PSI - Issue 59

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Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2023) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2023) 000 – 000

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 59 (2024) 307–313

© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2023 Organizers © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2023 Organizers Abstract The structural features of heat-resistant steel 12Kh1MF after long-term operation in the stretched zone of the bend main steam pipeline of the thermal power plant are analysed. It was established that the degradation of steel due to long-term combined effects of stress, temperature, and hydrogenating environment was manifested in transforming the ferrite-pearlite structure into a ferrite-carbide one. Changes in the sizes of grains and carbides and their quantities in the body and along grain boundaries are analysed. It was shown that, regardless of the standard sizes, the size of grains and carbides, and their number along grain boundaries, were greatest near the outer surface of the pipe. This, firstly, created favorable conditions for creep, which occurred more easily in large-sized grains. Secondly, the cohesion of adjacent grains to weakened boundaries was reduced due to creep defects on them, formed on large carbides at the junctions of three grains and chains of medium-sized carbides between them. The larger carbides formed at the grain boundaries, the less cohesion between adjacent grains became. As a result of such damage to the steel at the microstructural level, while its tensile strength remains practically unchanged at all levels of analysis along the wall thickness of the stretched bending zone of the pipe, a significant decrease in the characteristics of ductility and resistance to brittle fracture of the steel near the outer surface of the pipe was revealed. © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2023 Organizers VII International Conference “In -service Damage of Materials: Diagnostics and Prediction ” (DMDP 2023) Structural aspects of the degradation of the bend stretched zone Ivan Tsybailo a , Halyna Krechkovska a,b, *, Oleksandra Student a , Lesya Svirska a a Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv, 79060, Ukraine b Lviv Polytechnic National University, 12, Stepana Bandery St, Lviv, 79013, Ukraine Abstract The structural features of heat-resistant steel 12Kh1MF after long-term operation in the stretched zone of the bend main steam pipeline of the thermal power plant are analysed. It was established that the degradation of steel due to long-term combined effects of stress, temperature, and hydrogenating environment was manifested in transforming the ferrite-pearlite structure into a ferrite-carbide one. Changes in the sizes of grains and carbides and their quantities in the body and along grain boundaries are analysed. It was shown that, regardless of the standard sizes, the size of grains and carbides, and their number along grain boundaries, were greatest near the outer surface of the pipe. This, firstly, created favorable conditions for creep, which occurred more easily in large-sized grains. Secondly, the cohesion of adjacent grains to weakened boundaries was reduced due to creep defects on them, formed on large carbides at the junctions of three grains and chains of medium-sized carbides between them. The larger carbides formed at the grain boundaries, the less cohesion between adjacent grains became. As a result of such damage to the steel at the microstructural level, while its tensile strength remains practically unchanged at all levels of analysis along the wall thickness of the stretched bending zone of the pipe, a significant decrease in the characteristics of ductility and resistance to brittle fracture of the steel near the outer surface of the pipe was revealed. VII International Conference “In -service Damage of Materials: Diagnostics and Prediction ” (DMDP 2023) Structural aspects of the degradation of the bend stretched zone Ivan Tsybailo a , Halyna Krechkovska a,b, *, Oleksandra Student a , Lesya Svirska a a Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv, 79060, Ukraine b Lviv Polytechnic National University, 12, Stepana Bandery St, Lviv, 79013, Ukraine Keywords: heat-resisted steel, creep, microstructure, structure peculiarities, steam pipeline bends, thermal power plants, long-term operation. Keywords: heat-resisted steel, creep, microstructure, structure peculiarities, steam pipeline bends, thermal power plants, long-term operation.

* Corresponding author. Tel.: +38-067-811-2543 E-mail address: krechkovskahalyna@gmail.com * Corresponding author. Tel.: +38-067-811-2543 E-mail address: krechkovskahalyna@gmail.com

2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2023 Organizers 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2023 Organizers

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