Introduction to Low Temperature Corrosion
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Introduction to Low Temperature Corrosion
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 1
Philosophy • Provide the student with a basis for understanding aqueous corrosion • Start from a point of everyday familiarity – Corrosion is electrical so we will start from a car battery and a copper/zinc galvanic cell
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 2
Topics • Corrosion Definitions • Aqueous Electrochemistry Fundamentals • Electrochemical Cells
• Concentration Cells • Kinetics • Active/Passive Materials
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 3
Topics • Definitions • Electrochemistry review (thermodynamics) • Electrochemical kinetics
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 4
Definitions
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 5
Definition of Corrosion • Many possible definitions – Changes in definition change scope of study
• All interactions between a material and the environment • Undesired interactions between a material and the environment • We will use both definitions 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 6
Low Temperature Corrosion • Low temp corrosion – Fe2+(aq) + H2(g) + 2Cl-(aq)
• Keep track of ions and states
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 8
Strong and Weak Acids • Strong acids – 100% dissociation – HClO4, H2SO4, HCl, HNO3, HI, HBr
• Weak Acids – Less than 100% dissociation – CO2(g) + H2O(g) H2CO3(aq) H+(aq) + HCO3-(aq) 2H+(aq) + CO32-(aq) 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 9
Strong and Weak Bases • Strong Bases – 100% dissociation e.g. NaOH
• Weak Bases – Less than 100% dissociation e.g. NH3 – NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
• Ca(OH)2 and Mg(OH)2 are weak bases 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 10
Aqueous Corrosion Electrochemistry Review
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 11
Electrochemistry • Essentially all low temperature corrosion is aqueous • Aqueous corrosion is electrochemistry • What follows are some key points to remember – More details are in section 2
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 12
Copper Zinc Electrochemical Cell e
V
-
Cu
Cathode +
e-
KCl
Anode -
Cu
Zn 2+
Cu
2+
Zn
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 13
Copper Zinc Electrochemical Cell • For infinite resistance voltmeter – Arrows represent ATTEMPTS to flow – Potential is a measure of “how much” electrons “want” to flow
• Cu2+ + Zn --> Zn2+ + Cu • Half reactions – 2e- + Cu2+ --> Cu – Zn --> Zn2+ + 2e-
1.1V V half reaction? V half reaction?
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 14
Standard EMF Series Standard EMF Pt-Pt2+ Ag-Ag+ Cu-Cu+ H-H+ Pb-Pb2+ Ni-Ni2+ Fe-Fe2+ Cr-Cr3+ Zn-Zn2+ Al-Al3+ Mg-Mg2+
Standard Reduction Pt2+ + 2e- --> Pt Ag+ + e- --> Ag Cu+ + 2e- --> Cu H+ + e- --> H Pb2+ + 2e- --> Pb Ni2+ + 2e- --> Ni Fe2+ + 2e- --> Fe Cr3+ + 3e- --> Cr Zn2+ + 2e- --> Zn Al3+ + 3e- --> Al Mg2+ + 2e- --> Mg
Potential 1.2 V 0.799 V 0.337 V 0.799 V -0.126 V -0.250 V -0.440 V -0.744 V -0.763 V -0.744 V -2.363 V
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 15
Copper Zinc Electrochemical Cell • Standard Reductions – Cu2+ + 2e- --> Cu – Zn2+ + 2e- --> Zn
0.337 V -0.763 V
• Half Reactions (reverse oxidation half rxn) – Cu2+ + 2e- --> Cu – Zn --> Zn2+ + 2e-
0.337 V -(-0.763) = 0.763 V
• Sum = Cu2+ + Zn --> Zn2+ + Cu 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
1.1V Corrosion and Fouling Intro to low temp corr Oct, 01 16
Concentration Cell V
e-
Cu
Cathode +
KCl
Anode -
Cu
Cu 2+
Concentrated
e-
Cu
2+
Cu
Dilute
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 17
Concentration Cell • Why? – Lechatlier’s Principle – Equilibrium will shift to make concentrations even
• Nernst Equation E = Eo −
0.059 [products] log n [reac tan ts]
– Equation is not important - concept is 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 18
Electrochemical Kinetics Flow of Electrons - Not Just the Tendency to Flow
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Corrosion and Fouling Intro to low temp corr Oct, 01 19
Kinetics • The rate of corrosion is proportional to the flow of electrons • Cell potential is related to cell current • Must understand this concept to understand the behavior of active/passive metals • Consider almost dead car battery 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 20
Car Battery 12 Nothing On Radio On 9 potential (V)
Lights On 6
Starter On
3
0 0 Current (A) 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 21
Car Battery • The higher the current the lower the voltage • Actually the higher the current the lower the ∆V between anode and cathode • Consider the copper zinc cell again
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 22
Copper Zinc Cell, Current e
V
-
A
R Cu
Cathode +
e-
KCl
Anode -
Cu
Zn 2+
Cu
2+
Zn
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 23
Copper Zinc Cell, Current • Ammeter has no resistance • Arrows represent flow of electrons and ions not just the potential for flow • If potential was also measured would voltage be the same as the no current condition?
