Failure Pressure Prediction of Crack in Corrosion Defects in 2D by Using XFEM

Aging pipelines may experience several different types of degradation, such as crack and corrosion, which pose serious concerns for the pipeline integrity. Hybrid flaws such as crack-in-corrosion (CIC), can be challenging to model and understand. For instance, predicting the failure pressure using the finite element method (FEM) is relatively difficult; therefore, the extended finite element method (XFEM) is introduced here. Compared to the conventional FEM, which requires extremely fine meshes and is impractical for modelling dynamic crack propagation, XFEM is computationally efficient as there is no need to update the mesh elements for tracking the crack path. This paper aims to study the applicability of XFEM in predicting the failure pressure of CIC defects in 2D. In particular, mesh size sensitivity and the effects of different CIC parameters on the final failure pressure were examined. ABAQUS v 6.14 was used for this simulation study. For simplicity, only half of the pipe was modelled assuming symmetry around the horizontal plane. A CIC defect was placed at the exterior of the pipe. The corroded area was assumed to be semi-elliptical, and the crack was simulated as a longitudinal crack. In this paper, failure criterion was satisfied when the crack has propagated to the last element. Several models were built in which the length and width of the elements at the crack tip were changed. An optimum mesh size was determined and was applied subsequently in several other models to study the impacts of crack depths, corroded area widths, and corrosion profiles. The results showed that when the total defect depth was fixed at 50% of the wall thickness, the failure pressure decreased with increasing the crack depth, while both corroded area width and corrosion profile only have a secondary effect on the failure pressure. In addition, the failure pressure of a CIC defect was bound between that of a crack-only defect and a corrosion-only defect. When the depth of the crack is higher than 50% of the total defect area, the CIC defect can be treated as a crack only defect with a crack depth equal to the total defect depth.