Hydrogen is a simple, clean fuel that has potential to support an increase in the use of renewable energy in Australia’s energy markets. For this reason, development of hydrogen has strong government support, including the Council of Australian Governments (COAG) national hydrogen strategy and in the recently stated ambition of reducing costs below $2/kg – #H2under2.
A significant factor that will affect the uptake of hydrogen is the infrastructure that will be used to store and transport it. Hydrogen provides good energy density compared with batteries and other storage technology, but low energy density compared with other fuels (at least, in its gaseous form). If hydrogen is going to underwrite the most ambitious targets for sustainable, decarbonised energy use, a very large hydrogen inventory will be required.
This problem is solved neatly if we can use existing gas infrastructure. According to Energy Networks Australia (ENA), if Australia’s gas network were filled with hydrogen it could store the equivalent of six billion Tesla Powerwalls1.
As Gas Vision 2050 (prepared by ENA, APGA, GAMAA, and other industry partners) is realised, hydrogen could emerge as a dominant force in the Australian energy mix. As hydrogen use increases, usage of existing infrastructure will immediately be required to accept blending of hydrogen with natural gas.
This is already progressing in Australian low-pressure distribution networks, with two pilot plants planning to inject hydrogen in the imminent future. In the medium- to long-term, there will be a greater volume of hydrogen available. Hydrogen hubs will develop, and pure hydrogen pipelines will be required.
Research to support the use of existing infrastructure in future fuel service is both a high priority and a core competency of the Future Fuels CRC. Hydrogen blending is relatively straightforward in the low-pressure gas distribution infrastructure; however, in the case of high-pressure ring mains and transmission pipelines, there is one prominent issue that requires further research and development.
Hydrogen embrittlement
‘Embrittlement’ is a reduction in material toughness, which means a reduction in the ability of a material to resist cracking. Hydrogen is known to contribute to material cracking, and available evidence suggests it can contribute to every step of the process – crack formation, stable crack growth, rupture (when a crack in a pipe is large enough that the pipe ‘bursts’), rapid crack growth and crack arrest (when the crack stops growing).
Stable crack growth mechanisms include fatigue, which is gradual growth of a crack accumulating from repeated load cycles. Acceleration of fatigue is a significant effect of hydrogen and could limit the use of pipelines for storage. Using a pipeline for storage means having a ‘pack and deplete’ operation strategy, which involves large cycling of internal pressure.
Currently, the main standard available to design for hydrogen service is ASME B31.12. Under this standard, the options available for pipeline design are to: design for low stress (keep the ‘design factor’ below 0.5 and lower for high strength steels) or to do extensive material testing (which currently no Australian laboratories are able to do) and to control weld hardness (which is not current industry practice for natural gas pipelines).
Satisfying these would pose significant cost hurdles to using hydrogen in high-pressure pipelines; however, the requirements of ASME B31.12 do not reflect the severity of hydrogen embrittlement but rather uncertainty around the magnitude of its effect.
This uncertainty is due to scarcity of data and the difficulty of testing in a hydrogen environment. The significance of hydrogen’s impact on toughness will depend on the amount of hydrogen that permeates into the pipeline steel and the stress in the steel.
This means the lower the pressure is, the less severe the effect will be. Embrittlement will also be less severe for lower blend concentrations. Future Fuels CRC is undertaking a series of research projects that will obtain material data to answer this key question: how much are the material toughness and fatigue life reduced in hydrogen gas service?
In currently approved projects, the University of Queensland will undertake laboratory testing of steels using electrochemical hydrogen charging, while the University of Wollongong is developing a laboratory for gaseous hydrogen charging and work has commenced to scope out full-scale fracture initiation testing of hydrogen-filled pipe, to validate the laboratory-scale results.
All these programs will maximise their value by using a common set of steel samples provided by the pipeline industry, covering a range of steel types and vintages. There is cause to be optimistic that hydrogen embrittlement will be manageable in the transmission sector, and that ASME B31.12 will be found to be over-conservative.
There are other mechanisms – such as ‘sour’ raw gas service and cathodic over-protection events – that also cause hydrogen to permeate into steels. Both of these mechanisms cause higher levels of hydrogen (in the steel) than transportation of gaseous hydrogen does but are already effectively managed by pipeline operators and designers.
The pipeline industry can only safely proceed with the introduction of hydrogen in high pressure pipeline systems, however, with more data. The Future Fuels CRC research efforts in this area aim to provide needed evidence to quantify the effect of hydrogen embrittlement.
This will enable industry to reduce conservatism in hydrogen-service design and will reduce barriers for the use of high-pressure pipelines to efficiently transport and store hydrogen in the future.
This article was featured in the October 2020 edition of The Australian Pipeliner. To view the magazine on your PC, Mac, tablet or mobile device, click here.
For more information visit the Future Fuels CRC website.
If you have news you would like featured in The Australian Pipeliner contact Managing Editor David Convery at dconvery@gs-press.com.au
