Gas Inhibition as Technology to Mitigate Hydrogen Embrittlement Effects in Pipeline Steels

Abstract The assessment of transmission H2 pipelines requires consideration of H2 degradation on fracture toughness, ductility and fatigue life. Gas inhibition is a technology that could assist the integrity management of future pipelines. Oxygen has shown strong mitigating effects against H2 embrittlement in laboratory experiments. However, its effectiveness and transferability to real pipeline conditions must be understood before implementing this technology. National Gas Transmission in collaboration with ROSEN investigated the viability of oxygen inhibition. Our results showed that oxygen is effective inhibiting H2 embrittlement, increasing the fracture resistance JQ to in-air levels and reducing fatigue crack growth rates by up to an order of magnitude depending on grade, frequency and loading conditions. These findings were consistent with the observed transition from quasi-cleavage to ductile fracture surfaces. OLGA simulations identified the flow conditions necessary to maintain a safe and uniform oxygen concentration within the H2 gas stream in terms of flow velocity, mixing configurations, injection locations and intervals. A high-level model of oxygen consumption at the pipe wall was developed. If these results could be proven transferable to representative pipeline scales, the use of gas inhibitors could enable optimised network efficiency, reduce H2 adoption cost and facilitate the energy transition.