PSI - Issue 42

Olha Zvirko et al. / Procedia Structural Integrity 42 (2022) 522–528 Olha Zvirko / Structural Integrity Procedia 00 (2022) 000 – 000

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1. Introduction Green hydrogen currently plays an important role as a decarbonized energy carrier. It can be transported cost effectively over long distances by pipelines. According to the European Hydrogen Backbone vision (https://gasforclimate2050.eu/ehb/), one of the steps of hydrogen transport infrastructure extension can be repurposing of existing gas infrastructure. This possibility was also analysed by Haeseldonckx D. and D’haeseleer (2007). Ukraine has joined European Hydrogen Backbone plan as hydrogen-focused initiative to have operating network of hydrogen pipelines in Europe by 2040. Ukrainian natural gas transmission pipelines can be served as transit route for hydrogen from Ukraine and south-east Europe to other European Union countries. The prospect of using the existing network of transit pipelines for the transportation of hydrogen or a mixture of hydrogen with natural gas exacerbates the issue of possible violation of their integrity due to a loss of mechanical strength caused by hydrogen embrittlement. Such failures are usually explosive and difficult to control. Important factors are the operational degradation of steels of long-term operated gas transmission pipelines, as it was shown by Zvirko et al. (2019), Marushchak et al. (2019), Okipnyi et al. (2020), Zvirko (2021), as well as the potentially negative impact of transported hydrogen on their mechanical properties. Influence of hydrogen on mechanical behaviour of steels in as-delivered state is investigated in numerous issues by Nykyforchyn and Student (2001), Depover et al. (2014), Mohtadi-Bonab and Eskandari (2017), Alvaro et al. (2019), Dadfarnia et al. (2019), Dmytrakh et al. (2019), Mohtadi-Bonab and Ghesmati-Kucheki (2019), and others. A significant part of gas transit pipelines is near the end of their design life, therefore in-service degradation of gas pipeline steels should be taken into account at assessment of possibility of usage of existing gas pipelines for hydrogen transport. Long-term operated pipeline steels can be more susceptible to hydrogen embrittlement. Nykyforchyn et al. (2022) demonstrated that preliminary electrolytic hydrogenation has almost no effect on the plasticity of the steel in the as-received state, however, significantly reduces it in the case of the operated metal. In-service degradation of pipeline steels implies deterioration of the mechanical properties and it is intensified by hydrogen charging of a metal due to corrosion, which is one of the most active and dangerous damage mechanisms, leading to hydrogen embrittlement. A significant decrease in brittle fracture resistance of pipeline steels during operation caused by hydrogen embrittlement, as demonstrated by Nykyforchyn et al. (2016), Zvirko et al. (2018, 2019, 2021), and others, increases pipeline failure risk. A well-known phenomenon associated with pipeline steels is that of the anisotropy of mechanical properties, as demonstrated by Joo et al. (2013), Masoumi et al. (2015), Beltran-Zuñiga et al. (2018), and others. However, understanding the anisotropy of pipeline steels during long-term operation is still under consideration. Moreover, the studies carried out by Zvirko et al. (2018) and Marushchak et al. (2019) showed that anisotropic mechanical behavior of pipeline steels is influenced by long-term operation. Therefore, to assess whether the existing gas transmission system can be used to safely transport green hydrogen or its mixture with natural gas and justify the conditions of its safe operation, it is necessary to estimate the current technical condition of its components, evaluate the impact of hydrogen on degraded metal and residual life of the network at transporting hydrogen. The research is aimed to the assessing anisotropic hydrogen embrittlement behaviour of pipeline steels considering their operational degradation. 2. Hydrogen assisted degradation of pipeline steels Pipeline steels are usually subjected to hydrogenation under operation. Natural gas transporting pipelines experience hydrogen charging of steels as it was analysed by Shipilov and May (2006), Ohaeri et al. (2018), Nykyforchyn et al. (2020), Zvirko (2021) and others. Hydrogenation of pipeline steel occurs due to the evolution of hydrogen from the service environments (residual moisture in natural gas) as a result of corrosion reactions on the inner surface of pipeline. There is also a possibility of hydrogenation of steel from the external surface of pipeline due to cathodic protection and external corrosion of underground pipelines at coating disbanding. Once entered the metal, atomic hydrogen interacts with the metal structure and may produce damages of various forms, such as hydrogen embrittlement, hydrogen induced cracking, blistering and delayed fracture. Hydrogen charging of a metal from inside and outside the pipe due to electrochemical corrosion leads to molecular hydrogen