Mechanical properties of expansion casing and residual stress after expansion

The expansion properties of X52 pipe were improved by heat treatment process, and the performance difference before and after expansion was investigated. For pipes with diameter expansion up to 20%, the axial and circumferential residual stresses on inside and outside walls, weld fusion zone and heat-affected zone were measured by the stress releasing method. The results show that both the axial and circumferential residual stresses on the outside wall of the pipe are compressive after expansion, and in the weld fusion zone and weld heat affected zone the residual stress varies from tensile to compressive, especially for the axial residual stress. On the inside wall, residual tensile stress appears in both directions after expansion. In addition, the abnormal relationship of the mechanical properties and residual stress under different expansion is analyzed.