Subsea hydrogen pipelines represent a critical infrastructure component for offshore hydrogen production and transportation. The engineering challenges associated with these pipelines differ significantly from those of natural gas pipelines, particularly in material selection, corrosion protection, and leak detection. This article examines the technical considerations for subsea hydrogen pipelines and contrasts them with retrofitting existing natural gas pipelines for hydrogen service.

Material selection is a primary concern for subsea hydrogen pipelines due to hydrogen’s propensity to cause embrittlement in metals. High-strength steels such as X65 are commonly used for subsea applications, but hydrogen exposure can degrade their mechanical properties over time. To mitigate this, pipelines often incorporate hydrogen-resistant liners, such as those made from corrosion-resistant alloys (CRAs) or composite materials. These liners act as a barrier, preventing direct contact between hydrogen and the steel substrate. Additionally, weld zones require special attention, as they are more susceptible to hydrogen-induced cracking. Advanced welding techniques and post-weld heat treatments are employed to enhance durability.

Cathodic protection (CP) is another critical aspect of subsea hydrogen pipeline design. CP systems are used to prevent external corrosion caused by seawater exposure. For hydrogen pipelines, the CP system must be carefully calibrated to avoid over-protection, which can lead to hydrogen evolution at the pipeline surface and exacerbate embrittlement. Impressed current CP systems are typically preferred over sacrificial anodes for subsea applications due to their longer service life and adjustability. However, monitoring and maintenance are essential to ensure optimal performance.

Leak detection in subsea hydrogen pipelines is more challenging than in natural gas systems due to hydrogen’s smaller molecular size and higher diffusivity. Advanced monitoring systems, such as distributed fiber optic sensors, are often deployed to detect minute leaks in real time. These sensors can measure temperature and strain variations along the pipeline, providing early warning of potential failures. Additionally, subsea hydrogen pipelines are equipped with emergency shutdown systems that isolate sections of the pipeline in the event of a leak, minimizing environmental and safety risks.

Retrofitting existing natural gas pipelines for hydrogen transport presents a different set of challenges. While repurposing pipelines can reduce infrastructure costs, not all natural gas pipelines are suitable for hydrogen service. The primary concern is material compatibility, as older pipelines may not have been designed to resist hydrogen embrittlement. Pipeline operators must conduct thorough assessments, including non-destructive testing and finite element analysis, to evaluate the integrity of the pipeline under hydrogen exposure. In some cases, internal coatings or liners may be applied to improve compatibility, but this adds to the retrofit cost and complexity.

Another key difference lies in the operating pressure. Hydrogen pipelines typically operate at higher pressures than natural gas pipelines to achieve comparable energy throughput, given hydrogen’s lower energy density per unit volume. This requires upgrades to compression stations and pressure regulation systems. Additionally, the seals and gaskets used in natural gas pipelines may not be suitable for hydrogen, necessitating replacement with materials such as elastomers or thermoplastics that exhibit better hydrogen resistance.

The economic feasibility of retrofitting versus new construction depends on factors such as pipeline age, location, and intended hydrogen throughput. New subsea hydrogen pipelines offer the advantage of optimized design for hydrogen service but require significant capital investment. Retrofits may be more cost-effective in certain scenarios but come with technical limitations and uncertainties.

In summary, subsea hydrogen pipelines demand specialized engineering solutions to address material degradation, corrosion, and leak detection. While retrofitting natural gas pipelines is a potential pathway for hydrogen transport, it requires careful evaluation of material suitability and system compatibility. The choice between new construction and retrofitting depends on a balance of technical, economic, and operational considerations. As offshore hydrogen production scales up, advancements in pipeline technology will play a pivotal role in enabling safe and efficient hydrogen transportation.