Breakaway corrosion of austenitic steel induced by fireside corrosion

Abstract

The long-term fireside corrosion in biomass co-firing of Sanicro 25 was characterized employing advanced high-resolution electron microscopy methods. The analysed sample was exposed for 7000 h at 650 °C showing breakaway corrosion. The corrosion mode differed from type II hot corrosion. The main effects were the formation of a thick nickel sulphide layer and accelerated metal loss. This sulphide formation became possible due to subsurface zone chromium depletion by the formation of stable chromium carbides. With decreasing Cr activity both the ability to maintain the protective scale and the possibility to trap sulphur in Cr sulphides are reduced.