The effect of in-service steam temperature transients on the damage behavior of a steam turbine rotor

• Effect of in-service temperature transients on creep–fatigue behavior of a rotor is performed.
• A validated viscoplastic constitutive model is used to describe creep–fatigue behavior of a rotor.
• Heat transfer coefficients between steam and rotor are modelled for different regions of a rotor.
• Temperature fluctuations in steady state operation may induce an acceleration in creep damage.
• Correlation of the stress range due to the temperature fluctuations has been established.

This study was aimed at identifying the influence of the temperature transient on the creep–fatigue behavior of a steam turbine rotor. Especially, the steam temperature fluctuations during the steady state operation phase could lead the stress to the oscillation, which also contributes to the fatigue damage. Toward this end, in-service operating data during startup, shutdown and steady state operation phases was chosen to investigate the creep–fatigue damage of a 1000 MW steam turbine rotor. A viscoplastic constitutive model with damage was presented to describe creep–fatigue deformation behavior. A significant growth in creep damage was found under the influence of the temperature fluctuation compared to the creep damage under the stable temperature condition. In addition, steam temperature fluctuation induced the larger thermal gradient and temperature difference at the location where is closer to the rotor surface. The correlation of the stress range due to these temperature fluctuations has been established by carrying out the transient thermo-mechanical FE analysis. Frequent thermal fluctuations during the steady state operation phase were identified as one of the most influential factors for the creep–fatigue damage of the steam turbine rotor.