Corrosion and fouling

Introduction to Low Temperature Corrosion

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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

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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

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Corrosion and Fouling Intro to low temp corr Oct, 01 3

Topics • Definitions • Electrochemistry review (thermodynamics) • Electrochemical kinetics

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Corrosion and Fouling Intro to low temp corr Oct, 01 4

Definitions

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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 – <500F (260C) – “Aqueous”

• Over 500F considered high temp – Liquid water unlikely – Cutoff temp varies with industry

• “Dry” oil environments hard to classify 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 7

Basic Corrosion Mechanism • All corrosion is electrochemistry – Low temp is generally aqueous – Fe(s) +2 H+(aq) + 2Cl-(aq) => Fe2+(aq) + H2(g) + 2Cl-(aq)

• Keep track of ions and states

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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

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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

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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

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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

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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

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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?

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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

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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

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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

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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

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 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 – <500F (260C) – “Aqueous”

• Over 500F considered high temp – Liquid water unlikely – Cutoff temp varies with industry

• “Dry” oil environments hard to classify 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 4

Basic Corrosion Mechanism

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Corrosion and Fouling Intro to High Temp. Oct, 01 5

Basic Corrosion Mechanism • All corrosion is electrochemistry – High temperature corrosion is typically a direct reaction between species (unlike low temperature corrosion which is a reaction between ions – 2Fe(s) + O2(g) <==> 2FeO(s)

• Keeping track of states not so important 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 6

Basic Corrosion Mechanism • Result of high temperature corrosion is normally a scale • Scale growth normally due to diffusion of cations and/or anions through the scale

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Corrosion and Fouling Intro to High Temp. Oct, 01 7

Scale Growth Cation Diffusion Scale

Scale O2M2+

Metal

Metal

Metal

O-O

Scale 2eO M2+ O

O

Anion Diffusion Scale

M2+

Scale O2-

Metal

Metal

Metal

O-O

Scale 2e-

O2M2+

O

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O

Corrosion and Fouling Intro to High Temp. Oct, 01 8

Kinetics

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Corrosion and Fouling Intro to High Temp. Oct, 01 9

Scale Growth Rate • Because diffusion path gets longer as scales grow, growth is normally parabolic – Scale thickness proportional to square root of time

• Other rate laws possible • Linear if scale flakes off

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Corrosion and Fouling Intro to High Temp. Oct, 01 10

Scale Growth Rate 12 Thickness

10 8 6 4 2 0 0

50

100

Time

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Corrosion and Fouling Intro to High Temp. Oct, 01 11

Evaluation of High Temperature Corrosion Damage

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Corrosion and Fouling Intro to High Temp. Oct, 01 12

Damage Evaluation • Weight gain • Weight loss • Scale thickness • Total depth of attack

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Corrosion and Fouling Intro to High Temp. Oct, 01 13

Weight Gain • Good for adherent scales • In lab can be continuously measured – good for corrosion mechanism determination

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Corrosion and Fouling Intro to High Temp. Oct, 01 14

Weight Loss • Good for non-adherent scales • Scale removal still an involved process

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Corrosion and Fouling Intro to High Temp. Oct, 01 15

Scale Thickness • An indicator of corrosion rate – Doesn’t really tell rate of metal loss or extent of damage

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Corrosion and Fouling Intro to High Temp. Oct, 01 16

Total Depth of Attack • Measures total metal compromised by corrosion • Total depth of attack = (To -Tm) / 2

To

Tm

Internal Penetration

Metal Loss

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Corrosion and Fouling Intro to High Temp. Oct, 01 17

Chemical Composition of Scale

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Corrosion and Fouling Intro to High Temp. Oct, 01 18

Chemical Composition of Scale • Scale Composition varies – Position in scale – Composition of alloy – Composition of environment – Temperature

• Analysis of scale very good diagnostic tool

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Corrosion and Fouling Intro to High Temp. Oct, 01 19

Chemical Analysis of Scales • Energy Dispersive Spectroscopy / Wavelength Microprobe – Scanning electron microscope techniques which give elemental compositions at a “spot” on the surface of the scale

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Corrosion and Fouling Intro to High Temp. Oct, 01 20

Chemical Analysis of Scales • X ray Diffraction – Analyzes bulk scale, gives crystal structure – Crystal structure important

