Failure analysis of the defect-induced blade damage of a compressor in the gas turbine of a cogeneration plant

Gas turbine engines are being widely used for power generation recently because of their high efficiency and versatility. However, it is occasionally reported that a gas turbine under normal operation fails even though careful inspections were scheduled. In this paper, the recent failure of the gas turbines of a cogeneration plant is analyzed by focusing mainly on the crack initiation mechanism of blade fracture. Damage of several blades of the compressor was observed after a gas turbine was disassembled, and the root causes of the damage were investigated in detail by scanning electron microscopy as well as optical microscopy. The defects observed at the crack initiation site have been characterized by comparison with previous studies. The fracture of the blade was supposed to be initiated by a crack due to concentrated stresses around a preexisting defect which was possibly formed before the turbine was operated, e.g., a forging defect during the three-step forging process for blades manufacture.