CORROSIONDOE-HDBK-1017/1-93Properties of MetalsCORROSIONCorrosion is a major factor in the selection of material for a reactor plant. Thematerial selected must resist the various types of corrosion discussed in theChemistry Fundamentals Handbook.EO 1.20STATE the reason that galvanic corrosion is a concern indesign and material selection.Corrosionis the deterioration of a material due to interaction with its environment. It is theprocess in which metallic atoms leave the metal or form compounds in the presence of water andgases. Metal atoms are removed from a structural element until it fails, or oxides build up insidea pipe until it is plugged. All metals and alloys are subject to corrosion. Even the noble metals,such as gold, are subject to corrosive attack in some environments. The corrosion of metals is a natural process. Most metals are not thermodynamically stable inthe metallic form; they want to corrode and revert to the more stable forms that are normallyfound in ores, such as oxides. Corrosion is of primary concern in nuclear reactor plants.Corrosion occurs continuously throughout the reactor plant, and every metal is subject to it. Eventhough this corrosion cannot be eliminated, it can be controlled.General corrosioninvolving water and steel generally results from chemical action where thesteel surface oxidizes, forming iron oxide (rust). Many of the systems and components in theplant are made from iron. Some standard methods associated with material selection that protect against general corrosioninclude:The use of corrosion-resistant materials such as stainless steel and nickel,chromium, and molybdenum alloys. (Keep in mind that the corrosion iselectrochemical by nature, and the corrosion resistance of the stainless steelsresults from surface oxide films that interfere with the electrochemical process.)The use of protective coatings such as paints and epoxies.The application of metallic and nonmetallic coatings or linings to the surfacewhich protects against corrosion, but allows the material to retain its structuralstrength (for example, a carbon steel pressure vessel with stainless steel claddingas a liner).MS-02Page 32Rev. 0
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