Influence of post-expansion residual stress on the fatigue life of the supercharged boiler

The stress distribution on boiler tubesheets becomes very complex due to the combined effects of thermalmechanical load and residual stress from expansion in numerous expanded joints. This study determined the residual stress distribution generated by the expansion process on the boiler drum, which was used as the initial stress state boundary to simulate continuous steam charging and discharging cycles. Different fatigue assessment methods were employed to evaluate the impact of `residual stress on fatigue life. The results indicated that the residual stress exhibited higher values in the central region and lower values on the sides. When considering the post-expansion residual stress, there was a reduction of 10.4%/20% and 8.9% in the permissible number of cycles based on the maximum shear stress and distortion energy theories, respectively. It is crucial to account for the fatigue weakening caused by the expansion process in the fatigue evaluation of pressure vessels.