Metallurgical failure analysis of repeated turning gear failures in large gas turbine engines

Abstract Turning gear assemblies are used to turn rotors of turbomachinery after engine shutdown, until the rotor has cooled sufficiently to remain stationary. Turning gears are usually hydraulically driven, using the same turbine oil that is also used to lubricate the main bearings. In some engines in the field, failures of internal and external spline shafts occurred, resulting in complete loss of torque. Damaged spline connections were found to be causing this. It was concluded that a lack of surface hardening caused mechanical damage to the spline shafts. Overload with high torque in transient operations may or may not have contributed to these failures. This is a design flaw made by the original equipment manufacturer’s supplier, being responsible for the turning gear assembly. This supplier not only provided the hardware but also designed it. The design did not provide for surface hardening.