Corrosion-erosion study of iron and nickel based thermal spray coatings for biomass boiler application

Abstract

There is a surge in demand for biomass/biofuel boilers in Sweden. Iron based coatings and nickel based coatings are proven to be a better at protecting the boilers in the corrosive and harsh environment. The objective of this study is to see how the new High Velocity Air Fuel (HVAF) thermal spray process compares to the traditional High Velocity Oxygen Fuel (HVOF) thermal spray process in the domain of corrosion-erosion protection in a harsh environment and how do iron and nickel based coatings compare to each other. The corrosion behavior was studied when the samples were kept in furnace at 600˚C for different time periods of 12, 48, 96 and 168hrs. One set of samples were kept in ambient air and the other set were coated with KCl solution corresponding to 1.35 μmol K+/cm2. The resultant weight gain is studied and noted, and the oxide layer formed on the coating is studied and the results are concluded. The erosion testing was done with the help of an air jet erosion test rig at room temperature. The net loss in weight due to erosion was calculated and then noted for analysis. It was observed that the HVAF iron based coatings perform much better in term of corrosion and erosion resistance as the weight gain is minimum as compared to the HVOF iron based coating.The weight loss due to erosion is also lower in HVAF iron based coatings. When the iron based coatings were compared with the Nickel based coatings it showed that the Nickel based coatings which were sprayed with HVAF process performed much better in terms of corrosion-erosion performance when compared to HVAF iron based coatings. Thus, HVAF coatings are better than HVOF coatings in terms of corrosion-erosion performance and Nickel based coatings are better than iron based coatings in terms of corrosion-erosion performance.