Crack failure analysis of girth weld in high-grade-steel pipelines

Failure analysis of girth weld with crack was a necessary step to solve the quality risk of girth weld of X70 high-grade-steel pipelines. In this paper, the investigation and failure analysis of girth weld with cracks were summarized and analyzed to find their problems and rules in time, which provided suggestions and measures for subsequent safety management and cracking mechanism research. The existing failure analysis rules were summarized as follows. Girth weld cracks of X70 and X80 pipelines were mainly cracks in root welding. Girth weld cracks were easy to occur in the positions of variable wall thickness, top and bottom of pipe, which should be focused on to avoid missing evaluation and misjudgment as far as possible during welding construction and non-destructive testing and evaluation of defects. Overlap, misalignment reinforcement and other higher appearance detection indexes exceeded the standard resulted in poor formation of girth weld, affected the detection of crack defects and aggravated stress concentration at the root weld position. Based on the above rules, it was suggested to strengthen inspection process of appearance and root weld crack of girth weld for new pipelines. As for the in-service pipeline, the focus was on preventing influence of additional loads such as bending. Relying on crack failure analysis of girth weld, microscopic mechanism and control parameters of crack formation of girth weld was suggested to be further studied.Highlights: It was the first time to systematically summarize failure analysis process and results of girth weld with cracks in China, reveal the phenomenon and rule of girth weld with cracks, and put forward corresponding safety control measures for girth weld with cracks in newly-built pipelines and in-service pipelines.