The present study was designed to study the role of impurity adsorption and condensation behaviors in the corrosion mechanism of CO2 transport pipeline steel, based on the hypothesis that the impurity adsorption and condensation play a critical role in inducing the formation of aqueous electrolyte in the initial stage of the corrosion processes. The impurity adsorption and condensation behaviors including water adsorption, adsorption of sulfurous species (SO2/H2SO3), and H2SO3 condensation onto the Fe-coated quartz crystals were measured by the Quartz Crystal Microbalance (QCM) technique in water-unsaturated CO2/H2O flow and CO2/H2O/H2SO3/SO2 flow at 45°C and 1 bar. The connections between the water adsorption and acid condensation behavior onto Fe-coated quartz crystals with Fe corrosion were also studied by utilizing SEM and EDS techniques. The results showed that Fe suffered no corrosion in the water-unsaturated CO2/H2O gas flow but suffered localized corrosion in the water-unsaturated CO2/H2O/H2SO3/SO2 gas flow. It was suggested that the acid condensation initiated the Fe corrosion at water-unsaturated conditions with impurities instead of the pure water adsorption behavior.
CO2 captured from different sources for carbon capture and storage (CCS) will contain impurities. Although it is technologically possible to treat CO2 to near 100% purity in the gas conditioning process, it is preferable to have fewer rigid specifications to reduce both operational and capital costs. From a corrosion point of view, SOx, NOx, H2S, and O2 are considered to be the most aggressive impurities. There are no field cases that analyzed the effect of impurities on corrosion, however, laboratory experiments have shown that noticeable, and potentially severe, corrosion occurs at water-unsaturated conditions in dense phase CO2 with the presence of those impurities due to synergistic interactions between chemical species.1-11
Although many experimental works have been conducted to investigate the effects of water and various impurities on the corrosion behavior of pipeline steels in dense phase CO2, there is little study on the evaluation of corrosion mechanisms for the corrosion behavior of pipeline steels in dense phase CO2, especially for the corrosion mechanism in the water-unsaturated conditions.
