a s and is designated as an Am suundatld. Questions concerning the interpetation of the content of tbis smdard or commts aad que-stidns concerning d.le pn>oedures undet which this standard was developed should be directed in writing to the genemi manag;er of the Upslmm Segmeat, American Petmleum htimte, 1220L Street, N.W., Washington, D.C. 20005. Requests fot permission to repmduce or traoslate all or any par&of the material pubzishd herein shoutd also be addressed to the generalmanager. API smdards are published to facilitate the bmd availability of proven, swnd enginee~ ing and ope+g practices. These stan& are not intended to obviate the need for apply. ing sound engineering. judgment legardhg when and where these slandards should be utilized. The formulation and publication of API standards is not intended in any way to inhibit anyone fiPm using any o ~ p ~ . Any manufacturer marking equipment or materials in CanFmwce with the marking qukments of an API standard is solely responsible for comp1ying witb all the applicable requirements of &at standad Am does not represent, wamnt, or @manteethat such products do in fact cunfonnto the applicable AH standad.

All righe me& No pan ofh* work may be npmduce4 8 t d in o rehieVal system, a mnsmitted by my mans,ekctmk m e c h i d , phiacopyfng, mcoding, qr otherwise, w*thoutprior w&en penniss2on&na the publishex Cantkt the Publisk API fiblidzing S e r v h , 1122 0 Stmet, N.N,Warhingtcnr, D.C. 2W5. Cdwolght 0 IWArnrsIcan ~etroleum bdma

:

FOREWORD -

.

Chapter 4 of the Manual of Petmleum Mearur-ementStandards was prepared as a guide for the design, installation, calibration, and operation of meter proving systems'mmmonly used by the maj&ty of petroletun operaton. 'Ibe devices and practicescovered in this chap ter may not be applicable to aU liquid hydrocarbDns mdw all operating coaditions. Other types of proving &vices that not covered in this chapter may be appmpriate for use if agreedupon by the patties involved The informstion contained in this edition of Q a p x 4 supersedes the infonnation contained in Iheprevious edition (First Edition, May 1978). which is no longer in print It also supersedes the infmatiw on pmving systems contained in API Standard 1101, Meosmment of Pemlewn Liquid Hydmcarbons by Ibsitive Displacement Meter (First Edition, 1960); A H Standard 2531, Mechanical Dispbcemeent Meter Pmvers; APL Standard 2533, Metering Viscous Hydrocarbons;and A H Standard2534*M e m u m ?of liqu2tlydmqtr bons by 12trbine-Meter&stetmi, which are no longer in print lids publicatiqn is primarily intended for use in the United States and is related to the . standards, specifications, and p r o d m of the National Bnreau of Standards and Technol'Whenthe information provided h e ~ i nis used in other comtries, the speciticaogy tims a d procedures of the appropriate national standards organbations may apply. Where appmphate, other test codes zmd pmcedum for checking press= and electrical equipment may be used. For the pwposes of business msactiom, iimi?s on m e or ormeasurement tolerauce am usually set by law, &tion, or mutual agmmmt between conmc$ug parties. This pub& cation is not intended to set tolerances f a such pwpw&; it is intended anly to de&i methods by which acceptable approaches to any desired accm6 can be achieved. MPMS Chapter 4 now contains tb following sections: Section 1, 'Introduction" Section2, "Conmtional Pipe I'nmrs9' Section 3, ''Smalt%lum Promi* section 4, 'Tankbvm* Section5, 'Master-MeterProvers" Section 6, hterpo1ati011'' Section 7, 4FieldSimdardTkst Measures'' section 8, b 4 ~ m t i o n *mn Section 9. 'Calibration of ProvmW API publicationsmay be used by anyone desiring to do so. Every effort bas been made by the htitllte U, assure rhe aamacy and reliab'ility of the &la contained in them-, however, the institute makes no representation, w m t y , or guarantee in cwolectioa with this publication and hereby expressly disclaitn~any liability 0s responsibility for lass or darnage resulting firm its me or fm the violation of any federal, state, or municipal qphtion with which dris publicationmay oonffict . @%ed and should be submitted to the general &ag@ of the Suggested reviaions Upstream Segment, American Petrofeum Institute, 1220 L Sheef N.W., Washington, D.C.

20005.

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CONTENTS

4

..................... 1 .................................................2 ................................... 2

DOUBLE-CHRONOMEfRY PULSE lNTERlWLATIlOlV 4.1 ConditionsdUse 4 3 Flawmem Operating Req-e~ts

6 FIJNCllONAL OPERATIONSTEST REQ-

fi-

A-1 I)oub(d!hm~ometryT&

..................... 2

.................................. 7. ........................................... 8

Diagram A-2 Cefication Test Equipment for Double-CbronomeaY P u l s e I n ~ 1 a ~ oSystem m

generated during the proving run, and measlrting the time intervals, Tl and T2.TIis the time interval between the h t

flowmeter pulse afier tbe h t detector signal and tbe rn flowmeter pulse after the last detector signal. T +is the time interval between the first and last detector signals. The pdse countas, or timers, started and stopped by the signals from the pwer detector 6idetectom. T%e time intervals TI,m p o d i n g to N, p b , and T2,corresponding to the interpolated number ofpulses (NI), are measured by an rate clock. Tfae ioeerpdated pulse count ir given as faUows:

The use of doub~e-chronometryin meter proving requires

tbatthe di-tim of the time intervals TIand Tzbe better than i 0.01%. The t h e periods T1 and Tz shall therefore be at least 20,000tiraea greaterthan the reference period Tcof tbe clock that is used to measure the t h e intends. The clock fkquency F, must be bigh enough to ensure hat botb the TI and Tz timers accumulate at least 20,000 clock pulses during the pmve opemian. This is not dBcult to achieve, as current elecimnics 'technology u d for pulse interpdlation typically uses clock kquenciea in the megahertz range. '

The conditions described in 4.6.2.1.1 through 4.6.2.1.3 apply to doubl&n~metry pdse inkqolation as described mthischpm 4.1.l The inte~polatednumber of pulses, NI,will not be a whole numbek. N1 P therefore runnded off as d e s c n i in section 3.12 of MPMSChaptw 12.2, Part 3.

4.1.2 Pubinterpolation methods are baed an the assumptions that amal flow rate does not chauge substantially dming tbe period between succeseive meter pulses, and each pulse repments the same volume. lb maintainthe validity of thb assumption, the shoH period fluctuationsin the Bow rate dwbg the proving operatid shall be mhimbd

a. ~f& p& repetitim rate at constant Bow rate cannot be -bed within the limits given in MPMS Chqter 4.3. then the Bowmetercan be used with a pdse-interpalationsystem only at a Iower o da ~ l e d . vk~this case, a revised calibration accuracy evaluated m multiple nms with averaging techniques. b. The meter pulse continuity h rota* flowmeters should be in accordance with MPMS Chapter 4.3. The generated flowmeter pulse can be obse~edby an o s c i l l ( ~ ~ ~whose ~pe, time base is set to a lninimutn of one fall cycle, to venify meter puIse continuity of ?heflowmeter. c. The repeatability of nomtating flowmeters wiU be a function of the rate of change in pulse fbquency at a constant flow

rate. To apply polse-interpolation techniques to nonrotaring flowmeters, the meter pulse continuity of the flowinem should be in with MPMS Chapter 4.3 to maintain the &%ration accuracy. d. TBe size aud shape of the signal generated by the flow meter should be suitabIe for w n t a t i o n to the pulseinmpolation system. If necesssry, the signal should undergo ampMcation and nhaping befm it en- the pulse-intqx&hlsystem.

The proper operation of pulse interpolation elechnnics is crucial to accurate meter proving. A functional field test of the total system should be p e r f d paiodically to ensure that the equipment is perfomhg correctly. This may simply be a band calculation verifying that the equipment correctly calculates the interpolated pulses per 4.6.2, or if need be, a camplete certification test as described in 4.6.3.2. if a problem is suspected

6 Functional Operations Test

Requirements

Became pulse interpolation equipment contains high speed counters and timers, it is important tbat equipment be installed b accodance with the manuthcbmr's installation i n s ~ ' o n s&by , sdhizing the risk of counting S@MIB pulses caused by electrical. interference accurring during the proving opemiion. o he signal-to-noise ratio of the total systern SM be adequately high ta ensum bat typjcal levels of e l w W interference rejected, Refer to Chapter 5.4, Chapter 5.5, and atber sections of Chapter 4 for more deb&.

N o d indusfq practice is to use a rnimpmcessmbased prover computer to pmvi& the pulse inkqolation fun* tions. The prover computer should pmvide diagnosjic data displays or printed data rnports which show the vdue of all parameters md variables necessary to verify proper operation of the system by baod calculation. 'Ihese pactmeters md variables include, but an not limited to, tima TIand Tz,the number of whole flowmeter pulse8 N, and the calculated interpolated pulses Nl. Using the diagnostic displays provided, the unit shodd be functionidly tested by eerfonning a sequence of p v e nms and analyzing the displayed or printed mub.

The flowmeter that is being proved a d is providing the pulsa for the pubinterpolation system shaU meet the following requbmmts:

Certification tests shodd be performed by the prover computer m a a u f m r pdor shipment of the equipment, and if necessary, by the user on a scheduled basis, or as m u W y

4.1.3

a g r d upon by all interested parties. The certification testti provided in this chapter do not preclude the use of other tests that m y be performed on an actual fieldjnstallation. A block diagram of the msifmtion test equipment is provided in fgm A-2. An adjustable, certified, and traceable pulse generator with an output uncertainty equal to or less than 0.001% is installed hat provides an output signal offrequency Fm, shulating a flowmeter pulse train, This signal is connectedta the flowmeter input of the prover flow compum. A second adjustable, certified,and traceable pulse generator with an output unmlainty @to or less thaa 0.001% is installed hat provides an output pulse signal separated by time period T2,simulating the detector switch Signals. Tlxis signal is connected to the detecku switch inputs of the pmver COInputet.

The pulse iatqmlatjon function is more critical when thm are fewer flowmeter pulses collected between the detector switches. Set the output fkpency of the b t generator to p&uce i frwlwncy equal to the flowmeter that has the lowest number ofpulses per unit volume to be proved with the equipment, at the b i g k t plwing flowrateexpected. The pulse interpolationfunction is also more critical when there are fewer clock pulses collected between b detector switches. Set the pulse period of the second generator to provide a volume time, Tz equal to h t wbicb would be produced by the pnrver detectors at the M e s t proving flowrate expected. Example: A small volume prover with a watedraw volume of 0.81225 barrels will be used to prow rt turbine meter (K Factor 1000pulses per barrel) at a maxhntun of 3000 b m l s per hour.

Volume time Tz for 0.81225 barrels at 3000 bamIs per

born

Plowmeter frequency F, produced by flowmeter (KFactor 1000) at 3000hisper hots:

Tbe calculated interpolatsd flowm@r pulses N1 are simply the simulated flowmeter hquency . . F',,, times the simulated voIume time Tz.

N' =

564.0625

Verify the actual results displayed or printed by (he pmver computer under test, enswing that they are within 0.01% of cbe calcnlated valne. It is possible to select a simulation fhquency F L above whose pulse pied is exact multiple of time p.riod P2, thereby s y n c h r o ~ gthe simuIated flowmeter pulses and detector sigoala If this is the case, it will be necessary to modiEy either the simulated Bowmeter Grequeacy F',,,,or the simulated detector switch period T2 slightly to ensure that the interpolated pulses will inc1ude.afiaction'al part of a pulse.

*

8 Manufacturer's CertificationTests Certificatioatests should beperfozmed at a number of sirnula~edconditions. These condiiions should encompass the provex device's range of prover volume timea, T2,and flowmeter pulse fkquencies, Fm.The man&must provide, on request, a teat c d c a t e detailing the rmuhum and minimum values of prover volume time,Tz,and flowmeter firequency, 27,, that the equipment is designed to accept If the pulse-interpoiationeledmnics ~IEtested and verified using the equipment and pf0cedwe-sshown, they can be used during a flowmetep proving operation with confidence that they will contribute an u n c e h t y of less than & 0.01%to the overall uncertainty of the proving qmations within the pulsesignal-fiquencyrange tested.

-

APPENDIX A-PULSE-INTERPOl-ATION

At Generat

prover volume), in seconds = 2.43917 (CU-T').

The double-chronometry method of pulse interpolation is

If the required pulseinterpolation uncertainty is better than

described in 4.6.2. F i g w A-l, is a diagram of the eleclrical signah required for the teclmique. technique provide8 the numerical data requh-4 to resolve a fractional portion of a

* 0.01%. then

me

100,OOO > ( 2 0 , ~ O puIses)(S20 O hertz),

single whole flowmeter pulse. Doub1e-cbronometry p u k intaplation requites usmg the following three ei&cal counters: CTR-N, to count wbole Bowmeter pulses, CTR-TI to count the time required to accumulatethe whole flowmeter pulses, and m - T 2 to count the time between detector signals, which define the displaced prover volume. Tbe double-cbronomelry technique Feduces the total numbes of whole Bowmeter pukes m d y required for the displaced volume to fewer than 10,000 to acbieve a dis-tion u n ~ e h t oyf 0.02% (k 0.01%of the average) for a proof run. The requhd timdpulse dimhination guideha are pmsented in 4.6.2 and shall be used in conjunction with a prover d+ed in accordance with the sizing paramem &mibed in MPMS Chapter 4.3. The examples given in A.2, which conform to the guideline8 in 4.6.2, each repsent a single case of defined data and are not necessariIy representative of all available puke-interpolationmehods. .

> (IOOXSZO), > 52,000. Note: ' R e period ofthe clock is the rtd@ of the ~ ~ cT ry The period of 1 dock pulse ki therefore l/lm,ooo hem,, or 0.00001 second The discrimination of the clack is 0.00004 243914, or d.0004~.The requirement for the value of F, and the discrimination requirementin 4.62 are thereforesabfid

To calculate the interpolated pdses,

A,=

Using equipment m shown m Figure A-2, the following

Simulated data:

p;, = pulse frequency of generator number one simulating meter pdses, in hertz

A 2 1 EXAMPLE 1--INTERPOLATED PULSE CALCULATlON

= 233.000.

Tz= pulse period of generator numbertwo simulat-

The following data are given:

ing detector signals, in seconds = 1.6b6667.

Fc = clock frequency used to m e a s k the time intervals, k hertz > (20,M3Fm,

Observed data at pmver computer Wig tested:

N, = number of whole flowmeter p u b s =388. Tl = number of clock pulses m u l a b e d dwing

Fm = ffowmeter pulse output hqmcy (the maximum value for malySi8x.hhm =520.

whore e ~ ~ m e cormts t m N,,, = 166923.

N, = total number ofwhole flowmeter pulses = zoo ( m - N d .

T2 = number of clock pulse8 accumdated during simulated prove volume = 166,666.

N1 = number of intmplatedflowmeter pulses = (Td~lWm*

"

interval counted for pulses (N) in = 2,43914 (~~R-TI).

EXpMPLE HERTIFICAnON CALCULATION

data appliea:

A 2 Examples

r1 =

CALCULATIONS

Note &at both timers XI and Tz accumulated > 20,000 dock ~ s c ~ a t i O B lalviremrat delded in 4.6.2. Cornparism of rtx*

whole flowmeter

T~ = fimeinterval between die &st and -d volume &~gnals(that is, the displaoed

Nl = calculated interpolatedpulses based on cerdfied pulse gemratom, 5

,

The c e a c a t i m test agreement r ~ q u b dbetween N 1and Nz,is better than f 0.01%.then

Nl = calculated interpolated pdses based on pmver

(388.33341 - 388.33319)f 38833341 = 0.0000005

computero-ations,

The test device results agree with calcdated results based on traceable pulse genmtor data within O.COCW%. The cedfication test run is acceptable. .

Figurn A-2-Certlf lcetionTest Equipment lOr Doutlffihronmetry Pu$B tnterpolation Sydems

Addaionaf copies available from API PuMicatians and DlsMbutlon: (202)682-8375

lnfomafion about API Publiiwrs, Programs and Senrlces Is available on the World Wide Web at: MtpJM.apl.org

11'

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Order Na H06042

Manual of Petroleum Measurement Standards Chapter 4- Proving Systems Section 5-

Master-Meter Provers

FIRST EDITION, OCTOBER 1988 REAFFIRMED, OCTOBER 1993

0

American Petroleum Institute 1220 L Street, Northwest Washington, D.C. 20005

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I

Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 5-Master-Meter

Provers

Measurement Coordination Department

FIRST EDITION, OCTOBER f 988


SPECIAL NOTES 1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED. 2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANUFACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL, STATE, OR FEDERAL LAWS.

3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPER PRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDInONS SHOULD BE OBTAlNED FROM THE EMPLOYER,THE MANUFACTURER OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET. 4. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE

CONSTRUED AS GRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANUFACTURE, SALE, OR USE OF ANY METHOD, APPARATUS,OR P R O D U COVERED ~ BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABILITY FOR INFRINGEMENT OF LElTERS PATENT. 5. GENERALLY, API STANDARDS ARE REVIEWED AND REVISED, REAFFIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS. SOMETIMES A ONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW CYCLE. THIS PUBLICATION WILL NO LONGER BE IN EFFECT FIVE YEARS AFTER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR,WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLiCATION. STATUS ' O F THE PUBLICATION CAN BE ASCERTAINED J30M THE API AUTHORING DEPARTMENT [TELEPHONE (202) 682-8000].A CATALOG OF API PUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L STREET, N.W., WASHINGTON, D.C. 20005.

Copyright Q 1988 American Petroleum Instilute

FOREWORD Chapter 4 of the Manual of ~erroleumMeasurement Standards was prepared as a guide for the design, installationI calibration, and operation of meter provingsystems commonly used by the majority of petroleum operators. The devices and practices covered in this chapter may not be applicable to all liquid hydrocarbons under all operating conditions. Other types of proving devices that are not covered in this chapter may be appropriate for use if agreed upon by the parties involved. The information contained in this edition of Chapter 4 supersedes the information contained in the previous edition (First Ediiion, May 1978), which is no longer in print. It also supersedes the information on proving systems contained in API Standard 1101, Measuremenf of Perroleurn Liquid ~ ~ d r o c a & o nbys Positive Displacement Meter (First Edition, 1960);API Standard 2531, MechanicaiDisplacement Meter Provers; API Standard 2533, Metering Viscous Hydrocarbons; and API Standard 2534, Measurernenr of Liquid Hydrocarbons by Turbine-MeterSystems, which are no longer in print. This publication is primarily intended for use in the United States and is related to the standards, specifications, and procedures of the National Bureau of Standards (NBS). When the information provided herein is used in other countries, the specifications and procedures of the appropriate national standards organizations may apply. Where appropriate, other test codes and procedures for checking pressure and electrical equipment may be used. For the purposes of business transactions, limits on error or measurement tolerance are usually set by law, regulation, or mutual agreement between contracting parties. This publication is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved. Chapter 4 now contains the following sections: Section 1, "Int~oduction" Section 2, "~onventionalPipe Provers" Section 3, "'Small Volume Provers" Section 4, "Tank Provers" Section 5, "Master-Meter Provers" Section 6, "Pulse Jnterpolation" Section 7, "Field-Standard Test Measures" API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; how&er, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal replatian with which this publication may conflict. Suggested revisions are invited and shouId be submitted to the director of the Measurement Coordination Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C.20005.

iil

CONTENTS

SECTION %MASTER-METER

PROVERS Page

4.5.1 Introduction ................................................ 1 4.5.1.1 Scope................................................... 1 4.5.1.2 Definition of Terms ...................................... 1 4.5.1.3 Referenced Publications................................... 1 4.5.2 Equipment .................................................. 1 4.5.3 Meter Factor ................................................ 1 4.5.4 Procedures ...................................................2 4.5.4.1 Displacement Meters Used as Master Meters ................ 2 4.5.4.2 Turbine Meters Used as Master Meters ..................... 2 4.5.5 Records ........... ;........................................ 2 '

Chapter &Proving

Systems

SECTION &MASTER-METER 4.5.1

lntrbducti0n

4.5.1.3

AP1

Manual of Petroleum Measurement Standards Chapter 4, "Proving Sysrems" Chapter 5.3, "Measurement of Liquid Hydrocarbons by Turbine Meters" Chapter 5.5, "Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems"

4.5.2

Equipment

Any one of a fixed battery of meters that has suitable manifolding can be assigned to be a master meter. As an alternative, a selected portable meter or a meter at a test station can be assigned to be a master meter. The meter selected should be known from experience to be reliable and consistent. Master meters shall be well maintained. The master meter must not be temperature cornpensated. Its readout must indicate units of volume without corrections. The same accessories that are connected when the meter is proved must be connected when it k used to prove another meter. A master meter must have a direct drive from the measuring element to the pulse generator or the mechanical register. If the master meter is in portable service, it should be protected against damage during transportation, installation, and handling.

SCOPE

This chapter covers the use of both displacement and turbine meters as master meters. 4.5.1.2

REFERENCED PUBLICATIONS

The current editions of the following standards are cited in this chapter:

A master meter is selected, maintained, and operated to serve as the reference for the proving of another meter. A comparison of the two meter outputs is the basis of the master-meter proving method. The proving operation is considered a direct proving when a meter is proved against a pipe prover or tank prover. The operation is considered an indirect proving when a meter is proved against another meter that has already been proved by the direct method. Master-meter proving is used in situations in which proving by the direct method cannot be accomplished because of logistic reasons, such as the unavailability of provers. Where indirect proving is a practical requirement, satisfactory results can be achieved by using the master-meter method; however, the master-meter method introduces uncertainties between the meter being proved and the prover that is used to calibrate the master meter. Either the standing start-and-stop or the running start-and-stop method of proving may be used. The requirements in this chapter are intended for crude oil and refined petroleum products. Meter proving requirements for other fluids should be appropriate for the overall custody-transfer accuracy and should be agreeable to the parties involved. 4.5.1.1

PROVERS

DEFINITION OF TERMS

Terms used in this chapter are defined in 4.5.1.2.1 through 4.5.1.2.4.

4.5.3

Meter Factor

The meter factor that is applied to the master meter should be the average value of at least two meter proofs performed on the same Ijquid that wiIl be used during line meter proving. The meter factor should be developed at a flow rate 'within 10 percent of the flow rates expected during line meter proving. If the flow rates of line meter proving vary widely, a curve of master-meter factors may be developed over this range. This will provide the required master-meter factor for proving and verify the master-meter linearity. The master-meter factor shall be established by using the same operating conditions expected during line meter proving, with the master meter used as a reference standard.

4.5.1.2.1 Meter proof refers to the multiple passes or round trips of the displacar in a prover for purposes of detemining a meter factor. 4.5.1.2.2 A rneferprover is an open or closed vessel of known volume utilized as a volumetric reference standard for the calibralion of meters in liquid petroleum service. Such provers are designed, fabricated, and operated within the recommendations of Chapter 4. 4.5.1.2.3 A prover pass is one movement of the displacer between the detectors in a prover.

Aptover round nip refers to the forward and reverse passes in a bidirectional prover.

4.5.1 2.4

1

TOobtain the value of a line meter factor expressed to four decimal places, such as 1.0016 or 0.9983, it is necessary to obtain from both themaster-mete! and themeter to be proved an output that represents a discrimination of at least 1 in 10,000.

4.5.4 Procedures

'

a. If the registers can be precisely read to the nearest 0.1 barrel or 0.1 cubic meter, the minimum proof-run volume would be 3000 barrels or 1000 cubic meters; if the registers can be precisely read to the nearest 0.03 barrel or 0.01 cubic meter, the minimum proof-run volume would be 100 barrels or 100 cubic meters. If proof runs conducted in this manner are not repeatable because of factors such as slackness in the gear trains or parallax error, larger-volume proving runs shall be used, or the cause for the nonrepeatability shall be corrected. b. Both meters can be equipped with pulse generators or similar devices that are capable, of high-resolution output to obtain the required discrimination,

The master meter and the meter be proved be connected in series. and shall be close enough to rninimize corrections for volume during the proving period. Before the actual meter proving is performed, the two meters shall be operated at the desired flow rate long enough to purge the system and achieve a steady temperature and pressure. 4.5.4.2 TURBINE METERS USED AS MASTER Since it is not certain that the two meters will operate METERS at identical temperatures and pressures during the proof Turbine meters typically generate a large number of runs, the value's determined i t both r n e t e r ~ ~ h a d h a v e pulses per unit volume and are normally equipped with appropriate corrections applied. high-speed counters. The minimum 10,000 discrete volBoth the master meter and the meter to be proved ume units are therefore easily generated. should be equipped with meter registers or proving The following special precautions must be taken when counters connected so that all registers or counters can turbine meters are used as master meters: be started and stopped simultaneously. If the line meter proving registrat& is derived from something other a. A turbine master meter shall be a complete assembly than the meter register, steps shall be taken to ensure comprised of flow-straightening devices and a meter. that all volumes indicated by the proving counter are This assembly shall remain intact during transportation also reflected in the primary meter register. and operation. The master meter should be placed downstream of b. When both meters are turbines, they should both any fixed vapor separators, strainers, or other protective have flow-straightening devices (see Chapter 5.3) so that devices that service the meter to be proved. The meters one meter does not adversely affect the other. shall have no devices between them that might alter the c. Both counrers shall be started and stopped by the flow rate or the fluid properties. All fluid-diverting same signal. Electronic gating circuits are recomvalves between the meters shall be capable of demonmended. (See Chapter 5.5 for additional pulse-transmisstrating positive seals. sion and security recommendations.) When a master meter is proved against a prover, the master-meter factor that is used should be the average 4.5.5 Records meter factor of at least two consecutivemeter proofs that Complete records of all data pertaining to the master agree within 0.02 percent (&0.01 percent of the avermeter should be kept, since the historical reliability of age). the master meter is important to all parties in a measurement transaction. The records should be accessible to all 4.5.4.1 DISPLACEMENT METERS USED AS concerned parties. MASTER METERS The following two options are available for obtaining a discrimination of at least 1 in P0,000using a displacement meter:

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Manual of Petroleum Measurement Standards Chapter 4-Proving Systems


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Manual of Petroleum Measurement Standards Chapter &Proving Systems

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FOREWORD Chapter 4 of the Manual ofPetrolem Measurement Starubd?was prep& as a guide for the design, installation, calibration, and operation of meter p v h g systems c01mnOdy wed by the majority of petr~~eum operators. The devices and practices covered in this chapter may not be applicable to dl liquid hydrocarbons under all operating conditions. Other types of pr~vingdevices that are not covered in this chapter may be appmpiate for use if a& upon by the parties involved. The infozmation contained h tbis edition ofChapter 4 supersedes the information contained in the previous edition (Eust Edition, May 19781, wbich is no longer in print It also supersedes the information on pruving systems contained in Am Standard 1101, M m w ment 01Pemkm f i p i d Hydrocarfom by Positive Displacement Meter Fit Edition, 1960); API Standard 2531, Mechanical Displacement Meter Provers; APJ Standard 2533, Metering VEscous Hydmcadmw; and AH Standard 2534, Mearumment of LiquidHydmm bons by ?Mine-Meter@stew, wbich are no longer in print This publication is p r h d y intended for use in W United States and is ~ I a t e d10 W standards, specifications, and procedures of the National Bureau of Stawlards and Tecbnology (k+llST). When the information providedherein is used in other couutries, the specificslions and procedures of the appropriate national standards organizations may apply. Where appmpriate,otha test codes and procfxhuesfor checking pressure and electrical equipment may be used For the purposes of business msactions, limits on errw or measurement tolerance am usually set by law. regulation. or mutual agieement between contra* parties. This publication is not intended to set tolerances for such purposes; it js intended only to describe methods by which acceptable approaches to any desixed accwae can be achieved. MPMS Chpter 4 now contains the foI1awing sections: Section 1, 'In~uctioll" Section2, 'T3mvmtionalPipe Ptovm'' Section 3, " S d W I w Proversn section4, 'TamkProvenn Section 5, 'hrlamer-MebxProversn Section 6,"Pulse Inteqolation" Section7, 'Field-Standard Test Measureg" Section 8, "Operation ofhving Systems" Section 9. ''Calibration of hvers" Am publications may be used by anyone desiring to do so. Every effort has been made by the Instituteto assure the accuracy and reliability of the data mnlained in them; however, the Institute makes no represent~tion,warranty, or guatanteein conndon with this publication and hereby eqmasly disclaims any liability or responsibility for or damage resulting fmm ite mw or far the violah of any federal, state, or municipal regulation with wbich thk

publication may d c t Suggested revisions are invited and should be submitted to the general &ager of the Upsteam Segment, Amxican Petroleum Institute, 1220 L Stmet, N.W., Wmhingtou, D.C. 20005.

