Effect of pressure on supercritical CO₂ compatibility of structural alloys at 750 °C

Several power generation technologies have interest in employing a supercritical CO₂(sCO₂) cycle but relatively little compatibility work has been conducted at the target pressure range of 200–300 bar, particularly at ≥700 °C. With the goal of utilizing lower pressure data sets (especially with controlled O₂and H₂O contents), this initial assessment compared the effect of CO₂pressure at 1–300 bar on the compatibility of potential Fe- and Ni-base structural alloys after 500 h exposures at 750 °C. For highly-alloyed alumina- and chromia-forming alloys, a minimal effect of pressure was observed on the mass change and reaction products, which were similar to those observed in 1 bar dry air, CO₂, CO₂–0.15%O₂and CO₂–10%H₂O. After these relatively short exposures, there was no obvious indication of internal carburization and the Cr depletion in the precipitation strengthened Ni-base alloys (740 and 282) was minimal. In addition to coupons, 25 mm long tensile specimens of alloy 740, 247, 310HCbN, and E-Brite (Fe–Cr) were exposed in each condition but did not show any detrimental effect of the high-purity CO₂environments on room temperature tensile properties.