The rotating blades of a steam turbine perform the important task of converting the energy of the steam into rotating torque.  Hence, these blades have to be very robust and they need to be installed properly in the discs of the turbine.  Damping mechanisms are used to improve the stiffness of the blades and to minimize the vibrations of the blades.  Different types of blade damping mechanisms are being used in steam turbines.  Shroud bands, lashing or damping wires, pins, tie-bolts and lashing stubs are the most common types of damping mechanisms used in steam turbines.  Several factors such as stress distribution, additional centrifugal stresses due to the added weight of the damping mechanisms, aerodynamic advantages, resulting harmful mode shapes and critical vibration frequencies etc., need to be considered in the selection and the design of the damping mechanisms.

However due to the various types of operating conditions and stresses they experience, the damping mechanisms do experience failure in service.  Metallurgical evaluations of some recent failures of damping mechanisms are discussed here.  Failures of shroud bands, blade tenons, tie-bolts and lacing wires are the particular examples presented here.  Stress corrosion cracking, fatigue and overload were found to be the main modes of failures in these examples.


Blade Damping Mechanisms and Some Recent Failures

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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