Effects of Sulphate Deposits on Corrosion Behaviour of Fe-Based Alloys in Wet CO2 Gas at 750 °C

Abstract

The corrosion behaviour of several model and commercial Fe-based alloys, all with 25 wt% Cr, in CO2–H2O gases at 750 °C with and without sulphate deposits was studied. In the absence of sulphate deposits, ferritic alloys Fe–25Cr and Fe–25Cr–2Mn–1Si outperformed austenitic alloys Fe–25Cr–20Ni and 310 stainless steel. This pattern of behaviour is explained from the viewpoint of chromia and silica layer formation, using approximate analyses based on well-established diffusion models. Sulphate deposits exerted different effects on external scaling and internal sulphidation of the ferritic and austenitic alloys. Interactions between sulphur and metal cations at chromia grain boundaries are considered to be responsible for these effects.