Towards an engineering tool for the prediction of running ductile fractures in CO2 pipelines

Abstract

A prerequisite for the deployment of CO2 capture and storage (CCS) is to establish a large network of high-pressure transport pipelines. It is then vital to assess new and existing pipeline designs for running ductile fracture (RDF). RDF is a phenomenon in which a defect develops into a crack propagating along the pipeline, sustained by the pressure forces from the escaping fluid. The most common engineering method for RDF, the Battelle two-curve method (BTCM), was originally developed for natural gas (NG) and has proved non-conservative for CO2. In this work we examine the BTCM in the light of available RDF experiments with CO2-rich mixtures. We present an improved material curve, in which the change in fluid properties when replacing NG with CO2 results in a new effective toughness correlation. Furthermore, we present an improved method for calculating the crack-tip pressure. This delayed homogeneous equilibrium model (D-HEM) accounts for the non-equilibrium thermodynamics due to the rapid depressurization, resulting in boiling pressures below the saturation pressure. Together, the adaptation of the material and fluid treatment yields improved results, and is a step towards a viable engineering tool for the prediction of RDF in CO2 pipelines.