CONTENTS

3 4

........................................................ 1 DOUBLEC)IRoNOME'I'RY PULSE JBTIWOLATION..................... 1 4.1 Conditions ofurn ................................................. 2

. IUFERmces

4.2

Flowmeter Operaring Requirements

7

CERTIFJCATIONTEST

8

MANUFA-S

APPENDIX A

................................... 2

................................................

2

............................3 P U L S E . m L ATION CALCUUTIONS ................... 5 CERTIPICATIONTESTS

Aim= A-l D o u b ~ ~ n o m e t 'LEming ry Diagram A-2 CeltiG~tiw Test Equipment for DoubleChronometly Pulse Inwpdation Sys&m

.................................. 7. ........................................... 8

I

Chapter &Proving Systems Section &-Pulse Interpolation 0 Introduction

2.5 meter pulse continuity: The deviation of the interpulse period of a flowmeter expessed as a percentage of a full pulse period.

To prow meters tbat have pulsed outputs, e minimum number of pulm must be collezted during the proving period. The p r o m v01ume or the n u m k of pulses that a flowmeter canproduce per unit volume of throughput is often limited by design considerations. Under these condihm itis necessary to increase the readout discrimiaation of the flowmeter pulses to achieve an uncertainty of 0.01%. The dectronic signal &om a flowmeter can be treated so that interpoiation between adjacent pulses can occur. The techniqueeofimproving &e di6crimGation of a flowmetw's OUQMis h o w htWOhti0m Al&o''gh ~ulse-m* polation techniques were originally intended for use with small ~ I u m provers, e they can also be applied to other prov. . ing deem. 'The pulse-interpolation method known as doublechronometry, described in this chapter, is an established t~hnipueused in proving flowmeters. As'othm metbods of pulse interpolationbecome accepted industry practice, b e y should receive equal consideration, provided that they can meet the established verification tests and specifications desclrjbed hthis publication.

#

I

2.6 nonrotatlng meter. Any metering device for which the meter pulse output is not derived h m mechanical rotation as driven by the flowing s k a n ~For exampEe, vortex shedding, venturi tubes, ofice plates, sonic nozzles, and ultrascmic and electromagnetic flowmetes ~IE metering devices for which the output is derived from some chqcteristic o h than rotation that is pmpodonal to flow rate. - 2 7 pulse period: The recipmal of pulse fpequency, i.e., a pllrcfrequency of 2 a b a pllae ,,f ll2

.

I

seconds. .2.8 pulse generator: Aa electmnic device that can be programmed to output voltage pulses of a precise frquency or time -period.

2 9 puke interpolation': Any of the various t+niqucs by which &e whole number of meter pulses is counted two ems (such as dekW switch clomues); my remaining fiwtion of a pulse beiweea the two events js calculated.

Scope

2.10 rotating meter: Any metering device for which the meter pPlse output is derived frommechanical rotation as driven by the flowing steam, Por example, Wine and positive displacement meters are those metering &vfar which the output is ,derived fmm the continuous angular displacement of a ffow-driven member:

This chapter describes how the doub16chnometry method of pulse interpolation, including system opaahg req+ me& abd equipment testing, is applied to meter proving.

2.11 signal-to-noise ratio: The ratio of the magnitude of the elechical signal to that of the elmlrical noise.

2.1 detector signal: A contact closure chatlge or other signal that starts or s t o p a prover counter or timer and defbes the calkated volume of the prover,

22 double-chronometry: A puhe i

n ~ tech~ nique used to increase the readout discrimination level of flowmeier pulses detected between prover detector sigals. This is momplisbed by tesolving fbese pulses info a w&ob number ofpukes plus a fndmd part of a pule using two high speed t h e n and associated gating logic, controUed by rhe detector signals and the flowmeter

n

3 References The current editions of the following standards are cited in this chaptet:

Am MPMS Chapter 4, Pming Systems Section 3, "SSmailVolume Proyw~'' Ckopikr5, Mefehg Section 4, '%s&tation and Auxiliary Equipmeut for Liquid H y d l n m h Metering Systr:ms'*,W m 5, '%Seclty and Fidelity of Pulse Data"

2.3 flowmeter discrlminatlo,n:A measure of the stnttllest increment of change in the pulses per unit volume of the volume being ~ d .

2.4 frequency: The number of repetitions, 'orcycles, of a periodic, (for example, pubes, alternating voltage, or -nt) o c e gin a 1-second timeperiod. Tbe ntpber of cycles, that occur in a 1-secoad period is ,*tion*, expressedin hertz.

4 DoubleChronometry Pulse lnterpolatfan

,dm

Double-cfironometry p&e intmpo~atianrequires counting integer (whole) number of flowmetes pulses, N,,

the 1

i

I

generated during the provinggNn and meambg the eime intervals, TIand T2.TIis the time i n M between the first flowmeter pulse after the b t detector signal and the h flowmeter pulse after tbe last detectof signal Tz is tbe time in& between the first and last detector signals, The pulse counters, or timen, are started and stopped by ?& signals lbm the prover dekchx oi detectors.The time intends TI,companding to N, pulses, and Tz,ccmponding to the interplated number dpdses (NI), are m e a s d by an accurate clock. The interpolated pulse count is given as follows:

The use of double-chrmomehy in meter p r o wrequires that the clkhimtion of the time intends T1 and T2 be better than 0.01%. The time periods T1 and T2 shall therefmr: be at least UljHO times greater than the'refkmeMod T,of the c!&k that is used to measure the time infervals.The clock 6quency F, must be high enough to ensure that both the.TI and TZtimers acmmuIate at least 20,000 clock pulses chniug the p e operation. This is not M c u I t to achieve, as current e,lecmnics'tecbnobgy used for pulse interp6lation typically uses clock hquencies in the megahertz ~imge.

*

.

The conditions desm'bed in 4.6.21.1 tbrougb 4.62.1.3 apply to double-chron~letry pulse i n ~ l r r t i o n as described htbischttptez 4.1.1 The intapdated number of pulses. NI.will not be a whole n 4 . ATl is therefore rounded off as d e s w i in sdon 3.12ofMPMSChepfer122,Part 3. 4.1.2 Puke-interpolation methods are based on the assumprions that actual flow rate does not change substantially during the period between s u c c e s d meterpulses, and each pulse representsthe saine volume. 'ibmaintain the vaIidity of this assumon, the short H o d &ctuatim in t hflow rate dming rhc pmving operationshallbe n h i d z d

~f the pulse qetition

rate at constant flow rate cannot be within the limits given in MPMS Chapter 4.3, then the Bowmetercan be used with a pdse-interpola&n system only at a Iawer overall accuracy level. Jn tbis case, a revised caliiration ammcy evaluated or multiple rum with averaging techmique~. h me meter pulse continuity in rotating flowmetersshould be in aocordance with MPMS Chapter 4.3. The genexated flowmew pulse can be observed by an o ~ 0 8 c o p ewhose , time base set to a minirntllll of one full cycle, to verify meter p&e continuity of h flowmetea. c. me repeatability ofnomotating flowmeters will be a function of the late of change in pulse hquency at a constantflw rate. To apply pulse-intaplation techniques 10 nmtatkg flowmeters, the meter pulse continuity of the flowmeter should be in aixmdance with MPMS Chapter 4.3 to maintain the caliiratim accuracy, d The size and shape of the signal generated by the flow meter should be suitable for presentation to the pubintapcp lation system. If necessary, i k signal should undergo amplificrtticm and shaping b e f o it ~ enters the p&e-inter*tion system. a

5 Electronic EquipmentTesting The p p e r operation of pulse interpolation eIecbdcs is crucial to accurate meter proving. A A o n a l field teat of the total system should be perfbmed periadically to ensum that the equipment is perfadug correctIy. .This may simply be a hand calcnlatim verifying that lhe equipment correctly calculates the interpolated pulses per 4.6.2, cw if need be, a complete cwtiiication test aa described in 4.63.2. if a p b lemissuspeca

6 Functional OperationsTest

Requirements N d industry practice is to use a micropmssor baaed

4.1.3 Because puke interpolation equipment wnlains high speed counters and timers, it is hporhnt that equipment be installed in accordance with the m u f a c t u d s installation instructions, tlPereby mihimizing thexiskdcounthg splniaus pulses caused by electrical interference Occurring dwbg the p-g opemtion. The signal-to-noiseratio of dae total sy* tern shall be adequately high to ensure that.typical levels of elecbical interference 5qre r e j d . Refer to Chapter 5.4, Chapter 5.5, and other sections of Chapter4 for more details,

pmver computer to prmride the pulse interpoItttion h c tions. The pnwer computer should provide diaguostic data display6 or prinkd dau-repoI.tswhicb show the value of all parametes and dables necessary to verify proper operadon of the system by hand calcul~tim. These parameters and vadabIes include, but are not limited to, ttnesS Tl and T2,the number of whole flowpulses N, and the calculated interpoIated pulses Nl. Using the diagnostic displays pmvided, the unit should be htionally tested by performing a sequence of prove nms and analyzing the displayedor prjnted results.

4 2 FLOWMEPER OPEWTING REQUIREMENTS

7 CertifCcatlanTest

Tbe flowmeter &at is being proved and is providiug tbe pulses for the plllseinterpolation system shall meet the follawing lequhments:

Certification tes$~ should be Harmedby the prow computer manufacturer prior shipmt of the equipment, imd if necessary, by the user on a scheduled bask, m as m u t d y

a& upon by ail interested partis. The c&cation tests provided in this c@kr do not preclude the use of other tests that may be performed on an actual field installation.

3

Rowmeter fiquency F,,,produced by flowmeter (KFactor 0 at 3000 barfels per hour:

A block diagram of the certificationtest equipment is provided in Figure A-2. An adjustable, certified, and traceable puke generator with an atput uncertainty equal to or less than 0.001% is installed that pmvides an o u w signal of frequencyF',, simulating a flowmefer pulse train Tbis signal is connected to the flowmetesinput of the prover flow cornpatar. A second adjustable, certifiedi and tramable pulse g e m tor witb an output uncertainty equal to 01 less than 0.001% is installed that provides an output pulse signal separated by time period T2,simulating the detector switch signals. This signal is connected to the detector switch inputs of the p v e x

-P* The pulse interpolation functionis more critical when th& are fewer flowmeter p k ~ COObetween b detectm switches. Set the output frequency of the h t generator to prdduce i frquency equal to the flowmeter that has the lowest number of pulses pet unit volume to be proved witb the equipment, at the highest prwing flowrate expected. Thk pdse inlerpo1ationfunction is also more critical when thee are fewer.cloclc pulses collected between the detecta switches..Setthe p l ~ period e of the second generator to provide a-volumetime. Ta equal to that which would be produced by the prover detect- at the fastest proving flowrate a * Example: A small volume prover witb a waterdraw voIume of 0.81225 barrels will be used to prove a turbine mew (K Factar 1000 pulses per barrel) at a cumof 3000 bmki per horn Volune time T2 for 0.81225 b m I s at 3000 bands per

how

Tbe calculated interpolated flowrnefer pulses NJare s b ply the simlllated flowmeter frequency F',,, times the s h Iated ~ 1 u m time e P2.

= 833.33333 x 0.676875

v&& the actual results displayed or printed by the prover computer under test, emuring that they ate within i 0.01% of the calc111atedvalue. It is possible to select a simulation frequency F& above whose plllse period is an exact multiple of time period thereby synchronizing the simulated flowmeter pulses and detector signals. If this is the case, it will k necessary to modify either the simulated flowmeter frequency F',, or the simulateddetector switch period2' slightly to ensure that the interpolated pulses will M u & a fractional part of a pulse. 8 Manufacturer's CertificationTests Certification tests should be p e r f o n d at a number of &.nulated conditionsOllS These conditions should encompass the prover device's range of pmver volume times, T2,and flowmerespulse lkq~~encies, Fm..llbemanufacturer must provide, on request, a test certificate detailing the maximum and minimwn values of prover volume time, T2. and flowmeter f m quency, F, that the equipmeat is designed to acc* If the pulse-interpolationelechwnics an=tested and verified using the equipment and pnxedms shown, they can be used during a flowmeter proving operation with confidence that they will contribute an uncertainty ofless tbao 0.01% to the o v e d uncertainty of the proviagopewtio~uwithin the pulsesipd-mueacyrange tested. ,

APPENDIX A+ULSE-INTERPOLA'ON

A.l

prover volume), io secands = 2.43917 (CTR-2'2).

General

ha doubiechmn0metry method of fie inwpolatim is described in 4.62. Figure A-1 is a diagram of the e 1 d c a l signals requhdfor the technique. The teclmiqne pmvides the numerical data required to resolve a fiactiod portion of a single whole flow-mettr pulse. Double-cbronometzy @fie interpolation requires using the following three electrical co~tere:CTR-Nm to W U Uwhole ~ flowmeter pulses, C'ZR-Tl to count the time required to accumulate the whole flowmeter pulses, iqd CI1Z-T2to count rhe t h e between detector xignals, whicb d&e the & p M pmver volume. The doub1e-cJxonomeaytechnique r e d w the total number of whole flowmeterpulses n o d y %W, for tbe d b placed volume to fewer than 10,000 to achieve a discrimhatian uncertainty of 0.02% (k 0.01% ofthe average) for a proof nm. The reqnid WpuIse discrimination guidelines are presented in 4.63 and s W be used in cmjunction with a provex designed in accordance with the &hg parameters tksdbeb in MPMS Chapter 43. Tht? examples given in A2, which wnform to the guidelina in 4.6.2, each represat a single case of d e b 4 data and are nor necessarily representative of all available pulse-inBpolatimmethods.

Hthe required pulse-interpolationunce-ty

is better than

k 0.01%. then

100,OOO > (ZO,OOOPun, polses)(520 hertz), > t 1~)(Szo), > 52,000. Note: The period of tk?clock is the d tbe frequency, T = The perjod of 1 clock pulse is W o c p i lllooooO h a or OnOOOO1second. The discrimination ofthedock h o*~/ ,43914, or 0.04%. The requirement for the valw ofF, and the cliscihhation requirementin 46.2 are therefon: satisfied.

To calculare the intapdated pulm,

A22 EXAMPLE 2-4ERTlFlCAnON CALCtJLATlON Using equipment as shown in Figure A-2,the following data applies

Simulateddata:

A.2 Examples A.21 EXAMPE 1--INTERPOLATED CALCIJLATION

CALCULATIONS

Fm= pulse fresuency of generatar number one simu-

lating meter pulses, in hertz =233.000.

PULSE

T2= puke period of generator numk two simulat-

The following data m given:

ing detector signals, in mondg

= 1.666667. p, = ~ ~ ~ ~ c y ~ s e d t o m e & ~ ~ i n t a - data at paver computer W i g tested., Observed vals, in hertz > ( 2 0 , m I ) F m . N, = number of whole flowme& pulses = 388, F, = flowmeter pulse oUtpllt frequency (the dmum d u e far analy&);in hertz TI = number.ofclock pulses acmmulated during =520. whok flowrmter counts N,,,

N, =

Nl

. I

= 166,523.

total aurnber of whole flo~meterpulses

= zoo(ax-Nm).

T2 = number of clock pdses ammulated during simulated pmve volume

number ofinwlated flowmeter pulses

= 166,666.

=(T$Tl)N,.

Note t W both timm TIand T'- a c m m h d > 20,000 =lock . s a & ~ g the d i s c ~ a t i m detailed in 4.62. coq* of mults:

TI = time interval count4 for the whole flowmeter #a (N) in sfx:ands .a2.43914 (Cl'R-Tl1)-

T~= time i ab e r w ~ mtbe Grst and second vdmdetector signals (that is, the displaced

N1 = calculated btqmlated pulaea based on dfied pulse generam, 6

.

P

F;RxTZ

= 233 x 1.666667, = 388.33341.

Nl

r

calculated interpolated pulses based on prover computer ob~er~atiws,

=

N m (Tfll),

= 388 x 1666W166523,

The c e d f i d o n test agtwment required between N 1sad 0.01%. &en

N1,is bet@ than

*

(A", -ZVl)N1< 0.0OOl

(388.33341 - 38833319)/ 388.33341 = 05-

The test device results agree with calculated mulls based on traceable pulse peaator data within 0.000M%. The certification test nm is acceptable.

*

i, J!.

,G

n

.

---

!!I

I ~jgureA-1-DoubteChronometry Timing Diagram

Flgure A-2--Certification Test Equlprnent for DouMeChronometry Pulse Interpolation Systems

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Manual of Petroleum Measurement 'Standards Chapter 4-Proving Systems Section 7-Field Standard Test Measures SECOND EDITION, DECEMBER 1998

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Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 7-Field

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SECOND EDITION, DECEMBER 1998

American Petroleum Institute Helplng You Get The Job Done RigMP

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FOREWORD '

This publication consolidates the Iatest changes and improved technology in field Standard Test Measures since it was first published in October 1988. Units of measurement in this publication are in United States Customary ( U S 0 units and the International System (SI) consistent with North American industry practices. This standard has been developed through the cooperative efforts of many individuals from industry under the sponsorship of the American Petroleum Institute (API) and with the assistance of the National Institute of Standards and Technology (NIST). Joint participation between the API and NlST has enabled a new gravimetric calibration facility for test measures to be designed and built in Gaithersburg,MD. This new calibration laboratory will pmvide higher accuracies, improved calibration service, and r e d u d volume uncertainties in field standard test measure volumes determined at this new facility. API publications may bc used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the lns~itutemakes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted to the director of the Measure ment Coordination Department, American Petroleum Institute, 1220 L Street, N.W.,Washington, D.C. 20005.

CONTENTS page

..................................................... 1 SCOPE ...............................................................1 REFERENCED PUBLICATIONS.......................................... 1 DEFINITIONS......................................................... 1 EQUIPMENT ................,........................................2 4.1 Materials and Fabrication ...........................................2 4.2 GaugeGIass ...................................................... 2 4.3 Drain Lines ...................................................... 3 4.4 Levels and Leveling................................................ 3 4.5 Neck ............................................................ 3 . 4.6 Scale Plate and Graduations ......................................... 4 4.7 Case ............................................................ 5 4.8 Outletvalve ...................................................... 5 4.9 Nameplate ........................................................ 6 4.10 Assembly ........................................................ 6 CALI8RATION .......................................................6 5.1 General ..........................................................6 5.2 Calibrated Volume ................................................. 6 5.3 Calibration Frequency ..............................................6 5.4 .Number of Calibration Runs .........................................7 5.5 Test Measure Control Charts ......................................... 7 5.6 Seals ............................................................ 8 INTRODUCTION

5.7 Disputes.......................................................... 8

............................................. ..................... ....................

CALIBRATION METHODS 8 6.1 Gravimeuic Calibration of Neck Scale Test Measures 8 6.2 Gravimetric Calibration of Slicker-PlateTest Measures 9 6.3 Volumetric Calibration of Neck Scale and Slicker-PlateTest Measures........ 9

INSPECTlON ........................................................ 10 7.1 General 10 7.2 Documentation 10 7.3 Visual Inspection 10 7.4 Cleaning Procedures...............................................11 7.5 Integrity......................................................... 12

......................................................... ................................................... ................................................. ............................................... ................................ ....................................

OPERATION AND USE 12 Field Use of VolumetricTest Measures 12 8.2 Nonnal Test Measure Operation ......................................12 8.3 IrregularTest Measure.Operations 13 8.1

CONTENTS '

Page

A~1)ENDIXA ACCURACY REQUlREMENTS FOR VOLUMETRlC TEST MEASURES .........................................23 APP'ENDIXB CALCULATION OF UNCERTAINTY OF A FIELD ~'ANDARD TEST MEASURE ...............................27 APPENDIX C T l 3 T MEASURE CONTROL CHARTS 31 APPENDIX D LABORATORY WHGHTS AND MASS STANDARDS 33 APPENDIX E NIST CERTIFICATES OF CALIBRATION FOR HELD STANDARD TEST MEASURES (EXAMPLES)........... 35 APPENDIX F WATER DENSITY EQUATIONS ............................. 41

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Figures I Various Types of Standard Test Measures (I) 16 2 Various Qpes of Standard Test Measures (II) ............................17 3 Field Standard Test Measure- Invertible 7Lpe ...........................18 4 Field Standard Test Measure-Bottom DrainType ........................19 5 Gauge Glass and ScaleAssembly ...................................... 20 6 Field Standard Test Measure Control Chart ..............................21 7 Levels of the Petroleum Measurement Hierarchy 26

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Tables 3 1 Capillary Rise in Gauge Glass Tubes with Varying Water Quality 2 Effect of Out-Of-Level of Normal Sensitivity Test Measures on Gauge Glass Level ................................................4 Effect of Out-Of-Level of Normal Sensitivity Test Measures 3 on Measure Volumes 4 4 Scale Graduations for Normal-Sensitivity Test Measures .................... 5 5 Scale Graduations for High-SensilivityTest Measures 5 6 Scale Meniscus Errors Due to Contaminated Water ........................5 7 Range Limits versus Number of Calibration Runs 7 8 Volume Errors Due to Test Measure Internal Deposits .....................11 A l Hierarchy of Measurements for the Metered Volumes of Petroleum........... 23 A2 Uncertainty Requirements for a Petroleum Measurement Hierarchy Using a Single Custody Transfer Meter and the Waterdraw Calibration of a Displacement Prover .........................23 A3 Uncertainty Limits for Calibration of Normal Sensitivity Test Measures as Used in the Calibration of Conventional Displacement Provers 24 A4 Uncertainty Limits for the Calibration of High Sensitivity Test Measures as Used in the Calibration of Small Volume Provers 24 AS Uncertainty Limits for the Calibration &Test Measures Used for Displacement Provers 2.4 A6 Hierarchy of Petroleum Metered Volume Measurements including Calibration of Mder Provers by a Master Meter 24 A7 Uncertainty Requirements for a Petroleum Measurement Hierarchy Including a Single Custody Transfer Meter With Master Meter Prover Calibration 25

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CONTENTS

Total Hierarchy of Measurements of MeteredVolumes of Petroleum Showing International Standards, Calibration 8 of Test Measures Other Than by NIST and Meter Prover 25 Calibration by a Master Meter ........................................ Uncerhinty for the GravimetricDetermination of the Contained Volume at Room Temperature of ~ 1 S f ' s 28 100-gallon(0.379 m3) ~ e c ~k c a l e ~ e~set a s u r e .......................... . Uncertainty for the Gravirnetric Determination of the Contained Volume at Room Temperature of NIST's 29 50-gallon (0.189 m3) ~ e c scale k ~ e s~t e a s u r........................... e Uncertainty for the Gravimetric Determination of the Contained Volume at Room Temperature of NIST's 29 5-gallon (0.0189 m3) Neck Scale Test Measure. Uncertainty for the Gravimetric Determinalion of the Contained Volume at Room Temperature of NIST's .........................30 5-gal~on(0.01 89 m3)slicker plate ~ e s~easure. t Statistical Analysis Table of the Calibration Hislory of Test Measure #I23456 ..............................................31 Maximum and Minimum Limits for Density in g/cm3 .....................34 34 Application of Standard Mass Weights. .................................

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Manual of Petroleum Measurement Standards-Proving Systems . Field Standard Test Measures 0 Introduction

NET' Handbook 105 Specifications and Tolerancesfor Refreme Standards and Field Sfambd Weights and Measures, Pail 3- Specifiatiom and Tolerawes for GraduafedNeck-l)rpe Volumetric Field Standards

A field standard test measure is a vessel fabricated to meet specific design criteria and calibrated by an official agency such as the National Institute of Standards and Technology (NIST). Its primary puvose is lo provide a standardized volume, used for the calibration of displacement and tank provers, when calibrated by the waterdraw method.

