Effects of in-service strain on girth weld failure of an X80 pipeline

In general, transmission pipelines are designed considering the hoop stress caused by internal pressure and the maximum longitudinal stress. This paper focuses on analyzing the brittle fracture failure of an X80 pipeline’s girth weld, subjected to in-service strain. The digital image correlation (DIC) technique was employed in tensile tests to examine the permanent plastic strain on the girth weld metal under in-service strain. Subsequently, the Charpy impact test was conducted on the girth weld metal, which had undergone concentrated plastic strain, to assess the reduction in toughness. The study elucidates the mechanism behind the brittle fracture of the girth weld. Findings indicate that the girth welds can exhibit noticeable plastic deformation even under the pipeline’s elastic in-service strain. This deformation can significantly impair toughness, leading to pipeline failure under strain-controlled loading conditions.