Corrosion Control

364 Pages·1993·9.343 MB·English

by  Samuel A. Bradford (auth.)

Corrosion Control
Samuel A. Bradford
lfXm:I VAN NOSTRAND REINHOLD
~ _____ New York
Copyright © 1993 by Van Nostrand Reinhold
Softcover reprint ofthe hardcover 1st edition 1993
Library of Congress Catalog Card Number 92-25295
ISBN 978-1-4684-8847-0 ISBN 978-1-4684-8845-6 (eBook)
DOI 10.1007/978-1-4684-8845-6
All rights reserved. No part of this work covered by the copyright hereon may be
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16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Library of Congress Cataloging-in-Publication Data
Bradford, Samuel A., 1928-
Corrosion controll Samuel A. Bradford.
p. cm.
Inc1udes bibliographical references and index.
ISBN 978-1-4684-8847-0
1. Corrosion and anti-corrosives. I. Tide.
TA462.B648 1992
620.1'623--dc20 92-25295
CIP
To my parents,
Phariss Cleino Bradford (1905-1986)
and Arthur Lenox Bradford (1904-1987)
Contents
Preface xi
Acknowledgments xiii
1 Introduction 1
1.1 WHAT IS CORROSION? 1
1.2 THE COST OF CORROSION 3
1.3 SAFETY AND ENVIRONMENTAL FACTORS 4
1.4 CORROSION ORGANIZATIONS AND
JOURNALS 4
2 Basic Corrosion Theory 7
2.1 THERMODYNAMICS 7
2.2 ELECTRODE REACTIONS 8
2.3 ELECTRODE POTENTIALS 11
2.4 CORROSION PRODUCTS AND PASSIVITY 16
2.5 CLASSIFICATIONS OF CORROSION 17
*2.6 POURBAIX DIAGRAMS 23
2.7 CORROSION RATES 28
STUDY PROBLEMS 30
*
3 Electrochemical Corrosion Theory 33
3.1 EXCHANGE CURRENT DENSITY 34
3.2 ACTIVATION POLARIZATION 35
v
vi Contents
3.3 CONCENTRATION POLARIZATION 37
3.4 RESISTANCE POLARIZATION 40
3.5 POLARIZATION DIAGRAMS 40
STUDY PROBLEMS 45
4 Metallurgical Cells 47
4.1 METAL PURITY 47
4.2 CRYSTAL DEFECTS 48
4.3 GRAIN STRUCTURE 50
4.4 SOLID SOLUTION ALLOYS 53
4.5 GALVANIC CORROSION 54
4.6 DEALLOYING 61
4.7 INTERGRANULAR CORROSION 65
4.8 CORROSION OF MULTIPHASE ALLOYS 71
4.9 STRESS CELLS 74
STUDY PROBLEMS 74
5 Environmental Cells 77
5.1 CORROSIVE CONCENTRATION 77
5.2 VELO CITY 79
5.3 TEMPERATURE 80
*5.4 POLARIZATION CURVES 81
5.5 CREVICE CORROSION 83
5.6 PITTING 87
5.7 MICROBIAL CORROSION 90
5.8 TEMPERATURE CELLS 92
5.9 CONDENSATE CORROSION 94
5.10 STRAY CURRENT CORROSION 96
STUDY PROBLEMS 99
6 Corrosive-MechanicalInteractions 103
6.1 EROSION-CORROSION 103
6.2 CORROSIVE WEAR 109
6.3 CORROSION FATIGUE 112
6.4 HYDROGEN DAMAGE 115
6.5 STRESS-CORROSION CRACKING 118
STUDY PROBLEMS 127
Contents vii
7 Corrosion in Major Environments 131
7.1 NATURAL ENVIRONMENTS 131
7.2 ORGANIC ENVIRONMENTS 138
7.3 MINERAL ACIDS 144
7.4 COMMON INORGANICS 153
STUDY PROBLEMS 162
8 Corrosion Measurement and Failure
Analysis 164
8.1 TYPES OF TESTS 164
8.2 LABORATORY TESTS 166
8.3 TEST SPECIMENS 173
8.4 ELECfRONIC PROBES 175
8.5 FAlLURE ANALYSIS 181
SruDY PROBLEMS 184
9 Materials Selection 188
9.1 STAINLESS STEELS 189
9.2 NICKEL AND NICKEL ALLOYS 195
9.3 OTHER METALS AND ALLOYS 197
9.4 PLASTICS 202
9.5 OTHER NONMETALLICS 207
STUDY PROBLEMS 210
10 Protective Coatings 214
10.1 METAL COATINGS 215
10.2 CONVERSION COATINGS 220
10.3 ORGANIC COATINGS AND LININGS 224
10.4 GLASS AND CEMENT COATINGS 229
SruDY PROBLEMS 233
11 Corrosion Inhibitors 235
11.1 PASSIVATORS 236
11.2 BARRIER INHIBITORS 238
11.3 POISONS 243
viii Contents
*11.4 POLARIZATION WITH
INHIBITORS 243
11.5 SCAVENGERS 245
11.6 NEUTRALIZERS 245
STUDY PROBLEMS 246
12 Cathodic and Anodic Protection 249
12.1 CATHODIC PROTECTION 249
12.2 SACRIFICIAL PROTECTION 251
12.3 IMPRESSED-CURRENT CATHODIC
PROTECTION 252
12.4 ANODIC PROTECTION 257
*12.5 ELECTROCHEMICAL THEORY 260
STUDY PROBLEMS 261
13 Designing for Corrosion 265
13.1 ALLOW FOR UNIFORM ATTACK 266
