Within the last decade industrial gas turbines (GTs) have withstood numerous changes in both usage as well as in materials selection and design boundaries. The constraints aimed at lowering NO~x~ emissions for improving the footprint, have driven designers to increase the firing temperatures and to look for improved cooling systems of GTs nozzles. These factors led to more severe operating conditions for hot gas path components and to the need for more accurate and comprehensive thermo-mechanical models for life assessment purposes.  Within this context, a Lemaitre-Chaboche viscoplastic model has been coupled with a modified theta projection creep model for MAR-M-247 material to account for steady-state creep effects in a finite element transient analysis (FEA). These material models have been applied on a cooled, first stage nozzle for a recently developed high-efficiency gas turbine. A verification assessment has been performed on a over-fired, off-design transient analysis. The viscoplastic model developed showed the capability of dictating an accurate initiation zone of cracking. The Lemaitre-Chaboche model predicted a stress state in the location where the crack nucleated which led to estimate the number of cycles to initiate with an error of approximately 10%. Furthermore, the model demonstrates the capability of using the Lemaitre-Chaboche plastic model coupled with the theta projection creep model to predict reasonable inelastic strains for the entire lifetime of a gas turbine.


Improved Life Assessment for Ni-Based Gas Turbine First Stage High Pressure Turbine Nozzles

Division / Sponsor:
International Gas Turbine Institute (IGTI)

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

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