Corrosion Resistance of Inconel 625 CMT-Cladded Layers after Long-Term Exposure to Biomass and Waste Ashes in High-Temperature Conversion Processes

The present study investigated the effect of corrosion on an Inconel 625-cladded layer using the cold metal transfer (CMT) method. The corrosion was caused by various ashes and high process temperatures. The ashes were obtained from the biomasses of mixed wood and oat straw, as well as from sewage sludge, by ashing. Long-term corrosion tests were carried out at 650 °C over a period of 1000 h. The chemical composition, mineral phases, and corrosion effects were studied by X-ray fluorescence (XRF), scanning electron microscopy equipped with energy-dispersive X-rays (SEM–EDX), and X-ray diffraction (XRD) from the surface and on the cross-section of the samples. The chemical composition of the ashes was quite different, but representative of their particular fuel. Together with the effects of the operating temperature and mass transfer, significant differences in the degree of the corrosion depth were detected for the various ashes. For the investigated samples, the corrosion mechanisms were inferred based on the identified corrosion products.