Influence of PbCl2 and KCl salt mixture on high temperature corrosion of alloy 625

Aggressive corrosion can occur when firing waste or bio-based fuels, due to the presence of high concentrations of heavy metals, alkali metals, and chlorides. These deleterious compounds deposit on furnace walls and can form mixtures that can rapidly accelerate corrosion. The effect of salts containing lead had not been studied extensively at temperatures lower than 400 degrees C in nickel-based materials. This study investigates the effect of the individual salts PbCl2 and KCl and their mixture on the high temperature corrosion of alloy 625 at 340 degrees C and 380 degrees C. Samples of alloy 625 were covered with individual salts or a salt mixture and exposed to high tem-peratures in an atmosphere of synthetic air, 20-vol% H2O, and 100 ppm HCl. The results show that the presence of individual salts does not induce observable corrosion attack on alloy 625 after 168 h at any tested temper-ature. The salt mixture did cause a severe corrosion attack at 380 degrees C, observed after 24 h of exposure. It is suggested that the salt mixture induces the formation of lead chromates that may prevent or disrupt the for-mation of a protective chromia scale. It is believed that a key part of the mechanism is the formation of eutectic melts by the interaction of the scale with the salt mixture. Thermodynamic equilibria calculations show that the first melting temperature of PbCl2 and KCl salt mixture after reaction with oxygen can be as low as about 382 degrees C, and even lower (357 degrees C) if chromates are present.

Automated summary

Aggressive corrosion can occur when firing waste or bio-based fuels due to the presence of high concentrations of heavy metals, alkali metals, and chlorides. This study investigates the effect of lead chloride, potassium chloride, and their mixture on the high temperature corrosion of alloy 625. The results show that the salt mixture induces severe corrosion, potentially due to the formation of lead chromates and eutectic melts.