300MW机组高压主汽门阀杆失效分析

Failure analysis of high-pressure main steam valve stem in a 300 MW unit

高压主汽门是电站机组的关键部件之一,对机组安全启停和运行起着重要作用,长期承受高温高压工况下的复杂载荷。主汽门阀杆断裂是较为严重的一类故障,会造成巨大的经济损失。某电厂高压主汽门阀杆在机组运行过程中发生断裂,采用宏观检查、化学成分分析、金相组织观察、断口分析和力学性能测试等方法,对断裂原因进行了分析。结果显示,阀杆长期服役后材质劣化明显,力学性能严重下降,同时阀杆组织存在带状偏析,渗氮层和过渡层之间存在微裂纹。加工结构亦导致严重的应力集中,机组频繁启停导致阀杆疲劳损伤,这些因素共同导致阀杆断裂失效。

The high-pressure main steam valve is one of the key components in the power plant unit,plays an important role in the start-stop and safe running of the unit,and is subjected to complex loads under high-temperature and high-pressure conditions for a long time.The fracture of the main steam valve stem is a serious fault,which can cause significant economic losses.The high-pressure main steam valve stem of a power plant broke during the running process of the unit.The fracture reasons were analyzed by macroscopic examination,chemical composition analysis,metallographic observation,fracture analysis,mechanical property testing,and so on.The results show that after long-term service,the material degradation of the valve stem is significant,and the mechanical properties decrease severely.Meanwhile,band-shaped segregations appear in the valve stem structure,microcracks exist between the nitriding layer and transition layer,the processing structure also leads to severe stress concentration,and the frequent start-stop of the unit causes fatigue damage of the valve stem.These factors collectively lead to the valve stem fracture and failure.