Giannis, S; Salmeron-Perez, N; Spetsieris, N (2023) Challenges in Realising Composite Liquid Hydrogen Cryogenic Storage: A Materials and Standards Perspective. NPL Report. MAT 114

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Abstract

Hydrogen is an energy vector that has great potential to provide a viable solution for meeting climate challenges. A key element in an end-to-end hydrogen supply chain is storage that can be as a compressed gas or as a cryogenic liquid. Only high pressure compressed gaseous hydrogen offers a similar energy density to cryogenic liquid hydrogen at moderately low pressures. The latter offers the possibility of reducing the storage container mass and volume, however, requires the hydrogen to be cooled to a temperature of approximately -253 °C.

The transportation industry (air and land in particular) is keen in utilising hydrogen as fuel as it does not produce any carbon emissions during combustion. However, for commercially viable, large commercial aircraft the hydrogen needs to be stored cryogenically as a liquid. Similarly in heavy-duty land vehicle applications, storing hydrogen onboard the vehicle as a cryogenic liquid can increase the range of the vehicle by a factor of 1.5 to 2 compared to the hydrogen gas unit being replaced.

However, there are barriers associated with realising liquid hydrogen cryogenic storage, particularly when utilising lightweight polymer composite materials essential for applications like on-board vehicle storage.

Specifically, whilst at the top-end of the regulatory framework (Regulations) existing regulations for pressure equipment safety and carriage of dangerous goods and use of transportable pressure equipment, provide the legal framework for cryogenic liquid storage, the available technical standards are prescriptive and at present allow mainly for metallic materials to be utilised for the storage container. Having said that, available standards developed via the International Standards Organisation Technical Committees ‘ISO/TC 220 Cryogenic vessels’ and ‘ISO/TC 58 Gas cylinders’ provide a satisfactory framework that can be expanded to other materials and systems.

In the case of storage of liquid hydrogen as fuel onboard a vehicle, there is a gap left at the top of the regulatory framework with the recent repealing of Regulation (EC) 79/2009 and the narrower scope of UN/ECE Regulation No. 134 and several components critical for a hydrogen-powered vehicles were left with no applicable type-approval framework. As far as technical standards are concerned, ‘ISO/TC 197 Hydrogen technologies’ has published a document , ISO 13985:2006, which specifies the construction requirements for refillable fuel tanks for liquid hydrogen used in land vehicles, as well as the test methods required to ensure that a reasonable level of protection from loss of life and property resulting from fire and explosion is provided. The standard allows for the use of non-metallic materials, however further developments in measurement standards at cryogenic temperatures are required for this to be fully realised.

There is a significant body of primarily academic literature referring to the cryogenic performance of composite materials that has been produced over the last 30 years or so. The main class of polymer matrix composites studied have been thermoset based, although some thermoplastic systems have been covered. Materials have been characterised down to temperatures as low as 4K and properties including mechanical (tension, compression, flexure, fracture toughness etc.), thermal (thermal expansion, thermal conductivity) and physical (permeability characteristics) have been measured. Reported material properties show a high level of variability which can be largely attributed to the lack of validated measurement methods for composites at cryogenic temperatures.

A half-day virtual workshop was organised by the National Physical Laboratory focusing on cryogenic materials, properties and standards. The comprehensive discussion revealed that in addition to gaps in regulations, technical and measurement standards, there are also significant gaps in the measurement infrastructure itself. It was thought that temperature verification approaches, uncertainty of strain measurement systems as well as suitability of existing jigs and fittings being key for realising validated and trusted material properties data. The workshop attendees agreed that an Advisory Group to bring the community together would be extremely beneficial and could act as the springboard for the establishment of a future Joint Industry Project (JIP) to tackle generic cryogenic measurement issues across a range of industry sectors and applications.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MAT 114
Subjects:	Advanced Materials > Composites
Divisions:	Materials and Mechanical Metrology
Identification number/DOI:	10.47120/npl.MAT114
Last Modified:	03 Feb 2023 15:22
URI:	https://eprintspublications.npl.co.uk/id/eprint/9635