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 24
Copper Zinc Cell Current Potential (V)
0.4 0.2 0
Log i
-0.2 -0.4 -0.6
Potential and current of corroding cell
-0.8
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 25
Copper Zinc Cell Current • Slope of lines – Anodic and cathodic not necessarily same – Varies with environment
• Measurement of potential on an absolute scale requires reference electrode • With apparatus as drawn can only measure difference in potential 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 26
Active / Passive Materials Where making conditions worse actually reduces corrosion
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 27
Active Passive • Some alloy/environments form film which affects corrosion behavior – Iron, Chromium, Nickel, Titanium
• Produces counterintuitive corrosion results
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Corrosion and Fouling Intro to low temp corr Oct, 01 28
Iron and Nitric Acid • Will DILUTE nitric acid corrode iron?
Dilute HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 29
Iron Nitric Acid • With vigor!
Dilute HNO 3 Fe
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 30
Iron Nitric Acid • Will iron corrode in concentrated nitric acid?
Conc HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 31
Iron Nitric Acid • No
Conc HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 32
Iron Nitric Acid • Will iron that has been in concentrated nitric acid corrode when put into dilute acid?
Conc HNO 3
Dilute HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 33
Iron Nitric Acid • No
Conc HNO 3
Dilute HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 34
Iron Nitric Acid • If the dilute acid is shaken, will the iron corrode?
Conc HNO 3
Dilute HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 35
Iron Nitric Acid • Yes
Conc HNO 3
Dilute HNO 3 Fe
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Corrosion and Fouling Intro to low temp corr Oct, 01 36
Why • NO3 is an oxidizer • Iron will passivate
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Corrosion and Fouling Intro to low temp corr Oct, 01 37
Recall Copper Zinc Cell • Potential/current relationship for copper represented by lower line • Potential/current relationship for zinc represented by upper line • Lines cross at corrosion potential/current 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 38
Recall Copper Zinc Cell Potential (V)
0.4 0.2 0
Log i
-0.2 -0.4 -0.6
Potential and current of corroding cell
-0.8
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Corrosion and Fouling Intro to low temp corr Oct, 01 39
Iron Potential/Current • For active passive metal like iron, potential current diagram very different
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 40
Iron Potential/Current Diagram
Potential (V)
Iron
0
Log i
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Corrosion and Fouling Intro to low temp corr Oct, 01 41
Iron Corrosion Potential/Current • Corrosion potential/current is still the location where anodic and cathodic reactions cross
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Corrosion and Fouling Intro to low temp corr Oct, 01 42
Iron Potential/Current Diagram Iron
Potential (V)
Con c NO
3
-
Dilu te N O3
0
Log i Wa ter
H+
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Corrosion and Fouling Intro to low temp corr Oct, 01 43
What We Should Learn • Iron corrodes slowly in water • Iron corrodes faster in acid • Iron corrodes very slowly in concentrated nitric acid because concentrated nitric acid passivates the iron • Corrosion rate of iron in dilute nitric acid depends on the existence of a passive film 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 44
What We Should Learn • With an active/passive metal, making the situation “worse” sometimes makes it better • Current = corrosion rate • Don’t operate where pre-existing passive film is required for system to be passive 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 45
What We Should Learn • Active/passive state not answer to all “odd” corrosion behavior • Moderate concentration sulfuric acid corrodes steel more rapidly than concentrated – Probably due to availability of H+ ions – Pure H2SO4 without water does not ionize 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to low temp corr Oct, 01 46
Sulfuric Acid vs. Steel Rel. Corr. Rate
7 6 5 4 3 2 1 0 0
10 20 30 40 50 60 70 80 90 100 110 Wt% H2SO4
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Corrosion and Fouling Intro to low temp corr Oct, 01 47
General Low Temperature Corrosion Mechanisms
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Corrosion and Fouling General Low Temp Oct, 01 1
Philosophy • Provide an overview of how low temperature corrosion is categorized • Relate electrochemistry of corrosion to the appearance and location of corrosion • Specific, refinery corrosion problems are covered elsewhere 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 2
Topics • Galvanic corrosion • General corrosion • Under deposit corrosion • Crevice corrosion • Pitting • Environmental cracking • Erosion corrosion 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 3
Galvanic Corrosion An electrochemical cell without wires
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Corrosion and Fouling General Low Temp Oct, 01 4
Galvanic Corrosion • Similar to electrochemical cells • Corrosion current driven by potential difference between metal types • Cathode reaction may be H+ or O2 • Pay attention to anode/cathode areas
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Corrosion and Fouling General Low Temp Oct, 01 5
Galvanic Corrosion Solution Zn Zn e
2+
-
4OH
-
O2 Cu
2H O 2
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Corrosion and Fouling General Low Temp Oct, 01 6
Good and Bad Galvanic Corrosion • Galvanized steel? • Zinc blocks on steel ship hull? • Aluminum window screen with steel staples?
