Synergistic air port corrosion in kraft recovery boilers

Localized hot corrosion can occur on the cold-side of air-ports in Kraft recovery boilers. Depending on the basicity of the molten salt, either acidic or basic fluxing takes place, with a solubility minima at the transition between the two reactions. For stainless steel, if the basicity of the fused salt is between the iron and chromium oxide solubility minima, then a synergistic effect can occur that leads to rapid corrosion. The products of one reaction are the reactants of the other, which eliminates the need for rate-controlling diffusion. This effect can explain why stainless steel is attacked more readily than carbon steel