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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the operational stability of the energy system of Ukraine under green hydrogen transportation” addresses these issues, and the obtained results will be approved by IPP-CENTRE LLC and implemented in the case of successful approbation. It is a two-year project that began in August 2023 and is funded by the National Research Foundation of Ukraine under the c all “Science for the Recovery of Ukraine in the War and Post - War Periods” . 2. Objectives The project aims to develop a methodology for assessing the serviceability of pipe steels of existing natural gas pipelines in the case of hydrogen transportation, based on novel criteria of reaching the critical state for metal and operability criteria, taking into account the current structural and mechanical state and their hydrogenation. The actual state of gas transmission pipelines in Ukraine will be taken into account based on the physical and mechanical properties of operated steels and their compliance with the tasks of transporting hydrogen or its mixture with natural gas. The planned research activities entail:  Investigating the microstructure, the physical and mechanical properties and the fracture mechanism of as delivered and post-operated pipeline steels in order to evaluate the regularities of their operational degradation;  Determining the resistance to hydrogen embrittlement of pipe steels depending on their structural and mechanical state and hydrogen permeation conditions;  Development of a method of prolonged exposure of loaded specimens in hydrogen under pressure;  Development and validation of a method for obtaining and analysing true tensile diagrams of steels, taking into account their structural and mechanical state and hydrogen charging conditions;  Evidence of the correlation between hydrogen concentration and bulk material properties of gas pipeline steels;  Development and validation of new criteria for ensuring the serviceability of gas pipeline steels in the case of hydrogen transportation by pipelines. 3. Background Such a prospect of repurposing pipelines for hydrogen transportation can increase the risk of structural integrity loss. There are several key challenges to repurposing:  Operational degradation of steels of long-term operated gas pipelines, including their damaging, deterioration of corrosion and mechanical properties, pre-existing cracks, and so on;  Potentially harmful influence of transported hydrogen on the mechanical properties of pipeline steels, including fracture toughness as a key parameter. A significant part of natural gas pipelines in Ukraine is near the end of their design life. In-service degradation of steels usually implies embrittlement and deterioration of mechanical and corrosion properties (Gredil (2008), Okipnyi et al. (2020), Nykyforchyn et al. (2018, 2021b), Zvirko et al. (2021, 2022), and others). Therefore, it is advisable to assess the degradation degree of pipeline steels on different pipe branches as well as the susceptibility of post-operated metal to hydrogen action. Based on previous research results (Zvirko et al. (2021, 2022)), two main stages of degradation are distinguished – strain ageing and in-bulk material damage accumulation. It was demonstrated by Nykyforchyn et al. (2020) and Zvirko et al. (2021, 2022) that hydrogen charging of steel during operation plays an important role in accelerating degradation at both stages. The pipe can be hydrogenated from inside and outside the pipe due to electrochemical corrosion. Moreover, it can also evolve due to the dissociation of molecular hydrogen at gaseous hydrogen transportation, especially on the fresh surface of steel formed under deformation, for example, under cyclic loading. Therefore, long-term mutual action of corrosion, hydrogen charging and working stresses during operation promotes the formation, evolution and accumulation of damages in steel at the nano- and microscales. Hydrogen, on the one hand, intensifies the development of damages and accelerates the metal degradation, and on the other hand – facilitates crack initiation and propagation in the damaged metal. Once entered the metal, atomic hydrogen interacts