火电厂锅炉水冷壁焊缝泄漏失效分析

Failure Analysis on Weld Leakage of Boiler Water Wall in Thermal Power Plant

某12Cr1MoV水冷壁对接焊缝中部出现周向裂纹导致泄漏失效,为调查泄漏失效原因,对焊缝进行了宏观检查、磁粉检测、硬度检验、金相分析、全元素分析和能谱分析,并建立模型分四个阶段讨论了水冷壁焊缝泄漏失效的原因。研究表明:焊缝中夹杂的S元素是焊缝泄漏失效的主要因素,收缩拉应力为偏析在晶界的低熔点共晶物提供了形成沿晶热裂纹的条件,氧气的介入造成热裂纹的局部氧化,实际运行的综合应力使氧化的沿晶热裂纹多点扩展、融合,形成宏观裂纹,最终导致焊缝泄漏失效。

A circumferential crack appeared in the middle of a 12Cr1MoV water wall butt weld,leading to leakage failure.In order to investigate the cause of leakage failure,macro inspection,magnetic particle testing,hardness testing,metallographic analysis,full element analysis and energy spectrum analysis were carried out on the weld,and a model was established to discuss the causes of water wall weld leakage failure in four stages.The research shows that the inclusion of S element in the weld is the main control factor of the weld leakage failure.The contraction tensile stress provides the conditions for the formation of intergranular hot cracks for the low melting point eutectic that segregates at the grain boundary.The intervention of oxygen causes local oxidation of the hot cracks.The actual operation comprehensive stress makes the oxidized intergranular hot cracks expand and fuse at multiple points,forming macro cracks,and finally leading to weld leakage,It provides a theoretical reference for leakage failure caused by intergranular thermal cracks in water wall welds of thermal power plants.