The Erosion-Corrosion of a Nitrocarburized Low Alloy Steel in a Simulated FBC Environment

There is interest in the use of surface treatments to reduce the wastage caused by erosion-corrosion of in-bed heat exchanger tubing in fluidized bed combustors. The erosion-corrosion of a nitrocarburized low alloy steel was examined in a laboratory scale test rig based on a fluidized bed. It was found that the value and temperature of maximum wastage was reduced on nitrocarburizing the steel. Wastage of the compound layer of the nitrocarburized steel was found to be comparable or greater than that of the untreated steel, suggesting the improvements in wastage resistance observed were due to the diffusion layer. At low temperatures, the wastage of the nitrocarburized steel was greater than the untreated steel. It was proposed that this was due to the nitrocarburized steel having a greater initial oxidation rate.