An Operator’s Perspective on Fracture Control in Dense Phase CO2 Pipelines

Abstract

Carbon Capture and Storage (CCS) is an approach to mitigate global warming by capturing and storing carbon dioxide (CO2) from large industrial emitters. Pipelines will play a significant role in the transportation of CO2 in CCS projects. National Grid has an interest in this, and has carried out research to investigate the requirements for the safe design and operation of CO2 pipelines. CO2 pipelines are susceptible to long running fractures which are prevented by specifying an adequate pipe body toughness to arrest the fracture. There is no existing, validated methodology for setting pipe body toughness for pipelines transporting dense phase CO2 with impurities. The methods for estimating the pipe body toughness are semi-empirical so full scale fracture propagation tests are required to validate and extend these methods. As part of a major research programme into pipeline transportation of dense phase CO2, National Grid conducted two full scale fracture propagation tests using 900 mm diameter pipe in 2012. The tests demonstrated that the current natural gas practices for setting pipe body toughness was incorrect and non-conservative for dense phase CO2 pipelines. National Grid recognises the importance of understanding fracture arrest as it required to ensure design code compliance, impacts on pipeline design and provides reassurance to stakeholders. As the results of the two tests cannot be used directly to set the toughness requirements for a specific project pipeline, a third full scale test was necessary to confirm the fracture arrest capability of the pipe for the proposed pipelines. A third full scale fracture propagation test was conducted in July 2015. A propagating ductile fracture was initiated and successfully arrested in linepipe representative of that to be used on the proposed project.