PSI - Issue 59

Olha Zvirko et al. / Procedia Structural Integrity 59 (2024) 120–124 Olha Zvirko / Structural Integrity Procedia 00 (2019) 000 – 000

123

4

with the metal structure and may produce damage of various forms, such as hydrogen embrittlement, hydrogen induced cracking, blistering and delayed fracture. Hydrogen can get trapped and transported at various types of defects in steels (Koyama et al. (2017)); therefore, microstructural susceptibility to hydrogen embrittlement is an important issue. The current state of the operated metal is most often assessed by changes in strength, plasticity, hardness and impact toughness because these characteristics are mainly regulated by standards. However, the strength, plasticity and hardness aren’t sufficiently sensitive to the operational d egradation of pipeline steels (Zvirko (2021), Nykyforchyn et al. (2021b)). Moreover, elongation in degraded steel can be higher than that in as-delivered one. This phenomenon can be explained by the development of dissipated damages in steel, which could be facilitated by hydrogen permeating into steel during long-term operation. Degraded steel is sensitive to cracking at specimen tension and then elongation will summarise real plastic deformation and multi-cracks opening. Therefore, to correctly assess its degradation degree, it is important to choose informative indicators which are sensitive to degradation. Thus, the most sensitive are fracture toughness and impact strength. It was demonstrated by Nykyforchyn et al. (2021b) that the 30-year operated steel is characterised by the highest value of elongation, and, at the same time, by the highest value of residual hydrogen concentration and the lowest value of fracture toughness. The anisotropy of mechanical properties of rolled pipeline steels is a well-known phenomenon (Shinohara et al. (2012), Joo et al. (2013), and others). However, long-term operated pipeline steels exhibit a higher degree of anisotropy compared with those in the as-delivered state. It was shown that long-term operation significantly enhances the anisotropy of hydrogen embrittlement susceptibility of pipeline steels (Zvirko (2022)). Moreover, hydrogen-assisted delamination in the pipe wall of a gas pipeline after long-term operation can be formed, as demonstrated by Kharchenko et al. (2016); it is mainly associated with the high intensity of hydrogen permeation from the internal surface of the pipe due to electrochemical corrosion and susceptible pipe steel microstructure to crack propagation in the rolling direction. 4. Summary Since its beginning in August 2023, the experiments under the project implementation have only just begun. The project “Development of the methodology for assessing the serviceability of existing gas pipelines to improve the operational stability of the energy syste m of Ukraine under green hydrogen transportation” is focused on the Ukrainian gas pipeline system, which represents an important energy infrastructure for the whole European continent. Nevertheless, the findings and results of the project would be extended to other pipelines with similar pipeline steels and operating conditions. Acknowledgements This project has received funding from the National Research Foundation of Ukraine under grant agreement No 162/0099 on August 01, 2023 (Project No 2022.01/0099). References Boukortt, H., Amara, M., Hadj Meliani, M., Bouledroua, O., Muthanna, B.G.N., Suleiman, R.K., Sorour, A.A., Pluvinage, G., 2018. Hydrogen embrittlement effect on the structural integrity of API 5L X52 steel pipeline. International Journal of Hydrogen Energy 43(42), 19615 – 19624. Campari, A., Ustolin, F., Alvaro, A., Paltrinieri, N., 2023. A review on hydrogen embrittlement and risk-based inspection of hydrogen technologies. International Journal of Hydrogen Energy 48(90), 35316 – 35346. Dadfarnia, M., Sofronis, P., Brouwer, J., Sosa, S., 2019. Assessment of resistance to fatigue crack growth of natural gas line pipe steels carrying gas mixed with hydrogen. International Journal of Hydrogen Energy 44(21), 10808 – 10822. Depover, T., Pérez Escobar, D., Wallaert, E., Zermout, Z., Verbeken, K., 2014. Effect of hydrogen charging on the mechanical properties of advanced high strength steels. International Journal of Hydrogen Energy 39(9), 4647 – 4656. Dmytrakh, I., Syrotyuk, A., Leshchak, R., 2019. Specific effects of hydrogen concentration on resistance to fracture of ferrite-pearlitic pipeline steels. Procedia Structural Integrity 16, 113 – 120. Alvaro, A., Wan, D., Olden, V., Barnoush, A., 2019. Hydrogen enhanced fatigue crack growth rates in a ferritic Fe- 3 wt%Si alloy and a X70 pipeline steel. Engineering Fracture Mechanics 219(1), 106641.