In this study, we present results from a numerical model of a full-scale fracture propagation test where the pipe sections are filled with impure, dense liquid-phase carbon dioxide. All the pipe sections had a 24″ outer diameter and a diameter/thickness ratio of ∼32. A near symmetric telescopic set-up with increasing toughness in the West and East directions was applied.
Due to the near symmetric conditions in both set-up and results, only the East direction is modelled in the numerical study. The numerical model is built in the framework of the commercial finite element (FE) software LS-DYNA. The fluid dynamics is solved using an in-house computational fluid dynamics (CFD) solver which is coupled with the FE solver through a user-defined loading subroutine. As part of the coupling scheme, the FE model sends the crack opening profile to the CFD solver which returns the pressure from the fluid. The pipeline is discretized by shell elements, while the backfill is represented by the smoothed-particle hydrodynamics (SPH) method. The steel pipe is described by the J2 constitutive model and an energy-based fracture criterion, while the Mohr-Coulomb material model is applied for the backfill material. The CFD solver applies a one-dimensional homogeneous equilibrium model where the thermodynamic properties of the CO2 are represented by the Peng-Robinson equation-of-state (EOS).
The results from the simulations in terms of crack velocity and pressure agree well with the experimental data for the low and medium toughness pipe sections, while a conservative prediction is given for the high-toughness section. Further work for strengthening the reliability of the model to predict the arrest vs. no-arrest boundary of a running ductile fracture is addressed.