CORROSION AND CORROSION CONTROL

Transcription

1 CORROSION AND CORROSION CONTROL

2 CORROSION AND CORROSION CONTROL An Introduction to Corrosion Science and Engineering FOURTH EDITION R. Winston Revie Senior Research Scientist 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

3 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) , fax (978) , or on the web at Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) , fax (201) , or online at 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 specifically disclaim any implied warranties of merchantability or fitness 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 profit 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) , outside the United States at (317) or fax (317) 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 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 (cloth) 1. Corrosion and anti-corrosives. I. Revie, R. Winston (Robert Winston), 1944 II. Title. TA462.U dc Printed in the United States of America

4 Preface xvii 1 DEFINITION AND IMPORTANCE OF CORROSION Definition of Corrosion Corrosion Science and Corrosion Engineering Importance of Corrosion Risk Management Causes of Corrosion Change in Gibbs Free Energy Pilling Bedworth Ratio 6 References 6 General References 7 Problems 7 2 ELECTROCHEMICAL MECHANISMS The Dry-Cell Analogy and Faraday s Law Definition of Anode and Cathode Types of Cells Types of Corrosion Damage 15 References 18 General References 19 Problems 19 3 THERMODYNAMICS: CORROSION TENDENCY AND ELECTRODE POTENTIALS Change of Gibbs Free Energy Measuring the Emf of a Cell Calculating the Half-Cell Potential The Nernst Equation The Hydrogen Electrode and the Standard Hydrogen Scale Convention of Signs and Calculation of Emf 25 v

5 vi 3.6 Measurement of ph The Oxygen Electrode and Differential Aeration Cell The Emf and Galvanic Series Liquid Junction Potentials Reference Electrodes Calomel Reference Electrode Silver Silver Chloride Reference Electrode Saturated Copper Copper Sulfate Reference Electrode 36 References 37 General References 38 Problems 38 Answers to Problems 40 4 THERMODYNAMICS: POURBAIX DIAGRAMS Basis of Pourbaix Diagrams Pourbaix Diagram for Water Pourbaix Diagram for Iron Pourbaix Diagram for Aluminum Pourbaix Diagram for Magnesium Limitations of Pourbaix Diagrams 49 References 50 General References 50 Problems 50 Answers to Problem 51 5 KINETICS: POLARIZATION AND CORROSION RATES Polarization The Polarized Cell How Polarization Is Measured Calculation of IR Drop in an Electrolyte Causes of Polarization Hydrogen Overpotential Polarization Diagrams of Corroding Metals Influence of Polarization on Corrosion Rate Calculation of Corrosion Rates from Polarization Data Anode Cathode Area Ratio Electrochemical Impedance Spectroscopy 75

6 vii 5.11 Theory of Cathodic Protection 77 References 79 General References 80 Problems 80 Answers to Problems 82 6 PASSIVITY Definition Characteristics of Passivation and the Flade Potential Behavior of Passivators Passivation of Iron by HNO Anodic Protection and Transpassivity Theories of Passivity More Stable Passive Films with Time Action of Chloride Ions and Passive Active Cells Critical Pitting Potential Critical Pitting Temperature Passivity of Alloys Nickel Copper Alloys Other Alloys Effect of Cathodic Polarization and Catalysis 108 References 109 General References 111 Problems 112 Answers to Problems IRON AND STEEL Introduction Aqueous Environments Effect of Dissolved Oxygen Effect of Temperature Effect of ph Effect of Galvanic Coupling Effect of Velocity on Corrosion in Natural Waters Effect of Dissolved Salts Metallurgical Factors Varieties of Iron and Steel Effects of Composition 138

7 viii Effect of Heat Treatment Steel Reinforcements in Concrete 143 References 145 General References 147 Problems 147 Answers to Problems EFFECT OF STRESS Cold Working Stress-Corrosion Cracking Iron and Steel Mechanism of Stress-Corrosion Cracking of Steel and Other Metals Electrochemical Dissolution Film-Induced Cleavage Adsorption-Induced Localized Slip Stress Sorption Initiation of Stress-Corrosion Cracking and Critical Potentials Rate of Crack Growth (Fracture Mechanics) Hydrogen Damage Mechanism of Hydrogen Damage Effect of Metal Flaws Radiation Damage Corrosion Fatigue Critical Minimum Corrosion Rates Remedial Measures Mechanism of Corrosion Fatigue Fretting Corrosion Mechanism of Fretting Corrosion Remedial Measures 184 References 185 General References 188 Problems 190 Answers to Problems ATMOSPHERIC CORROSION Introduction Types of Atmospheres 192

