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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Serie: Wiley Series in Corrosion
- Sprache: Englisch
* Provides detailed methods to reduce or eliminate damage caused by corrosion * Explains the human and environmental costs of corrosion * Explains causes of and various types of corrosion * Summarizes the costs of corrosion in different industries, including bridges, mining, petroleum refining, chemical, petrochemical, and pharmaceutical, pulp and paper, agricultural, food processing, electronics, home appliances etc * Discusses the technical aspects of the various methods available to detect, prevent, and control corrosion
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Seitenzahl: 775
Veröffentlichungsjahr: 2015
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Table of Contents
Cover
Title Page
Copyright
Dedication
PREFACE
ACKNOWLEDGMENTS
CHAPTER 1: INTRODUCTION AND FORMS OF CORROSION
1.1 GENERAL OR UNIFORM OR QUASI-UNIFORM CORROSION
1.2 GALVANIC CORROSION
1.3 STRAY CURRENT CORROSION
1.4 LOCALIZED CORROSION
1.5 METALLURGICALLY INFLUENCED CORROSION
1.6 MICROBIOLOGICALLY INFLUENCED CORROSION (MIC)
1.7 MECHANICALLY ASSISTED CORROSION
1.8 ENVIRONMENTALLY INDUCED CRACKING (EIC)
REFERENCES
CHAPTER 2: CORROSION COSTS
2.1 INTRODUCTION
2.2 DATA COLLECTION AND ECONOMIC ANALYSIS
2.3 TRIBOLOGY
REFERENCES
CHAPTER 3: CORROSION CAUSES
3.1 INTRODUCTION
3.2 CORROSION IN CONVENTIONAL CONCRETE BRIDGES
3.3 CORROSION OF PRESTRESSED CONCRETE BRIDGES
3.4 REINFORCEMENT CORROSION IN CONCRETE
3.5 MECHANISM OF CORROSION AND ASSESSMENT TECHNIQUES IN CONCRETE
3.6 STEEL BRIDGES
3.7 CABLE AND SUSPENSION BRIDGES
3.8 CORROSION OF UNDERGROUND PIPELINES
3.9 WATERWAYS AND PORTS
3.10 HAZARDOUS MATERIALS STORAGE
3.11 CORROSION PROBLEMS IN AIRPORTS
3.12 RAILROADS
3.13 GAS DISTRIBUTION
3.14 DRINKING WATER AND SEWER SYSTEMS
3.15 ELECTRICAL UTILITIES
3.16 TELECOMMUNICATIONS
3.17 MOTOR VEHICLES
3.18 SHIPS
3.19 AIRCRAFT
3.20 RAILROAD CARS
3.21 HAZARDOUS MATERIALS TRANSPORT
3.22 OIL AND GAS EXPLORATION AND PRODUCTION
3.23 CORROSION IN THE MINING INDUSTRY
3.24 PETROLEUM REFINING
3.25 CHEMICAL, PETROCHEMICAL, AND PHARMACEUTICAL INDUSTRIES
3.26 PULP AND PAPER INDUSTRY
3.27 AGRICULTURAL PRODUCTION
3.28 THE FOOD PROCESSING SECTOR
3.29 ELECTRONICS
3.30 CORROSION PROBLEMS IN HOME APPLIANCES
3.31 CORROSION PROBLEMS IN THE US DEPT. OF DEFENSE
3.32 NUCLEAR WASTE STORAGE
REFERENCES
CHAPTER 4: CORROSION CONTROL AND PREVENTION
4.1 INTRODUCTION
4.2 PROTECTIVE COATINGS
4.3 METALS AND ALLOYS
4.4 CORROSION INHIBITORS
4.5 ENGINEERING COMPOSITES AND PLASTICS
4.6 CATHODIC AND ANODIC PROTECTION
4.7 SERVICES
4.8 RESEARCH AND DEVELOPMENT
4.9 CORROSION CONTROL OF BRIDGES
4.10 MITIGATING CORROSION OF REINFORCING STEEL IN UNDERWATER TUNNELS (36)
4.11 CORROSION OF UNDERGROUND GAS AND LIQUID TRANSMISSION PIPELINES
4.12 GAS DISTRIBUTION
4.13 WATERWAYS AND PORTS
4.14 HAZARDOUS MATERIALS STORAGE
4.15 CORROSION CONTROL OF STORAGE TANKS
4.16 AIRPORTS
4.17 RAILROADS
4.18 DRINKING WATER AND SEWER SYSTEMS
4.19 ELECTRIC UTILITIES
4.20 TELECOMMUNICATIONS
4.21 MOTOR VEHICLES
4.22 SHIPS
4.23 CORROSION CONTROL IN AIRCRAFT
4.24 HAZARDOUS MATERIALS TRANSPORT (HAZMAT)
4.25 OIL AND GAS EXPLORATION AND PRODUCTION
4.26 CORROSION AND ITS PREVENTION IN THE MINING INDUSTRY
4.27 PETROLEUM REFINING
4.28 CORROSION CONTROL IN THE CHEMICAL, PETROCHEMICAL, AND PHARMACEUTICAL INDUSTRIES
4.29 PULP AND PAPER INDUSTRIAL SECTOR
4.30 AGRICULTURAL PRODUCTION
4.31 FOOD PROCESSING
4.32 CORROSION FORMS IN THE ELECTRONICS INDUSTRY
4.33 HOME APPLIANCES
4.34 DEFENSE
4.35 PREVENTIVE STRATEGIES
REFERENCES
CHAPTER 5: CONSEQUENCES OF CORROSION
5.1 INTRODUCTION
5.2 CORROSION STUDIES
5.3 CORROSION DAMAGE, DEFECTS, AND FAILURES
5.4 AGE-RELIABILITY CHARACTERISTICS
5.5 HISTORICAL IMPLICATIONS OF CORROSION
5.6 SOCIAL IMPLICATIONS OF CORROSION
5.7 THE NUCLEAR INDUSTRY
5.8 FOSSIL FUEL ENERGY SYSTEMS
5.9 THE AEROSPACE INDUSTRY
5.10 THE ELECTRICAL AND ELECTRONICS INDUSTRY
5.11 THE MARINE AND OFFSHORE INDUSTRY
5.12 THE AUTOMOBILE INDUSTRY
5.13 BRIDGES
5.14 BIOMEDICAL ENGINEERING
5.15 THE DEFENSE INDUSTRY
5.16 CORROSION AND ENVIRONMENTAL IMPLICATIONS
REFERENCES
INDEX
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
CHAPTER 1: INTRODUCTION AND FORMS OF CORROSION
Figure 1.1 Even and uneven general corrosion and high-temperature attack.
Figure 1.2 Theoretical Tafel plots.
