Thermo-structural analysis and life-time evaluation of an heavy duty gas turbine rotor

After many years of efficient application in the field of energy production, heavy-duty gas turbine are nowadays a mature technology that requires an intense control and maintenance program, typically referred to as Life Time Extension and Evaluation program (LTE). This routine involves multiple actors in several activities, of which this paper covers the numerical analysis of the FR1500 rotor to assess the reliability of old parts and find the opportunity of re-design new ones to make them longer-running. This work, in collaboration with Ethos Energy company, has the potential of bringing to a beneficial impact, because the outcome of the task is to provide more efficient solutions, exploiting all available resources. Finite Element Model (FEM) was adopted to simulate the rotor in multiple operating conditions, thanks to the knowledge of exhaustive performance data and machine parameter trends, coming from multiple sensors installed on a real operating rotor. Both steady-state and transient analysis have been run and robust design criteria approach was used to verify static-structural acceptability and to perform Low Cycle Fatigue (LCF) prediction, according to OEM-recommended Factored Fired Starts (FFS) and Factored Fired Hours (FFH). The Results found reveal multiple critical regions in some components, where stress intensification and concentration is caused by high thermal gradients and notch effects. In particular, turbine rotor wheels seem to be the most worrying components because, considering a safety margin for transients' intensification, LCF evaluation estimates a low endurance limit for them. On account of this, re-design of critical areas and suggestions on further analysis have been proposed in the conclusions to this paper. Apart from localized issues, the entire review allowed to prove the general robustness of all the rotor components and ensures their creep resistance as well. Moreover, some of the investigated parts were believed to be promising candidates for life extension proposals, being the expected cumulated damage within the OEM specifications.