• Some crystal structures give tight adherent scales others flaky porous ones

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Corrosion and Fouling Intro to High Temp. Oct, 01 21

Low Temperature Corrosion, Specific Mechanisms of Interest in Refineries

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Corrosion and Fouling Specific Low Temp. Oct, 01 1

Contents • • • • • •

Sensitization (general) Rapid sensitization Weld Decay Knife Line Attack Slow sensitization Polythionic Acid Stress Corrosion Cracking

• Chloride Stress Corrosion Cracking • Alkaline Cracking • Hydrogen damage • Black Water • Ammonium Bisulfide • Dew Point Corrosion

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Corrosion and Fouling Specific Low Temp. Oct, 01 2

Sensitization

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Corrosion and Fouling Specific Low Temp. Oct, 01 3

Sensitization • Thermal process by which chromium and carbon react to form chrome carbides • Time and temperature are important • Not a corrosion mechanism

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Corrosion and Fouling Specific Low Temp. Oct, 01 4

Materials Affected • Austenitic stainless steels – primarily 304, 316, 317 – 321, 347 after long term exposure and specific welding and heat treat conditions – 904 - potentially after long exposure

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Corrosion and Fouling Specific Low Temp. Oct, 01 5

Cause • Stainless steel must have over about 14% Cr to be stainless • 300 series stainless has about 18% Cr – Cr must be in solution (not bound in CrxCy) – Not a lot of “extra” chrome available

• Chemical reactions involving Cr and C 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 Specific Low Temp. Oct, 01 6

Cause • Reduction in the available free Chromium to below that required to maintain passivation in the grain boundary area – i.e. grain boundaries become “non stainless” – corrosive agent will corrode grain boundaries as if they were carbon steel

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Corrosion and Fouling Specific Low Temp. Oct, 01 7

Chromium/Carbon Reactions • Below 950oF (510oC) – Carbon diffusivity slow – Carbon/chromium reaction kinetics slow • Nothing happens over the short term

• Below 700oF (370oC) – Diffusivity and kinetics very slow • Nothing happens over the long term

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Corrosion and Fouling Specific Low Temp. Oct, 01 8

Chromium/Carbon Reactions • Between 950oF and 1450oF (510 and 785oC) – Carbon diffusivity high – Carbon/chromium reaction kinetics high – Chromium carbides thermodynamically stable compared to dissolved chromium and carbon – Chromium carbides precipitate

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Corrosion and Fouling Specific Low Temp. Oct, 01 9

Chromium/Carbon Reactions • Above 1450oF (785oC) – Carbon diffusivity high – Carbon/chromium reaction kinetics high – Chromium carbides thermodynamically UNstable compared to dissolved chromium and carbon – No precipitate formed

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Corrosion and Fouling Specific Low Temp. Oct, 01 10

Sensitization Process • Dissolved carbon ==> 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

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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 (<400oF or 204oC) molecular hydrogen does not react with steel and does not penetrate • Atomic hydrogen comes from any wet corrosion reactions which makes H2 – Often associated with H2S 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 78

General Mechanism Cont. • Atomic Hydrogen generated by corrosion normally combines to form molecular hydrogen and escapes into solution • Some doesn’t • Recombination poisons promote penetration – CN-, As, S2-

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Corrosion and Fouling Specific Low Temp. Oct, 01 79

Hydrogen Blistering • Low tensile strength steel (high ductility) • Voids and inclusions – Particularly MnS stringers

• Atomic hydrogen finds void and recombines to molecular hydrogen

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Corrosion and Fouling Specific Low Temp. Oct, 01 80

Hydrogen Blistering H0 Void or Inclusion

H+

H2 H0

H+

H0

H+

H2 S2H0 Steel

H+

Solution

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Corrosion and Fouling Specific Low Temp. Oct, 01 81

Hydrogen Induced Cracking • Starts at elongated MnS inclusions • Cracks start at tips of blisters and grow parallel to steel surface • Link by growing perpendicular • Want low Mn and S steel with shape controlled inclusions

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Corrosion and Fouling Specific Low Temp. Oct, 01 82

Hydrogen Induced Cracking H2 H2 H2

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Corrosion and Fouling Specific Low Temp. Oct, 01 83

