In order to operate the turbo-machineries more flexibly, a lifetime counting method was developed which enables estimating lifetime consumption of high thermal-inertia components based on the temperature history of the components. It can account for consumed fatigue life at the locations of temperature measurement during the turbo-machine operation. By considering the operation history, the structural component can be operated closer to its lifetime limits, to increase the intervals between inspections, and therefore to extend the operational lifetime of the turbo-machine.
In this method the cold start (CS) to full load cycle, with the number of cycles to crack initiation Ncs, is defined as reference load cycle. The damage weighting factor Ni/NCS for cyclic event i is then calculated based on a semi-empirical correlation between Ni/NCS and the temperature history of the part. The semi-empirical correlation can be determined for each component or each location depending on the required precision. It is determined based on the Low Cycle Fatigue (LCF) life calculated for different Gas Turbine (GT) operation scenarios. The damage weighting factors are then employed to calculate the lifetime consumption using Miner’s rule.
The predictions of this method for the turbine housings of several Gas Turbines (GTs) were evaluated against finite element (FE) results. Multiple load cases were considered for each GT. It is shown that this approach can account for the lifetime consumption using the minimum required number of GT operation parameters.