3 Definitions 1 Scope This chapter details all the essentia! elements of field standard test lneasures by providing descriptions, construction details, ca]ibidon procedures, opemdon, inspection, and f etd use requirements. Accuracy and uncertainty require menh me also discussed. The nolma] volume range for test measures is 1 to 1,000 gallons, approxjmateIy 4 10 4,000 liters. The information contained in this chapter js limited to atmospheric, graduated neck type, mekt volumetic fieldstandard test measures. The volume is determined between an upper neck scale zero, and either a solid bottom or a tapered bottom with a drain line and shut-off valve, depending on the size of the test measure. Bottom-neck scale test measures and prover tanks are not addressed in this document. Test measures are classified as: a. 'To deliver" volumetric test measures. b. "To contain" volumetric test measures. Guidelines are provided in this document for the design, manufacture, calibration, and use of new andor replacement test measures and are not intended to make any existing test measures obsolete.

2 Referenced Publications The following standards, codes, and specifications mntributed to this standard and have been ,used as an appropriate resource for reference material: API Manual of Perroleurn Measurement Standards Chapter 1-Vocabulary Chapter 4.2- Conventional Pipe Provers Chapter 4.3-Small Volume Provers Chapter 4.4- Tank Provers Chapter 4.8-Guide to the Operarion of Pmving Systems Chapter 7 -Temperature Determinaiion Chapter 1 1 -Physical Properties Data Chapter 12- Calculation of Petroleum Quantities Chapter 13- Statistical Aspects of Measuring a d Sarnpling

3.1 borosilicate glass: A glass with a low coefficient of thermal ex~ansion. 3.2 brim test measure: A vessel similar to a field Stan-

dard test measure, except it has no sight glass and neck scale. It is filled until the liquid just extends to the lop of the neck due to surface tension. Any liquid overflow is caught in the reservoir beIow and drained away andor measured. .

3g calibrated volume: Also defined the Base Measure Volume (BMV);the delivered volume of a field standard test measure, at its reference lemperature,between its defined "full and empty" levels.

3.4 calibration: A set of operations which establish, under specified conditions, the relationship between the values indicated by a.measuring device and the corresponding known values indicated when using a suitable measuring standard. 3.5 Cessation of main flow: During the draining of a field standard test measure, the momenl when the fuH discharging water stream "breaks" and becomes a small trickle.

3.6 clingage: The film of liquid that adheres to the inside surface of a field standard test measure after it has been drained and is considered empty. 3.7 field standard test measure: Defined as a volumetric, nonpressurid, round, metal container, with a cylindrical neck containing a gauge glass and s~xle.Designed to stringent specifications, it "contains" or "delivers" an exact volume between a fixed bottom or a bottom shut-off valve and an upper neck scale reading.

3.8 high-resolution type: A field standard test measure designed with a smaller diameter neck, which is used to achieve greater neck volume resolution in reading the water level meniscus. This type of test measurr:is also characterized by the terms "high-sensitivity" or "high-accuracy". lNational Institute of Standards .and Technology, Gaithersburg, Maryland 20899.

'

2

API CHAPTER &-PROVING

3.9 measurement:A procedure to determine the value of a physical variable. Statements that best describe the quality of these measurements as used in this standard are defined below: .

a Accuracy. Describes the degree of closenessbetween measured values and the true value. b. ErrorJescribes the difference between a measured value and the true value. c. Precisiotz. Describes the degree to which all the data within the set of measurement variables is clustered together. d. Range. Describes the area belrveen a high value to a low value. . e. Repeatability. Describes the measure of agreement between the results of successive measurements of the same variable, by the same method, with the same instrument and operator, at the same location, over a short time period. f. ToCerance.Describes lhe maximum pennissibie error in a series of measurements. g. True value. Describes the only correct value of a variable. h. Uncertaiplty. Describes rhe range of deviation between a measured value and the true value, expressed as a percentage. For example, a device with an accuracy of 2% would have an dncertainty of 12%. 3.10 reference temperature: The temperature at which the test measure is intended 90contain" or "to deliver" its nominal capacity.

3.1 1 slicker-plate test measure: Described as a vessel similar to a field standard test measure, except it has no sight glass and neck scale. It is filled so that the Iiquld just extends above the top of the neck, due to surface Lension, where the excess is sheared off by sliding a transparent plale across the top pf the neck. 3.12 "toconta1n"volume: A method of characterization of a field standard test meahre that determines its contained volume, at reference temperature, when it is filled from a clean, dry, empty, condition.

3.13 "to deliver" volume: A method of characterization of a field standard test measure that determines its delivered volume, at reference temperature, when it is emptied from its full condition and drained in accordance with the prescribed draining time. 3.14 traceability: The property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international reference standards, through an unbroken chain of comparisons, all contmlled, and having stated uncertainties. It should be noted that traceability only exists, when scientifically rigorous evidence is collected, on a continuing basis, showing that the

measurement is producing documented results, for which the total measurement uncertainty in quantified.

SYSTEMS

4 Equipment AND FABR,~ATIoN

-A- iressel used as a field standard tesi measure shall be consrructed of corrosion-resistant stainless steel. All parts of the main body of the lest measure shall be made of the same material. All interior.sestms shall be filled and ground smooth enough to prevent any entrapment of air, liquid, or foreign material. Fabrication shall ensure that no pockets, dents, or crevices are present that may entrap air or liquid or impair the proper filling or draining of the standard. The materials of construction of the field standard test measure shall be thermally stable and not have an unduly high coefficient of thermal expansion, which might render the test measure unsuitable for field use. All applicable physical property data must be reliably documented. Any horizontal cross-section shall be circular, and the shape of the vessel shall permit complete emptying and draining. Dimensional requirements for U.S.Customary and MetricTest Measures are shown in Tables la and l b of the NIST Handbook 105-3, July 1997, pages 18-19. Where appropriate, reinforcing bands shall be used to prevent distortion of the measure or field standard when it is full of liquid. The opening at the top of the neck shall be stmcturally durable because of the thickness of the metal, or it shall be reinforced. The top of the neck shall be finished so that the level position of the field standard test measure can be determined by placing a machinist's precision spirit level across it. Proper adjustment of all replacement levels shall be achieved in this manner. The bottom of the field standard test measure shall be designed to prevent distortion when it is filled with liquid and plcvcnt damage during use. A field standard test measure in use must be leveled and stand solidly on a surface with its vertical axis perpendicular to that surface. 4.2 GAUGE GLASS A field standad test measure shall be e.quipped with a gauge glass mounted on the side of the neck. This gauge glass shall be made of borosilicate type glass or equivalent, and shall be free from any irregularities or defects that will distort the appearance of the liquid surface. Any gauge glass made of a substitute malerial must be impervious to petroleum prcducts. The gauge glass shall be installed to facilitate cleaning and removal. Replacement glass must conform to the original size and bore specified by the manufacturer. The bottom mounting of the gauge glass shall be made leak proof, without the use of cement, by using compressible gaskets or O-rings. Removal

SECTION7-FIEU) STANDARD TESTMEASURES

Table 1.-Capillary

3

Rise in Gauge Glass Tubes with Varying Water Quality Capillary Rise (in.)

Gauge Glass Tube

Diameter (in.)

Pure Water

and replacement of the glass shall be accomplished ~vithoui difficulty and without affecting the ca f ibration of the measure. Table 1 shows the effect of surface tension capillary rise within the glass tube, when using different size gauge glass tubes, due to variability of water quality. Dirty water is shosvn for comparison only and is not intended to endorse or recommend the use of dirty .or contaminated water in any test application.

4.3 DRAIN LINES If a drain line extends from the bottom center of a field standard test measure, the downward slope of the line must provide complete and proper drainage. This drain line shall be sized to provide the maximum drainage rate possible consistent with a smooth and conlrolIed drainage, while emptying the test measure. with the drain valve fully open and . adhering to the prescribed draining time. Minimum drain sizes are described in NIST Handbook 105-3, July 1997,. Tables la and lb, pages 18-19. A test measure drain is described as a gravity discharge line between the bottom of the bottom cone and the shut-off valve, It shall have a downward slope of at least 5" from the horizontal plane. All pipes cbnnected to the test measure drain line, dotvnstream of the shut-off valve, shall be positioned at an elevation to ensure the complete emptying of the test measure. A test measure that is not in a permanent installation, equipped with a bottom drain, shall have a minimum of three adjustable legs that will enabie the test mcasureto be leveled. 4.4

Aerated Water

Dirtv Water

be sealed and covered fw protection. All seals should be affixed with corrosion-resistant Series 316 stainless steel or equivalent wire. If a lrailer is used for mounting andlor transporting a Aeld standard test measure, then it shall have provision for leveling. Any truck on which a field standard test measure is mounted shall be equipped with leveling jacks-one near each comer of the vehicle. To achieve a higher precision in the calibration of field standard test measures and in their use, spirit-level precision requirements shaIl be specified, During each calibration run, operating instructions should require test-measure level verification prior to scale reading after filling. A minimum d i s crimination of two minutes (2') per division is recommended for all precision test measure levels. Liquid spirit levels vary in sensitivity from 30 minutes (30') per division to 5 seconds per division. Magnification must be used with high-precision spirit levels. The potential error due to an out-of-level test measure can be estimated as follows:

where e = Scale reading e m r (in.),

x = Distance from centerline of test measure to outside of gauge tube (in.), 8 = Out-of-level angle uncertainty,

LEVELS AND LEVELING

The level position of the field standard test measure can be determined by placing a precision machinist's spirit level across the top of the neck of the test measure. This level verification must be determined in two directions, 90"apart, and shall be used to verify the permanently mounted spirit levels. All field standard test rneasum shall be equipped with a minimum of hvo or more adjustable spirit levels, mounted at right angles to each other, or with equivalent leveling indicators on the upper cone in a protected position on the sides of the vessel. The adjusling screws for these levels shall be pmvided with a means of wire sealing and the level shall be equipped with a protective cover. Once set the levels should

Errors for various test measure sizes because of out-oflevel conditions are shown in Tables 2 and 3. The uncertainties in the tables do not include potential errors as a result of level instability of the test measures, or possible structural instability. For the purposes of measurement, errors are also caused by the failure to re-level the test measures prior to reading the scale each time. 4.5 NECK

The neck diameter of field standard test measures shall be consistent with their intended applications and required scale. resolution. The neck assembly, or the top cone area of the test

4

API CHAPTER &PROVING

SYSTEMS

Table 2-Effect of Out-Of-Levelof Normal SensitivityTest Measures on Gauge Glass Level

*

Size of Test Measure (gal.)

Uncertainty in Scale Rading, in.3, versus Level Discriminationa 530 minutes per division 10minutes per division

1 5

10 25 50 100 200 500 a Level discrimination is estimated as

Table &Effect Size of Test Measure (gal.)

*

0.011

0.004

0.011 0.01 1

0,004 0.004

&2 minutes per division

0.015 0.005 0.015 0.005 0.020 0.007 0.026 0.009 0.041 0.014 the minimum discrimination or resolution of the spirit level.

.

0.0007 0.0007 0.0007 0.0010 0.0010 0.0013 0.0017

0.0028

of Out-Of-Level of Normal SensitivityTest Measures on Measure Volumes

*

Uncertainty in Scale Readinn. .,. %Volume,versus Level Discriminations 2 minutes per division to minutes per division

rt 30 minutes per division

*

0.056 0.020 0.01 1 0.004 0.006 0.002 25 0.005 0.002 50 0.002 0.001 100 0.003 0.001 0.001 200 0.004 0.003 SO0 0.009 a Level discrimination is estimated as twice the minimum discrimination or resolution of the spirit levd. 1 5 10

ineasure and neck assembly, may be designed to open (swivel), provided that the assembly has a metal-to-metal joint, suficient clamping points to prevent distortion of the joint, and a means of ensuring that the device is properly assembled, leveled and leak-free. 4.6 SCALE PLATE AND GRADUATIONS

The scale plate shall be made of co~~osion-resistant metal and shall be mounted tangent to the front of or directly behind the gauge glass. In either case, it shall not be more than It4 in. (6 mm) from the glass. If tho scale is mounted behind the gauge glass, a shield should be provided to protect the glass and allow for replacs ment of the gauge glass without difficulty. If the scale adjus~mentprovides for movement by increments only, the maximum increment shall be 'J4 of the smallest scale division. Scale numbring on all field standard test measures shall be specifiedon the scale in milliliten (ml), cubic inches (in?), or other volume units. The units of measurement should be cleady marked on the scale. To avoid confusion and possible emrs in reading, dual numbering on any one scale (e.g. cubic inches and decimal fractions of a gallon) is not permitted. Dual numbering is permitted only if two scale plata are used; in this case. the US. customary units scale (in?) is preferred and located sn the left when the test measm is viewed from the

0.0036 0.0007 0.0004 0.0003 0.0002 0,oOCn 0.0003 0.0006

front. The melric scale (m3) is recommended situated on the light side of the gauge glass. Provisions shall be made allo\ving either scale to be adjusted individually so that the two zero lines will lie in parallel planes. The distance between scale graduations shall not be less than in. (1.5 mm). Scales shall be graduated both above and below the z m line. For neck sizes smaller than 17 in. (43 cm) in diameter, every fifth line on the scale shall be considered a major division and shall be longer than the intermediate or subdivision lines. Every major line shall be numbered with the volume to that mark. For neck diameters of 17 in. (43 cm) or larger, every tenth line may be designated a major division line. For smalldiameter, high-sensitivity measuEs that have diameters dZ3, or 4 in. (5,711~. or 10 cm),every fourth or fifth division is a major numbered division depending upon the scale incnments. A sufficientnumber of scale brackets (a minimum of two) shall hold the scale plate rigid. The brackets shall be mounted on adjusting rods. An adjusting rod shall be provided with a means for sealing that will prevent movement. The scale plate shall be securely attached to the brackets and provided with a means for sealing. ~ovemehtof the adjusting mechanism or scale plate shall not be possible without breaking the seal. All seals should be affixed with corrosion-resistant Series 316 stainless steel or equivalent wire.

Table 4-Scale Neck Diameter (id 3%

Nominal

Gallon Size 1

Table 5-scale Nominal Gallonsize

'

Neck Diameter (in)

Graduations for ~ormal-~ensilivil~ ~ e sMeasures t Minimum Number of ia3 Above & Below 0 15

Maximum Scale Spacing (in.) 0.085

Graduations for High-SensitivilyTest Measures Nominal Volume of in.3 Above &Below 0

?'he graduation lines, numbers, and other information on the scale plate shall be permanent. Graduation lines shall be of uniform width. The width of the lines shall be no more than 0.025 in. (0.6 mm) or less than 0.015 in. (0.4 mm). On scale plates mounted to the front of the gauge glass, the major (numbered) line. shall be at least in. (6 mm) in length. The intermediate Iines shall be at least 'I8 in. (3 mm) in length. The major and intermediatelines shall extend to the edge of the scale plate nearest the gauge glass. The zero line shall extend completely across the plate. On a scale plate maunted behind the gauge glass, the major (numbered) Iines shall be at least 3/4 in. (19 mm) in length. intermediate lines shall be k least in. (13 mm) in length. The zero line. shall extend completely acrass the plate. Two commercialIy available classes of test measum am designated normal sensitivity and high sensitivity. Uncertainty in the calibration is different for each class of the same size test measure. This is due to the improved scale sensitivity, and the repeatability of the smaller diameter neck in the high-sensitivity test measures. Scale graduations far normal sensitivity lest measures are listed in Table 4. Scale graduation for high-sensitivity test measures are listed in Table 5. Scale reading e m due to using contaminated water in test measures are shown in Table 6. 4.7

Minimum Discrimination Betwen Graduations ( in.3) 1

Minimum Discrimination Between Graduations ( ins3)

Maximum Scale Spacing (in.)

alter its volume. Adequate protection, such as a strong padded case, shall be provided for storing and transporting the test measure. 4.8 OUTLET VALVE It must be noted that the outlet (drain) valve of a field standard test measure is a critical component of the calibrated volume, which if modified or replaced will necessitate the recalibration of th'e test measure. Test measure dmin valves should be sealed, painted, or by some other method indicate whether the valve has been changed, modified, replaced, or repaired in any way since the last calibration. If seals are used they shouId be affixed with corrosion-resistant Series 316

Table 6-Scale Meniscus Errors Due to ContaminatedWater Error,% Volume Nominal Gallon Size

D i r t y Water

Air in Water -0.1 70

5 10 U

-0.034 -0.006

-0.108 -0.022 -0.011 -0.003

200

-0.003 6.004

4.0015 -0.002

1

-0.0 17

,

CASE

A field standard test measure is a precision instrument and must be handid with great care to avoid damage that may

,

500

-

L

6

API CHAPTER 4-PROVING

stainless steel or equivalent wire and provide positive integrity that the drain valve has not been replaced. Many test measures have drain valves that are simply screwed into the drain line. The volume is altered if this valve is turned to a different number of threads, either more or less. The importance of this valve to the calibrated volume cannot be overemphasized and properly sealing screwed drain valves should be an absolute priority for vo.olurnetric test measures. Alternatively, a metal-to-metal flange arrangement behveen the drain line and the drain valve is the preferred method of drain valve connection. This drain valve shall be a quick-acting full-openingvalve, open-ended for visual inspection, or shall have a visual-inspection device immediately downstream of the valve to detect valve failure, This valve must be leak-free at al t times. 4.9

NAMEPLATE

Each field standard test measure shall bear in a conspicuous place the name of the manufacturer, the nominal volume, and a serial or identification number. The material from which the slandard is constructed shall be shown together with its cubical coefficient of thermal expansion per "F (or 'C) for that material. 4.1 0 ASSEMBLY

All parts of the assembly d a field standard test measure and all piping and valves that affect the volume of the prover shall be fully assembled by the manufacturer or supplier.

5 Calibration 5.1 GENERAL

The National Institute of Standards and Technology (NIST) is the calibmting agency of choice in the United States for field standard test measures used to calibrate meter provers. Specifications for test.measures shall be in accordance with this standard and the latest edition of NIST Standard Handbook 105-3. Calibrations shall be made using clean potable water as the calibrating liquid. Certified laboratory graduates may be used for measuring partial volumes of the field-standard test measure. The actual capacity of the test measure,as shown on the laboratory report or calibration certificate, shall be used as the official capacity ralher than the nominal capacity of the measure. Whenever possible, calibrations of the test measure shall be maintained at an uncertainty of 2 0.01 percent or better. Water-density data provided in API MPMS Chapter 11 should be compatible with the density used by the calibrating agency, See Appendix F, Water Density Equations.

SYSTEMS

5 2 CALlBRA1E.DVOLUME Test measures may be calibrated either "to contain" or "to deliver." A field standard test measure can be designed and built "to contain" a precise liquid volume when filled from a clean, empty, and dry condition. Test measures calibrated "to contain" are not used in prover calibrations, because the "empty" condition means empty, clean, and dry before every use, usually an impractical field operations requirement. Normally test measure volumes are used in the "to deliver" mode. To prepare the rest measure for calibration use requires that it is welted prior to use. It should be filled with water to its zero mark, leveled, and then drained exactly for the prescribed draining time as given on the certificate of calibration.The test measure is then returned to an upright position or its drain vaive is closed leaving it with a controlled and repeatable amount of clingage (water) inside prior to use. To ensure that this clingage quantity is repeatable means that the test measure must be completely filled, and then emptied, in strict compljance ivith the operating procedures and draining times that are specified on its calibration certificate. Just wetting the interior of the test measure prior to use is completely unacceptable. This standard dictates that water shall be used as the calibrating liquid because of its stability, low thermal coefficient of expansion, and high heat capacity. Instructions sent to NlST for the calibration of a field standard test measure should clearly state that it is to be calibrated as a "to deliver" volume, and indicate whether this calibration shall be performed by the gravimetric or volumetric method. If the volumetric method of calibration is chosen, then the calibrated volume of the lest measure and all measurements subsequently made using it, will have a larger level of uncertainty than if calibrated by the gravimehic method. This must be acceptable to all parties using this test measure. The prescribed draining time for all test measures calibrated by NlST and drained by inverting, is currently 10 seconds afler the cessation of main jow. Similarly, the draining time for all NIST calibrated test measures having bottom drains, is currently 30 seconh afer the cessation of main jlaw. The actual prescribed draining time used however, shall be in accardance with the Certificate of Calibration for the particular test measure in use. 5.3 CALlBRATlON FREQUENCY

.

Field standard test measures calibrated by NIST, shall be recalibrated at the following regularly prescribed intervals of use:

a. Maximum certificationintervals shall be as follows: I. All new test measures shall be calibrated prior to use (initial certification). 2. All existing test measures, in regular use, shall be recalibrated every 3 years.

3. Test measures stored and infrequently used may have their recalibration suspended. Infrequent use has allowed some flexibility between successive recalibrations. In this situation, use of this test measure shall be allowed if it has a valid certificate of calibration current within the past 5

years. Coniml cbarls shall be maintained on every test measure (see Appendix C). b. Test measures shall be calibrated any time there is evidence of damage, distortion, repairs, alterations, maintenance to the test measure or replacement of the drain valve that could affect its volume or its use. c. If appropriate, it may be necessary to calibrate test measures afier change of ownership. This calibration may or may not be necessary. It shall depend on the transfer circumstances, i.e. the condition of the test measure at the time of transfer and its previously known calibration history. All these factors shall be considered in deciding whether a cdibmtion is necessary and should be determined after a careful check of all these parameters and in consultation with all interested parlies. The calibrated volume of all test measures shall he reported to five or more significant digits. All field standard test measures for prover calibrations in the United States, shall have a Certificate of Calibration, issued by NIST, that is current within the last 3 years. The Certificate of Calibration provided by NIST for the test measure shall be supplied to the owner, together with all the calibration data obtained during the calibration procedure. On some occasions, the same test measure may be calibrated by two or more different national calibration agencies; e.g. NIST and the Canadian Standards Agency (CSA) may both calibrate the same test measure for use in different cauntries. Similarly, on occasions the same test measure can be calibrated in different units of measurement. For example, the test measure may be calibrated in both in? and ml. This will require that two different cehficates of calibration, developed either by the same calibrating agency, or by two different agencies, need to be issued. Units of measurement, test measure volumes, and required drain times must all t>e folIowed exactly for the specific certificate af calibration being used. No interchanging of data or requirements between trvo different certificates of calibration for the same test measure is permitted. 5.4 NUMBER OF CAUBRATION RUNS

When calibrating a test measure, a sufficient number of calibration runs shall be conducted b ensure that the random uncertainty of the calibration measurementsare no greater than If2, and preferably of the overall uncertainty specified for the calibmtion.

For example, if the uncertainty limit for the calibration of a test measure is zk 0.01%, the random uncertainty due to variations of the calibration runs should not exceed + 0.0025% to + 0.050%. The mnge limit for a specific number of calibration runs to meet a prescribed uncertainty limit of the average can be calculated as follows, using equation 20 from the API MPMSChapter 13.2, November 1994. where

W(X) = Range Limit for a Set of Cali bration Runs (%), a(X) = Prescribed Uncertainty Limit for the Set of Calibration Runs (2 %),

Z(%, i i ) = Range to Estimated Uncertainty Conversion Factor for Averages. (See Table I1 in API MPMS Chapter 13, Section 2.) ,

If a 95% Confidence Level is required for data analykes, the range limits versus number of calibration runs for an uncertainty limit of the average of & 0.005% are shown below: For procedural uncertainty limits other than & 0.005%, the range limits can be modified from the above values as follows:

where W (X) = the value from Table 7. 5.5 TEST MEASURE CONTROL CHARTS

Every test measure shall have a data record prepared and maintained by NIST, containing all the relevant information pertaining to the history of the test measure. Table 7-Range Limits versus Number of Calibration Runs Number of Calibration Runs 2

Range Limits, W(X),%Avempe 0.00063

API CHAPTER 4-PROVING SYSTEMS

8

The relevant information should contain: a. The identity of the test measure by owner and the owner's number, h The maker's name, identification number, nominal volume, scale divisions, coefficient of expansion of material of construction, dates and details of all types of cleaning performed. c. Calibration dates, corresponding seal numbers, together with "to conlain" and "to deliver" volumes. d. Uncertainty history. The calibrarion Izistory Ma11 test measmes s M be documented and recorded and a control chart developedfor each rest measure. See Figure 6 and the discussion in Appendix C. 5.6 SEALS

Calibration and subsequent certification must include the affixing of a tamper proof seal on the adjustable scale and drain valve by the calibrating authority. 5.7

DISPUTES

In the case of a dispute between interested parties over the accuracy of a lest measure, the disputed test measure shall be submitted to NIST forjnal judgement of its accuracy.

6 Calibration Methods Volumetric and gravimetric calibration methods for test measures are described in the following sections. Uncertainties associated with the volumes determined by both methods are discussed in Appendix B.

6.1 GRAVIMETRIC CALlBRATlON QF NECK SCALE TEST MEASURES a. Inspect the test measure. for damage, rust, and internal cleanliness. b. Exercise the balance (mass comparator) several times to ensure smooth operation. . c. Test the balance wilh the appropriate lest weights to assure the balance response is within tolerance. If out of tolerance, recalibrate the balance in mass units prior to proceeding with the calibration of the rest measure. d. Measure and record the room air temperature, the atmospheric pressure, and the relative humidity e. Calculate the air density, p (Tai,), in kg/m3, using the formula:

where

From step d:

P = The atmosphericpressure (mm of Hg),

U = The relative humidity (%I, (TUir)= The air temperalure ("C). f. Level the test measure on the platform of the mass comparator. g. Weigh and record the empty mass of the clean and dry test measure to be calibrated. h. Fill the test measure with distilled water up to the region of the zero reference mark on the neck scale. Inspect the test measure for leaks. i. Measure and record the temperature of the distilled water (T,) in the test measure with a calibrated temperature probe. j. Read the water meniscus in the glass tube of the neck scale, and record the deviation of the reading from the zero reference mark in volume units. k. Weigh and record the mass of the filled test measure. 1. Drain the test measure for the prescribed draining period. At the end of the prescribed draining time, close the drain valve. m. Weigh and record the mass of the drained test measure. n. Calibrate the neck scale in volume units: 1. Refill the rest measure to a point approximately 50% below the zero reference mark on the test measure's neck scale. 2. Read and record the indicated value of the neck scale (1). 3. Add a known volume of distilled water using an appropriate device (V,,). 4. Read and record the indicated value of the neck scale (2). Calculate the neck-scale correction factor, k.

where V , = The volume of distilled water added,

hi = The indicated value of the scale reading (2), h2

= The indicated value of the scale reading (2).

Calculate the distilled water density from the Kelt Equation (see Appendix F),

0.

