Corrosion behaviours of two nickel-based coatings in H2S-containing environments

In view of the severe sulfidation of boiler tubes used in coal-burning power plants, exposures to mixed gas environments containing 10% H2S at 400, 500 and 600 °C were carried out to study the corrosion behaviour of two coatings arc sprayed on a mild steel substrate. One of the coatings is made from commercially available Ni70Cr30 alloy, and the other a high chromium (>40 wt.%) nickel-based alloy newly developed by the authors. The curves of corrosion kinetics were plotted according to thermogravimetric data of the coatings. Metallurgical microscopy was used to observe the morphologies of the corrosion products and SEM was used for elemental mapping. The results obtained indicate that the coating made from the high chromium alloy shows excellent resistance to sulfidation and is suitable for use as protective layers of boiler tubes.