Hot corrosion is a serious problem in power generation equipment, gas turbines for
ships aircrafts, energy conversion and chemical process systems. During combustion stage in
heat engines, particularly in gas turbines, sodium and sulphur impurities present either in fuel
or in combustion air, react to form sodium sulphate (Na2SO4). If the concentration of the
sulphate exceeds the saturation vapour pressure at the operating metal temperature for turbine
blades and vanes (700 °C-1100 °C), then deposition of the Na2SO4 will occur on the surface
of these components. At higher temperatures the deposits of Na2SO4 are molten (melting point
=884 °C) and can cause accelerating attack on high alloy or Cr-Mo steels. No alloy is immune
to hot corrosion attack indefinitely, although there are some alloy compositions that require a
long initiation time at which the hot corrosion process moves from the initiation stage to the
propagation stage. Nickel-based coatings have been reported to be widely used as they
combine several advantages such as abrasion, erosion and resistance to high-temperature
corrosive atmospheres. In this report a comparison on the experimental performance of
nickel-based coatings has been made to understand their hot corrosion mechanism.
Keywords: boiler tube steels; GTAW welding; parabolic constant (Kp); Na2SO4- 60%V2O5 salt environment; 80Ni-20Cr coating |
full paper (pdf, 6176 Kb)