超临界600MW机组主汽阀阀杆断裂原因分析

CUASE ANALYSIS OF VALVE STEM RUPTURE ON MAIN STEAM VALVE OF SUPERCRITICAL 600 MW UNIT

采用宏观形貌观察、化学成分分析、显微组织观察与力学性能试验等方法,对某超临界600MW机组主汽阀阀杆断裂原因进行了分析。结果表明,该高温合金阀杆母材弥散分布富Al、富Si、富Ti和富Mo的强化颗粒,显微组织异常,且拉伸塑性与冲击韧性较差,是导致其在丝扣退刀槽处发生脆性断裂的主要原因。建议对同批次和同类型的主汽阀阀杆采取适当的措施进行处理,确保机组安全运行。

By using the macro -observation of appearance, the chemical composition analysis, the micro- structure observation, and the mechanical test method, the causes leading to valve stem rupture of main steam valve used for one supercritical 600 MW unit have been analysed. Results show that some strengthened particles, such as A1 - rich, Si - rich, Ti - rich, and Mo - rich particles have dispersed into the base - metal of superalloy stem, its micro - structure being abnormal, boasting poor tensile ductility and bad impact toughness,and finally leading to brittle rupture at the knife- withdrawing slot of screw threads. It is recommended the treatment measures should be taken for main steam valve stems of same batch and similar modes,so as to ensure safe operation of units.