Schweitzer P.A. Fundamentals of corrosion. Mechanisms, causes, and preventative methods
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CORROSION
Fundamentals of
Mechanisms, Causes,
and Preventative Methods
Philip A. Schweitzer
CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway NW, Suite 300
Boca Raton, FL 33487-2742
© 2010 by Taylor and Francis Group, LLC
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Library of Congress Cataloging‑in‑Publication Data
Schweitzer, Philip A.
Fundamentals of corrosion : mechanisms, causes, and preventative methods / Philip
A. Schweitzer.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4200-6770-5 (hardcover : alk. paper)
1. Building materials--Corrosion. 2. Corrosion and anti-corrosives. I. Title.
TA418.74.S3847 2010
620.1’1223--dc22 2009028737
Visit the Taylor & Francis Web site at
http://www.taylorandfrancis.com
and the CRC Press Web site at
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v
Contents
List of Figures ........................................................................................................xv
List of Tables ........................................................................................................ xix
Preface .................................................................................................................xxiii
1 Introduction .....................................................................................................1
1.1 Economic Losses ...................................................................................1
1.2 Indirect Losses .......................................................................................2
1.2.1 Shutdown ..................................................................................2
1.2.2 Contamination..........................................................................2
1.2.3 Loss of Product .........................................................................3
1.2.4 Loss of Efciency .....................................................................3
1.2.5 Environmental Damage ..........................................................3
1.2.6 Overdesign ................................................................................3
1.3 Conservation Losses .............................................................................3
1.4 Nonmetallic Materials ..........................................................................4
1.5 Summary ................................................................................................4
2 Corrosion Mechanisms .................................................................................5
2.1 Cell Potentials ........................................................................................7
2.2 Types of Local Cell Formations ...........................................................8
2.2.1 Dissimilar Electrode Cells ......................................................9
2.2.2 Concentration Cells .................................................................9
2.2.3 Differential Temperature Cells ............................................ 10
2.2.4 Oxygen Concentration Cells ................................................ 11
2.2.5 Metal Ion Concentration Cells ............................................. 11
2.3 Potential–pH Diagrams ...................................................................... 11
2.4 Polarization .......................................................................................... 14
2.4.1 Activation Polarization .........................................................15
2.4.2 Concentration Polarization ...................................................17
2.5 Measuring Polarization ......................................................................19
2.5.1 Anodic Polarization ...............................................................21
2.6 Other Factors Affecting Corrosion ...................................................23
2.7 Corrosion Rate Measurement ............................................................25
2.7.1 Corrosion Rate Expressions ..................................................25
3 Forms of Metallic Corrosion ......................................................................27
3.1 General (Uniform) Corrosion ............................................................27
3.1.1 Passive Film on Iron ..............................................................28
3.1.2 Passive Film on Nickel ..........................................................29
3.1.3 Passive Film on Austenitic Stainless Steel ..........................29
vi Contents
3.1.4 Passive Film on Copper.........................................................29
3.1.5 Passive Film on Aluminum ..................................................30
3.1.6 Passive Film on Titanium .....................................................30
3.1.7 Passive Film on Tantalum .....................................................30
3.1.8 Uniform Corrosion Rates ......................................................30
3.1.9 Protective Measures ..............................................................31
3.2 Intergranular Corrosion .....................................................................32
3.2.1 Austenitic Stainless Steels ....................................................32
3.2.2 Ferritic Stainless Steels ..........................................................35
3.2.3 Other Alloys ...........................................................................35
3.3 Galvanic Corrosion .............................................................................36
3.3.3 Preventive Measures .............................................................38
3.4 Crevice Corrosion ...............................................................................38
3.4.1 Preventive Measures .............................................................40
3.5 Pitting Corrosion .................................................................................41
3.5.1 Preventive Measures .............................................................43
3.6 Erosion Corrosion ...............................................................................44
3.6.1 Preventive Measures .............................................................45
