2009:17 Effect of Welding Residual Stresses on Crack Opening Displacement and Crack-Tip Parameters

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. The fracture mechanical treatment of weld residual stresses in commonly used engineering assessment methods generally use the crack face pressure method and account neither for the displacement controlled nature of weld residual stresses, nor for multi-axial residual stresses. In this report, these effects are studied.

The principal objective of the project is to investigate the accuracy of the commonly used Crack Face Pressure (CFP) method, such as in the computer code ProSACC, for evaluating the stress intensity factor K for cracks located in multi-dimensional weld residual stress fields in piping geometries. Another aim is to investigate the accuracy of existing methods to evaluate the Crack Opening Displacement (COD) for through-wall cracks in pipes.