SECTION 7-FIELD

~ A N O C ~ TEST RD

p. Calculate the contained volume of the test measure at the temperature of the distilled water using the equation:

MEASURES

9

above. The slicker-plate test measure is filled such that the water extends above the top of the neck of the measuredue to surface tension and the excess is sheared off by sliding a transparent plate across the lop of the neck making,

h = dh e 0 ( iz is defined as "absoIutely equivalent to''), where

h = The deviation of the location of the meniscus from zero with the appropriate sign applied,

mi = The mass of the test measure filled with dis-

dh = One tenth of the least division of the neck scale,

tilled water,

read with a magnifier fitted with an anti-parallax device.

me = The mass of the clean, empty and dry test

measure,

p (T,) = The density of the distilIed water, p (Tair)= The density of the air, k = The deviation of the location of the meniscus from zero with the appropriate algebraic sign appfied. q. Calculate the delivered volume of the test measure at the temperatureof the water using the equation: .

where md

= The mass of the drained test measure.

r. Calculate the volume of the tesl measure at the desired reference temperature using the equation:

v,,(Td= Vc,(T)C1-Pr(T-

Tb)] {m3)

where

V,,I(TJ = The volume of the test measure calibrated either to contain or to &liver, T = The temperature of the distilled water, Tb = The standard reference temperature (60°For

1s0q,

p,

= The volume coefficient of thermal expansion for the test measure.

6.2 GRAVIMETRIC CALIBRATION OF SLICKERPLATE TEST MEASURES

The calibration of a slicker-plate tesl measure by the gravimetric method diffecs from that of the neck-scale type only in the way the measure is filled with distilled water, step h

Transparency of the slicker-plate enables visual inspection for air voids under the plate, which must not be allowed to occur. The equations for Ihe calculation of uncertainty in the calibration of neckiscale test measures (Appendix A) are also applicableto slicker-plate test measures with h E dh = 0 . Table 4 in Appendix B lists the uncertainty for a typical 5-gallon slicker-plate test measure. The uncertainty determined for a 5-gallon neck-scale test measure is more than 4 times that of a 5-gallon slicker-plate test measure. This is due to the uncertainty in the neck scale reading and is shown in detail in Tables 3 and 4 contained in Appendix B.

6.3 VOLUMETRIC CALIBRATION OF NECK SCALE AND SLICKER-PLATETEST MEASURES Calibration is achieved by the volumetric transfer of a known volume of water from a standard test measure into the test measure of unknown volume (test measure being calibrated), and calculating either the contained or delivered volume of the unknown test measure. Ideally, it is preferred to haves platform elevator and large storage lank for distilled water. The calibration can then be performed by the following method:

a. Select a standard test measure, designated (U), of known delivery volume at a specified reference' temperature, scale graduation, and known cubical coefficient of thermal expansion, (a), The standard test measure can be placed on an elevator, leveled, and raised to an appropriate height. b, Place the test measure to be calibrated, designated (Z), below the standard test measure and level. c. If the test measure is to be calibrated "to contain:' then its interior must be dry. If the test measure is to be ca1ibrakd "to deliver" then both the standard test measue and the measure to be calibrated must be wet. They are wetted by filling the standard tesr measure and then draining it into the measure to be calibrated with a 3Qsecond draining time of the standard tesr measure. Then drain the test measure under calibration in the same way. This process is only to \vet the surfaces and define the amount af dingage.

10

API CHAPTER 4-f 'ROVING SYSTEMS

'd. Ell the standard test measure, U, to any point on the neck

scale, LA, tvith distilled water from the storage. Record the water temperature, TA.Read the meniscus scale and record. e. Drain the standard test measure while ensuring no loss of water into the tcsl measure to be calibrated. Close the drain on the standard test measure after draining for the prescribed time. f. Read the meniscus scale reading in the test measure being calibrated. Record the neck scale reading, 4,and the water temperature, Tq. g. In situations where the standard Lest measure is smaller than test measure being calibrated, steps o f wiil have to be repeated the appiapriate number of times,each time draining the standard test measure for the specified time. h. After one complete calibration or "run" is completed, additional runs may be performed. i. A neck calibration as described in "Gravimetric Calibration" is performed. On test measures having dual scale plates, denote whelher one scale plate or both scale plates have been calibrated. Field Standard Test Measure volumes are always referenced to standard temperature, i.e. either 60°F or 15°C. For one transfer of the smndard test measure, U,to calibrate a test measure, Z.

This expression can be solved for ktwhich is the volume required. This can be either a "to contain" or a "to deliver" volume.

The standard test measure, U(j0,has a known volume at the wro graduation on the neck scale, Lo, The difference in volume, AA, between L, and LA may be calculated by knobvl-. edge of the neck calibration constant. The numerical value of A A is used in the calculation of 260.

7 Inspection 7.1

GENERAL

Measurement activities often include the inspection or examination d test measures. lnspections or examinations are most often required when a new test measure is received from the manufacturer. 7.2 DOCUMENTATION

where pA = Density of water in the Standard Test Measure, p,, = Density of~thewater in the Test Measure to be Calibrated,

M = The same mass of water transferred from the standard test measure Uaointo the test measure to be calibrated Zdo,

a = Cubical coefficient of ex pansionPF of the standard test measure, U,

= Cubkai coefficient of expan~ion/~Fof the k s t measure to be calibrated, 2,

Tb = Reference tempratuR, either 60°F or 15°C. Since the two masses of water are the same:

Documentation shall be available to all persons who have custody transfer interests in the test measure. This paperwork shall include the manufacturer's identification of the construction material, together with a statement of the primary caIihration. All subsequent records of calibrations along with the control charts shall be main&ned. Detail drawings, interiorcoating identification (if applicable), gauge-glass s i m , and all other relevant documents, shall be sustained on file for examination when required.

7.3 VISUAL INSPECTION A visual inspection of any field standard test measure shall be made before each use to ascertain thal the capacity has not been altered by dents, internal cornion or surface deposits. In addition inspect the test measure carefully to make sure it is free of rust, broken seals, broken gauge glasses or scales, broken or missing levels, leaks or defective drain valves. The effects of internal deposits on the calibrated volume of a test measure are shown in Table 8. Visual inspection shall include the following:

a. An examination of all surfaces that affect volume to ensure that they are free from dents. Any minor dents that are considered acceptable must be identified on the certificate of calibration

'ANDMID TEST MEASURES

Table 8-Volume Errors Due toTest Measure Internal Deposits Test Measure Siu: in Ga~lons

'

Errors Due to 0.0001 inch l~iternalDeposit Minus (-) Percenlaee ofTotal Volume

b. A verification that noninvcriible lest measures have a rigid, sloping drain line. The drain line must be equipped with a suitable drain valve and provide the capability to detect leaks. c. A verification that noninverdble test measures are equipped with two adjuslable spirit levels mounted at right angles to each other on the upper cone or equivalent equipment. The levels must be a shielded style and of high quality, or provided with a protective cover and h a w adjusting screws to permit leveling. Adjusting screws should allow a lead-andwire seal lo be inslalled by the calibrating authority. d. An examination of the surface finish to determine that it is clean and free from mill scale, grease, or other contaminants. If the exlerior surface is painted, the paint coating must be reasonably free from scratches and corrosion damage. e. An examination of welding quality to ensure that smooth, full-penetration welds are provided. f. If NIST 14andbook 105-3 is the specification used, verification must indicate that each test measure bears in a conspicuous place the name or trade mark of the manufacturer, the nominal volume (in gallons, cubic inches, liters, or other units), and a serial or other identification number. The material from which the standard is constructed shall be identified together wilh the cubical coefficient of thermal expansion per O F ar "Cfor that material. ~nteriorjointsand seams shall be smooth and uniform. Surfaces, including joints and seams, must be clean and firce from grease, dirt, or oil film. Surfaces must be smooth and free from rust corrosion. Potential air or water traps, resulting from either design or damage, are not permitted. Prolonged, and sometimes, even only isolated use of contaminated water in a test measure will cause corrosive damage, pitting, andlor deposits to adhere to the interior surfaces. The interior of test measurm should never be exposed to salt water or any type of water with high dissolved solids. If coating material is used inside lest measures then it must be uniformly applied to the surfaces and be free from any voids or bubbles. Any coating material used, such as epoxy or phenolic, must be resistant to the effects of alcohol, acetone, benzene, petroleum products, and water.

11

Noninvertible test measures must be equipped with a fixed anti-swirl plate to eliminate the formation of a vortex during draining. The neck on a lest measure shall be uniformly cylindrical in length and regular in diameter. The scale must be of corrosion-resistant metal, firm, secure, and easily adjustable. A provision must exist for affixing a lead-and-wire seal to provide a means for detecting unauthorized adjustment. l'he scale divisions or graduations must be linear. The scale length must be appropriate to the test measure. Applicable volume units (cubic inches, cubic millilitel*~, gallons, liters, or others) must be clearly indicated, and scale markings must be legible. The gauge glass must be clean and clear after wetting (that is, no droplets should be present), and it must be capable of being removed, cleaned, and replaced. The top surface of the neck of a test measure must be ground, machined, or smoothly formed to serve as a level benchmark. This surface shall be the primary level indication in two axial directions. Any lest measure that is normally Lransported to various locations shall be protected. A case, shipping container, or other means that sufficiently protects the test measure against dents and/or scaIe damage during storage or transportation shalI be used. Test measures mounted and moved on trailers shall be secured to prevent movement or damage during travel. 7.4

CLEANING PROCEDURES

All test measures shall be inspected and cleaned prior to calibration, unless clean water was used as the calibration fluid and the test measure was cleaned, dried, sealed, and put into storage at the complelion of the previous calibration. Prior to any cleaning of a test measure, it should be examined for any signs of damage as described in the inspection section. Normal cleaning of the interior of the test measure involves scrubbing with a biodegradable detergent and water. However, jf the interior of the lest measure contains oil residue then it may be necessary lo use solvents for cleaning prior to cleaning with detergents. In the event a test measure is heavily contaminated with oil residues the additional step of steam cleaning the interior of the test measure prior to ally solvent cleaning or detergent washing will be required. After the above cleaning, each test measure should be filled with walm and allowed to sland for seved minutes. During this time, a careful examination for leaks can be made. Once this inspection is made, the test measure should be rinsed with distilled water, then rinsed with alcohol and allowed to dry. Smaller test measures, without leveling feet, whose level is determined by the plane of their base, should sit on a level bedplate and be checked for firm seating. A vessel that cocks will not give a true meniscus reading during its calibration.

12

7.5

API CHAPTER 4-4

INTEGRITY

I

In addition to the initial testing a test measure undergoes when it is new, it should also be checked periodically to verify its leak integrity. The follo\ving systematic procedure is recommended: a. The test measure should be filled with warm-to-hot water 100-140°F (3860°C)and allowed to stand for 3 0 6 0 minutes, making certain that any thermometer installed will not be damaged by exceeding its range. All seams, joints, pipe fittings, and gauge glass along with the overall test measure should be checked for leaks. The drain valve should be checked for leaks and air entrapment. The valve should be opened and closed several times to verify positive sealing of the valve. An optional procedure involves taking and recording a level reading prior to cracking the drain valve open and drawing off approximately I gallon of water into a wetted test measure and returning it to the prover. If the level in the test measure is lower, either the piping ahead of the valve contained air or some part of the valve body cavity that was previously filled with air is now filled with water. b. The test measure should be drained to observe the effectiveness of the anti-swid plate while the fluid is draining. c. The test measure should be filled with the calibrating medium, and the checks listed above should be repeated. d. The thermometers used with the test measure should be routinely subjected to a calibration or a comparison with a standard reference thermometer to verify accuracy.

8 Operation And Use The primary use of field standard test measures is to determine the volume of a meter prover when using the waterdraw method of calibration. Test measures are constructed of stainless steel in a multitude of sizes, ranging from 1 gallon all the way up to 1,500 gallons, with many different intermediate sizes. Ir) fact, a test measup may be constructed in any convenient size, and frequently high-sensitivity test measures are built to accommodate the exact volume of a small volume prover. Some examples of unusual test measures sizes in regular use are 15 gallon, 21 gallon, 42 gallon, 225 gallon, and 227 gallon. Equivalent volume or different volume test measure s i m are also available in metric units. Only lest measures calibrated with a "to deliver" volume shall be used in the calibration of meter provers. 8.1 FIELD USE OF VOLUMETRICTES'I" MEASURES

Eeld standard test measures axe used in the wakrdmw calibration of pipe provers, small volume provers, and hnk provers. Full descriptions on the field use of these test measures will be found in API MPMS,Chapter 4.9.1, "Detennination of the Volume of Displacement and Tank Provers by the Waterdmw Method of Calibmtion." The procedure for calcu-

lating the Base Volume of a Displacement or Tank Prover, using field standard test measures, is described inAP1 MPMS, Chapter 12.2.4,"Calculation of Base Prover Volumes by the Waterdraw Method." Different techniques may be used to calibrate meter provers using field standard test measures. Any of the following methods can be used; however, normal operating practice currently uses Method 3. 1. Fill each test measure to its exact certified (zero) capacity, and allow the final water level to be read on completion in the last test measure filled. 2. Slightly overfill each test measure and then bring the level back to the exact capacity (zero) by withdrawing some of the liquid. The Iiquid that is withdrawn is then released into the next test measure to be filled. 3. With gladualed neck test measures it is not necessary to operate at the zero level. Therefore, the test measure may be filled to any location on its scale, the liquid level read, and its certified capacity is then adjusted mathematically using a plus or minus scale reading (SR). A minus signifies that the water level is below the certified capacity (zero mark) on the test measure scale, and a plus indicates that the water level is above the zero mark on the scale.

8.2 NORMALTEST MEASURE OPERATION Setting up a test measure for calibration use in the field normally involves the following preparatory steps. lnspect al! test measures to be used in the calibration for cleanliness, dents, unbroken sight glasses, scales and seals. Following the inspection, aH the test measures shall be leveled while they are in a water-filled condition, across at least two axes, 90' apart. After this filling and leveling, the test measure shall be leak tested. If free of leaks, draining of the test measures should now take place, until cessation crf the main flow allows the draining time (as specified on the calibration certificate) to be followed and a repeatable clingage condition established. After draining for the prescribed draining time, the bottom drain valve is closed or the.test measure is returned to its upright and level position to prepare the test measure for calibration use. During a calibration run, the test measure is filled with water to an upper scale reading, which is then recorded as a (+) or (-) volume, depending on whether the reading is above or below the zero line on the scale. Typically, most volumes are read as either cubic inches (in?) or milliliters (rnl) depending on the calibration units of the lest measure. Once the t a t measure is filled, the leveling verified, and the scale reading recorded, the temperature of the water in the test measure is then required. This temperature can be taken by different methods and in different locations. The temperature can be taken, while the test measure still contains the water foll~wingthe scale reading, by immersing, a thermometer inside the test measure or by holding a themometer in the

SECTION 7-FIELD

STANDARD TEST

flowing stream while the water is draining from the test measure, after the scale reading. At the cessation of the main flow,

it is essential that the draining time is carefully and exactly follorvcd to only allow the correct amount of water to escape. This will restore the test measure to ils ready-lo-fill-again condition, ensuring that the wakr clingage remaining inside the test measure is maintained each time as a repeatable quanlity, and replicates the drainage time sustained by Ihe calibrating agency.

8.3 IRREGULAR TEST MEASURE OPERATIONS In field use, sometimes irregular operating conditions can arise while using test measures in prover calibrations. Two of these conditions are identified as either requiring that a test measure be overfiIled or underfilled during the calibration cycle. If either one of these two conditions should arise during a prover calibration, the iechniques described below can be used to solve the deficiency. 8.3.1 Test Measure Pre-Fill

During a calibration, it is sometimes necessary to accurately determine the volume of a partially filled test measure. This determination can be made by a method known as pre filling. Pre-fiIling is accomplished by first filling a larger test measure with an amount of water taken from a smaller volume test measure. This will bring the watcr being drawn from the prover into the test measure to a level that can be read on the gauge glass'scale. As an example, consider a prover calibration with an approximate one-;vay volume of 145 gallons. To accomplish the volume delemination, the only test measures availabIe are of a lo@, 50-, and 5-gallon capacity. One method of calibrating this prover would be to fill the 100-gallon test measure one time and the 5-gallon test measure nine times. This would not be recommended due to the large number of test measure fillings required, using a 5-gallon test measure, which normally has a large uncertainty value in its calibration. A more practical solution would be to prefill either the Prefill BMV Pre-fiH SR

= 1155 =-la

MEASURES

13

100- or the 50-gallon test measure, with 5 gallons of water from the 5-gallon test measure and then fill the remainder of this test measure from the prover. The 100-gallon test measure for Fill No. 1 has a base volof 23100 in?. The 50-gallon tea measure for fill No. 2 has a bare volume of 11550 in.3. ~h~ pre-fill 5-ellm test measure has a base volumeof 1155 in,3. If only the 100-gallon and the SO-gallon test measures are used, at the end of the pass the rvater level in the last test measure filled will not reach the neck, and therefore, will not have a scale reading. In this instances pre-fill is used to pre-load the first measure filled with enough rvater to enable readings in the sight glasses on all the test measures filled to be achieved. Treat the pre-fill volume as a separate field standard test measure filling, but with both the Base Volume of the Test Measure (BMV)and the Scale Reading (SR) handled in a negative manner, FiIl the 5-gallon test measure with wastewater and take the Scale Reading (SR).The temperature is taken by immersion, after reading and recording the SR. Then drain the 5-gallon measure into the 100-gallon measure using the prescribed dmin time. In this example, SR on the 5-gallon test measure is {- 10)Fill No. I , of the 100-gallon test measure has a SR of (+20) in.3. Temperature is taken, while draining, after reading and recording the scale. Fill No. 2, of the 50-gallon test measure has a SR of (-6) in3. Temperatulxi is taken, while draining, after reading and recording the scale, (see below).

where

CTDW = The correction for the difference in density between the water in the prover and the rvater in the test measure, CCTS = The combined correction factor for the effect of temperature on the steel of the prover and the test measure,

,..Treated as a negative: BMY .,,Treated as a negative: SR

To delemine the adjusted Base Volume of the Test Mcasure (BMVa):

Pre-fill: RII No. 1: Fill No, 2:

BMV+ SR = BMVa BMV + SR = B M k

BMV+ SR = BMVa

kample: Example: Example: ToTALV W M E

-1 155 + (+lo)

23100+ (40) llSSO+ 1-61 (1 45.10 gals)

Calculating the Pte-fill volume the same way as any other test measure is calculated: Calculate Fill NO.1: CalculateF111Na 2: Calculate he-fill:

23120X CTDW x CTS = WD ...far Fill No. I 1 1544 X CTDWx CCTS= WD ...for RII No. 2 -1 145 X CTDM CCTS = WD . .forpre-fill

.

= I-11544

335 19 in."

14

APL CHAPTER 4-

WD = The BaseVolumeof the Test Measure adjusted for the scale reading, SR, and corrected for the effefects of CTDW and CCTS.

and shuts down the prover calibration run. Take the closing scale reading:

SR (closing) = + 215 in.3

8.3.2 Test Measure Neck Draw Another unusual operating condition that can arise with test measure use is the required controlled overfilling of test measures during a prover calibration run. In this case, the problem is that additional water needs to be contained in the already-full test measure. This is a situation where a neck drawdown (neck-fill) procedure would be used and examples of this situation are described in the text belorv. As an example, consider a prover calibration with an approximate one-way volume of 153 gallons. To accomplish the volume determination, the only test measures we have available are of a 100- and 50-gallon capacity. The total capacity of the combined filling of these two test measures would range from a minimum volume of 148.5 gallons to a maximum volume of 151.5 gallons. The 100-gallon test measure for Fill No. 1 has a base volume of 23100 in.? The 50-gallon test measure for RII No. 2 has a base volume of 11550 in?. It has been determined beforehand that after filling both measures to their maximum readable scale levels there will still be approximately 1.5 gallons of water remaining in the prover. This volume of water will somehow need to be accommodated in a test measure, so as to be measured. Fill No. I, of the 100-gallontest measure has a SR of (+230) in.3. Temperature is taken, by immersion, after reading and recording the scale. Fill No. 2, of a 50-gallon test measure has a SR of (-?-loo) in.3. Tempemture is taken, while draining, after reading and recording the scale. Neck Draw: Lower the water level in the neck of the 100gailon test measure, to waste, by careful manipulation of the drain valve, until the water level reaches the lowest readable value on the scale. Close the drain valve and take the scale reading. This value is recorded as the opening scale reading.

Treat this neck fill as if it were a separate field standard lest measure with a BMV = zero (0). The temperature is taken by immersion, of the neck portion only, after reading and recording the closing SR. To rationalize the Scale Reading: (SR) = [SR [closing) S R {opening)] = +215 (-220) = +215 + (220) = + 435 in.3

SR (opening) = -220 in.3 Draw water from the prover refilling the neck of the 100-gallon test measure until the detector switch activates

R11 No, 1: Fill No. 2;

BMV+SR-BM%

Neck Draw:

Example: BMV+SR= B m TCrrAL VOLUbE

Example: Exarnplc

BMV+SR=BMh

-

To determine BMVa: {see below) Similar situations can often occur in the calibration of new provers, or also when provers have been modified or worked on, such that the volume is not exactly known. Therefore, the first calibration run is very often a guess as to where the actual final volume will finish, relative to the test measures being used to determine the volume. In this situation, it often hap pens that the operator can find himself having to perform several neck draws to complete the calibration run, just because of the fact that this prover volume is not precisely known. Use of this method will allow a precise volume to be decided and enable the operator to refine the test measure fillings for the additional calibration runs required to be made.

8.3.3 Test Measure Pre-Fill and Neck Draw It is also possible to have a situation where a test measure pre-fill and a test measure neck draw are both necessaq during the same prover calibration run. Although this situation is uncommon, operators should be prepared for it, should this condidon arise in a calibration. Following the previous examples, consider a prover calibration with an approximate one-way volume of 147.5 gallons. To accomplish the volume determination, the only test measures that are available are the following; loo-, SO-, and 5-galIon capacity. Therefore, to perform the prover.calibrationwith 23100 t (-1-230) = +23330 11550 + (+loll) = +I1650 zero + (+435) = 1435 ( I 53.31 gals) 35415 in?

Calculate the Neck HI1 as any other measure fill is calculated.

Calculate Fill No. 1: 23330 x CTDWx CCTS= WD -..forFill No. 1 ...forFill No. 2 CalculateAll No. 2: 1 1650x CTDWx C C a = 435 x CTDWX CCZS = WD .. for Neck Draw Calculate Neck HI1:

.

S~mro 7-FIELD ~ STANDARD TEST MEASURES

these test measures would requjre the follo~vingsequence of events: Fill the 100-gallon test measure with a 5-gallon water prefill from the 5-gallon test measure, then fill the test measure up to the top of the readable scale with water drawn from Ule prover. Next, fill the 50-gallon test measure to the top of its readable scale with water draw Ivaler. At this point, the following situation muw: The volume in the 100-gallon test measure is I01 gallons from which 5 ga1lorts need to be subtracted, The volume in the 50-gallon test measure is 50.5 gallons. The total volume equals (101 + 50.5-5) = 146.5 gallons.

Therefore, with both test measures filled, and a pre-fill of5 gallons, a total amount of 146.5 gallons of water has been held. However, 147.5 gallons need to be contained and room in a test measure is needed for an additional one gallon of water. At this point, il is necessary to draw down the neck of the 100-gallon test measure. Drawing the water level down to the lowest rcadable scale tine will make a total volume space available in the 100-gallon lest measure for approximately an additional 2 gallons and allow the prover calibration run to be completed.

,

Figwe 1-Various Types of StandardTest Measurn (I)

SECTION?-FIELD

STANDARD TEST MEASURES

Figure 2-Various Types of Standard Test Measures (11)

17

1. 2. 3. 4.

Reinforcing bar Handle (raised)

Rolled bead Gauge assembly 5. Gauge mounting 6. Concave bottom

Figure 3--Field Standard Test Measure-Invertible Type

SECTION7-FIELD STANDARD TEST MEASURES

19

1. Draln valve 2. Draln slope 5T 3. Levels 4. Level cover 5. Gauge mountlng 6. Rolled bead 7. Top cone pitch 25r 8. Reinforcing bands 9. Bottom cone pitch 20r 10. Adjustable legs

Figure 4-Field Standard Test Measure-Bottom Drain Type

Figure 5-Gauge

Glass and Scale Assembly

Figure &Field Standard Test Measure Control Chart

APPENDIX A-ACCURACY REQUIREMENTS FOR VOLUMETRICTEST MEASURES Shown below are the uncertainty requirements for volume measurements in the normal petroleum measurement hierarchy, see Table A2. The uncertainties versus test measure size as shown in the table are appropriate to the petroleum industry convention for meter provers. No recommendations are made for uncertainly limits for small volume provers calibrated by master metedprover procedures. Fo! small volume provers, loiver uncerlainty limits are needed for test measures used in their calibration since smaller prover and lest measure volumes are used at the same metering rate involving conventional provers. Recommendations on uncertainty limits for test measures used for calibrating small volume provers are given below, see TableA4. The use of small volume provers and master meter/prover calibration of conventional provers dominates the uncertainty limit capabilities needed for test measure calibration. The uncertainty limits shown in the table below are the recommended levels that can be achieved by NIST,see TableA3. If master meter calibration of meter provers is introduced into the petroleum hierarchy, as in the case of proving a master meter with a master prover and then using the master meter to calibrate a field prover. The number of levels in the hierarchy is increased to seven as follows, (see Table A7):

In determining the accuracy requirements in the calibration of test measures, it is necessary to consider the hierarchy of petroleum custody transfer measurements so that the precision teve1s of test measures are consistent with other precision levels of measurement. The convenlional hierarchy in petroleum measurement is shown in Table Al. If, however, the master meter calibmtion techniques are introduced then the number of hierarchy levels will be increased to seven (see Table A6). Similarly, should a state agency or calibration source other than NIST be used in the test measure calibration, the number of hierarchy levels will be increased (see Table AS). Potential errors or uncertainties of each position in the hierarchy from the lowest to highest pcsition must be progressively lower so that overall uncertainty of the hierarchy can be controlled. Uncertainties from the highest to the lowest levets progressively add to each successive level. Each step in the hierarchy should normally experience uncertainties that are 25 to 50% of the uncertainty at the next lorvest level in the hierarchy. For measurements that are somewhat repetitious in nature, the margin beween adjacent steps in the hierarchy can be less because repeated measurements propagate the uncertainty on the overall average to a lower value. Table Al-Hierarchy

of Measurements forthe Metered Volumes of Petroleum Measurement Description

Hierarchy Position 1. Highest

CaIibration of NIST Standards Chlibmtion of Test Measures Calibration of Meter Prover Proving of Custody Transfer Meter Custody Transfer Meter Regislration

4. 5. Lowest

Table A2-Uncertainty Requirements far a Petroleum Measurement Hierarchy Using a Single Custody Transfer Meter and the Waterdraw Calibration of a Displacement Prover Overall Uncertainty Limits % Hierarchy

Position I. Highest

:I 4.

