The influence of SO₂ on the tolerable water content to avoid pipeline corrosion during the transportation of supercritical CO₂

A systematic study is undertaken to establish the influence of sulphur dioxide (SO2) concentration on the critical water content required to avoid substantial levels of internal corrosion during the transport of supercritical CO2 for carbon capture and storage (CCS) applications. Corrosion experiments were performed on X65 carbon steel in autoclaves containing supercritical CO2 at 80 bar and 35°C in the presence of 0, 50 and 100 ppm (mole) SO2. General and localised corrosion rates were determined over a period of 48 hours through the implementation of gravimetric analysis and surface profilometry, respectively. Analysis of corrosions products formed on the steel surface was performed using x-ray diffraction, Raman spectroscopy and scanning electron microscopy. The results indicate that the presence of SO2 reduces the critical water content required to maintain a general corrosion rate below 0.1 mm/year. Furthermore, the water content required to avoid excessive localised corrosion is far less than that to prevent significant general corrosion. Localised corrosion rates close to 1 mm/year were observed in the absence of SO2 when the CO2 system was water-saturated, but below water contents of ~1800 ppm (mole) and ~500 ppm, general and localised corrosion rates (respectfully) were found to be below 0.1 mm/year even in the presence of 100 ppm SO2. The research presented highlights that reducing water content is a more favourable option compared to reducing SO2 content to minimise internal pipeline corrosion during transportation. Consideration is also afforded to the consumption of impurities in the closed system experiments.