Session: 09-05 Part IV Integrity management of hydrogen pipelines

Submission Number: 186187

Are Gas Pipelines Ready for Oxygen-Inhibited Hydrogen? Lessons Beyond the Laboratory 

Pipeline network operators are exploring net-zero energy transition strategies, including repurposing natural gas transmission infrastructure for hydrogen. A primary integrity concern associated with this strategy is hydrogen embrittlement, which affects fracture toughness and fatigue life. A series of laboratory studies, including new and innovative approaches for testing in hydrogen, have demonstrated that the controlled addition of gaseous inhibitors, including oxygen at parts-per-million levels (≈100–1000 ppm) can inhibit hydrogen embrittlement mechanisms. However, translating these proof-of-concept findings into actual pipeline operating conditions within a nationally critical transmission system, such as the United Kingdom’s approximately 5000-mile National Transmission System (NTS), requires consideration of a broader set of system-level challenges beyond material performance alone.

These challenges can be grouped into five key categories: gas mixing and network dynamics; oxygen consumption and persistence; operational and infrastructure considerations; safety and risk management; and regulatory, commercial, and stakeholder constraints. Gas mixing and network dynamics determine whether trace oxygen can be reliably transported and distributed under realistic operating conditions, including transient flows, low-flow regions, stagnant sections, and dead legs, without stratification or local depletion. Oxygen consumption and persistence must also be understood, as corrosion and surface reactions may progressively reduce concentration along the network, necessitating top-up strategies. Operational and infrastructure considerations include the practicalities of large-scale oxygen production, transportation, storage, metered delivery, continuous concentration measurement, and integration with existing transmission system operations.

Safety and risk management considerations address the impact of oxygen on flammability envelopes, minimum oxygen content thresholds, the potential consequences of localised enrichment during abnormal or upset conditions, and overall system reliability. Regulatory, commercial, and stakeholder constraints may present significant barriers; in particular, existing gas quality specifications and contractual oxygen limits for sensitive end users such as underground gas storage facilities and gas turbine plants which may require renegotiation or exemption pathways.

To address these challenges systematically, a Technology Readiness Level (TRL) framework is applied to evaluate the maturity of oxygen inhibition as a mitigation strategy, identifying development milestones, validation requirements, and gaps between laboratory research and operational deployment. This paper outlines the network-scale challenges an Operator must contend with following laboratory-scale demonstrations. It includes the design of further testing requirements, such as laboratory tests, full-scale burst tests, flow loops, and operational trials; the selection of the optimal oxygen production and transportation methodology; effectiveness/quality monitoring; injection equipment design; and reliability. The results of early stakeholder engagement are also reported.  Alternative gas inhibitors to oxygen are also proposed, each with strengths and weaknesses.

Presenting Author: Nicholas Molnar, Penspen

Presenting Author Biography: Nick Molnar is currently the Head of Asset Integrity – East Region for Penspen, a leading global energy consultancy firm. His career spans over 13 years, starting in Calgary, Alberta as a Pipeline Engineering EIT for a consulting company. He then took a role at Union Gas (now Enbridge Gas Distribution) in Ontario as Pipeline Engineer, and held progressively senior roles in Engineering, Operations and Pipeline Integrity. At the end of his tenure, Nick was responsible for managing the Transmission Integrity Management Program as well as developing emerging threat management programs for SCC, geohazards and internal corrosion.

After 10 years at Enbridge he relocated to Abu Dhabi, UAE as a Senior Pipeline Integrity Engineer working in Penspen's Centre of Engineering Excellence, before recently stepping into the Head of Asset Integrity role for the East Region, including MEA and KSA. He has offered his skillset across a broad range of integrity services including fitness for service assessments, hydrogen repurposing studies, and in-line inspection support. He is also a contributing project member for the PDAM joint industry project.

Nick is a licensed Professional Engineer (P.Eng) in Canada and holds a Bachelor’s Degree in Mechanical Engineering from Carleton University in Ottawa.

Authors:

Nicholas Molnar Penspen
Christopher Wood Penspen Ltd
Kousseyla Hamadi National Gas Transmission
Robert Best National Gas Transmission