Corrosion and Corrosion Control : An Introduction to Corrosion Science and Engineering
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Corrosion and Corrosion Control : An Introduction to Corrosion Science and Engineeringand Engineering FOURTH EDITION
CANMET Materials Technology Laboratory Natural Resources Canada
Herbert H. Uhlig Former Professor Emeritus
Department of Materials Science and Engineering Massachusetts Institute of Technology
A JOHN WILEY & SONS, INC., PUBLICATION
CORROSION AND CORROSION CONTROL
CORROSION AND CORROSION CONTROL
and Engineering FOURTH EDITION
CANMET Materials Technology Laboratory Natural Resources Canada
Herbert H. Uhlig Former Professor Emeritus
Department of Materials Science and Engineering Massachusetts Institute of Technology
A JOHN WILEY & SONS, INC., PUBLICATION
Copyright © 2008 by John Wiley & Sons, Inc. All right reserved
Published by John Wiley & Sons, Inc., Hoboken New Jersey Published simultaneously in Canada
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978)750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifi cally disclaim any implied warranties of merchantability or fi tness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profi t or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com.
Library of Congress Cataloging-in-Publication Data:
Uhlig, Herbert Henry, 1907– Corrosion and corrosion control : an introduction to corrosion science and engineering / Herbert H. Uhlig, R. Winston Revie.—4th ed. p. cm. Includes bibliographical references and index. ISBN 978-0-471-73279-2 (cloth) 1. Corrosion and anti-corrosives. I. Revie, R. Winston (Robert Winston), 1944– II. Title. TA462.U39 2008 620.1′1223–dc22
2007041578
10 9 8 7 6 5 4 3 2 1
1 DEFINITION AND IMPORTANCE OF CORROSION 1
1.1 Defi nition of Corrosion 1 1.1.1 Corrosion Science and Corrosion Engineering 1
1.2 Importance of Corrosion 2 1.3 Risk Management 5 1.4 Causes of Corrosion 6
1.4.1 Change in Gibbs Free Energy 6 1.4.2 Pilling–Bedworth Ratio 6
References 6 General References 7 Problems 7
2 ELECTROCHEMICAL MECHANISMS 9
2.1 The Dry-Cell Analogy and Faraday’s Law 9 2.2 Defi nition of Anode and Cathode 11 2.3 Types of Cells 13 2.4 Types of Corrosion Damage 15 References 18 General References 19 Problems 19
3 THERMODYNAMICS: CORROSION TENDENCY AND ELECTRODE POTENTIALS 21
3.1 Change of Gibbs Free Energy 21 3.2 Measuring the Emf of a Cell 22 3.3 Calculating the Half-Cell Potential—The Nernst Equation 22 3.4 The Hydrogen Electrode and the Standard Hydrogen Scale 24 3.5 Convention of Signs and Calculation of Emf 25
vi CONTENTS
3.6 Measurement of pH 28 3.7 The Oxygen Electrode and Differential Aeration Cell 28 3.8 The Emf and Galvanic Series 30 3.9 Liquid Junction Potentials 33 3.10 Reference Electrodes 34
3.10.1 Calomel Reference Electrode 35 3.10.2 Silver–Silver Chloride Reference Electrode 36 3.10.3 Saturated Copper–Copper Sulfate Reference
Electrode 36 References 37 General References 38 Problems 38 Answers to Problems 40
4 THERMODYNAMICS: POURBAIX DIAGRAMS 43
4.1 Basis of Pourbaix Diagrams 43 4.2 Pourbaix Diagram for Water 44 4.3 Pourbaix Diagram for Iron 45 4.4 Pourbaix Diagram for Aluminum 47 4.5 Pourbaix Diagram for Magnesium 48 4.6 Limitations of Pourbaix Diagrams 49 References 50 General References 50 Problems 50 Answers to Problem 51
5 KINETICS: POLARIZATION AND CORROSION RATES 53
5.1 Polarization 53 5.2 The Polarized Cell 54 5.3 How Polarization Is Measured 56
5.3.1 Calculation of IR Drop in an Electrolyte 58 5.4 Causes of Polarization 58 5.5 Hydrogen Overpotential 63 5.6 Polarization Diagrams of Corroding Metals 66 5.7 Infl uence of Polarization on Corrosion Rate 68 5.8 Calculation of Corrosion Rates from Polarization Data 71 5.9 Anode–Cathode Area Ratio 73 5.10 Electrochemical Impedance Spectroscopy 75
CONTENTS vii
5.11 Theory of Cathodic Protection 77 References 79 General References 80 Problems 80 Answers to Problems 82
6 PASSIVITY 83
6.1 Defi nition 83 6.2 Characteristics of Passivation and the Flade Potential 84 6.3 Behavior of Passivators 88
6.3.1 Passivation of Iron by HNO 3 89
6.4 Anodic Protection and Transpassivity 90 6.5 Theories of Passivity 92
6.5.1 More Stable Passive Films with Time 95 6.5.2 Action of Chloride Ions and Passive–Active Cells 96
6.6 Critical Pitting Potential 97 6.7 Critical Pitting Temperature 99 6.8 Passivity of Alloys 100
6.8.1 Nickel–Copper Alloys 103 6.8.2 Other Alloys 108
6.9 Effect of Cathodic Polarization and Catalysis 108 References 109 General References 111 Problems 112 Answers to Problems 113
7 IRON AND STEEL 115
7.1 Introduction 115 7.2 Aqueous Environments 116
7.2.1 Effect of Dissolved Oxygen 116 7.2.2 Effect of Temperature 120 7.2.3 Effect of pH 120 7.2.4 Effect of Galvanic Coupling 127 7.2.5 Effect of Velocity on Corrosion in Natural Waters 129 7.2.6 Effect of Dissolved Salts 131
