Also, the tensile stress values on the shaft-flange transition radius, obtained by the Finite element analysis, for the load
case 2 (47.8 MPa) are higher than the recommended one (640 MPa) for this type of shafts [15,16].
The calculated induced stress intensity factor (SIF) range at the crack tip was 13.1 MPapm and that is higher than the
threshold SIF range for the material, 4.2 MPapm, which explains the stable crack growth on the shaft during service [17].
On the basis of all the above stated, it can be concluded that corrosive fatigue was the cause of the shaft failure. The root
cause of this turbine shaft failure can be found in the design of the seal box and insufficiently developed procedures for nondestructive
periodical inspection and anticorrosion protection of the transition zone.