Stress state at the root of variable-wall-thickness pipeline welded joint

In this study, root notch defects in the application of variable wall thickness designs of pipeline welded joints were analyzed. Considering variable-wall-thickness pipelines, various finite element models of butt-welded joints were established by changing the joint geometric parameters such as variable-wall-thickness ratio, butt misalignment, or variable wall thickness transition angle. This was followed by applying different internal working pressures of the pipeline to calculate the stress triaxiality and maximum principal stress near the root notch of the welded joints. The influence of the weld section shape and internal working pressure on the calculation results is summarized, and the corresponding fracture risk of the root notch is evaluated. Based on the aforementioned analysis, it was found that the root notch in the variable-wall-thickness joint reduced the safety of the welded joint. A greater irregularity of the joint geometric morphology results in a higher the stress triaxiality and maximum principal stress near the root notch, further severely increasing the brittle fracture risk of the joint.