7.3 Metallurgical Factors 138 7.3.1 Varieties of Iron and Steel 138 7.3.2 Effects of Composition 138
viii CONTENTS
7.3.3 Effect of Heat Treatment 142 7.4 Steel Reinforcements in Concrete 143 References 145 General References 147 Problems 147 Answers to Problems 148
8 EFFECT OF STRESS 149
8.1 Cold Working 149 8.2 Stress-Corrosion Cracking 150
8.2.1 Iron and Steel 151 8.3 Mechanism of Stress-Corrosion Cracking of Steel and
Other Metals 156 8.3.1 Electrochemical Dissolution 157 8.3.2 Film-Induced Cleavage 158 8.3.3 Adsorption-Induced Localized Slip 158 8.3.4 Stress Sorption 158 8.3.5 Initiation of Stress-Corrosion Cracking and
Critical Potentials 161 8.3.6 Rate of Crack Growth (Fracture Mechanics) 162
8.4 Hydrogen Damage 166 8.4.1 Mechanism of Hydrogen Damage 167 8.4.2 Effect of Metal Flaws 170
8.5 Radiation Damage 172 8.6 Corrosion Fatigue 173
8.6.1 Critical Minimum Corrosion Rates 177 8.6.2 Remedial Measures 178 8.6.3 Mechanism of Corrosion Fatigue 179
8.7 Fretting Corrosion 180 8.7.1 Mechanism of Fretting Corrosion 182 8.7.2 Remedial Measures 184
References 185 General References 188 Problems 190 Answers to Problems 190
9 ATMOSPHERIC CORROSION 191
CONTENTS ix
9.3 Corrosion-Product Films 192 9.4 Factors Infl uencing Corrosivity of the Atmosphere 195
9.4.1 Particulate Matter 196 9.4.2 Gases in the Atmosphere 197 9.4.3 Moisture (Critical Humidity) 199
9.5 Remedial Measures 201 References 202 General References 203 Problems 204
10 CORROSION IN SOILS 205
10.1 Introduction 205 10.2 Factors Affecting the Corrosivity of Soils 206 10.3 Bureau of Standards Tests 207
10.3.1 Pitting Characteristics 208 10.4 Stress-Corrosion Cracking 210 10.5 Remedial Measures 211 References 212 General References 212
11 OXIDATION 215
11.1 Introduction 215 11.2 Initial Stages 216 11.3 Thermodynamics of Oxidation: Free
Energy–Temperature Diagram 218 11.4 Protective and Nonprotective Scales 218
11.4.1 Three Equations of Oxidation 220 11.5 Wagner Theory of Oxidation 223 11.6 Oxide Properties and Oxidation 224 11.7 Galvanic Effects and Electrolysis of Oxides 227 11.8 Hot Ash Corrosion 229 11.9 Hot Corrosion 229 11.10 Oxidation of Copper 230
11.10.1 Internal Oxidation 231 11.10.2 Reaction with Hydrogen (“Hydrogen Disease”) 231
11.11 Oxidation of Iron and Iron Alloys 232 11.12 Life Test for Oxidation-Resistant Wires 233 11.13 Oxidation-Resistant Alloys 234
11.13.1 Reactive Element Effect (REE) 234
x CONTENTS
11.13.2 Chromium–Iron Alloys 235 11.13.3 Chromium–Aluminum–Iron Alloys 236 11.13.4 Nickel and Nickel Alloys 236 11.13.5 Furnace Windings 237
References 237 General References 239 Problems 239 Answers to Problems 240
12 STRAY-CURRENT CORROSION 241
12.1 Introduction 241 12.2 Sources of Stray Currents 242 12.3 Quantitative Damage by Stray Currents 244 12.4 Detection of Stray Currents 245 12.5 Soil-Resistivity Measurement 246 12.6 Means for Reducing Stray-Current Corrosion 246 References 247 General References 247 Problems 247 Answers to Problems 249
13 CATHODIC PROTECTION 251
13.1 Introduction 251 13.2 Brief History 252 13.3 How Applied 253
13.3.1 Sacrifi cial Anodes 254 13.4 Combined Use with Coatings 255 13.5 Magnitude of Current Required 257 13.6 Anode Materials and Backfi ll 258
13.6.1 Overprotection 259 13.7 Criteria of Protection 260
13.7.1 Potential Measurements 260 13.7.2 Doubtful Criteria 262 13.7.3 Position of Reference Electrode 262
13.8 Economics of Cathodic Protection 263 13.9 Anodic Protection 263 References 265 General References 265
CONTENTS xi
14 METALLIC COATINGS 269
14.1 Methods of Application 269 14.2 Classifi cation of Coatings 271 14.3 Specifi c Metal Coatings 272
14.3.1 Nickel Coatings 272 14.3.2 Lead Coatings 274 14.3.3 Zinc Coatings 274 14.3.4 Cadmium Coatings 276 14.3.5 Tin Coatings 277 14.3.6 Chromium-Plated Steel for Containers 279 14.3.7 Aluminum Coatings 280
References 281 General References 282
15 INORGANIC COATINGS 285
15.1 Vitreous Enamels 285 15.2 Portland Cement Coatings 286 15.3 Chemical Conversion Coatings 286 References 288 General References 288
16 ORGANIC COATINGS 289
16.1 Introduction 289 16.2 Paints 289 16.3 Requirements for Corrosion Protection 291 16.4 Metal Surface Preparation 293
16.4.1 Cleaning All Dirt, Oils, and Greases from the Surface 293
16.4.2 Complete Removal of Rust and Mill Scale 294 16.5 Applying Paint Coatings 295
16.5.1 Wash Primer 296 16.5.2 Painting of Aluminum and Zinc 296
16.6 Filiform Corrosion 296 16.6.1 Theory of Filiform Corrosion 298
16.7 Plastic Linings 299
17.1 Introduction 303 17.2 Passivators 304
17.2.1 Mechanism of Passivation 304 17.2.2 Applications of Passivators 308
17.3 Pickling Inhibitors 310 17.3.1 Applications of Pickling Inhibitors 312
