Transport of gaseous and dense carbon dioxide in pipelines: is there an internal stress corrosion cracking risk?

Transporting anthropogenic CO2 in pipelines is an essential component in the realisation and implementation of Carbon Capture and Storage (CCS). Transportation of dense CO2 has generally been the preferred economic solution, but projects in the United Kingdom (UK) have also considered transportation of gaseous CO2. Whichever option is selected, provision may need to be made to mitigate or prevent internal corrosion risks. This will require identifying and defining in the CO2 specification the maximum levels of water and impurities, e.g. nitrogen oxides (NOx) and sulphur oxides (SOx), such that internal corrosion risks are maintained at an acceptable level throughout the proposed service life of a pipeline. Equally, should there be a process upset in the CO2 stream conditioning procedure (e.g. failure of dehydration unit), then potential internal corrosion risks will need to be clearly defined in order to establish an effective mitigation strategy that maintains pipeline integrity. So far, while the corrosion research in this domain has focused on identifying plausible corrosion rates which may occur in these environments, the risk of Stress Corrosion Cracking (SCC) has not been extensively investigated. This paper explores whether SCC is possible in CO2 transporting pipelines. Gaps in current knowledge will be high-lighted. In addition some preliminary test results that indicate presence of SCC in simulated CO2 environments will be presented.