A New Alloy Designed for Superheater Tubing in Coal-Fired Ultra Supercritical Boilers

Future increases in the demand for clean and efficient electrical power production will be unrelenting. Meeting the coming challenges will require power generating systems capable of operating with increased boiler pressures and temperatures. In turn, meeting the demands of the application will also require materials which can withstand these extreme conditions. This paper describes a new nickel-base tubing alloy, INCONEL® alloy 740, developed for the purpose of meeting this challenge. This material possesses a unique combination of elevated temperature strength properties and resistance to coal ash corrosion required by the application. The material was developed to fulfill the minimum stress rupture requirement of 100,000 hour rupture life at a stress of 100 MPa and at a temperature of 750°C. In addition, metal loss of less than 2mm in 200,000 hours was defined as the target corrosion resistance for this material. The mechanical properties of this new material will be described, in addition to its coal ash corrosion resistance and weldability. Thermal stability will also be discussed, focusing upon microstructural features of long-term exposed samples. Early methodology utilized to arrive at the current chemical composition will also be presented.