Thermo-mechanical analysis of the repair welding residual stress of AISI 316L pipeline for ECA

Abstract

Through-thickness residual stress distribution is a fundamental input parameter for engineering critical assessment (ECA) according to BS 7910 Annex Q. In this paper, we investigated the through-thickness residual stress distribution at a weld toe/weld centerline. Firstly, we performed a simulation of the thermo-mechanical coupled-welding residual stress with/without repair welding of a thick wall pipeline. To further investigate the effects of component radius to wall thickness ratio(r/t) and heat input on the welding stress profile, we developed a welding pass size merging strategy on a mechanical basis. At least ten weld layers were utilized in finite element analysis(FEA) to improve efficiency, without affecting the through-thickness residual stress distribution. The influence of the r/t ratio on the through-thickness residual stress distribution was determined and described as membrane stress and bending stress. Hoop and axial bending stresses at a weld toe decreased gradually with the r/t ratio increased. In contrast, the hoop membrane stress at a weld toe gradually increased with the r/t ratio increased. Moreover, a similar trend was observed at weld centerlines. Analytical equations for predicting the through-thickness residual stress were established for both original welding and in-depth repair welding processes. It was shown that the residual stress distribution after the repair welding was more efficiently improved when a smaller repair depth was selected, i.e., the improvement was adversely related to the repair depth. The residual stress for the original and the repaired welds was expressed as a logarithmic function in terms of axial bending stress, hoop bending stress, and hoop membrane stress.