Modelling of environmentally assisted cracking in the stainless steel and low alloy steel/water systems at 2880C

Failure of structural components by stress corrosion or corrosion fatigue presents a possible life limiting factor in the operation of Light Water Reactors. The objective of this investigation (Ford et al. 1987) was to gain a quantitative knowledge of the mechanism of environmentally assisted cracking of ductile, structural steels in high temperature water. The specific uses of this knowledge were: (1) to provide a theoretical under-pinning to the empirically derived remedies for intergranular stress corrosion cracking of Type 304 stainless steel piping in Boiling Water Reactors, and (2) to evaluate the fundamental validity of the ASME XI (1980) life evaluation code for corrosion fatigue of low alloy pressure vessel steels in Light Water Reactor environments. The approach taken was to propose a working hypothesis for the mechanism of environmentally assisted crack propagation and then to independently evaluate the parameters of fundamental importance in this mechanism. On the basis of these data, theoretical values of the subcritical crack propagation rate could be predicted for different steady state and transient conditions of environment (e.g., degree of aeration, impurity content), material (e.g., degree of grain boundary sensitization, sulphur content), or stress, (e.g., static load, cyclic load). These predictions could then be compared with observed data in order to evaluate the quantitative validity of the original working hypothesis before applying it to the practical analyses referred to above. (orig.)