针对某电厂低压加热器疏水泵导流壳连接螺栓的断裂失效，采用宏观检查、化学成分分析、硬度试验、金相检验、扫描电镜断口分析等方法对螺栓断裂原因进行了分析。结果表明：螺栓断裂为典型的韧性过载断裂；一方面螺栓牙底存在成型缺陷产生应力集中，降低螺栓承载能力，另一方面疏水系统运行状态不稳使疏水泵受到较大冲击载荷，二者共同作用导致结合面部位的连接螺栓于螺牙底部应力集中部位发生过载断裂失效。最后提出了改进建议。

In view of the fracture failure of the connection bolts of diversion shell for low pressure heater drainage pump in a power plant, means such as macroscopic examination, chemical composition analysis, hardness test, metallographic examination and scanning electron microscope fracture analysis were used to analyze the fracture causes of the bolts. The results show that the fracture of the bolts was a typical toughness overload fracture. On the one hand, there were forming defects at the bottom of screw thread of the bolts, which resulted in stress concentration and reduced the bearing capacity of the bolts. On the other hand, the operating state of the drainage system was unstable and the drainage pump was subjected to a relatively large impact load. The co-action of the two above factors resulted in the overload fracture of the connection bolts at the bottom of the stress concentrated screw thread of the joint surface position. Finally, improvement suggestions were put forward.