Figure 1.3 Evans diagram for corrosion of zinc as a function of pH.
Figure 1.4 Evans diagram for corrosion of zinc alloys.
Figure 1.5 Galvanic corrosion of mild steel elbow fixed to a copper pipe.
Figure 1.6 Galvanic corrosion of painted auto panel in contact with stainless steel wheel opening molding.
Figure 1.7 Galvanic series of metals in seawater.
Figure 1.8 Effect of oxygen concentration on the corrosion of mild steel in slowly moving water (8).
Figure 1.9 Various forms of localized corrosion.
Figure 1.10 Deepest pit in relation with penetration in metal and pitting factor.
Figure 1.11 Metallurgically influenced corrosion.
Figure 1.12 Uniform dealloying of admiralty brass.
Figure 1.13 Association of anaerobic and aerobic bacteria. (Reproduced with permission of NACE International from Reference 53.)
Figure 1.14 Corrosion types of mechanically assisted degradation. (Reproduced with permission of NACE International from Reference 3.)
Figure 1.15 Quenched and tempered roller bearing after corrosive wear factor.
Figure 1.16 Erosion corrosion of a pump propeller. (Reproduced by permission, Elsevier Ltd., (2).)
Figure 1.17 Cavitation erosion damage of a cylinder liner of a diesel engine. (Reproduced by permission, John Wiley and Sons (8).)
Figure 1.18 Corrosion fatigue crack through mild steel sheet.
Figure 1.19 Extrusions and intrusions in copper after 6 × 10
5
cycles in air. (Reproduced by permission, John Wiley and Sons (8).)
Figure 1.20 Effect of the potential cracking of mild steel.
Figure 1.21 Hydrogen-induced cracking: (a) centerline cracks and (b) blister crack. (Figure originally published in Reference 104. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 1.22 SOHIC in plate steel exposed to sour gas. (Figure originally published in Reference 104. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 1.23 Possible mechanisms of hydrogen embrittlement: (a) chemical adsorption of hydrogen, (b) adsorption of atomic hydrogen, (c) decohesion of atoms, and (d) possible brittle hydride particle at the tip.
CHAPTER 2: CORROSION COSTS
Figure 2.1 Breakdown of industry indicators into its components (2).
Figure 2.2 Percentage contribution to the total cost of corrosion for the five sector categories (15).
Figure 2.3 Annual cost of corrosion of gas and liquid transmission pipelines (15).
Figure 2.4 Annual cost of corrosion of gas distribution (15).
Figure 2.5 Annual cost of corrosion in the motor vehicles industry (15).
Figure 2.6 Annual cost of corrosion in the oil and gas exploration and production industry (15).
CHAPTER 3: CORROSION CAUSES
Figure 3.1 Schematic of corrosion damage to rebar (7).
Figure 3.2 Example of deteriorating bridge element (7).
Figure 3.3 Golden Gate Suspension Bridge (7).
Figure 3.4 Brooklyn Suspension Bridge (7).
Figure 3.5 Cable-Stayed bridge in Tacoma (7).
Figure 3.6 Chart describing transmission pipeline sector (7).
Figure 3.7 Components of natural gas production, distribution, and transmission (7).
Figure 3.8 Internal corrosion of a crude oil pipeline (7).
Figure 3.9 External corrosion on a buried pipeline (7).
Figure 3.10 Example of stray current corrosion (7).
Figure 3.11 Iron-related bacteria reacting with chloride-producing acidic environment (7).
Figure 3.12 Example of a steel-reinforced concrete dam (7).
Figure 3.13 Corrosion profile of steel piling after 5-year exposure to seawater (7).
Figure 3.14 (a) Pressurized storage tanks; (b) Unpressurized storage tank (7).
Figure 3.15 Oil storage tank farm (7).
Figure 3.16 Internal and external corrosion modes of oil tanks (7).
Figure 3.17 Components of a natural gas production, transmission, and distribution (7).
Figure 3.18 Chart describing the oil and gas distribution pipeline sector (7).
Figure 3.19 Schematic diagram of boiling water reactor (7).
Figure 3.20 Schematic diagram of pressurized water reactor (7).
Figure 3.21 Schematic diagram of fossil fuel plant (7).
Figure 3.22 Schematic diagram of combined-cycle plant (7).
Figure 3.23 Schematic drawing of hydroelectric plant (7).
Figure 3.24 Exfoliation corrosion around fastener holes in Al alloy 7075-T6 (7).
Figure 3.25 Modern locomotive, corroded locomotive, and reconditioned one (7).
Figure 3.26 Corroded storage drums (7).
Figure 3.27 Oil and gas production flow diagram (7).
Figure 3.28 Stress corrosion cracking near a weld (7).
Figure 3.29 Destroyer with different shipboard coatings (7).
Figure 3.30 Yucca Mountain site for high-level nuclear waste storage (7).
CHAPTER 4: CORROSION CONTROL AND PREVENTION
Figure 4.1 Cost distribution of coating application on aboveground storage tank (adapted from 5).
Figure 4.2 Cost distribution of coating application on steel highway bridge structure (7).
Figure 4.3 Expected service life of galvanized steel under different atmospheric conditions.
Figure 4.4 Severe corrosion resulting in deficient bridges (6).
Figure 4.5 Examples of bridge deck corrosion (6).
Figure 4.6 (a) Corrosion in the free length of tendon (6). (b) Failed strands.
Figure 4.7 External corrosion on a buried pipeline (6).
Figure 4.8 Schematic of stray current corrosion (6).
Figure 4.9 Iron-related bacteria reacting with chloride ions to create acidic environment (6).
Figure 4.10 The phases of corrosion control.
Figure 4.11 SCC colony found on a high-pressure gas pipeline (6).
CHAPTER 5: CONSEQUENCES OF CORROSION
Figure 5.1 Interrelation among defects, failures, and faults (16).
Figure 5.2 Twelve-inch bolt from coupling. (David Raymond, City of Ottawa, Public Works & Services.)
Figure 5.3 Aluminum ladder rungs. (David Raymond, City of Ottawa, Public Works & Services.)
Figure 5.4 Tape-wrapped air valve. (David Raymond, City of Ottawa, Public Works & Services.)
Figure 5.5 Four-inch T-bolt from 8-in valve. (David Raymond, City of Ottawa, Public Works & Services.)
Figure 5.6 Hydrant bolt from base flange. (David Raymond, City of Ottawa, Public Works & Services.)
Figure 5.7 Out-of-service compressed air cylinder. (Copyright of her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2004, 2006.)
Figure 5.8 Overall view of internal surface. (Copyright of her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2004, 2006.)
Figure 5.9 Internal surface of the bottom of cylinder. (Copyright of her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2004, 2006.)
