Abstract: The leakage causes of the TP310HCbN austenitic heat-resistant steel elbow of final reheater of a boiler were analyzed through macroscopic inspection, chemical composition analysis, mechanical property test, metallographic examination and fracture scanning electron microscope analysis. The results show that the elbow leaked because it had been bumped and the passivation film on the outer surface of the steel tube was damaged. Under the combined action of corrosive media, tube internal compressive stress, residual stress of the elbow and additional internal stress at the pit, stress corrosion cracking occurred to the elbow.