17.4 Slushing Compounds 313 17.5 Vapor-Phase Inhibitors 313
17.5.1 Inhibitor to Reduce Tarnishing of Copper 314 References 315 General References 316
18 TREATMENT OF WATER AND STEAM SYSTEMS 317
18.1 Deaeration and Deactivation 317 18.2 Hot- and Cold-Water Treatment 321
18.2.1 Cooling Waters 322 18.3 Boiler-Water Treatment 323
18.3.1 Boiler Corrosion 323 18.3.2 Boiler-Water Treatment for Corrosion Control 326 18.3.3 Mechanisms 328
References 330 General References 331
19 ALLOYING FOR CORROSION RESISTANCE; STAINLESS STEELS 333
19.1 Introduction 333 19.2 Stainless Steels 335
19.2.1 Brief History 336 19.2.2 Classes and Types 337 19.2.3 Intergranular Corrosion 343 19.2.4 Pitting and Crevice Corrosion 350 19.2.5 Stress-Corrosion Cracking and Hydrogen Cracking 354 19.2.6 Cracking of Sensitized Austenitic Alloys in
Polythionic Acids 359
References 362 General References 365
20 COPPER AND COPPER ALLOYS 367
20.1 Copper 367 20.1.1 Corrosion in Natural Waters 369
20.2 Copper Alloys 371 20.2.1 Copper–Zinc Alloys (Brasses) 371 20.2.2 Dealloying/Dezincifi cation 372 20.2.3 Stress-Corrosion Cracking (Season Cracking) 374 20.2.4 Condenser Tube Alloys Including
Copper–Nickel Alloys 378 References 379 General References 381 Problems 381 Answers to Problems 381
21 ALUMINUM AND ALUMINUM ALLOYS 383
21.1 Aluminum 383 21.1.1 Clad Alloys 384 21.1.2 Corrosion in Water and Steam 384 21.1.3 Effect of pH 387 21.1.4 Corrosion Characteristics 388 21.1.5 Galvanic Coupling 392
21.2 Aluminum Alloys 393 21.2.1 Stress-Corrosion Cracking 394
References 396 General References 397
22 MAGNESIUM AND MAGNESIUM ALLOYS 399
22.1 Introduction 399 22.2 Magnesium 399 22.3 Magnesium Alloys 400
22.3.1 Stress-Corrosion Cracking 402 22.3.2 Coatings 403
22.4 Summary 404
23 NICKEL AND NICKEL ALLOYS 407
23.1 Introduction 407 23.2 Nickel 408 23.3 Nickel Alloys 411
23.3.1 General Behavior 411 23.3.2 Ni–Cu System: Alloy 400—70% Ni, 30% Cu 414 23.3.3 Ni–Cr–Fe System: Alloy 600—76% Ni, 16% Cr,
7% Fe 414 23.3.4 Ni–Mo System: Alloy B—60% Ni, 30% Mo,
5% Fe 415 23.3.5 Ni–Cr–Fe–Mo–Cu System: Alloy G—Ni, 22%
Cr, 20% Fe, 6.5% Mo, 2% Cu 416 23.3.6 Ni–Cr–Mo System: Alloy C—54% Ni, 15% Cr,
16% Mo, 4% W, 5% Fe 416 23.3.7 Ni–Fe–Cr System: Alloy 825—Ni, 31% Fe, 22% Cr 417
References 417 General References 418
24 COBALT AND COBALT ALLOYS 419
24.1 Introduction 419 24.2 Cobalt Alloys 420 References 423 General References 423
25 TITANIUM 425
25.1 Titanium 425 25.2 Titanium Alloys 427 25.3 Pitting and Crevice Corrosion 429 25.4 Intergranular Corrosion and Stress-Corrosion Cracking 430 References 432 General References 434 Problem 434
26 ZIRCONIUM 435
CONTENTS xv
26.3 Behavior in Hot Water and Steam 437 References 439 General References 440
27 TANTALUM 441
27.1 Introduction 441 27.2 Corrosion Behavior 441 References 443 General Reference 443
28 LEAD 445
28.1 Introduction 445 28.2 Corrosion Behavior of Lead and Lead Alloys 446
28.2.1 Lead–Acid Battery 447 28.3 Summary 448 References 449 General References 449
29 APPENDIX 451
29.1 Activity and Activity Coeffi cients of Strong Electrolytes 451
29.2 Derivation of Stern–Geary Equation for Calculating Corrosion Rates from Polarization Data Obtained at Low Current Densities 456 29.2.1 The General Equation 458
29.3 Derivation of Equation Expressing the Saturation Index of a Natural Water 461
29.4 Derivation of Potential Change along a Cathodically Protected Pipeline 467
29.5 Derivation of the Equation for Potential Drop along the Soil Surface Created by Current Entering or Leaving a Buried Pipe 469
29.6 Derivation of the Equation for Determining Resistivity of Soil by Four-Electrode Method 470
29.7 Derivation of the Equation Expressing Weight Loss by Fretting Corrosion 471
29.8 Conversion Factors 474 29.8.1 Additional Conversion Factors 475 29.8.2 Current Density Equivalent to a Corrosion Rate
of 1 gmd 475
xvi CONTENTS
29.9 Standard Potentials 476 29.10 Notation and Abbreviations 476 References 478
Index 479
xvii
PREFACE
The three main global challenges for the twenty - fi rst century are energy, water, and air — that is, suffi cient energy to ensure a reasonable standard of living, clean water to drink, and clean air to breathe. The ability to manage corrosion is a central part of using materials effectively and effi ciently to meet these challenges. For example, oil and natural gas are transmitted across continents using high - pressure steel pipelines that must operate for decades without failure, so that neither the groundwater nor the air is unnecessarily polluted. In design, operation, and maintenance of nuclear power plants, management of corrosion is critical. The reliability of materials used in nuclear waste dis- posal must be suffi cient so that that the safety of future generations is not compromised.
