Importance of Physics-based Prognosis for Improving Turbine Reliability Part 2: A Turbine Disc Case Study in a Fleet Environment by

This paper describes the results of a case study on the use of physics based prognosis to deal with the uncertainty of disc failures in a fleet of forty two W-101 turbines. The MIL-STD-1783 based damage tolerance analysis is used to predict a safe inspection interval for the design life expired discs. It is demonstrated that safe inspection interval limits based on traditional empirical methods are overly optimistic under creep crack propagation conditions and it is necessary to use physics based crack propagation models to make reliable life cycle management decisions. Physics based crack propagation approaches yield substantially more accurate results. It is further demonstrated that the use of sensitive inspection techniques at depot level, such as eddy current inspection, is necessary to avoid catastrophic failures during service. The prognostics based inspection and life cycle management strategy has saved the user over 1.5 Million dollars in maintenance costs on a yearly basis and allowed the operator to implement a phased approach to disc replacement that ensures safety of operation and affordability