The fatigue damage and failure of steam turbine rotors by torsional vibrations are investigated. Possible causes of the occurrence of torsional vibrations are discussed. Modeling of torsional vibrations of the shafting of a steam turbine, which occur under its operating conditions, has been performed, and the cyclic strength of the shafting under these vibrations has been estimated.The world experience of the long-term operation of turbine units of thermal and nuclear power stations allows the conclusion to be drawn that one of the causes of accidents and catastrophic failures of turbine rotors is fatigue damage accumulation due to torsional vibrations of shafting. This is indicated, e.g., by accidents at a thermal power station in the USA (Tennessee, 1974) [1], at the state district power station-4 at Kashira in Russia (October 2002) [2] and at one of the overhauled power generating units of the Pridneprovskaya thermal power station in Ukraine (2007). In the first case, an accident resulted in the failure of a medium-low pressure rotor ( Fig. 1 shows the lines along which the rotor fractured) and in the second case in the complete failure of the power generating unit No. 3 (K-300-240-1 turbine) and in the partial failure of two neighboring power generating units. Fragments of rotors were found within a radius of several hundreds of meters from the station. In the last case, the turbine had to be urgently stopped because of the occurrence of strong vibration, which prevented it from failure because of a considerable fatigue damage of the rotor, as was found out later. It was concluded from the results of investigations of these accidents that one of the main causes was fatigue of the rotor metal as a result of cyclic torsion.Taking into account the potential hazard of this phenomenon for all steam turbines being in operation, the task was set to evaluate the degree of the fatigue damage of turbine unit shaftings due to torsional vibrations. To perform this task, it is necessary to ascertain the causes of the occurrence of torsional vibrations of shaftings during operation, to model vibrations under the action of operating load and to evaluate the fatigue properties of their materials in operation.The ascertainment of the causes of the occurrence of shafting vibrations made it possible to model structure loading conditions which approached the operating conditions. Since no monitoring of torsional vibrations of turbine rotors is performed at present, the causes of their occurrence can only be conjunctured. The results of a number of theoretical studies [2,3] indicate that the main cause of the occurrence of torsional vibrations of shaftings is the dynamic load acting on the turbine shaft on the turbogenerator side mainly under its abnormal operating conditions, particularly under short-circuit (SC) conditions, at the moments of connection to network with rough synchronization, because of the dynamic instability of the turbogenerator-network system and the nonuniformity of the electric field of the generator, et...

373:534:621.6 and I. N. Litovchenko Sources of vibration in the main steam line have been determined during steady-state operation of the power-generating unit. Amplitude and frequency of the pressure pulsations in the heat carrier and behavior of forced vibrations of the pipeline system have been assessed using mathematical simulation methods. Keywords: vibrations in steam pipeline, pressure pulsations, mathematical modeling. General Formulation of the Problem, Scientific Tasks and Practical Applications. This work is concerned with development of design plans and specifications necessary to replace the main steam safety valves (Fig. 1) by new pulse type valves.Design solutions involving implementation of new pulse valves in the "closed-loop" steam exhaust pipelines imply changes in the dynamic behavior of these due to anchor support displacement along the "closed-loop" pipe axis and appearance of loose valves. This necessitates assessment of the general pipeline vibration strength at the design stage.The analysis of the available results of investigations shows that vibration strength evaluation for these pipelines in the design stage is not provided, moreover, it is difficult to carry out any corresponding experiments [1][2][3]. Therefore, design information technologies were used in this study for assessing vibration strength for steam pipelines [4]. Investigation technique has been developed which consisted of the following two stages: analysis of hydrodynamic impact on the steam pipeline and calculation of vibrations in the main steam line under unsteady-state loading conditions. Gas dynamic effects arise from pressure pulsations of the heat carrier that are determined by mathematical modeling of the unsteady-state steam flow in the pipeline. Flow Vision software [3] is used for performing computational simulations.As far as steady-state steam flow in the pipeline was considered, it would appear reasonable to assume that pressure pulsations are mainly caused by pipeline sections with structural deviations (pipe T-joints, gate valves, valves, etc.). Figure 2 shows the computational model corresponding to flow channel of the pipeline with "closed-loop" steam exhaust pipe. The model was generated using graphical package PK KOMPAS-3D V8.In order to describe steam flow behavior in the pipeline, we have used an analytical model for compressible gas, which is applicable for steam flow simulation at any Mach numbers (sub-, trans-, super-, and hypersonic flows). Within framework of this model, flow velocities and steam pressure values, as well as turbulent heat carrier flow distribution, have been assessed for a specific geometric volume.For identification of the origin of the pressure pulsations in the flow channel under study (Fig. 2) we have analyzed variation of turbulent steam flow in time. The calculations show that turbulent energy eddy forms at the leading edge of the lower pipe T-joint connected to the steam exhaust piping (Fig. 3), travels to the trailing edge of 124

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