The performance of Haynes 282 and its weld in supercritical CO2

Abstract

The supercritical carbon dioxide Brayton cycle is being considered as a replacement of the steam Rankine cycle due to the potential for higher operational efficiency and lower capital cost. Higher temperature and pressure conditions allow for higher efficiencies, leading to a demand for materials with high strength at these elevated temperatures. Haynes 282® has been found to have good high temperature strength and corrosion resistance, but the mechanical and weld performance in CO2 has not been studied. This work addresses that gap in knowledge by testing the mechanical properties of both base and gas tungsten arc welded samples before and after exposure to either supercritical carbon dioxide at 750 °C, 20 MPa or argon at 750 °C, 0.12 MPa for 1000 h. Both exposures resulted in a small increase in yield strength and a loss in ductility in welded and base material, with the fusion line exhibiting the most severe loss of ductility. Corrosion analysis revealed attack at a maximum of 20 μm for both base and fusion zones, with no impact of a depth-dependent effect in the fracture surfaces. Bulk analysis revealed the presence of grain boundary carbides – intermittent in base material and constant in the fusion zone – which created a region devoid of γ’ strengthening precipitates. This morphology, as well as all observed mechanical effects, was caused by the thermal aging of 282. Corrosion in CO2 was not mechanically detrimental to 282 at 750 °C, 20 MPa after 1000 h for the sample size and orientation used in this study.