The phenomenon of droplet impingement erosion of a wet-steam turbine’s last-stage blades is conditionally considered in the aspect of two “opposing” processes: the force impact of droplets on metal and “resistance” of the metal to this impact. The article places its focus on “resistance” of the metal surface layer to the force impact under the influence of electrified steam and concomitant electrophysical phenomena on its mechanical properties. It has been established that the electrophysical phenomena accompanying wet-steam flow electrization facilitate saturation of the metal with hydrogen (6–10 times higher in comparison with a neutral flow) and have a significant effect on its microhardness (the changes toward its decreasing may be as much as 50%). These changes take place in a thin surface layer, and their extent and nature depend on the flow polarity and also on the frequency and polarity of the electric field induced on the turbine blade. The decrease of microhardness observed in the thin surface layer can be attributed to the phenomenon of local microplasticization, which occurs as a result of facilitating the incipience of microshears when hydrogen cations interact with the dislocation nuclei generated in introducing an indenter. Such plasticization at the microlevel facilitates the development of hydrogen brittleness at the macrolevel. It has been established that, as far as the maximal erosion-induced strength degradation of blade materials is concerned, a positively charged wet steam flow is the most dangerous factor, which most frequently takes place in the case of using water chemistry with pH > 9 (ammonia water chemistry). It is shown that it is possible to alter the development kinetics of destruction caused by droplet impingement erosion by changing the physicochemical properties of thin surface layers of metals.
This is a preview of subscription content, log in to check access.
Buy single article
Instant access to the full article PDF.
Price includes VAT for USA
A. L. Shubenko and A. E. Koval’skii, “Drop-impact erosion of the blade apparatus of steam turbines. Prediction and protection methods,” Visn. NTU KhPI Ser. Energ. Teplotekh. Protsesi Ustatkuvannya, No. 7, 76–87 (2012).
A. A. Tarelin and V. P. Sklyarov, Electrophysical Phenomena and Nonequilibrium Processes in Steam Turbines (Energotekh, St. Petersburg, 2012) [in Russian].
A. A. Tarelin and N. V. Surdu, “The influence of electrophysical phenomena in the flow part of steam turbines on the physical and mechanical properties of elements,” Probl. Mashinostr., No. 3–4, 100–108 (1999).
A. A. Tarelin, N. V. Surdu, and A. V. Nechaev, “Electrophysical aspects of drop-impact fracture of elements of the flow part of steam turbines,” Visn. NTU KhPI Ser. Energ. Teplotekh. Protsesi Ustatkuvannya, No. 7, 88–96 (2012).
B. A. Kolachev, Hydrogen Fragility of Metals (Metallurgiya, Moscow, 1985) [in Russian].
V. A. Soshko, I. P. Siminchenko, and V. S. Lyashkov, “Hydrogen brittleness and hydrogen plasticity of steel,” Metallofiz i Noveish. Tekhnol. 36 (12), 1701–1710 (2014).
S. V. Konovalov, N. V. Kotova, O. A. Stolboushkina, and V. E. Gromov, “Management of metal ductility by weak electrical effects,” Vestn. Novosib. Gos. Univ. Ser.: Fiz. 4 (4), 65–70 (2009).
N. V. Surdu, “Micromechanism of the influence of media on plastic deformation and fracture of metals. 2. The model of the micromechanism,” Vopr. Proekt. Proizvod Letatel’nykh Appar., No. 24, 139–147 (2001).
GOST 9450-76. Measuring Microhardness by Indentation by Diamond Instruments (Izd. Standartov, Moscow, 1977).
A. A. Tarelin, “Postfact phenomena of the wet-steam flow electrization in turbines,” Therm. Eng. 64, 810–816 (2017). https://doi.org/10.1134/S004060151711009X
N. V. Surdu, “Adsorption effect of media during grinding of metals,” Probl. Mashinostr. 2 (1–2), 106–113 (1999).
P. A. Rebinder, Surface Events in Dispersion Systems. Selected Works (Nauka, Moscow, 1979) [in Russian].
Translated by V. Filatov
About this article
Cite this article
Tarelin, A.A., Surdu, N.V. & Nechaev, A.V. The Influence of Wet-Steam Flow Electrization on the Surface Strength of Turbine Blade Materials. Therm. Eng. 67, 60–67 (2020). https://doi.org/10.1134/S0040601520010073
- steam turbine
- droplet impingement erosion
- hydrogen saturation
- adsorption-plasticization effect