Alloy design employing Ni and Mo low alloying for 3Cr steel with enhanced corrosion resistance in CO2 environments

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 CO2 environments, and the corresponding corrosion resistance mechanism was investigated by comprehensively evaluating corrosion behavior of three low-Cr steels exposed to CO2-saturated NaCl solutions over time periods of 6-168 h at 90 and 180 degrees 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 FeCO3 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 cor-rosive species. In addition, Mo accelerates an enrichment of Cr during early stages of im-mersion and followed by facilitating a rapid re-passivation capacity once films are broken, which reduces risks of perforation failure of pipelines. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).