Effect of CO on the corrosion behavior of 304 stainless steel in wet CO2 gas at 710°C

The corrosion behavior of 304 stainless steel in wet CO2 gas with or without CO and CO plus 400 ppmv SO2 was investigated in this study. Corrosion kinetics was studied by thermogravimetric analysis at 710 degrees C for 100 h under three gas conditions. After isothermal exposure, the corroded coupons were characterized in detail by X-ray diffraction, scanning electron microscopy, an electron probe microanalyzer, and transmission electron microscopy. CO addition to wet CO2 resulted in lower oxygen partial pressure and lower oxide growth kinetics. It also suppressed iron-rich oxide nodule formation, as compared to the wet CO2 gas environment. A Cr-depletion zone was observed underneath the oxide scale in the substrate, but no obvious internal carburization was observed in all three gas environments. A thin, protective oxide scale consisting of an outer layer of a Cr-rich spinel and an inner Cr-rich chromia layer was developed in CO-containing gas conditions, with or without SO2. The effect of CO on oxidation and scale formation is discussed in comparison with that in wet CO2 conditions.