Effect of Impurity SO₂ on Corrosion and Stress Corrosion Cracking of X65 Steel in Supercritical CO₂ Streams

Pipeline transportation is a critical section in the context of carbon capture and storage (CCS) systems. Transported supercritical CO₂ (sc-CO₂) usually contains corrosive impurities, particular SO₂, that can lead to exacerbated corrosion damage on pipeline integrity. However, there is still no clear image to describe how the impurities affect corrosion due to very limited database and some controversial results. More importantly, there is a serious concern on the stress corrosion cracking (SCC) susceptibility of the pipeline because of the presence of corrosive agents and high operating pressure of sc-CO₂ mixtures. Surprisingly, few works have been done on this issue. In this paper, the effects of SO₂ on corrosion and SCC susceptibility of X65 steel were investigated in sc-CO₂ environment containing impurities SO₂, O₂ and H₂O. The results show that the addition of only 100 ppm SO₂ into the sc-CO₂ system significantly increases corrosion rate, consistent with some previous results. Under such corrosive condition, however, SCC crack is not found in the steel specimen even heavily strained up to 0.6%. This finding opens a new window on the development of corrosion control strategy of sc-CO₂ pipelines. Corresponding corrosion mechanisms in the media are also discussed and proposed.