8 ix 9.3 Corrosion-Product Films Factors Influencing Corrosivity of the Atmosphere Particulate Matter Gases in the Atmosphere Moisture (Critical Humidity) Remedial Measures 201 References 202 General References 203 Problems CORROSION IN SOILS Introduction Factors Affecting the Corrosivity of Soils Bureau of Standards Tests Pitting Characteristics Stress-Corrosion Cracking Remedial Measures 211 References 212 General References OXIDATION Introduction Initial Stages Thermodynamics of Oxidation: Free Energy Temperature Diagram Protective and Nonprotective Scales Three Equations of Oxidation Wagner Theory of Oxidation Oxide Properties and Oxidation Galvanic Effects and Electrolysis of Oxides Hot Ash Corrosion Hot Corrosion Oxidation of Copper Internal Oxidation Reaction with Hydrogen ( Hydrogen Disease ) Oxidation of Iron and Iron Alloys Life Test for Oxidation-Resistant Wires Oxidation-Resistant Alloys Reactive Element Effect (REE) 234

9 x Chromium Iron Alloys Chromium Aluminum Iron Alloys Nickel and Nickel Alloys Furnace Windings 237 References 237 General References 239 Problems 239 Answers to Problems STRAY-CURRENT CORROSION Introduction Sources of Stray Currents Quantitative Damage by Stray Currents Detection of Stray Currents Soil-Resistivity Measurement Means for Reducing Stray-Current Corrosion 246 References 247 General References 247 Problems 247 Answers to Problems CATHODIC PROTECTION Introduction Brief History How Applied Sacrificial Anodes Combined Use with Coatings Magnitude of Current Required Anode Materials and Backfill Overprotection Criteria of Protection Potential Measurements Doubtful Criteria Position of Reference Electrode Economics of Cathodic Protection Anodic Protection 263 References 265 General References 265

10 xi Problems 266 Answers to Problems METALLIC COATINGS Methods of Application Classification of Coatings Specific Metal Coatings Nickel Coatings Lead Coatings Zinc Coatings Cadmium Coatings Tin Coatings Chromium-Plated Steel for Containers Aluminum Coatings 280 References 281 General References INORGANIC COATINGS Vitreous Enamels Portland Cement Coatings Chemical Conversion Coatings 286 References 288 General References ORGANIC COATINGS Introduction Paints Requirements for Corrosion Protection Metal Surface Preparation Cleaning All Dirt, Oils, and Greases from the Surface Complete Removal of Rust and Mill Scale Applying Paint Coatings Wash Primer Painting of Aluminum and Zinc Filiform Corrosion Theory of Filiform Corrosion Plastic Linings 299

11 xii References 300 General References INHIBITORS AND PASSIVATORS Introduction Passivators Mechanism of Passivation Applications of Passivators Pickling Inhibitors Applications of Pickling Inhibitors Slushing Compounds Vapor-Phase Inhibitors Inhibitor to Reduce Tarnishing of Copper 314 References 315 General References TREATMENT OF WATER AND STEAM SYSTEMS Deaeration and Deactivation Hot- and Cold-Water Treatment Cooling Waters Boiler-Water Treatment Boiler Corrosion Boiler-Water Treatment for Corrosion Control Mechanisms 328 References 330 General References ALLOYING FOR CORROSION RESISTANCE; STAINLESS STEELS Introduction Stainless Steels Brief History Classes and Types Intergranular Corrosion Pitting and Crevice Corrosion Stress-Corrosion Cracking and Hydrogen Cracking Cracking of Sensitized Austenitic Alloys in Polythionic Acids 359

12 xiii Galvanic Coupling and General Corrosion Resistance 361 References 362 General References COPPER AND COPPER ALLOYS Copper Corrosion in Natural Waters Copper Alloys Copper Zinc Alloys (Brasses) Dealloying/Dezincification Stress-Corrosion Cracking (Season Cracking) Condenser Tube Alloys Including Copper Nickel Alloys 378 References 379 General References 381 Problems 381 Answers to Problems ALUMINUM AND ALUMINUM ALLOYS Aluminum Clad Alloys Corrosion in Water and Steam Effect of ph Corrosion Characteristics Galvanic Coupling Aluminum Alloys Stress-Corrosion Cracking 394 References 396 General References MAGNESIUM AND MAGNESIUM ALLOYS Introduction Magnesium Magnesium Alloys Stress-Corrosion Cracking Coatings Summary 404

13 xiv References 405 General References NICKEL AND NICKEL ALLOYS Introduction Nickel Nickel Alloys General Behavior Ni Cu System: Alloy % Ni, 30% Cu Ni Cr Fe System: Alloy % Ni, 16% Cr, 7% Fe Ni Mo System: Alloy B 60% Ni, 30% Mo, 5% Fe Ni Cr Fe Mo Cu System: Alloy G Ni, 22% Cr, 20% Fe, 6.5% Mo, 2% Cu Ni Cr Mo System: Alloy C 54% Ni, 15% Cr, 16% Mo, 4% W, 5% Fe Ni Fe Cr System: Alloy 825 Ni, 31% Fe, 22% Cr 417 References 417 General References COBALT AND COBALT ALLOYS Introduction Cobalt Alloys 420 References 423 General References TITANIUM Titanium Titanium Alloys Pitting and Crevice Corrosion Intergranular Corrosion and Stress-Corrosion Cracking 430 References 432 General References 434 Problem ZIRCONIUM Introduction Zirconium Alloys 436

