SCC Test Verification of Effect of Moving Heat Source on FEM Evaluation for Weld Residual Stress of Butt-Weld Pipe

Abstract

Weld residual stress of a small bore pipe was evaluated using three-dimensional thermal elasto-plastic analysis, which was based on the finite element method (FEM), taking into consideration the effect of a moving heat source during the butt-weld process. A moving heat source during the weld process complicates analysis process due to the necessity of considering the set welding conditions at each time step and this increases computation time. Therefore, there are remarkably few studies on the effect of a moving heat source during the weld process on the analytical results of weld residual stress for small bore pipes. We used this analysis to find the effect of the welding start/end on weld residual stress. Weld residual stress is not a circumferentially uniform state. Increased tensile and compressive residual stress occurred near the end position of the final welding pass. In addition, an accelerated stress corrosion cracking (SCC) test was carried out using a boiling 42% magnesium chloride (MgCl2) solution. In particular, butt-weld joints of low-carbon austenitic stainless steel (Type 316L) pipe, which is often used in boiling water reactors (BWRs), were examined. Comparison between three-dimensional thermal elasto-plastic analysis and accelerated SCC testing showed the tensile stress zone indicated by analysis agreed well with SCC occurrence indicated by examination.