Relaxation of Exemption Requirement of PWHT for SA-508 Grade 1A, by Consideration Surface Welding Residual Stress As Evaluated by Instrumented Indentation Testing Method

Generally, post-weld heat treatment is applied to decrease welding residual stress and improve the mechanical properties and microstructure of weldment, and its performance has been recommended for many years [1, 2]. However, current steel-making technology has improved significantly and, steel toughness levels have generally improved substantially [1]. Additionally for several quenched and tempered steels, it is reported that in some cases, mechanical properties such as tensile strength and impact toughness are degraded after post-weld heat treatment [3]. In addition, for large steel assemblies, post-weld heat treatment can be expensive, so that there is an economic incentive to avoid post-weld heat treatment [2]. The research presented here suggests a way to exempt post-weld heat treatment for SA-508 Grade 1A material, which is used for pressure vessels in nuclear power plants, by considering both mechanical properties and residual stress to simplify the welding procedure. Weldments made of 120 mm thick SA-508 Grade 1A should be post-weld heat treated, according to current ASME BPV Code. In order to increase the PWHT exemption thickness to 120 mm, we performed mechanical tests using welding coupons without PWHT; the test results satisfied current mechanical property criteria. We present a residual stress acceptance criterion based on brittle fracture criteria in this research.