60MW high pressure turbine rotor brittle fracture analysis and remanent life investigation

Abstract The continued safe operation of a 60MW high pressure turbine rotor was investigated in a recent study carried out by ESB (Electricity Supply Board). The integrity of the rotor was threatened by fears of excessive material embrittlement and/or excessive creep damage, at locations exposed to elevated temperatures (>450°C). Power utilities worldwide have cited many examples of catastrophic failures of turbine rotors as a consequence of long term material degradation. The study carried out utilised a combination of sophisticated finite element stress analysis and metallurgical testing. The FEA was used to establish transient stresses and temperatures in the rotor during a typical unit start-up while a novel material sampling technique was used to provide material toughness properties for the brittle fracture analysis. The study concluded that the likelihood of catastrophic brittle failure was remote and that creep damage was tolerable. A further ten years operation of the rotor was advised with inspection of critical locations at specified intervals.