Fireside Corrosion Performance of NiCr Coatings in Simulated Coal-biomass Combustion Environment

Higher operating temperatures coupled with biomass-derived fuels can lead to aggressive corrosion damage to the superheater/reheater tubes in power plants. In this study, HVOF sprayed NiCr coating was deposited onto T92 substrate, which were exposed in simulated coal-biomass combustion gases with a screening deposit containing Na₂SO₄, K₂SO₄ and Fe₂O₃ at 700-750°C for 1000 h. The tests were carried out using the “deposit-recoat” test method and pre and post-exposure dimensional metrology was used to quantify the coating damage in terms of metal loss distributions. The exposed samples were also examined in a SEM/ EDX. The coatings developed a protective Cr₂O₃ layer at the coatings/ deposit interface and a Cr depleted zone was observed underneath the oxide layer. The coating- substrate interface showed formation of an intermetallic layer at both 700 and 750ºC. NiCr coating provided suitable corrosion protection to the T92 steel with a median metal loss of ~35µm in 1000h.