Investigating the effect of water content in supercritical CO2 as relevant to the corrosion of Carbon capture and storage pipelines

Steel coupons were exposed to a supercritical carbon dioxide (CO2) environment in which water contamination was deliberately added over the range from 100 ppmw to 50,000 ppmw. Exposure was carried out in a laboratory scale autoclave at 8 MPa and 40°C for 7 days. Contaminant water in CO2 permits the speciation of carbonic acid (H2CO3), which can itself be a threat to durability, but also permit further contaminants to segregate to the aqueous acid phase. A systematic investigation of corrosion in supercritical CO2 over a range of water concentrations is lacking in the literature, despite being a significant elementary issue. Herein, weight-loss tests were performed, and subsequent scanning electron microscopy suggested all specimens displayed some extent of corrosion. The main corrosion mechanism observed was uniform corrosion. Supplementary optical profilometry suggested that water concentration has a small effect on any pitting corrosion that occurred. In general, increased mass loss was observed with an increase in water concentration beyond ~1,000 ppmw H2O, concomitant with a rate of change in the H2CO3 concentration.