During the investigation of hidden dangers in the circumferential welds of an X70 gas pipeline,a crack defect was found in one of the circumferential welds.Experimental analysis was conducted on the failed circumferential welding seam through macroscopic morphology analysis,non-destructive testing,mechanical property testing,metallographic analysis,scanning electron microscopy,and energy spec-trum analysis.The results indicated that the tensile strength,Charpy impact toughness,and bending performance of the circumferential weld met the requirements of SY/T 0452-2021 standard.The surface of the crack fracture was black brown,which was the morphology after high-temperature oxidation.There were intergranular cracks at the crack tip,therefore the crack should have been generated during the welding process,and it had the characteristics of welding hot cracks.There were non-metallic foreign objects inside the crack,and their composition was mainly composed of elements such as Na,Mg,Al,Si,Ti,and Mn through energy spectrum analysis.It was determined that the non-metallic foreign object was the slag generated by the welding coating.Cracks in the circumferential weld seam of pipeline butt joints were formed during the welding process.There was welding slag generated by the welding coating in the weld metal,and under the ac-tion of stress,the crack expands to form a crack in the area with high stress at the inner weld toe.
NETL
NSTL
万方数据
维普
