Failure Analysis of Condensate Pump Shaft in Power Plant

摘要

Failure analysis of condensate pump shaft used in power generation plant was investigated. After 5 years of operation, the pump shaft fabricated from free-machining 416 martensitic stainless steel was suddenly ruptured into two parts. Detailed study was carried out using VT, PT together with microstructure investigation using optical and scanning electron microscope (SEM), fractography, chemical analysis and hardness testing to find out the cause of shaft failure. Failure analysis investigation revealed that the shaft was failed by torsion fatigue. Rupture was initiated from the sharp edge of the shaft outer surface at which sulphide inclusions were existed The failure is attributed to simultaneous action of both stress concentration resulted from sharp corner (design fault) and sulphide inclusions that segregate in 416 free-machining martensitic stainless steel base alloy near shaft surface (metallurgical fault). To overcome the shaft failure, sharp corner must be smooth turned and eliminate sulphide segregation in base alloy by heating prior to hardening at 1020°C for lhr to dissolve and redistribute MnS segregates followed by oil quenching followed by tempering at 590-650°C to improve mechanical properties.