The effect of H2S and corrosion inhibitor on the aqueous corrosion behavior of mild steel was evaluated at high CO2 partial pressure conditions. The experiments were performed in a 7.5 L autoclave with different temperatures (25°C and 80°C) and different H2S concentrations (1000 ppmv and 2000 ppmv) at 12 MPa CO2. The corrosion rate of steel samples was determined by electrochemical and weight loss measurements. The surface and cross-sectional morphology and the composition of the corrosion product layers were analyzed by using surface analytical techniques (SEM, EDS and XRD). Results showed that the presence of 1000 ppmv and 2000 ppmv H2S decreased the corrosion rate of mild steel compared with pure CO2 condition. However, the final corrosion rates were still higher than the targeted threshold (< 0.1 mm/y). Surface and cross-sectional analyses revealed the formation of FeS in the presence of H2S and no localized corrosion was observed. The addition of 400 ppmv of an imidazoline-based corrosion inhibitor reduced the corrosion rate below 0.1 mm/y in high pressure CO2 conditions with 2000 ppmv H2S.


Over the past decade, there has been increasing interest in the corrosion behavior of carbon steels in supercritical CO2 conditions. Unlike the case of carbon capture and storage (CCS) where small amounts of water are present, the exploitation of fields with high pressures of CO2 needs to consider the presence of formation water, which presents strong corrosivity. It has been reported that the aqueous corrosion rate of carbon steel at high CO2 pressures (liquid and supercritical CO2) without protective FeCO3 corrosion product layers is very high (>20 mm/y) due to the high concentrations of corrosive species such as H+ and H2CO3.1-5 Steels with low Cr contents (i.e., 1% Cr and 3% Cr) have shown no beneficial effect in terms of reducing the corrosion rate to admissible values.6 Therefore, controlling corrosion in these cases usually involves the use of corrosion resistant alloys (CRAs) or corrosion inhibitors (CI). Adequate protection of carbon steel was achieved by applying CI in high pressure CO2 environments.6

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