3.7 Stress Corrosion Cracking (SCC) ......................................................46
3.7.1 Preventive Measures .............................................................49
3.8 Biological Corrosion............................................................................50
3.8.1 Preventive Measures .............................................................54
3.9 Selective Leaching ...............................................................................55
3.9.1 Preventive Measures .............................................................57
3.10 Hydrogen Damage ..............................................................................57
3.10.1 Sources of Hydrogen .............................................................58
3.10.2 Types of Hydrogen Damage .................................................59
3.10.2.1 Hydrogen Embrittlement ......................................59
3.10.2.2 Hydrogen Blistering ...............................................62
3.10.2.3 Flakes, Fisheyes, and Shatter Cracks ...................63
3.10.2.4 Hydrogen Attack ....................................................63
3.10.3 Preventive Measures .............................................................65
3.10.3.1 Hydrogen Blistering ...............................................65
3.10.3.2 Hydrogen Embrittlement ......................................66
3.10.3.3 Hydrogen Attack ....................................................67
3.11 Liquid Metal Attack ............................................................................68
3.11.1 Liquid Metal Embrittlement (LME) ....................................69
3.11.1.1 Requirements for Embrittlement .........................69
3.11.1.2 Factors Inuencing LME .......................................71
3.11.1.3 Delayed Failure .......................................................72
3.11.1.4 Preventive Measures ..............................................72
3.11.2 Corrosion by Liquid Metals .................................................72
3.12 Exfoliation ............................................................................................73
3.12.1 Preventive Measures ............................................................. 74
3.13 Corrosion Fatigue ................................................................................ 74
Contents vii
3.13.1 Preventive Measures .............................................................75
3.14 Filiform Corrosion ..............................................................................75
3.14.1 Preventive Measures .............................................................76
References ....................................................................................................... 76
4 Atmospheric Corrosion ...............................................................................77
4.1 Atmospheric Types .............................................................................78
4.2 Factors Affecting Atmospheric Corrosion.......................................79
4.2.1 Time of Wetness .....................................................................80
4.2.1.1 Adsorption Layers ..................................................80
4.2.1.2 Phase Layers ............................................................81
4.2.2 Composition of Surface Electrolyte .....................................83
4.2.2.1 Oxygen .....................................................................83
4.2.2.2 SO
x
............................................................................83
4.2.2.3 NO
x
...........................................................................83
4.2.2.4 Chlorides .................................................................84
4.2.2.5 CO
2
............................................................................84
4.2.2.6 Concentration of Different Species ......................84
4.2.3 Temperature ............................................................................84
4.2.4 Initial Exposure ......................................................................85
4.2.5 Sheltering ................................................................................85
4.2.6 Wind Velocity .........................................................................86
4.2.7 Nature of Corrosion Products ..............................................86
4.2.8 Pollutants Present ..................................................................87
4.3 Mechanisms of Atmospheric Corrosion of Metals ........................89
4.3.1 Damp Atmospheric Corrosion (Adsorption Layers) ........90
4.3.2 Wet Atmospheric Corrosion (Phase Layers) ......................92
4.3.2.1 Dew ..........................................................................92
4.3.2.2 Rain ..........................................................................92
4.3.2.3 Fog ............................................................................93
4.3.3 Deposit of Pollutants .............................................................93
4.4 Corrosion Products .............................................................................94
4.5 Specic Atmospheric Corrodents .....................................................96
4.5.1 Sulfur-Containing Compounds ...........................................97
4.5.2 Nitrogen-Containing Compounds ......................................99
4.5.3 Chlorine-Containing Compounds ....................................100
4.5.4 Carbon Dioxide (CO
2
) .......................................................... 101
4.5.5 Oxygen (O
2
) ........................................................................... 101
4.5.6 Indoor Atmospheric Compounds ..................................... 101
4.6 Summary ............................................................................................ 101
4.7 Resistance of Specic Metals and Alloys to Atmospheric
Corrosion ............................................................................................ 102
4.7.1 Carbon Steel .......................................................................... 102
4.7.2 Weathering Steels................................................................. 104