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Corrosion and Fouling General Low Temp Oct, 01 7
Area Effects • Big anode, little cathode not bad – Anodic current density small
• Big cathode little anode causes trouble – Anodic current density large
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Corrosion and Fouling General Low Temp Oct, 01 8
Area Effects
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Corrosion and Fouling General Low Temp Oct, 01 9
Area Effects Corrosive Environment Coating Carbon Steel
Stainless Steel
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Corrosion and Fouling General Low Temp Oct, 01 10
Galvanic Series • Not exactly the same as EMF series • Galvanic series – Corrosion of alloys in seawater
• EMF series – Potential of elements under standard conditions
• Although some differences, series generally parallel each other 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 11
Galvanic Series • Cathodic – – – – – – – –
Platinum Gold Silver Hastelloy C Austinitic Stainless Copper (brass bronze) Hastelloy B Steel
– Aluminum – Zinc – Magnesium
• Anodic • Active stainless steels and nickel alloy are slightly more cathodic than steel
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Corrosion and Fouling General Low Temp Oct, 01 12
Refinery Examples • Heat exchangers with different bundle/shell metallurgies • Titanium exchangers
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Corrosion and Fouling General Low Temp Oct, 01 13
What to do about it • Consider the consequences of any bimetallic connection • Fully isolate bimetallic bolted connections
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Corrosion and Fouling General Low Temp Oct, 01 14
Insulate Flanged Connections Insulating Washer
Bolt
Flange Gasket Flange
Insulating Sleeve
Nut
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Corrosion and Fouling General Low Temp Oct, 01 15
General Corrosion One type of one metal corrosion
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Corrosion and Fouling General Low Temp Oct, 01 16
General Corrosion • Normally one metal corrosion – Anode reaction often H+ or O2
• Can be uniform or non uniform – Non uniform often called pitting • Closely spaced shallow pits
• Be aware of the difference between pitting and pitting as reported by inspectors 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 17
General Corrosion Metal
Solution
Anode m m e
2+
-
H2O O2
Cathode H3O
+
Anode and cathode locations are almost random and move with time 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 18
General Corrosion
Potential (V)
Iron
0
Log i General Corrosion
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Corrosion and Fouling General Low Temp Oct, 01 19
General Corrosion
Potential (V)
1.0
0.5
Ox yg en pH
Ox yg en pH
0
14
0
Log i Fe
-0.5 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 20
General Corrosion • General corrosion is the only corrosion type for which thickness measurements and (typically) field electrochemical measurements are reliable!!!!!
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Corrosion and Fouling General Low Temp Oct, 01 21
Refinery Examples • Many locations – Liquid water – Acids or oxygen – Chlorides – Sites of condensation
• Crude tower overhead
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Corrosion and Fouling General Low Temp Oct, 01 22
What to do about it • Understand the environment • Understand the chemistry • Remember the trace contaminants • Monitor the environment and the corrosion rate • Metallurgy upgrade AFTER understanding problem 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 23
Under Deposit Corrosion
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Corrosion and Fouling General Low Temp Oct, 01 24
General Concepts • Films and deposits change the environment to which the metal is exposed – Can be advantageous or detrimental to corrosion
• Anode and cathode may be separated – Location of deposits not necessarily the same as location of metal loss 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 25
General Concepts • Under deposit corrosion is at least partly a concentration cell • Recall the copper concentration cell • Same concept works for anode and cathode reactions 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 26
Concentration Cell V
e-
Cu
Cathode +
KCl
Anode -
Cu
Cu 2+
Concentrated
e-
Cu
2+
Cu
Dilute
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Corrosion and Fouling General Low Temp Oct, 01 27
Water Drop en xyg hO Hig
g sin ea n cr e De xyg O
Hig hO xyg en
Water Drop
OH
2+
Fe
-
O
2
Fe2O3 e-
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Corrosion and Fouling General Low Temp Oct, 01 28
Location of Anodes and Cathodes • Consider a garden shovel partly covered with wet dirt – Where will the rust stains be – Where will metal be lost from
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Corrosion and Fouling General Low Temp Oct, 01 29
Location of Anode and Cathode
Wet Dirt
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Corrosion and Fouling General Low Temp Oct, 01 30
Location of Anode and Cathode
rust Metal Loss
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Corrosion and Fouling General Low Temp Oct, 01 31
Effect of Films • Films can reduce corrosion by altering corrosive environment • Corroding iron forms an iron hydroxide (Fe(OH)2) film – Film has pH of 9
• Recall iron, oxygen, pH diagram 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 32
Iron, Oxygen, pH
Potential (V)
1.0
0.5
Ox yg en pH
Ox yg en pH
0
14
0
Log i Fe
-0.5 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 33
Iron, Oxygen, pH • Corrosion rate higher at low pH • Corrosion rate should change linearly with pH • Because of film iron sees higher pH than bulk environment
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Corrosion and Fouling General Low Temp Oct, 01 34
Relative Corrosion Rate
Iron, pH Corrosion Rate 12 10 8 6 4 2 0 0
2
4
6
8
10
12
pH
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Corrosion and Fouling General Low Temp Oct, 01 35
