The IEA predicts that repurposed natural gas pipelines will provide most capacity for long range transport of hydrogen by 2050. Design codes exist for new hydrogen pipelines, but at present no generally accepted guidance exists for converting an existing hydrocarbon pipeline to hydrogen service. Many international pipeline standards include hydrogen in their scope but provide no specific integrity or materials requirements for H2 and as the result the ASME B31.12 standard has been used as a template for many feasibility assessments.
ASME B31.12 includes different mandatory and non-mandatory requirements related to composition, hardness, strength, and toughness to assure long-term integrity in hydrogen service. Before a natural gas pipeline is filled with hydrogen, the challenges and impact that hydrogen brings need to be understood and accounted for a given pipeline. A particular challenge for converting natural gas to hydrogen pipelines is to demonstrate that fracture and fatigue control can be maintained with the new fluids. B31.12 allows two methods, a prescriptive option and a performance-based option which allows a higher operating pressure to be achieved. However, the performance-based option requires fracture toughness testing of the pipe and welds in hydrogen.
Current conversion projects are now finding that some of the ASME B31.12 requirements may not be appropriate for existing pipeline systems. In this paper we will explore these issues, will present DNVs approach to pipeline conversion and show how non-compliance with the ASME requirements might be mitigated.