Performance of Ni3Al and TiO2 Coatings on T91 Boiler Tube Steel in Simulated Boiler Environment at 900°C

Abstract

Boiler steel tube corrosion in coal fired boiler is main subject during design and operation of thermal power plant and it leads to both direct and indirect loss of cost and energy, including losses due to plant shut down time and inefficiency of operation. One of the feasible solutions to solve out this problem is providing surface coating on boiler steel tube, which on one hand protects the tube from highly corrosive flue gaseous and on other hand increase their operating life. Ni3Al and TiO2 and coatings were sprayed on ASTM SA213-T91 steel by using the HVOF process. Hot corrosion studies were performed on the uncoated as well as coated sprayed samples in molten salt environment of Na2SO4-60%V2O5 at 900ºC for 50 cycles. In the experiment each cycle includes 1 h of heating in tube furnace followed by 20 min of cooling in air. The various thermo-gravimetric techniques were used in order to establish the kinetics of corrosion. XRD, SEM/EDS testing were used to examine the corrosion specimens. The result reveals that both the coated samples are beneficial to corrosion resistance over uncoated samples. TiO2 coating was found to be most protective followed by the Ni3Al coating.