Corrosion Behavior of Carbon Steel Under H2SO4 Droplets and Dense Phase CO2

Abstract As carbon capture and storage advances, understanding material degradation in dense phase CO2 is crucial. Impurities like SO2, NO2, O2, H2S, and H2O can generate strong acids that accelerate corrosion. This study examines the corrosion of X65 carbon steel exposed to concentrated sulfuric acid droplets under dense phase CO2 conditions. Before testing with sulfuric acid, the stability of a water droplet on 316 stainless steel was assessed in a 20 L autoclave equipped with sapphire windows. The water droplet remained stable through CO2 phase changes. At atmospheric pressure, concentrated sulfuric acid (95 wt.%) showed rapid spreading on 316 stainless steel and X65 carbon steel due to low contact angles. Therefore, a custom X65 steel holder was designed to retain 0.5 mL of acid for corrosion studies. The corrosion test was performed under dense phase CO2 at 45 °C and 84 bar for five days. Corrosion evolution was monitored via a camera placed near the autoclave window. After exposure, weight loss measurements indicated a corrosion rate of 0.24 mm/year. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis revealed Fe, S, and O, suggesting iron sulfate (FeSO4) as the main corrosion product on the X65 steel surface.

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