Surface Transverse Crack Growth in Steam Turbine Shaft A. Bovsunovsky1,∗ National Technical University of Ukraine " Igor Sikorsky Kyiv Polytechnic Institute " ∗ apbovsunovsky@gmail.com Keywords: Transverse Vibration, Steam Turbine Shaft, Crack Growth. Operation of steam turbine structural elements is characterized by heavy mechanical and thermal loading in corrosive environment. One of the main consequences of such operation conditions is damage of steam turbine structural elements, which accumulates for a long time and finally develops into local damage of a crack type. The initial defects in turbine structural elements appear in the process of their manufacture because almost all technological operations such as forging, turning, and milling, heat treatment damage the surface layers of the material in the form of pores and micro-cracks. Besides a huge amount of stress concentrators in turbine structural elements is the additional reason of crack initiation and growth. The stage of crack growth usually is relatively short and may lead to catastrophic failures if crack will not be detected in time. The intensity of crack growth is dependent on operational factors and crack resistance characteristics of rotor steel. To estimate the edge transverse crack growth rate in steam turbine shaft in the process of transverse vibrations when rotor passes through the first critical speed the analytical model has been developed. As a model object the high-pressure rotor of the K-210-130 steam turbine was chosen. The durability of cracked rotor in terms of start-ups number was estimated with the fracture mechanics theory based on the calculated stresses in the cracked area, as well as on the experimentally determined crack growth rate for the rotor steel. As it was demonstrated, the angular acceleration, rotor’s eigenfrequency and geometrical characteristics have the most essential impact on the intensity of crack growth. Thus, the intensity of crack growth can be decreased crucially by the increase of angular acceleration and/or rotor’s diameter and by the decrease of rotor’s eigenfrequency. Of the factors, which are the mechanical properties of rotor steel, the damping characteristic is most influential. In such a way, the creation of high damping rotor steels and the utilization of effective mechanical dampers are the promising ways to prevent crack growth in turbine rotors. 49
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