Corrosion of materials in an environment typical of coal gasification plants

Candidate metallic construction materials for heat exchangers and uncooled metal components of coal gasification plants were tested in synthetic gas mixtures at 600 and 800 °C. Corrosion rate and mechanistic post-corrosion analyses were obtained for alloys exposed for 100, 400 and 900 h. The corrosion rate is strongly dependent on the balance between the sulphur and the oxygen activities and on the temperature; a critical value lies in between the two temperatures considered. In most of the alloys tested, the corrosion mechanism is governed by the formation of oxide surface layers composed of Cr2O3 and spinel-type structures, eventually followed by sulphur penetration and grain boundary sulphidation. The triggering period for internal sulphidation is dependent on the nature of the substrate, the sulphur activity, the exposure time and the exposure temperature, all of which are important.