核电厂低压氮气系统不锈钢管件的开裂原因及应对措施  

Cause and Countermeasures of Stainless Steel Pipe Cracking in Low Pressure Nitrogen System of Nuclear Power Plant

作　　者：廖雪波 蒲晶菁 李汭 高超 LIAO Xuebo;PU Jingjing;LI Rui;GAO Chao(Fujian Ningde Nuclear Power Co.,Ltd.,Ningde 352000,China)

机构地区：[1]福建宁德核电有限公司,宁德352000

出　　处：《腐蚀与防护》2024年第7期102-107,共6页Corrosion & Protection

摘　　要：某核电厂低压氮气系统不锈钢三通发生泄漏,切割后检查发现管件存在开裂。通过形貌观察、能谱分析、化学成分分析、硬度检测、晶间腐蚀试验以及残余应力测试等手段对该不锈钢三通失效的原因进行分析。结果表明:三通在加工过程中存在较大冷变形且未进行固溶处理,导致基体组织中存在大量滑移带,造成材料硬度偏高、残余应力增大,这是导致三通开裂的根本原因;三通中的C含量偏高,焊接时存在晶间碳化物析出;冷变形导致三通存在较大的残余拉应力,使材料的电化学活性提高,材料点蚀电位降低,腐蚀敏感性提高。上述因素共同导致了三通在潮湿海洋大气环境中发生沿晶应力腐蚀开裂。Leakage occurred in the stainless steel tee-junction of a low-pressure nitrogen system in a nuclear power plant.After cutting,cracking was found in the pipe fitting.The failure causes of the stainless steel tubes were analyzed by means of morphology observation,scanning electron microscopy,energy spectrum analysis,metallographic examination,chemical composition analysis,hardness test,intergranular corrosion test,and residual stress test.The results show that there was a large cold deformation and no solid solution treatment during the processing of the tee-junction,which led to a large number of slip bands in the matrix structure,resulting in high hardness of the pipeline and increased residual stress,which was the root cause of the tee-junction fracture.The C content of the tee-junction was relatively high,and there was intergranular carbide precipitation during welding.Cold deformation led to large residual tensile stress in the tee sample,which increased the electrochemical activity of the material,reduced the pitting potential of the material,and increased the corrosion sensitivity.The above factors together led to intergranular stress corrosion cracking of the tee-junction in a humid marine atmosphere.

关 键 词：三通 滑移带 残余应力 硬度 沿晶应力腐蚀 

分 类 号：TG174.4[金属学及工艺—金属表面处理]