Failure of a steam turbine rotor due to circumferential crack growth influenced by temperature and steady torsion

• Circumferential crack shape evolution due to high cycle fatigue in a steam turbine (Besat power plant) is evaluated.
• Temperature variation along the rotor and corresponding Paris coefficients for crack front evolution is considered.
• Roughness induced crack closure effect due to steady torsion in a factory roof surface is modeled.
• By presented analytical model the effect of steady torsion in reduction of crack growth rate due to alternating mode I loading has been computed.

High cycle fatigue as a final mechanism of failure in rotating systems, especially steam turbines, is a serious phenomenon. Incomplete information of its effective parameters could lead into catastrophic failure of the rotor. In high cycle fatigue, one of the most effective factors in crack growth is high temperature. In fact, a high-temperature change alters mechanical characteristics of material including their fracture mechanic. Therefore, the investigation of crack growth of fatigue and crack front development in various steam temperatures requires a careful consideration of the different parts of the rotor along the steam turbine rotor. This study investigated the propagation of a circumferential crack at three points of the turbine rotor in 24,149 and 260 ∘ C under the influence of rotor weight loading. In addition, the study addressed torque as another important parameter in crack growth which is caused by steam pressure in the turbine. Through the obtained results, a crack front shape is achieved which can be used in rotor vibration analysis. Reviewing the related literature indicated that crack growth rate associated with alternative mode I loading in the presence of steady mode III loading is reduced. To investigation this phenomenon, the study considered roughness induced crack closure due to steady torsion and its corresponding equations by analytical method were derived. Finally, the study investigated the influence of roughness on crack growth rate in abovementioned three points of the rotor.