Fracture behavior analysis of X80 pipelines welded joints with unequal wall thickness

Pipeline transportation is one of the main methods for transporting oil and natural gas worldwide. The structural safety of welded joints of large diameter pipes with cracks and unequal wall thickness has become a research focus due to discontinuous geometrical structure and cracks in weld seams. In this paper, the tensile experiment and analysis of specimens with unequal wall thickness across welding seam based on the digital image correlation technology are carried out. Moreover, the influence of transition length and transition form on fracture behavior of welded joints of unequal wall thickness pipeline is obtained. In addition, a three-dimensional finite element model of welded joint of unequal wall thickness pipe with oblique line transition form and circular arc transition form is established. and the accuracy of the full-scale pipeline finite element model modeling method is verified by small-scale experiment data. On this basis, the influence of geometrical parameters of the transition section and wall thickness ratio, pipe diameter, and weld strength matching coefficient on the crack driving force of welded joints with unequal wall thickness is obtained. From the perspective of strain-based design, a method for obtaining the minimum transition length section and avoiding girth weld fracture is proposed. The research results guide the design and safety evaluation of welded joints with unequal wall thickness.