High-temperature corrosion of Ni-base alloys by waste incineration ashes

Ni-Cr-Mo alloys, e.g. Inconel 625 and 686, exhibit high-temperature corrosion, oxidation and wear resistance. For this reason, these alloys are typically used as a coating material in different environments as effective solid-state diffusion barriers between the corrosive atmosphere and the base metal. To perform: the Ni-base weld overlays, without introducing too much Fe, a new welding technique called cold metal transfer was used. High-temperature corrosion of boiler parts during incineration of waste was investigated. Boiler tubes were coated with Inconel 625 and Inconel 686 nickel alloys and, after subjecting them to waste incineration ashes, they were examined by scanning electron microscopy with energy dispersive X-ray spectrometer to reveal different corrosion mechanisms and their causes. Results indicate a strong dependence of the boiler steel corrosion on anions in the incineration waste ash. X-ray diffraction characteristics of the scale showed that surface corrosion processes induce the formation of CrO₂, NiO. The presence of iron in the clad weld surface is conductive to the formation of the Fe₂O₃ oxide.