Effect of SO₂, O₂, NO₂, and H₂O Concentrations on Chemical Reactions and Corrosion of Carbon Steel in Dense Phase CO₂

Carbon capture, utilization, and storage is expected to be an important method for reducing CO₂ emissions to prevent global warming. Several species (impurities) could follow the CO₂ through the capture plant as carry over. It is expected that nitrogen dioxide (NO₂), sulfur dioxide (SO₂), oxygen (O₂), and water (H₂O) can be present as impurities (concentrations at the ppmv level) in the captured CO₂. The exact composition will depend on the flue gas type, the CO₂ capturing process, and multiple other parameters. Some of these impurities are reactive and may cause corrosion in carbon steel pipelines and could therefore be a threat for safe CO₂ transport. The present study used a novel experimental setup to realistically simulate a CO₂ transport pipeline system with a controlled and variable concentration of impurities at a total pressure of 10 MPa and a temperature of 25°C. The water concentration was increased and decreased with constant concentration of SO₂ and O₂, to observe and identify possible reactions or threshold levels which could cause corrosion. A similar experiment was conducted with NO₂. First, experiments were performed without steel coupons, to observe uncatalyzed reactions, and then with coupons to measure corrosion rates. The first sign of corrosion appeared at 350 ppmv of water with NO₂ present. At 670 ppmv water with 75 ppmv NO₂ the overall corrosion rate was about 0.57 mm/y and the main product was iron oxide. The corrosion process for SO₂, O₂, and water was much slower, and the first sign of corrosion appeared around 1,900 ppmv of water, with about 75 ppmv of SO₂ and 230 ppmv of O₂. The corrosion rate increased some when the water concentration was increased to 2,400 ppmv, but the overall corrosion rate was only 3.6 μm/y and the main product on the surface was iron sulfate.