Figure 5.10 Close-up view of internal surface of the opened cylinder. (Copyright of her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2004, 2006.)
Figure 5.11 SEM photo of intergranular pit. (Copyright of her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2004, 2006.)
Figure 5.12 SEM photo of enlarged cross section of corrosion pit (19).
Figure 5.13 (a) Fatigue striations on fractured surface (19). (b) Outer surface of wing panel and door after paint stripping and removal of catches (19).
Figure 5.14 Exfoliation corrosion on the inner surface of panel and door around a catch location. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.15 Cross section through panel showing exfoliation corrosion (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.16 Ductile fracture surface of center of bolt. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.17 Intergranular region of fracture surface of bolt. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.18 General view of bridge. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.19 Close-up view of exposed tie rods. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.20 Close-up view of upright column with missing tie rod. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.21 Close-up view of tie rods showing corroded threads, nuts, and washer. (Reproduced by permission of the Society of Petroleum Engineers (20).)
Figure 5.22 Schematic diagram of hot water system (19).
Figure 5.23 Atmospheric contamination (19).
Figure 5.24 Galvanic anode cathodic protection in concrete (19).
Figure 5.25 Arc-sprayed galvanic layer anode system (19).
Figure 5.26 Impressed current system line diagram (19).
Figure 5.27 Pressure plate with a dress cap. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.28 Aluminum corrosion products on interior surface of dress cap. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.29 Cross section through a bulge in copper cladding on a dress cap. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.30 Hard deposits inside the tubes (20).
Figure 5.31 Deep pits inside the tube (20).
Figure 5.32 Hard deposit inside GE 16 tube (20).
Figure 5.33 Perforated tube (20).
Figure 5.34 Top section of condenser tube showing corrosion. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.35 (a) Pitting pattern with several pits surrounding a large pit. (b) Pinhole size pit inside the tube. (c) Close-up of pit. (d) Close-up of inside of pit. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.36 (a, b) Copper oxide ringlets round pits. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.37 Tube that failed in waste-to-energy boiler. (Figure originally published in Reference 29. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.38 Surface appearance of uniform composite tubes with alloy 625 weld overlay. (Figure originally published in Reference 29. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.39 309 uniform overlay on 1¼ Cr ½ Mo boiler tube after service in coal-fired boiler. (a) Weld overlay with visible weld beads. (b) Weld overlay cross section showing no corrosion and no cracking. (Figure originally published in Reference 29. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.40 Appearance of large crankshaft crack. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.41 Fatigue fracture face showing crack growth direction. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.42 Metallographic specimen: fatigue fracture (F), Web (W), and Journal (J). (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.43 Chromium layer at fatigue initiation site. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.44 Drive shaft fatigue fracture face, showing initiation point (arrow) and foreign keyway material (K) (19).
Figure 5.45 Polished and etched section: Fracture profile (F), weld overlay (W), foreign key material (K), and original shaft material (S) (19).
Figure 5.46 Fracture pipe clamp and fasteners. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.47 Transgranular cracking in failed clamp (19).
Figure 5.48 Dark red and greenish spots on the outside surface (19).
Figure 5.49 The exterior surface without red spots (19).
Figure 5.50 Visible crack on the exterior surface (19).
Figure 5.51 Internal surface of pipe with thick black deposit (19).
Figure 5.52 Green deposits of copper compounds (19).
Figure 5.53 Shiny copper and green deposits (19).
Figure 5.54 Pits where copper is surrounded by green deposits (19).
Figure 5.55 Well-developed pits impinging on one another (19).
Figure 5.56 Pits typical of microbiologically induced corrosion (19).
Figure 5.57 Swellex rock bolt. (Figure originally published in Reference 31. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.58 Visual examination of the fracture of a rock bolt (19).
Figure 5.59 Failed bolt with dimples (19).
Figure 5.60 Fractured surface of a bolt from hard rock mine (19).
Figure 5.61 Close-up of dimpled surface (19).
Figure 5.62 Longitudinal section showing extreme localized attack (19).
Figure 5.63 Fragmentation of metallic surface (19).
Figure 5.64 Fracture surface showing equiaxial grains (19).
Figure 5.65 Figure showing elongated grains (19).
Figure 5.66 High-pressure still and condenser. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.67 Top portion of HPS condenser. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.68 Inner surface of the tube covered by black/brown oxide. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.69 Circumferential crack in the tube. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.70 Chloride stress corrosion cracking in stainless steel. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.71 (a) Multiple initiation of stress corrosion cracks. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org). (b) Crack that penetrated wall thickness leading to failure. (Figure originally published in Reference 26. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)
Figure 5.72 Cast iron pipe with large hole (19).
Figure 5.73 Ductile iron pipe with large corrosion pit (19).
Figure 5.74 Boeing 737 that lost major portion of fuselage (16).
Figure 5.75 Pillowing of faying surfaces (16).
List of Tables
CHAPTER 1: INTRODUCTION AND FORMS OF CORROSION
Table 1.1 Forms of Corrosion
1
Table 1.2 List of Some Systems Leading to SCC (9)
Table 1.3 Comparative Features of HIC and SSC (10)
CHAPTER 2: CORROSION COSTS
Table 2.1 Direct and Indirect Costs of Corrosion
Table 2.2 UK National Cost of Corrosion
Table 2.3
Estimated Potential Savings of the UK National Costs by Industry
Table 2.4 Costs to Prevent Corrosion by Protection Method
Table 2.5 Costs to Prevent Corrosion by Industry Sector
Table 2.6 Capital and Maintenance Costs
Table 2.7 Best Practice Ratings
Table 2.8 Estimated Losses Because of Friction and Wear in Canadian Economic Sectors
Table 2.9 Corrosion Costs in the Mining Sector
Table 2.10 Corrosion Costs in Various Countries
Table 2.11 Corrosion Costs in Farming in the United Kingdom
CHAPTER 3: CORROSION CAUSES
Table 3.1 North American Railroads (1999)
Table 3.2 Summary of Miles of Gas Distribution
Table 3.3 Corrosion and Water Quality Problems Caused by Materials in Contact with Drinking Water (17)
Table 3.4 O&M Costs for 1996
Table 3.5 Percentage of the World's Fleet by Class of Ship
Table 3.6 Percentage of World's Fleet by Class of Ship on the Basis of Gross Tonnage
Table 3.7 Major Carrier Jet Fleets in 1997
Table 3.8. Commodities Transported by Railroad Car Loads
Table 3.9 Hazard Classifications
Table 3.10 Daily and Annual Number of Hazmat Shipments
Table 3.11 Hazardous Materials Carried by Trucks as Reported in VIUS
Table 3.12 Corrosion Failure Modes Along with the Frequency of Occurrence
Table 3.13 Distribution of Stress Corrosion Cracking of Different Construction Materials
Table 3.14 Major Input Items and Farm Production Expenditures on 1997
Table 3.15 Instruments System Automation Society Classes
Table 3.16 Number and Percentage of Corrosion-Affected Parts in HMMWV Vehicles
Table 3.17 Data on HMMVS with Deteriorated CARC Paint
Table 3.18 Helicopters and Duties
Table 3.19 Elements of Total Corrosion Maintenance Cost to Air Force
Table 3.20 Corrosion Maintenance Cost for Individual Military Aircraft in 1990 and 1997
Table 3.21 Annual Maintenance Demand on Sailors for Coating Maintenance
Table 3.22 Volume of Low-Level Waste Received at US Disposal Facilities
CHAPTER 4: CORROSION CONTROL AND PREVENTION
Table 4.1 Costs of Corrosion Control Methods and Services
Table 4.2 Value of Corrosion-Related Architectural Coatings
Table 4.3 OEM Corrosion Control Coatings
Table 4.4 Value of Special-Purpose Corrosion Control
Table 4.5 Summary for Corrosion Control Coatings Sold in 1997
Table 4.6 Distribution of 1998 Coating Sales by End-Users
Table 4.7 Stainless Steel Consumption
Table 4.8 Prices of Metals
Table 4.9 Consumption of Corrosion Inhibitors in the United States in 1998
Table 4.10 Distribution of Composite Shipments (K. Walshon, Society of Plastics Industry, Composites Institute, Personal communication, Oct. 1999.)
