PURPOSE: To diagnose a remaining lifetime of a steam turbine rotor so as to enhance reliability of the rotor by measuring the hardness of a high temperature portion of the rotor after operation, and obtaining a creeping damage rate on the basis of a temperature, at which the high temperature portion is exposed, and a stress.
CONSTITUTION: A hardness Hv of the high temperature portion of a rotor is measured in periodic inspection of a steam turbine. A hardness reducing rate ΔHv/HVo=(Hvo-Hv)/Hvo is calculated on the basis of an initial hardness Hvo of the high temperature portion of a new rotor or of the low temperature and low stress portion thereof after the actual operation of an engine. In a formula, wherein A1-A4 represent constants, by the hardness reducing rate ΔHv/Hvo, a creeping stress σ and a creeping temperature T are substituted, thus obtaining a creeping damage rate t/tr. A lifetime of the rotor is diagnosed based on the creeping damage rate t/tr. Consequently, it is possible to enhance reliability of the rotor.
TAKEI MASAO
GOTO TORU