5. Lowest

Measurement Description Calibration of NlST Stds Calibration dTcst Measures Calibration of Meter Prover Proving of Custody Transfer Metw Custody Transfer Meter Registration

Lbv

Medium

High

Accuracy

Accuracy

Accuracy

0.050

0.020 0.050 0.100 0.150

0.010 0.020 0.050 0.075

0.100 0,200 0.350

Table A3--Uncertainty Limits for Calibration of Normal Sensitivity Test Measures as Used in the Cafibrationof Conventional Displacement Provers Size of Test Measure, Gallons

Uncertainty Limit%

I

0.030

Table A4-Uncertainty Limits for the Calibration of High Sensitivity Test Measures as Used in the Calibration of Small Volume Provers

.

Size of Test Measure, Gallons

Uncertainty Limit%

1

0.030

Table A5-Uncertainty Limits for the Calibration of Test Measures Used for Displacement Provers Overall Unceminly Limits %

Size of Test Measure,Gallons

f

"

Hierarchy Position 1. Highest

5. 6. 7.Lowest

W~thMaster Meter Prover Calibration 0.025

W~lhoutMaster Meter Prover Calibration

0.050

Table AbHierarchy of Petroleum Metered Volume Measurements Including Calibration of Meter Provers by a Master Meter Measurement Description Calibrationof NIST Standards Calibration of Test Measures Calibration of Master Prover Calibration of Master Meter Calibration of Meter Prover Proving of Custody Transfer Meter Custody Transfer Meter Registration

STANDARD TEST MEASURES

SECTION7-FIELD

25

Table A7-Uncertainty Requirements for a Petroleum Measurement Hierarchy Including a Single Custody Transfer Meter With Master Meter Prover Calibration Hierarchy Position 1. Highest

5. 6.

1

7. Lowest

Measurement Description Cali bration of NIST Standards Calibrationof Test Measures Calibration of Master Prover Calibration of Master Meter Calibration of Meter Prover Proving of Custody Transfer Meter Custody Transfer Meter Registration

h v

Medium

Accuracy

Accuracy

0.010 0.025 0.050 0.100 0.200 0.350

0.005

0.010 0.020 0.050 0.100 0.150

. 0.005

0.500

0.250

0.100

High Accuracy

0.0025

0.010 0.020 0.050 0.075

The extreme case of total expansion of the Petroleum Measurement Hierarchy is shown below:

Table A8-Total Hierarchy of Measurements o i Metered Volumes of Petroleum Showing International Standards, Calibration of Test Measures other than by NlST and Meter Prover Calibration by a Master Meter Hierarchy Position 1. Highest

:

6. 7. 8.

1

9.Lowest

.

Measurement Description International Base Slandard Units Calibration of NIST Standwds Calibrationof Other Body Standards Calibration of Test Measures Calibration of Master Prover Calibrationof Master Meter Calibration of Meter Prover Proving of Custody Transfer Meter Custody Transfer Meter Registration

International Base Standard Units

I L

I

Calibratlon of NIST Standards t

1 I I I I I I I I I I

1 I I f 1 I I I I I I

I

I

I

! Calibration ot Other Callbration Agency Standards

I I

Callbratlon of Field Standard Test Measures

Calibration of Field Standard Test Measures

I

I

I

I I

I I

I I

Calibraiion of Field Prover by Waterdraw Method

Calibrallon of Master Prover by Waterdraw Method

Calibration of Master Prover by Waterdraw Method

I

1

Calibration of Field Standard Test Measures

I

I I I I

I

I

I I I L I

I

I 1

Calibration of Master Meter

Calibration of Master Meter

I I

I I I

I

I 11

I

I 1 I 1

Calibratlon of Field Prover by Master Meter Method

Calibration of Field Prover by Master Meter Method

I I

I I

I

1

Prcvlng of Custody Transfer Meter

Proving of Custody Transfer Meter

Proving of Custody Transfer Meter

I I

I I

I I

I

I

Custody Transfer Meter Reglstration

Custody Transfer Meter Regltstratlon

I

Custody Transfer Meter Registration

Figure 7-Levels of the Petroleum Measurement Hierarchy

APPENDIX 3-CALCULATION OF UNCERTAINTY OF A FIELD STANDARD TEST MEASURE about the mean air density are known to rarely exceed 3%. Analysis indicates that modest accuracy in the required measurements produces a satisfactory uncertainty in the air density. For example, temperature measured within an accuracy of rc_O040C, atmospheric pressure within k1.1 mm Hg, and relative humidity within f 16 %, will result in a contribution to the uncertainfy of the above equation on the order of one part per million (1 ppm).

While the contained volume (T,)is the actual scientific value determined by NIST, test values of the delivered volume and calculated values of volume (Tb),required by industry, are also provided by NIST. Accordingly, the equation for the mntained volume (below) must be subjecl to uncertainty analysis.

It is convenient to make a change in notation at this pint, let

The above equation contains the expression p (T,) which is derived from the equation:

v = Vconrlrin(Td.

The relative uncertainty in V may be expressed as:

The equation is very unwieldy for the purposes of uncertainty analysis. To make the analysis simpler, the first-order approximation is used:

I

he^

xi = The measured variables in K

k = The coverage factor, normally taken to be 2, consistent with NIST policy. where

Tables 1-3 list typical calculated uncertainties for conrained volumes at (T,) for loo-, SO-, and 5-gallon field standard test measures, respectively. Values are listed in S1 units. "Guidelines for Evaluating and Expressing the Uncertainty of NlST Measurement Results," NIST Technical Note 1297, suggests classifying the uncertainties forxi as: Type A: Uncertainties which are evaluated by statistical methods. Type 3:Uncertainlies which are evaluated by other means. Once a value for the uncertainty of an xi is determined, it receives the identical mathematical treatment in the equation whether it is either Q p e A or Type B. The sources of the unmrTainties for thexi's and their type are: dh is one-lenth of the least division of the neck scale read with a magnifier fitted with an anti-parallax device, Qpe B. dmfand dm, are calculated from:

p, = The density of the distilled water a1 the reference lemperature, Tb,

p,,

= The volumelFic thermal expansion coefficient for water appropriate for Tb,

Tb

= The reference lemperature, either 6O0For15°C.

While the accuracy of this equation is inferior to that of the full Kell density equation, it is extremely satisfactory for the pqmes of uncertainty analysis.

substituting:

.I

=

Vcatltatttlrr(Tw)

--me

po[l.- hATw- Td1- P(T,,)

+ h m3

Air density is a function of air temperature, atmospheric pressure and relative humidity. At a given altitude, fluctuations

where .

,s

= The slandard deviation of the residuals of the comparator calibration equation,

27

b = The slope of the calibration equation,

where

P = The number of calibration measurements,

p, =

m = The mass of the test measure, m,i~ar~g,= The midpoint of

the calibrated range ofthe

cornparalor, mi

= The mass value for which the calibrations were done.

one would expect the uncerlainties of the masses to be included in dm, but they are negligible compared to the standard deviation of the residuals, Type A, dp, and da,, are derived from the Kcll Density Formula, 5 p e B. dT, is based on the Standard Deviation from N1ST Calibration Data, 5 p e B. dp,,, is derived from A Primerfor Mass Metrology, Jaeger & Davis, NBS Publication 700-1. Volume calibrations are normally done in a climate-controlled laboratory environment at a temperature around 23°C. The normal requirement from the petroleum industry is to convert volumes measured at normal room or ambient temperatures to a reference temperature, usually 60°F or 15OC, via the formula:

. -

Tb = The reference temperature of the test measure, . typicaily 60°F or 15°C. Since the volumetric coefficient of thermal expansion is not directly measured, common practice has been to use the thermal expansion coefficient for Series 304 stainless steel. The Using this value for contained volvalue used is 0.000048/"C. umes, the uncertainty due to the calculation using the above volume equation is (T,- ~ , ) d f i , where dj3, is 7 x 10 -7/0C, which is to be added in quadrature to the appropriate uncertainty from the tables. The uncertainty in applying the above volume equation to the delivered volumes is compounded by the fact.that when the temperature decreases from 23" to 15.56"C,the viscosity of water increases by 21% and the surface tension increases by 1.6%.These increases will have an effect on the way the water drains from the test measure. If less water drains from a given measure at 15.56OC in the 30 seconds than from the 'same measure at 23°C in 30 seconds, then there is an uncorrected residual effect that will make it difficult to calculate the delivered volume at the lower temperature with any level of confidence.

Table B1-Uncertainty for the Gravimetric Determinationof the ContainedVolume at Room Temperature of NIST's 100-Gallon (0.379m3) Neck Scale Test Measure

-

xi

The volumetric coefficient of thermal expansion for the test measure,

Value

I av --

v ax;

Value

Ai

1E d X ,x I od V axi

SECTION 7-FIELD

STANDARD TESTMEASURES

29

Table B2-.Uncertainty for the Gravimetric Determination of the Contained Volume at RoomTemperature of NIST's 50-Gallon (0.189m3) Neck Scale Test Measure Xi

Value

I av --

V ~ X ,

Value

dri

' C d x , x lo4

v ax,

Table 53--Uncertainty for the Gravimetric Determination of the Contained Volume at Room Temperature of NIST's 5-Gallon (0.0189 m3) Neck Scale Test Measure

av

xi

Value

I --

V ~ X ,

Value

4

Lv axi e d ~ , . 10,,

30

API CHAPTER 4--PROVING SYSTEMS

Table B4--Uncertainty for the Gravimetric Determination of the Contained Volume at Room Temperature of NIS'T~&Gallon (0,0189 m3)Slicker-Plate Test Measure

xi

Value

I av --

V~X,

Value

h i

laVdx,xlo4~ Vax,

APPENDIX C-TEST

MEASURE CONTROL CHARTS

Every test measure shall have a data record prepared and maintained by the national calibrating agency, containing all the rele vant information pertaining M the history of the test measure. The relevant information should contain:

a. The identity of the test measure by owner and the owner's number. b. The maker's name, identification number, nominal volume, scale divisions, coefficient of expansion of material of construction, dates and details of all t y p of cleaning performed. c. Calibration dates, corresponding scal numbers, togeiher with "to contain" and "to deliver" volumes. d. Uncertainty hislory. The calibration history of all rest measures shall be documented and recorded and a control chart developedfor each test measure. An example of a Test Measure Control Chart is shown in Figure 6, which plots the calibrated volume against time for each ca1ibration performed, and shows the total documenled calibratian history of this particular test measure. Analysis of the control chart shown in Figure 6 yields the foflovving data shown in Table C1. Calibrations that are more frequent should have been performed on the test measure in the early years, because sufficient data was unavailable until 1972or 1973to construct a control chart with calculated limits, Initially, the calibration facility's uncertainty estimates could have been used until sufficient data was available to calculate control levels. For measurements as critical as test measure calibrated volumes, conservative confidence limits levels should be used to set warning, action, and toierance limits. The following statistical confidence levels are recomrnendcd: Con#oi Level Co~~jTdence Level % Warning Limits 90 Action Limits 95 Tolerance Limits 99 From the control chart in Figure 6, and the statistical analysis table C1, the follotvjng control limits are calculated after four calibrations by the year 1973: Center Line = 4.99788 = 4.99761 and 4.99815 Warning Limits = 4.99751 and 4.99825 Action Limits = 4.99720 and 4.99856 Tolerance Limits From the control chart in Figure 6, three of the past calibrations are outside of the warning limits but no results fall outside of the action limits, This history of each test measure is recorded and kept on file by NIST for every test measure calibrated. It is also advisable for the owners of field standard test measures to keep their own current records on file, including detailed information on all maintenance and modifications performed. Table C1-Statistical Analysis Table of the Calibration History of Test Measure #I23456 (5-Gallon Slicker-Plate Test Measure) Year 1%0 1965 1972 1973

Volume in Gallons

1982

4.99780 4.99W 4.99817 4.99809

1982 1982

1982 1992 1994 1996 1996

I996

4.99790 4.99802 4.99780 4 . w ~

Moving Average

Moving Range

-

-

4997%

0.00012 0.00022

4.99791 4.99788 4.88786 4.99789

4.99793

0.00M4 0.00024

0.00028 0.00039 0.00039 0.00042 0.00042 0,00045

4.W817

4.99795 4.99798 4.99798 4.99796 4.99798

4.99772

4.W96

0.00048

4.9~820 4.99800 4.99775

0.00045

APPENDIX D-LABORATORY WEIGHTS AND MASS STANDARDS Various classes of weights and mass standards are used for Laboratory Procedures and in Gravimetric Calibrations, and their specifications in OIML R 111 describe weigh&in classes asEl,B,Fl,M,MI,M2,andM3. For complete information. see OlML R 1 11. This appendix briefly describes the principal physical characreristics and metrologica1 requirements for classes of weights, that are used: a. For the verification of weighing instruments. b. Far the verification of weights of a lower class of accuracy. c. With weighing instruments. For verification of 'weighing instruments, it is r e m mended that the tolerance of the weight be < If4 of the precision needed from the instrument.

D.1 Terminology a. Weigh: A material measure of mass, regulated in regard to its physicat and metrological characteristics: shape, material, surface quality, norninaI value, and maximum permissible emr. b. Accuracy class of weighls:A class of weights which meets certain metrological requirements intended to keep errors within specified limits. c. Traceability: The "property of the result of a measurement of the value of a standard whereby jt can be reIated to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties".

D.2 Physical Characteristics D.2.1 CONSTRUCTION

Weights are divided into two types based on design; a. Type I: T h m weights are one piece construction and contain no added adjusting material. They should be specified when weights are to be used as standards of the highest order and where maximum stability is required. A precise measurement of density can be made only for one-piece weights. b. Type I]: Weights of this type can be of any appropriate design, such as screw knob, ring, or sealed plug. Adjusting material can be used as it is of a material at least as stable as the base material and is contained in such a way that it will not became separated from the weights. Cims El ' I and weights shall be Type I which is solid and shall have no cavity open to the atmosphere. They shall have an integral construction, i.e.,consist of a single piece of materid. C h s F1 and F2 weights from lg to 50 kg may be 5 p e I or Type 11, i.e., one or more pieces from the same material. They may contain an adjusting cavity; however, the volume of this cavity shalI not exceed one-fifth of the total volume of

the weight, and the cavity shall be closed by means of a lifting knob or other suitable device. Class M1 weights from 100 g to 50 kg shall have an adjusting cavity. For weights from 10 g to 50 g, the cavity is optional, and weights from 1 g to 10 g shall be manufactured bvi thout an adjusting cavity. Class M2 and M3 weights from 100 g to 50 kg shall have an adjusting cavity. For weights of 20 g and 50 g, the adjusting cavity is optional and weights of 10 g and less shall be sofid'without any adjusting cavity.

D.3 Design A weight may have any shape that does not introduce features that reduce the reliability. All weights shall be free of ragged or sharp edges or ends. Weights less than 1 g shall be flat polygonal sheets or wires, with appropriate shapes, which permit easy handling. The shapes shall be indicative of the nominal value of the weights. Weights of 5 g to 50 kg may have different shapes suitable for 'their method of handling. Instead of a lifting knob they may have rigid handling devices embodied wilh the weights, such as axles, handles, etc.

D.4 Material All weights shall be corrosion-resistant.The quality of the materials used in construction shall be such that the change in mass of the weights shall be negligible, relative to the maximum errors permitted in their accuracy class under normal conditions of use. Class El and E2 weights shall be constructed of metal or alloy that is practically nonmagnetic. The hardness of this material and its resistance to wear shall be similar or htter than that of austentilic stainless steel. Clcrss F1 and F2 weights shall be constructed of material that has briltleness and hardness equal to drawn brass. The material used for weights of this class shall be practicaIly nonmagnetic. Class MI cyJindrical weights of 10 kg and below shall be made of brass or other material whose quality is similar or better than that of brass. Weights of 1 g and less shall be made of a material that is sufficiently resistant to corrosion and oxidization. The surface shall not be coated and the material in the weights shall be practically nonmagnetic. Class M2 and M3 cylindrical weights of 10 kg and below shall be made of material which has a hardness and corrosion resistance equal to Ulat of cast brass and a brittleness nat exceeding that d gray cast iron. Gray cast iron shall not be used in weights less than 100 g. Weights shall be practically nonmagnetic.

34

API CHAPTER&--PROVING SYSTEMS

0.5 Density Because of the effects of the buoyant force d air on a weight, precision measurements of mass require that the volume d the weight be known, as well as the density of the air volume in which it is being measured, so that the appropriate corrections can be made. For weights of high precision, the range of density is limited to values at or near the density of well-established standards, such as are used by NEL, NIST, etc. As lower precision of measurement is required, so the range of density is broadened.

D.6 Finish The surface of the weights shall be smooth and the edges shall be rounded. The surface of classes El, J3,F1, and F2 weights up to and including 50 kg shall not appear to be porous and shall present a glossy appearance when visually

examined. The surfaceof classes MI, M2, and M3 cylindrical weights from 1 g to 50 kg shall be smooth and shall not appear to be porous when visually examined.

~ . 7Adjustment Type I weights including classes El and E2 shall be adjusted by abrasion, grinding or any appropriate method. The surface requirements shall be met at the end of the process. Type I1 weights including classes F1, F2, MI,M2, and M3 solid weights shall be adjusted by abrasion grinding or any appropriate method that does not alter the surface. Weights with adjusting cavities shall be adjusted with the same material from which they are made, with tin, or with tungsten. For weights that have sealing caps, the cap may be made of aluminum.

Table Dl-Maximum and Minimum Limlts for Density in g/cm3 (P,~,,, p,,,,) Nominal Value >5kg 2 5 kg-50 mg c 50 mg

Class El 7.934-8.067 7.934-8.067 > 2.2

Classes E2, F1 7.81-8.1

Class l?2

7.0-8.1 7.7-8.1 > 2.2

7.7-8.1.

> 2.2

Classes Ml, hA2, M3 > 4.4 > 22 > 2.2

Table D2-Application of Standard Mass Weights Application Primary Reference Standards Reference Standards for Calibrating E2 Weights Reference Standardsfor Calibrating F1 Weighls Standards Used for Calibrating F2 Weights Standards Used for Calibraling MI Weights StandardsUsed for Calibrating M2 Weights Standards Used for Calibrating M3 Weights Creating Balances of Accuracy Qass I Creating Balances of Accuracy Uass II Laboratory Weights for Routine Adytical Work Calibrating Balances of Accuracy Class 111, IIIL and 1111 Dial Scales, Trip Balances,and Platform Scales Built-In Weights for High Quality Al~alyticalBalances Student laboratory Use

QF I 1

Class El El

I 11

M

11

F2

II

M1

n

F1

M2

I1

ED

11

F1

11

M1,M2,M3

1or I1 11

E 2 . MZ

APPENDIX E-NIST CERTIFICATES OF CALIBRATION FOR FIELD STANDARD TEST MEASURES (EXAMPLES)

36

AP! CHAPTER 4.7

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Gaithersburg, Maryland 20899 REPORT OF CALIBRATION

OF A ONE HUNDRED (100) GALLON VESSEL (Graduated Neck Type)

Mfg: Exact Fabricators Canton, OH.

NlST Seat No: 2345 Material: Stainless Steel Makers No: 8865 Submitted by:

ABC Pipeline Company Mytown, TX. .(PurchaseOrder Number XYZ 222-345678 dated August 22, 1997) Assumed Volumetric Coefficient of Expaqsion, 0.0000265per degree Fahrenheit. The internal volume of the vessel described above has been determined by the volumetric test method using a NlST Standard Test Measure. This method utilizes a volumetric test measure that has a volume that has been compared against NlST reference mass standards. With the vessel in a standing position and the reference attitude established by leveling the attached levels, and drained for 30 seconds after cessation of the main flow, the results for the volume of water delivered are as follows, using the units in parentheses. Scale"

Reading 0

Volume Delivered Volume Delivered (U.S. gal at 60°F) (in.3 at 60°F) 23099.24 99.9967

'The scale reading is determined by the intersection of the horizontal plane, tangent to fhe bottom d t h e meniscus reading in the gauge tube. A scale division, befween -725and +125 is equivalent to 5 in.3.

The NlST Standard Volumetric Test Measure used above has an expanded uncertainty of symbol of k0.02% according to Reference 121.This reference gives the definitions of terms used betow and details on this method far producing expanded uncertainty assessments. The expanded uncertainty quoted above is obtained by computing the standard deviation of the mean for two

[2] Taylor, B.N.and Kuyatt, C.E., "Guidelinesfor Evaluating and Expressingthe Uncertainty of NlST Measurement Results,"NlST Technical Nore 1297, National Instilute of Standards and Technology (January 1993). NlST Test No.: 444/123456.97-8 Calibration Date; August 29, t987

Page 1 of 2

REPORT OF CALIBRATION ABC Pipeline Company, Volume Standards

independent measurements; this is defined as Type A Evaluation of Standard Uncertainty, U,qA,as a percentage of the mean value. This Type A Standard Uncertainty is i0.004%; it is composed of the imprecision of all the components of the NlST measurement process; it includes gauge scale readings, interior wall drainage characteristics, etc. The Type B Evaluation of Standard Uncertainty, ue, for the volume transfer standard is estimated to be 10.01%; this is based on volume measurement experience. These Type A and B Standard uncertainties are combined using the root-sumsf-squares (RSS) method to produce the Combined Standard Uncertainty, u, This Combined Standard Uncertainty is multiplied by a coverage factor, k, that is taken to be 2 to give the expanded uncertainty, U.In the equation form, this procedure is:

'

She test results shown above are the arithmetic means of two independent observations. The stated volume is corrected to a reference temperature of 15.56"C (60°F). The reported volume has an estimated uncertainty that is computed by first taking the standard deviation of the mean of two measurement results, this is referred to as Type A Evaluation of the Standard uncertainty of the test measure. This Type A Standard Uncertainty is squared and added to the square of the Type I3 Standard Uncertainty which is taken to be that for the NlST capability, k0.015.The square root of this sum gives the Combined Standard Uncertainty for the test measure. By multiplying this Combined Standard uncertainty by a coverage factor of 2 produces the expanded uncertainty. The expanded uncertainty for this test measure is k0.045.

For the Director, National Institute of Standards and Technology

Dr. George E. Mattingly Leader, Fluid Flow Group Process Measurements Division Chemical Science and Technology Laboratory

NtST Seal No.: 2345 NlSTTest No.: 444123456-97-8 Calibration Date: August 29, 1997

Page 2 of 2

U.S. DEPARTMENT OF COMMERCE NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Gaithersburg, Maryland 20899

REPORT OF CALIBRATION

OF A ONE HUNDRED (1001 GALLON VESSEL (Graduated Neck q p e )

Mfg.: Exact Fabricators Canton, OH.

NlST Seal No.: 2345 Material: Stainless Steel Makers No.: 8865

Submitted by: ABC Pipeline Company Mytown, TX. (Purchase Order Number XYZ 723 dated August 22,1997)

Assumed Volumetric Coefficient of Expansion, 0.0000265 per degree Fahrenheit. The internal volume of the vessel described above has been determined by the gravimetric test method. The gravimetric method requires weighing the empty vessel and re-weighing when filled with a fluid of known density. The fluid used was water. Wth the vessel in a standing position, the reference attitude was established by leveling the attached levels. The internal volume determined in this way is termed the contained volume and the value is given below using the units - requested in parentheses:

Scale*

0

Volume Contained Volume Contained (U.S. gal a1 60°F) (ina3at 60°F)

99.9800

23095.4

Per request, the delivered volume of this vessel was determined by the following procedure. To establish the delivered volume, the contained volume is drained through the bottom valve. When the main flow of liquid ceases, a 30-second drain time is observed before closing the valve. Subsequent re-weighing completes the gravimetric procedure and enables determination of the delivered volume. The results for the delivered volume of water are as follows, using the units requested in parentheses:

NlSTTest No.: 123112345 Calibration Date: August 29, 1997

Page 1of 2

API CHAPTER4.7

39

REPORT OF CALIBRATION ABC Pipeline Company, Volume Standards

Scale*

Volume Delivered (U.S.gal at 60°F)

Volume Delivered Reading 60°F)

at

*The scale reading is determined by the intersection of the horizontal plane, tangent to the bottom of the meniscus reading in !he gauge tube. A scale division, befween -200 and +200 is equivalent to 2 id!

The expanded uncertainty in the measured volume is *0.003%. It was calculated according to Reference [2] with a coverage factor of 2 and is traceable to NlST reference mass standards.

For the Director, National Institute of Standards and Technology

Dr. George E. Mattingly Leader, Fluid Flow Group Process Measurements Division Chemical Science and Technology Laboratory

[2]Taylor, B.N. and Kuyatt, C.E., "Guidelinesfor Evaluating and Expressingthe Uncertainty of NlST Measurement Results", NlST Technical Note 1297, National Institute of Standards and Technology (January 1993).

