Cracking failure in gas-turbine blades

The present paper describes the findings of a failure investigation on the basis of metallographic examination of Gas-Turbine blades of a 3MW power plant in the province of Punjab, Pakistan. Two blades were randomly picked up for inspection from a lot of 61 blades that had been removed from the turbine after annual inspection. The blades were removed on the recommendations of the inspectors (from the manufacturers of turbine) according to which the blades had suffered from corrosion-fatigue cracking at the inlet of the cooling air passage. The objective of the present examination was to establish whether there were any cracks at the inlet of the cooling air passage, and in case any cracks were present, what was the possible cause of such cracking. The investigation showed that cracking at the air-inlet was not due to corrosion-fatigue, but instead the cracks were a manufacturing defect that could be described as 'solidification shrinkage' cracks. (author)