核电站高温取样冷却器失效机理

摘要

采用化学分析、体视显微镜和SEM／EDS对核电机组泄漏的高温取样冷却器蛇形管材料的化学成分、腐蚀宏观和微观形貌进行了分析观察，结合冷却器的环境工况，提出了蛇形管腐蚀失效的机理。腐蚀产物的EDS能谱分析显示，蛇形管腐蚀失效部位有大量Fe、P和微量Na元素存在，说明蚀坑和穿孔是因为磷酸盐诱发的碱性腐蚀所致。蛇形管外壁局部过热，促进局部液体沸腾汽化，使得近壁处水中的磷酸盐和杂质含量达到饱和，从而以固相析出附着在管壁上。一方面，析出的磷酸盐与蛇形管表面氧化物发生磷酸盐反应；另一方面，介质的浓缩与沉积使传热恶化，导致磷酸盐隐藏和碱性腐蚀的发生，从而造成蛇形管形成蚀坑和穿孔。%The chemical composition and maeroscopical g〉. microscopical corrosion morphology of a leaky high temperature sampling cooler in a nuclear power plant were analyzed and observed by chemical analysis, stereoscopic microscopy and SEM/EDS. The mechanism of coiled pipe corrosion failure was put forward combining with consideration for working condition of the cooler. EDS analysis of corrosion products showed that large amounts of Fe and P as well as trace Na existed in failure positions of the coiled pipe, indicating that pitting corrosion and perforation were caused by phosphate induced alkaline corrosion. The outer wall of coiled pipe was overheated. Then phosphate and impurities reached saturation under the condition of local liquid boiling, and were precipitated onto the tube wall. On the one hand, phosphate reacted with oxide on the coiled pipe surface; on the other hand, the concentration and deposition of media made heat transfer deteriorate. Phosphate hiding and alkaline corrosion occurred, and then pitting corrosion and perforation formed.