某发电公司1 000 MW燃煤发电机组在运行中, Q235B钢循环水母管发生断裂。通过宏观检验、化学成分分析、力学性能测试、金相检验、扫描电镜及能谱分析等方法, 对循环水母管的断裂原因进行了分析。结果表明: 循环水母管焊缝部位存在未焊透现象及焊渣、焊瘤等夹杂物, 焊接质量低、显微组织异常导致焊缝处承载能力差; 在腐蚀环境存在的情况下, 裂纹在焊渣处形成并快速扩展, 导致循环水母管断裂失效。

A circulating water main pipe of Q235B steel in a 1 000 MW coal-fired power generation of a power plant fractured during operation. The fracture causes of the circulation water main pipe were analyzed by means of macroscopic inspection, chemical compositions analysis, mechanical properties testing, metallographic inspection, scanning electron microscope analysis, energy spectrum analysis and so on. The results show that: incomplete penetration phenomenon and inclusions, such as welding slag, welding beading and so on, existed in the welding seam of the circulating water pipe; low welding quality and abnormal microstructure caused poor bearing capacity of the welding seam. In the corrosion environment, cracks generated in the area of welding slag and expanded rapidly, resulting in the fracture failure of the circulating water main pipe.