Engineering Materials and Processe
Contents
1 Introduction 1
1.1 Definition and Main Groups of Corrosion – Terminology 1
1.2 Importance of Corrosion and Prevention Efforts 1
1.3 Corrosion Science and Corrosion Technology 3
References 4
2 Wet Corrosion: Characteristics, Prevention and
Corrosion Rate 5
2.1 Description of a Wet Corrosion Process 5
2.2 Crucial Mechanisms Determining Corrosion Rates 6
2.3 Corrosion Prevention Measures 7
2.4 Expressions and Measures of Corrosion Rates 8
2.5 Basic Properties That Determine if Corrosion Is Possible
and How Fast Material Can Corrode 10
References 10
Exercises 10
3 Thermodynamics – Equilibrium Potentials 13
3.1 Introduction 13
3.2 Free Enthalpy and Cell Voltage 13
3.3 The Influence of the State of Matter on Free Enthalpy
and
the Change of Free Enthalpy 16
3.4 Change of Free Enthalpy in Chemical Reactions.
Reversible Cell Voltage 18
3.5 Electrode Reactions and Electrode Potentials 19
3.6 Series of Standard Potentials 23
3.7 Equilibrium Potentials of Reactions with Iron at 25C 23
3.8 Pourbaix Diagram 26
3.9 A Simplified Presentation of Equilibrium Potential and
Deviation from It 29
3.10 Possible Range for Real Potentials Under Corrosion
Conditions 31
4 Electrode Kinetics 35
4.1 Introduction: Anodic and Cathodic Reactions 35
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viii Corrosion and Protection
4.2 Polarization and Overvoltage 36
4.3 Exchange Current Density 37
4.4 Activation Polarization 37
4.5 Concentration Polarization 38
4.6 Overvoltage Due to Concentration Polarization 42
4.7 Combined Activation and Concentration Polarization 43
4.8 Resistance (Ohmic) Polarization 44
4.9 Determination of Corrosion Potential and Corrosion Rate
44
4.10 Recording Polarization Curves with a Potentiostat 47
4.11 Conditions That Affect Polarization Curves, Overvoltage
Curves
and Corrosion Rates 50
References 50
5.1 Passivation and Passivity Described by Anodic
Polarization and
Overvoltage Curves 53
5.2 Passivity – Reasons and Characteristic Features 54
5.3 Breakdown of Passive Films 57
5.4 Stable and Unstable Passive State 58
5.5 Practical Utilization of Passivation and Passivity 61
References 62
Exercises 62
6 Corrosion Types with Different Cathodic Reactions 65
6.1 General 65
6.2 Corrosion under Oxygen Reduction 66
6.2.1 General Circumstances and Data 66
6.2.2 Effect of Temperature 68
6.2.3 Effect of Surface Deposits 70
6.2.4 Effect of Flow Velocity 70
6.2.5 Corrosion under Thin Films of Water 74
6.3 Corrosion under Hydrogen Evolution 75
6.4 Corrosion under Effects of Bacteria 77
6.5 CO2 Corrosion 78
6.5.1 General 78
6.5.2 Mechanisms 78
6.5.3 Corrosion Rate 80
6.6 H2S Corrosion 82
6.7 Other Cathodic Reactions 83
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Contents ix
7 Different Forms of Corrosion Classified on the
Basis of Appearence 89
7.1 Introduction 89
7.2 Uniform (General) Corrosion 91
7.3 Galvanic Corrosion 94
7.3.1 Conditions That Determine Corrosion Rates 94
7.3.2 Prevention of Galvanic Corrosion 105
7.3.3 Application of Galvanic Elements in Corrosion
Engineering 107
7.4 Thermogalvanic Corrosion 107
7.5 Crevice Corrosion 108
7.5.1 Occurrence, Conditions 108
7.5.2 Mechanism 109
7.5.3 Mathematical Models of Crevice Corrosion 113
7.5.4 Crevice Corrosion Testing 115
7.5.5 Practical Cases of Crevice and Deposit Corrosion 119
7.5.6 Galvanic Effects on Crevice Corrosion 120
7.5.7 Prevention of Crevice Corrosion 121
7.6 Pitting Corrosion 122
7.6.1 Conditions, Characteristic Features and Occurrence 122
7.6.2 Mechanisms 124
7.6.3 Influencing Factors 126
7.6.4 The Time Dependence of Pitting 127
