PSI - Issue 59

Myroslava Hredil et al. / Procedia Structural Integrity 59 (2024) 151–157 Myroslava Hredil, Oleksandr Tsyrulnyk, Ivan Shtoyko, Olha Zvirko / Structural Integrity Procedia (2024)

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1. Introduction The Ukrainian gas transmission network is one of the biggest in Europe, capable of transporting vast amounts of natural gas. Nowadays, following the worldwide trend for green hydrogen production, the authorities are considering the prospects of using the Ukrainian gas transmission network to transport hydrogen or its mixtures with natural gas. Sukurova et al. (2023) pointed out that the European Union (EU) countries consider Ukraine a potential hydrogen supplier. They are interested in establishing a large-scale production and further exporting hydrogen to Western Europe to meet European energy demand. In addition, Haeseldonckx and D’haeseleer (2007 ), Ogden et al. (2018), Neacsa et al. (2022), and Vries et al. (2017) stated that the use of a mixture of natural gas and hydrogen in local gas distribution networks is promising. However, Messaoudani et al. (2016), Maestre et al. (2021), and Laureys et al. (2022) forewarned that comprehensive investigations are needed to repurpose that infrastructure effectively. Some crucial issues have to be solved taking into account the operating time of the pipeline system and its current technical state, specified by Nykyforchyn et al. (2022). It is assumed by Campari et al. (2023) that transporting hydrogen through pipelines could initiate or intensify hydrogenation of a pipe followed by a variety of bad consequences for the pipeline integrity. In particular, hydrogen may influence the motion of dislocations (Andreikiv and Hembara (2022)), thus changing the plastic strain rate and, therefore, contributing to hydrogen embrittlement (HE) of a metal. Moreover, Tsyrul’nyk et al. (2018), Hredil et al. (2022) showed that it might reduce the resistance of pipeline steels to hydrogen-assisted cracking as one of the main characteristics of their workability under the action of a hydrogenating environment. Natural gas, transported through main pipelines under pressure up to 7.5 MPa, is suggested to have a low humidity. However, in real conditions of pipeline operation, gas flux contains noticeable amounts of water which can either condense on the top of the pipe’s inner surface (due to a significant difference in temperatures in side and outside the pipe, for example, in winter) initiating top-of-the line corrosion (Vitse et al. (2003), Seiersten et al. (2021), Al-Moubaraki and Obot (2021)) or it can accumulate on the bottom of the pipe. This water contains dissolved corrosive species inducing electrochemical corrosion. Trautmann et al. (2020) concluded that the presence of electrolyte promotes hydrogen uptake from gaseous hydrogen at ambient temperature. Our previous investigations by Nykyforchyn et al. (2020) showed that hydrogen can form as a result of these corrosion processes, causing hydrogenation of the pipe. It is well known from Kharchenko et al. (2016), Shtoyko et al. (2019), Nemchuk et al. (2019), Nykyforchyn et al. (2019), Zvirko et al. (2021), Krechkovska et al. (2022) that hydrogen worsens the serviceability of structural steels causing degradation of their mechanical and electrochemical properties. A potential risk of hydrogen transportation thus requires strict monitoring of the equipment exposed to hydrogen, safety enhancements and the development of preventive measures against hydrogen impact on structural steels. Holbrook et al. (2012) and Barrera et al. (2018) discussed possible ways to mitigate or prevent hydrogen embrittlement, particularly by applying coatings to minimize hydrogen access to the ste el’s surface and chemical modification of the hydrogen-containing environment with inhibitors, such as oxygen O 2 , carbon monoxide CO, sulfur dioxide SO 2 . Zhao et al. (2023) have recently confirmed the prospects of using CO as a potential H-absorption inhibitor, however, further research is needed to implement this technology. The paper aims at revealing a possible effect of gaseous hydrogen on corrosion and hydrogenation of the inner surface of the pipe when transporting hydrogen or its mixtures with natural gas. 2. Materials and methods Low-alloy steel API 5L X70, widely used for pipeline production, has been tested in the as-received state and after its 37-year operation. Chemical compositions for each steel state are presented in the Table.

Table. Chemical composition of the steel in the as-received and operated states.

Content, wt. % C

Steel state

Mn

Si

S

Fe

As-received

0.12 0.11

1.62 1.42

0.34 0.26

0.04 0.04

Balance

Operated