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In this work, low-Cr steels with enhanced corrosion resistance by employing Ni and Mo alloying were self-designed to provide an alternative option compared to a common 3Cr steel in CO 2 environments, and the corresponding corrosion resistance mechanism was investigated by comprehensively evaluating corrosion behavior of three low-Cr steels exposed to CO 2 -saturated NaCl solutions over time periods of 6–168 h at 90 and 180 °C, involving electrochemical and immersion tests. The results indicate that a decrease of general corrosion rates only expresses at early stages of corrosion after an addition of Ni and Mo, whereas FeCO 3 crystals instead of inner Cr-enrichment films play a decisive role in retarding long-term general corrosion rates. On the other hand, localized corrosion behavior of low-Cr steels is obviously retarded by employing Ni and Mo alloying, in which non-reactive nickel occupies a large amount of vacancies and restricts a diffusion of corrosive species. In addition, Mo accelerates an enrichment of Cr during early stages of immersion and followed by facilitating a rapid re-passivation capacity once films are broken, which reduces risks of perforation failure of pipelines.
Zhang et al. (Thu,) studied this question.