Hot corrosion and steam oxidation properties of new heat resistant steels for ultra super critical boilers

Achieving higher plant efficiency in thermal power plants is one of the major global challenges from the viewpoint of reducing carbon dioxide emission levels, particularly in coal-fired boilers, irrespective of the type of coal being burned. In recent times, it has been possible to increase the steam temperature in coal fired ultra supercritical (USC) plants without too much of a cost impact. The temperature has already been increased to 600 degrees C for main steam and 610 degrees C for reheat steam. The main enabling technology is the development of stronger high temperature materials such as newly developed high Cr ferritic steels and austenitic steels, capable of operating under high stresses at increasing high temperatures. Other key demands for those materials are hot corrosion resistance such as coal ash corrosion in superheater and reheater tubes and sulfidation of waterwall tubes, and steam oxidation resistance. This paper will mainly present the hot corrosion and steam oxidation properties of newly developed high strength heat resistant steels for their application to USC boilers and long-term experience in an actual plant.