Materials for ultra-supercritical coal-fired power plant boilers

The efficiency of conventional fossil power plants is a strong function of the steam temperature and pressure. Research to increase both has been pursued worldwide, since the energy crisis in the 1970s. The need to reduce CO2 emission has recently provided an additional incentive to increase efficiency. The main enabling technology in achieving the above goals has been the development of stronger high-temperature materials. Extensive R and D programs have resulted in numerous high strength alloys for heavy section piping, and tubing needed to build boilers. The study reported here is aimed at identifying, evaluating and qualifying the materials needed for the construction of the critical components of coal-fired boilers capable of operating with 760 deg. C (1400 deg. F)/35 MPa (5000 psi) steam. The economic viability of such a plant has been explored. Candidate alloys applicable to various ranges of temperature have been identified. Stress rupture tests have been completed on the base metal and on welds to a number of alloys. Steamside oxidation tests in an autoclave at 650 (1200 deg. F) and 800 deg. C (1475 deg. F) have been completed. Fireside corrosion tests have been conducted under conditions simulating those of waterwalls and superheater/reheater tubes. Weldability and fabricability of the alloys have been investigated. The capability of various overlay coatings and diffusion coatings have been examined. This paper provides a status report on the progress achieved to date on this project