Hydrogen transport: conversion & replacement - [Ask the Experts] Questions Answered
Originally published by Pipeline Technology Journal, June 2022.*
What do you think about hydrogen usage in the heating sector (supply network, house installation, gas boilers)?
Shane Finneran: In the effort to reduce carbon emissions, the implementation of hydrogen enriched natural gas within the mains gas supply is gaining popularity the world over. Hydrogen, like natural gas, is flammable and can be burned for energy, but it doesn't release carbon dioxide during combustion which makes it a compelling alternative for gas utilities looking to continue business-as-usual while meeting decarbonization goals or requirements.
To this end, blended hydrogen and natural gas for fueling residential and many commercial heating appliances, has been extensively and successfully tested for efficacy, safety, and sustainability with little to no modifications required. The future, however, may see a need for a higher hydrogen blend, or even pure hydrogen fuel. This remains largely unexplored, and further research and testing is required to assess the necessary modifications (e.g. orifice change, etc.) to allow for interchangeability.
When we talk about re-purposing existing pipelines for transportation of hydrogen, are they usable as they are, or do they need an internal lining, make changes to compressors, or other aspects that could be expensive?
Jan Fredrik Helgaker: When re-purposing existing pipelines for transportation of hydrogen, the challenges, and impacts that hydrogen brings need to be understood and accounted for. For steel pipelines, components, and associated welds, it is well recognized that hydrogen may promote hydrogen embrittlement which could have an adverse effect on the pipeline system integrity and hence impact both the design and operation of such pipeline systems.
Hydrogen piping and pipeline systems can be designed according to ASME B31.12 Hydrogen Piping and Pipeline Code. For typical onshore pipeline steel grades, existing pipelines can be re-purposed according to ASME B31.12, which was originally developed for onshore pipelines, given that some mitigation measures are taken, and certain materials testing is performed. To better understand the required CAPEX, a detailed study is required.
For offshore pipelines, there is currently on-going work to develop standards for safe and reliable design, construction, and operation of hydrogen pipelines.
Shane Finneran: Additionally, assessing the readiness of any particular existing pipeline for conversion to hydrogen requires a detailed asset specific assessment. DNV is currently leading many such studies, and is in process of developing industry guidance on this subject to publish with a number of industry partners.
In short, the readiness for hydrogen will depend on the material and methods of construction for the existing pipeline (including specific base material properties, weld properties, etc.) as well as the condition and operating parameters.
Where materials are susceptible to hydrogen embrittlement, the effects and impacts of hydrogen embrittlement will depend on the initial material properties, operating stress, and the hydrogen partial pressure. This can be a complicated asset specific analysis, but we are finding that some systems may be compatible nearly as-is, with minimal modifications, while some may require modification or upgrading of certain components, whereas other systems may not be feasibly converted without significant upgrades and costs associated.
How can we gauge if our existing network is suitable for hydrogen from a material standpoint?
Jan Fredrik Helgaker: Re-qualification of existing pipelines shall comply with the same requirements as for pipelines designed specifically for transportation of hydrogen. ASME B31.12 provides guidance to assess whether existing pipelines networks are suitable for transportation of hydrogen from a materials standpoint.
Guidelines for offshore hydrogen pipelines are currently under development, as discussed above. A practical issue will be to obtain more information regarding the performance of vintage steel grades in hydrogen gas environments.
Shane Finneran: Network compatibility will require an asset specific assessment, considering a variety of factors, from the materials in the network (and records of those materials/properties) to the individual components along the network.
As noted, ASME B31.12 provides guidance for assessment of material compatibility. However, B31.12 does offer two options for assessment, a prescriptive based approach which clearly defines compatibility (and incompatible) materials, as well as a performance based methodology, which considers more of the network specific parameters to assess compatibility where they may not meet the stricter prescriptive limits.
What risk factors should we account for when switching to hydrogen?
Jan Fredrik Helgaker: Factors which should be accounted for when switching to hydrogen include, but are not limited to:
- Hydrogen impact on pipeline materials properties
- Safety issues related to hydrogen
- Pipeline condition
- Physical properties of hydrogen
- Operating conditions
- Remaining lifetime
How much blending with natural gas is safe to start with? How does one decide the blending percent?
Jan Fredrik Helgaker: The safe blending percentage will likely be a combination of several factors, including pressure, partial pressure of hydrogen, materials properties, and operational conditions, and should be determined on a case-to-case basis. Some natural gas specifications allow some limited amount of hydrogen without any limitations (up to 1% - 2%), so such hydrogen amount is assumed to be acceptable for the natural gas transmission.
ASME B31.12 is applicable for hydrogen amount ≥10%. Hydrogen below 10% is supposed to be covered by the existing codes for natural gas. However, hydrogen, even at small fractions and low partial pressure, can have negative effect on pipeline steel when operating under certain conditions. This needs to be assessed.
Shane Finneran: There is no blanket acceptance value defined as ‘safe for all systems’, as hydrogen compatibility is a product of numerous factors mentioned above. Therefore, an asset specific assessment is necessary, either following the existing approach defined in B31.12 or similar guidance, or by performing a detailed performance-based assessment.
Testing has shown some materials to be susceptible to hydrogen embrittlement, even at low partial pressures. However, the impact of this embrittlement depends largely on the original properties of the material, the current condition of the pipe or equipment, and the planned operating conditions. For example, a pipe having high initial toughness, few crack-like flaws, and operating at low stress, may be compatible even with some level of embrittlement. However, a different system at higher stress and poor or unknown initial toughness may have little margin for embrittlement before it is considered incompatible. Hence the need for asset specific assessment.
What should be checked in existing pipelines before blending hydrogen with natural gas?
Jan Fredrik Helgaker: When blending hydrogen with natural gas you are changing the content of the transported fluid. Hence, the pipeline will have to be re-purposed for use with hydrogen, as discussed above. Risk factors when switching to hydrogen shall be assessed.
In addition to the current condition of the infrastructure, the remaining expected lifetime, and the effect of hydrogen on asset integrity, safety and the potential revenue are to be assessed as well. Further, existing technical specifications, policies and operating procedures will need evaluation and possibly adaptation before the pipeline system is hydrogen ready.
The Experts
Jan Fredrik Helgaker, Senior Engineer, DNV
Jan Fredrik Helgaker is working with flow assurance and pipeline operations. He has an MSc in Applied Physics and a Ph.D. in Fluid Mechanics from the Norwegian University of Science and Technology. He is currently the project manager of the H2Pipe JIP, a joint industry project developing standards for offshore hydrogen pipelines.
Shane Finneran, Principal Engineer and Head of Section for the Hydrogen and Modeling Services section, DNV
Shane Finneran is a licensed Professional Engineer (PE). He has been with DNV for over 14 years overseeing the computational modeling services for all applications from design, Fitness-for-Service, and forensic analyses. His current role as Hydrogen Lead involves overseeing and developing onshore projects related to hydrogen and low carbon fuels, including conversion of existing oil and gas infrastructure to transport pure or blended hydrogen in efforts to decarbonize utility networks.
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*To view the original article, visit Pipeline Technology Journal