L555M管线钢自动焊工艺焊接裂纹原因分析

Analysis of welding cracks in L555M pipeline steel automatic welding process

全自动焊技术因其可靠的焊接质量、高效的焊接效率在油气长输管道建设中被广泛使用。针对国内某在建天然气管道工程L555M钢在焊接过程中出现的裂纹,采用化学成分分析、无损检测、宏观分析、微观分析、扫描电镜联合能谱等分析方法,分析了该裂纹产生原因。研究结果表明:该裂纹缺陷为铜元素富集所致。铜元素富集的原因为:全自动焊接设备的铜质导电嘴在焊接过程中与焊缝坡口碰壁产生短路,短路电流产生的高温导致铜质导电嘴部分熔化,随着焊接完成,被熔化的铜元素聚集在母材和焊缝的晶界处,晶界铜富集区域在焊缝残余拉应力作用下发生脆化进而导致产生裂纹。

Automatic welding technology has been widely used in the construction of long-distance oil and gas pipelines due to its reliable welding quality and efficiency.To analyze the cracking cause during the L555M steel welding in an ongoing domestic natural gas pipeline project,various methods are applied,including chemical composition analysis,non-destructive testing,macroscopic analysis,microscopic analysis,and scanning electron microscopy along with energy spectrum analysis.It is found that the crack results from copper enrichment,which occurs when the copper conductive nozzle of the fully automatic welding equipment collides with the weld groove during the welding process and gets short-circuited.The heat generated by the short circuit current melts a part of the copper conductive nozzle in contact with the weld groove.As the welding is completed,the melted copper aggregates at the grain boundary between the base material and the weld seam.Under the residual tensile stress of the weld seam,the copper enrichment area at the grain boundary undergoes embrittlement and then the crack forms.