Stress Oriented Hydrogen Induced Cracking (SOHIC) • Starts from wet corrosion producing H0 which diffuses in • H0 collect at lattice defects but don’t necessarily form voids • Cracks form in plane of inclusions and link in plane perpendicular to stress • Often at hard spots near welds 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 84

Stress Oriented Hydrogen Induced Cracking

Stress

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Stress

Corrosion and Fouling Specific Low Temp. Oct, 01 85

Sulfide Stress Cracking • High strength steel or hard welds • Stress or residual stress • Temperature and hydrogen flux affect cracking • Unlike other types of hydrogen damage significant wet corrosion is not required • Heat treat steel, welds < HRc 22 (HV 248) 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 86

Sulfide Stress Cracking, Hydrogen Stress Cracking

Stress

Stress

High Strength Steel

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Corrosion and Fouling Specific Low Temp. Oct, 01 87

Examples • HF units • Sour water strippers • FCC – HP and LP separators – Stripper tower overhead

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Corrosion and Fouling Specific Low Temp. Oct, 01 88

What to do about it • Minimize wet corrosion (generates H0) • Minimize recombination poisons (H2S etc.) • Use low Mn, S steels with inclusion shape control • Avoid high strength steels • Heat treat welds to below HRc 22

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Corrosion and Fouling Specific Low Temp. Oct, 01 89

Black Water The Effect of pH on Sulfide Scales

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Corrosion and Fouling Specific Low Temp. Oct, 01 90

Black Water • pH, chlorides and cyanides have dramatic effect on corrosivity of wet H2S environments • Many complex equilibria – Extent to which sulfide scale protects metal from further corrosion depends on equilibria

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Corrosion and Fouling Specific Low Temp. Oct, 01 91

Hydrogen Sulfide • H2S <==> H+ + HS• HS- <==> H+ + S= • Position of equilibrium depends on pH

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Corrosion and Fouling Specific Low Temp. Oct, 01 92

Iron Sulfide • Iron sulfide very low solubility • Low pH, H2S almost all in molecular form – Fe corrodes due to H+ present – Fe finds what little S= is present and precipitates in solution

• Scale formation is minimal and porous • Corrosion rate is high 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 93

Iron Sulfide • At higher pH > 7 S= in solution exceeds Fe2+ – Fe, S reaction occurs at metal surface

• Scale formed is tight and protective

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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

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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

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Corrosion and Fouling Specific Low Temp. Oct, 01 99

Ammonium Bisulfide

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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

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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

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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

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Corrosion and Fouling Specific Low Temp. Oct, 01 103

Solutions • Water wash – Prevent fouling – Reduce corrosivity

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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

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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

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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%

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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

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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

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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

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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

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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

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Corrosion and Fouling Specific Low Temp. Oct, 01 118

New Solution • NH4Cl is water soluble • Water wash will remove foulant

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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

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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

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Corrosion and Fouling Specific Low Temp. Oct, 01 121

Operational Guidelines • Desalt well < 2lb salt/1000bbl • Caustic injection – 2-3% NaOH, <4lb 1000bbl, <300F

• Automate pH control – Aim for 6 - 6.5 in crude units, 7-9 FCCs

• Continuous water wash – At least 10% free water 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, 01 122

Specific High Temperature Corrosion Mechanisms of Interest in Refineries

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Corrosion and Fouling Specific High Temp. Oct 2003 1

Topics • Oxidation • Carburization • Metal Dusting • Sulfidation • Hydrogen • Liquid Metal • Naphthenic Acid 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 High Temp. Oct 2003 2

Specific Mechanisms • The corrosion problems addressed in this section are of specific concern in refineries • Some problems discussed are a general class while others are quite specific

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Corrosion and Fouling Specific High Temp. Oct 2003 3

Specific Mechanisms • This section will attempt to provide specific corrosion conditions and control actions which may be taken • Many of these corrosion problems are found in more than one unit – Generally the causes and controls are similar – Differences will be pointed out 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 High Temp. Oct 2003 4

Oxidation

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Corrosion and Fouling Oxidation July, 02 1

Topics • Oxidation issues • Refinery examples • Control techniques • References

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Corrosion and Fouling Oxidation July, 02 2

Oxidation Issues

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Corrosion and Fouling Oxidation July, 02 3

Oxidation • Most common high temperature corrosion • Air is not the same as combustion atmospheres – Combustion most common – Air most studied