Table 4.11 The Use of Polyethylene Pipe in the United States in 1998 (14)
Table 4.12 Fraction of Polymers Used for Corrosion Control in 1997
Table 4.13 Total Cost of Components for Cathodic and Anodic Protection
Table 4.14 Cost of Installation of Cathodic Protection Systems
Table 4.15 Summary of Costs and Life Expectancy for New Construction Corrosion Control
Table 4.16 Summary of Costs and Life Expectancy for Rehabilitation Methods
Table 4.17 Cost and Life Expectancy for Overlay and Patching Options for Concrete Bridges
Table 4.18 Cost of Alkyd, Epoxy, and Epoxy/Urethane Coatings
Table 4.19 Coating System Time-to-Failure Estimates in Marine Environment
Table 4.20 Estimated Costs for Painting Options
Table 4.21 Cost Distribution of Coating Application on Steel Bridge Structure (34)
Table 4.22 Estimated Costs for Operation and Maintenance Associated with Corrosion and Corrosion Control
Table 4.23 Factors to be Considered for Pipeline Rehabilitation
Table 4.24 Summary of Miles of Gas Distribution Main and Number of Services by Material
Table 4.25 Total Annual Corrosion-Related Costs
Table 4.26 Volume of Low-Level Waste Received in the US Disposal Facilities
Table 4.27 Corrosion Control Methods for Aboveground Storage Tanks
Table 4.28 The Most commonly Used Corrosion Control Methods for Water Systems
Table 4.29 Commonly Used Inhibitors in PoTable Water systems (45, 46)
Table 4.30 Costs of Chemicals Used for Corrosion Control (47)
Table 4.31 Materials Used in Transmission Water Pipes
Table 4.32 Estimated Costs for Water Pipe Rehabilitation by Cement Mortar Lining
Table 4.33 Types and Frequency of Failure of Copper Plumbing in the United States in 1983
Table 4.34 Corrosion Control Program Implementation Flowchart for Internal Corrosion
Table 4.35 Repair Methods for Water Systems with Corrosion Damage
Table 4.36 Summary of Issues in Corrosion Control and Prevention
Table 4.37 Field Data on Corrosion Defects
Table 4.38 Automobile Corrosion
Table 4.39 Performance of Plain Steel, Prepainted Steel, and Zn/Zn Coated Steels
Table 4.40 Two Methods of Phosphating on Automobiles
Table 4.41 Typical Costs for One Large Oilfield
Table 4.42 Field Histories
Table 4.43 Material Selected for Flow Lines and Trunk Lines
Table 4.44 Coating Systems and Initial Cost
Table 4.45 Comparison of the Relative Costs of Various Alloys
Table 4.46 Corrosion Failure Mode with Average Frequency of Occurrence
Table 4.47 Stress Corrosion Cracking Failures of Different Alloys
Table 4.48 Relative Costs of Some Alloys Used in Corrosion Control
Table 4.49 Corrosion Monitoring Techniques with Advantages and Disadvantages
Table 4.50 CARC Paint System Performance
Table 4.51 Annual Coating Maintenance of Navy Surface Ships
CHAPTER 5: CONSEQUENCES OF CORROSION
Table 5.1 Direct and Indirect Costs of Corrosion
Table 5.2 Corrosion Costs in the United Kingdom by Major Industry
Table 5.3 Costs of Corrosion Protection Methods in Japan
Table 5.4 Cost of Corrosion in the Japanese Industrial Sector (Hoar Method)
Table 5.5 Capital and Corrosion Maintenance Costs of Government Assets
Table 5.6 Cost of Cathodic Protection and Replacement of Water Main
Table 5.7 Failure Modes in 2002
Table 5.8 Applications of Overlay Technology
Table 5.9 Corrosion Resistance of Some Steels
Table 5.10 Pipeline Accidents and Injuries Between 1989 and 1998
Table 5.11 Summary of Corrosion-Related Accidents in Pipelines
CHALLENGES IN CORROSION
Costs, Causes, Consequences, and Control
V. S. SASTRI
Sai Ram Consultants, Ottawa, Ontario, Canada
Copyright © 2015 by John Wiley & Sons, Inc. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging-in-Publication Data:
Sastri, V. S. (Vedula S.), 1935-
Challenges in corrosion : costs, causes, consequences and control / V.S. Sastri.
pages cm
Includes index.
ISBN 978-1-118-52210-3 (cloth)
1. Corrosion and anti-corrosives–Industrial applications. 2. Corrosion and anti-corrosives–Costs. 3. Machine parts–Failures–Economic aspects. I. Title.
TA462.S31485 2015
620.1'1223–dc23
2015000694
Dedicated to Sri Vighneswara, Sri Venkateswara, Sri Anjaneya, Sri Satya Sai Baba, my parents and teachers, my revered wife Bonnie, and children, Anjali Eva Sastri and Martin Anil Kumar Sastri.
PREFACE
This book is an attempt to present a subject which affects everyone of us in our daily lives in a simple form. Corrosion manifests itself in many forms. Without the use of metals, our society would not have advanced, but we allow our most valuable natural resources to be wasted through corrosion.
