CORROSION AND CORROSION CONTROL An Introduction to Corrosion Science and Engineering

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1 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 V^INTERSCIENCE A JOHN WILEY & SONS, INC., PUBLICATION

2 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

3 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 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 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

4 vii 5.11 Theory of Cathodic Protection 77 References 79 General References 80 Problems 80 Answers to Problems 82 PASSIVITY Definition Characteristics of Passivation and the Flade Potential Behavior of Passivators Passivation of Iron by HN 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 113 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

5 7.3.3 Effect of Heat Treatment 7.4 Steel Reinforcements in Concrete References General References Problems Answers to Problems EFFECT OF STRESS 8.1 Cold Working 8.2 Stress-Corrosion Cracking Iron and Steel 8.3 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) 8.4 Hydrogen Damage Mechanism of Hydrogen Damage Effect of Metal Flaws 8.5 Radiation Damage 8.6 Corrosion Fatigue Critical Minimum Corrosion Rates Remedial Measures Mechanism of Corrosion Fatigue 8.7 Fretting Corrosion Mechanism of Fretting Corrosion Remedial Measures References General References Problems Answers to Problems ATMOSPHERIC CORROSION 9.1 Introduction 9.2 Types of Atmospheres

6 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

7 X CONTENTS 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 References General References

8 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

9 XII CONTENTS 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

10 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

11 XIV CONTENTS References 405 i 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% Си Ni-Cr-Mo System: Alloy С 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

12 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

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