Abstract
To significantly reduce CO2 in the atmosphere, CO2 must be captured, compressed, and transported to a sequestration site for permanent storage. When injecting CO2 emitted from various industrial sources into a well, injected fluid and formation water will be in contact with injection strings, which is saturated with CO2 with corrosive impurities. Corrosion resistant alloys, such as duplex stainless steel and super duplex stainless steel, are candidates for injection tubing. The objective of this work is to evaluate the effect of SO2, NO2, O2, and chloride concentrations on the duplex (S82551) and super duplex (S39274) stainless steels in the aqueous phase under supercritical CO2 environment. Exposure experiments of samples in 5 or 25 wt% NaCl were carried out at 150°C with 120 bar (1740 psi) CO2 in a 7L autoclave. Up to 100 ppm of SO2, NO2, O2 were introduced into the autoclave. The steel samples were examined for uniform corrosion and localized corrosion. In supercritical CO2 environment up to 100 ppm SO2, both stainless steels showed good corrosion resistance. However, with 100 ppm NO2, crevice corrosion was observed on the duplex stainless steel. When O2 was introduced in addition to NO2, super duplex stainless steel also showed signs of crevice corrosion. The localized attack further intensified with higher chloride concentration. Compared to pitting corrosion and uniform corrosion, crevice corrosion should be emphasized in such an environment.
