Evaluation of the hot corrosion behavior of LPG assisted HVOF NiCr wire sprayed boiler tube steels in molten salt environments

Abstract

NiCr coatings were deposited on some boiler tube steels by High Velocity Oxy Fuel spraying process using LPG as fuel gas. Hot corrosion behaviour of uncoated as well as HVOF sprayed specimens was studied in an environment of Na2SO4-60%V2O5 at 900°C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. SEM/EDAX, XRD and EPMA techniques were used to analyse the corrosion products. The NiCr coating found to be very effective in decreasing the corrosion rate of the uncoated steels. The NiCr coated samples showed no cracking or spelling of oxide scale during hot corrosion. The formation of protective oxide scale as observed may be contributing to the development of hot corrosion resistance in the coatings studied, which mainly consists of oxides of NiO, NiCr2O4 and Cr 2O3. © 2006 ISIJ.