核电厂阀前三通泄漏失效原因分析

Fracture Analysis of Pressure Tapping Pipeline Downstream of Isolation Valve in Nuclear Power Plant

某核电厂在机组日常运行期间一三通先后发生两次穿孔,导致内部蒸汽介质泄漏。为了查找泄漏原因,对三通的宏观形貌、微观形貌、化学成分和金相组织等方面的分析,发现不锈钢三通在现场原始焊接时已被焊穿,穿孔部位由一块碳钢进行堵漏,在长期运行过程中被腐蚀穿透泄漏,堵漏之后由于原始马鞍型焊缝存在未融合和夹渣且焊缝中间存在间隙,导致了第二次泄漏的发生。两次泄漏的原因均为焊缝质量不良,工艺和工程控制不当。

During the daily operation of a nuclear power plant,the tee was perforated twice,resulting in internal medium leakage.In order to find out the cause of leakage,the macro morphology,micro morphology,chemical composition and metallographic structure of the tee were analyzed.It was found that the stainless steel tee had been welded through during the original welding on site,and the perforated part was blocked by a piece of carbon steel.It was penetrated and leaked by corrosion during long-term operation.After plugging,the second leakage occurred due to the lack of fusion and slag inclusion in the original saddle weld and the gap in the middle of the weld.Two events of leakage were caused by poor weld quality and improper process and engineering control.