Investigation of the Thermal Strength of Steam Turbine Diaphragms with Reduction of Axial Dimensions

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DOI https://doi.org/10.15407/pmach2021.02.037
Journal Journal of Mechanical Engineering – Problemy Mashynobuduvannia
Publisher A. Pidhornyi Institute for Mechanical Engineering Problems
National Academy of Science of Ukraine
ISSN  2709-2984 (Print), 2709-2992 (Online)
Issue Vol. 24, no. 2, 2021 (June)
Pages 37-49
Cited by J. of Mech. Eng., 2021, vol. 24, no. 2, pp. 37-49

 

Authors

Borys P. Zaitsev, A. Pidhornyi Institute of Mechanical Engineering Problems of NASU (2/10, Pozharskyi St., Kharkiv, 61046, Ukraine), e-mail: b.zajtsev@gmail.com, ORCID: /0000-0003-2411-0370

Viktor L. Shvetsov, Joint-Stock Company Turboatom (199, Moskovskyi Ave., Kharkiv, 61037, Ukraine), e-mail: shvetsov@turboatom.com.ua, ORCID: 0000-0002-2384-1780

Oleksandr M. Hubskyi, Joint-Stock Company Turboatom (199, Moskovskyi Ave., Kharkiv, 61037, Ukraine)

Serhii A. Palkov, Joint-Stock Company Turboatom (199, Moskovskyi Ave., Kharkiv, 61037, Ukraine), e-mail: sergpalkov@gmail.com, ORCID: 0000-0002-2215-0689

Tetiana V. Protasova, A. Pidhornyi Institute of Mechanical Engineering Problems of NASU (2/10, Pozharskyi St., Kharkiv, 61046, Ukraine), e-mail: tatyprotasova@gmail.com, ORCID: 0000-0003-1489-2081

 

Abstract

The problem of reducing the axial dimensions of steam turbine diaphragms is associated with the problem of steam turbine modernization performed by increasing the number of reactive blading stages and using existing foundations. Evaluation of the suitability of diaphragm design versions with established steam flow characteristics was carried out with constraints on short- and long-term strength conditions, as well as the accumulation of axial deflections due to creep. For computational research, there was introduced a methodology using the finite element method and Yu. M. Rabotnov’s theory of strain aging. The calculation of creep was reduced to solving an elastic-plastic problem with a deformation curve, which was represented by an isochronous creep curve for the time chosen. A software was used providing for the automated construction of the original computer diaphragm model with the help of guide-vane profile drawings and axial cross-sections of the diaphragm rim and body, as well as several geometric parameters. The calculated model of a welded diaphragm reproduces the main essential features of the structure, the material properties of its elements, as well as steam load. The exploratory studies of diaphragms with reduced axial dimensions were performed on the example of the second- and third-stage diaphragms of the high-pressure cylinder of the K-325-23.5 steam turbine. The original second- and third-stage diaphragm designs were considered to be basic, in relation to which, according to strength and rigidity parameters, the alternative ones were compared. Calculated data for the basic diaphragm design versions for 100 thousand operating hours were obtained. According to the calculations, maximum deflections are achieved at diaphragm edges, and the stresses, that are maximum at the points where the guide vanes are attached to the diaphragm rim and body, undergo a significant redistribution due to creep. Two approaches to the reduction of the axial dimensions of the second-stage diaphragm design of the steam turbine high pressure cylinder were involved. In the first approach, the reduction of the dimensions was achieved by proportionally reducing the guide-vane profile with a corresponding increase in the number of the guide vanes. In the second approach, the profile remained unchanged, but the axial dimensions of the diaphragm rim and body were reduced. The parameters of strength both in the elastic state at the beginning of operation and in the conditions of creep, as well as the accumulation of axial deflections were investigated. Based on the comparisons with the basic design, it was established that the second approach is more effective. Additional recommendations for the use of more heat-resistant steels for outlet guide vanes and the conditions of diaphragm attachment in the turbine casing are given.

 

Keywords: steam turbine, diaphragm, axial dimensions, creep, axial deflection, short- and long-term strength.

 