Effect of Scales • Scales, thick films and foulant material exclude oxygen and create a concentration cell • If chlorides are present, H+ “drawn” under deposits – pH drops to below 4, corrosion rate increases
• How this happens is described in “pitting” section 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 36
Refinery Examples • Any location in which in which scaling and/or fouling occur especially if oxygen and chlorides are present
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Corrosion and Fouling General Low Temp Oct, 01 37
What to do about it • Treat the source of the problem (i.e. corrosion or fouling) • Anti foulant may be helpful – Consider downstream implications – Start early in run - antifoulant prevents but does not reverse many types of fouling
• Metallurgy upgrades may solve corrosion problem but not performance loss 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 38
Crevice Corrosion Geometry dependent one metal corrosion
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Corrosion and Fouling General Low Temp Oct, 01 39
Crevice Corrosion • Crevice Corrosion and pitting can be related – Crevice can be a preformed pit
• Crevice Corrosion also related to under-deposit corrosion • We will consider the most simple aspect of crevice corrosion 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 40
Crevice Corrosion High Oxygen Cathode
Low Oxygen Anode
Flange
Corroded Area
Gasket 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 41
Crevice Corrosion Rolling Grooves
Tube Sheet Tube Crevices
Crevices
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Corrosion and Fouling General Low Temp Oct, 01 42
Crevice Corrosion • Crevice corrosion is an oxygen cell • Crevice must be small enough to form stagnant zones • Corrosion uses up oxygen in crevice – Anode
• Oxygen plentiful outside crevice – Cathode 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 43
Refinery Examples • Anywhere where there is a crevice and general corrosion may be expected – Flanged connections especially with fiber gaskets – Threaded connections – Tube/tubesheet connections – Plate type heat exchangers
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Corrosion and Fouling General Low Temp Oct, 01 44
What to do about it • Use materials less sensitive to pitting • Eliminate crevices - especially those with porous gaskets
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Corrosion and Fouling General Low Temp Oct, 01 45
Pitting Random, local, one metal corrosion
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Corrosion and Fouling General Low Temp Oct, 01 46
Pitting • What inspectors call pitting and actual pitting are sometimes different • Pitting is normally discrete pits that are deeper than they are wide • Pitting is most common on the tops of horizontal surfaces and rare on the bottoms of horizontal surfaces 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 47
Pitting • Normally found in active/passive metals in passive state • Requires incubation time for pit to initiate • Some crevice corrosion is pitting in a preformed pit (crevice)
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Corrosion and Fouling General Low Temp Oct, 01 48
Strong and Weak Bases • Some metal hydroxides are strong bases and others are weak • Strong bases dissociate completely in water • M(OH)2 M2+ + 2OH– Sodium - all the way to the right – Calcium, Magnesium - substantially to the right – Iron - far to the left 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 49
Hydrolysis • Adding M2+ + 2OH- M(OH)2 and H2O H+ + OHGives M2+ + 2H2O M(OH)2 + 2H+ • Cations which form weak base hydroxides react with water to form the molecular base and an acid solution
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Corrosion and Fouling General Low Temp Oct, 01 50
Pitting Mechanism O2
OH
-
Cl
H2 O
-
Passive
Passive +
Fe(OH)
H e-
2
2+
Fe
H 2O Active
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Corrosion and Fouling General Low Temp Oct, 01 51
Pitting Comments • Without hydrolysis, no pits - metal hydroxide does not form - water does not acidify, chloride does not concentrate • Pits random - must get active spot on surface to remain stable until pit forms • Pitting relies on ion rich solution in pit grows best with gravity. 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 52
Refinery Examples • 300 Stainless + chlorides – Under chloride leaching insulation – Seawater cooling systems
• Remember that not all of what is reported to be pitting actually is
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Corrosion and Fouling General Low Temp Oct, 01 53
What to do about it • Understand environment • Avoid material/environment combinations prone to pitting • If unavoidable or exist in present design watch: – velocity – temperature – cleanliness 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 54
Environmental Cracking
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Corrosion and Fouling General Low Temp Oct, 01 55
Environmental Cracking • Specific interaction between metal and environment – Marginal passivation and/or differences in electrochemical potential within metal (e.g. grains to grain boundary
• Hydrogen embrittlement – Adsorption of H0 (created by general corrosion) by the metal 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 56
Environmental Cracking A Few Problem Combinations • 300 series stainless - chlorides • Carbon steel - hydroxides • Brass - ammonia • Aluminum - chlorides
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Corrosion and Fouling General Low Temp Oct, 01 57
Refinery Examples Environment/Metal Combination • Boil dry of caustic • crude units • Vent gas wash towers
• Stainless steel in sea or brackish water • Admiralty brass in ammonia environments • Condensers in crude overheads
• Shut down of reformers – Water, chlorides, thermal stress at nozzles 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 58
Environmental Cracking Hydrogen Embrittlement • Can accompany any wet corrosion involving H+ • Normally associated with carbon steel • Often involves H2S