4.7.3 Zinc ........................................................................................ 106
viii Contents
4.7.4 Zinc and Zinc Alloy Coatings on Steel ............................. 109
4.7.4.1 Zinc-Aluminum Hot Dip Coatings.................... 111
4.7.4.2 Zinc-Aluminum Thermally Sprayed
Coatings ................................................................. 111
4.7.4.3 Zinc-Iron Alloy Coatings .................................... 112
4.7.4.4 Cast Zinc Alloys ................................................... 112
4.7.5 Copper ................................................................................... 112
4.7.6 Copper Alloys ....................................................................... 114
4.7.6.1 Brasses .................................................................... 114
4.7.6.2 Bronzes .................................................................. 116
4.7.6.3 Copper-Nickel Alloys .......................................... 116
4.7.7 Aluminum Alloys ................................................................ 116
4.7.7.1 Protective Measures ............................................. 120
4.7.7.2 Applications ..........................................................121
4.7.8 Stainless Steel .......................................................................122
4.7.8.1 Austenitic Grades .................................................123
4.7.8.2 Ferritic Grades ......................................................124
4.7.8.3 Martensitic Grades ............................................... 124
4.7.8.4 Duplex Grades ......................................................125
4.7.9 Nickel .....................................................................................125
4.7.10 Monel Alloy ..........................................................................125
4.7.11 Inconel Alloy 600 .................................................................125
4.7.12 Inconel Alloy 625, Incoloy Alloy 800, Incoloy
Alloy 825 ................................................................................126
4.8 Atmospheric Corrosion of Nonmetals ...........................................126
4.8.1 Plastics ................................................................................... 126
4.8.1.1 Thermoplastics .....................................................127
4.8.1.2 Thermosets ............................................................129
4.8.2 Elastomers .............................................................................133
4.8.3 Masonry Materials ...............................................................134
4.8.3.1 Protecting Concrete .............................................137
4.8.3.2 Coating Selection .................................................. 139
4.8.3.3 Polymer Concrete ................................................. 140
4.8.3.4 Mortars and Grouts .............................................. 140
4.8.4 Ceramics ................................................................................ 141
4.8.4.1 Forms of Corrosion .............................................. 143
4.8.4.2 Corrosion of Specic Ceramics .......................... 145
4.8.5 Wood ...................................................................................... 145
4.8.5.1 Plywood ................................................................. 149
4.8.5.2 Reconstituted Wood Products ............................150
4.8.5.3 Applied Exterior Wood Finishes ........................ 151
4.8.6 Indoor Atmospheric Corrosion .......................................... 153
References .....................................................................................................154
Contents ix
5 Corrosion of Polymer (Plastic) Materials .............................................. 157
5.1 Radiation ............................................................................................158
5.2 Permeation .........................................................................................159
5.3 Absorption ......................................................................................... 163
5.4 Thermoplasts (Thermoplastic Polymers) .......................................166
5.5 Thermoset Polymers ......................................................................... 167
5.6 Environmental Cracking .................................................................. 169
6 Corrosion of Linings .................................................................................. 171
6.1 Liquid Applied Linings .................................................................... 172
6.1.1 Design of the Vessel .............................................................172
6.1.2 Lining Selection ................................................................... 176
6.1.3 Lining Application ............................................................... 181
6.1.4 Cure of the Applied Lining ................................................ 182
6.1.5 Causes of Coating Failure ................................................... 182
6.2 Sheet Linings .....................................................................................183
6.2.1 Shell Design .......................................................................... 184
6.2.2 Considerations in Liner Selection ......................................185
6.2.2.1 Bonded Linings .................................................... 186
6.2.2.2 Unbonded Linings ............................................... 187
6.2.3 Design Considerations ........................................................ 188
6.2.3.1 Permeation ............................................................. 188
6.2.3.2 Absorption.............................................................190
6.2.4 Inspection of the Lining ...................................................... 191
6.2.5 Causes of Lining Failure ..................................................... 192
6.2.5.1 Liner Selection ...................................................... 192
6.2.5.2 Inadequate Surface Preparation ......................... 192
6.2.5.3 Thermal Stresses ..................................................192
6.2.5.4 Permeation ............................................................. 192
