Gaseous inhibitors: A comprehensive overview on mitigating hydrogen embrittlement in pipeline steels

Hydrogen transport via new and existing natural gas pipelines is promising in the shift to more renewable energy as an efficient energy carrier is of utmost importance due to the discrepancy in timing between production and use of the energy. However, the risk of hydrogen embrittlement (HE) in pipeline steels exposed to pure hydrogen gas poses a significant challenge. An emerging approach to this issue involves adding trace amounts of inhibitor gases to the hydrogen gas such as oxygen or carbon monoxide. This work provides a comprehensive overview of the mitigation of HE in pipeline steels using these gaseous additives. While there is limited literature on the hydrogen/surface interaction with pipeline steels, numerous studies focus on the surface science of individual gaseous additives on clean iron surfaces. This overview delves deeper into the surface chemistry of these inhibitor gases when exposed to clean iron surfaces, emphasizing the competitive interactions of these gases in the presence of pure hydrogen. Introducing gaseous inhibitors in pure hydrogen reduces hydrogen absorption by slowing down the adsorption kinetics of hydrogen gas. However, during longer exposure times, the presence of inhibitors does not prevent hydrogen from reaching an equilibrium condition. Hence, a continuous supply of these inhibitors is essential for sustained mitigation. Moreover, various factors, including the type of mechanical test, hydrogen pressure, and inhibitor gas concentration influence the effectiveness of the HE mitigation by gaseous inhibitors. A clear overview on these parameter influences for pipeline steels is given in this work. Preprint submitted to International Journal of Hydrogen Energy July 26, 2024.