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Corrosion and Fouling General Low Temp Oct, 01 59
Environmental Cracking Hydrogen • Wet corrosion, H+ initially --> H0 • H0 combines to H2 • If too much generated or recombination poison present, H0 penetrates steel – poisons include CN-, As, S2-
• Depending on conditions embrittles or forms blisters 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 60
What to do about it • Avoid combinations sensitive to cracking • Pay close attention to conditions in which cracking occurs – Concentrations – Temperature – Contaminants
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Corrosion and Fouling General Low Temp Oct, 01 61
Refinery Examples Hydrogen Embrittlement • HF alkylation • Sour water scrubbers • FCC (cyanides) – High pressure separator/low pressure separator – Stripper tower overhead
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Corrosion and Fouling General Low Temp Oct, 01 62
What to do about it • Minimize corrosion to minimize hydrogen production • Pay attention to hydrogen recombination poisons • Monitor hydrogen • Use clean, killed steels or upgraded metallurgy 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 63
Erosion Corrosion The combined effects of erosion and corrosion
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Corrosion and Fouling General Low Temp Oct, 01 64
Erosion Corrosion • Combination of general corrosion and the physical process of erosion. • May be just flowing fluid or may be 2 phase flow (gas/liquid, liquid/solid) • Active/passive metals which depend on surface films most vulnerable • Turbulence and Impingement are critical 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling General Low Temp Oct, 01 65
Refinery Examples • REACs • Heater tubes • Any location with two phase flow is suspect
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Corrosion and Fouling General Low Temp Oct, 01 66
What to do about it • Pay attention to velocities!!!!!! • Understand corrosion environment and minimize corrosion • Filters may help especially in raw water cooling systems
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Corrosion and Fouling General Low Temp Oct, 01 67
Introduction to High Temperature Corrosion
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Corrosion and Fouling Intro to High Temp. Oct, 01 1
Topics • Definition of high temperature corrosion • Basic mechanism of high temperature corrosion • Kinetics • Evaluation of high temperature corrosion damage • Chemical composition of scale 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Intro to High Temp. Oct, 01 2
Definitions
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Corrosion and Fouling Intro to High Temp. Oct, 01 3
High Temperature Corrosion • Low temp corrosion – to grain boundaries • At correct temperatures chromium reacts with carbon to form chrome carbides • Dissolved chromium depleted to less than 14% near grain boundaries • Grain boundaries preferentially corroded • Continuous chromium carbides, problem 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 11
Time Scale • Sensitization occurs on both short and longer time scales – Short - associated with welding – Long - associated with process conditions
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Corrosion and Fouling Specific Low Temp. Oct, 01 12
Rapid Sensitization
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Corrosion and Fouling Specific Low Temp. Oct, 01 13
Materials Affected • Primarily 304, 316, 317
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Corrosion and Fouling Specific Low Temp. Oct, 01 14
Cause • Given sufficient carbon (.08%) sensitization can occur in seconds • Narrow band in weld HAZ meets criteria – Closer to weld, cools too fast – Farther from weld, temps too low
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Corrosion and Fouling Specific Low Temp. Oct, 01 15
Weld Thermal History • Consider a weld operation in which thermocouples are placed at varying distances from the weld • Recall the critical temperature range is about 950 to 1450oF (510 and 785oC)
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Corrosion and Fouling Specific Low Temp. Oct, 01 16
Weld Time Temp Position 2500 2000
Decay
1500 (a)
1000
Weld
(b) (c)
500
(d)
0 0
10 20 Time (sec)
(a) (b) (c) (d)
30
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Corrosion and Fouling Specific Low Temp. Oct, 01 17
Time Temp Position (a) 2500 10 seconds in sensitizing range
2000 1500
Decay
1000
Weld
(a)
500 0 0
5
10
15
20
25
30
(a) (b) (c) (d)
Time (sec)
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Corrosion and Fouling Specific Low Temp. Oct, 01 18
Time Temp Position (b) 2500
12+ Seconds in sensitizing range
2000 1500
Decay
1000
Weld
(b)
500 0 0
5
10
15
20
25
30
(a) (b) (c) (d)
Time (sec)
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Corrosion and Fouling Specific Low Temp. Oct, 01 19
Time Temp Position (c) 2500 11 seconds in sensitizing range
2000 1500
Decay
1000
Weld (c)
500 0 0
5
10
15
20
25
30
(a) (b) (c) (d)
Time (sec)
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Corrosion and Fouling Specific Low Temp. Oct, 01 20
Time Temp Position (d) 2500 0 seconds in sensitizing range
2000 1500
Decay
1000
Weld
500 0 0
5
10
15
20
25
(a) (b) (c) (d)
30
Time (sec)
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Corrosion and Fouling Specific Low Temp. Oct, 01 21
Summary • Primarily a function of time in the sensitizing temperature zone (950-1450oF) (510 and 785oC) • Other issues play a role
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Corrosion and Fouling Specific Low Temp. Oct, 01 22
Weld Decay
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Corrosion and Fouling Specific Low Temp. Oct, 01 23
Problem • Intergranular corrosion in a narrow band of the weld heat affected zone • Corrosion occurs when material is exposed to an environment which is corrosive to carbon steel
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Corrosion and Fouling Specific Low Temp. Oct, 01 24
Alternatives • Heat treat after welding - not practical • Use low carbon steels – Below 0.05 C sensitization by welding unlikely