Materials reliability is becoming ever more important in our society, particu- larly in view of the liability issues that develop when reliability is not assured, safety is compromised, and failure occurs. Notwithstanding the many years over which university, college, and continuing education courses in corrosion have been available, high - profi le corrosion failures continue to take place. Although the teaching of corrosion should not be regarded as a dismal failure, it has cer- tainly not been a stellar success providing all engineers and technologists a basic minimum “ literacy level ” in corrosion that would be suffi cient to ensure reliabil- ity and prevent failures.
Senior management of some organizations has adopted a policy of “ zero failures ” or “ no failures. ” In translating this management policy into reality, so that “ zero ” really does mean “ zero ” and “ no ” means “ no, ” engineers and others manage corrosion using a combination of well - established strategies, innovative approaches, and, when necessary, experimental trials.
One objective of preparing the fourth edition of this book is to present to students an updated overview of the essential aspects of corrosion science and engineering that underpin the tools that are available and the technologies that are used for managing corrosion and preventing failures. A second objective is to engage students, so that they are active participants in understanding corrosion and solving problems, rather than passively observing the smorgasbord of infor- mation presented. The main emphasis is on quantitative presentation, explana- tion, and analysis wherever possible; for example, in this new edition, the galvanic series in seawater is presented with the potential range of each material, rather than only as a qualitative list. Considering the potential ranges that can be involved, the student can see how anodic/cathodic effects can develop, not only
xviii PREFACE
when different materials form a couple, but also when materials that are nomi- nally the same are coupled. In this edition, some new numerical problems have been added, and the problems are integrated into the book by presenting them at the ends of the chapters.
Since the third edition of this book was published, there have been many advances in corrosion, including advances in knowledge, advances in alloys for application in aggressive environments, and advances of industry in response to public demand. For example, consumer demand for corrosion protection of auto- mobiles has led to a revolution of materials usage in the automotive industry. For this reason, and also because many students have a fascination with cars, numer- ous examples throughout this book illustrate advances that have been made in corrosion engineering of automobiles. Advances in protecting cars and trucks from corrosion must also be viewed in the context of reducing vehicle weight by using magnesium, aluminum, and other lightweight materials in order to decrease energy usage (increase the miles per gallon, or kilometers per liter, of gasoline) and reduce greenhouse gas emissions.
Although the basic organization of the book is unchanged from the previous edition, there is in this edition a separate chapter on Pourbaix diagrams, very useful tools that indicate the thermodynamic potential – pH domains of corrosion, passivity, and immunity to corrosion. A consideration of the relevant Pourbaix diagrams can be a useful starting point in many corrosion studies and investiga- tions. As always in corrosion, as well as in this book, there is the dual importance of thermodynamics (In which direction does the reaction go? Chapters 3 and 4 ) and kinetics (How fast does it go? Chapter 5 ).
After establishing the essential basics of corrosion in the fi rst fi ve chapters, the next 23 chapters expand upon the fundamentals in specifi c systems and appli- cations and discuss strategies for protection. There are separate chapters on alu- minum (Chapter 21 ), magnesium (Chapter 22 ), and titanium (Chapter 25 ) to provide more information on these metals and their alloys than in the previous editions. Throughout this book, environmental concerns and regulations are pre- sented in the context of their impact on corrosion and its control — for example, the EPA Lead and Copper rule enacted in the United States in 1991. The indus- trial developments in response to the Clean Air Act, enacted in 1970, have reduced air pollution in the United States, with some effect on atmospheric cor- rosion (Chapter 9 ). To meet the requirements of environmental regulations and reduce the use of organic solvents, compliant coatings have been developed (Chapter 16 ).
