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MCrAlY coatings can be corroded due to the basic fluxing (type-I hot corrosion) of the supposeto-be protective alumina scale in a molten sulphate environment. In this study, two MCrAlY coatings, coating A (10 wt.% Al, 20 wt.% Cr) and coating B (7 wt.% Al, 28 wt.% Cr), were tested in 48-hour cycles at 900 °C in a sodium-potassium sulphate environment with and without SO 2 (500 ppm). The aim was to study the effect of SO 2 at the typical type-I-hot-corrosion temperature -900 °C. The results showed that the corrosion behavior of the MCrAlY coatings depended not only on the coating composition but also on the corrosion environment. It was found that in coating A alumina scale was more resistant in the sulphate-plus-SO 2 condition than that in the sulphate-only condition. Such phenomenon indicated a beneficial effect of SO 2 . On Coating B, however, mixed oxide layers, consisting of alumina and other oxides and sulphides, formed after a certain number of cycles in the sulphate environments with or without SO 2 gas. In this coating, the addition of SO 2 in the sulphate environment promoted the formation of non-dense chromia oxides which may form from oxidation of Cr-sulfides.

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With an expanding use of low quality bio fuels, corrosion problems on water wall tubes are increasing. In this study, the possible corrosion reducing effect when adding digested sewage sludge to the fuel in a used wood (also known as waste or recycled wood) fired furnace has been evaluated. The low alloyed steel 16Mo3 and the stainless steel 310S were exposed for 14.25 h at the furnace wall position when firing only used wood and used wood with sewage sludge additions. The exposures were performed in a bubbling fluidized bed boiler and the metal temperature of the test samples was controlled to 350 °C. Chemical analysis of the deposits and microscopic evaluation of the metallic samples showed reduced amount of alkali metals and chlorine in the deposit together with reduced initial corrosion for both materials when co‐firing with digested sewage sludge. In the corrosion process, metal chlorides were formed for both materials when firing only used wood, iron chlorides for the low alloyed steel, and chromium chlorides for the stainless steel. When co‐firing with sewage sludge, this behavior was suppressed.

High amounts of lead in waste/recycled wood fuel are known to be a contributing factor to the increased corrosion often related to this type of fuel. In combination with potassium, usually present in the fuel, low‐melting point salt mixtures between lead chloride (PbCl 2) and potassium chloride (KCl) are expected to form. The purpose of this study is to investigate reactions in the mixed salt of PbCl 2 and KCl and its interactions with carbon steel P265GH and its oxide. Laboratory exposures were performed in an isothermal tube furnace with a salt mixture of PbCl 2/KCl (50/50 mol%) put on steel samples. The test duration was 24 hr at either 300°C or 340°C in an atmosphere of 100 ppm HCl and 20 vol% H 2O in synthetic air. After exposure, the salt mixture consists of distinct areas of KCl and PbCl 2 but also the compounds K 2PbCl 4 and KPb 2Cl 5. A general observation is that the oxide thickness increases with temperature and that areas with Pb/K‐mixed salt are frequently found in close connection to more corroded areas. Often the more lead‐rich phase KPb 2Cl 5 is located closest to the corrosion product indicating its importance for the corrosion.