Selection of Control Valves

COMPLETE REVISION March 2003

Process Industry Practices Process Control

PIP PCCCV001 Selection of Control Valves

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES In an effort to minimize the cost of process industry facilities, this Practice has been prepared from the technical requirements in the existing standards of major industrial users, contractors, or standards organizations. By harmonizing these technical requirements into a single set of Practices, administrative, application, and engineering costs to both the purchaser and the manufacturer should be reduced. While this Practice is expected to incorporate the majority of requirements of most users, individual applications may involve requirements that will be appended to and take precedence over this Practice. Determinations concerning fitness for purpose and particular matters or application of the Practice to particular project or engineering situations should not be made solely on information contained in these materials. The use of trade names from time to time should not be viewed as an expression of preference but rather recognized as normal usage in the trade. Other brands having the same specifications are equally correct and may be substituted for those named. All Practices or guidelines are intended to be consistent with applicable laws and regulations including OSHA requirements. To the extent these Practices or guidelines should conflict with OSHA or other applicable laws or regulations, such laws or regulations must be followed. Consult an appropriate professional before applying or acting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Team and will be reviewed every 5 years. This Practice will be revised, reaffirmed, or withdrawn. Information on whether this Practice has been revised may be found at www.pip.org.

© Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3925 West Braker Lane (R4500), Austin, Texas 78759. PIP member companies and subscribers may copy this Practice for their internal use. Changes, overlays, addenda, or modifications of any kind are not permitted within any PIP Practice without the express written authorization of PIP.

PIP will not consider requests for interpretations (inquiries) for this Practice. PRINTING HISTORY October 1995 Issued March 2003 Complete Revision Not printed with State funds

COMPLETE REVISION March 2003

Process Industry Practices Process Control

PIP PCCCV001 Selection of Control Valves Table of Contents 1. Introduction................................. 2 1.1 Purpose ............................................. 2 1.2 Scope................................................. 2

2. References .................................. 2

9.2 Pressure-Drop Determination for Nonpumped Systems ...................... 14 9.3 Pressure-Drop Determination for Pumped Systems............................. 15 9.4 Secondary Control Valves ............... 15 9.5 Operating Range ............................. 15

2.1 Process Industry Practices ................ 2 2.2 Industry Codes and Standards .......... 2 2.3 Government Regulations ................... 3

10. Noise Considerations .............. 15

3. Definitions ................................... 4

11. Actuator .................................... 17

4. Body - General ............................ 5 5. Globe Valves ............................... 7 6. Rotary Valves.............................. 9 7. Trim............................................ 10 8. Bonnet ....................................... 11 8.1 8.2 8.3 8.4

General ............................................ 11 Gaskets............................................ 12 Packing ............................................ 12 Bolting .............................................. 13

11.1 11.2 11.3 11.4

General ............................................ 17 Diaphragm Actuator......................... 19 Piston and Vane Actuators .............. 20 Volume Tank ................................... 20

12. Positioner/Current-to-Pneumatic Transducer (I/P)........................ 21 13. Accessories .............................. 21 13.1 Handwheel Operator........................ 21 13.2 Limit Switches and Solenoid Valves 22

14. Marking, Identification, and Nameplate ................................. 23

9. Sizing Considerations.............. 14 9.1 General ............................................ 14

Process Industry Practices

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PIP PCCCV001 Selection of Control Valves

1.

COMPLETE REVISION March 2003

Introduction 1.1

Purpose This Practice provides designers and vendors the requirements for the selection and sizing of control valves.

1.2

Scope This Practice specifies requirements for selection and sizing of pneumatically actuated control valves, including requirements for body, bonnet, trim, actuator, accessories, and noise considerations. This Practice, along with a completed PIP PCSCV001, PIP PCECV001, and the individual control valve data sheets (i.e., ISA20 or equivalent), defines the minimum requirements for selection, materials, construction, and installation of control valves. This Practice does not cover requirements for motor-operated valves, on-off valves intended for emergency isolation, or valves with hydraulic actuators. Comment: The intention is that the owner will fill out the PIP PCSCV001 control valve specification sheet to define company and location generic requirements for control valves. This document is a complete revision of PIP PCCCV001, and therefore, revision markings are not provided.

