Low Cycle Fatigue Life Estimation and Tracking for Industrial Gas Turbine Blades Using Fatigue Factor Approach

Abstract

Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped method for estimating fatigue cycles to failure. Damage summation rule was applied to estimate the fatigue damage accumulated over a given period of engine operation. The concept of fatigue factor which indicates how well engine is operated was introduced to make engine life tracking feasible. The developed fatigue life tracking method was incorporated in PYTHIA, Cranfield University in-house software and applied to 8 months of engine operation. The results obtained are similar to those of real engine operation. At a set power level, fatigue life decreases with increase in ambient temperature with the magnitude of decrease greater at higher power levels. The fatigue life tracking methodology developed could serve as a useful tool to engine operators.

Creep-Fatigue Interaction Life Consumption of Industrial Gas Turbine Blades

“…The fatigue life model adopted in this work is the modified universal slopes method which is expressed in terms of nominal alternating stress amplitude, a σ as, ( ) σ . Fatigue life is estimated using a developed stress model of the blades and details could be found in [4].…”

“…Creep-fatigue interaction factor is used to assess the severity of engine operation under creep-fatigue interaction life consumption; this is similar to the fatigue factor approach [26], and the fatigue factor approach [4]. The creep-fatigue interaction factor at any point of engine operation is expressed by Equation 10…”

“…It has PYTHIA at centre with creep life analysis and fatigue life analysis sub-systems providing inputs to the creep-fatigue interaction life analysis system. Details of the creep life analysis procedure could be found in [1] while fatigue life analysis procedure and system is presented in [4]. An engine model which behaves like the real engine in the field is created in PYTHIA for the life analysis as in [1].…”

“…Gas turbine blades, especially the compressor turbine blades of aero derivative Although, creep might be the most dominant mode of failure, but if gas turbines are operated and shut down often, in some cases daily, fatigue failure will equally set in [4] [5]. Turbine blades failure in such cases may not be solely due to creep or fatigue, but may occur in the form of creep-fatigue interaction which is a combined mode of failure [6] [7].…”

“…In creep life prediction, Addul-Ghafir et al [26] introduced the concept of creep factor in analysing engine creep life consumption where creep factor is the ratio of the predicted engine life to a reference life. The concept of fatigue factor was by Saturday and Thank-God [4] blades. Following same trend, in this work, the concept of creep-fatigue interaction factor is used, where creep-fatigue interaction factor is the ratio of the creep-fatigue interaction life at any point or time frame of engine operation to the creep-fatigue interaction life at a reference point of engine operation.…”