This paper discusses work currently being undertaken to develop an integrity based strategy for fracture control during the re-design process for the conversion of oil/gas pipelines to transport CO2. The paper reviews the requirements that need to be fulfilled to ensure that any potential running fractures (from different defect types - manufacturing, construction, corrosion, etc) are adequately arrested to avoid catastrophic failure following the change of service of the pipeline. The available decompression models for CO2 are discussed to evaluate their applicability to the transportation of “captured” CO2.
In order to ensure the suitability of the pipeline for the “change of use” a methodology for the fracture control evaluation from the relevant information derived from the as-design, as-built and as-found condition is discussed. Once the integrity condition of the pipeline has been determined, a comparative risk assessment to define the main threats under the new operating conditions is described.
Both the risks of long running brittle fracture and ductile fractures are important and have been considered. The influence of material properties such as the embrittlement behaviour under low temperatures, and also the influence of the composition of the transported liquid on the fracture of the pipes need to be analysed. The decompression at the location of any opening/defect would result in local changes in pipe temperature which would affect the integrity of the pipe. Key operating parameters such as corrosion control strategy, control of water content, flow assurance, control risk of hydrate formation and the effect of impurities in the gas decompression behaviour have been outlined.