• Use stabilized steels – Type 321 - titanium stabilized – Type 347 - columbium stabilized • Ti and Cb “lock up” C by forming carbides • Cr remains in solution 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 25
Refinery Examples • Anywhere welded 304 or 316 including L grades are used – L grades occasionally have a problem because welders tend to “clean” surfaces with oily rags before welding
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Corrosion and Fouling Specific Low Temp. Oct, 01 26
Knife Line Corrosion
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Corrosion and Fouling Specific Low Temp. Oct, 01 27
Problem • Very narrow band of intergranular corrosion immediately adjacent to weld – Closer to the weld and narrower than weld decay
• Corrosion occurs when material is exposed to an environment which is corrosive to carbon steel 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 28
Materials Affected • 321 (titanium stabilized) • 347 (columbium (niobium) stabilized)
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Corrosion and Fouling Specific Low Temp. Oct, 01 29
Cause • Welding and post weld heat treat remove stabilizing titanium or columbium carbides and allow the formation of chromium carbides
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Corrosion and Fouling Specific Low Temp. Oct, 01 30
Carbide Reactions Temp (F)
Columbium Carbides
Chromium Carbides
Temp (C) Tm
Tm Dissolve 2250
1230 Form
Dissolve 785
1450 Form 950 32
No Reaction Slow kinetics and diffusion
510 No Reaction Slow kinetics and diffusion
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0
Corrosion and Fouling Specific Low Temp. Oct, 01 31
Summary • Band near weld heated so columbium carbides dissolve • Cools rapidly so no carbides form • Heat treat temps typically in chromium carbide formation zone • Material sensitized – subject to intergranular corrosion 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 32
Refinery Examples • Not common but possible in refineries • Heat treating welded 321 or 347 not a common practice – Could occur by accident
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Corrosion and Fouling Specific Low Temp. Oct, 01 33
Long Duration Sensitization
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Corrosion and Fouling Specific Low Temp. Oct, 01 34
Materials Affected • 304, 316 (including low carbon versions) • 321, 347 • Unstabilized nickel alloys 600, 800 • Stabilized nickel alloys 800H, 835 • One source reported no sensitization in nickel alloys 825, 625 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 35
Cause • Conversion of Cb or Ti carbides to Cr carbides • Diffusion of carbon from the environment into the steel followed by the formation of Cr carbides – Primarily at grain boundaries
• Surface Cr depletion 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 36
Long Term Sensitization 304, 304L 650 C
1200 F
304 600
Temp
1100
304L
550 1000
500 900
450 1
10
100
1000
10000
Time (hr)
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Corrosion and Fouling Specific Low Temp. Oct, 01 37
Long Term Sensitization 321, 347 650 C
1200 F
321 600
Temp
1100
550
347 1000
500 900
450 1
10
100
1000
10000
Time (hr)
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Corrosion and Fouling Specific Low Temp. Oct, 01 38
Summary • Long term sensitization of all 300 series stainless steels will occur • Time and temperatures required vary with material • 700oF is considered the minimum temperature for sensitization 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 39
Problem • Sensitized material has corrosion resistance of carbon steel – Primarily along grain boundaries – Environments not normally corrosive to stainless steels will corrode it
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Corrosion and Fouling Specific Low Temp. Oct, 01 40
Solutions • Assume steel is sensitized • Avoid corrodants corrosive to carbon steel • Neutralize acids • Exclude oxygen
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Corrosion and Fouling Specific Low Temp. Oct, 01 41
Polythionic Acid Stress Corrosion Cracking
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Corrosion and Fouling Specific Low Temp. Oct, 01 42
Problem • Cracking of austenitic stainless steels exposed to sulfur at high operating temperatures occurs during down time • Attributed to direct reaction of polythionic acid and sensitized austenitic stainless steel • Polythionic acid is a class of acids H2SxOy – Worst H2S4O6 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 43
Polythionic Acid SCC
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Corrosion and Fouling Specific Low Temp. Oct, 01 44
Conditions • Sensitized austenitic stainless steel • Sulfide scale • Liquid water • Oxygen • Stress
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Corrosion and Fouling Specific Low Temp. Oct, 01 45
Conditions • Sensitization – Welding – Long term exposure 800-1500oF (425-815oC) – 304, 316 sensitize relatively quickly – 321, 347 take longer - 347 longer than 321
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Corrosion and Fouling Specific Low Temp. Oct, 01 46
Conditions • Sulfide Scale – High temperature operation – Sulfur present in feed – Sulfur injected to prevent coking or carburization – Sulfur present in fuel gas
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Corrosion and Fouling Specific Low Temp. Oct, 01 47
Conditions • Liquid water – Condensed water vapor from air is sufficient
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Corrosion and Fouling Specific Low Temp. Oct, 01 48
Conditions • Oxygen – Oxygen from air is sufficient – Unclear if dissolved oxygen from water is sufficient
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Corrosion and Fouling Specific Low Temp. Oct, 01 49
Conditions • Stress – Must be tensile stress – High stress not required • Residual stresses are sufficient • Must assume always present
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Corrosion and Fouling Specific Low Temp. Oct, 01 50
