X70输气管道对接环焊缝开裂原因分析

Cracking Causes of Girth Weld of X70 Gas Pipeline

某X70输气管线在进行环焊缝隐患排查时,发现1处环焊缝存在裂纹缺陷。通过宏观形貌分析、无损检测、力学性能试验、金相分析、扫描电镜及能谱分析等对失效环焊焊缝进行了试验分析。结果表明,环焊缝的抗拉强度、夏比冲击韧性和弯曲性能等均符合SY/T 0452—2021标准的要求。裂纹断口表面呈黑褐色,为高温氧化后的形貌。裂纹尖端存在沿晶裂纹,因而该裂纹应是在焊接过程中产生,具有焊接热裂纹的特征。裂纹内存在非金属异物,经过能谱分析,其成分主要为Na、Mg、Al、Si、Ti和Mn等元素,判断该非金属异物为焊接药皮产生的熔渣。管道对接环焊缝中的裂纹是在焊接过程中形成,焊缝金属中存在焊接药皮产生的焊渣,在应力的作用下,该裂纹在内焊趾处应力较大的部位扩展后形成开裂裂纹。

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 spectrum 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 action of stress,the crack expands to form a crack in the area with high stress at the inner weld toe.