Abstract
In this study, four testing cycles (total 480 h) were conducted to investigate corrosion and stress corrosion cracking (SCC) of X65 steel in H2O-saturated supercritical CO2 (s-CO2) containing SO2 and O2 impurities. The results showed that X65 steels experienced severe corrosion and formed a porous corrosion layer composed of iron sulfates, carbonates and oxy-hydroxides. Increasing time from 120 to 480 h resulted in the shift of dominant corrosion products from iron carbonates to iron oxy-hydroxides due to acid regeneration cycle. The mass loss of X65 steel almost linearly increased with exposure time, indicating a nearly constant corrosion rate in the s-CO2 environment. In comparison with previous studies, timely replenishing s-CO2 fluid in a static autoclave is crucial to accurately determine the long-term corrosion kinetic of pipeline steel. Based on literature survey and current study, several factors (SO2 content, H2O content, addition of NO2) affect the long-term corrosion rate in s-CO2 environments, and a power-function-based empirical model is purposed to depict the long-term corrosion rate of X65 steel in H2O-saturated s-CO2 + O2 + 100/2000 ppm SO2. The long-term SCC assessments showed that the SCC susceptibility of X65 would be still quite low, which might be related to the O2-depressed hydrogen cracking and/or the lack of localized stress concentration.
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