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Registration Number

0224U002201, 0120U101658 , R & D reports

Title

Theoretical and practical basis for increasing the reliability of operation of TPPs

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Head

Dmitrik Vitaliy V., Доктор технічних наук

Registration Date

07-02-2024

Organization

National Technical University "Kharkiv Polytechnic Institute"

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 A significant number of power units of the thermal power plants of Ukraine have used up their park resources. Their total working time under conditions of creep and fatigue is about 250-300 thousand hours. With regard to the working time, the structural phase state and properties of the metal of the power equipment have undergone significant changes. Identification of such features is considered expedient for assessing the reliability and residual resource of the equipment, including steam pipelines and their welded joints. Operating conditions of steam pipelines and elements of their systems (temperature 500-585° C, pressure 20-25 MPa) cause structural and phase changes, creep and damage of their metal to a greater extent than steam pipelines, their welded joints are damaged, which is facilitated by structural, chemical and mechanical inhomogeneity of the metal of welded joints. The given inhomogeneity in the process of increasing the service life of welded joints, for example after 270 thousand hours, receives additional development and is strengthened. In the process of long-term working of welded joints of steam pipes in their metal, physico-chemical processes take place with varying intensity: self-diffusion of chromium, molybdenum and vanadium alloying elements occurs in α-phase crystals; carbide reactions M3C→M7C3→M23C6 take place, carbides M7C3 and M23C6 coagulate; new VC and Mo2 carbides are formed; the phase composition of M23C6 carbide changes; the integrity of dislocations changes; dislocations move by the mechanism of sliding and creep. The above processes provide a gradual transformation of the original structure into a ferrite-carbide mixture, which significantly contributes to the damage of welded joints. The considered features of degradation are more typical for the metal of welded joints than for the main metal of steam pipelines, which is facilitated by the original structure and chemical heterogeneity of welded joints.

Product Description

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Harashchenko Olena S.
Нlushko Alona V.
Kasianenko Ihor V.

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2024-02-07