Cracking selectivity, influencing factors

A nonchemical factor also influences a sand fly s selection of egg sites She prefers narrow cracks and crevices rather than open surfaces. A gravid sand fly, then, is quite exacting about where she deposits her eggs. She avoids exposed areas and looks for a site that already contains eggs of her own species along with simple organic nutrients. Her concerns seem well placed, for these characteristics promise safety, protection from the elements, and food for newly hatched larvae. 

The mechanistic differences between SSC and SCC (anodic type) have a significant influence on the test methods used. Stated simply, the critical vciriable in SSC of carbon and low-alloy steels is the stress (strain) required to initiate and sustain cracking in an arbitrarily selected severe environment. In SCC, the critical variables are the electrochemical polarization characteristics of the metal/environ-ment system that control the anodic processes involved in crack initiation and growth. Therefore, alloy SCC susceptibility comparisons are done by determining the critical environmental factors (e.g., temperature, H2S partial pressure, chloride concentration) required to cause failure of a severely stressed specimen. 

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