For a blade root to be effective and meet its design functions, it is necessary for the mating portion to be produced on the rotor rim with the same degree of precision as the blade. It is also necessary to recognize that the steeple produced on the rotor is subject to various forms of damage and deterioration, which can influence the overall capability of load transfer.

The damage sustained by the rotor or wheel can be as severe as that sustained by the blade roots themselves. In terms of maintenance considerations, such damage is normally of greater concern to the engineer, as the material of the rotor in this region is subject to high-level stresses, and the damage cannot be as easily corrected, i.e., such damage cannot be easily remedied by the replacement of parts, and if a new rotor is required its delivery requires a long lead time. This can make a unit unavailable for extensive periods, which is expensive compared to the costs associated with the purchase of replacement blading.

This wheel rim steeple is defined as the blade root mating portion, which is machined onto the rotor or wheel rim to receive the blade. This attachment configuration is designed to affect a satisfactory load transfer, and be able to carry the blade loads and locate it during all conditions of load and steam environment. In those root forms of the tangential and radial entry types, the wheel is tangentially...