2.

References Applicable requirements in the latest edition (or the edition indicated) of the following standards shall be considered an integral part of this Practice. Short titles will be used herein when appropriate. The owner shall be informed if portions of this Practice do not comply with referenced codes, standards, and regulations. 2.1

Process Industry Practices (PIP) – PIP PCECV001 - Guidelines for Application of Control Valves – PIP PCSCV001 - Specification of Control Valves – PIP PCSIP001 - Instrument Piping and Tubing Systems Specifications

2.2

Industry Codes and Standards • American Society for Mechanical Engineers (ASME) – Boiler and Pressure Vessel Code, Section VIII, Division 1 – ASME B16.5 - Pipe Flanges and Flanged Fittings – ASME B31.3 - Process Piping • Fluid Controls Institute Inc. (FCI) – ANSI/FCI 70-2- Control Valve Seat Leakage

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Process Industry Practices

COMPLETE REVISION March 2003

PIP PCCCV001 Selection of Control Valves

• The Instrumentation, Systems, and Automation Society (ISA) – ISA20 - Specification Forms for Process Measurement and Control Instruments, Primary Elements, and Control Valves – ISA75.03 - Face-to-Face Dimensions for Integral Flanged Globe-Style Control Valve Bodies (ANSI Classes 125, 150, 250, 300, and 600) – ANSI/ISA75.04 - Face-to-Face Dimensions for Flangeless Control Valves (ANSI Classes 150, 300, and 600) – ANSI/ISA75.05.01 - Control Valve Terminology – ANSI/ISA 75.08 - Installed Face-to-Face Dimensions for Flanged Clamp or Pinch Valves – ISA 75.08.04 - Face-to-Face Dimensions for Buttweld-End Globe-Style Control Valves (Class 4500) – ISA 75.08.07 - Face-to-Face Dimensions for Separable Flanged Globe-Style Control Valves (ANSI Classes 150, 300, and 600) – ANSI/ISA 75.15 - Face-to-Face Dimensions for Buttweld-End Globe-Style Control Valves (ANSI Classes 150, 300, 600, 900, 1500, and 2500) – ANSI/ISA 75.16 - Face-to-Face Dimensions for Flanged Globe-Style Control Valve Bodies (ANSI Classes 900, 1500, and 2500) – ISA 75.17 - Control Valve Aerodynamic Noise Prediction – ANSI/ISA 75.22 - Face-to-Centerline Dimensions for Flanged Globe-Style Angle Control Valve Bodies (ANSI Classes 150, 300, and 600) • International Electrotechnical Commission (IEC) – IEC 60534-8-3 - Industrial-Process Control Valves, Part 8, Noise Considerations, Section 8: Control Valve Aerodynamic Noise Prediction Method – IEC 60534-8-4 - Industrial Process Control Valves, Part 8, Noise Considerations, Section 8: Prediction of Noise Generated by Hydrodynamic Flow 2.3

Government Regulations • U. S. Environmental Protection Agency (EPA) Code of Federal Regulations (CFR) – EPA 40 CFR, Part 60, Appendix A, Attachment 1, Reference Method 21 Determination of Volatile Organic Compound Leaks – EPA 40 CFR, Part 61 - Monitoring Requirements – EPA 40 CFR, Part 63, Subpart H - National Emissions Standard for Organic Hazardous Air Pollutants from Synthetic Organic Chemical Manufacturing Industry Equipment Leaks • U. S. Occupational Safety and Health Administration (OSHA) – OSHA 1910.95 - Occupational Noise Exposure

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PIP PCCCV001 Selection of Control Valves

3.

