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

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.