|Journal||Journal of Mechanical Engineering|
|Publisher||A. Podgorny Institute for Mechanical Engineering Problems
National Academy of Science of Ukraine
|ISSN||0131-2928 (Print), 2411-0779 (Online)|
|Issue||Vol. 22, no. 1, 2019 (March)|
|Cited by||J. of Mech. Eng., 2019, vol. 22, no. 1, pp. 4-8|
It is known that in wet steam turbines the wet steam flow is electrified when passing through the turbine flow path. In this, the mutual electrification of the condensed moisture flow and flow path surfaces occurs. Until now, experts in the field of steam turbine operation have been aware of the problem of electrical phenomena in flow paths in terms of electroerosion phenomena associated with the accumulation of electric charges on the rotors. Similar phenomena in the working fluid flow are less known. As a result of the research conducted at IPMash NAS of Ukraine, it has been established that the electrification of the wet steam flow leads to the formation of a volume charge in the flow path, which can have a significant value (up to 10–3 C/m3) and exert a significant effect on the working processes in the turbine and condenser. The volume charge of the steam flow in the flow path also generates electric fields with constant and variable components. As a result, parts and assemblies of the flow path may be under the action of an electric field. In particular, turbine blades may be in the electric field of the volume charge of the working fluid. As is known, the impact of an electric field can reduce the strength of the metal surface layer. Therefore, an experimental study of the effect of electric fields, similar to those occurring in the turbine flow path, on the strength properties of blade steel is an important task. The article presents the results of the experimental determination of the microhardness of the 15H11MF blade steel surface layer exposed to a constant or variable electric field. It is shown that its effect significantly reduces the microhardness of the blade steel surface layer. Since the strength of the surface layers of the working blades is one of the most important characteristics of their erosion resistance, the effect of the electric field of the steam flow volume charge can be one of the negative factors that reduce the erosion resistance of turbine blade surfaces. Based on the obtained results, it can be concluded that it is necessary to further improve the system for neutralizing the accumulation of electric charges in the flow path, which currently mainly performs the function of turbine rotor grounding.
Keywords: microhardness, electric field, blade steel.
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Received 29 November 2018
Published 30 March 2019