Analytical study on rationalize and reliability improvement of maintenance against stress corrosion cracking in stainless steel welds of lwr primary system

SCC (stress corrosion cracking) may occur in stainless steel welds of the LWR primary systems, which required the welding repair after detecting it over nondestructive inspection (NDI) during the regular inspections. Recently, a new peening method was developed to convert the tensile residual stress of the weld into compressive residual stress, which relieved the SCC issue in the new plant although SCC problems still exist in conventional plant. It was found that fatigue crack and SCC can be rendered harmless by the compressive residual stress over a peening method. This paper proposes a method for increasing the validity and reliability of the weld maintenance for SCC by the following methods. ① Evaluate the depth (ahml) of SCC cracks that can be rendered harmless by peening in advance. ② Detect the cracks of approximately 0.7 ahml or more by NDI. ③ Repair only crack of 0.7 ahml or more by welding. ④ Apply peening to all welds. This paper proposes a method for evaluating ahml, and analyzed the dependence of residual stress and crack aspect ratio (As) via peening. The study showed that it was possible to improve the reliability and rationalize the maintenance for SCC by applying the surface crack nondamaging technology.