Mazza, E.

New challenges in the design optimisation of turbine rotors

WORKSHOP ON OPTIMAL DESIGN OF MATERIALS AND STRUCTURES Laboratoire de Mécanique des Solides Ecole Polytechnique 91128 Palaiseau (France) November 25-27, 2002

Abstract

The progressive liberalisation in the electricity market leads to significant changes in the design requirements of power generation turbines: the steady state temperature in the hot turbine sections is increased to enhance turbine’s efficiency; flexibility becomes a key factor for competitiveness and thus turbines experience an increasingly high number of start- shut cycles, even on a daily base, following the fluctuation of the electricity prices. The ability of the turbine to reach rated values of power generation within very short start-up times becomes therefore a primary goal in design optimisation. This, of course, should be achieved without compromises on reliability and availability.

Due to the increase in steady state temperature and the severity of the transient stresses, the rotor lifetime assessment evolves from a low cycle fatigue dominated problem to a typical, but fairly complex creep-fatigue interaction problem.

This development leads to real new challenges for the mechanical analyst. In this paper, the influence of the constitutive model and the damage evaluation rule on the lifetime prediction is analysed. As well, the requirements on the properties of the rotor material in future turbines are evident from the results of this analysis.

Design optimisation requires in-depth knowledge of the material behaviour under service conditions. The new challenges cannot be faced only with the information derived from isothermal fatigue tests with dwell time or monotonic creep experiments. Rather, thermo mechanical fatigue (TMF) tests must be performed. In this paper the results of dedicated TMF tests are presented in which the temperature and stress history is representative for the conditions of the critical rotor location. Endurance and constitutive behaviour of 1%CrMoV steel are determined from these experiments.

03.01.2003 | compiled by Stephan Kaufmann | ZfM | ETH