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Corrosion and Fouling Oxidation July, 02 4

Oxidation Issues • Oxygen concentration • Alloy composition • Temperature

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Corrosion and Fouling Oxidation July, 02 5

Oxygen Concentration • Oxygen must exceed thermodynamic values • After oxygen sufficient, little effect on corrosion rate. Corrosion rate function of scale thickness • Oxygen may be from CO/CO2, H2/H2O equilibria – 2CO + O2 <==> 2CO2 – 2H2 + O2 <==> 2H2O 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 Oxidation July, 02 6

Oxygen Scales • Scale composition varies with – alloy composition – position in scale – temperature

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Corrosion and Fouling Oxidation July, 02 7

Oxygen Scales O2 O2Fe2+

Fe2O3 Fe3+

Fe2+

O2-

Fe3O4 FeO

Fe2+

Fe3+

Fe Above 570C

Below 570C

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Corrosion and Fouling Oxidation July, 02 8

Parabolic rate constant

Scale Chem and Corrosion Rate 1.E-06

FeO/Fe3O4/Fe2O3 (Fe)

Fe-Cr oxide/FeO/Fe3O4/Fe2O3 (Fe-2Cr) (Fe,Cr)O3/Fe2O3 (Fe-9Cr)

1.E-07 1.E-08

FeFe (2-n) CrnO4(internal)/ Cr2O3/Fe3O4/Fe2O3 (Fe-16 Cr)

1.E-09 1.E-10

Cr2O3 (Fe-28Cr)

1.E-11 0

10

20

30

40

50

60

70

80

Wt % Cr

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Corrosion and Fouling Oxidation July, 02 9

Oxidation Rates of Alloys (Air) 1

100

2 3

10

4

1 = Carbon Steel 2 = 1 Cr - 1 /2 Mo 3 = 2 Cr - 1 /2 Mo 4 = 5 Cr - 1 /2 Mo 5 = 7 Cr - 1 /2 Mo 6 = 5 Cr - 1 /2 Mo - 1 1 /2 Si 7 = 9 Cr - 1 Mo 8 = TP 304 Stainless Steel 9 = TP 309/310 Stainless Steel 5 6 7 8

1.0

0.1

9

1000

1100

1200

1300 1400 1500 Temperature, ºF

1600

1700

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Corrosion and Fouling Oxidation July, 02 10

Metal Temperature, a Key Issue • Metal temperature, not process temperature or flame temperature is critical • In fired heaters if heat transfer drops metal temperatures rise – Watch for coking or fouling • Decreases heat transfer • Increases firing rate

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Corrosion and Fouling Oxidation July, 02 11

Refinery Examples

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Corrosion and Fouling Oxidation July, 02 12

Refinery Examples • Fired heaters

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Corrosion and Fouling Oxidation July, 02 13

Control Techniques

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Corrosion and Fouling Oxidation July, 02 14

Control Techniques • Decrease temperature • Increase alloy – Cr, Ni, Al, Si

• Control environmental contaminants – Metals, e.g. V, in fuel – Sulfur

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Corrosion and Fouling Oxidation July, 02 15

Carburization

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 1

Topics • Carburization Issues • Refinery Examples • Control Techniques

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 2

Carburization Issues

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 3

Carburization • Ingress of carbon into metal • Occurs when carbon activity in the environment is greater than in the metal • Identical to carburization heat treatment – Increased strength, Decreased ductility

• Kinetic and thermodynamic issues • Consider ≈500C, bigger issue 1000C 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 Carb., Coke, Metal Dust Oct 2003 4

Carbon Activity • Governed by several equilibria – CO + H2 <==> C + H2O – 2CO <==> C + 2H2O – CH4 <==> C + 2H2

• Water and hydrogen reduce tendency to carburize

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 5

Carburization • Causes the formation of carbides in grain boundaries (primarily) and grains • Factors affecting carburization – Temperature – C diffusion rate – Alloy (diffusion rate and existence of scale) – C solubility – C activity gradient 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 Carb., Coke, Metal Dust Oct 2003 6

Carburization Resistance • Complex – Without scale follows parabolic rate law • Diffusion of C through metal

– With scale much slower

• Cr, Ni, Si affect rate – Formation of scales – Diffusion of C 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 Carb., Coke, Metal Dust Oct 2003 7

