高频电阻焊管弯头破裂原因分析

Analysis of Fracture Cause of Elbow of High Frequency Resistance Welded Pipe

为了减少油田集输管道用高频电阻焊管及管件的失效事故,找出高频电阻焊管失效的原因,对某油田开裂失效的高频电阻焊管弯头进行了检测和分析,通过弯头外观及壁厚检查、理化检验、宏观观察、电镜金相分析等方法,查找高频电阻焊管弯头破裂泄漏原因。结果表明,弯头所用焊管母材基体质量不高,抗焊接应力能力较差;在焊缝熔合线位置存在偏析和硫化锰夹杂,使得硫化物夹杂和母材基体边界产生应力集中,在挤压变形时,外加应力导致熔合线位置微裂纹萌生;弯头内、外壁防腐层脱落导致壁厚减薄,加快了裂纹开裂速度,引发弯头最终失效。

In order to reduce the oil pipeline with high frequency resistance welded pipe and pipe fittings failure accident and find out the high frequency electric resistance welded pipe failure reason,the high frequency resistance welded pipe elbow with cracking failure in an oil field was detected and analyzed,by means of appearance and wall thickness inspection,physical and chemical inspection,macroscopic observation,electron microscope metallographic analysis and other methods,the cause of fracture and leakage of high frequency resistance welded pipe elbow is found.The results show that the quality of the base material of the welded pipe used in the elbow is not high and the welding stress resistance is poor.Segregation and manganese sulfide inclusions exist at the position of weld fusion line,which results in stress concentration at the boundary of sulfide inclusions and base metal matrix.During extrusion deformation,the applied stress results in microcrack initiation at the position of weld fusion line.The falling off of the anticorrosive layer of the inside and outside of the elbow leads to the thinning of the wall,which accelerates the crack cracking speed and leads to the failure of the elbow.