Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy, Ltd Introduction CORROSION is the deterioration of a material by a reaction with its environment. In a study by the U.s Federal Highway Administration in cooperation with the National Association of Corrosion Engineers(NACE), it was estimated that the annual cost of corrosion was between $121 and $138 billion in 1998 in the United States. These costs included cost of corrosion-control methods, equipment, and services; cost of labor attributed to corrosion management; cost of use of more expensive materials to lessen corrosion damage; and cost of lost revenue, loss of reliability, and loss of capital due to corrosion deterioration. Only selected industrial sectors were analyzed in the study. When extrapolated to all U.S. industries, the total cost estimate is $276 billion, or more than 3% of the U.S. gross domestic product(Ref 1). This great cost is a measure of the importance of corrosion management and an indication of the significance of potential cost saving that corrosion abatement can yield Reference cited in this section 1."Corrosion Costs and Preventive Strategies in the United States, FHWA-RD-01-156, Federal Highway Administration 2002 Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy Ltd Electrochemical Nature of Corrosion The articles in this Section are devoted to the identification and analysis of corrosion- related failures, the categorization of corrosion failures by form and mechanism, and the application of preventive measures. The mechanisms of corrosion are described in more detail in Corrosion, Volume 13 of the asm handbook However, as a brief introduction, the electrochemical nature of corrosion can be illustrated by the attack on zinc by hydrochloric acid. When zinc is placed in dilute hydrochloric acid, a vigorous reaction occurs; hydrogen gas is evolved and the zinc dissolves, forming an acidic aqueous solution of zinc chloride. The reaction is Zn+2HCl→ZnCl2+H (Eq I Since the chloride ion is not involved in the reaction, this equation can be written in the simplified form Zn+2H+→Zn2++H2 (Eq2) Zinc reacts with the hydrogen ions of the acid solution to form zinc ions and hydrogen gas. Equation 2 shows that during the reaction, zinc is oxidized to zinc ions and hydrogen ions are reduced to hydrogen. Thus, eq 2 can be conveniently divided into two reactions: the oxidation of zinc and the reduction of hydrogen ions Oxidation(anodic reaction)Zn-Zn+2 Reduction(cathodic reaction) 2H 2e H2Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy, Ltd. Introduction CORROSION is the deterioration of a material by a reaction with its environment. In a study by the U.S. Federal Highway Administration in cooperation with the National Association of Corrosion Engineers (NACE), it was estimated that the annual cost of corrosion was between $121 and $138 billion in 1998 in the United States. These costs included cost of corrosion-control methods, equipment, and services; cost of labor attributed to corrosion management; cost of use of more expensive materials to lessen corrosion damage; and cost of lost revenue, loss of reliability, and loss of capital due to corrosion deterioration. Only selected industrial sectors were analyzed in the study. When extrapolated to all U.S. industries, the total cost estimate is $276 billion, or more than 3% of the U.S. gross domestic product (Ref 1). This great cost is a measure of the importance of corrosion management and an indication of the significance of potential cost saving that corrosion abatement can yield. Reference cited in this section 1. “Corrosion Costs and Preventive Strategies in the United States,” FHWA-RD-01-156, Federal Highway Administration, 2002 Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy, Ltd. Electrochemical Nature of Corrosion The articles in this Section are devoted to the identification and analysis of corrosion-related failures, the categorization of corrosion failures by form and mechanism, and the application of preventive measures. The mechanisms of corrosion are described in more detail in Corrosion, Volume 13 of the ASM Handbook. However, as a brief introduction, the electrochemical nature of corrosion can be illustrated by the attack on zinc by hydrochloric acid. When zinc is placed in dilute hydrochloric acid, a vigorous reaction occurs; hydrogen gas is evolved and the zinc dissolves, forming an acidic aqueous solution of zinc chloride. The reaction is: Zn + 2HCl → ZnCl2 + H2 (Eq 1) Since the chloride ion is not involved in the reaction, this equation can be written in the simplified form: Zn + 2H+ → Zn2+ + H2 (Eq 2) Zinc reacts with the hydrogen ions of the acid solution to form zinc ions and hydrogen gas. Equation 2 shows that during the reaction, zinc is oxidized to zinc ions and hydrogen ions are reduced to hydrogen. Thus, Eq 2 can be conveniently divided into two reactions: the oxidation of zinc and the reduction of hydrogen ions: Oxidation (anodic reaction) Zn → Zn2+ + 2e (Eq 3) Reduction (cathodic reaction) 2H+ + 2e → H2 (Eq 4)