Analytical Creep Rupture Life Prediction of Multiple-Lug Rotor Steeples

Abstract

An analytical prediction method of brittle and ductile creep rupture lives was proposed for 1CrMoV steel multiple-lug rotor steeples which have a tendency of degradation in creep ductility after long-term service. Rupture time was evaluated as a sum of crack initiation life and crack growth life with consideration of creep ductility and load-carrying factors of multiple-lugs in the steady creep state.
This method was experimentally verified by creep rupture tests of notched thick plate specimens and interrupted creep tests and microstructure observation of notched thick plate specimens and blade-root and rotor-steeple models at 600°C. Two kinds of 1CrMoV steel in creep ductility were tested. The main conclusions are as follows.
1) An estimation method of load-carrying factors of multiple-lugs in the steady creep state was proposed and a uniforming tendency of load-carrying factors was recognized in the present models.
2) An estimation method of creep stress at the lug root with consideration of the stress-dependent creep strain rate was proposed for damage analysis and its validity was verified.
3) Creep rupture life of 1CrMoV rotor steeples can be evaluated in a practically reasonable accuracy as a sum of creep crack initiation life and creep crack growth life with consideration of creep ductility and load carrying factors of multiple-lugs in the steady creep state.