Effects Of End Loading On The Creep FailureBehaviour Of CrMoV Welds In Main SteamPipelines

Abstract

This paper describes an investigation into the effects of end (system) loading on the creep failure behaviour of internally pressurised thick walled pipe welds, using the FE method with simplified axisymmetric models. Steady-state and creep damage analyses were performed for a series of new, service-aged, and repaired welds in main steam pipes in power generation plants. The material properties used were related to CrMoV weldment materials at 640° C. Stress distributions were obtained and failure lives were predicted for each weld situation, under a closed-end condition and with additional axial loading. The rupture stresses showed very little variation across the heat-affected zone (HAZ), in the dominant stress regions, for closed-end loading. However, the variation is more significant when additional axial loading is applied. The results of damage variations across the HAZ in these critical regions confirmed the effect of end loading indicated by steady-state results. This suggests that, in addition to the pressure, for the welds investigated, there is a high probability of type IV cracking occurring in pressurised pipes, as the axial loading is increased, which is consistent with laboratory and power plant experience.