Strain-based fracture response of X80 steel pipe welded girth based on constraint-modified J-R curves: from SENT specimen to full-scale pipe

In the study, a methodology is proposed based on the SENT experiments and crack-tip constraint theory to determine the tensile strain capacity of a flawed pipe welded girth. Firstly, the clamped SENT specimens with a wide range of geometrical variations are conducted to determine the J-R curves. The constraint-quantified J-R curves are then formulated using the out-of-plane extension of bending modified J-Q theory, and show well match with the experimental data. Finally, the extrapolated resistance curves from SENT to full-scale pipes are used for strain-based fracture assessment of a flawed pipeline. A relatively good agreement in terms of tensile strain capacity between the present work and ExxonMobil's approach can be achieved except that the latter gives conservative predictions when the crack length 2c/t is longer than 3.0.