Images of Flaws in Generator Retaining Rings Using SAFT Reconstruction of TOFD Data
Retaining rings are assembled onto each end of electric generator rotors to support the rotor end-turn windings against rotational forces. They are attached to the ends of the slotted portion of the rotor body with an interference fit. Many of the rings presently in service are susceptible to intergranular stress corrosion cracking (IGSCC) in the presence of moisture. IGSCC seems to occur first, and tends to be more severe, at stress concentrations in the rings and adjacent to geometric discontinuities in the mating rotor surface, such as, the edges of the rotor teeth. These same geometric features also tend to cause ultrasonic reflections that are difficult to discriminate from real damage. The capability of SAFT processing of TOFD data to discriminate IGSCC from geometric reflectors was investigated using several retired retaining rings assembled to mandrels simulating the generator rotor.
KeywordsLateral Wave Electric Power Research Institute Circumferential Crack Crack Profile Intergranular Stress Corrosion
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