COMPLETE REVISION March 2003

Definitions The following terms and their definitions are derived from ANSI/ISA75.05.01: ball valve: a valve with a rotary motion closure member consisting of a full ball or a segmented ball butterfly valve: a valve with a circular body and a rotary motion disk closure member, pivotally supported by its stem closure member: the movable part of the valve that is positioned in the flow path to modulate the rate of flow through the valve. Examples include the plug for a plug valve, the disk for a butterfly valve, and the ball for a ball valve. eccentric rotary disk: a spherical segment in a rotary motion valve that is not concentric with the disk shaft and moves into the seat when closing equal percentage characteristic: an inherent flow characteristic, which, for equal increments of rated travel, will ideally give equal percentage changes of the existing flow coefficient (Cv) flangeless control valve: a valve without integral line flanges, which is installed by bolting between companion flanges, with a set of bolts, or studs, generally extending through the companion flanges full ball: a closure member having a complete spherical surface with a flow passage through it. The flow passage may be round, contoured, or otherwise modified to yield a desired flow characteristic. globe body: a valve body distinguished by a globular-shaped cavity around the port region, wherein the closure member motion is linear and normal to the plane of the port lugged body: a thin annular section body with lug protrusions on the outside diameter of the body, having end surfaces mounted between the pipeline flanges or attached to the end of the pipeline without any additional flange or retaining parts, using either through bolting and/or tapped holes plug valve: a valve with a closure member that may be cylindrical, conical, or a spherical segment segmented ball: a closure member that is a segment of a spherical surface, which may have one edge contoured to yield a desired flow characteristic travel: the movement of the closure member from the closed position to an intermediate or the rated full open position wafer body: A thin annular section butterfly body having end surfaces located between the piping flanges and clamped there by bolts extending from flange to flange

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PIP PCCCV001 Selection of Control Valves

March 2003

4.

Body - General 4.1

Material, end connections, pressure rating, gaskets, and packing of valve body shall, as a minimum, conform to the applicable piping specification. The materials engineer shall approve any deviation from the piping specification. Comment: Special alloy bodies that differ from the piping specification may be required in conditions such as high temperature, severe erosion/corrosion, or critical applications such as oxygen.

4.2

Valves shall not be cast iron. Carbon steel shall be the minimally acceptable material on control valve bodies.

4.3

Control valves in flashing water service require harden body material such as 5 Cr-1/2 Mo.

4.4

Ratio of nominal pipe size to body size shall not be greater than 2:1.

4.5

Valves 1 inch and larger shall not be screwed.

4.6

Valves with welded end connections shall be approved by the owner. Comment: Welded valves are often used in high-pressure steam applications and in high-temperature applications.

4.7

Flanged connections shall be required in the following services: •

Flammable, toxic, or lethal services

•

Services above 400ºF

•

Where subject to deep thermal cycling

•

Where steam pressure is greater than 50 psig

•

Where fire-safe design is required

4.8

Control valve body size shall not exceed the line size.

4.9

Body sizes 1-1/4, 2-1/2, 3-1/2, 5, or higher odd numbers shall not be used. If valve calculations indicate a requirement for such sizes, reduced trim shall be used in standard size valve bodies, i.e., NPS 3 valve with 2-1/2-inch trim.

4.10

Face-to-face dimensions of valve body shall conform to ISA standards in accordance with the following Table 1: Table 1 - Valve Body Face-to-Face Dimensions Body Style Globe-style with integral flanges Globe-style with separable flanges Flangeless Buttweld-end globe Globe-style angle flanges

4.11

ISA Standard ISA75.03 or ANSI/ISA75.16 depending on ANSI class rating ISA75.08.07 ISA75.04 ISA75.08.04 or ANSI/ISA 75.15 depending on ANSI class rating ISA75.22

Flanged connections shall be raised face (RF), conforming to ASME B16.5.

