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Pipelines subjected to displacement-controlled loading such as ground movement may experience significant longitudinal strain. This can potentially impact pipeline structural capacity and their leak-tight integrity. Reliable calibration of the tensile strain capacity (TSC) of pipelines plays a critical role in strain-based design (SBD) methods. Recent studies were focused mostly on high toughness modern pipelines, while limited research was performed on lower-grade vintage pipelines. However, a significant percentage of energy resources in North America is still being transported in vintage pipelines. Eight full-scale pressurized four-point bending tests were previously conducted on X42, NPS 22 vintage pipes with 12.7 mm wall thickness to investigate the effect of internal pressure and flaw size on TSC. The pipes were subjected to 80% and 30% specified minimum yield strength (SMYS) internal pressures with different girth weld flaw sizes machined at the girth weld center line. This paper evaluates the TSC of X42 vintage pipeline by utilizing ductile fracture mechanics models using damage plasticity models in ABAQUS extended finite element method (XFEM). The damage parameters required for simulating crack initiation and propagation in X42 vintage pipeline are calibrated numerically by comparing the numerical models with the full-scale test results. With the appropriate damage parameters, the numerical model can reasonably reproduce the full-scale experimental test results and can be used to carry out parametric analysis to characterize the effect of internal pressure and flaw size on TSC of X42 vintage pipes.

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The extended finite element method (XFEM) has recently become a very effective method to investigate the propagation of cracks in various structures under complex loading conditions. However, its use in the pipeline industry has been limited. This paper aims to apply XFEM to model our previous experimental results on NPS 12 grade of X52 steel pipes in which circumferential cracks with different sizes were pre-machined near the middle length and then eccentric tension was applied to the pressurized pipe specimens. Our previous experiments showed that the propagation of a surface crack was affected by the original crack configuration, the internal pressure level, and the external loading applied. The crack depth showed greater influence than the crack length on the burst load and the tensile strain capacity of the pipe. In this paper, the fracture criterion for modelling crack propagation using XFEM was defined by two damage parameters, the maximum principle stress and the fracture energy. The values of the damage parameters were varied until excellent agreement was obtained between one of our previous experiments and its numerical model. Then, this set of damage parameters was used to model another one of the experiments for verification. This paper describes our methodology for validation of XFEM and the adequate values of the damage parameters required to model crack propagation in X52 pipes.