某电站3B循环水泵连接法兰和螺栓断裂原因

Fracture Cause of Connecting Flange and Bolts of a 3B Circulating Water Pump in a Power Station

某电站3B循环水泵连接法兰及螺栓发生断裂。采用宏观观察、化学成分分析、显微组织观察、力学性能测试、扫描电镜及能谱分析等方法,分析了法兰及螺栓断裂的原因。结果表明:在海水介质环境中,法兰结合面与螺帽压紧面发生缝隙腐蚀,引起螺栓松动,在螺纹根部形成疲劳裂纹,从而发生疲劳断裂,法兰承受的应力大幅增加,在导流体自重、叶轮转动及流体扰动等共同作用下,最终导致法兰发生过载断裂。

The connecting flange and bolts of a 3B circulating water pump in a power station were fractured. By means of macroscopic observation, chemical composition analysis, microstructure observation, mechanical property test, scanning electron microscopy and energy dispersive spectrometer analysis, the reasons for the fracture of flange and bolts were analyzed. The results showed that in the seawater medium environment, crevice corrosion occurred between the flange joint surface and the nut pressing surface, causing the bolts loosen and fatigue cracks nucleated at the root of screw thread, resulting in fatigue fracture and the stress on the flange was greatly increased. Under the combined action of self-weight of the fluid, the rotation of impeller and fluid disturbance, the flange was eventually be overloaded and fractured.