Corrosion is inevitable, but it can be controlled. Scientists have a major responsibility by their contributions and efforts to reduce unnecessary levels of corrosion, and it is the responsibility of everyone who uses metals to the best advantage. An understanding of corrosion and its control is important for everybody, if only for the obvious reason that it saves money. Studies of the effects of corrosion on society have shown that we seem unable to learn from our mistakes. Thus, the aim and scope of this book is to address corrosion problems, the resulting costs and methods of preventing and controlling the corrosion problems to achieve reduced corrosion costs, save lives and lessen environmental damage.
This book is centered around five facets of corrosion science: (i) introduction and forms of corrosion; (ii) corrosion costs in various economic sectors; (iii) causes of various forms of corrosion; (iv) various methods of corrosion control and prevention in various sectors and (v) consequences of corrosion.
The first chapter constitutes an introduction to corrosion and various forms of corrosion such as general or uniform or quasi-uniform corrosion, galvanic corrosion, stray current corrosion, localized corrosion, such as pitting and crevice corrosion, metallurgically influenced and microbiologically influenced corrosion, mechanically assisted corrosion and environmentally induced cracking.
The second chapter deals with corrosion costs in various countries such as the United States of America, the United Kingdom, Australia, Kuwait, West Germany, Finland, Sweden, India and China in various industry sectors such as highway bridges, gas and liquid transmission pipelines, waterways and ports, hazardous materials transport and storage, airports, railroads, utilities, gas distribution, drinking water and sewer systems, electrical utilities, telecommunications, transportation, motor vehicles, ships, aircraft, railroad cars, production and manufacturing, oil and gas exploration and production, mining, petroleum refining, chemical, petrochemical and pharmaceutical production, pulp and paper, agricultural production, food processing, electronics, home appliances, government, defense, nuclear waste storage and tribology.
The third chapter discusses causes of corrosion in a variety of industry sectors such as concrete and steel bridges, underground pipelines, waterways and ports, hazardous materials storage, corrosion problems in airports, railroads, gas pipelines, drinking water and sewer systems, electrical utilities, telecommunications, automobiles, ships, aircraft, mining industry, petroleum refining, chemical, petrochemical and pharmaceutical industries, pulp and paper, agricultural production, food processing, electronics, home appliances and nuclear waste storage.
The fourth chapter is concerned with corrosion control and prevention, including topics such as protective coatings, metals and alloys, corrosion inhibitors, engineering composites and plastics, cathodic and anodic protection, corrosion control of bridges, mitigating corrosion of steel in underwater tunnels, gas and liquid pipelines, waterways and ports, hazardous waste storage, storage tanks, railroads, drinking water and sewer systems, electric utilities, telecommunications, automobiles, ships, aircraft, oil and gas industry, mining industry, hazardous materials transport, petroleum refining, chemical and petrochemical industry, pulp and paper industry, agricultural products, food industry, electronics, home appliances, defense and other preventive strategies.
The final chapter discusses the consequences of corrosion such as economic losses, loss in production, fatal accidents resulting in injuries and loss of lives and damage to our living environment by polluting the environment.
This monograph will be useful to students in engineering and applied chemistry as a prescribed book in both undergraduate and graduate courses. The book may also be used by students in general arts as a general interest elective course.
V. S. Sastri
ACKNOWLEDGMENTS
I wish to express my deep gratitude to my wife, Bonnie, for her painstaking efforts in transcribing the text. I also wish to thank my son-in-law, Gerry Burtenshaw, and my daughter, Anjali, for imaging the figures and my son, Martin, for his moral support.
I wish to thank the following organizations for granting permission to reproduce figures:
American Society of Metals, Canadian Institute of Mining, Metallurgy and Petroleum, Elsevier, National Association of Corrosion Engineers, Society of Petroleum Engineers, John Wiley & Sons. Thanks are also due to David Raymond, City of Ottawa (retired), for using his photographs.
Finally, I wish to express my gratitude to the editorial and production staff of John Wiley & Sons for their kind support throughout the writing, reviewing and production of the manuscript.
V. S. SastriSai Ram Consultant
Ottawa, Ontario, Canada
CHAPTER 1INTRODUCTION AND FORMS OF CORROSION
Corrosion is basically a combination of technical and economic problems. To understand the economics of corrosion, it is necessary that one is proficient in both the science of corrosion and the fundamental principles of economics. There are many forms of corrosion, which can be deleterious in a variety of ways. It is logical to discuss the various forms of corrosion of metallic structures occurring in different corrosive environments.
1.1 GENERAL OR UNIFORM OR QUASI-UNIFORM CORROSION
General corrosion is the most common form of corrosion. This can be uniform (even), quasi-uniform, or uneven. General corrosion accounts for the greatest loss of metal or material. Electrochemical general corrosion in aqueous media can include galvanic or bimetallic corrosion, atmospheric corrosion, stray current dissolution, and biological corrosion (Table 1.1).
Table 1.1 Forms of Corrosion1
1. General corrosion
Uniform, quasi-uniform, nonuniform corrosion, galvanic corrosion
2. Localized corrosion
Pitting corrosion, crevice corrosion, filiform corrosion
3. Metallurgically influenced corrosion
Intergranular corrosion, sensitization, exfoliation, dealloying
4. Microbiologically influenced corrosion
5. Mechanically assisted corrosion
Wear corrosion, erosion–corrosion, corrosion fatigue
6. Environmentally induced cracking
Stress-corrosion cracking; hydrogen damage, embrittlement; hydrogen-induced blistering; high-temperature hydrogen attack; hot cracking, hydride formation; liquid metal embrittlement; solid metal-induced embrittlement
1 ASM Metals Handbook, Corrosion, Vol. 13, 9th ed., Craig and Pohlman, pp. 77–189.
Dissolution of steel or zinc in sulfuric or hydrochloric acid is a typical example of uniform electrochemical attack. Uniform corrosion often results from exposure to polluted industrial environments, exposure to fresh, brackish, and salt waters, or exposure to soils and chemicals. Some examples of uniform or general corrosion are the rusting of steel, the green patina on copper, tarnishing silver, and white rust on zinc on atmospheric exposure. Tarnishing of silver in air, oxidation of aluminum in air, attack of lead in sulfate-containing environments results in the formation of thin protective films and the metal surface remains smooth. Oxidation, sulfidation, carburization, hydrogen effects, and hot corrosion can be considered as types of general corrosion(16).
Liquid metals and molten salts at high temperatures lead to general corrosion(1). Microelectrochemical cells result in uniform general corrosion. Uniform general corrosion can be observed during chemical and electrochemical polishing and passivity where anodic and cathodic sites are physically inseparable. A polished surface of a pure active metal immersed in a natural medium (atmosphere) can suffer from galvanic cells. Most of the time, the asperities act as anodes and the cavities as cathodes. If these anodic and cathodic sites are mobile and change in a continuous dynamic manner, uniform or quasi-uniform corrosion is observed. If some anodic sites persist and are not covered by protective corrosion products, or do not passivate, localized corrosion is observed (1).
