Quantification of the effects of crack tip plasticity on environmentally-assisted crack growth rates in LWR environments

Crack tip plasticity, such as stress and strain distribution/redistribution during crack propagation in environments, represented by crack tip strain rate (CTSR), plays a critical role in promoting environmentally assisted crack growth. Crack tip plasticity, in terms of stress/strain distribution, as well as plastic zone size, can enhance crack tip oxidation rates by causing physical degradation of the interfacial oxide film or by promoting mass transport, and/or electron-transfer processes in the crack tip region, and at grain boundaries in the case of intergranular stress corrosion cracking. Quantification of crack tip mechanics is critical for determining oxidation/deformation interactions and subsequent crack growth rate (CGR) formulations. The results of CGR vs. CTSR for sensitized 304 SS with or without warm rolling, for alloy 182 weld metal in simulated boiling water reactors environments, and for alloy 600 in simulated pressurized water reactors (PWRs) environments show a consistency between crack growth and the deformation/oxidation interaction represented by CTSR. The deformation by cold or warm rolling can significantly increase CTSR and thus accelerate stress corrosion cracking growth in both boiling water reactors and PWR environments, for both stainless steels and, Ni-base alloys.