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.