Some macroelectrochemical cells can cause a uniform or near-uniform general attack of certain regions. General uneven or quasi-uniform corrosion is observed in natural environments. In some cases, uniform corrosion produces a somewhat rough surface by the removal of a substantial amount of metal that either dissolves in the environment or reacts with it to produce a loosely adherent, porous coating of corrosion products. After careful removal of rust formed because of general atmospheric corrosion of steel, the surface reveals an undulated surface, indicating nonuniform attack of different areas (1) as shown in Figure 1.1.
Figure 1.1 Even and uneven general corrosion and high-temperature attack. (Reproduced by permission, Elsevier Ltd. (2).)
In natural atmospheres, the general corrosion of metals can be localized. The corrosion morphology is dependent on the conductivity, ionic species, temperature of the electrolyte, alloy composition, phases, and homogeneity in the microstructure of the alloy, and differential oxygenation cell. The figure also shows high-temperature attack that is generally uniform. It is also possible to observe subsurface corrosion films within the matrix of the alloy because of the film formation at the interface of certain microstructures in several alloys at high temperatures (3).
The main factors governing general corrosion are: (i) agitation, (ii) pH of the medium, (iii) temperature, and (iv) protective passive films.
The agitation of the medium has a profound influence on the corrosion performance of the metals as agitation accelerates corrosion performance of the metals, accelerates the diffusion of corrosive species, or destroys the passive film mechanically.
Low pH (acidic) values accelerate the rate of corrosion as for an active metal such as iron or zinc, the cathodic reaction controls the rate of reaction in accordance with the equation
The plot of electrode potential against the logarithm of current density gives rise to a Tafel plot shown in Figure 1.2. From this plot, a logarithm of corrosion current density can be obtained. The Evans diagrams obtained by the extrapolation of Tafel slopes for the cathodic and anodic polarization curves shown in Figure 1.2 can also been seen in Figures 1.3 and 1.4. In general, the cathodic Tafel slopes are reproducible and reliable for evaluation of corrosion rates as they represent noncorroded original surface of the metal. It is obvious that the corrosion current is greater in acidic solution. The influence of pH also depends on the composition of the alloy as seen in Figure 1.4. When the zinc is present with mercury amalgam, the corrosion current is lower than when the metal is zinc alone. When zinc is present along with platinum, high corrosion rates are observed as platinum provides effective cathodic sites for hydrogen evolution. In addition to this, the stability of the passive film in acid, neutral, or alkaline pH is a contributing factor. Some examples are the stability of magnesium fluoride in alkaline medium and the amphoteric nature of aluminum oxide in pH of 4–8 solutions.
Figure 1.2 Theoretical Tafel plots. (Reproduced by permission, ASM International (4).)
Figure 1.3 Evans diagram for corrosion of zinc as a function of pH. (Reproduced by permission, Elsevier Ltd., (2).)
Figure 1.4 Evans diagram for corrosion of zinc alloys. (Reproduced by permission, Elsevier Ltd., (2).)
The difference in temperature can create a corrosion cell in the case of copper tubes. In general, increase in temperature results in increased corrosion rate. The corrosion rate of steel in acid solutions doubles for an increase of 10 °C between 15 and 70 °C. At temperatures above 70 °C, the solubility of oxygen in aqueous solutions is low, and the rate of reaction cannot be doubled.
Protective passive films similar to that of stainless steels result in uniform corrosion because of the mobility of the active sites that passivate readily. Corrosion products and/or passive films are characteristic of numerous electrochemical reactions of the alloys. The film is protective depending on coverage capacity, conductivity, partial pressure, porosity, toughness, hardness, and resistance to chemicals and gases. Rust, oxides of iron, and zinc oxide (white rust) are not protective, while patina (CuO), Al
2
O
3
, MgO, and Cr
2
O
3
are protective in certain environments. Corrosion is generally controlled by diffusion of active species through the film.
1.2 GALVANIC CORROSION
When a metal or alloy is electrically coupled to another metal or conducting nonmetal in the same electrolyte, a galvanic cell is formed. The electromotive force and the current of the galvanic cell depend on the properties of the electrolyte and the polarization characteristics of the anodic and the cathodic reactions. Galvanic corrosion is caused by the contact of two metals or conductors with different potentials. The galvanic corrosion is also called as dissimilar metallic corrosion or bimetallic corrosion where the metal is the conductor material.
Galvanic corrosion can lead to general corrosion, localized corrosion, and sometimes both. Although the dissolution of active metals in acids is because of the numerous galvanic cells on the same metallic surface, it is generally referred to as general corrosion. In less aggressive media such as natural media consisting of dissimilar electrode cells, galvanic corrosion can start as general corrosion that can lead to localized corrosion because of different microstructures or impurities in several cases. Localized galvanic attack depends on the distribution and morphology of metallic phases, solution properties, agitation, and temperature. Localized galvanic corrosion can result in the perforation or failure of the structure.
Galvanic corrosion occurs when two metals with different electrochemical potentials are in contact in the same solution (Figs. 1.5 and 1.6). In both cases(5,7) the corrosion of iron/steel is exothermic, and the cathodic reaction controls the rate of corrosion. The more noble metal, copper, increases the corrosion rate through the cathodic reaction of hydrogen ion reduction and hydrogen evolution. A passive oxide film on stainless steel can accelerate hydrogen reduction reaction.
Figure 1.5 Galvanic corrosion of mild steel elbow fixed to a copper pipe. (Reproduced by permission, National Association of Corrosion Engineers International (5).)
Figure 1.6 Galvanic corrosion of painted auto panel in contact with stainless steel wheel opening molding. (Reproduced by permission, ASM International (6).)
In engineering design, a junction of two different metals is seldom recommended. It is possible to use alloys with close values of potential in a certain medium. Some of the factors that can be deleterious are mechanical shaping, bending, or lamination of part of the metal, thermal treatment of metallic structure, welding, and cooking coils in vessels and heat exchangers can create galvanic cells of the same metal. These cells are known as macrogalvanic cells, which are different from microgalvanic cells present even in pure metals in a corrosive medium (5, 7).
In general, the galvanic cell is influenced by (i) the difference in potential between two metals/materials, (ii) the nature of the medium or environment, (iii) polarization of the metals, and (iv) the geometry of the cathodic and anodic sites such as shape, relative surface areas, distance.
