某核电厂大修期间, 发现高压加热系统中疏水阀气动头与阀门本体连接的6颗内六角沉头螺栓中有5颗发生了断裂。通过分析断裂螺栓材料、力学性能、显微组织和断口等, 并结合阀门实际运行信息, 认为疏水阀气缸中的工作压力超过公称压力致使螺栓长期处于高的拉-拉型交变应力状态, 从而引起螺栓的疲劳断裂。同时提出了防止该类螺栓在其使用过程中发生类似断裂事故的建议。

In the process of shutdown maintenance of a nuclear power unit, it was found that five of six pneumatic actuator bolts in steam trap valve of high pressure heating system had been breakdown. A comprehensive analysis which was based on chemical composition analysis, mechanical properties testing, metallographic examination and microstructure observation, as well as actual operating information, was made on the breakdown of the pneumatic actuator bolts. The results showed that working pressure exceeding nominal pressure in value cylinder induced that the bolts were in long-term tension-tension alternating stresses state, causing the bolts fatigue rupture. In the meanwhile, several measures for the failure control were proposed.