Carbon capture, utilisation and storage (CCUS) and hydrogen are low-carbon technologies with the potential to reduce net greenhouse gas (GHG) emissions and contribute to reaching the goal of net zero.

While CCUS in particular remains contested for its potential contribution to maintaining the status quo of fossil fuel dominance, net zero pathways developed by organisations such as the Intergovernmental Panel on Climate Change (IPCC) and the International Energy Agency (IEA) show the need for both technologies and their increased deployment by and beyond 2050. In particular, this applies to the decarbonisation of hard-to-abate sectors such as industry.

Political willingness to support the drive towards technically- and commercially-viable CCUS and hydrogen deployment in the industrial sector has wavered over the years, but has been revived with examples such as the European Union’s Net-Zero Industry Act and the US’ Inflation Reduction Act.

One aspect often overlooked in discussions on the viability of CCUS and hydrogen is the infrastructure required to deploy these technologies. In most cases this includes pipelines, as they are the primary means of transportation. As an extensive network of oil and gas pipelines already exist, stakeholders involved in developing CCUS and hydrogen projects including various associations and regulators such as the North Sea Transition Authority (NSTA) have identified the potential of repurposing existing assets. Ideally, repurposed existing infrastructure can support the energy transition in multiple ways.

Building infrastructure is a costly endeavour, so repurposing existing oil and gas assets such as pipelines could reduce the costs associated with low-carbon projects. This means that repurposing can help to address the significant hurdle of economic viability of such projects compared to unabated technologies. According to the IEA, adapting an existing natural gas pipeline for hydrogen service can reduce investment costs for a pipeline by 50–80%. In an extensive transition that may cost up to £60bn/y in the UK alone, repurposing can therefore generate essential savings.

Additionally, repurposing infrastructure can accelerate the speed of the transition. This is particularly crucial as long lead times for project development and implementation can impede progress. Currently, CCUS projects require an average lead time of five to seven years to reach commissioning, increasing to seven to 10 years for the development of storage projects, according to the Carbon Capture and Storage Association (CCSA).

Repurposing infrastructure also carries the potential of reducing overall waste and carbon emissions. The vast network of associated infrastructure also faces accelerated retirement as decarbonisation policies take effect. By repurposing this infrastructure, stranded assets could be minimised, again reducing overall infrastructure costs of a project and contributing to a reduction in carbon emissions.

Technical challenges 
For both CCUS and hydrogen projects, it is vital to demonstrate that repurposing infrastructure can be performed without compromising safety.

The challenges that need to be considered and managed in order to ensure safe operation range from fracture control, managing corrosion and risks of releases, minimising potential effects on people and the environment, and ensuring continued stakeholder consent, according to DNV. For CCUS, the technical considerations that enable safe and efficient CO₂ transport include ensuring that the CO₂ stream transported in the pipelines does not impact the pipeline’s structural integrity.

This includes decisions about phase and pipeline location. For example, the gas phase CO₂ stream could be transported within an onshore section of the pipeline and dense (liquid) phase CO₂ stream in the offshore section. This decision must be made taking into account the thermodynamic properties of the fluid, ensuring that corrosion phases do not form, as well as the proximity of habitation close to the pipeline route.

An essential puzzle piece in safe repurposing is controlling the potential of pipeline fractures. Like pipelines transporting natural gas, CO₂ pipelines are susceptible to long-running fractures, also known as propagating fractures. These can destroy a long length of pipeline, so must be mitigated and managed for new and repurposed pipelines alike. Mitigations in a repurposed pipeline that help arrest a fracture in natural gas service, such as pipe body toughness, pipe wall thickness and/or material grade, are more challenging to meet for CO₂ service. This potentially means that other aspects of a repurposed system must be adapted, such as operational conditions or the use of mechanical crack arrestors.

