Shakedown Analysis of Post-Weld Residual Stress in a Pressurizer Surge Nozzle Full-Scale Mockup

Computational weld residual stress analyses are commonly evaluated at room temperature in order to validate against weld residual stress measurements, which are conducted at room temperature. However, in addition to weld residual stress produced in the course of manufacturing, plant components are subject to internal water pressure and elevated temperature during operation. The current work explores the changes in weld residual stress state due to the presence of internal pressure and temperature at operating conditions. This paper is a follow-up to earlier work, which presented a numerical finite element simulation of the weld residual stress in a pressurizer surge nozzle full-scale mockup as a part of a broader program of cooperative work on weld residual stress organized by the U.S. Nuclear Regulatory Commission and the Electric Power Research Institute. The analysis is performed using two different constitutive hardening models (isotropic and nonlinear kinematic). Two main effects on the weld residual stress field result from the application of internal pressure and temperature: one is elastic, and reversible, and the other is plastic, which is irreversible. The results indicate that the majority of the change in plasticity, and hence the change in stress, occurs during the initial increase in internal pressure and temperature. Furthermore, the results demonstrate that the additional stress due to operating conditions is largely due to the thermal expansion between the ferritic steel, stainless steel, and nickel-based alloy weld.