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March 2003

4.12

Flanges with tag welds or flanges with partial penetration welding are not acceptable.

4.13

Flangeless valves shall have centering means (e.g., lugs, holes, or equivalent) to ensure proper alignment of valve and gasket. Valve body gasket surface areas shall be the same as that of the mating flanges.

4.14

Separable flanges must be approved by the owner. The manufacture shall supply a permanent, yellow tag on the valves with separable flanges that can rotate when the bolts are loosened. The tag shall be inscribed with the following statement: “Warning - This valve has separable flanges and may rotate when bolts are loosened. The actuator must be supported before loosening the bolts.”

4.15

If separable flanges are specified, the flange-retaining ring shall be zinc-plated or shall be made of stainless steel.

4.16

Welding procedures, performance of welders, and welding operators shall meet the requirements of ASME B31.3.

4.17

Only valves in critical applications that require minimum leakage shall have ANSI Class VI seat leakage rating. Valves with this seat leakage rating shall be submitted to the owner for approval before they are incorporated into the design.

4.18

Flow direction, where applicable, shall be permanently marked on the valve body.

4.19

Mechanically linked valves shall not be used for split process flows in lieu of threeway valves.

4.20

Severe service valves (e.g., globe or angle with hardened trim, specially designed multi-hole/path cavitation trim, or noise abatement trim) shall be used for applications where conventional valves (globe, ball, butterfly, etc.) are not appropriate because of loss of control characteristics over time. Examples of conditions where severe service valves shall be considered are as follows: •

Liquid valves Cavitation potential exists: (P1-P2)/(P1-Pv) > 0.6 Application is a flashing service: (P2 < Pv)

•

Gas valves (P1-P2)/P1 > 0.5 where P1 is the upstream pressure; P2 is the downstream pressure; Pv is the vapor pressure of the process fluid at flowing temperature.

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4.21

5.

PIP PCCCV001 Selection of Control Valves

Severe service valves shall be used in the following service applications: •

Intermittent letdown (e.g., high-noise, errosive service) in daily service

•

Recirculation in daily service where cavitation is predicted

•

Where high vibration and/or high noise is expected from the application

•

Where history of valve failures or need for severe service trim exists

Globe Valves 5.1

Globe valves are acceptable for all applications and pressure classes listed in Table 2, as follows.

Process Industry Practices

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COMPLETE REVISION

PIP PCCCV001 Selection of Control Valves

March 2003

Table 2 - Acceptable Applications for Valve Body Types Body Type (Note 1)

Process Characteristic A.

Globe (Angle)

Wafer Eccentric Disc

Rotary E-Disc / Segmental Ball

Ball and Plug

M,S,O

---

M,O

M,S,O

S,O

= 300

M,S,O

---

M,O

M,S,O

S,O

Globe (Straight)

= 150

Process Gas or Liquid

1. Clean service (liquid - no cavitation or flashing) (Note 4) B.

Valve ANSI Flange Rating (Note 2)

= 600

M,S,O

---

---

M,S,O

---

> 900

M,S,O

---

---

---

---

= 150

M,S,O

M

---

---

---

= 300

M,S,O

M

---

---

---

Process Liquid

1. Clean service (cavitation or flashing condition) 2. Suspended solids (erosive) (Note 3)

3. Corrosive

4. Viscous or nonerosive slurry

= 600

M,S,O

M

---

---

---

> 900

M,S,O

M

---

---

---

= 150

---

M,S

---

M,S (Note 6)

S,O (Note 7)

= 300

---

M,S

---

M,S (Note 6)

S,O (Note 7)

= 600

---

M,S

---

M,S (Note 6)

---

> 900

---

M,S

---

---

---

= 150

M,S,O

---

---

M,S,O

M,S,O (Note 8)

= 300

M,S,O

---

---

M,S,O

M,S,O (Note 8)