14 xv 26.3 Behavior in Hot Water and Steam 437 References 439 General References TANTALUM Introduction Corrosion Behavior 441 References 443 General Reference LEAD Introduction Corrosion Behavior of Lead and Lead Alloys Lead Acid Battery Summary 448 References 449 General References APPENDIX Activity and Activity Coefficients of Strong Electrolytes Derivation of Stern Geary Equation for Calculating Corrosion Rates from Polarization Data Obtained at Low Current Densities The General Equation Derivation of Equation Expressing the Saturation Index of a Natural Water Derivation of Potential Change along a Cathodically Protected Pipeline Derivation of the Equation for Potential Drop along the Soil Surface Created by Current Entering or Leaving a Buried Pipe Derivation of the Equation for Determining Resistivity of Soil by Four-Electrode Method Derivation of the Equation Expressing Weight Loss by Fretting Corrosion Conversion Factors Additional Conversion Factors Current Density Equivalent to a Corrosion Rate of 1 gmd 475

15 xvi 29.9 Standard Potentials Notation and Abbreviations 476 References 478 Index 479

16 PREFACE The three main global challenges for the twenty - first century are energy, water, and air that is, sufficient 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 efficiently 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 disposal must be sufficient so that that the safety of future generations is not compromised. Materials reliability is becoming ever more important in our society, particularly 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 - profile corrosion failures continue to take place. Although the teaching of corrosion should not be regarded as a dismal failure, it has certainly not been a stellar success providing all engineers and technologists a basic minimum literacy level in corrosion that would be sufficient to ensure reliability 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 information presented. The main emphasis is on quantitative presentation, explanation, 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 xvii

17 xviii PREFACE when different materials form a couple, but also when materials that are nominally 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 automobiles 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, numerous 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 investigations. 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 first five chapters, the next 23 chapters expand upon the fundamentals in specific systems and applications and discuss strategies for protection. There are separate chapters on aluminum (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 presented 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 The industrial developments in response to the Clean Air Act, enacted in 1970, have reduced air pollution in the United States, with some effect on atmospheric corrosion (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 understanding of corrosion. The book is also a reference and starting point for engineers, researchers, and technologists requiring specific 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 engineering literature, alloys are identified with their UNS numbers as well as with their commonly used identifiers. To answer the question from students about why so

18 PREFACE xix many alloys have been developed and are commercially available, the contributions of individual elements to endow alloys with unique properties that are valuable for specific applications are discussed. Throughout the book, there are numerous references to further sources of information, including handbooks, other books, reviews, and papers in journals. At the end of each chapter, there is a list of General References pertinent to that chapter, and most of these were published in 2000 and later. This edition includes introductory discussions of risk (Chapter 1 ), AC impedance measurements (Chapter 5 ), Ellingham diagrams (Chapter 11 ), and, throughout the book, discussions of new alloys that have been developed to meet demands for increasing reliability notwithstanding the increased structural lifetimes that are being required in corrosive environments of ever - increasing severity. Perhaps nowhere are the demands for reliability more challenging than in nuclear reactors, discussed in Chapters 8 and 26. In the discussion of stainless steels (Chapter 19 ), the concept of critical pitting temperature (CPT) is introduced, as well as the information on critical pitting potential (CPP). The important problem of corrosion of rebar (reinforced steel in concrete) is discussed in Chapter 7 on iron and steel. In addition to new technologies and new materials for managing corrosion, new tools for presenting books have become available; hence, this book is being published as an electronic book, as well as in the traditional print format. An instructor s manual is also being prepared. Experience has been invaluable in using the book in a corrosion course in the Department of Mechanical and Aerospace Engineering at Carleton University in Ottawa, which Glenn McRae and I developed along with other members of the Canadian National Capital Section of NACE International. It would be a delight for me to hear from readers of this book, with their suggestions and ideas for future editions. I would like to acknowledge my many friends and colleagues at the CANMET Materials Technology Laboratory, with whom it has been my privilege to work for the past nearly 30 years. I would also like to thank the many organizations and individuals who have granted permission to use copyright material; acknowledgments for specific material are provided throughout the book. In addition, I would like to thank Bob Esposito and his staff at John Wiley & Sons, Inc. for their encouragement with this book and also with the Wiley Series in Corrosion. I would like to thank the Uhlig family for their generosity and hospitality during five decades, beginning when I was a student in the M.I.T. Corrosion Laboratory in the 1960s and 1970s. In particular, I would like to acknowledge Mrs. Greta Uhlig, who continues to encourage initiatives in corrosion education in memory of the late Professor Herbert H. Uhlig ( ). Lastly, I would like to quote from the Preface of the first edition of this book: If this book stimulates young minds to accept the challenge of continuing corrosion problems, and to help reduce the huge economic losses and dismaying wastage of

19 xx PREFACE natural resources caused by metal deterioration, it will have fulfilled the author s major objective. Indeed, this remains the main objective today. Ottawa, Canada September 2007 R. Winston Revie