Influence of the Oxygen Partial Pressure on the High Temperature Corrosion of A 38Ni-34Fe-25Cr Steel in Presence of NaCl Salt

Abstract : In biomass gasification process, some molten salts of the feed can generate high temperature corrosions. In this study the chromia-forming austenitic alloy Haynes ® HR-120 was oxidized with a deposit of sodium chloride during 96 hours at 825°C and 900°C. Two different atmospheres were selected; one with a high oxygen partial pressure (Ar/O 2 90/10 %vol.) and one, named syngas, with a low oxygen partial pressure (CO/H 2 /CO 2 45/45/10 %vol.). While at 900°C the behaviour of the alloy in presence of sodium chloride was catastrophic in high oxidizing conditions, the impact of sodium chloride was insignificant in the other atmosphere. Under Ar/O 2 mixture, the catastrophic oxidation was attributed to the setting up of an active oxidation. At 900°C under syngas atmosphere, the protective behaviour of the alloy seems linked to the association of a faster evaporation of the salt and a very low oxygen partial pressure. At 825°C a catastrophic behaviour is observed under syngas atmosphere as the NaCl evaporation rate is much slower.