反应堆停冷系统阀门接管失效分析

Failure analysis for valve nozzle of shutdown cooling system in reactor

反应堆检修过程中发现停冷系统的阀门接管出现裂纹,裂纹出现在焊缝坡口部位,为分析裂纹产生的原因,需对阀门接管进行失效分析。采用目视检测和渗透检测方法,对裂纹出现的区域进行无损检查,确定了裂纹的数量和方向。根据无损检查结果对典型裂纹区域进行了显微分析和成分分析。检查结果表明,裂纹从管壁内侧向外侧扩展,裂纹周围晶粒未发现变形痕迹,裂纹区域与非裂纹区域晶粒未发现区别;裂纹横断面呈现脆性断裂特征,裂纹内部发生了腐蚀,腐蚀产物的主要成分为氧;结合阀门接管的运行工况分析认为,该阀门接管失效原因为应力腐蚀。

Cracks found in the weld groove parts of valve nozzle of the shutdown cooling system of a reactor in repairing is analyzed. The reasons of the cracks, the crack number and orientations are confirmed by visual inspection and penetranting testing. According to the results of nondestructive inspection, typical cracks regions are cut into some samples including crack transect samples, longitudinal crack samples and transverse crack samples. Scanning electron microscopy is used to investigate the microstructure and micro zone composition of the crack transect. Optical microscopy is used to analyze the microstructures of the longitudinal crack and the transverse crack. The results show that cracks may extend from the inside to outside wall and that grain deformation around the crack is not found. There are no obvious grain differences between crack and non-crack regions. Brittle fracture characteristic exists in crack cross section, and the internal corrosion of crack is found. The main component of corrosion products is oxygen, and the corrosion is caused by oxidation of stainless steel. Combined with the valve nozzle operating conditions, the reason for the failure of valve nozzle is believed to be stress corrosion cracking.