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

In biomass gasification processes, some molten salts formed during the process can promite high temperature corrosion. In this study the chromia-forming austenitic alloy Haynes(A (R)) HR-120 was oxidized with a deposit of sodium chloride for 96 h at 825 and 900 A degrees 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/CO2 45/45/10 %vol.). While at 900 A degrees 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 syngas atmosphere. When exposed to the Ar/O-2 mixture, the catastrophic oxidation was attributed to the setting up of an active oxidation. At 900 A degrees C under the 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 A degrees C a catastrophic behaviour is observed under the syngas atmosphere as the NaCl evaporation rate is much slower.