Recent Developments in High Temperature Corrosion Protection Coatings for Chemical and Petrochemical Industries

摘要

Present research in high temperature corrosion protection is driven by the aim to develop advanced power plant systems as well as petrochemical and chemical plants with increased thermal efficiency, increased life-time and resistance against highly aggressive environments. For economic reasons in most cases steels have to be used in these plants. However, steels suffer from extensive corrosive attack if temperatures are increased above the presently used level or if environments with low oxygen partial pressure but high activities of carbon, chlorine and/or sulfur are introduced. The latter can lead to severe problems in several gasification, combustion or chemical reaction atmospheres so that a strong need for new material solutions exits. Since the use of high alloy structural materials would increase costs to a significant amount and sometimes even manufacturing problems may be associated with their use the present development activities very much focus on different types of protective coatings on steel substrates. Much of this work is directed towards the investigation of the potential of new co-diffusion or two-step diffusion coatings based on Al, Cr, Si and Ti for protection in the above mentioned environments. Al, Cr and Si are well known alloying elements for high temperature corrosion protection since they are able to form thermodynamically stable protective oxides scales even in environments of relatively low oxygen partial pressure. Recent investigations including Ti reveal that this alloying element can increase protection by a synergistic interaction with the other protective elements, an effect which is deliberately used for the development of new diffusion coatings. The limits of diffusion coatings become evident at joining sites of components which is the reason why overlay coatings are also included in the present research activities although from a thermo-mechanical point of view diffusion coatings may be preferred. Also for advanced overlay coatings the synergistic effect of Ti and Al is used, and these coatings are applied by APS and HVOF spraying which both are economically viable methods. In the presentation the present state in the development of protective diffusion and overlay coatings is discussed and their performance in highly aggressive environments of high C, Cl and/or S activities will be addressed. At the end recommendations for the use of the coatings can be given.