Ensuring the Vibration Reliability of Steam Turbine Rotor Blades during Manufacture

The power unit availability factor depends in many respects on the reliability of the steam turbine's last-stage rotor blades. In the course of operation, rotor blades experience static and vibration loads caused by steam flow, due to which they are often damaged as a result of fatigue stresses. Relatively long last-stage rotor blades of steam turbines are components that especially often suffer from damage. Emergency shutdowns of a turbine caused by blade system faults account for one quarter of their total number, and the time of power unit emergency outages resulting from blade breakdowns accounts for more than half the total time of their being in the outage state. In manufacturing high-capacity steam turbines, special attention is paid to ensuring vibration reliability of last-stage rotor blades. The article describes a technology applied to ensure the dynamic vibration reliability of the last-stage rotor blades of the steam turbines produced by Leningrad Metal Works (LMZ) at the stage of manufacturing them with the use of vibration tests carried out on a dedicated bench (the Campbell machine) in the rotor speed range in which resonances excited at engine orders from three to ten are observed. The article also presents the Campbell diagram of the last-stage rotor blade of a high-capacity steam turbine with the maximal stresses in the rotor blade that occur during resonances excited at engine orders from two to six and also the results from a comparison between the predicted and experimental distributions of relative stresses at the leading and trailing edges over the blade length during disc vibration at engine order four.