This is primarily a textbook for students and others who need a basic under- standing of corrosion. The book is also a reference and starting point for engi- neers, researchers, and technologists requiring specifi c information. The book includes discussion of the main materials that are available, including alloys both old and new. For consistency with current practice in metallurgical and engineer- ing literature, alloys are identifi ed with their UNS numbers as well as with their commonly used identifi ers. To answer the question from students about why so
PREFACE xix
many alloys have been developed and are commercially available, the contribu- tions of individual elements to endow alloys with unique properties that are valuable for specifi c applications are discussed. Throughout the book, there are numerous…
CANMET Materials Technology Laboratory Natural Resources Canada
Herbert H. Uhlig Former Professor Emeritus
Department of Materials Science and Engineering Massachusetts Institute of Technology
A JOHN WILEY & SONS, INC., PUBLICATION
CORROSION AND CORROSION CONTROL
CORROSION AND CORROSION CONTROL
and Engineering FOURTH EDITION
CANMET Materials Technology Laboratory Natural Resources Canada
Herbert H. Uhlig Former Professor Emeritus
Department of Materials Science and Engineering Massachusetts Institute of Technology
A JOHN WILEY & SONS, INC., PUBLICATION
Copyright © 2008 by John Wiley & Sons, Inc. All right reserved
Published by John Wiley & Sons, Inc., Hoboken New Jersey Published simultaneously in Canada
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978)750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifi cally disclaim any implied warranties of merchantability or fi tness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profi t or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com.
Library of Congress Cataloging-in-Publication Data:
Uhlig, Herbert Henry, 1907– Corrosion and corrosion control : an introduction to corrosion science and engineering / Herbert H. Uhlig, R. Winston Revie.—4th ed. p. cm. Includes bibliographical references and index. ISBN 978-0-471-73279-2 (cloth) 1. Corrosion and anti-corrosives. I. Revie, R. Winston (Robert Winston), 1944– II. Title. TA462.U39 2008 620.1′1223–dc22
2007041578
10 9 8 7 6 5 4 3 2 1
1 DEFINITION AND IMPORTANCE OF CORROSION 1
1.1 Defi nition of Corrosion 1 1.1.1 Corrosion Science and Corrosion Engineering 1
1.2 Importance of Corrosion 2 1.3 Risk Management 5 1.4 Causes of Corrosion 6
1.4.1 Change in Gibbs Free Energy 6 1.4.2 Pilling–Bedworth Ratio 6
References 6 General References 7 Problems 7
2 ELECTROCHEMICAL MECHANISMS 9
2.1 The Dry-Cell Analogy and Faraday’s Law 9 2.2 Defi nition of Anode and Cathode 11 2.3 Types of Cells 13 2.4 Types of Corrosion Damage 15 References 18 General References 19 Problems 19
3 THERMODYNAMICS: CORROSION TENDENCY AND ELECTRODE POTENTIALS 21
3.1 Change of Gibbs Free Energy 21 3.2 Measuring the Emf of a Cell 22 3.3 Calculating the Half-Cell Potential—The Nernst Equation 22 3.4 The Hydrogen Electrode and the Standard Hydrogen Scale 24 3.5 Convention of Signs and Calculation of Emf 25
vi CONTENTS
3.6 Measurement of pH 28 3.7 The Oxygen Electrode and Differential Aeration Cell 28 3.8 The Emf and Galvanic Series 30 3.9 Liquid Junction Potentials 33 3.10 Reference Electrodes 34
3.10.1 Calomel Reference Electrode 35 3.10.2 Silver–Silver Chloride Reference Electrode 36 3.10.3 Saturated Copper–Copper Sulfate Reference
Electrode 36 References 37 General References 38 Problems 38 Answers to Problems 40
4 THERMODYNAMICS: POURBAIX DIAGRAMS 43
4.1 Basis of Pourbaix Diagrams 43 4.2 Pourbaix Diagram for Water 44 4.3 Pourbaix Diagram for Iron 45 4.4 Pourbaix Diagram for Aluminum 47 4.5 Pourbaix Diagram for Magnesium 48 4.6 Limitations of Pourbaix Diagrams 49 References 50 General References 50 Problems 50 Answers to Problem 51
5 KINETICS: POLARIZATION AND CORROSION RATES 53
5.1 Polarization 53 5.2 The Polarized Cell 54 5.3 How Polarization Is Measured 56
5.3.1 Calculation of IR Drop in an Electrolyte 58 5.4 Causes of Polarization 58 5.5 Hydrogen Overpotential 63 5.6 Polarization Diagrams of Corroding Metals 66 5.7 Infl uence of Polarization on Corrosion Rate 68 5.8 Calculation of Corrosion Rates from Polarization Data 71 5.9 Anode–Cathode Area Ratio 73 5.10 Electrochemical Impedance Spectroscopy 75
CONTENTS vii
5.11 Theory of Cathodic Protection 77 References 79 General References 80 Problems 80 Answers to Problems 82
6 PASSIVITY 83
6.1 Defi nition 83 6.2 Characteristics of Passivation and the Flade Potential 84 6.3 Behavior of Passivators 88
6.3.1 Passivation of Iron by HNO 3 89
6.4 Anodic Protection and Transpassivity 90 6.5 Theories of Passivity 92
6.5.1 More Stable Passive Films with Time 95 6.5.2 Action of Chloride Ions and Passive–Active Cells 96
6.6 Critical Pitting Potential 97 6.7 Critical Pitting Temperature 99 6.8 Passivity of Alloys 100
