Large gas turbine design and service business are challenged with increased demands towards flexible operations, increasing number of starts and intermediate cycles. Probabilistic fracture mechanics (PFM) simulation design tools have matured and became robust and reliable. These methods allow the consideration of the inherently heterogenous properties of forging flaws, their size distribution, material property scatter and non-destructive testing (NDT) specifications. By means of Monte-Carlo (MC) simulations, the probability of failure as a function of load cycles can be quantified. This probability can then be compared to regulatory limits as defined by international and OEM specific regulations in order to minimize risks of power plant personnel and the public environment.

The application of PFM however is not limited to design of new frames and can also support the evaluation of mature rotor components such as E- and F-class frames. These frames have been designed 10-20 years ago by traditional deterministic design methods relating to “critical location” analysis and typically ignoring the statistical size effect, or the total component volume exposure. We are illustrating the difference and consequences of these two approaches -— probabilistic and deterministic— for different rotor designs.

Finally, we present a probabilistic re-evaluation of SIEMENS E-class turbine disks by the combination of probabilistic 2-dimensional axisymmetric part analysis of the disk, and a novel probabilistic approach for the 3-dimensional blade attachment. The latter combines the risk of crack initiation, which itself is a highly scattered mechanism, and the variation of crack propagation rates and fracture toughness. These novel concepts developed at SIEMENS allow for an optimization of resource usage and safety, as well as the development of new service and inspection concepts.


Probabilistic Fracture Mechanics for Mature Service Frame Rotors

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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