Corrosion and Carburization Behavior of Fe- and Ni-Base Alloys in S-CO₂ Environment at Two Temperatures




Introduction: The supercritical-CO2 (S-CO2) is a versatile, cross-cutting power conversion technology being developed for various energy applications such as nuclear, fossil and concentrated solar power plants. Recently, many studies have been performed focusing on corrosion and carburization behavior of various structural materials in S-CO2 environments. Generally, it has been reported that high Cr content (above 20 wt.%) is needed for Fe-base alloys to maintain a continuous chromia (Cr2O3) layer. Ferritic-martensitic steels such as G91 (9 wt.% Cr) have been found to show poor corrosion resistance, forming thick duplex Fe- and Cr-rich spinels [1]. Ni-base alloys form continuous chromia layer even with relatively less Cr contents (14 wt.%) and show superior corrosion and carburization resistance in S-CO2 especially at higher temperatures [2]. However, the significantly higher costs of Ni-base alloys would restrict its use to crucial components such as heat exchangers and turbomachinery, while Fe-base alloys may be used for most other parts of the power plants. Thus, practical consideration of materials based on various perspectives such as corrosion resistance, mechanical property and costs should be made. In this study, various Fe- and Nibase alloys ranging from ferritic-martensitic to austenitic alloys were subjected to corrosion testing in S-CO2 environments at 550 and 700 oC for up to 1500 h, as part of the international round robin S-CO2 corrosion testing program that began in 2015. The corrosion behavior of the alloys between the two test temperatures were evaluated and compared in view of the chemical compositions.

Authors:  Sung Hwan Kim, Gokul Obulan Subramanian, and Changheui Jang

Keywords: S-CO2 corrosion, Chromia, Oxide layer

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3 pages


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