The envisaged European hydrogen network considers several offshore hydrogen pipelines, either connecting offshore hydrogen-producing windparks to shore, or functioning as interconnectors between producing and consuming regions. In Europe, much activity is focused on the North Sea and Baltic Sea areas, and on the Mediterranean.
While the onshore hydrogen backbone is progressing, with both repurposing and new-built projects gathering pace, offshore hydrogen pipelines face several specific technical challenges, that are directly related to the offshore environment and offshore design practices.
Offshore pipelines differ significantly from onshore systems in the way they are designed, specified and constructed. They are typically designed for higher internal and external pressure, unburied, a high stress utilization, and dynamic internal and external loading.
The introduction of hydrogen as transported medium negatively affects material behaviour that is important for offshore application, i.e. the reduction of ductility which is required for spanning and buckling, reduction of fracture toughness, and the effect of hydrogen-accelerated fatigue crack growth. The latter interacts with the typical offshore dynamic design and is further complicated by high (residual) stress levels at the girth welds.
Establishing accurate limit states for offshore pipelines is more critical and urgent than for onshore pipelines, as the offshore mitigation measures and field repair are costly.
This paper discusses the key differences between onshore and offshore pipeline design for hydrogen and presents the current approach to address the specific challenges associated with hydrogen transportation in an offshore environment.