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References

  1. Shubenko-Shubin, L. A. (Eds.). (1973). Prochnost parovykh turbin [Strength of steam turbines]. Moscow: Mashinostroyeniye, 456 p. (in Russian).
  2. Taylor, V. L. (1951). Stress and deflection tests of steam-turbine diaphragm. Transactions of the ASME. No. 7. P. 877–890.
  3. Naumov, V. K. (1960). Raschet diafragm parovykh i gazovykh turbin [Calculation of diaphragms of steam and gas turbines]. In book: Issledovaniya elementov parovykh i gazovykh turbin i osevykh kompressorov [Research of elements of steam and gas turbines and axial compressors]. Leningrad: Mashgiz, pp. 310–312.
  4. Sentsov, N. D. (1958). O nekotorykh rezultatakh issledovaniya progibov i napryazheniy v svarnykh diafragmakh parovykh turbin [About some results of research of deflections and stresses in welded diaphragms of steam turbines]. Energomashinostroyeniye – Power Engineering, no. 8, pp. 6–11 (in Russian).
  5. Ingultsov, V. L. (1961). Raschet diafragmy kak polukoltsa na uprugom opornom konture [Calculation of a diaphragm as a half-ring on an elastic support contour]. Energomashinostroyeniye – Power Engineering, no. 11, pp. 1–5 (in Russian).
  6. Kulagina, G. F. (1960). Eksperimentalnoye issledovaniye napryazheniy i progibov diafragm [Experimental study of stresses and deflections of diaphragms]. In book: Issledovaniye ele-mentov parovykh i gazovykh turbin i osevykh kompressorov [Research of elements of steam and gas turbines and axial compressors]. Leningrad: Mashgiz, pp. 333–346 (in Russian).
  7. Zaytsev, B. F., Shulzhenko, N. G., & Asayenok, A. V. (2006). Napryazhenno-deformirovannoye sostoyaniye i kontaktnyye yavleniya v opiranii diafragmy parovoy turbiny [Stress-strain state and contact phenomena in the support of a steam turbine diaphragm]. Problemy mashinostroyeniya – Journal of Mechanical Engineering, vol. 3, no. 3, pp. 35–45 (in Russian).
  8. Rozenblyum, V. I. (1954). Raschet polzuchesti turbinnykh diafragm stupeney vysokogo davleniya [Calculation of creep of turbine diaphragms of high pressure stages]. Inzhenernyy sbornik – Engineering Collection, vol. 20, pp. 49–54 (in Russian).
  9. Tseytlin, I. Z. (1974). Raschet polzuchesti diafragm parovykh turbin [Calculation of creep of diaphragms of steam turbines]. Energomashinostroyeniye – Power Engineering, no. 12, pp. 6–11 (in Russian).
  10. Vinogradov, N. N. (1970). Issledovaniye polzuchesti naturnykh diafragm moshchnykh parovykh turbin [Study of creep of full-scale diaphragms of powerful steam turbines]. Teplovyye napryazheniya v elementakh konstruktsiy – Thermal stresses in structural elements, iss. 10, pp. 35–43 (in Russian).
  11. Malinin, N. N. (1975). Prikladnaya teoriya plastichnosti i polzuchesti [Applied theory of plasticity and creep]. Moscow: Mashinostroyeniye, 400 p. (in Russian).
  12. (1986). Turbiny parovyye statsionarnyye. Normy rascheta na prochnost korpusov tsilindrov i klapanov [Stationary steam turbines. Standards for calculating the strength of cylinder and valve bodies]: OST 108.020.132-85. Moscow: Ministry of Power Engineering, 31 p. (in Russian).
  13. Shul’zhenko, N. G., Zaitsev, B. F., Asaenok, A. V., Grishin, N. N., & Gubskii, A. N. (2016). Creep of steam-turbine diaphragm under variable loading conditions. Strength of Materials, vol. 48, iss. 6, pp. 733–739. https://doi.org/10.1007/s11223-017-9819-y.
  14. Shabrov, N. N. & Znamenskaya, M. V. (1991). Raschet diafragmy parovoy turbiny metodom superelementov [Calculation of the steam turbine diaphragm by the superelement method]. Trudy Tsentralnogo kotloturbinnogo instituta – Proceedings of the Central Boiler and Turbine Institute, no. 265, pp. 43–47 (in Russian).
  15. Shulzhenko, N. G., Asaenok, A. V., Zaitsev, B. F., Grishin, N. N., & Gubskii, A. N. (2012). Creep analysis of steam turbine welded diaphragm. Strength of Materials, vol. 44, iss. 4, pp. 419–428. https://doi.org/10.1007/s11223-012-9396-z.
  16. Shakhmatov, M. V. & Shakhmatov, D. M. (2009). Prochnost mekhanicheski neodnorodnykh svarnykh soyedineniy [Strength of mechanically inhomogeneous welded joints]. Chelyabinsk: TSPS Svarka i kontrol Ltd, 223 p. (in Russian).
  17. Vinokurov, V. A., Kurkin, S. A., & Nikolayev, G. A. (1996). Svarnyye konstruktsii. Mekhanika razrusheniya i kriterii rabotosposobnosti [Welded constructions. Fracture mechanics and performance criteria]. Moscow: Mashinostroyeniye, 576 p. (in Russian).
  18. (1987). Diafragmy parovykh statsionarnykh turbin. Raschety na prochnost [Diaphragms of stationary steam turbines. Strength calculations]: OST 108.210.01-86. Moscow: Ministry of Power Engineering, NPO Central Boiler and Turbine Institute, 39 p. (in Russian).

 

Received 22 March 2021

Published 30 June 2021