Solutions • NACE RP-01-70 • Must assume sulfur and stress present • Should assume sensitized • Eliminate water and/or oxygen – Keep equipment hot, use nitrogen purge
• 2% sodium carbonate wash – Neutralizes acids as form 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 51
Solutions • Soda ash wash precautions – Good coverage – 2 hour wash - soak through scale – Drain solution well (chlorides and carbonates can build up) – 150 ppm chlorides max – Repeat if carbonate residue disturbed
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Corrosion and Fouling Specific Low Temp. Oct, 01 52
Refinery Examples • Hydrodesulfurizers • Hydrocrackers • Hydrogen Reformers • FCC • Fired Heaters (outside of tubes)
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Corrosion and Fouling Specific Low Temp. Oct, 01 53
Chloride Stress Corrosion Cracking and Pitting
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Corrosion and Fouling Specific Low Temp. Oct, 01 54
Problem • 300 Series stainless steel (and some nickel alloys) crack or pit in the presence of chlorides
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Corrosion and Fouling Specific Low Temp. Oct, 01 55
Pitting Conditions • Primarily 304 – Mo in 316 retards pitting
• PPM level chlorides • Pitting due to – Marginal passivation – Acid formation in the pit
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Corrosion and Fouling Specific Low Temp. Oct, 01 56
Chloride SCC Crack
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Corrosion and Fouling Specific Low Temp. Oct, 01 57
Chloride SCC Crack
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Corrosion and Fouling Specific Low Temp. Oct, 01 58
Cracking Conditions • ppm level Cl• ppm level O2 for neutral pH • No oxygen required acid pH • Above 140oF (60oC) – Lower with other contaminants (H2S)
• Tensile stress • Sulfur can speed cracking or sub for O2 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 59
Cracking Conditions • Field survey 304, 316, and 321 performed the same • Either intergranular or transgranular – Normally transgranular
• Branched
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Corrosion and Fouling Specific Low Temp. Oct, 01 60
Stress, Time, Material 80 304 304L
Stress (ksi)
70 60 50
305 309 316 347
310 314
40 30 20 10 0 0.1
1
10
100
1000
Fracture Time (hr)
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Corrosion and Fouling Specific Low Temp. Oct, 01 61
Temperature (F)
Time, Temp, Material 400 350 300 250 200 150 100 50 0
347 316
0
20
40
60
80
100
120
Time to crack (hr)
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Corrosion and Fouling Specific Low Temp. Oct, 01 62
Oxygen, Chlorides Oxygen (ppm)
1000 100 10 1 0.1 0.1
1
10
100
1000
Chlorides (ppm)
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Corrosion and Fouling Specific Low Temp. Oct, 01 63
Examples • Seawater piping or exchanges • Under insulation – SS compatible insulation a must
• Anywhere SS and chlorides are present
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Corrosion and Fouling Specific Low Temp. Oct, 01 64
Alkaline Cracking
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Corrosion and Fouling Specific Low Temp. Oct, 01 65
Problem • Cracking is observed under certain conditions when carbon steel is exposed to caustic, carbonates, and amines
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Corrosion and Fouling Specific Low Temp. Oct, 01 66
Materials Affected • Carbon steel • Stainless steel
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Corrosion and Fouling Specific Low Temp. Oct, 01 67
Conditons, Caustic • Over 150oF - varies with concentration • Needs some oxygen but not a lot • Normally intergranular • Normally not branched
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Corrosion and Fouling Specific Low Temp. Oct, 01 68
Temperature (F)
Conditions, Caustic 280 260 240 220 200 180 160 140 120 100 80 60 40
Nickel Alloys Stress Relieved Carbon Steel Carbon Steel
0
10
20
30
40
50
60
Wt % NaOH
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Corrosion and Fouling Specific Low Temp. Oct, 01 69
Caustic Cracks
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Corrosion and Fouling Specific Low Temp. Oct, 01 70
Caustic Cracks
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Corrosion and Fouling Specific Low Temp. Oct, 01 71
Conditions, Carbonate • Over 100oF • Cracks may be either intergranular or transgranular • Slow growing cracks intergranular
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Corrosion and Fouling Specific Low Temp. Oct, 01 72
Conditions, Amine • Cause not completely clear • May be due to carbonate • Occurs in non-post weld heat treated material
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Corrosion and Fouling Specific Low Temp. Oct, 01 73
Solutions • Caustic – Control temperature – Proper metallurgy
• Carbonate, Amine – Stress relieve
• All related – Marginal passivation 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 74
Examples • Caustic Cracking – Boilers – Use care in Merox, crude units
• Carbonate – Downstream of downtime protected units
• Amine/Carbonate – Sour gases / Amine units 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 75
Hydrogen Damage
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 76
Low Temp Hydrogen Damage • Several terms applied – Hydrogen blistering – Hydrogen induced cracking (HIC) – Stress oriented hydrogen induced cracking (SOHIC) – Sulfide stress cracking (SSC) or hydrogen stress cracking
• All variations of same phenomenon 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 77
General Mechanism • Penetration of atomic hydrogen (H0) into steel • At low temperatures ( 7 S= in solution exceeds Fe2+ – Fe, S reaction occurs at metal surface
• Scale formed is tight and protective
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 94
Iron Sulfide • At intermediate pH (6-8) HS- ion concentration is high • Forms soluble complex ion FeSH+ • Increases iron in solution, should increase corrosion rate – Must compete with scale formation reactions
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 95