An essential puzzle piece in safe repurposing is controlling the potential of pipeline fractures. Like pipelines transporting natural gas, CO₂ pipelines are susceptible to long-running fractures, also known as propagating fractures. These can destroy a long length of pipeline, so must be mitigated and managed for new and repurposed pipelines alike.

Similarly, for hydrogen service, the physical phenomenon of hydrogen embrittlement is a significant technical hurdle when repurposing pipelines. This refers to the degradation of mechanical properties due to the diffusion of atomic hydrogen into the metal, which interact with flaws at an atomic level. Effects include a reduction in strength, ductility, fracture toughness and an increase in fatigue crack growth rates.

Hydrogen potentially requires higher operating pressures compared to natural gas, given its lower calorific value, necessitating modifications to pipeline infrastructure to ensure its safe transport. Additionally, hydrogen purity requirements demand stringent measures to prevent contamination, as even trace amounts of other elements and compounds can significantly affect end-user applications, particularly in sectors like electronics and fuel cells. It’s no wonder that ensuring that existing infrastructure is compatible with hydrogen’s unique properties remains a critical technical consideration in repurposing efforts.

To mitigate hydrogen’s effects, inspection, maintenance and integrity requirements must be adjusted. Therefore, thorough risk assessment and ongoing integrity management are essential to minimise potential hazards.

Industrial approaches to safe repurposing of infrastructure
The Energy Institute’s Technical + Innovation department collaborates with a range of representatives from industry, academia, regulators and wider stakeholders to address technical challenges and help accelerate the energy transition. With more than 30 new projects each year, the EI’s Technical Committees (including CCUS and Hydrogen) as well as Working Groups develop a raft of guidelines and comprehensive resources. Both the CCUS and Hydrogen Committees have published guidance about the repurposing of infrastructure.

The CCUS Committee’s Repurposing and design guidelines for carbon dioxide pipelines aims to support industry by outlining the required data and assessments needed to demonstrate that a pipeline and associated assets are fit for repurposing for CO₂ service. The guideline outlines industry CO₂ pipeline codes, recommended practices and standards. It also highlights the lack of dedicated standards and guidance when it comes to repurposing of pipelines from hydrocarbon to CO₂ service.

At the heart of the document is guidance on detailed technical assessments required for CO₂ pipelines such as on flow assurance, corrosion protection and pipeline mechanical design. In particular, the document points out the main differences between fossil fuel and CO₂ service. A specific focus is on fracture control; the document outlines an approach to repurposing specifically considering the prevention of running ductile fracture.

The EI’s Hydrogen Committee has published an initial Literature review of asset integrity in repurposing natural gas infrastructure for hydrogen. It identifies sector-specific information as well as knowledge gaps relating to materials, operations, failure modes, inspection, maintenance, degradation and management. A second literature review further expands on this by pinpointing ongoing or forthcoming technical initiatives, joint industry projects (JIPs) and research relevant to hydrogen transport asset integrity, with the intention of assessing what ongoing workstreams would fill the knowledge gaps. The report highlights the need for management of change to quantify some of these unknowns and offers a way forward that is asset-specific.

Management of change
The latter project demonstrates management of change (MoC) for repurposing of existing natural gas infrastructure for hydrogen applications. The objective is to ensure that this transition can be achieved without compromising public safety or damaging plant infrastructure. Initially, it was recognised that a lack of available information or data hampered work to draft comprehensive MoC guidance. The literature reviews intend to address those issues.

In transitioning to transporting hydrogen, operators are likely to need to conduct asset-specific analyses to determine safe working limits based on varying conditions and material properties across the network. These analyses are essential for input into risk-based inspection programmes and selection of suitable inspection technologies. Asset-specific risk-analyses will need to be performed as part of the MoC process to comprehensively assess the potential risks associated with the transition to hydrogen.

• Further reading: ‘A revolution for green hydrogen production?’. Learn more about the advantages of generating hydrogen from biogas.
• Find out more about a North Sea project to convert gas pipelines to hydrogen that has won technical approval.