Assessment of Tensile Strain Capacity of Girth Welds in X70 and X100 Pipeline With Surface Cracks Under Bending

This paper presents a detailed analysis of the tensile strain capacity (TSC) in X70 and X100 girth weld pipelines, each featuring external semi-elliptical surface cracks in the heat-affected zone (HAZ), under remote bending conditions. The objective of this study is to explore the effects of internal pressure, and HAZ softening levels on TSC for both steel types. First, comprehensive finite element analyses were performed to assess the crack driving force, quantified by the J-integral. The relationships between the crack driving forces and the applied remote strains on the pipeline under bending were established. Then, TSC were obtained using both crack initiation and ductile tearing criteria. Results indicate that the differences in TSC between the initiation and ductile tearing criteria are minimal, suggesting that the more convenient initiation criteria could be sufficient for practical assessments of TSC. The study then further demonstrates that increased internal pressures and HAZ softening reduce TSC. Comparisons of the TSC pipeline welds, obtained previously for remote tension loading, were also performed. The current results emphasize the significant impact of the factors on the structural integrity and safety of pipeline systems, highlighting opportunities to refine design practices and advance research into pipeline performance under complex loading conditions.