Corrosion of carbon steel underneath a lead/potassium chloride salt mixture

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 (PbCl2) and potassium chloride (KCl) are expected to form. The purpose of this study is to investigate reactions in the mixed salt of PbCl2 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 PbCl2/KCl (50/50 mol%) put on steel samples. The test duration was 24 hr at either 300 degrees C or 340 degrees C in an atmosphere of 100 ppm HCl and 20 vol% H2O in synthetic air. After exposure, the salt mixture consists of distinct areas of KCl and PbCl2 but also the compounds K2PbCl4 and KPb2Cl5. 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 KPb2Cl5 is located closest to the corrosion product indicating its importance for the corrosion.