Effect of Pressure on Metal Dusting Initiation on Alloy 800H and Alloy 600 in CO-rich Syngas

Abstract

The effect of pressure on metal dusting initiation was studied by exposing conventional alloys 600 and 800H in CO-rich syngas atmosphere (H2, CO, CO2, CH4, H2O) at ambient and 18 bar total system pressure and 620 °C for 250 h. It was verified that, at constant temperature, increasing the total system pressure increases both oxygen partial pressure (pO2) and carbon activity (a C), simultaneously. Both samples exposed at ambient pressure showed very thin oxide scale formation and no sign of metal dusting. By contrast, samples exposed in the high-pressure experiment showed severe mass loss by metal dusting attack. Iron- and chromium-rich oxides and carbides were found as corrosion products. The distinct pressure-dependent behavior was discussed by considering both thermodynamic and kinetic aspects with respect to the protective oxide formation and pit initiation.