Stress state analysis of root notch for X80 girth welds with variable wall thickness and misalignment geometric features

Notches formed due to weld geometric features seriously affect the structural safety of the pipeline. In this paper, the stress states of girth welds under various forming conditions and internal pressures are thoroughly evaluated via numerical simulation analysis. Controlled studies are carried out between crack-free and cracked welds. The susceptibilities of stress state to variations in internal pressure under different forming conditions are elucidated. Also, newly modified single-edge notch tensile specimens (MSENT) are manufactured, and the strain charac-teristic and fracture behavior analysis are performed. The calculation results reveal that the stress states of either the root notch or the crack tip are significantly intensified by welds' geometric features, and the increased brittle fracture sensitivity can be qualitatively demonstrated by MSENT analysis. Simultaneously, the misalignment continuously enhances the sensitivity of stress states to internal pressure variation. However, opposite patterns are observed between crack-free and cracked welds characterizing variable-wall-thickness features. The research results can provide a strong reference for the structural design, service evaluation, and related research of pipelines.