In the latter stages of steam turbines, the moisture content can increase to a level which degrades thermal efficiency and increases water impact erosion of the latter stage buckets. One approach for removing this moisture is to groove the leading edges of the buckets (or blades) to capture the water, and to use centrifugal force generated by the rotating turbine rotor to throw the water out to stationary moisture collection devices. With this approach, the entrance edge of the annular tip cover or shroud extending over the leading edges of the buckets must be severely cut back (i.e., axially shortened by reducing the width of the cover) to allow the water to be thrown out to the stationary moisture collection devices without interference from the cover.
A radical cut back of the cover can, however, significantly affect the bucket design and associated vibration frequencies, and in some cases, requires separate bucket designs with and without a moisture removal capability. The radical cut back of the cover also eliminates or at least degrades sealing at the entrance edge of the cover, thereby reducing the stage thermal efficiency. Another disadvantage is the requirement for the design of a new tenon (and vane tip build-up for the new tenon) on the blade tip for receiving individual segments of the cover.