Residual Stress Modelling in PWR Reactor Pressure Vessel Welded Joints

Abstract

Residual stress and strain measurements were performed on a narrow gap weld mock-up consisting of a 130 mm thick low-alloy ferritic steel plate of type SA508 Grade 3 Class 1. A submerged arc welding (SAW) process with two beads per layer was used. The thermal response during welding was recorded to provide information for numerical modelling of heat transfer. Detailed through-thickness measurements of residual stresses were made in the as-welded state using both incremental deep hole drilling and the contour method, and after post-weld heat treatment using deep hole drilling.In this paper, a finite element model of the mockup is described as well as some recent modelling improvements achieved thanks to internal EDF R&D activities and within the framework of NeT Task Group 8. Comparison between measurements and simulations are in very good agreement. The results presented in this paper are useful for the validation of numerical models for the prediction of residual stress states, including the description of the material behavior which depends on phase fraction evolution and tempering effects. Post-weld heat treatment significantly relieves the welding residual stresses and a focus on its modelling is presented in this paper as it is seen as a key step of the manufacturing operation, reducing the level of residual stresses in reactor pressure vessel’s welded joints.