Effect of Liquid Impurities on Corrosion of Carbon Steel in Supercritical CO₂

The increasing urgency to mitigate global warming has driven many efforts to control green house gas emissions. One solution among many is carbon capture and storage. However, CO₂ emitters are not necessarily in the close vicinity of potential geologic storage sites. In consequence CO₂ will be transported from generation site to storage sites under high pressures. This will necessitate a network of pipelines gathering supercritical CO₂ from diverse sources and transporting it through transmission lines to the storage sites. These pipelines will be under corrosion risks, particularly because of possible carryover of trace impurities produced from the different sources, such as water, chloride, NO_x, SO_x, and O₂. The effects of impurities on corrosion in supercritical CO₂ have yet to be evaluated systematically. Corrosion of carbon steel associated with water and impurities in supercritical CO₂ was studied by Electrochemical Impedance Spectroscopy in autoclaves. Five impurities were studied by introducing them in the liquid condensed phase: water, amine, HCl, HNO₃ and NaOH. Results were analyzed in terms of the phase behavior and speciation.