Corrosion Protection of Municipal Solid Waste Incinerator Superheaters by HVOF Thermal Spray Coatings

Corrosion is a very important problem in the Municipal Solid Waste Incinerator (MSWI) superheaters. This problem causes the plant stops and tube replacements, promoting the loss of energy generation rate. The main corrosion agent is the chlorine deposits. HVOF coatings have been sprayed to improve corrosion resistance of the superheaters inside the MSWI boilers. Inconel 625 and Hastelloy C22 alloys have been sprayed as a powder feedstock material. The spray process has been analyzed by a Spray Watch system that allows carrying out the temperature and velocity measurements of the particles in flight in order to optimize the spraying process. The produced coatings have been characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) to evaluate the porosity and oxidation produced in the spray process. Laboratory oxidation test have revealed the formation of Cr₂O₃, NiO and Fe₂O₃ as corrosion products as well as Microanalysis by Energy dispersion Spectroscopy (EDS) composition profiles have been used to evaluate the penetration of the corrosion front inside the coating. The Nickel alloys show a good resistance in aggressive environment test and can be a good solution for the corrosion problems in the superheater tubes in MSWI.