CorrosionDOE-HDBK-1015/1-93SPECIALIZED CORROSIONRev. 0CH-02Page 37Specialized Corrosion Summary (Cont.)Stress corrosion cracking (SCC) is a great concern due to the hazard that it canreadily crack metal of appreciable thickness. The crack can lead to a seriousfailure of the component, or system, and all the attendant results such as:ContaminationLoss of coolantLoss of pressureSCC is prevented in reactor system by:Proper designReducing stress levelsAvoiding stagnant areas and crevices in heat exchangers, where chloridesand hydroxides might become concentrated.Chloride stress corrosionThe three conditions that must be present for chloride stress corrosion to occurare:Chloride ions presentDissolved oxygen presentMetal under tensile stressChloride stress corrosion is controlled by maintaining low chloride ion andoxygen content in the environment and the use of low carbon steels.Caustic stress corrosionCaustic stress corrosion is similar to chloride stress corrosion. The metalsinvolved are mild steels (steel with low carbon and low alloy content). Themetals are exposed to concentrated caustic environments and under tensile stress.The presence of oxygen is not required for cracking to initiate. Concentration ofgreater than 10,000 ppm is required for cracking to initiate. The level may behigher for different caustic environments.
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