6.8.1 Nickel–Copper Alloys 103 6.8.2 Other Alloys 108
6.9 Effect of Cathodic Polarization and Catalysis 108 References 109 General References 111 Problems 112 Answers to Problems 113
7 IRON AND STEEL 115
7.1 Introduction 115 7.2 Aqueous Environments 116
7.2.1 Effect of Dissolved Oxygen 116 7.2.2 Effect of Temperature 120 7.2.3 Effect of pH 120 7.2.4 Effect of Galvanic Coupling 127 7.2.5 Effect of Velocity on Corrosion in Natural Waters 129 7.2.6 Effect of Dissolved Salts 131
7.3 Metallurgical Factors 138 7.3.1 Varieties of Iron and Steel 138 7.3.2 Effects of Composition 138
viii CONTENTS
7.3.3 Effect of Heat Treatment 142 7.4 Steel Reinforcements in Concrete 143 References 145 General References 147 Problems 147 Answers to Problems 148
8 EFFECT OF STRESS 149
8.1 Cold Working 149 8.2 Stress-Corrosion Cracking 150
8.2.1 Iron and Steel 151 8.3 Mechanism of Stress-Corrosion Cracking of Steel and
Other Metals 156 8.3.1 Electrochemical Dissolution 157 8.3.2 Film-Induced Cleavage 158 8.3.3 Adsorption-Induced Localized Slip 158 8.3.4 Stress Sorption 158 8.3.5 Initiation of Stress-Corrosion Cracking and
Critical Potentials 161 8.3.6 Rate of Crack Growth (Fracture Mechanics) 162
8.4 Hydrogen Damage 166 8.4.1 Mechanism of Hydrogen Damage 167 8.4.2 Effect of Metal Flaws 170
8.5 Radiation Damage 172 8.6 Corrosion Fatigue 173
8.6.1 Critical Minimum Corrosion Rates 177 8.6.2 Remedial Measures 178 8.6.3 Mechanism of Corrosion Fatigue 179
8.7 Fretting Corrosion 180 8.7.1 Mechanism of Fretting Corrosion 182 8.7.2 Remedial Measures 184
References 185 General References 188 Problems 190 Answers to Problems 190
9 ATMOSPHERIC CORROSION 191
CONTENTS ix
9.3 Corrosion-Product Films 192 9.4 Factors Infl uencing Corrosivity of the Atmosphere 195
9.4.1 Particulate Matter 196 9.4.2 Gases in the Atmosphere 197 9.4.3 Moisture (Critical Humidity) 199
9.5 Remedial Measures 201 References 202 General References 203 Problems 204
10 CORROSION IN SOILS 205
10.1 Introduction 205 10.2 Factors Affecting the Corrosivity of Soils 206 10.3 Bureau of Standards Tests 207
10.3.1 Pitting Characteristics 208 10.4 Stress-Corrosion Cracking 210 10.5 Remedial Measures 211 References 212 General References 212
11 OXIDATION 215
11.1 Introduction 215 11.2 Initial Stages 216 11.3 Thermodynamics of Oxidation: Free
Energy–Temperature Diagram 218 11.4 Protective and Nonprotective Scales 218
11.4.1 Three Equations of Oxidation 220 11.5 Wagner Theory of Oxidation 223 11.6 Oxide Properties and Oxidation 224 11.7 Galvanic Effects and Electrolysis of Oxides 227 11.8 Hot Ash Corrosion 229 11.9 Hot Corrosion 229 11.10 Oxidation of Copper 230
11.10.1 Internal Oxidation 231 11.10.2 Reaction with Hydrogen (“Hydrogen Disease”) 231
11.11 Oxidation of Iron and Iron Alloys 232 11.12 Life Test for Oxidation-Resistant Wires 233 11.13 Oxidation-Resistant Alloys 234
11.13.1 Reactive Element Effect (REE) 234
x CONTENTS
11.13.2 Chromium–Iron Alloys 235 11.13.3 Chromium–Aluminum–Iron Alloys 236 11.13.4 Nickel and Nickel Alloys 236 11.13.5 Furnace Windings 237
References 237 General References 239 Problems 239 Answers to Problems 240
12 STRAY-CURRENT CORROSION 241
12.1 Introduction 241 12.2 Sources of Stray Currents 242 12.3 Quantitative Damage by Stray Currents 244 12.4 Detection of Stray Currents 245 12.5 Soil-Resistivity Measurement 246 12.6 Means for Reducing Stray-Current Corrosion 246 References 247 General References 247 Problems 247 Answers to Problems 249
13 CATHODIC PROTECTION 251
13.1 Introduction 251 13.2 Brief History 252 13.3 How Applied 253
13.3.1 Sacrifi cial Anodes 254 13.4 Combined Use with Coatings 255 13.5 Magnitude of Current Required 257 13.6 Anode Materials and Backfi ll 258
13.6.1 Overprotection 259 13.7 Criteria of Protection 260
13.7.1 Potential Measurements 260 13.7.2 Doubtful Criteria 262 13.7.3 Position of Reference Electrode 262
13.8 Economics of Cathodic Protection 263 13.9 Anodic Protection 263 References 265 General References 265
CONTENTS xi
14 METALLIC COATINGS 269
14.1 Methods of Application 269 14.2 Classifi cation of Coatings 271 14.3 Specifi c Metal Coatings 272
14.3.1 Nickel Coatings 272 14.3.2 Lead Coatings 274 14.3.3 Zinc Coatings 274 14.3.4 Cadmium Coatings 276 14.3.5 Tin Coatings 277 14.3.6 Chromium-Plated Steel for Containers 279 14.3.7 Aluminum Coatings 280
References 281 General References 282
15 INORGANIC COATINGS 285
15.1 Vitreous Enamels 285 15.2 Portland Cement Coatings 286 15.3 Chemical Conversion Coatings 286 References 288 General References 288
16 ORGANIC COATINGS 289
16.1 Introduction 289 16.2 Paints 289 16.3 Requirements for Corrosion Protection 291 16.4 Metal Surface Preparation 293
16.4.1 Cleaning All Dirt, Oils, and Greases from the Surface 293
16.4.2 Complete Removal of Rust and Mill Scale 294 16.5 Applying Paint Coatings 295
16.5.1 Wash Primer 296 16.5.2 Painting of Aluminum and Zinc 296
16.6 Filiform Corrosion 296 16.6.1 Theory of Filiform Corrosion 298
16.7 Plastic Linings 299
