PSI - Issue 59

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

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Keywords: pipeline steel, hydrogen energy, hydrogen transportation, gas pipeline, serviceability, degradation, hydrogen embrittlement, fracture.

1. Introduction Recently, the special attention of scientists and society, in general, has been drawn to the development of hydrogen energy, which is part of the policy on the issues of green energy transition, achieving climate neutrality, sustainable energy and strengthening energy security. Green hydrogen, along with renewable energy sources, is an important factor in the decarbonization of the global energy system. The European Green Deal was defined as one of the main strategic priorities of the European Union in 2019, even before the war in Ukraine. In May 2022, the European Commission presented a plan to rapidly reduce the consumption of oil and gas in general, as well as the introduction and use of “ green ” energy sources (REPowerEU). One of the urgent issues for the recovery of Ukraine in the war and post-war periods is ensuring its energy and economic security through the development of hydrogen energy. A radical modernization of the Ukrainian energy system, in particular, by green hydrogen production and the decarbonization of industry, will help overcome the global energy crisis, address environmental security issues and bring Ukraine to a new level of competitiveness. Therefore, the possibility of repurposing the existing network of transit gas pipelines of Ukraine to transport hydrogen or its mixture with natural gas to the countries of the European Union is considered today at the state level (Project of the Recovery Plan of Ukraine (2022), Draft Resolution of the Verkhovna Rada of Ukraine (2022)). In particular, this corresponds to the vision of the European Hydrogen Backbone (EHB) initiative, which Ukraine has joined. Using the gas transmission network for hydrogen transportation will also allow Ukraine to maintain its importance as a transit country of energy resources and contribute to increasing its energy security. Hydrogen transportation through gas pipelines is a complex problem (Haeseldonckx and D’haeseleer (2007), Nykyforchyn et al. (2021a), Pluvinage et al. (2021)), in which a crucial aspect is a possible violation of the pipe integrity due to the well-known negative effect of hydrogen on the mechanical properties of steels (Depover et al. (2014), Mohtadi-Bonab and Eskandari (2017), Boukortt et al. (2018), Alvaro et al. (2019), Dadfarnia et al. (2019), Dmytrakh et al. (2019), Zvirko (2022), Martin and Sofronis (2022), Campari et al. (2023), Hoschke et al. (2023) and others). The most important from this point is that hydrogen absorbed by the pipe wall from its internal surface reduces the resistance to brittle fracture (hydrogen embrittlement), which often causes a hardly predictable low energy failure of pipes. On the other side, the existing gas pipeline network in Ukraine has a long operation time, which leads to a significant reduction of the initial (before operation) properties of steel, most intensively the resistance to brittle fracture (Okipnyi et al. (2020), Nykyforchyn et al. (2018, 2021b), Zvirko (2021), Zvirko et al. (2021)). Accordingly, there is a high risk of integrity violation of operationally degraded pipes in the case of pipe hydrogenation from the inner surface during hydrogen transportation. The influence of soil environment on corrosion and stress corrosion cracking of the pipe outer surface in the case of insulating coating damage is usually considered (Voloshyn et al. (2015) , Kryzhanivs’kyi et al. (2019), Shtoyko et al. (2019)), whereas less attention is paid to the processes on the pipe inner surface, though they also can serve as factors of pipe integrity violation. In particular, natural gas transported by transit pipelines could be a source of pipe wall hydrogen charging from its internal surface due to the interaction of the pipe steel with condensed moisture which, albeit in a small amount, is always present in the transported gas and promotes corrosion on the internal pipe surface (Hredil and Tsyrulnyk (2010), Nykyforchyn et al. (2020)). As a result, the combined action of mechanical loads and hydrogen absorbed by a metal during long-term operation leads to degradation of pipeline steels and, therefore, deterioration of their initial properties. The operational degradation of the metal is primarily manifested in a decrease in resistance to brittle fracture, characterized most often by impact strength and fracture toughness. At the same time, the susceptibility to hydrogen embrittlement can also increase due to degradation (Zvirko (2022)), however, this aspect requires further research. To evaluate the prospects of using the existing gas transmission system of Ukraine for the transportation of hydrogen or its mixture with natural gas, it is necessary to analyse the current technical state of pipelines, estimate the impact of hydrogen on long-term operated metal, and substantiate the conditions of safe operation of the gas transmission network, taking into account the degradation of steel and hydrogen permeation during transportation. The project “Development of the methodology for assessing the serviceability of existing ga s pipelines to improve