Effect of Cr on Corrosion Performance of Steels in Supercritical CO₂ Environments

As a promising technology, carbon capture and storage (CCS) can significantly reduce CO₂ emissions while retaining the core value of fossil fuel power plants. CO₂ transportation is a crucial step to ensure the successful deployment of CCS, which is achieved by pipeline network. However, the impurities in the captured supercritical CO₂ (s-CO₂) may cause severe corrosion damages to pipeline steels. As a control strategy, Cr-bearing steels are proposed as potential candidate materials to mitigate corrosion, especially at the crucial parts of the transportation system. In this paper, corrosion behaviors of steels with different Cr contents were studied in s-CO₂ streams with impurities (H₂O, SO₂, O₂, etc.) at 10 MPa and 45°C. The corrosion rates were measured by mass loss method and the corrosion products were characterized. The effect of Cr on corrosion behavor of steels was also discussed.

In recent years, several novel technologies have been proposed and developed to produce energy in a clean and sustainable way. However, in the foreseen future, fossil fuel will still be the major source to meet our needs on energy.¹ The combustion of fossil fuel for power and heat is always accompanied by CO₂ emission, which is believed to be in large correlation to global warming.² To control the CO₂ emission and reduce the negative effects, carbon capture and storage (CCS) has been rapidly developed in fossil fuel combustion power plants.^{3, 4} One of the crucial parts of CCS is the long-distance transportation of CO₂, during which a large amount of captured CO₂ is transported to storage sites. Pipeline network is chosen as transportation system due to its high efficiency and moderate cost.⁵ And the transported CO₂ streams are usually compressed into supercritical CO₂ (s-CO₂).⁶

Due to the wide accessibility and relatively low price, some high-strength carbon steels from API⁽¹⁾ Grade 5 were selected as the construction materials for the pipeline network.⁷ However, the integrity of pipeline steels is threatened by impurity-induced corrosion issues. These impurities, including H₂O, H₂, O₂, H₂S, SO_x, NO_x, CO, and acids, originate from the combustion or capture processes and often cause great corrosion damage to pipeline steels.⁸ Among them, SO₂ seems to be one of the most notorious impurities. It is generated when sulfur-containing fossil fuels are combusted. It arouses severe degradation of pipeline steels even at ppm level and the corrosive effect is proportional to its concentration.⁹ Some researchers attributed the high corrosive effect of SO₂ to its conversion to sulfuric acid and the dissociated H⁺ in the presence of H₂O.¹⁰ Other researchers found that corrosion damage is further enhanced by the synergistic effect of SO₂ with other impurities.¹¹ Up to now, a lot of researchers have been made and several review articles have been tried to summarize the corrosive effects of SO₂.^{1, 12} More efforts should be made to ensure the safe operation of s-CO₂ transportation system.