As part of the Dutch energy transition, Gasunie and its subsidiary Hynetwork Services are developing a national hydrogen transport network that will connect five industrial clusters, neighboring countries and underground storage facilities. Approximately 75% of this network will consist of repurposed high-pressure natural gas pipelines, significantly reducing societal costs and environmental impact.

This paper presents Gasunie’s generic integrity assessment framework for evaluating the suitability of existing natural gas pipelines for safe and reliable hydrogen service. This framework is based on the Dutch standard “Requirements for pipeline systems” (NEN 3650 series), emphasizing external safety, integrity and lifecycle risk management of pipeline systems.

The degradation mechanism that needs to be assessed is hydrogen-enhanced fatigue crack growth in welded steel pipelines. For onshore pipelines longitudinal welds in the line pipes are the most critical for this mechanism, while girth and spiral welds are less susceptible to pressure-induced fatigue loading. Gasunie applies a defect growth of only 0.25 mm to derive conservative limits on the pressure fatigue loading.

For pipelines constructed before 1994, internal EMAT inspections will be conducted to verify the quality of the welds. The first EMAT inspection has been carried out successfully and detected anomalies are scheduled for investigation in field to understand the true nature of the anomalies and for comparison with the ILI dimensions.

In addition to the generic integrity assessment, a specific assessment will be conducted for each pipeline to address whether it is suitable for safe hydrogen transport according to the NEN standards. This assessment is the basis for a fit-for-service statement by the relevant Notified Body.

The paper concludes that, under defined conditions - and using Gasunie’s generic integrity assessment framework - existing pipelines can be safely repurposed for hydrogen transport. This approach enables a rapid, safe, and regulatory-compliant rollout of hydrogen infrastructure across The Netherlands.