采用宏观分析、金相检验以及能谱分析等技术,分析了超声波探伤发现的X70直缝双面埋弧焊钢管接头中超标缺陷的性质及形成原因。结果表明: 缺陷位于熔合线处, 其颜色及形态在抛光态和侵蚀后发生明显变化, 缺陷端部未见开叉, 两边界面也未见沿晶或穿晶裂纹; 缺陷区域的碳和氧元素含量异常升高; 从而确认该缺陷既不是钢板中的夹杂物或焊缝中的固体夹杂, 也不是裂纹, 而是接头中的未熔合缺陷, 因坡口表面污物未清除干净引起。

By means of macroscopic analysis, metallographic examination and energy spectrum analysis, properties and formation reasons of the overweight defects which were found by ultrasonic detection in the joints of X70 longitudinal double submerged arc welded steel pipes were analyzed. The results indicate that the defects located at the fusion line and their color and formation had a marked change compared polishing state with erosion state. There was no fish tail at the end of the defects and no inter-granular and trans-crystalline cracks at both sides of the interfacial defects as well. Carbon and oxygen content of the defect region was much higher than that of the normal area. So it can be confirmed that the defects were incomplete fusion which was caused by dirt on groove, not inclusions in the steel plate, and also not solid inclusions or cracks in the welding.