Alkali Induced Corrosion of 304-Type Austenitic Stainless Steel at 600°C; Comparison between KCl, K₂CO₃ and K₂SO₄

Abstract:

The influence of KCl, K2CO3 and K2SO4 on the initial stages of corrosion of 304-type (Fe18Cr10Ni) stainless steel was investigated at 600°C in 5% O2 + 40% H2O. Small amounts of salt (1.35 .mol K+/cm2) were added before exposure. The exposures were carried out in a thermobalance. Exposure time was 24 hours. Reference exposures were carried out in 5% O2 and in 5% O2 + 40% H2O. The oxidized samples were analyzed by SEM/EDX, XRD and IC. KCl and K2CO3 are very corrosive towards 304L, producing thick non-protective scales. Corrosion is initiated by the reaction of the potassium salts with the protective, chromium-rich oxide forming K2CrO4. This depletes the oxide in chromia and converts it into iron-rich non-protective oxide. In contrast, K2SO4 does not accelerate corrosion significantly.