深水SCR X65管线钢环缝无衬垫全自动GMAW焊接接头疲劳行为

Fatigue Behavior of Girth Joint of X65 Pipeline Steel by Full-Automatic Gas Metal Arc Welding Without Backing in Deepwater SCR Riser

对钢悬链线立管X65管线钢进行无衬垫全自动熔化极气体保护焊(Gas Metal Arc Welding,GMAW),然后对焊接接头开展疲劳试验。疲劳试验载荷值根据API RP 2A-WSD的规定进行设定,为了弥补小尺寸试件焊接残余应力的释放,对焊接后的管子测试残余应力,将残余应力作为平均应力进行考虑。在疲劳试验后,采用扫描电镜进行疲劳断口分析。试验结果表明,X65管线钢环缝无衬垫全自动GMAW焊接接头在高、中、低3个应力水平下的疲劳寿命最低值和平均值均高于API RP 2A-WSD标准的要求,疲劳断裂以盖面焊缝焊趾断裂为主。疲劳断口分析结果表明,部分试件盖面焊缝焊趾处存在微咬边缺陷,根部焊缝存在微小未熔合缺陷。

X65 pipeline steel of Steel Catenary Riser(SCR)is welded by full-automatic Gas Metal Arc Welding(GMAW)without backing,and fatigue test is carried out on the welded joints.The load of the fatigue test is set according to the provisions of API RP 2 A-WSD.In order to make up for the release of welding residual stress in small-size specimens,the measured residual stress of the welded pipe is tested and considered as the mean stress in the fatigue test.After fatigue test,the fatigue fracture is analyzed by SEM.The test results show that the minimum and average fatigue lives of X65 pipeline steel girth joint under high,medium and low stress levels are higher than the requirements of API RP 2 A-WSD standard.The fatigue failure mainly occurs at the welded toe of the welding seam on the cover surface.The results of fatigue fracture analysis show that there are micro-undercut defects at the toe of the welding seam on the cover surface of some specimens and micro-unfused defects at the root seam.