Cause Analysis on Leakage of Steel Pipe of Final Superheater in a Ultra Supercritical Unit Boiler

The boiler steel pipe of a ultra supercritical clean and efficient coal-fired power plant leaked. The leakage causes of steel pipe were analyzed by means of macroscopic examination, chemical composition analysis, tensile test, hardness test and metallographic examination. The results show that steel pipe of the final superheater was in the state of overheating operation because it was blocked by foreign matters, which led to the deterioration of the mechanical properties of steel pipe, and then caused the decrease of the pressure bearing capacity of steel pipe. Under the action of internal pressure stress, the creep rate of steel pipe accelerated, and the creep cracks were generated on its surface, resulted in the leakage of steel pipe.