NIST Seal No.: 2345 NIST Test No.: 234112345 Calibration Date: August 29,1997

Page 2 of 2

,

APPENDIX F-WATER

DENSITY EQUATIONS

In 1981, a working group of the API Cornmiltee on Static Petroleum Measurement was set up to review standards, and advise on the water density equation lo be used byAPI. They recommended the use of the internationally accepted water density versus temperature equation of Wagenbreth and Blanke. The relationship is shown below:

Note: Wagenbrelh, H., and Blanke, H., "The Densiiy of Water in the

International System of Units and in the International Practical Temperature Scale of 1968," Mitteiluigen der Pltysikalish-Techizischen Budt~sanstali(RB-Mitt), pp. 412415, June 1971.

where (in compatible units) p = True water density in kg/m3,

T, = Water temperature, "C,

Evaluation of these two equations showed that the calculated water densities could differ by two parts in a million; e.g., 999.012 versus 999.014 kg/rn3 respectively, for the density of water at 60"E However, the volumetric correction fao tors (density ratios) developed by either equation are essentially constant and unaffected by the mathematical treatments under consideration. The Wagenbreth and Blanke equation is used to generate water densities at various temperatures. The ratio of the water density between the test measure )p (, and the prover(p,) is equivalent to the correction factor CTDW PTM) CTDW = (-

(PTP)

I

'

c = 9.106025564 x I 0 -3 kg/m3 "C-2,

where

d = 10.05272999 x 10" k g / d "@, e = 112.6713526 x

t

p = the water density, kglm3, T = temperature, "C, [(temperature OF - 32)/1.8]

k g h 3 T4,

TM = the test measure temperature,

f = 659.1795606 x 10-I]kg/m3 0C-5. NlST used this standard until recently; however, their water density calculations have now been converted to the equation developed by G.S. Kell. IS relationship is shown below: P(T,,) =

+

a + bT,,+ CT,:+ d ~ ei~ , : + fl,; kg/m3 1 4. gTw -

Note: Kell, G.S., "Density.Thermal Expansion, and Compressibility of Liquid Water from 0' to 150°C: Correlations and Tables for

Atmospheric Pressure and Saturation Reviewed and Expressed in 1968 Temperature Scale:' Jourrnl of Chemicd and f i ~ @ n e e r g Data, Volume 20. pp. 97-16, 1975.

where (in compatible units)

p = True water density in kglm3,

T, = Water temperature, OC, a = 999.83952kg/m9,

b = 16.945176kglm-30~1, c = -7.9870401 x

kdm-3 'C-2,

.

TP = the prover temperature. The limits in prover temperatures are 35 to 105'F and in measure temprmtures 32.i to 105.E This is the lure range used for the Wagenbreth equation, and, therefore, any extrapolation outside of this temperature range is not recommended. The Kell equation, however, can be used for calculating CTDW values when the temperature is outside of the range recommended for the Wagenbreth equation. Using the Wagenbrelh equation yields a maximum uncertainty in any CTDW value of *0.000007. As discussed previously, use of the Wagenbreth quation versus the Kell b e s not yield any differences in CTDW values.That is, CTDWvaIuesfrom the two equations will differ by less than 0.0000005, within the temperature range of the standard. On rounding to six decimal places app&imately, less than 9% of the equivalent values could differ by &0.000001.For this reason, it is not recommended that the Kell equation be used to duplicate the Wagenbreth standard. Operators should be aware, however, that all test measures calibrated by NlST will .haye the volumes calculated using the density of water derived from the Kell equation. '

Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 8-Operation of Proving Systems FIRST EDITION, NOVEMBER 1995 This material is electronically reproduced by CSSinfo, (734) 930-9277, www.cssinfo.com. No part of the printed publication, nor any part of this electronic file may be reproduced or transmitted in any form, including transmittal by e-mail, by file transfer protocol (FTP), or by being made part of a network-accessible system, without the prior written permission of the Publisher, American Petroleum Institute, 1220 L Street, NW, Washington, D,C.20005.

American Petroleum Institute 1220 L Street, Northwest Washington, D.C. 20005

Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 8-Operation of Proving Systems Measurement Coordination

FIRST EDITION, NOVEMBER 1995

American Petroleum lnstltute

SPECIAL NOTES 1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE AND FEDERAL LAWS AND REGULAnONS SHOULD BE REVIEWED. 2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANUFACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED,CONCERNING HEALTH AND SAPETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL, STATE, OR FEDERAL LAWS. 3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPER PRECAUTIONS WlTH RESPECT TO PARTICULAR MATERIALS AND CONDITIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER OR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

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5. GENERALLY, API STANDARDS ARE REVIEWED AND REVISED, REAPFIRMED,OR WITHDRAWN AT LEAST EVERY FIVEYEARS. SOMETiMES A ONETIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW CYCLE. THIS PUBLICATION w n L NO LONGER BE IN EFFECT FIVE YEARS AFTER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR, WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. 'THE STATUS OF THE PUBLliCATlON CAN BE ASCERTAINED FROM THE API AUTHORING DEPARTMENT [TELEPHONE (202) 682-8000]. A CATALOG OF APT PUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L STREET, N.W.,WASHMGTON, D.C.20005.

Copyrighl Q 1995 Amedcan Petroleum Institute

B

FOREWORD API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted to the Measurement Coordinator, Exploration and Production Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

ill

CONTENTS ~

~

Page

CHAPTER &PROVING SYSTEMS SECTION 8-OPERATION OF PROVING SYSTEMS

................ 1 ...................................................................... 1 4.8.1.2 Definition of Terms ........................................................................................ 1 4.8.1.2.1 Meter Proving.......................................................................................... 1 4.8.1.2.2 Meter Factor ......................................................................................... I 4.8.1.2.3 Base Prover Volume ...............................................................................1 4.8.1.2.4 Proving or Calibration Run ............................................................... 1 ..........................................1 4.8.1.3 API Referenced Publications ..................... . 4.8.2 Pertinent Information. Applicable to ~ A e Proving r Systems in Chapter 4.8 ......1 . 4.8.2.1 The Need To Prove.......... ...........................................................................1 4.8.2.2 Typical Metering Instaliations...................................................................... 2 4.8.2.3 Preparation for Proving With a Mobile Prover ............................................ 2 4.8.2.4 Temperature. Pressure, and Density Measurements....................................... 2 4.8.2.5 Indicated Volume Correction......................................................................... 2 4.8.2.5.1 Meter Factor ................... .. ......................... ...................................2 4.8.2.5.2 K-Factor ................... . . ........................................................................2 4.8.2.6 Pulse Generating Meters ........................................................................... 2 4.8.2.7 Pulse Integrity Check .............................. . . ................................................5 4.8.2.8 Potential Proving Problems ............................................................................ 5 4.8.2.8.1 Flow Conditioning................................................................................... 5 4.8.2.8.2 Temperature Variations.;................ . ................................................. 5 4.8.2.8.3 Valve(s) Leakage .................................................................. ..............5 4.8.2.8.4 Effect of Wear. Damage. and Deposits on Meters and Straightening i ..................................5 Sections ................................................................

4.8.1

lntroductjon .......................................................................................

.

4.8.1 1 Scope and Field of Application

;

4.8.2.8.5 Electronic Equipment and Instrumentation............................................. 6 4.8.2.8.6 Flow Rate Variations 6 4.8.2.9 Meter Registration (Head) Check 6 4.8.2.10 Frequency of Meter Proving 6 4.8.2.11 Prover Recalibration Frequency ................................................................... 6 4.8.2.12 Filling and Pressuring the Prover ................... ....................................... 7 4.8.2.13 . Certification ...................................... . . 7 ............. 7 4-83 Conventional Pipe Provers 7 4.8.3.1 Principle of Operation .................................................................................. 4.8.3.1.1 Prerun Requirements............................................................................. 9 . 4.8.3.1.2 The Bidirectional Conventional Prover................................................... 9 4.8.3.1.3 The Unidirectional Conventional Prover . . ............... 9 4.8.3.2 Equipment Description........................ 9 4.8.3.2.1 Detector Switches.................................................................................. 9 4.8.3.2.2 Prover Displacers 9 4.8.3.3 Inspection ..................................................................9 4.8.3.4 Preparation........................... 11 4.8.3.5 Operating Procedures ...................................................................................11 4.8.3.6 Assessment of Results 11 4.8.3.7 Trouble-shooting .................................................................................... 14 4.8.4 Small Volllme Rovers .............................................. 14 4.8.4.1 Principle of Operation ................................ ..........................14 4.8.4.2 Equipment Description ................. ..................................................... 18 4.8.4.2.1 Pulse Interpolators 18

............................................................................... ............................................................... .......................................................................

. .

............,....................

........................... ................................................. ............................................................................... ............................... . . . . ......................... .................................. .................................... ...........

...........

...............................

page

Prover Djsplacers...................................................................................... 18 4.8.4.2.3 Detector Switches.................................................................................. 19 4.8.4.3 Inspection .................................................................................................... 19 4.8.4.4 Preparation .............................................-.................................................... 19 4.8.4.5 Opemting Procedures ................................................................................... 19 4.8.4.6 Assessment of Results................................................................................ 19 4.8.4.7 Trouble-shooting ................ ; ........................................................................ 19 4.8.5 Tank Provers .................................................................................................... 19 4.8.5.1 Principles of Operation ............................................ ......... .. 19 4.8.5.2 Equipment Description ................................................................................. 19 4.8.5.3 Inspection ...................................................................................................19 ..........................*............................................ 4.8.5.4 Preparation 24 4.8.5.5 Operating Procedures .......................................................................... 24 4.8.5.6 Assessment of Results ................................................................................. 24 4-8-57 Trouble-shooting....................................................................................... 24 4.8.6 Master Meter Provers....................................................................................... 25 4.8.6.1 Principle of Operation ................................................................................ 25 4.8.6.2 Equipment Description................................................................................. 25 . 4.8.6.3 Inspection ............................................................................................... . 25 4.8.6.4 Preparation ................................................................................................. 26 4.8.6.5 Operating Procedures ........................ :........................................................ 26 4.8.6.6 Assessment of Results ................................................................................ 26 4.8.6.7 Trouble-shooting ................... ............................................................... 26 4.8.4.2.2

..............

...................... .

. .

APPENDIX A-ESTIMATING RANDOM UNCERTAINTY ..................................... 27 APPENDIX B-TROUBLE-SHOOTING GUIDE 29

.......................................................

Tables A-1-Variable Range Criteria for d.00027 Random Uncertainty in Average Meter Factor................................A..................................................................... 28 A-2-Variable Range Criteria for d.00073 Random Uncertainty in Average Meter Factor ; .................................................................................................... 28 B-1-Trouble-Shooting Guide for Pipe Prover Operators. Part 1 ............................... 31 B-2-Trouble-Shooting Guide for Pipe Prover Operators. Part 2 ...............................33 B-3-Trouble-Shooting Guide for Small Volume Prover Operators 35 36 3-4-Trouble-Shooting Guide for Master-Meter Prover Operators B-5-Trouble-Shooting Guide for Tank Prover Operators..........................................37

............

..........................

.........................

Figures I-Simple Turbine Flowmeter Installation................................................................. 3 2-mica1 Multi-Stream Meterjng Installation............................................................. 4 3-Calibration Section of Pipe Prover................................. ................................7 4-Typical Bidirectional U-Qpe Sphere Prover System .................-................. : 10 9 5-Typical Unidirectional Return-Type hover System 4-43eneral Purpose Meter Proving Rbport for Use With Pipe Provers ......................12 7-Meter Proving Report With Pulse Interpolation ................................................. 13 8--C ontrol Chart for Individual Meter Factors ........................................................... 14 9 S y s t e m Overview of SVP With Internal Valve .....................................................15 l O S y stem Overview of SVP With Pass-Through Displacer With fisplacer Valve 16 11-System Overview of SVP With Internal Bypass Porting With External Valve.... 17 12-Small Volume Prover Automatic Computing System .......................................................... 18

...... ................................................

....

.................................................

Page

13-System Overview of Unjdirectional Spheroid Displacer With interchange System ........................................................................................ 20 14-Meter Proving Report for Master Meter Method ................................................. 21 15-Meter Proving Report for Tank Prover Method ................................................... 22 l-pen Stationary Prover Tank (Drain-ta-Zero or Bottom Gauge-Glass Type) ..... 23 1 7 - 4 Iosed Stationary Tank Prover........................................................-.........-........ 23 18-Typical Master Meter Manifold ........................................................................... 25

Chapter 4-Proving

Systems

SECTION &OPERATION OF PROVING SYSTEMS .4.8.1

I

i

I

Introduction

This guide is intended to provide essential information on the operation of the various meter-proving systems used in the petroleum industry. In the petroleum industry, the term proving is used to refer to the resting of liquid petroleum meters. A meter is proved by comparing a known prover volume to an indicated meter volume. The meter and prover volumes are then subjected to a series of calculations using correction factors to convert volumes to standard conditions for the effects of temperature and pressure to establish a meter factor. Liquid petroleum meters used for custody transfer measurement require periodic proving to verify accuracy and repeatabiIity and to establish valid meter factors. Conventional pipe provers, small volume provers, master-meter provers, and tank provers vary in size and may be permanently installed or mobile. These prover types are described in API MPMS Chapter 4.2 and in more detail in their respective sections of this chapter of the API Martual of Petroleum ~eaiurenzentStandards (MPMS). 4.8.1.1

SCOPE AND FIELD OF APPLICATION

This guide provides information for operating .meter provers on single-phase liquid hydrocarbons. It is intended for use as a reference manual for operating proving systems. The requirements of API MPMS Chapter 4.8 are based on customary practices for crudc oils covered by Table 6A and products covered by Table 6B in API MPMS, Chapter 11.1. Much of the information in API MPMS Chapter 4.8 is applicable to other fluids. Specific requirements for other fluids should be agreeable to the parties involved. 4.8.1.2 DEFINITION OF TERMS 4,8.1.2.1 Meter proving is the comparison of a known prover volume to the indicated meter volume; the meter and prover volumes are then subjected to a series of calculations using correction factors for temperature, pressure, and API gravity (or relative density) to establish a meter factor. 4.8.1.2.2 A meter factor i s a dimensionless number obtained by dividing the volume of liquid passed through the meter {as measured by a prover during proving) by the corresponding meter-indicated volume, both at standard conditions.

4.8.1 -2.3 Base prover volume is the volume dispIaced between detectors at standard conditions, in other words, 15°C (6O0F),101.325 kPa (0 psig).

'

4.8.1.2.4 A proving run or calibration run consists of one round trip of a bidirectional prover, one pass of a unidirectional prover, one filling of a tank prover, or one test run with a master meter. 4.8.1.3 API

API REFERENCED PUBLICATIONS

~ a n u aolf Petroleum Measurement Standards (MPMS) Chapter 1, "Vocabulary" Chapter 4, "Proving Systems," Section 2, "Conventjonal Pipe Provers"; Section 3, "Small Volume Provers"; Section 4, "Tank Provers"; Section 5, "Master-Meter Provers"; Section 6, "Pulse Interpolation" Chapter 5, "Metering," Section 2, "Measurement of Liquid Hydrocarbons by Displacement Meters"; Section 3, Measurement of liquid Hydrocarbons by Turbine Meters"; Section 4, "Accessory Equipment for Liquid Meters"; Section 5, "Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems" Chapter 7, "Temperature Determination," Section 2, "Dynamic Temperature Determination" Chapter 11, :'Physical Properties Data," Section 1, "Volume Correction Factors" . Chapter 12, "Calculation of PetroIeum Quantities," Section 2, "Calculation of Liquid Petroleum Quantities Measured by Tbrbine or Displacement Meters" Chapter 13, "Statistical Aspects of Measuring and Sampling," Section 2, "Statistical Methods of Evaluating Meter Proving Data"

4.8.2

Pertinent Information, Applicable to Meter Proving Systems in Chapter 4.8

4.8.2.1 THE NEED TO PROVE A meter in service should be periodically proved to confirm its accuracy. The previously determined meter factor may no longer bc applicable due to changes in fluid characteristics, operating conditions, and meter wear. Specific reasons for praving meters include the folIowing: a. The meter has been opened for inspection or repair. b. The meter calibrator has been changed or requires changing. c. Any of the meter accessorieshave been changed, repaired, or removed. d. Changes in operating conditions have occurred, such as '

Pressure gauges or pressure transducers should be selected to a scale resolution as recommended in API MPMS Chapter 4 and recorded as recommended in API MPMS Chapter 12.2. or relative density) is determined by Density (API using either a densitometer, a thermohydrometeror hydrometer and thermometer, with density resolution equivalent to 0.1 degree API gravity or better, and recorded as recommended in API MPMS Chapter 12.2.

API gravity, relative density, viscosity, temperalure, pressure, or flow rate. e. Contractual requirements exist, such as scheduled meter maintenance based on volume throughput and/or elapsed time. 4.8.2.2

TY PlCAL METERING INSTALLATIONS

Typical metering installations are shown in Figure I and Figure 2. There are many variations encountered because ofspecific design requirements. Mobile provers are usually used with single meter installations. Installations with ' multiple meters usually have a permanently installed prover.

4.8.2.5

4.8.2.5.1

1NDlCATED VOLUME CORRECTION Meter Factor

A meter is a mechanical device and is affected by slippage, drag, and wear. A meter reacts differently when metering different liquids. A meter factor is used to correct the indicated volume to the actual metered throughput. The meter factors CTL and CPL (see API MPMS Chapter 12.2) are used to correct the indicated meter volume to gross standard volume on a measurement ticket. A meter factor is the ratio of the gross standard volume of liquid passed through the prover (GSVp) to the indicated standard volume of the meter (ISV,), expressed by the following equation: MF = GSVp1ISVm Meter and prover volumes shall be corrected to base conditions (for example, 60'F, 0 psig). The values of GSVp and ISV,, shall always be expressed in the same units. This makes the meter factor a nondimensional number. See API MPMS Chapter 12.2.

PREPARATION FOR PROVING WITH A MOBILE PROVER This section summarizes the preparatory work that should be done in a specific sequence. The specification of the mobile prover must be reviewed to ensure that the prover is suitable for the flow rate, pressure, and the temperature of the metering facility. Pressure and temperature ratings must satisfy all regulations and standards. Prover materials must be compatible with the metered liquids. Elastomers are especially susceptible to damage. from incompatibility. The elastomers of the spherelpiston,flange o rings and gaskets, valve sealsiseats, hoses, swivel fittings, and so forth, must be compatiblewith the liquid. Check that the product in the prover is compatible with the current product to prevent conlamination. If incompatible, it may be necmsary to drain and flush the prover, On arrival at the site, the operator should (a) report to the site supervisor to arrangefor assistance, (b) identify the meter to be proved, (c) identify connections, (d) arrange for electric power (if required), (e) arrange for disposal of liquid (if not returned to the pipe line), ( f ) set up traffic barriers, and so on. The prover should be properly positioned, leveled, braked, and electrically grounded. If a vapor recovery system is used during normal metering operations, consideration should be given to operating the vapor recovery system during the meter proving. Before removing blind flanges or end caps from the connecting stubs, make absolutely certain there is no pressure behind the flanges. Always inspect the h ~ s e before s and after connecting the prover for signs of wear and damage. Make all necessary electrical connections.

Some meters such as turbines may not be equipped with a counter that reads directly in units of volume. Their output is a series of electrical pulses {n) that is proportional to the volume ( v ) passed through the meter. K-factor is defined as the number of pulses generated by the meter per unit volume, as expressed as the following: K =n / v A new K-factor may be determined during each proving to correct the indicated volume to gross volunie. If a new Kfactor is not used, a constant K-factor may be used, and the new meter factor will correct indicated volume to gross . volume.

TEMPERATURE, PRESSURE, AND DENSITY MEASUREMENTS Use thermometers or temperature transducers with the highest practical scale resolution as recommended in API MPMS Chapter 7.2, and record as recommended in API MPMS Chapter 122.

4.8.2.6 PULSE GENERATING METERS A meter must produce a high-resolution electrical pulse to drive a proving counter. Tho basic types of pulse-generating meters commonTy used in the petroleum industry are turbine and displacement meters. A turbine meter uses the energy of the fluid stream to turn

4.8.2.3

4.8.2.4

,

Section &-Operation of Proving Systems

3

of Proving Systems

n bladed rotor which produces an electrical signal that is propo'rtional to flow. A displacement meter mechanically separates the liquid into discrete quantities of fixed volume. The rotation of the displacement meter is used to drive a pulse-generating device with its output proportional to flow. 4.8.2,7 PULSE INTEGRITY CHECK

The displacement-meter pulse generator should be checked for pulse integrity. One method is to check the number of pulses per revolution of the disk. Each time the slotted disk used to generate pulses completes a revolution, a fixed number of pulses (1000 for example) should be generated. A magnetic or optical switch on the disc starts and stops the proving counter. The proving counter should indicate 1000 pulses plus or minus 1 pulse (that is, 999 to 1001 pulses). This procedure should be repeated until at least the minimum number of pulses equals one pass of the prover displacer. If the pulse integrity check fails, then the meter drive train, the puIse generator, the counter, cables, or connections are faulty and should be repaired or replaced before proving is undertaken. Turbine meter pulse integrity can bechecked by displaying the pulse train on an oscilloscope, A missing pulse may be the result of a loose or missing turbine meter rim butlon or blade. If a nonuniform pulse train is produced, the meter should be repaired or replaced before proving is resumed. POTENTIAL PROVING PROBLEMS The meter and all of its associated equipment (such as gear trains, registers, compensators, and counters) must be maintained in good working order, both mechanically and electrically. The meter should also be inspected whenever its performance is jn question, if mechanical or electrical problems exist, or as required by contract or regulations. The meter should be operated in the linear portion of its performance curve, and the prover should be operated within its flowrate limitations. The meter should be proved as close as practical to the same conditions under which it normally operates. Meter performance is dependent upon flow rate. Therefore, during proving it i s essential that flow rate be maintained as steady as possible within the normal operating flow range of the meter. 4.8.2.8

4.8.2.8.1

5

Flow conditioning upstream and downstream of a turbine meter should be per API MPMS,Chapter 5, Section 3. It is essential that the pressure in the meter and the prover be higher than the vapor pressure of the liquid. With turbine meters, this back pressure must not be less than that specified in APIMPMS, Chapter 5, Section 3. A common method of preventing vaporization is the use of a back-pressure control device downstream of the meter. Entrained vapor will cause erroneous proving results. Any time a system is filled with liquid, all vapors must be vented. If the venting is not properly done, vapor left in the line will subsequently be swept through the meter/proving system. When liquid is withdrawn from a tank with a low liquid level, a vortex at the tank discharge may form, causing air or vapor to be drawn into the meter stream. A vortex breaker may be installed in the tank to prevent vortex formation, and an aidvapor eliminator is often installed upstream of the meter to prevent vapor from flowing through the meter. 4.8.2.8.2

Temperature Variations

For best results, the prover temperature and the meter temperature should be stabilized. When a prover has been off line, more time is required for temperature equifibrium to be attained. The ability to detect temperature changes during proving is essential if accurate results are to be obtained with a meter prover. 4.8.2.8.3

Valve(s) Leakage

During proving, it is essential that all liquid flowing through the meter flows through the prover, Therefore, the sphere interchange in a unidirectional prover, the four-way valve in a bidirectional prover, and every valve between the meter and the prover must seal leak-dght when closed. Any leakage through the valves will cause an error in proving. These valves should be of a double block-and-bleed type or o f a similar valving configuration to insure seal integrity. All valves to the prover from other meter runs must be isolated without leakage during proving. Drains, vents, and relief valves must seal during proving. The space between the seals on a double block- and-bleed valve or valving configuration is connected to a small bleed valve, pressure gauge, or pressure switch to verify seal integrity. Seal integrity should be checked each time a vaIve is closed.

Flow Conditioning

A strainer or filter should be provided upstream of the meter to protect it from being damaged by foreign materials and entrained solids. Downstream of a partially opened valve or a pipe fitting, the cross-sectional velocity will be nonsymrnetrical. This velocity profile has little or no effect on the performance of displacement meters, but seriously affects turbine meters.

4.8.2.8.4

Effect of Wear, Damage, and Deposits on Meters and Stralghtenlng Sections

As a displacement or turbine meter wears, its meter factor will gradually change. Therefore, all meters should be proved at regular intervals. Turbine meters and their straightening sections with tube-bundles or vanes are susceptible to collecting foreign

objects traveling in the flow stream. They should be inspected and cleaned periodically. Turbine meters are especially susceptible to the effects from deposits because they are velocity devices. Layering or coating of the meter's internals will change the velocity of the liquid flowing through the meter and cause the meter to register incorrectly. Temperature changes can affsct the mechanical clearances of displacement meters, as well as the viscosity of the fluid being metered. This may result in changes in slippage. 4.8.2.8.5

,

Electronic Equipment and Instrumentation

All electrical and electronic equipment, such as counters, switches, interconnecting cables, and grounding cables, shall be periodically inspected for condition and for proper installation and operation. Operating procedures may require. special permission or permits before equipment is connected. . A counter may miss some of the pulses generated by the meter, in which case the counter will read low. Counting too few pulses is usually caused by setting the sensitivity control on the counter too low,or by an electrical fault which has developed. By adjusting the sensitivity control or by eliminating the electrical fault, the trouble can usually be corrected. A counter may include signals from outside sources as pulses. These signals, not generated by the meter, will cause the counter to.read high. Signals not generated by the meter can originate from electrical power supplying the counter, electrical welding equipment, radio transmitters, and so forth. These pulses may be intermittent and difficult to detect. See API MPMS,Chapter 5, Section 5. Signal transmission cables should be kept as far away from power cables as possible and should cross power cables at right angles. Shielded signal transmission cable is norrnally grounded only at the instrument-receiving end to prevent a ground loop (current that travels along the shield and adversely affects the signal transmission). 4.8.2.8.6

Flow Rate Varlations

Meter performance is dependent upon flow rate; lhus, flow rate during proving shall be maintained at or near the normal operating fiow rate. 4.8.2.9 METER REGlSTRATlON(HEAD) CHECK Compare the meter register (indicated volume) to the proving-counter registration. This can be done by manually gating (starting and stopping) a prover counter connected to the transmitter, based on a significant volume registered by the meter counter or register. The pulses displayed on the prover counter are then compared to the volume displayed on the mechanical register. If the meter generates 8400

pulses per barrel, the prover counter should show approximately 84,000 pulses for each 10barrels on the register. 4.8.2.10 FREQUENCY OF METER PROVING The frequency required for proving varies from several times a day to twice a year or even longer depending upon the value of the liquid, costhenefit to prove, meter proving history, meter system stability, and variations of operating systems. For large volumes or different liquids, a permanently installed prover i s normally used. The meters should be proved whenever the flow rate, temperature, pressure, API Gravity (relative density), or viscosity changes significantly. Normally, time or volume is used to determine when the meter should be proved. When metering a single or similar liquid, the meter factor is normally applied forward to the meter's indicated volume until the meter is reproved. Normally, there is a prescribed deviation limit between consecl~tivemeter factors on the same or similar liquid. When this deviation limit is exceeded, the previous and the new meter factors are normally averaged and applied to the indicated volume during this period. If the deviation limit is consistently exceeded, it may be appropriate to reduce the interval between meter proving. It may also be appropriate to inspect and repair the meter and the proving system. When batching operations permit, a new meter factor should be determined for each batch. This applies to batching operations involving different liquids or lengthy down time. When a meter is proved during a batch, the meter factor should be applied forward until the meter is reproved during the batch. If the meter is reproved during the batch, a deviation limit may be installed between consecutive meter factors, or the meter factors may be averaged. When this deviation limit is exceeded, the previous and new meter factors are normally averaged and applied to the meter's indicated volume between these provings. If it is impractical to prove each batch, meter factors are normally applied forward until the next proving, as is the case with nonbatching operations. The proving frequency for new systems should start at short intervals and be extended to longer intervals as confidence increases in the system. See API MPMS Chapter 13.2 for statistical evaluation of meter proving data.

