Managing Compressor Rotor Rim Fatigue Damage

Abstract

Described within this paper are the results derived from an investigation into the root cause of cracks which are prematurely forming within the aft end rotor rim attachments of large combustion turbine compressors. The overall objective for this program was to use these results to develop a means for projecting the remaining service life of similarly affected rotors based on non-destructive measurements which identified the degree of fatigue damage sustained in the critical disc rim fillets. Projected rotor retirement was identified by systematically calculating the change in stress intensity for a crack as it propagated from a corner of the attachment fillet through the disc rim. Risk of catastrophic failure was identified when the stress intensity along the front of a given crack size and depth exceeded the fracture toughness of the rotor material, risking failure. Estimates of both crack initiation and propagation relied on properties derived from fatigue tests of specimens obtained from a retired rotor and stress results from a transient thermal analysis of the stages. When compared, projections of crack growth correlated well against field measurements of damaged rims.