Investigating the effect of salt and acid impurities in supercritical CO₂ as relevant to the corrosion of carbon capture and storage pipelines

A series of corrosion exposure tests were performed in a supercritical CO₂ environment used to represent the potential conditions for carbon capture and storage (CCS) pipelines. Impurities from various CO₂ capture processes are potentially present, which segregate to the aqueous phase, hence combining with any free water present in the pipeline. Herein, salt (NaNO₃, Na₂SO₄, NaCl) and acid (HNO₃) impurities were added, along with 10g of water, to an autoclave at 7.6MPa and 50°C (supercritical CO₂) for a 7 day steel specimen exposure. The tests conducted in supercritical CO₂ were also compared with aqueous tests in atmospheric conditions. Weight loss and optical profilometry revealed that corrosion rates for all samples are significant, along with the potential for localised attack. The corrosion mechanism differs for each solution tested. The work herein contributes to a holistic appraisal of understanding the corrosion of CO₂ pipelines.