Failure analysis of steam turbine blade

The steam turbine blade had failed by fatigue. The fatigue crack had initiated at the blade root T-joint fillet. Fatigue appears to be of high cycle – low stress type. From the evidences, the most probable reason for fatigue crack initiation appears to be presence of nonmetallic inclusions in the blade material and/or excessive clearance between the blade guiding rib on the disc and the blade root