Hot corrosion studies of HVOF NiCrBSi and Stellite-6 coatings on a Ni-based superalloy in an actual industrial environment of a coal fired boiler

Hot corrosion of boiler tubes used for super-heaters and re-heaters in steam-generating systems has been recognized as a severe problem, resulting in tube wall thinning and premature failure. Attempts to decrease the maintenance costs of these components have increased interest in shielding them with protective coatings. The present investigation is an attempt to evaluate the hot corrosion behaviour of high velocity-oxy fuel (HVOF) sprayed NiCrBSi and Stellite-6 coatings on a nickel-based superalloy in an actual industrial environment of a coal fired boiler. The cyclic studies were performed in the platen superheater zone of a coal fired boiler where the temperature was around 900 °C. Experiments were carried out for 10 cycles each of 100 h duration followed by 1 h cooling at ambient temperature. Both the coatings deposited on Ni-based superalloy imparted better hot corrosion resistance than the uncoated one. The Stellite-6 coated superalloy performed better than the NiCrBSi coated in the given environment.