Hydrogen

In the previous edition of this column, we looked at the opportunities for non-destructive evaluation (NDE) in the carbon capture, use and storage (CCUS) sector. This month, we are looking at a sector that often goes hand-in-hand with CCUS: hydrogen.

Unlike CCUS, hydrogen has been used in industry for several decades as a chemical in its own right, not for decarbonisation purposes. In fact, the majority of hydrogen currently used is produced using a process called ‘steam methane reforming’, which emits carbon dioxide into the atmosphere. In 2025, global demand for hydrogen surpassed 100 million tonnes^[1]. Efforts are underway to produce this hydrogen using alternative ‘low carbon’ production methods. Furthermore, there are several new applications of hydrogen being considered and adopted. Hydrogen is a potential alternative for fossil fuels in various applications, including off-grid power (for example replacing diesel generators) and for transportation where electrification is not feasible (for example some large, long-distance land vehicles). Hydrogen is a long-term energy storage solution that could be used to store surplus renewable energy to bridge seasonal gaps between peak supply and high demands.

Some readers might have heard of different colours of hydrogen. Hydrogen produced using steam methane reforming is referred to as ‘grey’ hydrogen – and if the resultant carbon dioxide is captured, this is referred to as ‘blue’ hydrogen. Hydrogen produced from the electrolysis of water, with electricity from renewable sources, is referred to as ‘green’ hydrogen. Sometimes the ‘hydrogen rainbow’ is not used and instead the carbon intensity of the hydrogen production method is used to distinguish between types of hydrogen instead, as is the case in the UK Low Carbon Hydrogen Standard^[2].

The UK government has ambitious targets for low-carbon hydrogen production and considers hydrogen to present significant growth and economic opportunities across the UK^[3]. The Hydrogen Allocation Rounds (HARs) are a government funding mechanism to support low-carbon hydrogen production across the UK. The Round 1 projects (11) are mostly in the final planning stages and one is under construction; 27 projects have been shortlisted in Round 2; and Rounds 3 and 4 have been announced but not yet opened. Readers are encouraged to look out for the upcoming new UK Hydrogen Strategy to learn the latest.

There are material integrity and thus inspection challenges throughout the hydrogen sector (making it, moving it, using it), but storage and transmission of hydrogen is the most pertinent aspect when it comes to NDE, with various properties of hydrogen causing challenges. As well as the construction of purpose-built pipelines for transporting hydrogen, there are several initiatives to repurpose existing gas pipelines to transport hydrogen, for example Project Union in the UK. Therefore, it is essential that the specific properties of hydrogen and requirements for its safe storage are fully understood.

Hydrogen molecules are extremely small and prone to leaking through tiny gaps and seals. As well as material integrity, the field of hydrogen sensing and leak detection is therefore an extremely important one, with several research and development (R&D) projects and start-ups in this space. Hydrogen has a very low volumetric energy density (energy per unit of volume) so takes up a huge amount of space compared to natural gas under normal conditions. It is therefore often stored as a compressed gas or as a cryogenic liquid at very cold temperatures. This makes material integrity critical and also limits the use of certain in-service inspection techniques. Hydrogen pipelines are typically made of metals, with polymers and composite materials also options for low-pressure applications. Cryogenic hydrogen storage tanks are typically made of metal or composite materials, with the latter offering corrosion resistance and strength-to-weight benefits that are especially attractive for aerospace applications.

Hydrogen is responsible for the process ‘hydrogen embrittlement’^[4], where metal loses it strength and becomes brittle because hydrogen atoms enter the metal lattice structure. This can be hard to detect and can cause unexpected catastrophic failure at relatively low loads. Cracking associated with hydrogen embrittlement is referred to by different terms, including hydrogen-induced cracking (HIC) or hydrogen pressure-induced cracking (HPIC). Such defects are challenging to detect due to their small critical size and often complex geometries. Applicable NDE methods include wet fluorescent magnetic particle inspection for surface defects and advanced ultrasonic inspection for subsurface defects, for example work presented at this year’s European Conference on Non-Destructive Testing (ECNDT) by the University of Bristol on complex defect geometries^[5].

The excitement around hydrogen has perhaps waned in recent years and several projects have been delayed, but most agree that the hydrogen sector in the UK and globally will take off, bringing with it immense infrastructure that will need to be maintained and inspected.

This column will return in December with a look at NDE for another of the clean energy industries. Please send any comments or queries to editor Corinne Mackle at: ndtnews@bindt.org

References