Abstract: The shaft seal steam return pipe of a small turbine in a supercritical unit fractured after operation for 8.1×10⁴ h. The fracture cause of the steam return pipe was analyzed by macromorphology observation, metallographic examination, hardness test and mechanical property test, etc. The results show that the intergranular corrosion resistance of TP304H austenitic stainless steel used for the steam return pipe was poor. The pipe was not treated by solid solution after cold processing, resulting in the increase of dislocation densities and residual stresses at the elbow, which accelerated the precipitation of chromium containing compounds, finally leading to intergranular chromium-depleted zones. Under the combined action of corrosion environment and residual stresses, intergranular corrosion cracks were initiated on the inner and outer surfaces of the pipe, and expanded along the weakened grain boundaries in the chromium-depleted zone, eventually leading to intergranular corrosion fracture of the steam return pipe.