High temperature corrosion of power boiler components cladded with nickel alloys

Incineration of biomass, waste and sorted rubbish in industrial boilers results in the formation of very aggressive chlorides and sulfur dioxides in off-gases. Harmful action of those substances and dusts in off-gases requires appropriate protection of certain boiler elements, such as heat exchanger pipes and the combustion chamber, against corrosion and erosion.The paper presents the results of attempts to perform pad welding of heat exchanger pipes with nickel alloys Inconel 625 and Inconel 686, and high-temperature resistance tests of the padded welds in an atmosphere of N2 + 9% O2 + 0.08% SO2 + 0.15%HCl for 750 h.Corrosion processes induce the formation of a Cr2O3 oxide film of 5–10 μm thickness on the Inconel padded welds, which constitutes a passivation layer, reducing the corrosion rate. The presence of iron on the padded weld surface is conducive to the formation of Fe3O4 oxide, which worsens the padded welds' resistance to corrosion and erosion.It has been found that the pad welding technology developed and the padded weld properties of Inconel 625 and 686 comply with the requirements of standards and users, and therefore, it can be used for pad welding of components of boilers for waste utilization and biomass incineration.