While hydrogen is gaining momentum as a clean energy carrier in the context of energy transition, the absence of specific and dedicated design guidelines for the safe and efficient transportation of gaseous hydrogen via offshore pipeline presents a considerable obstacle. Notably, the existing experience primarily pertains to onshore applications, while offshore hydrogen pipelines pose unique and unaddressed design challenges. Different governing design limit states emerge for onshore pipelines, low-pressure shallow water pipelines (e.g., exporting green hydrogen from the offshore wind parks to shore) and high-pressure deepwater transmission pipelines (e.g., shipping hydrogen between supply and demand locations for green energy). To qualify the linepipe and welds for an offshore hydrogen project, a project specific material testing program would be imperative.
The rapid expansion of offshore wind industry is driving the development of subsea hydrogen pipeline systems. As produced energy volumes increase, industry focus is shifting from energy production (green electrons) to energy transportation and storage of gaseous hydrogen (green molecules). Large-scale offshore hydrogen production using offshore wind energy in the North Sea, located further than 100 km offshore, and collectively connected to European demand centres via an offshore hydrogen backbone system, is well suited for domestic European hydrogen production (Wingerden, 2023). These offshore wind developments are typically located on the continental shelf (shallow water) and a relatively low pressure is often sufficient to bring the hydrogen to shore via the hydrogen backbone. These pipelines impose different design requirements compared to the long-distance deepwater transmission pipeline systems, e.g., Gulf-to-Europe hydrogen pipeline (https://eepower.com/market-insights/european-firms-float-gulf-hydrogen-pipeline-concept/), which often demand a much higher design pressure and that transit rugged seabed where critical (dynamic) issues such as lateral buckling and large free spans need to be addressed.
In absence of applicable design guideline / Recommended Practice for hydrogen application as supplement to the existing offshore pipeline standard (e.g., DNV-ST-F101), building on our recent experience in hydrogen related projects, this paper provides an overview of the key design issues to be addressed, identifies and evaluates the difference between the shallow water and deepwater pipeline design for hydrogen transportation. This paper firstly provides a brief status review of the hydrogen effect on the pipeline material and the available design codes applicable for hydrogen pipelines. Then a generic overview is presented pertinent to offshore hydrogen pipeline design aspects. Utilizing a simplified fracture assessment for a deepwater pipeline, this study evaluates the potential impact of hydrogen embrittlement interconnecting the lab testing parameters and critical pipeline design scenarios. Brief insights into design considerations for shallow water hydrogen pipelines are also provided. This paper concludes by elaborating on several critical uncertainties related to offshore hydrogen pipeline design.
