Fatigue Life Assessment And Prediction Of Steam Turbine Rotor Based On Linear Cumulative Damage

During the start-up,shutdown and peak-shaving operation of steam turbine units,the main force that the rotor bears is alternating stress.Low-cycle fatigue cracks will occur on the rotor surface of steam turbine after a certain cycle of cyclic operation.At the same time,when the rotor operates under rated conditions for a long time,it will be subject to constant stress,and the material of the rotor will suffer creep damage,which will lead to the generation of rotor cracks.Under the interaction of low cycle fatigue and creep damage,the crack will continue to expand with the operation of the unit until it breaks.It will also cause serious consequences for the service of steam turbines.Therefore,life damage prediction of steam turbine rotor is of great significance to the safe and stable operation of the unit.In this paper,the starting state of the cold-slip parameters of a domestically produced 135 MW steam turbine is taken as the research object,and the finite element software ANSYS is used to simulate the temperature field and stress field during the startup process.Using the Miner linear cumulative damage method and the Manson-Coffin formula to predict the low cycle fatigue life of the rotor,and considering the creep damage of the rotor during steady state operation,the linear creep method is used to determine the rotor creep time.The research work in this paper is as follows:(1)The cold-state start-up scheme of steam turbine units is formulated with the Cold-state sliding parameter start-up as the main research condition.The possible fatigue failure modes of steam turbine rotor during operation are analyzed,and the low cycle fatigue life loss and life prediction methods are studied.(2)The finite element model of steam turbine rotor is established.In this paper,solid works three-dimensional finite element software is used to build a three-dimensional full-scale model of the turbine rotor.During the operation of the rotor,centrifugal force generated by rotating blades is simplified by loading equivalent mass blocks.Based on the knowledge of heat transfer and engineering thermodynamics,the steam temperature and convection heat release coefficient at all levels of the turbine rotor are calculated,and the thermal boundary conditions of the turbine rotor are established.(3)Analyzing and calculating the distribution of temperature field and stress field of the rotor.The temperature field and stress field distribution of steam turbine rotor during cold sliding parameter start-up are simulated by using finite element software ANSYS.The stress field of the rotor is solved by indirect coupling method.The transient temperature field of the turbine rotor is taken as the temperature load of the stress field of the turbine rotor,and the centrifugal force of the turbine blade is considered.(4)Rotor life prediction.Using Manson-Coffin formula and Miner's linear cumulative damage theory,the fatigue life loss of steam turbines during cold sliding parameter start-up is predicted,and the measures for life management of steam turbines' rotors are put forward.(5)Solving the creep damage of the rotor.By applying steady temperature field and rated speed to the rotor,the stress distribution of the rotor can be obtained.The creep breaking time of the rotor material can be obtained by experimental data,and the creep loss of the rotor can be calculated.(6)Life prediction under the interaction of creep and low cycle fatigue.The total life loss of the rotor under cold start-up and rated condition is calculated by linear cumulative method.Through the research of this paper,the life loss of cold sliding parameter start-up and the creep breaking time of rotor of domestic 135 MW unit are obtained,and the safe service life of the unit is calculated.Suggestions for optimization of cold sliding parameter start-up of turbines are put forward,which provides an effective basis for ensuring the safe and economic operation of turbines,and also provides a reference for the study of life loss of this type of rotor under other start-up modes.