The last-stage blades of high-power steam turbines operate in a humid steam environment, which gives rise to erosion damage, leading to a decrease in their residual life and possible emergencies. The potential ways of extending the trouble-free operation of turbine blades of a K-1000-60/3000 type are evaluated. The change in maximum stresses of the blades at nominal loads from the steam flow in the presence of one damaged blade after reconditioning is determined. Three-dimensional finite element models of components and corresponding software for the computation of steady-state harmonic vibrations are used. The finite element model of the blade–disk system consists of 60,000 elements and more than 175,000 nodes. Prismatic and tetrahedral curvilinear finite element models were employed. Maximum equivalent stress amplitudes against frequency were determined in the ranges of rotation frequency of 50 Hz and excitation frequency from the steam flow of 2100 Hz (42 guide blades). The nominal load from the steam flow is assumed to be 1 MPa at the top of the blade, which linearly decreases to 0 at its root. The change of maximum stresses for the damage-free system and that with all similarly damaged blades is estimated. It is assumed that the physicomechanical properties of the blade material are maintained (as for the initial version) after repairing the damaged blade and machining of its surface. The graphs of maximum equivalent stresses against excitation frequency for the blades in the disk–blade system with the break of its cyclic symmetry in the presence of a damaged blade are presented. The results are compared with the data for the systems with undamaged blades and all equally damaged blades after reconditioning. Maximum vibration stresses of the blades in the disk–blade system with one damaged blade increase as compared to that with all equally damaged and machined blades after reconditioning.
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A. P. Zinkovskyi is deceased.
Translated from Problemy Mitsnosti, No. 4, pp. 14 – 24, July – August, 2022.
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Shulzhenko, M.G., Zinkovskyi, A.P. & Olkhovskyi, A.S. Vibration Stress of the Last-Stage Blades of a Steam Turbine After Repair of a Single Blade. Strength Mater 54, 565–575 (2022). https://doi.org/10.1007/s11223-022-00433-z
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DOI: https://doi.org/10.1007/s11223-022-00433-z