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

Several power generation technologies have interest in employing a supercritical CO 2 (sCO 2 ) 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 O 2 and H 2 O contents), this initial assessment compared the effect of CO 2 pressure 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, CO 2 , CO 2 –0.15%O 2 and CO 2 –10%H 2 O. 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 CO 2 environments on room temperature tensile properties.