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To enable nondestructive inspection, construction rules generally specify the final surface condition of components only in terms of limiting roughness values. However, the microgeometry is only one of many important surface characteristics. Failure to ensure overall cleanness of circuits (i.e., of all exposed surfaces) by taking certain precautions can have serious consequences. Furthermore, the presence of a heavily cold-worked surface layer, from machining or other causes, can completely modify its corrosion behavior in service. It has long been known that the oxidation resistance of stainless steels in steam or carbon dioxide (CO{sub 2}) at temperatures in the vicinity of 500 C is considerably improved by a cold-worked surface layer, which enhances Cr diffusion and promotes the formation of a tenacious and protective oxide scale. More recently, the effect of cold-worked surface layers on the susceptibility to stress corrosion cracking has been clearly revealed in components that have been subjected to strain during manufacture by tube bending, expansion operations, or even welding. Very high residual stresses can be induced in the skin region, and if the cold-worked layer is sufficiently thick, cracks can be initiated in a very short time. Based on the difference in the depth of cold work induced by various mechanical treatments, it has been possible to model this effect and to explain the wide scatter in the service behavior of certain pressurized water reactor components. It is essential to take these factors into account to predict correctly the service behavior of the components concerned, without which satisfactory plant maintenance planning is impossible.
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