Material Selection • Select specifically for environment and temperature – Both affect which oxides will be stable – Stable oxide highly desirable

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 8

Refinery Examples

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 9

Refinery Examples • Furnace tubes (in general) • Ethylene pyrolysis tubes • Ethylene and Olefin plant pigtails

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 10

Control Techniques

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 11

Control Techniques • Keep temperature low • Select best metallurgy for conditions • Maintain conditions – Temperature and environment

• Maintain oxide scale • Maintain sulfide scale – See section of sulfidation 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 Carb., Coke, Metal Dust Oct 2003 12

Metal Dusting

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 1

Topics • Metal Dusting Issues • Refinery Examples • Control Techniques

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 2

Metal Dusting Issues

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 3

Metal Dusting • Pitting, thinning and wastage of metal • Fine powder residue – Metals, Carbides, Oxides

• Area beneath pits will be carburized

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 4

Metal Dusting Environments • 480 to 900oC (900 to 1650oF) • Occurs first in “no flow” locations • CO, H2 environments – Water in environment should reduce tendency for dusting but sometimes makes it worse

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 5

Carbon Adsorption Environment H

H-H

H

O C

C-O

H-H C-O

H

H O C

Metal

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 6

Metal Dusting Mechanism • Mechanism not fully understood – Carburization form Fe3C – C diffusion in Fe3C is slow, graphite forms on surface – Fe3C decomposes • Graphite grows into metal • Iron “particles” diffuse out through graphite, catalyze coke formation 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 Carb., Coke, Metal Dust Oct 2003 7

Metal Dusting Mechanism • Many alternate mechanisms e.g. – Formation of chromium carbides depletes Cr in solution. Remaining Fe Ni matrix may be easily corroded by environment

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 8

Materials Affected • Carbon steel • Cr Mo steel • Stainless steel • Iron based alloys • Nickel based alloys

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 9

Refinery Examples

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 10

Refinery Examples • Synthesis gas reactors • Butane dehydrogenation • Reformers (petroleum, methanol, ammonia)

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 11

Control Techniques

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Corrosion and Fouling Carb., Coke, Metal Dust Oct 2003 12

Control Techniques • Find a resistant alloy • Minimize carbon activity (if possible) • Minimize “dead spots” • Sulfur addition? • Complete SiO2, Cr2O3, or Al2O3 scales help – Kinetics of scale formation at low end of temp range may be a 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 Carb., Coke, Metal Dust Oct 2003 13

Sulfidation

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Corrosion and Fouling Sulfidation July, 02 1

Topics • Definitions • Thermodynamics • Kinetics • Prediction tools

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Corrosion and Fouling Sulfidation July, 02 2

Definitions

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Corrosion and Fouling Sulfidation July, 02 3

Sulfidation • Use care in discussing. Means different things to different people – Injection of S to form a protective scale – Formation of S rich scale – Loss of metal grains from the surface of metal due to intergranular corrosion – Penetration of S along grain boundaries 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 Sulfidation July, 02 4

Sulfidation • The interaction of sulfur and metal, even for the purpose of forming a protective sulfide scale is corrosive and some metal is lost • Sulfide scales separate metal from environment and eliminate metal catalyzed coking • Sulfide scales resist diffusion of carbon and reduce carburization 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 Sulfidation July, 02 5

Thermodynamics

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Corrosion and Fouling Sulfidation July, 02 6

Thermodynamics Log PH2O/PH2 and PCO2/PCO -10

-6

-8

-4

-2

0

2

4

6

8

-8

-4

0

Cr2S3 CrS

N Ni iS O

F Fe eS O

NiS Ni

FeS Fe

CrS Cr

-16 -36

Ni NiO

-12

Fe FeO

3

Cr Cr S 2O

-8

Cr Cr2O3

Log PS2 Atm

-4

3

C Cr r2 S 2O 3

o

-32

-28

-24

-20

-16

-12

Log P02 Atm

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Corrosion and Fouling Sulfidation July, 02 7

Life Expectancy Based on Scale CrS Sulfidation Log PS2

Limited Life

Cr

Cr2O3

Resistant

Generally Resistant Log PO2

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Corrosion and Fouling Sulfidation July, 02 8

Scale Composition • Varies with environment and alloy composition • Want single layer, chromium rich adherent scale • Often get multiple layer, less than fully adherent scale

