High Temperature Corrosion of a Ternary Ni–29Mo–4Fe Alloy in a Mixed Hydrogen Chloride–Water Vapour Atmosphere

Abstract

The corrosion of a Ni–29Mo–4Fe (wt-%) ternary alloy in an atmosphere containing HCl, water vapour and some free oxygen has been studied at 600° and 700°c. The alloy shows a linear weight loss as a function of time, due to the formation of different volatile compounds predicted on thermodynamic grounds for the system, but at the same time it is covered by a complex scale composed mainly of oxides but containing also some chlorine. Comparison with the corrosion behaviour of the corresponding binary Ni–29Mo alloy shows that the addition of iron has a deleterious effect on the corrosion resistance of the alloy in this environment at 700°c, although it is slightly beneficial at 600°c. Possible reasons for this effect are discussed on the basis of the observed scale structure and of the formation of iron compounds.