6.2.5.5 Absorption............................................................. 193
6.2.5.6 Welding Flaws ...................................................... 193
6.2.5.7 Debonding ............................................................. 193
6.2.5.8 Operation ...............................................................193
6.2.5.9 Environmental Stress Cracking ......................... 193
6.3 Elastomeric Linings .......................................................................... 194
7 Corrosion of Paint ....................................................................................... 197
7.1 Mechanisms of Protection ............................................................... 198
7.2 Composition of Paint ........................................................................200
7.2.1 Binder.....................................................................................200
7.2.2 Pigments ................................................................................201
7.2.3 Solvents ..................................................................................202
7.2.4 Additives ...............................................................................204
7.2.5 Fillers (Extenders) ................................................................206
7.3 Causes of Bond and Coating Failures ............................................206
x Contents
7.3.1 Surface Preparation and Application ................................207
7.3.2 Atmospheric Effects ............................................................207
7.3.3 Types of Failures .................................................................. 210
7.3.3.1 Strength of Paint Film .......................................... 210
7.3.3.2 Cohesive Failure ................................................... 212
7.3.3.3 Stress and Chemical Failures ............................. 213
7.4 Types of Corrosion under Organic Coatings ................................ 213
7.4.1 Wet Adhesion ....................................................................... 214
7.4.2 Osmosis ................................................................................. 215
7.4.3 Blistering ............................................................................... 215
7.4.4 Cathodic Delamination ....................................................... 216
7.4.5 Anodic Undermining .......................................................... 217
7.4.6 Filiform Corrosion ............................................................... 217
7.4.7 Early Rusting ........................................................................ 218
7.4.8 Flash Rusting ........................................................................ 218
7.5 Stages of Corrosion ........................................................................... 218
7.5.1 First Stages of Corrosion ..................................................... 218
7.5.2 Second Stage of Corrosion .................................................. 219
7.5.3 Third Stage of Corrosion ..................................................... 219
7.5.4 Fourth Stage of Corrosion ................................................... 219
7.5.5 Fifth Stage of Corrosion ...................................................... 219
7.5.6 Final Stage of Corrosion ......................................................220
7.6 Surface Preparation ...........................................................................220
7.6.1 Metal Substrate Preparation ...............................................220
7.6.1.1 Abrasive Cleaning ................................................222
7.6.1.2 Detergent Cleaning ..............................................222
7.6.1.3 Alkaline Cleaning ................................................223
7.6.1.4 Emulsion Cleaning ...............................................223
7.6.1.5 Solvent Cleaning...................................................223
7.6.1.6 Vapor Degreasing .................................................223
7.6.1.7 Steam Cleaning .....................................................223
7.6.2 Metal Surface Pretreatment ................................................223
7.6.2.1 Aluminum .............................................................224
7.6.2.2 Copper....................................................................224
7.6.2.3 Galvanized Steel ...................................................224
7.6.2.4 Steel ........................................................................224
7.6.2.5 Stainless Steel ........................................................224
7.6.2.6 Titanium ................................................................224
7.6.2.7 Zinc and Cadmium ..............................................225
7.6.3 Plastic Substrate Preparation ..............................................225
7.6.3.1 Solvent Cleaning...................................................226
7.6.3.2 Detergent Cleaning ..............................................226
7.6.3.3 Mechanical Treatments .......................................227
7.6.3.4 Chemical Treatment .............................................227
7.6.3.5 Other Treatments..................................................229
Contents xi
7.7 Application of Coatings....................................................................229
7.7.1 Application Methods ...........................................................230
7.7.1.1 Brushing ................................................................ 231
7.7.1.2 Rolling ....................................................................231
7.7.1.3 Roller Coating ....................................................... 231
7.7.1.4 Spray Painting .......................................................232
7.7.1.5 Powder Coating ....................................................233
7.7.1.6 Electrodeposition of Polymers ............................234
7.7.2 Multilayer Coatings .............................................................235
7.7.3 Curing ....................................................................................238
7.7.3.1 Air-Drying .............................................................239
7.7.3.2 Baking ....................................................................239