7.6.5 Pitting Corrosion Testing 130
7.6.6 Prevention of Pitting Corrosion 131
7.7 Intergranular Corrosion 131
7.7.1 General Characteristics, Causes and Occurrence 131
7.7.2 Austenitic Stainless Steels 132
7.7.3 Ferritic Stainless Steels 134
7.7.4 Ni-based Alloys 135
7.7.5 Aluminium Alloys 135
7.8 Selective Corrosion (Selective Leaching) 135
7.9 Erosion and Abrasion Corrosion 138
7.9.1 Characteristic Features and Occurrence 138
7.9.2 Types and Mechanisms 139
7.9.3 Erosion and Erosion Corrosion in Liquid Flow with
Solid Particles 140
7.9.4 Influencing Factors and Conditions in Liquids and
Liquid–Gas Mixtures 144
7.9.5 Critical Velocities 146
7.9.6 Abrasion and Other Wear Processes Combined with
Corrosion 149
7.9.7 Preventive Measures 150
7.10 Cavitation Corrosion 152
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x Corrosion and Protection
7.11 Fretting Corrosion (Fretting Oxidation) 154
7.12 Stress Corrosion Cracking (SCC) 156
7.12.1 Characteristic Features and Occurrence 156
7.12.2 Mechanisms 157
7.12.3 Fracture Mechanics Quantities 163
7.12.4 Cracking Course and Data for Some SCC Conditions 164
7.12.5 Prevention of SCC 170
7.13 Corrosion Fatigue 170
7.13.1 Definition, Characteristic Features and Occurrence
170
7.13.2 Influencing Factors and Mechanisms 171
7.13.3 Factors Most Important for Crack Initiation and
Early Growth 175
7.13.4 Crack Growth Rate and Factors Affecting It 176
7.13.5 Calculation of Number of Cycles to Failure of Welded
Steel Structures 179
7.13.6 Prevention of Corrosion Fatigue 180
8 Corrosion in Different Environments 193
8.1 Atmospheric Corrosion 193
8.1.1 Environmental Factors and Their Effects 193
8.1.2 Atmospheric Corrosion on Different Materials 196
8.2 Corrosion in Fresh Water and Other Waters 198
8.3 Corrosion in Seawater 203
8.4 Corrosion in Soils 206
8.5 Corrosion in Concrete 210
8.6 Corrosion in the Petroleum Industry 212
References 215
Exercises 217
9 Corrosion Testing, Monitoring and Inspection 219
9.1 Corrosion Testing in General 219
9.1.1 Objectives 219
9.1.2 Test Methods 220
9.1.3 Testing Procedure 221
9.2 Electrochemical Testing 223
9.3 Corrosion Monitoring and Inspection 226
9.3.1 Monitoring of Cathodic Protection 227
9.3.2 Inspection and Monitoring of Process Plants 229
9.3.3 Monitoring and Testing in Other Environments 232
References 233
Exercise 234
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Contents xi
10 Corrosion Prevention 237
10.1 Materials Selection 237
10.1.1 General Considerations 237
10.1.2 Some Special Aspects of Materials Selection for the
Offshore Industry 240
10.1.3 Unalloyed and Low-alloy Steels and Cast Irons 241
10.1.4 High-alloy Cast Irons 242
10.1.5 Stainless Steels 243
10.1.6 Nickel Alloys 250
10.1.7 Copper and Its Alloys 250
10.1.8 Aluminium and Its Alloys 254
10.1.9 Titanium and Its Alloys 256
10.1.10 Other Metallic Materials 257
10.1.11 Non-metallic Materials 258
10.2 Change of Environment 259
10.3 Proper Design 262
10.4 Cathodic Protection 266
10.4.1 Principle 266
10.4.2 Protection Criteria and Specifications 269
10.4.3 Cathodic Protection with Sacrificial Anodes 273
10.4.4 Cathodic Protection with Impressed Current 276
10.4.5 Electrolyte Resistance, Potential Variation and
Current
Distribution in CP Systems and Galvanic Elements. 278
10.5 Anodic Protection 281
10.6 Corrosion Protection by Coatings 282
10.6.1 Metallic Coatings 283
10.6.2 Other Inorganic Coatings 292
10.6.3 Paint Coatings 293
10.6.4 Other Forms of Organic Coatings 299
10.6.5 Pre-treatment Before Coating 300
References 302
Exercises 304
Subject Index 309
