Failure Analysis of Gland Seal Steam Drain Pipe of Reheat Stop Valve

Fracture and leakage happened at the gland seal steam drain pipe of a reheat stop valve in Third Qinshan Nuclear Power Co., Ltd. The failure location was near the nozzle of the valve. Examination was conducted on the failed section of the pipe. The chemical compositions, microstructure and corrosion products of the parent metal, heat affected zone and butt weld of the pipe were examined. The fracture surface was observed. It is concluded that the main failure causes should be as follows: (1) oxidation corrosion on the pipe inner surface near the valve caused by high temperature steam resulted in the pipe wall thinning significantly; (2) corrosion fatigue due to pipe vibration lead to the final fracture.