For example, it is not desirable to have a small anode connected to a large cathode as this favors accelerated localized anodic dissolution. Rivets of copper on a steel plate and steel rivets on a copper plate on immersion in seawater for a period of 15 months resulted in the steel plate covered with corrosion products while the steel rivets were corroded completely and disappeared. As copper is more noble than iron, it accelerated the hydrogen reduction reaction for the oxidation of the steel plate. In the case of the copper plate with steel rivets, the steel rivets corroded because of the relatively important cathodic surface of copper. The same reasoning applies to the corrosion of noncoated auto parts in contact with a large stainless steel surface (Fig. 1.6).
Galvanic corrosion occurs because of : (i) nonmetallic conductors and corrosion products, (ii) metallic coatings and sacrificial anodes, (iii) polarity inversion, (iv) deposition corrosion, (v) hydrogen cracking or damage, (vi) high temperature.
Nonmetallic Conductors and Corrosion Products
. Carbon brick in vessels, graphite in heat exchangers, carbon-filled polymers, oxides such as mill scale (magnetite Fe
3
O
4
), iron sulfides on steel, lead sulfate on lead can act as effective cathodes with an important area to that of anodes. Very often the pores of the conductive film are the preferred anodic sites that lead to pitting corrosion.
Metallic Coatings and Sacrificial Anodes
. Some sacrificial metal coatings provide cathodic protection for base metals, such as galvanized steel or Alclad aluminum. If the metal coating is more noble than the base metal such as nickel on steel pitting of the base metal at pores, damage sites and edges can occur. It is important to note that the coatings should be kept free of pores, scratches, or any penetrating chemical attack or deterioration of the coat such as paint.
Sacrificial anodes, such as magnesium, zinc, and aluminum are used extensively for cathodic protection in some locations where impressed current systems are forbidden because of stray currents.
Polarity Inversion
. The properties of the electrolyte such as pH, potential, temperature, fluid flow, concentration of different ions, dissolved gases, and conductivity can change with time and influence the polarization, the properties of the interface, and the galvanic potential of the components. The change in ion activity of one metal can reverse the polarity of iron–tin couple for iron-plated tin food cans. This shows the importance of media in galvanic corrosion where the canned food boxes are made of iron with a coated inside layer of tin. The tin may then react with food constituents forming a soluble complex. The concentration of tin is sufficient to the extent that it becomes anodic to that or iron and begins to corrode. Also, iron is protected by zinc coating as a sacrificial anode (galvanization) because of the formation of Zn(OH)
2
and white rust, and at temperatures above 60° a hard compact ZnO layer is formed, which is cathodic to iron, and this layer is able to reverse the polarity sign of the couple Fe–Zn. This phenomenon is observed with Cu–Al or Ag–Cu couples (8).
Deposition Corrosion
. Dissimilar metallic corrosion can occur following the cementation of a more noble metal. In copper pipes carrying soft water containing carbonic acid into galvanized tank, any dissolved copper ions can be deposited according to the reaction
which causes additional galvanic corrosion of zinc.
Severe corrosion may occur in active Al or Mg alloys in neutral solutions of heavy metal salts (salts of Cu, Fe, or Ni). This type of corrosion occurs when the heavy metal salts plate out to form active cathodes on the anodic magnesium surface. This type of galvanic corrosion can lead to localized pitting corrosion.
Hydrogen Cracking
. Self-tapping of martensitic stainless steel screws attached to aluminum roof in seacoast atmosphere failed by cracking. Hardened martensitic stainless steel propellers coupled to steel hull of a ship failed by cracking in service. Tantalum is embrittled by hydrogen on polarization or coupled to a more active metal in an electrolyte (8).
High-Temperature Galvanic Corrosion
. High-temperature galvanic corrosion is involved in the reaction of silver with gaseous iodine at 174 °C in 1 atm oxygen, which is accelerated by contact of silver with tantalum/platinum/graphite (8).
1.2.1 Factors involved in Galvanic Corrosion
Electromotive force (emf) series and “practical nobility” of metals and metalloids are given in Table 1.2. The emf series, also known as the Nernst scale of solution potentials, are proportional to the free energy changes of the corresponding reversible half-cell reactions with respect to the standard hydrogen electrode. The “thermodynamic nobility” may differ from “practical nobility” because of the formation of passive layer and electrochemical kinetics.
Table 1.2 List of Some Systems Leading to SCC (9)
Alloy
Environment
Aluminum alloys
Aqueous chloride, cyanide, high-purity hot water
Carbon steels
Aqueous amines, anhydrous ammonia, aqueous carbonate, CO
2
, aqueous hydroxides, nitrates
Copper alloys
Aqueous amines, aqueous ammonia, hydrofluoric acid, aqueous nitrates, aqueous nitrites, steam
Nickel alloys
Aqueous chlorides, concentrated chlorides, boiling chlorides, aqueous fluorides, concentrated hydroxides, polythionic acids, high-purity hot water
Austenitic stainless steels
Aqueous/concentrated chlorides, aqueous/concentrated hydroxides, polythionic acids sulfides plus chlorides, sulfurous acid
Duplex stainless steels
Aqueous/concentrated chlorides, aqueous/concentrate hydroxides, sulfides along with chlorides
Martensitic stainless steels
Aqueous/concentrate hydroxides, aqueous nitrates, sulfides plus chlorides
Titanium alloys
Dry hot chlorides, hydrochloric acid, methanol plus halides, fuming nitric acid, nitrogen dioxide
Zirconium alloys
Aqueous bromine aqueous chloride, chlorinated solvents, methanolic halides, concentrated nitric acid
Ignoring the kinetics and assuming that the passivating films are protective, the practical nobility depends on (i) immunity and passivation domains, and (ii) the stability domain of water. Practical nobility is greater when the immunity and passivation domains extend below and above the stability domain of water and the greater the overlap of these domains with the part of the diagram between pH 4 and 10. Table 1.3 shows the classification of 43 elements according to thermodynamic stability and practical nobility. This table of thermodynamic nobility and practical nobility must be regarded as a guide as the electrochemical equilibrium diagrams are themselves approximate in nature.
Table 1.3 Comparative Features of HIC and SSC (10)
Phenomenon
Hydrogen-Induced Cracking
Sulfide Stress Cracking
Crack direction
Parallel to applied stress
Perpendicular to stress
Applied stress
No effect
Affects critically
Material strength
Primarily in low-strength steel
Primarily in high-strength steel
Location
Ingot core
Anywhere
Microstructure
Trivial effect
Critical effectQuenching and tempering enhances SSC resistance
Environment
Highly corrosive conditions, considerable hydrogen uptake
Can occur even in mildly corrosive media
1.2.2 Galvanic Series and Corrosion
The practical change of the potential of the components of a galvanic couple as a function of time is important. When the potential difference between two metals is sufficient to form a sustained galvanic cell, the potential of every electrode can be varied because of the active–passive behavior, the properties of the passive or corrosion barriers, and the change in ion concentrations. The galvanic series is a list of corrosion potentials, each of which is formed by the polarization of two or more half-cell reactions to a common mixed potential, Ecorr measured with respect to a reference electrode such as a calomel electrode. The galvanic series is a list of corrosion potentials in seawater as shown in Figure 1.7. The material with the most negative potential has a tendency to corrode when it is in contact or connected to a metal with more positive or noble potential.