= 600

M,S,O

---

---

M,S,O

---

> 900

M,S,O

---

---

---

---

= 150

---

---

---

M,S,O

M,S,O

= 300

---

---

---

M,S,O

M,S,O

= 600

---

---

---

M,S,O

---

> 900

---

---

---

---

---

Notes: 1. "M" indicates valves that are acceptable for modulating service; "S" indicates valves that are acceptable for shutdown service; "O" indicates valves that are acceptable for on/off service. 2. The ANSI flange rating relates to the pipe flanges for flangeless valves. 3. Valve selection for nonerosive suspended solids service is the same as that for process gas or liquid (A1). 4. Utility (steam, air, water) valve selection is the same as that for process gas or liquid (A1 and B1). 5. Control valves used in streams that have a combination of the above process characteristics or process characteristics not listed shall be selected according to project requirements. 6. Valve must be installed in accordance with the manufacturer's recommendation. 7. Full port valves only. 8. Plug valves are acceptable in corrosive service. Ball valves are not typically available in corrosionresistant materials.

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PIP PCCCV001 Selection of Control Valves

March 2003

5.2

Single-seated globe valves are required unless otherwise approved by the owner.

5.3

Cage guiding shall not be used in applications with suspended solids. Globe valves shall be used for high-pressure-drop applications, low-flow applications, clean liquid and gas service applications (corrosive and non-corrosive), and clean liquid service, particularly where cavitation, flashing, or noise are design considerations.

5.4

Globe valves with split bodies shall not be used unless otherwise approved by the owner.

5.5

To reduce the exit velocity of the valve and to dissipate energy, control valve bodies in the following applications shall be no smaller than one size less than line size. Comment: The proper reduced trim size must also be specified in these severe service applications: •

To reduce the valve body liquid flow velocity below a maximum of 33 ft/sec

•

To reduce the valve body gas/vapor outlet velocity below a maximum of 0.3 Mach

•

When the calculated noise not including special noise trim or other noise reduction methods exceeds the maximum continuous operating noise level entered on PIP PCSCV001 data sheet. Comment: Velocity must be below 0.3 Mach for effective noise treatment.

6.

•

Choked flow services

•

Flashing services

•

Erosive services maximum velocity shall not exceed 20 ft/sec

Rotary Valves 6.1

Rotary valves include all types of ball or plug valves (e.g., ball, segmented ball) and butterfly valves (e.g., eccentric disk). Rotary valves are acceptable for all applications and pressure classes listed in Table 2.

6.2

Rotary valves in applications where cavitation or high-noise conditions are present require approval by owner. These applications normally use a globe valve.

6.3

Flangeless valves shall have centering guides to ensure proper alignment of valve and gasket.

6.4

Flangeless and wafer-style valves shall not be used in toxic and/or highly corrosive services.

6.5

Flangeless valves that exceed a body width of 5-1/2 inches shall be subject to owner approval. Lugged body flanges shall be through-bolted. Threaded lugged flanges require owner approval.

6.6

Unless otherwise specified, the valve shaft shall be oriented in the horizontal plane.

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PIP PCCCV001 Selection of Control Valves

6.7

COMPLETE REVISION March 2003

Rotary valves shall be designed such that a mechanical failure will not expel the shaft of the stem from the valve body. Comment: When the stem breaks and is expelled from the valve, a leak path develops that is equal to the cross section of the stem. This failure scenario has caused considerable damage to plants. Since maintenance may remove the actuator while under pressure, the preferred mechanism to retain the stem should be independent of the actuator. If the actuator is used to retain the stem, the valve shall have a tag that states this possibility as a warning statement.

7.

6.8

The actuator end of the valve stem shall be the spline or keyed design. Shear pins are not acceptable. Shafts shall be made of one piece. The shear safety factor shall be a minimum of 150% at the specified shutoff-pressure-drop condition. The valve stem bearing shall be designed to prevent the stem guide bushing from rotating in the valve body. Bearing material shall be selected to prevent galling of the bearing or valve stem.

