Elastic limit load resource when reaming holes in turbine rotor discs

Abstract

The main topic of the article is the evaluation of load capacity by elastic stress analysis of impulse steam turbine rotors with bore drilled discs used for pressure equalization. Long-time operation of such turbines leads to fatigue fractures. The authors have analyzed stress distribution around the holes in turbine rotors in their nominal state and after reaming, which is the preferred method of removing fractures. Two approaches were used in analysis of bore drilled disc problem: continuous model and its mathematical solution and numerical based on finite element modeling. Both confirmed co-existence of stress concentration and crack initiation. Results show significant range for possible holes reaming - even with lowering stress level at critical area. These results were successfully used in overhaul practices and further turbine life time extension. It also allows to predict optimum hole layout and sizing at the design process for possible rotor disc notch effect reduction.