Nechaiev A. Study of damaging electrified steam effects on the working blades of wet-steam turbines and development of methods for blade protection

The thesis deals with the study of the physical nature of the electrified steam damaging effects on the working blades of wet-steam turbinesand the development of methods for their protection. The study is aimed at enhancing the service life of the working blades of wetsteam turbines under the conditions of the occurrence of condensed moisture electrifying and the electrophysical phenomena in the flow path part. In the course of the experimental study, it has been found that when the blade steels contact with a flow of wet steam, an increase of hydrogen concentration occurs, with the charged steam the concentration of sorbed hydrogen being the highest. A positively charged steam flow has been established to exert the most harmful impact on the strength properties of the surface layer of the blades, while the effect of a negatively charged flow is insignificant.It has been revealed that the microhardness of the surface layer of the blade material changes when exposed to an electric field. Depending on the magnitude and sign of the electric potential on the metal surface, the microhardness can increase or decrease by up to 12%. It has been shown that the action of a variable electric field leads to a change in the microhardness of the surface layer of the blade material, and the magnitude of the effect depends upon the frequency. The maximum reduction of microhardness in the surface layer up to 2 μm thick can reach 35% within the frequency range 2.5÷ 20 kHz. A method for preventing the formation of coarse particle moisture, which takes into account the electrification of the steam flow, as well as the recommendations for eliminating or significant reducing the intensity of electrophysical phenomena in the exhaust part of the turbine and increasing the service life of the working blades, have been developed .