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2021 №09 (05) DOI of Article
10.37434/as2021.09.06
2021 №09 (07)

Automatic Welding 2021 #09
Avtomaticheskaya Svarka (Automatic Welding), #9, 2021, pp. 38-42

Structural condition and damage of metal of welded joints of steam pipelines

V.V. Dmitrik, I.V. Kasyanenko, Yu.M. Latynin
National Technical University «Kharkiv Polytechnic Institute». 2 Kyrpychova Str., 61002, Kharkiv, Ukraine. E-mail: igorkasyanen@gmail.com

In the process of long-term operation (over 270 thou. h) in the conditions of creep and fatigue, the initial structure of welded joints of steels 15Kh1М1F and 12Kh1МF of HPP steam pipelines turns into a ferrite-carbide mixture. The rate of mentioned structural-phase transformation in the areas of the heat-aff ected-zone, as well as in the weld metal and in the base metal of welded joints diff ers signifi cantly. At the same time, the α-phase grains are softened, segregation precipitations are formed, carbide reactions and coagulation of carbides of the fi rst group take place, new carbides of the II group are formed (VC, Mo2C). The presence of softening areas in the heat-aff ected-zone of welded joints facilitates an increase in their deformation capacity. For example, the level of deformation of the area of partial recrystallization in the HAZ is higher than the similar level in other areas, as well as the weld metal and the base metal. It was established that the presence of the corresponding structural-phase state, deformation and softening of the metal of welded joints in general accelerates its damage by the mechanism of fatigue and creep. At the stage of transition from the II to the III stages of deformation, the damage to the metal of welded joints by the abovementioned mechanisms grows, which requires appropriate repairs. The carried out investigations allow revealing which structural-phase state namely corresponds to the transitional stage of deformation, as well as the level of deformation of the metal of welded joints and the state of its softening. 8 Ref., 7 Fig.
Keywords: welded joints of steam pipelines, creep, fatigue, heat-aff ected-zone, deformation, area of partial recrystallization


Received: 06.07.2021

References

1. Dmitrik, V.V., Glushko, A.V., Sirenko, T.O. (2017) Structural changes in the metal of welded joints of steam pipelines. The Paton Welding J., 7, 15-18. https://doi.org/10.15407/tpwj2017.07.03
2. Dmitrik, V.V., Glushko, A.V., Syrenko, T.A., Grigorenko S.G. (2018) Peculiarities of welded joints weakening in operating steam pipelines. Ibid., 5, 7-11. https://doi.org/10.15407/tpwj2018.05.02
3. Glushko, A.V., Dmitrik, V.V., Syrenko, T.A. (2018) Creep of welded joints of steam pipelines. Metallofi zika. Noveyshie Tekhnologii, 40, 683-700 [in Russian].
4. Khromchenko, F.A. (2002) Life of welded joints of steam pipelines. Мosсow, Mashinostroenie [in Russian].
5. (1995) IGD 34.17.401-95: Control and extension of the service life of metal equipment of thermal power plants. Typical instructions. Pt 1. Boilers, turbines and pipelines with a pressure of 9 MPa and higher [in Ukrainian].
6. (1998) SROLP 0.00-1.11-98: Rules of construction and safe operation of steam and hot water pipelines [in Ukrainian].
7. Dmytryk, V.V., Tsariuk, A.K., Harashchenko, O.S., Syrenko, T.O. (2020) Structural condition and fatigue damageability of welded joints of steam pipelines. The Paton Welding J., 6, 14-19. https://doi.org/10.37434/tpwj2020.06.03
8. Feltam, P. (1978). Deformation and strength of metals. Мosсow, Metallurgiya [in Russian].

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