PSI - Issue 36

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V. Zapukhlyak, Yu. Melnychenko , І . Оkipnyi et al. / Structural Integrity Procedia 00 (2021) 000 – 000

V. Zapukhlyak et al. / Procedia Structural Integrity 36 (2022) 378–385 © 2022 The Authors. Published by EL SEVIER 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 the conference Guest Editors Keywords: gas transportation system, incomplete loading, hydrogen embrittlement. 1. Introduction The gas-transport complex of Ukraine is one of the most complex systems of main pipelines in Eurasia. The basis of the gas-transport system is the system of trans-Ukrainian gas pipelines Soyuz, Urengoi-Pomary-Uzhgorod, and Progress to provide Western Europe consumers with Russian natural gas. The calculated capacity of the system taking into account season irregular gas consumption and hydraulic efficiency of gas pipelines is 152 billion м3 per year but it has not been reached for the whole period of the system operation. The highest capacity was 92,8% maximum in 1998. Till 2007 the system capacity was within the boundaries (80 – 90) % which was considered to be the normal load. Since 2007 the system capacity’s gradual decline was observed with a minimum capa city of 40.9% in 2014 and in 2020 the system capacity was 36,7%. Such a situation is considered as the incomplete load of the gas-transport system or the system operation under transit limited volumes conditions (Pirani, S., & Yafimava, K., (2016), Bouzarovski et al., (2018) , Tóth et al., (2020)). It is known that due to the GTS of Ukraine gas transit decrease it is necessary to switch off some of its components to provide its power-efficient operation: compressor stations, separate assemblies of compressor stations, separate sections, or the whole gas pipeline strings. Thus, some of the system facilities are unloaded which can be used for the transportation of products different from pure natural gas. In particular, some alternative ways of transportation of natural gas and hydrogen mixture have been considered recently, which can partially increase the system capacity. GTS use for hydrogen transportation deals with the development by GTSOU its own strategy on decarbonization based on the roadmap to transition to carbon-free economy till 2050 approved by the European Union – “Green Deal”. According to the strategy fossil , fuel-based energy systems should be replaced by renewable energy systems including – renewable gases, hydrogen in particular, which moves from the “industrial gases” category to “energy source materials” because its use is determined as one of the key ways of the EU decarbonization, so the demand for this compound will increase (Guandalini et al., 2018, Tlili et al., 2020). In 202 0 Gas Transmission System Operator of Ukraine joined “The European Clean Hydrogen Alliance” that will allow preparing the regulatory and technological basis for the implementation of joint projects on renewable gases transportation according to the “Energy Systems Integration Strategy”. Recently Operators of gas -transport systems of Ukraine, Germany, the Czech Republic, and Slovakia have announced the partnership to create a Central European hydrogen corridor that will supply hydrogen from Ukraine to the European Union (A European Green Deal, (2019), An EU Strategy for Energy System Integration, (2020), Abdalla et al., (2020)) As Ukraine has the required resources for “green hydrogen” production, and main pipelines are necessary to join the sectors of the energy industry, then the possibilities of renewable gases transportation and storage (hydrogen in particular) have been one of the urgent problems for Ukraine. While choosing certain objects or GTS sections for the hydrogen-natural gas mixture transportation these parameters are very important as their taking into account will allow continuing more efficient and reliable objects be used which require less economic and energy expenditure to conduct current or capital repair and their servicing. Thus, the purpose of the paper under discussion is the development of reliability assessment methods in gas-hydrogen mixture transportation by long-used pipeline systems. 2. Main gas pipelines hydrogenation and its physical-chemical pre-requisites The existing gas pipelines system has been used from 25 to 52 years on average depending on the date of its components introduction into operation. 64 % of all gas pipelines have exceeded their life cycle and are out of date (Kryzhanivsky and Nykyforchyn, (2011), Syrotiuk et al., (2018)). Therefore, in the current stage of the oil-gas complex of Ukraine development, the most important questions deal with providing reliable and continuous operation of the gas transmission system, especially under hydrogen-methane mixture transportation conditions. Any increase in pipelines operation reliability and service to provide their failure-free functioning can be achieved by continuously carrying out a complex of works, the most important of which are preventive and capital 379