Reinhart & Associates, Inc. has, in the last 40 years, performed boresonic examinations of more than 1,000 steam turbine and generator rotors.  The type of damage detected during service on these rotors include mechanical and thermomechanical fatigue cracking in the axial-radial and circumferential-radial planes.  These service related defects will propagate perpendicular to the stress induced during service.  For example, bore circumferential or hoop stress caused by thermal and mechanical stresses during startup and operation will induce bore surface connected defects in the axial-radial plane.  Axial and bending stress applied on the shaft by thermal and mechanical forces will induce surface connected defects in the circumferential-radial plane.