6.9

The valve shaft bearing shall be designed to prevent the shaft guide bushing from rotating in the valve body.

6.10

Bearing material shall be selected to prevent galling of the bearing or valve shaft and to operate at the maximum and minimum process temperatures.

6.11

The valve disk and shaft for lined, carbon steel, and stainless steel valves shall be made of stainless steel. Other trim parts shall also be made of stainless steel, as a minimum, or of material that meets the process requirements.

6.12

Because the disk in wafer-style valves may project beyond the valve body during part of the disk rotation, clearance shall be maintained between the disk and the pipe wall, particularly if the pipe is of heavy wall construction.

Trim 7.1

For maximum allowable control valve seat leakage, refer to PIP PCSCV001 control valve specification sheet. On individual valves, the maximum allowable seat leakage ANSI/FCI 70-2 Class shall be stated on the individual control valve data sheet.

7.2

Control valves that must provide a tight shutoff (TSO) shall be an ANSI/FCI 70-2 Class V or better. The actual leakage rate shall be communicated to the process engineer for approval. Comment: This requirement does not pertain to isolation valves and safety valves. Leakage requirement for these valves must be defined individually by process requirements.

7.3

Because of close tolerances between the cage and plug, cage trim valves shall be used only in clean liquid, vapor, or gas service.

7.4

Cage-guided trim in dirty services shall be subject to owner approval.

7.5

Trim shall be 13 Cr (400 series SS) as a minimum for control valves with cageguided design and for other valves where such metallurgy is of standard construction.

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March 2003

7.6

Trim for valves in services that contain erosive or solids-bearing fluids shall be hardened with a minimum hardness of 38 Rockwell C.

7.7

Trim material shall meet the requirements of Table 3 as a minimum. Table 3 Hardened Trim Applications Flowing dP psid 0-100 100-200 200-400 500-600 600-800 800-up

Gases 1 1 1 1 1 1

Steam 2 2 2 3 3 3

Water 1 4 4 4 4 4

HC Liquids 1 2 4 4 4 4

1 = Manufacture’s standard valve trim (316 or 400 series stainless minimum) 2 = 400 series stainless minimum 3 = Stellite trim (alloy 6 or 316/alloy 6 overlay for the seat ring and plug) 4 = Standard trim 400 series stainless or hard-faced stellite unless valve is cavitating or flashing. • If cavitating, use anti-cavitating trim or harden trim according to the manufacturer’s recommendation. • If flashing, use harden trim (stellite, 440C, or Colmonoy® 6)

7.8

Valve stem and plug shall be pinned and welded or be of a one-piece design.

7.9

Threaded trim parts, except seat rings, shall be pinned or spot-welded to supplement the threaded attachment.

7.10

In erosive or corrosive services, self-flushing valves shall be preferred instead of permanent flushing connections built into the control valve.

7.11

Permanent flushing connections shall be subject to owner approval.

7.12

Valves that require cavitation or noise trim shall be submitted to the owner for approval. Do not use small passage cavitation/noise trim on processes that contain particulates, solids, or plugging material. Comment: To avoid plugging, conical strainers shall be considered for installation upstream of valves with anti-noise or anti-cavitation trim.

7.13

8.

If operating temperature exceeds 700°F, guide post areas and rings shall be hardfaced stellite or equivalent.

Bonnet 8.1

General 8.1.1

The bonnet shall have a bolted design.

8.1.2

Extended or finned bonnet shall be used for service temperatures below 0°F and above 750°F.

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March 2003

Comment:

8.1.3 8.2

8.3

Extended bonnets may be avoided in processes above 400°F and below 750°F if graphite-based or other high-temperature packing is used.

Bonnet bolts shall not be used to attach actuators or mounting brackets.

Gaskets 8.2.1

Default bonnet gasket material shall be as specified on the PIP PCSCV001 control valve specification sheet.

