One of the pathways for achieving the goal of utilizing the available large quantities of indigenous coal, while at the same time reducing emissions, is by increasing the efficiency of power plants by utilizing much higher steam conditions. The Advanced Ultra-Supercritical Steam (AUSC) power plant project, funded by US Department of Energy (DOE) and the Ohio Coal Development Office (OCDO), promises to increase the efficiency of pulverized coal-fired power plants by as much as nine percentage points, with an associated reduction of CO_2 emissions by as much as 30%, compared to current sub-critical steam power plants by increasing the operating temperature and pressure to 760°C (1400°F) and 35 MPa (5000 psi), respectively. One of the major limitations in designing these plants is the creep damage of the materials used in the boiler and in the steam turbine. The limiting temperatures for use of available superalloy materials have now been defined based on long-time creep tests. The strength of weldments made of these materials, and the accompanying weld reduction factors have been studied. Composite configurations in which the turbine rotor is made of welded construction between a precipitation-hardened, high-strength superalloy, and a solution-strengthened superalloy and ferritic steel have been made and evaluated. Solid samples tested under uniaxial stress, and tubular samples tested under hoop stress, have been compared and correlations have been made. This paper will present typical results obtained in the course of this project relating to creep deformation and rupture.
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