4.8.2.1 1 PROVER RECALlBRATlON FREQUENCY Qpiically a prover's base volum~is originally certified at the manufacturer site by the water draw method in the presence of the purchaser and other interested parties. Prover volumes may change as the result of warn or faulty detector switches; the reduction of internal coating thickness; or loss of internal material due to oxidization, abrasion, or the accumulation of foreign material (such as wax) buildup. Subse-

Section 8--Operationt of Proving Syslems quent calibration is required whenever a change in base volume could have occurred. Six considerations determine how frequentIy a prover should be recalibrated. They are usage, time, calibration history, calibration costlbenefit, contractual requirements, and value of the metered liquids. Usage causes wear, and time contributes to deterioration of the prover. For the recommended procedure for calibrating a prover, refer to API MPMS Chapters 4 and 12.2. Recalibration of provers should occur when any one of the following conditions exist: a. Alterations or repairs which affect the certified volume are made to the prover. b. A meter controI. chart indicates a change in prover volume, c. The maximum interval indicated bdow has elapsed. 1. Three years for small volume provers and mobile provers. 2. Five years for permanently installed pipe provers. 3. Five years for permanently installed tank provers. 4. Three months for master meter provers. The prover displacer and the inside surface of the prover should be inspected periodically. The surface of a sphere or the contact edge of a piston cup or seal may indicate the internal condition of the prover. If these surfaces or edges are scored or worn, this may indicate that the prover requires further inspection or repair and may require recalib~ation. FlLLlNG AND PRESSURING THE PROVER This section refers to conventional pipe provers, small volume provers, and master meter provers. This section does not pertain to tank provers, which are covered in 4.8.5.4. After checking that end closures and any openable fittings are properly fastened and that all vent and drain valves are closed, proceed with filling the prover in the following sequence: 4.8.2.12

a. Partially open the prover isolation valve to fill the prover slowly. b. Observe the system for leaks. Wait until the system is completely filled and the conneclions have been shown to be leak-tight. Verify the seal integrity of all vents, drains, reliefs, and all double block-and-bleed valves. c. Open the vents to allow discharge of aidgas when the fluid is admitted into the prover. d. Fully open the prover inlet and outlet valves. e. Close the valve to divert all flow through the prover, f. Operate the prover and continue to vent the high points until no air is observed. g. Close the vents when air or vapor is no longer observed.

7

4.8.2.13 CERTIFICATION Verify that the prover bas a valid calibration certificate and that the certificate is f ~the r prover being used, by verifying the prover serial number with the serial number on the certificate. If a conventional pipe prover is being used, check 10 ensure that he prover volume between detectors is sufficient to accumulate a minimum of 10,000 pulses. If not, pulse interpolation techniques are required. Since some provers have more than one calibrated volume, verify that the proper calibration certificate is being used. If a tank prover is used, verify that the prover volume is equal to a minimum of one minute of the maximum operating flow rate. See API MPMS, Chapter 4.4. If a master meter is used, all data that is used to develop the master meter factor(s), including the prover calibration report, certificate, and master meter factor(s) reports should be available. If a small volume prover is used, verify that the interpolation system has a valid and current calibration certification. Refer to API MPMS, Chapter 4, Sections 3 and 6. '

4.8.3

Conventional.Pipe Provers

4.8.3.1 PRINCIPLE OF OPERATION The basic principle on which the pipe prover operates is shown in Figure 3. A sphere or piston known as a displacer L installed inside a specially prepared length of pipe. When the prover is connected in series with a meter, the displacer moves through the pipe and forms a sliding seal against the inner wall of the pipe so that it always travels at the same speed as the liquid flowing through the pipe. In some conventional provers, the displacer is a piston with elastomer or plastic seals. However, in most conventional provers, the displacer is an elastomer sphere. To provide good sealing, the pipe bore must be smooth. At two or more points in Figure 3, there are devices known as detecrors fixed to the pipe wall. These detectors emit an electric signal when the displacer reaches them. The signal from the first detector switch is used to start the electronic counter, which accumulates pulses from the meter. When the displacer reaches the second detector, its signal stops the proving counter. The number of pulses shown on the proving counter is the total pulses generated by the meter while the displacer was travelling between the two detectors. Conventional pipe provers (both bidirectional and unidirectional) are those that have a volume between detectors that permits a minimum acculuation of 10,000 direct (unaltered) pulses from the meter. Thus a unidirectional prover typically accumulates a minimum of 10,000 pulses per proving run, and a bidirectional, prover typically accumulates a minimum of 20,000 pulses per voving run. Direct (unaltered)pulses include those that are the output of high frequency pulse generators,considered to be a 'kart of' the meter. It should also be noted that

Calibrated length

L I

I

---Inner wall of pipe

Figure 3-Calibration Section of Pipe Prover there are occasions when 10,000 pulses cannot be accumulated during proving passes. This may occur because of a change or a constraint in operating conditions. Agreement between parties to use less than 10,000 pulses per proving pass is required in these instances. 4.8.3.1 .I

Prerun Requirements

A prerun (or run-up) length of pipe is essential. This length is the distance between the entry of the displacer and the first detector switch of sufficient length to give the valve time to close and seal before the displacer reaches the detector. This type of prover must never be used at more than its rated flow rate, or this prerun length may not be adequate. As an alternative, some provers are provided with mechanical means of holding the djsplacer near the beginning of its travel until the valve is fully seated; by this means the premn length can be shortened considerably. 4.8.3.1.2

The Bidirectional Conventional Prover

Bidirectional provers can use either a sphere or a piston as a displacer. Spheres are more commonly used because they will go around bends, and the prover can be built in the form of a compact loop, as in the example shown in Figure 4. A four-way valve is normally used to reverse the flow through the prover, The sphere in Figure 4 is shown in the position that it occupies at the end of a proving run. The sphere will start to travel on its return pass when the four-way valve begins to reverse the flow, but it will not reach its full speed until the movement of the four-way valve is complete. Displacer detectors are never quite symmetrical in their operation, and consequently the effective calibrated volume when the displacer travels between detector 1 and detector 2 will not be quite the same as when the displacer travels between detector 2 and detector 1. The calibrated base volume of the prova js the sum of both directions and is

termed the round trip volume. The prover counter totals the pulses collected in both directions.

4.8.3.1.3 The unidirectional Conventional Prover A unidirectional prover is shown in Figure 5. It uses a sphere displacer and sphere interchange. The sphere interchange is for receiving, holding, and launching the sphere. After falling through the interchange, the sphere enters the flowing stream of liquid and is swept around the loop of pipe. At the end of its pass, the sphere enters the sphere transfer valve, where it lies until the next proving pass. The calibrated base volume of the prover is the one-way volume between the detector switches. 4.8.3.2

'

4.8.3.2.1

EQUIPMENT DESCRIPTION Detector Swltches

The detectors fitted to a pipe prover are highly sensitive devices. The most common type of pipe-prover detector switch uses a ball-end steel plunger, which projects through the wall of the pipe a short distance. When the sphere makes contact, it forces the plunger to actuate the switch, Replace ment procedures must conform with manufacturers' recornmendations. Replacing a detector switch may change the prover volume. Replacement or adjustment of detector switches on bidirectional provers is less critical than on unidirectional provers. The decision to recalibrate a bidirectional prover should be made on a case-by-case basis. When a detector is replaced or adjusted on a unidirectional prover, recalibration shouId occur at the earliest possible opportunity. A record should be kept of the time and date of the replacement. 4.8.3.2.2

Prover Displacers

The majority of pipe prover displacersare hollow spheres made of an oil resistant elastomer such as nitrile, neoprene,

Sectton 8--Operation of Proving Systems

Section &Operatlon of Proving Systems or polyurethane. These displacers are fitted with an inflation valve, or valves, and are intended to be inflated with water or glycol to a diameter which maintains an effective seal in the prover bore without creating excessive sliding friction. The manufacturer will usually specify the amount (typically between 2 and 4 percent) by which the sphere diameter needs to exceed the pipe bore. Small bore provers may employ a sphere made of solid elastomer. Spheres should not be stored in an inflated condition on a flat surface. They should either be suspended in a net or supported by a hollowed-out bed of sand to prevent the development of a flat spot. If a piston is used as a displacer it may be fitted with cuptype seals, especially in older provers. In many of the modern piston provers, the seals are made of teflon with stainless steel backup rings. INSPECTION The internal surfaces should be inspected for coating failures, adhesions (any foreign material build-up on the internal surface), or corrosion that would change the calibrated volume of the prover. If the prover is internally coated, the lining should be checked for coating wear or failure which would cause the calibrated volume to increase. The most likely location for such failures will be in the elbows. The djsplacer should be removed from the prover and examined at the intervals prescribed by the manufacturer or by the operating company. The sphere or seals should be inspected and replaced if there js any sign of mechanical damage or of softening by chemical action. Spheres should also be inspected for roundness and proper inflation. This is done with either a sizing ring supplied by the manufacturer or a tape measure. A piston prover displacer may be subjected to a leak test. This may be done by positioning the displacer so that its seals straddle a pressure tap in the prover wall where a bleed valve is located so pressure may be applied between the seals. Pressure may also be applied through the body of the piston to the seal area. Other means for checking seal leakage may be provided by the prover manufacturer. 4.8.3.3

4.8.3.4 PREPARATION Examples of meter proving forms are shown in Figures 6 and 7, Other forms or documents may be required before proving is started, Refer to API MPMS, Chapter 12.2 for meter factor calcutation requirements. Check that end closures and any openable fittings ere properly fastened and that all vent and drain valves on the prover are clased. Proceed wjth filling the prover as follows:

a. Partially open the prover inlet valve to fill.the prover slowly. b. Observe the system for leaks. Wait until the system is cdmdetely filled and the connections have been shown to be

11

leak-tight before fully opening the prover inlet valve. c. Open vents to allow discharge of air or vapor when fluid is admitted into the prover. d. At this point the prover outlet valves may be safely opened. e. After all the connecting valves are fully opened, the meter divert valve between the prover inlet and outlet valves may then be closed. f. Operate the prover displacer at least one proving cycle and vent the high points. The vents should be checked repeatedly until it is certain that no vapor remains in the prover. g. Verify the seal integrity of all vents, drains, reliefs, and double block-and-bleed valves between the meter and the outlet of the prover. 4.8.3.5 OPERATING PROCEDURES Maintain the flowthrough the proving system until stable conditions of pressure, temperature, and flow rate exist. Once stability is achieved, proving operations may proceed. Determine the actual flow rate on the first pass of the displacer and make spot checks thereafter. Determine the meter temperature aild pressure during each pass of the displacer. When using a bidirectional prover, record the meter temperature and pressure, using the average of readings taken for each pass of any given round trip. Using both inlet and outlet thermometers and pressure gauges, determine the average prover temperature and pressure during each pass. The average prover temperature and pressure is recorded on a round trip basis in the case of a bidirectional prover. If using a bidirectional prover, record the reading of the prover counter at the end of each round trip of the displacer. For a unidirectional prover, record the reading of the prover counter at the end of each pass of the displacer. Repeat the proving operation until the required minimum number of proving funs (per agreement between parties) are attained. As a measure of repeatability, the range of the proving set is determined as follows: Range of Repeatability =

Maximum Value - Minimum Value x 100 Minimum Value

Assess the repeatability of the set of results, and if necessary cany out additionalrunsin an attempt to gain the required repeatability. If suitable repeatability is not obtained, discontinue the proving operation and refer to Appendix B. 4.8.3.6 ASSESSMENT OF RESULTS One common practice is to require a minimum of five consecutive runs that agree within a range of 005 percent. Another common practice requires a minimum of five out of six consecutive runs that agree within a range of 0.05 percent. For low volume locations including some LACT units, a minimum of three c~nsecutiveruns that agree within

-

AMBlENl TEMP.

DATE

REPORT NO.

1

II PROVER DATA

1I

PREVlWS REWRT

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I REMARKS, REPAIR& AaJUSTMENf8, E x .

I

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DATE

COMPANY REPFESENTEO

I

Purpose Meter Proving Report for Use Wifh Pipe Provers

Figure +General

I

Section 8--OperatIan of Provlng Systems

Meter No. 21x2 Ownerand/or operating company: Location of meter being proving: Meter, SIN AK-12345 Last overhaul date: 10/20/94

13

Report No. 3 Dale: DECEMBER 20,1994 D P & C PETROLEUM PIPELINE COMPANY 897665 BELL RECEIVING STATION Totalizer: Size: 4 Inch Type: TURBINE Model: BM-4444 Old Seab: 456789 & 456790 New: 457201 & 457202

1 Prover calibration date:

JULY 4.1994 Prover Calibration Certificate No. 200007 1 Small Volume Prover {serlal number) SP-5555 Small Volume, Single Wall, Unidirectional 12",External Detectors Prover outside dlameter >>>>z 14.000 OD (inches) APlobs 45.8 Product Prover inside diameter >>>>> 12.250 ID (inches) 80.0 JET FUEL Tobs Prover wall thickness z>>>> 0.875 WT (inches) APlb 44.0 Seconds Pulses Pass Whole Seconds Interpolated Flowrate PulsesIGal. per pass per second Pulses No. Pulses of pulses Gross Gross . N Time 1 Tlme 2 Frequency N' GPM K Factor

Pass No.

Temperature in degrees F TP Tm

Interpolated Pulses per Prwing RunlPass

Pressure in psig PP ~m

-- -

Average data per run >>>>>>> Test range percent (YO) 0.019 >>>>5>> Nominal K Factor

I

I

BASE PROVER VOLUME

m &

7 1

Stainless Steel CTLp CPLp CCFp GROSS STANDARD VOLUME

INDICATED VOLUME OF METER CTLm CPLm CCFm INDICATED STANDARD VOLUME

I

75.5 $15 104 Temperalure of lnvar Rod 25.000 NKF = Pulses per lndlcated Unit Gallon

377.31

I

I

15.086 BPV= Prover Volume @ 60 deg. F & 0 pslg 1,0002Ga = 0.0000120 GI = . 0.0000008 1 deg F 1.0001 E = Modulus of Elasticity E = 28500000 0.9918 Tables 58 & 6B, API Standard 2540 1 .OD07 "Fp'factor from 11.2.1 (Pe = 0) = 0.00000614 0.9928 CCFp = (CTSp CPSp " CTLp 'CPLp) 14.977 GSVp = {BPVp ' CCFD) 15.092 IVm = N'avg / NKF 0.9921 Tables 55 & 6B,API Standard 2540 1.0006 'Fm' factor from 11.2.1 {PB = 0) 0.00000613 0,9927 CCFm = (CTLm CPLm) 14.982 lSVm = (IVm 'CCFm) 0.9997 O How rate of 25.008 Pulses per Gallon

METER FACTOR K FACTOR

-

747 Gallons per Minute I

CPL 8 Normal Pressure of 110 psla Meter Provlng History lnltial MF 1 ?revlous 4 Current 5 Remarks &history Inltlal to Current MF

76.0 75.0 =

-

Composite M Factor 1.0007 Composite K Factor

= 1.0004 = 24.991

psig

s>>z> > >

Date Meter Factor GPM APlb Degrees F 08f20194 1.0002 770 44.2 74.5 11/zo/g4 0.9991 732 44.4 78.0 12/20/94 0,9997 747 44.0 76.6 Meter overhauled on October 20,1994 before the lnltisl proving Long-term change percent (%) since the initial proving

>>>>>

Short-term change percent ( O h ) since the last proving

tO.06

>>>>r

>>>r> >ssrr >>>ws

102 I la 104 -0.05

-0.05 Previous to Current MF Signed by:

Figure 7-Meter Proving Report With Pulse Interpolation

4.8.3.7 TROUBLE-SHOOTING To help operators evaluate a system more quickly, the experience of a number of prover operators has been compiled in Appendix B. Common problems are listed, as well as the usual causes and the typical methods of solving each. The guide contains tables which give the corrective action needed to rectify the fault once its cause has been ascertained.

a range of 0.5 percent may be required. Alternative methods are described in Appendix A. The evaluation of repeatability of the proving data is normally performed with raw meter pulses. If conditions cannot be held constant, it may be necessary to compare the range temperature compensated raw pulses or meter factors for each run. This is particularly true when proving LACT displacement meters equipped with mechanical temperature compensators where the temperature varies during the proving process. If the repeatability of the meter runs is unacceptable, it is recommended to implement another series of runs. If the repeatability of a second set is within the prescribed range, [his set of results may be used. If the repeatability remains unacceptable, it is necessary to stop proving and look for the cause of the problem. A common practice is to Iirnit the change in consecutive meter factors of proving periods to 33-25 percent or less. This is a measure of reproducibility and is determined as follows: Range of Reprodpcibility=

4.8.4.1 PRINCIPLE OF OPERATION Small volume provers have a volume between detectors that does not permit a minimum accumulation of 10,000 direct (unaltered) pulses from the meter. Small volume provers require meter pulse-interpolation techniques to increase the resolution (see API MPMS, Chapter 4.6). This high resolution pulse determination permits the volume between detector switches to be substantially less in a small volume prover than would be permitted in a conventional pipe prover. Qpical small volume provers are illustrated in Figures 9, 10, and 11. Additional information on small volume provers is contained in API MPMS,Chapter 4.3. Since the volume of a small volume prover is less than a conventional pipe prover, high-precision detectors are normally used with pulse-interpolation techniques. Double chronometry puke-interpolation is a method of counting a

New Meter Fnctor - Old Meter Fnctor 100 Old Meter Factor

Changes in the linearity of the historical meter factors over time is also a good check for prover functioning. Historical meter factor data should be maintained and is best assessed by keeping a control chart which is a graph of meter factor plotting against the dates of tests. A specimen control chart is shown in Figure 8. See also API MPMS, Chapter 13.2. 1.0050

Small Volume Provers

4.8.4

Individuals o t m s Upper tolerance limit (WL)

/

:M

1m0020

1%

I

1.0010

It

l.0000

a -

0.9990

m3

%

-C

--- -------------------

- - l l l l l _ _ _ - _ - _ _ + - - - - - -

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0-Q980 -

0.9970

-

0.9960

-

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-

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-

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_

-

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_

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-

-

Upper action limit (UAL) Upper warnlng limit (UTL)

Central line (CL)

-

_

-

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-

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-

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_

-

-

-

-

-

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_

-

-

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-

-

-

l

-

-

l

-

-

-

-

-

-

-

Meter Factor Sequence

Figure 8--Control Chart for Individual Meter Factors

Lower warning limit (LWL) Lower action limit (LAL)

Lower tolerance limit (LTL)

Section 8--Operation of Proving Systems

15

Sectlon 8--Operation of Proving Systems

17

4.8.4.2.1

Pulse lnterpolator~

Series of whole meter pulses and multiplying by the ratio of the time between the detector switches and tk time to accumulate the whole meter pulses. Pulse interpolators are electronic devices that allow a meter pulse at least One part in '0,000. They perform best with meters whose puIses are emitted uniformly. This method results in a calculation of meter pulses to a discrimination of at least 1 part in 10,000.

pulse internolators are electnvlic devices allow meter pulse resolution to at least one part in 10,000. They perform best with meters whose pulses are emitted uniformly. Pulse intevolation is described in detail in MPMS, Chapter 4, Section 6.

4.8.4.2 EQUIPMENT DESCRIPTION Small volume provers may be of any configuration 10 include bidirectional or unidirectional sphere or piston provers such as shown in Figure 12.

Small volume prover displacers may be either sphere or piston type. Piston displacers typically have dual hollow ring seals made of tcflon with stainless steel backup rings. Sphere displacers are typically nitrile, neoprene, or polyurethane and

4.8.4.2.2

Prover Displacers

Process fluid diverter valve (double block-and-bleedvalve)

C Flow

Note: UO = lnput/ou$ut.

Figure 12-Small Volume Prover Automatic Computing System

Section +Operation of Proving System

are fitted with inflation valves. See Figure 13 for a System Overview of a Unidirectional Sphere Displacer. 4.8.4.2.3

. ~etector Switches

The detectors along with the pulse interpolation electronics are the most critical elements of a small volume prover. Special designs may be used, for example optical, and most are relatively delicate. When the prover uses optical detector switches, they must be protected from any external light source during operation. Any outside source of light can have a detrimental effect on proving results. For other types of detector switches, see 4.8.3.2.1. 4.8.4.3 INSPECTION Seal integrity should be periodically verified since any leakage has a significant effect on proving results. To perform a seal integrity test, refer to the manufacturer's recommendations. 4.8.4.4 PREPARATION An example of a meter-proving form was shown in Figure 7. Other meter proving reports are shown in Figures 14 and 15. Other forms or documents may be required before proving is started. Refer to API MPMS, Chapter 12.2 for meter factor calculation requirements. 4.8.4.5 OPERATING PROCEDURES Operate the proving system until stable conditions of pressure, temperature, and flow rate exist. Once stability is achieved, proving operations may proceed as follows. Determine the actual flow rate on the first run of the displacer and make spot checks thereafter. Determine the meter temperature and pressure during each pass of the displacer. Record the average pressure and temperature of each valid run and average them all. Assuming the prover is equipped with both inlet and outlet thermometers and pressure gauges, determine the average prover temperature and pressure during each pass. The average prover tempeiature and pressure is recorded on a round trip basis in the case of a bidirectional prover. If the prover is equipped with only onc thermowell, the thermowell should be located at the prover outlet. Determine the prover temperature during each pass of the displacer and record the average during each pass of a bidirectional prover. In the case of a bidirectional prover, record the reading of the prover counter at the end of each round trip of the displacer. For a unidirectional prover, record the reading of the prover counter at the end of each pass of the displacer. Repeat the proving operation until the required minimum number d proving runs (per agreement between parties) are attained. As a measure of repeatability, the range of the proving set is determined as follows: ,' Range of Repeatability =

Maximum Value - Minimum Value x 100 Minimum Vdue

19

Assess the repeatability of the set of results, and if necessary carry out additional runs in an attempt to gain the required repeatability. If suitable repeatability is not obtained, discontinue the proving operation and look for the cause of the trouble listed in Appendix B. 4.8.4.6 ASSESSMENT OF RESULTS For common practices refer to Section 4.8.3.5. Flowme-. ters that have a non-uniform pulse output such as displacement meters with mechanical gear-driven pulsers may require averaging groups of prover passes and comparing the repeatability between the group averages. Refer to API MPMS, Chapter 4, Section 6, and to Appendix A. 4.8.4.7 TROUBLE-SHOOTING To help operators find faults in a system more quickly, the experience of a number of prover operators has been compiled in Appendix B. Common problems are listed, as well as the usual causes and the typical methods of solving each. Finally, the tables in the guide gives the corrective action needed to rectify the fault once its cause has been ascertained. The prover manufacturer's trouble-shooting guide should be referred to for any problems that may relate to the specific make or prover being used.

4.8.5

Tank Provers

4.8.5.1 PRINCIPLES OF OPERATION A tank prover is a calibrated vessel used to measure the volume of Bquid passed through a meter. The known volume of the tank prover is compared to the meter's indicated volume to determine the meter factor or meter accuracy factor. Tank proven are not recommended for viscous fluids. It is suggested that a displacement-type master meter and a pipe prover be used with viscous products. 4.8.5.2 EQUIPMENT DESCRIPTION A tank prover is an open or closed volumetric measure that generally has a graduated top neck and may have a grad-

uated bottom neck. The volume is established between a shutoff valve or bottom-neck graduation and an upper-neck graduation. The two basic types of tank provers are the open type (atmospheric pressure), and the closed type (pressure containing). Both of these come in a variety of configurations to meet the needs of the service required. Refer to Figures 16 and 17 which illustrate the types referred to previously. 4.8.5.3 INSPECTION Inspect the prover tank for any dents that are not recorded on the calibration certificate,any foreign objects or clingage inside the tank, or failure of an internal coating that would

Sectlon &Operation of Proving Syst0n'Is

LOCATWN

TENDER

AMBIENT TEMP.

DATE

#Fl

LiQUID

21

REPORT NO. i

METER DATA

SEML NO

METER NO.

PULSEW

TEMP. COMPENSATED

SIZE

MODEL

FACTOR

DATE

MANUFACTURER

PRWIOUS REPORT NO. R O W RATE

FLOW RATE

NON RESET COUNTER

M~T. MASTER METER DATA t

CLOSllW READING. bbldoslp

2

OPENING READING, w g a b

3

INDICATE0VOLUME (UNE 1

4

TEMPEMTURE AT METER, 'F

5

PRESSURE AT METER, pig

B

MASTER MEIER FACTOR

7

CY

a

c,

9

CCF (LINE 6 x LINE 7 x LINE 0)

10

SIZE

MAKE:

-

M

O

D

E

L SERIAL NO.

-

LIME 2)

CORRECTED PROVER VOLVME (LINE L x

LINE 9)

P ROE0 MElER M T A ti

CLOGINQ METER RUOIHD, Wl#p&

92

OPENING METER AMMNO. W 0 4 h

13

INDICATEOVOLUME 6fNE 11

14

TEMPWTURE AT MEIER. ' F

11

PRE8SUdE AT M W R WlQ

10

c,

- LINE 12)

I I

17

c,

10

CCF &IN€ 16 x UNE 17)

10

CORRECTED METER VOLUME &tNf 13

?O

METER FACTOR (LINE I 0 + UNE 19)

X

U E 18)

tAVEFt4GE VALUE)

PRESSURE APPLICATION

- - - DATE

SIGNATURE

COMPANY REPREQENTAtlYS

Figure 14-Meter

Proving Report for Master Meter Method

C

LOCATION

TENDER

DAE

'API

LIQUID

AMBIENT TEMP.

REPORT NO.

PREVIOUS REPORT NO.

PROVER DATA NOMINAL VOLUME AT W F AND 'W pelp.

SERIAL NO.

FLOW RATE

13-1

METER DATA METER NO.

SERIAL NO.