7.7.3.3 Force Drying .........................................................240
7.7.3.4 Reowing ...............................................................240
7.7.3.5 Radiation Curing .................................................. 240
7.7.3.6 Vapor Curing.........................................................240
7.7.4 Inspection ..............................................................................240
7.8 Maintenance of the Coating ............................................................ 241
7.9 Selecting a Paint System ...................................................................242
7.9.1 Area 1: Mild Exposure ........................................................247
7.9.2 Area 2: Temporary Protection, Normally Dry
Interiors .................................................................................248
7.9.3 Area 3: Normally Dry Exteriors ......................................... 248
7.9.4 Area 4: Freshwater Exposure .............................................250
7.9.5 Area 5: Saltwater Exposure ................................................251
7.9.6 Area 6: Freshwater Immersion ...........................................251
7.9.7 Area 7: Saltwater Immersion ..............................................251
7.9.8 Area 8: Acidic Chemical Exposure (pH 2.0–5.0) ..............251
7.9.9 Area 9: Neutral Chemical Exposure (pH 5.0–10.0) ..........252
7.9.10 Area 10: Exposure to Mild Solvents ..................................252
7.9.11 Area 11: Extreme pH Exposure ..........................................252
8 Corrosion of Metallic Coatings ...............................................................255
8.1 Corrosion Cell ....................................................................................255
8.2 EMF Control Protection by Noble Metals .....................................264
8.2.1 Mechanism of Control Protection .....................................264
8.2.1.1 Copper Coatings ...................................................264
8.2.1.2 Gold Coatings .......................................................266
8.3 Anodic Control Protection by Noble Metals ................................. 267
8.3.1 Mechanisms of Control Protection.................................... 267
8.3.1.1 Nickel Coatings ....................................................267
8.3.1.2 Chromium Coatings ............................................271
8.3.1.3 Tin Coatings (Tinplate) ........................................273
8.3.1.4 Lead Coatings ....................................................... 276
8.4 Cathodic Control by Sacricial Metal Coatings ...........................277
xii Contents
8.4.1 Mechanism of Control Protection ..................................... 281
8.4.1.1 Zinc Coatings ........................................................281
8.4.1.2 Corrosion of Zinc Coatings .................................283
8.4.1.3 Zinc-5% Aluminum Hot Dip Coatings .............285
8.4.1.4 Zinc-55% Aluminum Hot Dip Coatings ...........286
8.4.1.5 Zinc-15% Aluminum Thermal Spray ................287
8.4.1.6 Zinc-Iron Alloy Coatings ....................................288
8.4.1.7 Aluminum Coatings ............................................289
8.4.1.8 Cadmium Coatings ..............................................289
8.4.1.9 Manganese Coatings ............................................290
8.5 Mixed Control Protection ................................................................290
8.5.1 Phosphate Coatings ............................................................. 291
8.5.2 Chromate Coatings ..............................................................292
8.5.3 Oxide Coatings .....................................................................294
8.5.4 Anodized Coatings ..............................................................295
8.6 Eclipse Molding Framework (EMF) Control Protection..............296
9 Cathodic Protection .................................................................................... 297
9.1 Background ........................................................................................297
9.2 Theory .................................................................................................298
9.2.1 Sacricial Anodes ................................................................300
9.2.1.1 Anode Requirements ...........................................300
9.2.1.2 Anode Materials and Backll .............................303
9.2.2 Impressed Current Systems ...............................................303
9.2.2.1 Current Requirements .........................................304
9.2.2.2 Anode Materials and Backll .............................304
9.2.2.3 Testing for Completeness of Protection ............305
9.3 Use with Coatings .............................................................................306
9.4 Economics ..........................................................................................307
10 Corrosion Inhibitors ..................................................................................309
10.1 Inhibitor Evaluation .......................................................................... 310
10.2 Classication of Inhibitors ............................................................... 311
10.2.1 Passivation Inhibitors .......................................................... 311
10.2.1.1 Mechanism of Passivation .................................. 311
10.2.2 Organic Inhibitors................................................................ 315
10.2.3 Precipitation Inhibitors (Cathodic Inhibitors) .................. 317
10.2.4 Vapor-Phase Inhibitors ........................................................ 317
10.3 Inhibition in Acid Solution .............................................................. 318
10.3.1 Physical Adsorption ............................................................ 319
10.3.2 Chemisorption .....................................................................320
10.3.3 Interactions between Adsorbed Inhibitors ...................... 321
10.3.4 Relationships between Inhibitor Reactivity and
Efciency ............................................................................... 321
10.4 Inhibition of Near-Neutral Solutions ............................................. 321