Causes of seamless steel pipe leakage of boiler superheater

Leakage occurred in the seamless steel pipe of a boiler superheater after use. The leakage causes of the steel pipe were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, hardness test, scanning electron microscope and energy spectrum analysis, X-ray diffraction analysis and other methods. The results show that the chemical composition, microstructure and hardness of the boiler superheater steel pipe met the standard requirements. However, due to the long-term operation of the superheater under high temperature and high pressure conditions, the carbides containing Cr elements precipitated along the grain boundary, which seriously weakened the corrosion resistance of the grain boundary. In addition, the inner surface of the tube was corroded by corrosive media, and the outer surface of the tube was scoured by corrosive high-temperature flue gas, resulting in stress corrosion cracking on the inner and outer surfaces of the pipe, and the cracks continued to expand. Finally, the leakage of the steel pipe occurred.