某核电站凝汽器密封结构用镍铝青铜螺栓发生断裂现象,采用宏观观察、化学成分分析、扫描电镜分析、力学性能测试、金相检验等方法对螺栓断裂的原因进行分析。结果表明:螺栓在潮湿的NH₃环境下发生了应力腐蚀开裂;断裂螺栓在服役过程中受到不均匀的应力载荷,使表面应力腐蚀倾向变大,且螺栓长期处于自身应力腐蚀敏感介质中,在二者的耦合作用下,应力腐蚀裂纹萌生;裂纹沿残余应力较高的相界区域向内扩展,最终导致螺栓发生断裂。

The Ni-Al bronze bolt used for the sealing structure of a certain nuclear power plant condenser fractured. The causes of bolt fracture were analyzed by macroscopic observation, chemical composition analysis, scanning electron microscopy analysis, mechanical property testing and metallographic examination. The results show that the bolts experienced stress corrosion cracking in a humid NH₃ environment. During service, fractured bolts were subjected to uneven stress loads, resulted in an increased tendency for surface stress corrosion. Moreover, the bolts were exposed to their own stress corrosion sensitive medium for a long time. Under the coupling effect of the two, stress corrosion cracks initiated on the bolts. The crack propagated inward along the phase boundary area with high residual stress, ultimately led to bolt fracture.