Effect of the Groove Shape on Residual Stress Distribution of Narrow Gap Welds

Abstract

Recently, in Korea, the reactor coolant main loop piping and the steam generator have been connected with narrow gap welding (NGW) method after the replacement of steam generator of Korean nuclear power plants. The NGW method has many advantages, for instance, the reduction of welding time and the shrinkage of weld, and the small deformation of a component resulting from the small groove angle and welding bead width. In the actual welding process with NGW, some different groove shapes have been adapted. Noting that the distribution of a weld residual stress is significantly affected by welding conditions, for instance, shape of weld groove, direction of welding and width of weld groove etc., the weld residual stress due to NGW with different welding conditions should be accurately investigated for its application to life assessment considering actual conditions since these residual stress distributions can affect the susceptibility of parent and weld material to the primary water stress corrosion cracking (PWSCC) which is one of main issues in the nuclear component integrity. In this context, the present paper investigates the distribution of the weld residual stress as well as the deformation behavior of ER308L weld due to NGW using the nonlinear 2-dimensional (2-D) finite element (FE) analysis in which the detailed actual welding process of NGW was simulated. In particular, the effect of shape of weldment, i.e., the shape of welding groove (“single-side weld” and “double-side weld”) and the width of weld, on the residual stress is emphasized. Based on the FE results, the relevant groove shape is discussed in the sense that it provides lower residual stress values at the inner surface of pipe, which might reduce susceptibility to PWSCC.