Influence of geometry change on creep failure life of 90° pressurised pipe bends with no initial ovality

The influence of the geometry change during creep on the failure life of 90° pipe bends, subjected to internal pressure, was investigated using finite element creep damage analyses. The bends were considered to be circular in shape with no initial ovality. The failure lives obtained using the material properties for a CrMoV pipe steel at 640 °C clearly show a significant life reduction when the geometry change is included. In the range of the pipe bend dimension ratios investigated, it was found that the failure lives could be reduced to between 65 and 78% of those obtained from constant geometry cases, indicating that the influence of geometry change may need to be appraised for detailed numerical analysis. The results were compared with those of the corresponding straight pipes and their relevance considered. It has been shown that under constant geometry conditions, the failure life for pipe bends is about 30% lower than that for the straight pipes.