Two factors that have been found to have an important influence on stresscorrosion crack initiation, in certain cases, are the extent of environmental access and the presence of residual surface stresses. These are discussed, and examples from service are cited where such effects have played a major role. Restricted environmental access can be particularly significant in high-purity aqueous systems, such as exist in steam turbines, where the resulting stagnation can lead to the formation of aggressive environments and thus cause cracking. Residual stresses arising from machining operations can assist the initiation of cracks, while controlled shot-peening treatment has been found to be beneficial.
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