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The increased installation of renewable energy resources results in a requirement for higher steam turbine cycling capabilities. In addition, there is a strong demand to save our environment by improved efficiency, as well as acceptable life-cycle costs whilst keeping a high level of reliability and availability. Optimization using state of the art deterministic methods for dimensioning of components is the traditional way addressing such challenges. The use of more advanced methods like fracture mechanics, assisted by probabilistic design are innovative alternatives that have been pushed significantly in recent years. However, to fully exploit the latest developments of advanced engineering methods, acceptance criteria are essential. Due to the lack of specific steam-turbine standards for several calculation tasks, today acceptance criteria are often based on OEM internal standards and are part of the specific OEM know-how. New methods require the definition or modification of existing acceptance criteria. In case of lack of acceptance criteria one option is to refer to available standards for industries dealing with comparable components, materials and loading conditions. An example is the adaption of acceptance criteria from pressure-vessel codes for high-pressure steam turbine components. The obvious advantage is the ease of use, but the drawback might be an unnecessary conservatism in the design. Another option is the development of acceptance criteria for advanced methods. The main intent of the paper is to contribute to the discussion of acceptance criteria for the application of advanced design methods for steam turbine components. A selected steam-turbine example is discussed, acceptance criteria are compared with available standards and the need for the development of component specific criteria are highlighted. |
