Effect of PWHT on Dominating Parameters Affecting SCC Growth Rate of Ni-base Weld Metals

Abstract

Stress corrosion cracking (SCC) growth rate disposition curves for Alloy 82 in BWR environments were proposed by the EPRI international expert panel. A comprehensive evaluation of the extensive database revealed that SCC crack growth rate (CGR) of Alloy 82 with post-weld heat treatment (PWHT) is notably lower compared to that of as-welded condition. PWHT can affect both chemical and mechanical aspects of the material, such as grain boundary chemistry and hardness. However, the dominating factor that causes the difference in SCC CGR remains unclear. In this study, a preliminary discussion of possible dominating factors will be made based on macroscopic mechanical properties, e.g., welding residual stress and hardness on Alloys 82 and 52M weldments. It suggests that the reduction in material hardness after PWHT can be a contributing factor to the lower CGR in PWHT materials and its spatial distribution may have caused the large scatter in laboratory CGR data.