This paper presents the repurposing of a 13 km legacy natural gas pipeline, operated by Hamburger Energienetze (HNE), for hydrogen transport. Originally built in 1973 with limited documentation, the pipeline runs from Moorburg to Leversen and is intended to connect both the emerging Hamburg Hydrogen Industry Grid and the Hamburg Green Hydrogen Hub to the national hydrogen infrastructure. Due to component limitations and gaps in historical data, the pipeline currently operates at 25 bar, with upgrades planned to enable hydrogen transmission at pressures of up to 70 bar.

To assess its suitability, HNE initiated a comprehensive project involving advanced Inline Inspection (ILI) services. The inspection program included cleaning, geometry and metal loss assessments, wall thickness measurements, and pipe grade determination. Extensive operational support was provided, including temporary trap installations, water batching, pump operations, hydrotesting, and treatment of wastewater to potable standards for regulatory compliance.

Key challenges included the lack of as-built data, multi-diameter pipeline sections (16–20”), and limited availability of compatible ILI tools. A custom gas-liquid batching strategy was developed to ensure effective propulsion of cleaning and inspection tools through variable geometry and restricted liquid storage at the receiving site. This paper details the customized batching setup, tool adaptations, and the validation procedures implemented to ensure reliable inspections under complex conditions.

The successful inspection campaign demonstrates the technical and operational feasibility of repurposing legacy, multi-diameter pipelines for hydrogen service. By addressing documentation gaps, validating material integrity, and confirming operational readiness, this project offers a replicable model for hydrogen infrastructure conversions.