Diagnosis of ring cracks on the shafting line of a turbo unit

Abstract

Due to the growing number of accidents associated with damage to turbine unit shafts, there is a pressing need to diagnose the occurrence and growth of ring cracks not only during planned repair work on the turbine unit, but also directly during its operation to prevent emergency failures and costly repairs of the machine. Ring cracks that develop in the shafting do not lead to an increase in the level of vibration of the rotor or its support bearings and, therefore, cannot be detected by standard operational vibrodiagnostic systems. In this paper we propose a method that allows for the diagnosis of the occurrence and growth of ring cracks on the turbine unit shafting. The method is based on the influence of the depth of an annular crack in the shaft on the angle of its twist during machine operation. The presence of this relationship is determined through calculations based on the parameters of the experimental low-pressure turbine 2, used by the Central Boiler and Turbine Institute named after I. I. Polzunov. The practical implementation of this method is proposed to be carried out using the twist angle determination technique developed based on the discrete-phase method by means of measuring and analyzing changes in the shaft twist angle during turbine unit operation. Technically, this is achieved by employing a system consisting of inductors and sensors fixed to the stator and rotor parts of the machine. The proposed method can be used as a supplement to existing methods of operational control of the actual condition of the shafting, as well as, in the future, to assess the actual efficiency of the turbomachinery cylinders.