A study on welding residual stress analysis of a small bore nozzle with dissimilar metal welds

Recently, it is reported that axial and circumferential PWSCCs (primary water stress corrosion cracking) occurred on the dissimilar metal welds of the small bore nozzle such as a steam generator drain nozzle in PWR. In order to identify root causes of the PWSCCs and prevent the PWSCCs in the future, it is necessary to evaluate PWSCC initiation potential and growth rate of the dissimilar metal welds via residual stress assessment. In this study, the residual stress analysis has been performed in order to investigate the effect of various finite element analysis variables on PWSCC assessment result. The residual and operating stress distributions are calculated by finite element method. Based on the stress analysis results, PWSCC initiation locations are predicted by comparing the stresses with PWSCC initiation threshold values. The predicted locations are compared with the examination results using penetration, eddy current and destructive tests. It is identified that the finite element residual stress analysis methodology is valid from the fact that the PWSCC prediction has reasonable agreement with the examination results. The parametric study for various finite element analysis variables derives effect of the variables on the total stresses at steady state during normal operation including residual stress and the PWSCC initiation/growth.