CCS and Power Systems
Crosscutting Research - Plant Optimization Technologies
Low Cost Fabrication of ODS Materials
Performer: Pacific Northwest National Laboratory
Project No: FWP-60098
Program Background and Project Benefits
To obtain significant increases in the efficiency of coal fired power plants, steam pressure and temperature must be increased beyond current technology to advanced ultra-supercritical (A-USC) conditions -temperatures and pressures up to 760 degrees Celsius (°C) and 35 megapascals (MPa). The upper bounds of operating pressure and temperature are limited by the properties of the current set of materials employed in the boiler components. Key concerns are creep resistance, corrosion resistance, and cost-effectiveness of the materials used for critical pressure-boundary components such as boiler waterwall tubing, steam headers, piping, and superheater/reheater tubes.
Historically, materials selection for these components has focused on ferritic steels, which are less costly than austenitic stainless steels and nickel based alloys. These alloys display greater thermal conductivities and lower coefficients of thermal expansion (CTE) than austenitic stainless steels, making them less susceptible to thermal fatigue cracking.
However, at temperatures higher than 620 °C, steamside oxidation and fireside corrosion of ferritic steels increases. Corrosion rates can be reduced to some extent by increasing the chromium content of the steel, but at chromium levels greater than ten weight percent, the creep strength of ferritic steels is reduced. Such operating conditions typically require the use of austenitic stainless steels, but at about 700 °C the corrosion resistance and creep strength of these materials also degrades. Although Ni-based superalloys meet the creep- and oxidation/corrosion resistance requirements of the various boiler components, they are very expensive in terms of raw material cost and processability (e.g., in casting and welding).
Adding insoluble nanoscale oxide dispersoids to ferritic alloys greatly improves their high-temperature mechanical properties. However, several barriers currently limit the deployment of these advanced materials in fossil fuel power plants. The National Technology Energy Laboratory (NETL) is partnering with Pacific Northwest National Laboratory (PNNL) to develop a process to fabricate these materials at lower cost and thus overcome the barriers to their deployment.
Development of effective fabrication methods to maintain the material performance of high-performance alloys will enable the use of such alloys in high-temperature, high-pressure, corrosive environments including A-USC steam turbines and boilers. This project will contribute to more efficient use of fossil fuels in A-USC power plants, which will simultaneously lead to lower emissions of carbon dioxide and other emissions.
Goal and Objectives
The goal of this project is to develop a low-cost method of producing high-strength, creep resistant ODS ferritic steel mill product for high-temperature applications. Specific objectives include adapting a high shear, friction-based method of consolidating metal powders directly into round billets, rods, and tubes.