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Corrosion and Fouling Sulfidation July, 02 9

Kinetics

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Corrosion and Fouling Sulfidation July, 02 10

Sulfidation Kinetics • Faster than oxidation • Normally parabolic – Diffusion of metal ions through scale – S does not diffuse inward

• Thick scales spall off – Linear (very fast) kinetics

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Corrosion and Fouling Sulfidation July, 02 11

Breakaway Corrosion • Preexisting oxide scale or oxygen/sulfur environment • Patchy sulfide scales form inside and outside of oxide • Sulfur penetration along grain boundaries • Corrosion rate initially moderate. Dramatically accelerates after incubation. 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 Sulfidation July, 02 12

Prediction Tools

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Corrosion and Fouling Sulfidation July, 02 13

Sulfur Corrosion Rates • Two sets of corrosion curves • McConomy (API) – Based on total sulfur – UOP uses variation of this set of curves

• Couper Gorman – Based on hydrogen/hydrogen sulfide

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Corrosion and Fouling Sulfidation July, 02 14

Hot H2S Corrosion 10

0.1

Carbon Steel 50 Corrosion 30 20 Rate 40 mpy 10 25 1 3 5 15 2

Corrosion Rate mpy

1 Mole % H2S

Mole % H2S

1

10

3 2 1 .6

0.1

.4 .2

0.01

0.01

4

No Corrosion

No Corrosion

18 8 Stainless

0.001

0.001 400

600

800

1000

Temperature F

400

600

800

1000

Temperature F

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Corrosion and Fouling Sulfidation July, 02 15

High Temp Sulfur Corrosion

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Corrosion and Fouling Sulfidation July, 02 16

High Temperature Hydrogen

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Corrosion and Fouling Hydrogen July, 02 1

Topics • Mechanism • Refinery examples • Control techniques

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Corrosion and Fouling Hydrogen July, 02 2

Mechanism

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Corrosion and Fouling Hydrogen July, 02 3

Hydrogen • At high temperatures H2 dissociates on the metal surface to form 2 H0 • H0 can diffuse through metal (just the same as at low temperature only faster) • Causes two problems – Hydrogen attack – Hydrogen embrittlement 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 Hydrogen July, 02 4

Hydrogen Attack • Above 232oC (450oF) Hydrogen will decarburize carbon and low alloy steels – Reduces mechanical properties

• 4H + C ==> CH4 • Methane can’t diffuse - acts like low temp hydrogen blister 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 Hydrogen July, 02 5

Hydrogen Attack • Extent of hydrogen attack determined by available carbon • Chromium carbides more stable than iron carbides – Resist reaction of hydrogen to form methane

• As temperature increases, more chromium is required to resist hydrogen attack 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 Hydrogen July, 02 6

Nelson Curve (API-971) 1400

External Decarburization

1300 1200

Internal Decarburization

6 Cr-0.5 Mo

1100 3 Cr-1Mo or 2.25 Cr-1Mo-V

1000 900 800

2.25 Cr-0.5 Mo

1 Cr

700

1 or 1.25 Cr-0.5 Mo

600 500 400

Carbon Steel

0

500

1000

1500

2000

2500

3000

Hydrogen Pressure (psia)

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Corrosion and Fouling Hydrogen July, 02 7

Carbon 1/2 Moly • Used to be specific zone of acceptability on Nelson curves • Later found to be no better than carbon steel • UOP position – Should be replaced – If not, thorough and frequent inspection • Cracks random and grow quickly, inspection not really practical 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 Hydrogen July, 02 8

Hydrogen Embrittlement • Hydrogen solubility greater at high temps • If hydrogen rich metal cooled too quickly, supersaturates – Ductility dramatically reduced – Normally appears only below 149oC (300oF)

• Cooling rates between 28-56oC/hr (50100oF) normally acceptable 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 Hydrogen July, 02 9

Refinery Examples

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Corrosion and Fouling Hydrogen July, 02 10

Refinery Examples • Hydrotreaters • Hydrocrackers

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Corrosion and Fouling Hydrogen July, 02 11

Control Techniques

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Corrosion and Fouling Hydrogen July, 02 12

Control Techniques • Select proper alloys • Monitor metal temperatures – Fouling and changes in throughput will affect metal temperature and hydrogen attack

