Assessment of brittle fracture in CO2 transportation pipelines: A hybrid fluid-structure interation model

In order to transport dense-phase CO2 captured from power and industrial emission sources in the Carbon Capture and Storage (CCS) chain, pressurised steel pipelines are considered the most practical tool. However, concerns have been raised that low temperatures induced by the expansion of dense-phase CO2, for example following an accidental puncture or during emergency depressurization, may result in a propagating brittle fracture in the pipeline steels.

The present study describes the development of a hybrid fluid-structure model for simulating dynamic brittle fracture in buried pressurised CO2 pipelines. To simulate the state of the flow in the rupturing pipeline, a compressible one-dimensional Computational Fluid Dynamics (CFD) model is applied, where the pertinent fluid properties are determined using a thermodynamic model. In terms of the fracture model, an extended Finite Element Method (XFEM) is used to model the dynamic brittle fracture behaviour of the pipeline steel.

Using the coupled fluid-structure model, a study is performed to evaluate the risk of brittle fracture propagation in a (real-scale) 1.22m diameter API X70 steel pipeline, containing CO2 at 0°C and 11MPa. The simulated results are found to be in good agreement with the predictions obtained using a semi-empirical model accounting for the pipeline fracture toughness. From the results obtained it is observed that a propagating fracture is limited to a short distance. As such, for the conditions tested, there is no risk of brittle fracture propagation for API X70 pipeline steel transporting dense-phase CO2.