MPNS COST Action 536
Alloy development for Critical Components of Environmental friendly Power plantT (ACCEPT )
Descriptions are provided by the Actions directly via e-COST.
The main objective of the Action is to develop highly efficient steam power plant with low emissions, through three development steps, on the nano-scale, the meso-scale and the macro-scale, from innovative alloy development to validation of component integrity.
The Action will develop, qualify and introduce improved materials of the 9 to 12%Cr class with improved high temperature strength for the manufacture of critical components required for the fabrication of advanced steam power plants. Specifically, materials are to be introduced for heavy forgings (such as for turbine rotors), castings (such as casings for turbines and valves) and thick-walled pipes (such as for headers and main steam pipes). The process of introduction entails the following steps:
- alloy design on the basis of computer-aided phase stability predictions validated by investigations of model alloys,
- production and investigations of promising novel alloys to evaluate their fitness for the application,
- manufacture of larger melts to verify the scale-up to sizes appropriate for full industrial exploitation.
Specific requirements are for:
- a high creep strength at the maximum temperature of up to 650°C (typically 100MPa at a duration of 100,000 hours),
- resistance to steam oxidation such that no unacceptable growth or spalling of oxide particles occurs within 100,000 hours (alternatively low cost coatings should be qualified and introduced, with which oxidation of high temperature components can be prevented).
The extreme difficulty in simultaneously achieving these two targets has only recently been recognised as a result of basic research on long-term precipitation reactions, whereby the presence of high chromium levels, which improve oxidation resistance, encourages the formation of Z phase, which effectively consumes the MX particles, which promote creep-strength. Alternatively it may be possible to promote oxidation resistance through the addition of low levels of silicon and sulphur.
In addition, manufacturing routes must be available for forgings, castings and thick-walled pipes, including forming processes and welding.
Benefits of the Action lie in the increased efficiency of electricity production of at least 2% without significant cost increase. The results are lower cost of electricity, hence contributing to reducing costs for all manufactured goods. This efficient production of electricity also minimises the corresponding environmental impact. Within the next 5 years it is expected that many new power plants will have to be ordered both to replace older inefficient plant and to provide replacement power for the nuclear plant which are scheduled for closure.
New power plant may be either gas-fired combined cycle plant or coal-fired steam power plant. A mix of both fuels will be needed to provide fuel diversity and political stability of supply. Fuel costs and availability will determine the numbers of each kind of plant to be built.
In each case materials (steels and nickel-based alloys) capable of withstanding higher operating temperatures will be required to improve the operating efficiency.
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