• Control cooling rates

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Corrosion and Fouling Hydrogen July, 02 13

Liquid Metal Embrittlement

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Corrosion and Fouling Liq. Metal Embrittlement July, 02 1

Topics • Mechanisms • Refinery examples • Control techniques

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 Liq. Metal Embrittlement July, 02 2

Mechanisms

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Corrosion and Fouling Liq. Metal Embrittlement July, 02 3

Liquid Metal Embrittlement • Related to stress corrosion cracking • Certain combinations big problem – Others no problem

• Cracking is essentially instantaneous

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Corrosion and Fouling Liq. Metal Embrittlement July, 02 4

Liquid Metal Embrittlement • Not the same as liquid metal corrosion • Generally little solubility of the two materials in either solid or liquid forms • Generally no intermetallic compounds • Theory is adsorbed metal weakens base metal bonds and allows crack to propagate with lower than normal stress 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 Liq. Metal Embrittlement July, 02 5

Refinery Examples

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Corrosion and Fouling Liq. Metal Embrittlement July, 02 6

Refinery Examples • Mercury – Aluminum/water – 302, 304, 321, 347 – Copper and many brasses – Nickel – Monel – Alloy 600 – Titanium 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 Liq. Metal Embrittlement July, 02 7

Refinery Examples • Zinc (galvanizing, primers) – Austenitic stainless steel • Cracks are instant and very severe

– Ferritic steels • Some slow degradation of properties

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Corrosion and Fouling Liq. Metal Embrittlement July, 02 8

Control Techniques

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Corrosion and Fouling Liq. Metal Embrittlement July, 02 9

Control Techniques • Avoid liquid metal and base metal contact – Oxide scales good unless ruptured

• Consider fire scenario – Zinc paints should not be used on stainless – Don’t grind galvanized steel near stainless (dust will melt in a fire and embrittle

• Consider welding – Don’t weld galvanized to stainless 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 Liq. Metal Embrittlement July, 02 10

Naphthenic Acids

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Corrosion and Fouling Naphthenic Acid July, 02 1

Topics • Corrosion conditions • Refinery examples • Control techniques

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Corrosion and Fouling Naphthenic Acid July, 02 2

Corrosion Conditions

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Corrosion and Fouling Naphthenic Acid July, 02 3

Naphthenic Acids – Not a single acid

• MW varies greatly – Normally heavy

O -R-C-O-H =

• Class of acids

R = Hydrocarbon chain 1 or more 5 or 6 member rings

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Corrosion and Fouling Naphthenic Acid July, 02 4

Naphthenic Acid Corrosion • Direct reaction between metal and acid – Water and ionization not required

• Corrosive temperature range 450-750oF – Max 520-535oF

• Leaves metal bare (no scale) • Sharp ridges and grooves • Sulfur scale 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 Naphthenic Acid July, 02 5

Corrosion Prediction • TAN best method readily available – Not very good – Acids other than Naphthenic acids part of TAN • Other acids don’t corrode by same method

– <0.5 TAN normally considered OK • Works part of the time

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Corrosion and Fouling Naphthenic Acid July, 02 6

Corrosion Prediction • For different crudes – Ratio of naphthenic acids to other acids varies – Molecular weight of naphthenic acids varies

• For crudes with only naphthenic acids and only a narrow range of molecular weights even a very low TAN will give high corrosion in one cut 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 Naphthenic Acid July, 02 7

Sulfur Corrosion vs Naphthenic Acid Corrosion • Sulfur corrosion – Shallow scoops – Scale – Resolved by 410 metallurgy

• Naphthenic acid – Sharp ridges – Bare metal – Not resolved by 410 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 Naphthenic Acid July, 02 8

Refinery Examples

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 Naphthenic Acid July, 02 9

Refinery Examples • Primarily crude units and vacuum units – Areas where temperatures are between 450-750oF

• Feed heaters and piping of downstream units – Same temperature range – Naphthenic acids destroyed by catalysts and temperatures over 750oF

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Corrosion and Fouling Naphthenic Acid July, 02 10

Control Techniques

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 Naphthenic Acid July, 02 11

Control Techniques • Blend crudes to reduce TAN – Not perfect solution but best available – Check acid in individual cuts

• Use 317 ss in areas subject to naphthenic acid 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 Naphthenic Acid July, 02 12