Examination of the corrosion behaviour of selected power plant materials under various operating conditions

Abstract

To ensure efficient and climate-friendly power generation low CO 2-emitting power plant technologies are currently being developed. In addition to pre- and post-combustion processes this also includes the oxyfuel process. In comparison with conventional power plant systems the implementation of these technologies alters the process parameters, which in turn has an effect on the corrosion behaviour of the materials employed. In general corrosion is present in all interactions between a material and its surroundings, resulting in measurable changes in properties of the material and impairment of the function of the material, surroundings or technical systems in which it is a component. Layer formation as a result of soiling or slagging is a preliminary stage of corrosion. Flue gas-side corrosion in fossil fuel-fired power plants is a known problem that has been present for decades, which seriously impairs power plant operations as a result of material damage in evaporator and superheater tubes. However corrosion resulting in the formation of oxide layers is expressly desired as these can act as protective layers, inhibiting further corrosion reactions. Within the framework of an ongoing research project the Chair of Power Plant Technology is investigating the corrosion behaviour of selected power plant materials. The following sections will feature the method, procedure as well as the preliminary results of the investigation, which was conducted at the Jänschwalde pilot plant. Overall the light microscopic recordings showed that the oxide layer was partially destroyed and characterised by higher porosity, whilst the SEM-micrographs showed that there was hardly any difference between chrome oxide concentrations for the selected materials. However it was apparent that by increasing chrome content in the alloy a considerable concentration of chrome was identifiable on the inner oxide layer, leading to the formation of a protective layer. Given the relatively short analysis period of 110 h it was not possible to make further precise statements concerning corrosion mechanisms. Ultimately, with an increase in chrome content and greater probe placement timeframe a decline in corrosion activities would be expected. A greater placement timeframe would also make it possible to define corrosion mechanisms more precisely. Consequently there are plans for further investigations to be carried out at the Chair of Power Plant Technology’s laboratory test rig, where corrosion will occur for a period of 900 h.