Corrosion behavior and mechanism of 316SS and Hastelloy C276 in supercritical water containing ammonia and ethanol

Ammonia serves as a promising hydrogen-rich carrier, with supercritical hydrothermal combustion offering a viable route for green ammonia utilization. The harsh environment in supercritical water, however, challenges material durability. This study investigates the corrosion behavior of Fe-based 316SS and Ni-based Hastelloy C276 under ammonia-containing atmospheres during the ignition/stabilization stages of hydrothermal combustion. Tests were performed at 520 °C and 25 MPa for 120 h in environments with 10,000 ppm NH 3 , 28290 ppm ethanol (when added), and oxidation coefficients from 0 to 2. Results show that 316SS suffered more severe corrosion than C276 in both oxygen-free and oxygenated ammonia-containing supercritical water. Under oxygen-free condition, insufficient O 2− and consumption of metal ions by ammonia inhibited formation of complete bilayer oxide film on 316SS. Under oxygen, thinning of the inner Cr 2 O 3 layer reduced 316SS corrosion resistance, while higher Cr, Ni content in C276 inhibited inward oxygen diffusion. However, adding ethanol altered the oxide film on 316SS to a denser outer layer and thicker inner layer with flaky, interpenetrating morphology and porous three-dimensional network structure. Conversely, ethanol caused coarse, poor protective oxide layers on C276, accelerating corrosion. These findings can provide theoretical guidance for material selection in ammonia-fueled supercritical hydrothermal combustion systems. • Corrosion behaviors of 316SS and C276 in SCW with NH 3 and C 2 H 5 OH are studied. • 316SS suffered severe corrosion than C276 in ammonia-containing SCW. • High Cr/Ni in C276 hinders oxygen inward diffusion enhancing corrosion resistance. • Ethanol densifies 316SS oxide structure but induces spallation at high O 2 . • Ethanol coarsens C276 oxides accelerating corrosion despite Cr/Mo layer formation.