TEMP. COMPENSATED

0 YES

SIZE

MANUFACTURER

MODEL

0 NO REMARKS, REPAIRS, ADJUSTMENTS. EfC.

FLOW RITE

NMJ RESET COUNTER WVhr -

---

RUN NO. I

PROVER T M K W U M E U T A 1

DEUVERY TO TANK, QaMbla

2

TANK TEMPERATURE (AVERAQE) 'F

'a

c.

4

Cd

6

COMBINED CORRECTION FACTOR (LINE 9

6

CORRECTED PROVER VOLUME CINE 1 x UNE 4

%

RUN NO. Z

RUN NO. 3

LINE 4)

PRWEO MEIER DATA 7

FINAL MEIEA REAt)lHQ

8

INITIAL METER READING

Q

INOICATED VOLUME BY METER. bM6 [UNE 7

- LINE 8)

10

INDICATED VOLUME BY METEA. unlr (LINE 7

-

I1

TEMPERATURE AT METER, T

12

PRESSURE AT METER, prlp

13

CdUSE 1.mIF TEMP. dOMPEN8ATED

14

%

16

CCP (LINE 13 x W E 14)

18

CORRECTED METER VOLUME fL1NE to

17

METER FACTOU (UNE 6 + LINE 16)

X

LlNE a) OR (42 x LlNE 9)

LINE 13)

- - - - - -

DATE

BIGMATURE

Figure 1+Meter

COMPANY REPRESENTATIVE

Proving Report for Tank Prover Method

RUN NO. 4

Section 8--Operation of Proving SyslemS

Sealing wire and seal Gauge glass and scale

--,Splash

23

dome (optional) 0.5percent of prover volume Calibrated volume 0.5 percent of prover volume

Overlapping gauge glasses

Temperalure sensor

Swirl plate (optional)

Bottom inlet (optional) Bottom valve must be In vertlcal line

Drain for calibration purposes and for zeroing liquid level

Figure 16--Open Stationary Prover Tank (Drain-to-Zero or Bottom Gauge-Glass Type)

,-Relief - valve Spray llne and nozzle {optional) ---,

Vapor recovery system connection (optional)

Pressure gauge must be above 0.5 percent prover volume

Seallng wire and seal Gauge glass Gauge scale

Calibrated volume 0.5 percent prover volume

Temperature sensor Temperature sensor Overlapping gauge glasses Swirl plate (optional) Cone bottom, dlsh bottom (0ptIOfIal) Flanged for cleanout (opttonal) 0.5 percent of tank bottom


L hhor discharge Figure 17-Closed Stationary Tank Prover

glass

have an effect on the calibrated~volumeof the prover tank. Verify that the gauge scales are sealed. Also check for a current and valid calibration certificate. 4.8.5.4 PREPARATION Examples of meter proving forms were shown earlier in Figures 6 and 7. Other forms or documents may be required before proving is started. Refer to API MPMS, Chapter 12.2 for meter factor calculation requirements. Check that all connections are properly made and isolat ion/diverter valves are properly aligned. Verify the integrity of all vents, drains, reliefs, and double block-and-bleed valves between the meter and the prover. Proceed with the preparations as follows: ,

a. The initial step prior to the first proof run is to wet down the prover tank. Fill the tank with metered liquid. Check the level indicators on the tank. Then empty the tank. b. If the tank is equipped with a lower-gauge glass, close the main drain valve just prior to the liquid level reaching the zero mark. Allow a minimum of 30 seconds drain down time (or that which is staled on the calibration report); then using the small drain valve, drain the liquid to the zero mark. Whatever drain time is allowed after closing the main drain valve and drawing the liquid down to zero must be used on all subsequent proof runs. c. If the tank is not equipped with a lower-gauge glass, leave the drain valve open until continuous flow ceases and dripping starts. The drip should be allowed to continue for a minimum of 30 seconds (or that which is stated on the calibration report) before closing the drain valve. Whatever drip time allowed between flow cessation and closing the drain valve must be used on all subsequent proof runs. d. When reading gauge glasses, read the bottom of the meniscus for transparent liquids and the top of the meniscus for opaque liquids. e. If the system has vapor recovery, the vapor recovery should have makeup gas or must be disconnected prior to emptying the prover so that air can enter the prover and prevent a vacuum that could damage the prover. 4.8.5.5 OPERATING PROCEDURES There are two unique features of an open tank prover. The first is that vapor is allowed to escape (evaporale) fron! within the tank as the tank is filled. If a vapor recovery system is used during normal metering operations, consideration should be given to operating the vapor recovery system during the meter proving. The second unique feature is that the meter is operated from as stop-run-stoucondition. Thus the meter experiences a static-to:dynnmic'and back-to-static cycle of operation. This method of operation depicts normal operating conditions of the proverlmeter system. It is important to use consistent tank prover operating

.

techniques without interruption to obtain satisfactory repeatability between consecutive proof runs. Flow rate through the meter during the prpof runs should replicate the operating conditions during normal use. a. using a tank prover report or worksheet record the appropriate meter, tank, and flow data as indicated in the meter factor calculation section of API MPMS,Chapter 12.2. b. Record the meter register, or zero the proving counter if one is being used. Record the reading of the prover tank's bottom gauge glass, if so equipped. These become the opening readings far this proving run. c. Start the flow through the meter into the tank. d. While the tank is filling, record the average meter temperature and verify that the meter is operating at the desired proving rate. e. Stop the meter flow when the liquid level is within the upper gauge scale range. f. Record the prover tank temperature. If the tank has mare than one thermometer, the recorded temperature is the average of all thermometer readings. g. Record the meter register or the proving counter reading and the prover tank's upper gauge glass reading. These are the closing readings for this proving run. h. Calculate the meter factor for this run as outlined in API MPMS, Chapter 12.2. This completes one proving run. The next proving run is initiated by draining down and zeroing the tank as just described, and then starting over with the steps described previously. i. At least two consecutive proving runs in which the meter factors agree within a 0.05 percent range are required. The average of these meter factors is the final meter factor. If an adjustment to the meter factor is made mechanically, that is, with a calibrator or mathematically, additional runs typically are made to confirm that the meter factor is correct. j. Upon conclusion of the proving operation, if a prover tank is a portable unit, isolate the prover from the flow stream; drain down; remove all connections made; and prepare the tank for removal from the site. If the tank is permanently located, isolate the prover from the flow stream; drain down; and place the tank in a protected idle mode. 4.8.5.6 ASSESSMENT OF RESULTS Common practice is to require a minimum of two consecutive runs that agree within a range of 0.05 percent. If the repeatability of the meter factor is unacceptable, it may be necessary to carry out additional proving runs. If the repeatabilily is within the prescribed range, these results may be used. But if the repeatability remains unacceptable, it is necessary to stop proving and look for the cause of the problem. 4.8.5.7 TROUBLE-SHOOTING To help operators evaluate a system more quickly, the experience of a number of prover operators has been

Section 8--Operation

of Provlng Systems

compiled in Appendix B. Common problems are listed, as well as the usual causes and the typical methods of solving each. The table also gives the corrective action needed.

4.8.6

start-and-stop method of proving may be used: With the standing start-and-stopmethod, the meter registration is read before end after the proving run with flow stopped to dexermine indicated volume. With the running start-and-stop method, the flow is uninterrupted, and the proving counters must be simultaneouslystarted and stopped.

Master Meter Provers

A proving operation is considered a direct proving when a meter is proved against a prover. Indirect proving is when a meter is proved by a master meter that has been proved by the direct method. Master meter proving is used when proving by the direct method cannot be accomplished because of logistics, time, space, and cost considerations. Satisfactory results can be achieved by using the master meter method; however, the master-meter method introduces additional uncertainties for the meter being proved. When practical, uncertainties may be reduced by proving the master meter under similar line-meter operating conditions prior to, during, or after proving the line meter.

~ ti

I

4.8.6.1 PRINClPLE OF OPERATION A master meter is a meter selected, weli maintained, and operated as a reference for the proving of another meter. The master meter factors shouid be linear over the expected range of operating conditions and shall have a history of consistent performance. The calibration of the master meter shall be performed under conditions similar to those expected during the line meter proving. A curve of master meter factors should be established over the range of flow rates to be encountered while proving a line meter. The meter factor applied to the master meter shall be the average of proof runs on a similar liquid and within 10 percent of the flow rates expected during the proving of the line meter. Either the standing start-and-stop or the running

25

4.8.6.2 EQUIPMENT DESCRIPTION The master meter output/registrationmust not be mechanically temperature compensated. The master meter must not have a mechanical adjustor or calibrator between the primary element and the output/registration. When proving a meter with a master meter, the same meter output and instrumentation accessories must be connected to the master meter as were used when the master meter was proved to establish its meter factor. Qpically, master meters are displacement or turbine meters because of the repeatability requirements of proving (see API MPMS, Chapter 4.5). .

.

4.8.6.3 ~NSPECT~ON Prior to the meter-proving operation the master meter prover and line meter to be proved shall be inspected to ensure proper operation. This inspection shall include, but not be limited to, the following steps: a. Ensure that all liquid flowing through the line meter to be proved, and only that liquid, passes through the master meter with no leakage or diversion between meters. Refer to Figure 18 for an illustration of a master meternine meter manifold, which permits the removal of either meter for calibration or servicing. Double block-and-bleed valves ensure that no leakage or diversion can occur either during proving or linemeter operation.

Note: 1,2.3 = double-blaek-and-bleed; 4,5 = shut-off valve.

Figure 18-Typical Master Meter Manifold

b. Verify that all temperature, pressure, and density measurement devices to be used during the proving operation are properly installed, recently calibrated or verified, and operating within acceptable tolerances as stated in APE MPMS, Chapters 7 and 12.2. c. All electronic instrumentation such as counters, switches, and interconnecting wiring shall be inspected for proper installation and operation. Care should be taken to ensure that all electrical pulse transmission cable is properly shielded and grounded. d. It is essential that a run of sufficient quantity be made to verify the ratio between the pulse transmitter and the meter register. See APT MPMS, Chapter 4.5.

temperature and pressure are recorded for both meters during the proving run. Flow rate through the meters during the proving operation should be within 10 percent of the rate,at which the line meter will operate. The flow rate must remain relatively stable for all proving runs entered in the meter factor calculation. c. After sufficient volume has passed through the meters, the counters are simultaneously gated off. The indicated counter readings for the run are recorded. This completes one run. d. There are various ways of assessing whether the repeatability of a set of readings is acceptable. The repeatability should not exceed the limits agreed upon by all parties. In some circumstances, statutory authorities or government departments will set the limits for the range of a set of results. One method of conducting a proving is to make five "within a consecutive meter proof runs within 0.05 rafige of 0.05 percent*'is defined as a value that does not exceed 0.05 when applying the following formula:

PREPARATION Examples of meter-proving forms were shown earlier in Figures 6 and 7. Master meter calibration reports and curves, and orher forms or documents may be required before proving is started. Refer to APT MPMS,Chapter 12.2 for meier factor calculation requirements. . The master meter should be jnstalled as close as possibIe to the line meter to minimize temperature and pressure differences between the meters. The master meter normally is installed downstream of the line meter. The following steps should be taken: a. If the master meter has an electrical output, care should be taken to ensure all electrical equipment is properly grounded to prevent elTors from electrical noise. b. If the mastet meter is permanently piped in a manifold with the line meier to be proved, the isolation valves should be opened and the flow directed through both meters. c. Before the meter proving is made, the two meters shall be operated at the desired flow rate for a period of time sufficient to purge the system of vapor and to achieve steady temperature, pressure, and flow rate. 4.8.6.4

OPERATING PROCEDURES h c h proving run shall be of sufficientvolume to discriminate volume units to 1 part in 10,000. In the case of loading rack meters, each proving run sbwld depict the start up, shutdown, and interim flow patterns of a normal loading. If electronic counters and high resolution meter transmitters are used to register metered volume, at least 10,000 pulses must be collected during the proving run. Once the proving operation is started, it should be carried to conclusion in a continuous process, without interruption or delay. The following steps should be taken: a. Using a work sheet or master meter proving report (see Figure 6), record the appropriate meter and flow data as indicated in the factor calculations section of API MPMS, Chapter 12.2.

-

Maximum Value Minimum Value x 100 Minimum Value e. Checks should be made during the proving to ensure all equipment is functioning properly and all test parameters are remaining within their constraints. f. Meter factor calculations shall be made as detailed in API MPMS,Chapter 12.2. An example "Meter Proving Report for the Master Meter Method" was shown in Figure 14. g. After completion of the proving operation, the master meter should be isolated from the flow stream if the meter is permanently installed, or disconnected if the,meter is portable. A master meter should not be on stream any longer than necessary for the proving operation. This precaution is to limit meter wear and resulting factor shift. h. Thermometers, pressure gauges, counters, and any other proving equipment that is not a permanent part of the manifolding should be removed and stored until the next proving.

4.8.6.5

b. With flow through the meters, a proving run is initiated by simultaneously gating both meter counters on. Meter

'

4.8.6.6 ASSESSMENT OF RESULTS A common practice is to require a minimum of two consecutive runs that agree within a range of 0.05 percent. If the repeatability of the meter factor is unacceptable, it may be necessary to carry out additional proving runs. If the repeatability is within the prescribed range, these results may be used. But if the repeatability remains unacceptable, it is necessary to stop proving and look for the cause of the problem.

4.8.6.7 TROUBLE-SHOOTING To help operators evaluate a system more quickly, the experience of a number of prover operators has been compiled in Appendix B. Common problems are listed, as well as the usual causes and the typical methods of solving each. The tables give the corrective action needed.

APPENDIX A-ESTIMATING

RANDOM UNCERTAINTY

Chapter 13.1 of API MPMS states that the 95-percent level of statistical confidence is recommended for evaluating uncertainties associated with commercial applications of petroleum measurement. It is also stated that in certain limited circumstances, a different degree of (statistical) confidence may be required. The random uncertainty of the average value of a set of meter proving runs can be estimated in accordance with Chapter 13.1 at the 95-percent confidence level as follows:

Where: a(MF) = random uncertainty of the average of a set of meter proving runs. r(95, n-1) = student "t" distribution factor for 95 percent confidence level and n-1 degrees of freedom (see Table 2 ofAPI 13.1). w,, = range of values (high minus low) in the meter proving set. n = number of meter proving runs. D(,, = conversion factor for estimating standard deviation for n data points (see Table 1of API 13.1). For the common practice of five proving ,runs that agree within a range of 0.0005, the random uncertainty of the average of this set can be estimated as follows:

For meter proving sets of 3 to 25 proving runs, a variable range limit can be calc~llated that maintains the same random-uncertaintyin the average value of 5 runs that agree within a range of 0.0005. These variable range limits are as shown in Tables A-1 and A-2.

Table A-1-Variable Range Criteria for ~0.00027Random Uncertainty in Average Meter Factor Numkr of Proving Rons, n

3 4 5 6 7 8 9 I0 11

12 13

Moving (Variable) Range Limit

0.0002 0.0003 0.0005 0.0006 0.0008 0.0009 0.0010 0.0012 0.0013 0.0014 0.0015

15

0.0016 0.0017

16 17 18 19 20

0.0018 0.0019 0.0020 0.0021 0.0022

14

For low volume locations such as small LACT units where five runs within a range of 0.0005 may not be practical or cost effective, three runs within a range of 0.0005 may be practiced. The random uncertainty of the average of three proving runs that agree within a range of 0.0005 is as follows:

For meter proving sets of three to fifteen proving runs, a variable range limit can be calculated that mainlains the same random uncertainty in the average of three runs that agree within a range of 0.0005. These variable range limits are as shown in Table A-2. Table A-2-Variable Range Criteria for k0.00073 Random Uncertainty in Average Meter Factor Number of Pmving Runs, n

Moving (Variable) Range Limit

The scatter in erratic meter proving data can be normalized by averaging the results of several meter proving runs and comparing the averages of these small sets for agreement with deviation limits. In these instances, at least three consecutiveproving runs are recommended for each set. The averages of two Or more of these sets can be compared for agree ment of meter-proving deviation limits.

APPENDIX B-TROUBLE-SHOOTING

GUIDE

31

Section 8--0oeratlon of Proving Syst0tm

Table B-I- rouble-shooting Guide for Pipe Prover Operators-Part 1 Sy~rlptom

Lmtion and Possible Cause

Tesrfinspection

Corrective Action

-

I. Poor Repeatability

1. Entrapped aidvapor

Open vent with sphere traveling, check for airlvapor. (This nay not give positive response because of possible airlgas pockets.)

a. Check for air in fluid to prover, vent ail high points, and mn prover sevcd times and vent. b. lncrease meter back pressure.

2. Flashing in 4-way

Measure pressure at the valve at rnaxinlum flow rate and see if in accordance with specification,

Increase p~ssureby using back pressure valve.

3. Isolating valve leakage

Check double block-and-bleed for leakage.

a. Seat valve more firmly by increasing actuator or hnndwheel toque. b. Repair valve. c. Cycle valve to remove debris.

4. Leakage in 4-way diverter valve or sphere-handling valve

Check double block-and-bleed for leakage.

a. Seat vnlve more firmly by increasing actuator or handwheel torque. b. ' ~ e ~ avalve. ir c. Cycle valve to remove debris.

5. Cycle time of 4-way diverter valve or spherehanding valve _ -

Check double block-and-bleed closur~before sphere mches the first .detector.

lncrease speed of operation of the valve or decrease flow rate through the prover.

Check detectors against . external signal source. Use ohm meters to check eohtinuity of switch closure. Check for corrosion on terminals. lnspcxt mechanical parts of detectors.

Calibration may be . required if detector(6) are adjusted or changed. Clean terminals.

7. Temperature Variation

Verify letnpemlure measutelnenls.

Stabilize temperature at meter and prover.

B. Sphere

Remove, inspect for cuds, blister, abrasions andlor deterioration. Check roundness and sizing.

Inflate or deflate if necessary; replace if damaged.

9. Piston

Apply bleed tcst to check for leakage and inspect seals for cuts, abrasions and deterioration.

Replace seals if necessary.

10.Meter bearing wear

Disniantle and inspect. Analyze pulse train with oscill~cope.

Repairheplace as requid.

11. Accessory gear wenr

Analyze pulse train with oscilloscope.

Rcpairiclcan as needed.

12.Turbine meter straightening section

Remove and inspect for d a m e and foreign matdal.

Repnirlclean as required.

divmer valve or spl~ere-handling valve

Clean and repair as needed

,

Table B - l - T r ~ u b l ~ - ~ Guide h ~ ~ for t ~ Pipe ~ ~ Prover Operators-Part 1 (continued) Sy~nprom

2. Poor Linearity

Locntion and Possible Cause

Tesl/lnspection

13.Random elecirical intcrference

Identify sources. Analyze pulse train with oscilloscope.

Reroute cable. Use shielded cable. Check cable ground connection.

14.Cavitation in meter

a) Draw sample and observe for stability at

Incmsc pressure.

15. Pulse generator faully

At constani flow rate check that pulse frequency is constant. Pulse integrity check. Analyze pulse train with oscilloscope.

Repairlreplaceas required.

Andyze pulse train with oscilloscope.Adjust Up/ down, evaluate MF changes.

Repair/replace as required.

Evalunte MF changes. See 5 above.

Repnirtreplace as required. See 5 above.

Verify temperature measurements.

Stabilize temperature at meter and prover.

3. Baring wear

Dismantle and inspect.

Repairlreplace os required.

4. Damnged DM rotor

Dismantle nnd inspect. Analyze pulse train with oscilloscope.

Repairlreplace os required.

Hend check or successive runs.

Re-alignireplace as required.

1. Cycle tirne of 4-

way divelter valve or sphere handling valve. 2. Temperature

varialion.

Darnaged TM 5. Dmg or wear, gem,

couplers, etc.

Corrective Action

atmospheric pressure. b) If unstable, rntxyhit equilibrium vapor pressure of liquid. c) Measure pressure downstream of the meter. d) Evaluate back pmsuE.

Section 8--Operalion of Provlng Systems

33

Table B-2-Trouble-Shooting Guide for Pipe Prover Operators-Part 2 Syn~ptom

Location and Possible Cause

Comtive Action

MiscelIanmus problems encountered when proving. a. Less meter registration factor increase

Meter

Rebuild meter. Replace bearings.

Less meter registration factor increase

More or less, meter registration factor increaseidw~ase

Meter cnlibrator

Lubricete or reptaw.

Less meter registmtion foctor increase

Prover temperatute loo low

Stabilizetemperature.

Prover temperrttute too high reading

check thermometer.

More meter registration factor decrease

Fluid viscosity increase

Stabilize viscosity.

Less meter regismtion

Build-up on pipe wall

b. More meter ~egistmtion factor decrease

factor decrease

Investigate reason for

. build-uplclean prover.

Severe change in MF

Malfunction in ATC assetnbly

HoWcold tat.

Severe decrease in MF

ColIaspsed bulb and bellows

Replace B & B.

Severe increase in MF

Malfunction of calibrator Inner-mechnnical problem

Repairlreplace.

Severe dtxrease in MF

Displocer undersized

Table B-3-Trouble-Shooting Symplo~n

Locetion and Possible Cause

Guide for Small Volume Prover Operators Testnnspection

Corrective Action

PROVER I. Poor repeatability

1. Entrapped airfgas in prover

Open prover vents lo see if nirlgas is present.

Open vents and cause displncer to travel until aulgas is removed.

2. Lenknge by isolation valves

Chcck double block-andbleed.

a. Open and reclose valve. b. Seat valve more finnly by increasing torque. c. Replace seats.

3. Leakage at bypass or diverter valve

Check double blwk-and-

a. Seat vdw more firmly by applying more pressure. b. Replace seals

4. Leaknge by displacer

Check for leak by method

bleed.

Repjace seal(s).

recornmended by manufacturer. Measure pressure loss through tbe melerfpmving system to see if within specification.

a. Reduce flow rate. b. Increase back-pressure on proving system.

Check delectors for proper operation.

If faulty replace detectors. Shield optical swilches from ambient light.

7. Electronics, pulse

check per instructions in API MPMS Chapter 4, Section 6.

Adjust/repair/replace as required.

8. Improper plenum pressure

Verify plenum pressure per manufacturer's specification.

Adjust as required.

1. Internal wear

Dis~nantteand inspect.

Repairlreplace as required.

2. Random electtical interference

Trnce and eliminate interferenca

Remove or replace pmblem.

3. Cavitation in meter

Measure pressure a few pipe diameters downstream of [he meter at a maximum low rate and see if within specifications.

l n m e pressure by using back pressure.

4. Pulse generator, faujt

At unifonn flow rate check that pulse frequency is constant.

a. Check gear train. b. Repairlreplace as required.

5. Turbiae meter s tmighlening section

Remove and inspect for damage or blockage by f o r e i s abject.

Repair or replace as required. Clean out forcign object.

1. Leakage thmugh bypass or diverter valve

Same as 3 above.

Same as 3 above.

2. Temperature variation

Measure temperature accurately.

Correct for tempetaturn effects at meter and prover.

3. Bearing wear

Dismantle and inspect.

Replacehepair ns required.

4. Cavitation

Check prercun loss through proving system

Apply back pressure and or reduce flowme.

5. Cavitation in proving system

METER

PROVER 2. Poor lincarily

35

Section 8--Operation of Ptovlng Systems

Table B-3-Trouble-Shooting Guide for Small Volume Prover Operators (continued) Syrnptoln

Location and Possible Cause

Tesl/lnspection

Corrective Action

PROVER (continued) At co~~stant flowrate check

5. Pulse generator,

that pulse frequency is constant.

fnult

6. Damaged rotor

Table B-4-Trouble-Shooting Symptom 1. Poor repeatability

Dismantte and inspect.

a. Check gear tmin. b. Repairireplnce as required. RepairhpIace as required.

Guide for Master-Meter Prover Operators

Location and Possible Cause MASTER-METER PROVER 1. Cavitation

Testllnspection

Corrective Action

Apply excessive back pressure for a brief period.

Adjust back pressure 10 appropriate level.

2. Pulse generntor, f~ult

At u~iiformtlowrate check that pulse frequency is conscant.

Repair or replace as required.

3. Electrical noise

Check for random electrical i~iterfemnce.

Tmce and eliminate inlerference.

4. Entrapped airlgas

andlor cauitalion

Open vents slowiy, then close.

Locate airlgas source nnd eliminate.

5. Worn meter parts

Dismantleand inspeet.

Reassemble with new parts as reqlnir~ldand repmve master-meter.

6. Leaking valves

Check for full openlclose posilion and leak tightness;


FIELD-METER 1. Cavitation

Sanie PS 1 above.

Same as 1 above.

2. Pulse generator, fault 3. Temperalure variation

Same as 2 above.

Same as 2 above.

Measure temperature orten and accurately.

Correct for temperature effects on field-meter and mnasler-meter.

4. Worn meter parts

Same as 5 above.

Same as 5 above.

5. Turbine meter straightening section

Remove and inspect for damage.


6. Pressure variation

Check gauges.

Look for cavitation. Check back pressure.

7. Temperature variation

Check temperature senson.

Maintain stable flow condition.

Table B-5-Trouble-shooting Guide for Tank Prover Operators Symptom

I. Poor repeatability

Localion and Possible Cause PROVER 1. Inconsistent drain down time.

Test/lnspeclion

Measure drain down time.

Corrective Action .

Follow drain down time on calibration certificate.

2. Drnin valve leaks

Fill prover to capacity read upper scale and let stand for 15 minutes, then then read scale again lo see if any leakage.

Repair valve w/o removing. Replace valve and recalibrate.

3. Unstable prover

Try rocking by applying a modest force.

Level prover and make secure.

4. Unsatisfactory fill

Fill pipe must nlways drain completely or always retain the same amount of nuid befoce and after each run.

a Secure fill pipe position b.Provide vent in fill pipe.

Monitor Bowrate.

a. Secure flowrate

condition

5. Unstable fl owmte

control valve. b.Stabilize back pressure. Lower flowrate.

Change fill procedure.

1. Bearing wear

Disrnnntle and inspect.

Replacdnpnir as required.

2. Counter does not

Remove counter and hold input shaft firmly while resetting, to see if it resets to zero each time.

a Repairheplace as required. b. Check gear backlash in meter head.

3. Meter cavitation

Apply excessive back pressure for a brief time.

Adjust bnck-pressure according to requirements.

4. Meter calibrator

Isolate and test teinperature mechanism.

Repairhplace as required.

METER

. repeat

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