Corrosion of 9-12Cr ferritic-martensitic steels in high-temperature CO2

The high temperature corrosion behavior of two 9Cr and 12Cr ferritic-martensitic steel grades was studied under CO2 pressures varying from 1 to 250 bar for exposure times up to 8000 h. No “breakaway” oxidation was observed. 9Cr steel grades suffered from fast parabolic uniform oxidation and fast carburisation. Increasing CO2 pressure had very little effect on the oxidation rate but increased the carburisation rate. The corrosion behavior of both 12Cr steel grades differed and might be influenced by gas composition, minor elements or surface finish. A corrosion mechanism coupling oxidation and carburisation is proposed.