Impact of iron-sulfide deposits on oxidized austenitic steels as simulation of corrosion and fireside-tube wastage in coal combustion

Abstract

The sulfidation effect of molten iron sulfides was studied on oxidized austenitic steels as a simulation of furnace-wall corrosion in PC combustion enûironments. The test coupons were oxidized to produce an external oxide scale and pyrite was placed on the oxide and thermally treated in an inert atmosphere to decompose the pyrite into pyrrhotite. DSC-TGA and XRD indicated that FeS interacts with the Fe2O3 oxide layer, eûen at 700°C if the contact is good, changing the oxidation state of iron and the physical structure. On the other hand, the interaction of FeS with Cr2O3 between 1100 to 800°C, 24 hr in the inert atmosphere, consisted of the formation of a chromium sulfide layer beneath the oxide scale. SEM-EDX showed that the diffusion of sulfur in the steel matrix can be 30 μm deep, indicated by small particles of chromium sulfide. It is demonstrated that iron sulfide deposits could be responsible for sulfidation of the alloys.