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