Modelling and Measuring Experiences to Evaluate the Modal Behaviour of an Industrial Gas Turbine High Pressure Bucket

Abstract

In gas turbines, High Cycle Fatigue (HCF) bucket failures are mainly prevented by avoiding resonance frequencies in the operative range. Due to the high number of stimuli present, avoiding potential resonance crossings is often not possible. In these cases, failures can be avoided by controlling vibratory stress levels in order not to exceed high cycle fatigue endurance limits. This paper describes the processes used in GE Infrastructure, Oil&Gas to design, develop and test a new high-pressure turbine bucket for a 32 MW-class industrial gas turbine for mechanical drive and power generation applications. Initial design phases, material selection, concurrent engineering efforts, bench testing characterization and final validation on FETT (First Engine to Test) are described. A particular focus is given to the analytical tools (i.e. Modal Cyclic Analysis) used in the design phase and the validation tests (i.e. Ping Test and Laser Doppler Vibration) including the development of a dedicated instrumentation technique, which allowed the unit not to be disassembled (High Temperature Strain Gauge Splicing).