Investigation of blade failure in a gas turbine

A gas turbine abruptly tripped to a stop during its daily morning start-up period. Out of a total of 81 blades in the first row only one blade was broken at its root. Prior to this accident, there were three blade failure accidents in the same plant during the last 10 years. First, the fracture surface of the troubled blade was investigated. Stress analysis of the blade showed that the maximum stress occurred due to the pressure profiles developed during operation. Modal analysis for one blade and the assembly of blades was performed and Campbell diagram and Interference diagram were drawn to check the dynamic characteristics of the blades. The vibration of the turbine was measured using accelerometers during the operation condition. The result shows that the fatigue fracture of the blade was originated during transient events internal to the combustion chamber which was close to the resonance condition of the assembled blades.