Complications • Competing reactions from chlorides, cyanides and oxygen make H2S reactions more difficult to predict • FeS + H+ + Cl- FeSH+ + Cl– Driven by the Cl- which disrupts scale
• FeS + 6NH4CN + 6H2O Fe(CN)64- + 6NH4OH +6H+ + S= – Increases Fe solubility and therefore corrosion 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 96
Black Water Corrosion Rate (mpy)
250
50000 ppm NH4Cl
200 150
5000 ppm NH 4Cl
100
0 ppm NH4Cl 50 0 0
2
4
6
8
10
pH
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 97
Black Water • Named because tail water turns black when crossing or operating in high corrosion range • UOP idealized representation – Remember this in operating your unit – Don’t cross black water region 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 98
Corrosion Rate (mpy)
Black Water 14 12 10 8 6 4 2 0 2
4
6
6.8 7.3
8
10
pH
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 99
Ammonium Bisulfide
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 100
Ammonium Bisulfide Formation • High temperature, catalyst, nitrogen, sulfur, hydrogen – 2N + 3H2 2NH3 – S + H2 H2S
• As gases cool – NH3 + H2S NH4HS
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 101
Ammonium Bisulfide Issues • Ammonium bisulfide condenses from gas to white fluffy solid – Aggressive foulant – Highly water soluble
• Water wash to combat fouling creates corrosive solution/slurry
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 102
Refinery Examples • Reactor effluent air coolers (REACs) for hydrotreaters and hydrocrackers • Sour water stripper overhead • FCC fractionation section
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 103
Solutions • Water wash – Prevent fouling – Reduce corrosivity
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 104
Operating Guidelines • Kp (mol% H2S x mol% NH3 in dry gas) – No corrosion to carbon steel if Kp < 0.02
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 105
Operating Guidelines • Header configuration / single vs. multiple water injection points – Balanced system with multiple injection points reduced corrosion – Unbalanced system • Significant corrosion at Kp > about 0.1
– Balanced system • Significant corrosion at Kp > 0.2 to 1.0 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 106
Balanced REAC
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Corrosion and Fouling Specific Low Temp. Oct, 01 107
Operating Guidelines • Water vaporization – Retain 20% (min) liquid water at injection point • Prevents fouling • Prevents dew point corrosion of HCl if present
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 108
Operating Guidelines • Ammonium bisulfide concentration in water – Unbalanced system • Significant corrosion when concentration > 2wt%
– Balanced system • Significant corrosion when concentration > 8wt%
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 109
Operating Guidelines • Velocities – Unbalanced system • Corrosion at velocities > about 3 m/s
– Balanced system • Corrosion at velocities > 6 m/s
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 110
Operating Guidelines • Alloy materials – Alloys 800, S31803, 321, and 400 have performed well – Alloy 825 should perform well – Consider polythionic acid for austenitic alloys (e.g. alloy 800) – Consider pitting failure for alloys subject to chloride pitting (e.g. alloy 800 and 321) 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 111
Operating Guidelines • Advantages of alloy materials – Increased Kp – Increased velocities (9 m/s) – Potential reduction in water wash rates
• UOP guidance is to select alloy material if Kp >0.4
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 112
Dew Point Corrosion
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Corrosion and Fouling Specific Low Temp. Oct, 01 113
Dew Point Corrosion • Normally the temperature at which liquid water forms from vapor • Often also used as the temperature at which solids precipitate from vapor – Ammonium bisulfide – Ammonium chloride
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 114
Dew Point Corrosion • First drop of liquid water contains dissolved gases in equilibrium with gas phase – Solutions can be very concentrated
• Sublimation of gas to solid may cause extensive fouling
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 115
Refinery Example • Condensation of hydrochloric acid – HCl(g) + H2O ==> H3O+ + Cl– First drop of water will be a saturated solution • pH will be in the negative range
– Crude column overhead – FCC main column overhead • Chlorides from distillation column, catalyst • Water from stripping steam in reactor, main column 2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 116
Solution • Ammonia addition to neutralize HCl in the gas phase – NH3 + HCl NH4Cl
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Corrosion and Fouling Specific Low Temp. Oct, 01 117
New Problem • NH4Cl sublimes to a solid and fouls the system
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 118
New Solution • NH4Cl is water soluble • Water wash will remove foulant
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 119
New Problem • Ammonium chloride solutions are corrosive – NH4Cl + H2O NH4+ + Cl- + H2O – NH4+ continues to react – NH4+ + H2O NH3 + H3O+
• Reaching a neutral pH requires substantial excess ammonia
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 120
The Worst Problem • Wet ammonium chloride – Not enough water to dissolve but enough to make corrosive – Foulant – Under Deposit corrosion
• If you are going to water wash - do it well
2003 ENGINEERING DESIGN SEMINAR – LIMITED DISTRIBUTION: This material is UOP LLC technical information of a confidential nature for use only by personnel within your organization requiring the information. The material shall not be reproduced in any manner or distributed for any purpose whatsoever except by written permission of UOP LLC and except as authorized under agreements with UOP LLC.
Corrosion and Fouling Specific Low Temp. Oct, 01 121
Operational Guidelines • Desalt well < 2lb salt/1000bbl • Caustic injection – 2-3% NaOH,