17.1 Introduction 303 17.2 Passivators 304
17.2.1 Mechanism of Passivation 304 17.2.2 Applications of Passivators 308
17.3 Pickling Inhibitors 310 17.3.1 Applications of Pickling Inhibitors 312
17.4 Slushing Compounds 313 17.5 Vapor-Phase Inhibitors 313
17.5.1 Inhibitor to Reduce Tarnishing of Copper 314 References 315 General References 316
18 TREATMENT OF WATER AND STEAM SYSTEMS 317
18.1 Deaeration and Deactivation 317 18.2 Hot- and Cold-Water Treatment 321
18.2.1 Cooling Waters 322 18.3 Boiler-Water Treatment 323
18.3.1 Boiler Corrosion 323 18.3.2 Boiler-Water Treatment for Corrosion Control 326 18.3.3 Mechanisms 328
References 330 General References 331
19 ALLOYING FOR CORROSION RESISTANCE; STAINLESS STEELS 333
19.1 Introduction 333 19.2 Stainless Steels 335
19.2.1 Brief History 336 19.2.2 Classes and Types 337 19.2.3 Intergranular Corrosion 343 19.2.4 Pitting and Crevice Corrosion 350 19.2.5 Stress-Corrosion Cracking and Hydrogen Cracking 354 19.2.6 Cracking of Sensitized Austenitic Alloys in
Polythionic Acids 359
References 362 General References 365
20 COPPER AND COPPER ALLOYS 367
20.1 Copper 367 20.1.1 Corrosion in Natural Waters 369
20.2 Copper Alloys 371 20.2.1 Copper–Zinc Alloys (Brasses) 371 20.2.2 Dealloying/Dezincifi cation 372 20.2.3 Stress-Corrosion Cracking (Season Cracking) 374 20.2.4 Condenser Tube Alloys Including
Copper–Nickel Alloys 378 References 379 General References 381 Problems 381 Answers to Problems 381
21 ALUMINUM AND ALUMINUM ALLOYS 383
21.1 Aluminum 383 21.1.1 Clad Alloys 384 21.1.2 Corrosion in Water and Steam 384 21.1.3 Effect of pH 387 21.1.4 Corrosion Characteristics 388 21.1.5 Galvanic Coupling 392
21.2 Aluminum Alloys 393 21.2.1 Stress-Corrosion Cracking 394
References 396 General References 397
22 MAGNESIUM AND MAGNESIUM ALLOYS 399
22.1 Introduction 399 22.2 Magnesium 399 22.3 Magnesium Alloys 400
22.3.1 Stress-Corrosion Cracking 402 22.3.2 Coatings 403
22.4 Summary 404
23 NICKEL AND NICKEL ALLOYS 407
23.1 Introduction 407 23.2 Nickel 408 23.3 Nickel Alloys 411
23.3.1 General Behavior 411 23.3.2 Ni–Cu System: Alloy 400—70% Ni, 30% Cu 414 23.3.3 Ni–Cr–Fe System: Alloy 600—76% Ni, 16% Cr,
7% Fe 414 23.3.4 Ni–Mo System: Alloy B—60% Ni, 30% Mo,
5% Fe 415 23.3.5 Ni–Cr–Fe–Mo–Cu System: Alloy G—Ni, 22%
Cr, 20% Fe, 6.5% Mo, 2% Cu 416 23.3.6 Ni–Cr–Mo System: Alloy C—54% Ni, 15% Cr,
16% Mo, 4% W, 5% Fe 416 23.3.7 Ni–Fe–Cr System: Alloy 825—Ni, 31% Fe, 22% Cr 417
References 417 General References 418
24 COBALT AND COBALT ALLOYS 419
24.1 Introduction 419 24.2 Cobalt Alloys 420 References 423 General References 423
25 TITANIUM 425
25.1 Titanium 425 25.2 Titanium Alloys 427 25.3 Pitting and Crevice Corrosion 429 25.4 Intergranular Corrosion and Stress-Corrosion Cracking 430 References 432 General References 434 Problem 434
26 ZIRCONIUM 435
CONTENTS xv
26.3 Behavior in Hot Water and Steam 437 References 439 General References 440
27 TANTALUM 441
27.1 Introduction 441 27.2 Corrosion Behavior 441 References 443 General Reference 443
28 LEAD 445
28.1 Introduction 445 28.2 Corrosion Behavior of Lead and Lead Alloys 446
28.2.1 Lead–Acid Battery 447 28.3 Summary 448 References 449 General References 449
29 APPENDIX 451
29.1 Activity and Activity Coeffi cients of Strong Electrolytes 451
29.2 Derivation of Stern–Geary Equation for Calculating Corrosion Rates from Polarization Data Obtained at Low Current Densities 456 29.2.1 The General Equation 458
29.3 Derivation of Equation Expressing the Saturation Index of a Natural Water 461
29.4 Derivation of Potential Change along a Cathodically Protected Pipeline 467
29.5 Derivation of the Equation for Potential Drop along the Soil Surface Created by Current Entering or Leaving a Buried Pipe 469
29.6 Derivation of the Equation for Determining Resistivity of Soil by Four-Electrode Method 470
29.7 Derivation of the Equation Expressing Weight Loss by Fretting Corrosion 471
29.8 Conversion Factors 474 29.8.1 Additional Conversion Factors 475 29.8.2 Current Density Equivalent to a Corrosion Rate
of 1 gmd 475
xvi CONTENTS
29.9 Standard Potentials 476 29.10 Notation and Abbreviations 476 References 478
Index 479
xvii
PREFACE
The three main global challenges for the twenty - fi rst century are energy, water, and air — that is, suffi cient energy to ensure a reasonable standard of living, clean water to drink, and clean air to breathe. The ability to manage corrosion is a central part of using materials effectively and effi ciently to meet these challenges. For example, oil and natural gas are transmitted across continents using high - pressure steel pipelines that must operate for decades without failure, so that neither the groundwater nor the air is unnecessarily polluted. In design, operation, and maintenance of nuclear power plants, management of corrosion is critical. The reliability of materials used in nuclear waste dis- posal must be suffi cient so that that the safety of future generations is not compromised.