Figure 1.7 Galvanic series of metals in seawater. (Reproduced by permission, National Association of Corrosion Engineers International (11).)
The galvanic series is useful in giving a qualitative indication of the possibility of galvanic corrosion in a given medium under some environmental conditions.
1.2.3 The Nature of the Metal/Solution Interface
Cast iron corrodes because of the exposure of graphite content of cast iron (graphitic corrosion), which is cathodic to both low alloy and mild steels. The trim of a valve must be cathodic to the valve body to avoid pitting attack. Thus in aggressive media valve bodies of steel are preferred to cast iron bodies. Steel bolts and nuts coupled to underground mild steel pipes or a weld rod used for steel plates on the hull of a ship should always be of a low nickel, low chromium steel, or from a similar composition to that of the steel pipe (8).
1.2.4 Polarization of the Galvanic Cell
The different phenomena of polarization of the anodic and cathodic reactions (activation, diffusion, convection) should be well known as a function of the evolution and change of the properties of the interface as a function of time. The polarization behavior of the cathode and anodic reactions on the two electrodes should be examined. In natural atmospheres, the cathodic reaction controls frequently the rate of attack. The diffusion of oxygen is an important parameter to avoid control and polarization of the corrosion by the rate of the cathodic reaction (8) (Fig. 1.8).
Figure 1.8 Effect of oxygen concentration on the corrosion of mild steel in slowly moving water (8).
The resistance overpotential of the cell IR is mainly a function of the conductivity of the electrolyte solution and the distance between the electrodes as the electrolytic resistance is more important than the electric resistance of the metals. Thus if dissimilar pipes are butt-welded with the flow of electrolyte, the most severe corrosion will occur near the weld on the active metal. In soft water, the critical distance between copper and iron may be 5 mm and several decimeters in seawater. The critical distance is greater when the potential difference between the anode and cathode is larger. The geometry of the circuit affects galvanic corrosion as observed in stray current corrosion (8).
The relative area ratio of anodic to cathodic sites is critical for general and/or localized corrosive attack. The anode to cathode area ratio along with the conductivity of the electrolyte controls the corrosion rate. When the surface area of the anode is small as compared to the cathode and the solution is of low conductivity, the uniform corrosion can change to quasi-uniform corrosion, severe pitting, or other types of localized corrosion. When the diffusion of oxygen is rate-determining, large cathode/anode area ratios will result in severe galvanic corrosion (12).
In the case where diffusion of corrosive ions is a rate-controlling reaction, it has been found that the relationship
is valid, where P is the penetration that is proportional to the corrosion rate, P0 is the corrosion rate of less noble uncoupled metal, Ac and Aa are the areas of more noble and active metal, respectively (8). When galvanic cell cannot be avoided, a large anode and a limited size cathode are recommended for use. Stagnant condition and weak electrolytes may cause pitting corrosion in spite of the large area of the exposed active metal.
An example illustrative of the effect of relative areas of anodic and cathodic surfaces consists of steel reservoirs covered with phenolic paint with the bottom clad with stainless steel filled with corrosive solutions. After a few months the perforation of the steel wall at about 5 cm away from the weld of steel wall close to the stainless steel bottom was observed. Large cathodes and small anodes are not desirable as there is no perfect coating, and the paint on steel has some defects such as pores. The pores act as anodes and the stainless steel bottom as the cathode. The corrosion current can be multiplied by a factor of 10–20 resulting in a quick penetration of the anodic sites. This failure shows (i) the cathodic control, which limits the corrosion current in several aqueous solutions is not operational; (ii) the distance factor and its effect on the failure is evident as the perforation occurred near the welding junction in low-conducting solutions. Galvanic corrosion can be prevented or reduced by (i) avoiding contact between metals with different potentials; (ii) protection by metallic, nonmetallic, nonorganic, organic (paints, lacquer) coatings is recommended; (iii) large cathodes and small anodic surfaces should be avoided; (iv) electrochemical testing and determination of polarization characteristics of all the components as recommended in Pourbaix diagrams of the system should be consulted; (v) use of corrosion inhibitors should be considered; (vi) prediction of the anodic and cathodic components of the galvanic cell and inversion of the polarity of the cell should be considered; (vii) cathodic protection is the only complete protection of the metallic surface.
1.2.5 Testing of Galvanic Corrosion
Corrosion testing for galvanic corrosion may be predicted by ASTM standards in the form of potential measurements. The driving force for galvanic corrosion is the potential difference between the anode and cathode. The galvanic currents between two dissimilar metals are measured using a zero resistance ammeter (ZRA) for a chosen length of time. The ratio of anode to cathode areas is 1:1.
1.3 STRAY CURRENT CORROSION
In the past, stray currents resulted from DC-powered trolled systems, which are now obsolete. An electric welding machine on board the ship with a grounded DC line located on shore will cause accelerated attack of the ship's hull as the stray currents at the welding electrodes pass out of the ship's hull through the water back to the shore. Houses in close proximity can dramatically corrode at the water line. The pipe in one house may be heavily corroded while the pipes in a neighboring house may be intact.
The majority of stray current problems occur in cathodic protection systems. The current from an impressed current cathodic protection system will pass through the metal of a neighboring pipeline at some distance before it returns to the protected surface. Increased anodic corrosion is frequently localized on the pipe at the zone where the current leaves the pipe back to the protected steel tank.
Stray current flowing along a pipeline very often will not cause damage inside the pipe, because of the high conductivity of the electric path compared with the electrolytic path. The damage occurs when the current reenters the electrolyte and will be localized on the outside surface of the metal. If the pipe has insulated joints and the stray current enters the internal fluid, localized corrosion on the internal side of the pipe will occur. The best solution to avoid this mode of corrosion is the electrical bonding of nearby structure and adding additional anodes and increasing rectifier capacity (13). Stray currents follow paths other than their intended circuit. They leave their intended path because of poor electrical connections or poor insulation around the intended conductive material. The escaped current then will pass through the soil, water, or any other suitable electrolyte to find a low-buried path such as metallic pipe. Stray currents cause accelerated corrosion when they leave the metal structure and enter the surrounding electrolyte. These corrosion sites can be several hundreds of meters away.
