1000MW超超临界机组电动闸阀阀杆的断裂原因

Fracture Cause of Electric Gate Valve Stem in a 1000MW Ultra-Supercritical Unit

某1000 MW超超临界机组给水泵出口电动闸阀阀杆在阀门开启过程中发生断裂,采用宏观形貌观察、化学成分分析、力学性能测试和显微组织观察等方法分析了阀杆断裂的原因。结果表明:阀杆的显微组织不均匀,心部存在局部疏松,组织中存在较多条状或块状铁素体,导致阀杆的塑韧性不足,综合力学性能不均匀;同时在阀门打开过程中,出口侧阀瓣与滑轨之间发生严重卡涩,且阀杆环形平台的加工质量较差,阀杆底部环形平台变截面根部过渡圆弧角较小。在阀门开启时,裂纹在环形平台变截面根部的应力集中区域萌生并快速扩展,最终导致阀杆发生脆性断裂。

A electric gate valve stem at the outlet of feedwater pump in a 1 000 MW ultra-supercritical unit fractured during valve opening. The fracture cause of the stem was analyzed by macromorpholgy observation, chemical composition analysis, mechanical performance test and microstructure observation. The results show that the microstructure of the stem was nonuniform, and there was local porosity in the center area. A lot of striped or massive ferrite existed in the microstructure resulting in insufficient plasticity and uneven comprehensive mechanical properties of the stem. The serious jam occurred between the valve disc and the slide rail on the outlet side during valve opening. The machining quality of the annular platform surface of the stem was poor, and the transition arc angle of the variable section root of the annular platform at the bottom of the stem was small. The cracks initiated at the stress concentration area of the variable cross-section root of the annular platform when opening the valve, and then expanded quickly, resulting in the brittle fracture of the stem finally.