8.2.2

Bonnet gasket shall be compatible with the process, the maximum temperature, and maximum pressure. The gasket material shall be in compliance with the piping specification.

8.2.3

Gaskets containing asbestos are unacceptable.

8.2.4

If the valve is required to be fire safe, the following materials are considered fire safe: •

Metal gaskets

•

Flexible graphite gaskets

Packing 8.3.1.

Packing material shall be compatible with piping specification. 8.3.1.1 Packing shall not require lubrication. 8.3.1.2 The cooling effects from use of an extended bonnet shall not be taken into account when selecting the packing. 8.3.1.3 Packing material containing asbestos is unacceptable. 8.3.1.4 For applications in temperatures above 750°F, an extended bonnet shall be used to protect the positioner and actuator from heat. 8.3.1.5 See the PIP PCSCV001 control valve specification sheet for packing type for non-fugitive emission and fugitive emission versus process temperature. 8.3.1.6 Packing shall conform to vendor’s sizing and selection criteria for temperature/pressure curves. The packing material shall be in compliance with the piping specification. 8.3.1.7 For fire-safe applications, graphite-based packing shall be used. 8.3.1.8 Bellow seals shall require owner approval.

8.3.2

Fugitive emissions considerations are as follows: 8.3.2.1 Packing shall limit fugitive emissions. Fugitive emissions of any substance containing more than 5% by weight of volatile hazardous air pollutant as defined in the EPA 40 CFR, Part 63, shall be limited in accordance with the applicable local regulation or limited to a maximum of 500 parts per million, whichever is more stringent.

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8.3.2.2 Determination of leaks and monitoring requirements shall comply with EPA 40 CFR, Parts 60 and 61, respectively. Comment: Methods of meeting the above-mentioned requirement include application of twin packing designs, live-loaded packing, and bellows seals. Bellows seals, while relatively expensive, should be considered for cases in which no leakage across the stem can be tolerated or for cases in which excessive packing friction results in unreasonably large packing friction forces. Comment: Increased emphasis on limiting packing leaks has resulted in the development of new packing materials and methods. Valve vendors are offering increasingly effective designs, and they should be consulted for recommendations on specific fugitive emission control applications. Comment: To meet fugitive emissions, the stem should be finished to a maximum of 8 microinches RMS. Smooth finish assists in reducing fugitive emissions over service life of control valve. 8.3.2.3 Packing design shall be approved by the owner before implementation. 8.3.2.4 Control valves shall be designed, selected, and installed to permit easy access of monitoring packing areas prone to fugitive emissions without removing equipment or devices. 8.3.2.5 PIP PCSCV001 control valve specification sheet, which indicates the testing criteria, identifies whether fire-safe packing is required. 8.4

Bolting 8.4.1

Vendor-recommended bonnet bolts shall be used unless owner specifies differently.

8.4.2

Valve bonnets shall be bolted type with a retained-type gasket.

8.4.3

Plated bolting material shall not be used for pressure-containing parts.

8.4.5

The following valve components shall be 304 or 316 SS minimum: •

Gland studs and nut (e.g., packing bolts)

•

Packing flange and follower

8.4.6

Packing glands and followers shall be bolted for valves larger than 1 inch.

8.4.7

Carbon steel screwed packing followers shall not be acceptable.

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9.

March 2003

Sizing Considerations 9.1

General 9.1.1

Valve-sizing procedure shall address the full range of expected flow conditions. Appropriate differential pressure shall be applied as load changes. Flow equations specified in PIP PCSCV001 control valve specification sheet shall be used.

9.1.2

When sizing a valve, only the characteristcs of the plug shall be considered for an accurate understanding of the plug stroke at the various conditions. A positioner with characterization such as equal percentage may be used on trim with an inherent linear characterization to enhance control.

9.1.3

Linear trim design shall be preferred if pressure drop across valve does not vary more than 20% between maximum flow and minimum flow; i.e., dP(max flow) – dP(min flow)/dP(min flow)