13.2 MINIMIZE ATTACK TIME 266
13.3 RESTRICT GALVANIC CELLS 271
13.4 PROTECT AGAINST ENVIRONMENTAL
CELLS 275
13.5 AVOID CORROSIVE-MECHANICAL
INTERACTION 279
13.6 DESIGN FOR INSPECTION AND
MAINTENANCE 283
STUDY PROBLEMS 285
14 Oxidation: Metal-Gas Reactions 289
*14.1 THERMODYNAMICS OF OXIDATION 289
14.2 OXIDE STRUCTURE 290
14.3 KINETICS OF OXIDATION 296
14.4 OXIDE SCALES 299
14.5 OTHER GAS-METAL REACTIONS 304
14.6 HOT CORROSION 306
STUDY PROBLEMS 310
Contents ix
15 Oxidation Control 313
15.1 ALLOY THEORY 313
15.2 HIGH-TEMPERATURE ALLOYS 317
15.3 COATING REQUIREMENTS 320
15.4 OXIDE COATINGS 322
15.5 OXIDIZABLE COATINGS 323
STUDY PROBLEMS 327
References 330
Index 333
Preface
Human beings undoubtedly became aware of corrosion just after they made
their first metals. These people probably began to control corrosion very
so on after that by trying to keep metal away from corrosive environments.
"Bring your tools in out of the rain" and "Clean the blood off your sword
right after battle" would have been early maxims. Now that the mechanisms
of corrosion are better understood, more techniques have been developed
to control it.
My corrosion experience extends over 10 years in industry and research
and over 20 years teaching corrosion courses to university engineering
students and industrial consulting. During that time I have developed an
approach to corrosion that has successfully trained over 1500 engineers.
This book treats corrosion and high-temperature oxidation separately.
Corrosion is divided into three groups: (1) chemical dissolution including
uniform attack, (2) electrochemical corrosion from either metallurgicalor
environmental cells, and (3) corrosive-mechanical interactions. It seems
more logical to group corrosion according to mechanisms than to arbitrarily
separate them into 8 or 20 different types of corrosion as if they were
unrelated.
University students and industry personnel alike generally are afraid of
chemistry and consequently approach corrosion theory very hesitantly. In
this text the electrochemical reactions responsible for corrosion are summed
up in only five simple half-cell reactions. When these are combined on a
polarization diagram, which is explained in detail, the electrochemical pro
cesses become obvious.
The purpose of this text is to train engineers and technologists not just to
understand corrosion but to control it. Materials selection, coatings, chemical
inhibitors, cathodic and anodic protection, and equipment design are covered
in separate chapters. High-temperature oxidation is discussed in the final two
chapters-one on oxidation theory and one on controlling oxidation by
xi
xii Preface
alloying and with coatings. Accompanying most of the chapters are questions
and problems (- 300 in total); some are simple calculations but others are
real problems with more than one possible answer. This text uses the metric
SI units (Systeme Internationale d'Unites), usually with English units in
parentheses, except in the discussion of some real problems that were origi
nally reported in English units where it seems silly to refer to a 6-in. pipe as
15.24-cm pipe. Units are not converted in the Memo questions because each
industry works completely in one set of units.
For those who want a text stripped bare of any electrochemical theory at
all, the starred (*) sections and starred chapter can be omitted without loss
of continuity. However, the author strongly urges the reader to work through
them. They are not beyond the abilities of any high school graduate who is
interested in technology.