Fracture Mechanics at the Core of Hydrogen Pipelines Design: A Fracture Mechanics Approach in Design Life Prediction Based on Material Performance Measured in H2 Environment

Abstract Energy transition from the current fossil fuel-based economy to the renewable and sustainable technology era is one of the most important challenges of the future. Different promising options are being investigated, with particular attention to carbon capture & storage and hydrogen-based energy systems. Onshore and offshore pipelines have been identified as the primary mean for H2 transport and are now on stage for pipeline contractors. In the transportation of gaseous hydrogen one of the main issues is associated to hydrogen embrittlement (HE), in particular, gaseous hydrogen can dissociate into atomic hydrogen and permeate the metal matrix causing embrittlement of the steel, especially for high steel grades, manifested by a reduction in the material toughness and tensile ductility of the steel and an increased fatigue damage behavior. Hydrogen embrittlement reduces the steel’s tolerance to defects, making the pipeline more vulnerable to failure and potentially susceptible to worsen relevant failure modes. Therefore, for evaluating the effect of HE on metals, an Engineering Critical Assessment (ECA) using fracture mechanics principles can be used, to assess the consequences on fatigue resistance and fracture toughness properties for carbon steel pipelines in hydrogen service. The fracture mechanics assessment will also concur to the definition of the wall thickness, the fracture toughness and the fatigue testing requirements. The design by fracture and fatigue for hydrogen offshore pipelines is described in the paper along with a review of applicable standards and the ongoing research to fill the area of lack of evidence with respect to assumptions and material behavior, considering that for offshore pipeline no standard exists regulating hydrogen gas transport. Currently, a Joint Industry Project (JIP) from DNV (H2Pipe) is targeting the development of a DNV Recommended Practice within 2025 (Østby E., Thodla R., 2023 [1]). Also, EPRG guidelines aim to provide a recommended practice [2]. The paper addresses also the effect of transporting hydrogen on seam weld material and girth weld material providing the results in terms of fatigue and fracture resistance by design approach for new pipelines and by recommending interventions and remedial actions for existing lines to be retrofitted in hydrogen service. The work is part of the new qualification process required by an EPCI and T&I contractor to guarantee the integrity of the new or the repurposed pipelines for Hydrogen transport.