Evaluation of Creep Damage in a Gas Turbine First Stage Blade

This paper presents creep damage evaluation in the service exposed air cooled first stage blade 1100 °C class of a gas turbine after 24000 operation hours. The blade is made of Inconel 738 LC Nickel based superalloy. The gas turbine inlet temperature (TIT) is 1100 °C. To get blade operational load, a thermomechanical analysis was performed using the Finite Element Method (FEM) including centrifugal stresses and thermal stresses. Blade airfoil temperature distribution obtained from previous Computational Fluids Dynamics (CFD) analyses was used for thermal stress determination in the blade. The effect of multi-axial stresses has been taken into account. Using the thermomechanical stress level value obtained and its distribution on the blade airfoil, some creep life prediction models were evaluated including the Norton-Bailey, Dorn-Bailey and Larson-Miller Parameter, comparing them to real bucket life. On the basis of results obtained, a new analytical model for gas turbine blade creep life prediction is proposed, which includes the influence of blade material ultimate tensile strength to reflect heat-to-heat variation in strength. The results obtained were validated to real bucket life and found in a good concordance to experimental creep data for an Inconel 738 LC super alloy.