核级316L不锈钢管道射线插塞孔开裂原因分析

摘要

In order to find out the reason of cracking on one nuclear class 316L stainless steel pipe with screwed hole for radiographic test , the analyses of macrostructure/microstructure ,chemical composition ,mechanical properties ,Vickers‐hardness ,mor‐phology of fracture ,corrosion products and stress distribution of the screwed hole on the cracking pipe were done .The results show that the crack propagates along the grain boundary and the material in the fracture exhibits a rock candy pattern and a large amount of corrosion products with polygonal crystals ,which indicates that the cause of failure is attributed to inter‐granular stress corrosion cracking (IGSCC ) induced by interaction of stagnant water of pressured water reactor and material .The main reason of strain‐hardening is the interference fit between the plug and screwed hole which suffering higher welding residual stress .More non‐destructive tests on the similar struc‐ture in the in‐service NPPs and less uses in new NPPs are strongly suggested .%为查明某核电厂核级316L奥氏体不锈钢管道射线插塞孔裂纹显示的成因，对含插塞孔不锈钢管段的宏／微观形貌、化学成分、力学性能、维氏硬度、断口形貌、腐蚀产物、应力分布等进行了分析。结果表明：裂纹以沿晶方式扩展，断口呈冰糖块脆性断裂花样并伴有大量氧化腐蚀产物，属于典型的压水堆一回路水介质条件下由插塞孔局部应变‐硬化导致的晶间应力腐蚀开裂。引起应变‐硬化的主要原因是插塞孔和插塞的过盈配合以及射线插塞孔密封焊缝焊接残余应力过高。建议加强在役机组同类结构的检查，减少新建机组类似结构的使用。