Estimation of Fatigue Crack Growth at Transverse Vibrations of a Steam Turbine Shaft

Abstract

AbstractDuring operation, a steam turbine shaft is subjected to a wide range of thermomechanical and thermochemical loading. Despite significant reserve of static and dynamic strength, laid down at the stage of turbine design, fatigue cracks still appear in its structural elements, which lead to catastrophic failures. Potential reasons of damage in turbine shafts are all technological operations used in the process of manufacture (forging, turning, and milling, heat treatment), since they are accompanied with plastic deformation of material. Damage accumulates during long-term cyclic deformation and turns into local damage of a fatigue crack type. In addition, cracking in turbine shafts is caused by the presence of stress concentrators. The analytical model of high-pressure rotor of the K-200-130 steam turbine has been developed to study the transverse vibrations when rotor passes through the first critical speed. The growth of crack is predicted based on fracture mechanics approaches through the determined maximal stresses in the cracked section and on the experimental dependences of the crack growth rate on the stress intensity factor range for the rotor steel.KeywordsSteam turbine shaftFatigue damageTransverse vibrationCrack growth