Failure Investigation of Frame 6FA Gas Turbine Compressor Blades

This investigation elucidates failure of a land based 6FA gas turbine compressor 2nd stage blade. During discussions with site officials, it was learnt that this particular compressor operated in good condition for over 20,000 h at two other sites. In this power station, this was second such failure with less operation duration. Due to failure of blades, it was requested for a detailed root cause analysis by the utility officials in order to avert such failures in future. Failed blade samples were collected from the site and cut into the suitable sizes for investigation procedures. Investigation techniques like visual observation, stereomicroscopic, metallographic, scanning electron microscopic examinations (SEM), etc. are employed to ascertain the root cause for failure. During the investigation it was noticed that there is no degradation in the material. During stereomicroscopic examination, a number of beach marks were observed to be present on the fractured surface of the blade. It was also noticed from both stereomicroscopic and SEM examinations that the blade failed due to fatigue. The cracks have originated from micro-cracks developed at the trailing edge during shot peening process in the blade root. These cracks grew as the blades have vibrated beyond their natural frequency due to air surge during operation. It was recommended to examine the air filtration mechanism of the compressor regularly.