Coatings for Boiler Components Exposed to Vanadium-Containing Oil Ash in Oxidizing Atmosphere

Corrosion in oil-fired boilers is accelerated in the presence of vanadium, sodium, and sulfur from low-grade fuels. In order to avoid sulfate—–vanadate-induced corrosion of boilers made from 10CrMo9-10 steel, several diffusion coatings (Cr, Al, and AlSi) were investigated together with additional model alloys which could potentially be applied as coatings, such as TiAl, Cr, and CrSi16. All samples were immersed for an exposure time of 100 h in 60 mol% V₂O₅–40 mol% Na₂SO₄ salt at 600 and 650 °C. Materials performance was analyzed using substrate recession rate and metallographic characterization of the corrosion scales and of the metal subsurface zones to characterize the extent of corrosion and mechanism. Thus, the present results provide deep insight into materials resistance and degradation in vanadium-containing environments under simulated boiler conditions. The corrosive attack follows a combined effect of sulfidation and acceleration of metal loss by dissolution of the formed scale under such vanadate salts.