Turbine blades with radial fasteners (T-shank, radial fir-tree, etc.) are commonly used in current steam turbomachinery, especially in power generation applications. However, this reliable and cost-effective design is limited by the strength of the axial pins which lock the closing part in the radial entry slot in the disc. In applications with high speed rotors or heavy blades, the centrifugal force of the blade exceeds the pin strength. In those applications, the airfoil portion of the closing blade is cut off leaving only the bottom portion which is located in the radial entry slot. Some original equipment manufactures (OEMs) also remove the airfoil of the blade 180 degrees opposite for better balancing. The absence of two airfoils is detrimental to efficiency and reliability of the entire row. Siemens Demag Delaval Turbomachinery, Inc. (SDDTI) developed a new locking arrangement which eliminates the above described shortcoming associated with standard radial entry blades. This paper presents the design of the new patented locking arrangement and mechanical stress calculations (FEA) of its major components. In order to verify the validity of the design and calculations, a full-scale row of modernized radial entry blades for an existing US Navy turbine with the new locking arrangement was tested. The testing was done over the full range of operating speeds in a vacuum bunker. The paper also describes the special test rotor, instrumentation used, and the test results which were compared with the stress calculations. The tests confirmed all the advantages of the new locking arrangement and showed acceptable correlation with the stress calculations. The patented design will expand applications for radial entry blades, modernize radial entry blades with missing blade airfoils, and provide a cost-effective method to repair localized cracks in the fastener area of the turbine discs.
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