2009:15 Improvement and Validation of Weld Residual Stress Modelling Procedure

Weld residual stresses have a large influence on the behavior of cracks growing under normal operation loads and on the leakage-flow from a through-wall crack. Accurate prediction of these events is important in order to arrive at proper conclusions when assessing detected flaws, for inspection planning and for assessment of leak-before-break margins. Therefore, it is very important to have verified procedures to estimate weld residual stresses (WRS). During the latest years, there has been a strong development in both analytical procedures to numerically determine WRS and experimental measurements of WRS. The present report is the result of an effort to acquire and to develop the latest research results in the field of WRS.

The major changes applied in the new weld residual stress modelling procedure are: Improved procedure for heat source calibration based on use of analytical solutions. Use of an isotropic hardening model where mixed hardening data is not available. Use of an annealing model for improved simulation of strain relaxation in re-heated material. The new modelling procedure is demonstrated to capture the main characteristics of the through-thickness stress distributions by validation against experimental measurements. Three austenitic stainless steel butt-welds cases are analysed, covering a large range of pipe geometries. From the cases it is evident that there can be large differences between the residual stresses predicted using the new procedure, and earlier recommendations.