Is Steel Grade Important When Converting a Pipeline to Hydrogen?
Proceedings Publication Date
Neil Gallon
Neil Gallon, Daniel Sandana, Ollie Burkinshaw
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Hydrogen is currently the hot topic in the pipeline industry, with a lot of research underway looking at the impact of the energy transition on pipeline integrity. It is fair to say that the amount of work being undertaken is a reflection of the number of unknowns associated with the conversion of existing (natural) gas pipelines to hydrogen transport. That said, one of the few topics where a general industry consensus exists is in the assumption that higher-grade materials are less suitable for hydrogen transport than lower-grade materials. This restriction has some significant effects on the economic feasibility of construction or conversion, because the benefits of higher-strength steels are very difficult to realise when a significant portion of the existing pipeline system consists of higher grades. The restriction also does not address the difference between actual and specified minimum yield strength. Finally, it introduces the coercive enforcement of potentially undue conservatism regarding the use of higher-strength line pipe grades.

This paper will challenge the basis of the assumption that low-strength steels (e.g., L360/X52) are automatically safe for hydrogen repurposing while higher-grade materials are inevitably less suitable for hydrogen service. It will review the mechanisms that affect steel suitability in hydrogen and demonstrate that a single nominal grade of steel can include a wide variety of different microstructures, toughness levels and strengths. A review will be presented of literature and industry data indicating that higher-grade materials can be shown to be more suitable for hydrogen service than lower-grade materials. A holistic integrity management approach will be outlined, recognising the central importance of the response of material properties to hydrogen and offering a robust alternative to relying only on the nominal grade of a pipe to judge hydrogen readiness.

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