Thermochemical study of high temperature corrosion of iron in a diluted HCl+SO2 environment

Depending on the chemical make-up of the waste stream and operational param eters, a variety of high temperature corrosive environments are generated i n the incinerator. As corrosion of industrial equipments is essentially due to high content of sulfur and chlorine in the combustion gas, this study i s focused on the interpretation of degradations of pure iron in experimenta l air environment containing 1000 ppm of HCl and 100 ppm of SO2. Thermochem ical calculations were used to estimate the role of these corrosive element s considering chemical potential diagrams and stability paths in pseudo-bin ary diagrams involving iron and the corrosive atmosphere. The influence of chlorine has been described by the "active corrosion" mechanism proposed by Grabke and confirmed by our calculations. The role of sulfur has been poin ted by its "cycle" leading to the formation of eutectic metallic tri-sulfat es, promoting a liquid phase corrosion type in the range of the industrial temperatures.