某核电站安全厂用水系统奥氏体不锈钢仪表管焊缝处发生泄漏。采用宏观观察、化学成分分析、硬度测试、金相检验和扫描电镜分析,分析了该仪表管泄漏的原因。结果表明:该仪表管内壁焊接热影响区形成严重的回火色,即贫铬氧化层,在海水中氯离子的作用下,管道内壁形成点蚀坑,点蚀坑不断扩展,最终贯穿整个管壁,导致仪表管泄漏。

A leak occurred in the weld of austenitic stainless steel instrumentation pipe for the essential service water system in a nuclear power plant.Macroscopic observation,chemical composition analysis,hardness test,metallographic inspection and scanning electron microscope analysis were used to analyze the reasons for the leakage of the instrumentation pipe.The results showed that the welding heat-affected zone on the inner wall of the instrumentation pipe formed a serious temper color,that was,a chromium-poor oxide layer.Under the action of chloride ions in seawater,pitting pits were formed on the inner wall of the pipe,the pitting pits continued to expand,and finally penetrate the entire pipe wall,causing the instrumentation pipe to leak.