Fractographic investigations of the failure of L-1 low pressure steam turbine blade

(in lingua inglese)

During the expansion of steam through the turbine, the solubility of these nonmetallic inclusions in the steam decreases, and they condense onto surface of the blades at concentration much higher than the original concentration in the steam. These concentrated nonmetallic inclusions enhance corrosion of the blade. Formation of corrosion pits on the blade airfoil region results in distortion of steam passages, which in turn alters steam velocities and pressure drops, which can cause excessive rotor thrust causing vibration problems. The SEM fractographs of the fractured surface revealed that transgranular cleavage fracture and beach marks are present on the fractured surface. The presence of these marks indicated that the crack propagation occurred because of fatigue resulting from the vibration of the blade.