Corrosion behaviour of Ni and nickel aluminide coatings exposed in a biomass fired power plant for two years

Ni and Ni2Al3 coatings were applied to superheater tubes that were built into a wood-fired boiler with an outlet steam temperature of 520 °C. The present paper evaluates the performance of the coatings after two years of service. The corrosion performance of the coatings is discussed with respect to the temperature histograms and deposit composition and compared to the performance of the coatings after the first year. The Ni coatings showed extremely protective behaviour for 1 year however after 2 years exposure, the Ni coating was chemically attacked, thick NiO was formed and sulphur containing precipitates were present at the base of the Ni layer indicating grain boundary ingress of corrosive species. For the Ni2Al3 coatings, localized attack was observed after the first year of exposure, but after two years no intact nickel aluminide coatings were observed. •1 and 2 year exposure of Ni and Ni2Al3 coated superheater tubes in a biomass boiler with 520°C steam temperature•Ni coatings were protective for 1 yr but revealed oxidation, intergranular attack and metal sulphide formation after 2 yrs•Ni2-Al3 coatings were mainly protective after 1 year but suffered chemical degradation after 2 years•The differences from 1 to 2 years show the necessity for long-term plant exposures