60MW HIGH-PRESSURE TURBINE ROTOR BRITTLE-FRACTURE ANALYSIS AND REMANENT LIFE INVESTIGATION

The continued safe operation of a 60 MW high pressure turbine rotor wa s investigated in a recent study carried out by ESB (Electricity Suppl y Board). The integrity of the rotor was threatened by fears of excess ive material embrittlement and/or excessive creep damage, at locations exposed to elevated temperatures (> 450 degrees C). Power utilities w orldwide have cited many examples of catastrophic failures of turbine rotors as a consequence of long term material degradation. The study c arried out utilised a combination of sophisticated finite element stre ss analysis and metallurgical testing. The FEA was used to establish t ransient 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 wa s remote and that creep damage was tolerable. A further ten years oper ation of the rotor was advised with inspection of critical locations a t specified intervals.