In order to analyze the torsional fatigue life loss of the shaft system in real-time during sub-synchronous oscillation and accurately assess the safety of the shaft system

the relationship between the torsional vibration stress and the torsional angle of the shaft was investigated.Moreover

against the phase deviation

boundary effect and other problems occurred during the torsional angle extraction

a new analysis method was put forward

which uses zero-phase band-pass filter- " moving window"-modal superposition method to calculate the stress history of torsional vibration in dangerous section

and then analyzes the shafting torsional fatigue life loss.The results show that

this method can ensure both the analysis accuracy and the real-time tendency

it can be applied in online monitoring

investigation and system protection of the torsional vibration of shafting system in the steam turbines.