Materials reliability is becoming ever more important in our society, particu- larly in view of the liability issues that develop when reliability is not assured, safety is compromised, and failure occurs. Notwithstanding the many years over which university, college, and continuing education courses in corrosion have been available, high - profi le corrosion failures continue to take place. Although the teaching of corrosion should not be regarded as a dismal failure, it has cer- tainly not been a stellar success providing all engineers and technologists a basic minimum “ literacy level ” in corrosion that would be suffi cient to ensure reliabil- ity and prevent failures.
Senior management of some organizations has adopted a policy of “ zero failures ” or “ no failures. ” In translating this management policy into reality, so that “ zero ” really does mean “ zero ” and “ no ” means “ no, ” engineers and others manage corrosion using a combination of well - established strategies, innovative approaches, and, when necessary, experimental trials.
One objective of preparing the fourth edition of this book is to present to students an updated overview of the essential aspects of corrosion science and engineering that underpin the tools that are available and the technologies that are used for managing corrosion and preventing failures. A second objective is to engage students, so that they are active participants in understanding corrosion and solving problems, rather than passively observing the smorgasbord of infor- mation presented. The main emphasis is on quantitative presentation, explana- tion, and analysis wherever possible; for example, in this new edition, the galvanic series in seawater is presented with the potential range of each material, rather than only as a qualitative list. Considering the potential ranges that can be involved, the student can see how anodic/cathodic effects can develop, not only
xviii PREFACE
when different materials form a couple, but also when materials that are nomi- nally the same are coupled. In this edition, some new numerical problems have been added, and the problems are integrated into the book by presenting them at the ends of the chapters.
Since the third edition of this book was published, there have been many advances in corrosion, including advances in knowledge, advances in alloys for application in aggressive environments, and advances of industry in response to public demand. For example, consumer demand for corrosion protection of auto- mobiles has led to a revolution of materials usage in the automotive industry. For this reason, and also because many students have a fascination with cars, numer- ous examples throughout this book illustrate advances that have been made in corrosion engineering of automobiles. Advances in protecting cars and trucks from corrosion must also be viewed in the context of reducing vehicle weight by using magnesium, aluminum, and other lightweight materials in order to decrease energy usage (increase the miles per gallon, or kilometers per liter, of gasoline) and reduce greenhouse gas emissions.
Although the basic organization of the book is unchanged from the previous edition, there is in this edition a separate chapter on Pourbaix diagrams, very useful tools that indicate the thermodynamic potential – pH domains of corrosion, passivity, and immunity to corrosion. A consideration of the relevant Pourbaix diagrams can be a useful starting point in many corrosion studies and investiga- tions. As always in corrosion, as well as in this book, there is the dual importance of thermodynamics (In which direction does the reaction go? Chapters 3 and 4 ) and kinetics (How fast does it go? Chapter 5 ).
After establishing the essential basics of corrosion in the fi rst fi ve chapters, the next 23 chapters expand upon the fundamentals in specifi c systems and appli- cations and discuss strategies for protection. There are separate chapters on alu- minum (Chapter 21 ), magnesium (Chapter 22 ), and titanium (Chapter 25 ) to provide more information on these metals and their alloys than in the previous editions. Throughout this book, environmental concerns and regulations are pre- sented in the context of their impact on corrosion and its control — for example, the EPA Lead and Copper rule enacted in the United States in 1991. The indus- trial developments in response to the Clean Air Act, enacted in 1970, have reduced air pollution in the United States, with some effect on atmospheric cor- rosion (Chapter 9 ). To meet the requirements of environmental regulations and reduce the use of organic solvents, compliant coatings have been developed (Chapter 16 ).
This is primarily a textbook for students and others who need a basic under- standing of corrosion. The book is also a reference and starting point for engi- neers, researchers, and technologists requiring specifi c information. The book includes discussion of the main materials that are available, including alloys both old and new. For consistency with current practice in metallurgical and engineer- ing literature, alloys are identifi ed with their UNS numbers as well as with their commonly used identifi ers. To answer the question from students about why so
PREFACE xix
many alloys have been developed and are commercially available, the contribu- tions of individual elements to endow alloys with unique properties that are valuable for specifi c applications are discussed. Throughout the book, there are numerous…
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