The modern energy mix demands a flexible operation with an increased number of fast starts, and this results in enhanced requirements for the steam turbine and its components. Turbine admission valves, which are increasingly operated under instationary conditions to follow the changing power grid requirements, are mainly in charge. Therefore, continuous improvement of the tribological characteristics and oxidation resistance of valve components is required.
This paper discusses technical experience in steam turbine valve hard-facings over time, the current status and developments in this regard. Typical wear and crack findings of CoCr-based hard-facings are presented. The relevant investigations on the crack formation mechanism resulted in requirements and influences for the development of the current hard-facings. These concepts made for new products and service applications are introduced.
Furthermore, in consideration of a future increase in flexibility and efficiency demands, technical requirements for functional coatings are specified, and the development results of an integrated material concept are depicted.