FAILURE ANALYSIS AND STRATEGY INVESTIGATION OF THE RUPTURE ON THE GLAND SEAL STEAM DRAIN PIPELINE OF THE REHEAT STOP VALVE

摘要

Macroscopical inspection and analysis of the pipe component, microstructure, fracture and corrosion product were conducted on the pipe parent metal, heat affected zone and the weld zone of the ruptured reheat stop valve shaft seal steam pipe of Qinshan III. The main failure cause could be concluded that oxidation corrosion on the pipe inner surface near the valve with high temperature steam cause the wall thickness largely reduced, and corrosion fatigue due to pipeline vibration eventually lead to fracture. The thinning rate of the failure pipe is assessed. There are total 32 similar pipelines in the two units of Qinshan III. The preventive repair strategies for this kind of pipelines are investigated. Wall thickness measurement and evaluation should be conducted in the outage sixth years after the pipeline replacement. The inspection location is 30mm～150mm extent downstream of reheat stop valve outlet nozzle. The pipe section should be replaced in accordingly outage when the minimum measured wall thickness is less than 2mm.