Creep-fatigue defect development and risk of brittle fracture in the ultrasupercritical steam turbine rotors

ABSTRACT The paper presents a critical analysis of the procedures for defect propagation assessment recommended by British standards and their application to rotating components. The way of applying these procedures was shown by an example of a steam turbine rotor with particular use of a characteristic strain model of high-temperature creep. Calculations of the flaws located at the rotor axis have shown that their growth in the design life is small. The performed analyses have also shown that crack development due to low-cycle fatigue is comparable to that due to creep and cannot be ignored under typical service condition. It was also shown that there is no risk of brittle fracture in the rotor under typical start-up conditions. The presented results prove the usefulness of the methods included in the British standards and guidelines for crack growth assessment in components subject to centrifugal load.