Application of a Reliability Model to Gas Turbine Design

The most important attribute of a product is quality. Quality influences the economics of an investment but also the economics of the manufacturer and can be a break point to the manufacturer’s prosperity. Consciously but often subconsciously quality is “just” expected and can therefore be seen as a straight measure of customer satisfaction — in the Kano-terminology quality is a “Must Have” parameter. In the power industry quality is generally being expressed and measured in RAMS (Reliability, Availability, Maintainability and Safety). For the development of new power generation equipment like gas turbines the targets are being laid out very early in the project. Since the development of gas turbine components can be a multi year undertaking it is paramount that the targets contain this element of future customer expectations. This ultimately drives the design team to challenge the technical boundaries — a gas turbine parameter that is satisfactory in today’s market environment might not be pleasing anymore in tomorrow’s changing environment. This is not only valid for the engines thermal performance but also for its reliability and availability. Siemens industrial gas turbines and components are therefore being developed with “Reliability Centered Design” in mind. This report describes the application of a predictive reliability engineering methodology to the development of new gas turbine components and how it influenced the design team’s decision making. The reliability analysis and prognosis is based on a predictive fault tree model with supporting Markov models to address consecutive failures or failure probabilities of stand by equipment. It has been validated with field data. While observation data retrieved from operational engines are being used for direct improvements of existing turbine designs the model based approach has its merits in supporting new designs by considering design or system alternatives. Further more it provides the sensitivities of the reliability of the gas turbine with respect to the components’ reliabilities. The model comprises the core engine but also the auxiliary systems within the package. This paper has been jointly prepared by the industrial gas turbine design team located in Lincoln (UK) and Finspa˚ng (Sweden) as well as Siemens reliability engineering team from Corporate Technology in Munich (Germany).