The effect of residual stress on the creep deformation of welded pipe

Abstract

The finite element method has been used to study the creep deformation of pipe butt welds in the presence of an initial residual stress distribution. The study has used values for pipe dimensions, temperature (575°C) and internal pressure (70 bar) which correspond to the conditions being used in a pressure vessel testing programme which is investigating transverse weld metal cracking in CrMoV reheat pipe welds. Two sets of steady state creep data for the weld metal have been used, one to represent a weld weaker than the parent and the other one that was stronger. A residual stress distribution, consistent with experimental data, has been generated as àn initial condition for the analysis. The results are presented, discussing the effects of residual stress on both the total and creep strain accumulations for the two weld properties. The steady state creep laws used in the analysis do not allow for damage accumulation, but the possibility of such an effect is discussed using the Kachanov model. The results of the finite element analysis are compared with the experimental creep strain data from the pressure vessel testing programme.