HyTap-In-Service Welding: Tapping and Stoppling of a 66 Bar (950 Psi) Hydrogen Line

Abstract HyTap is a collaborative project undertaken by N.V. Nederlandse Gasunie and T.D. Williamson aimed at establishing safe working methods for in-service welding, hot tapping, and stoppling on hydrogen lines. The project involved a comprehensive analysis of materials and work methods to assess the implications of transitioning from natural gas to hydrogen. Based on these analyses, adapted methods were employed to conduct a full-scale experiment on a DN 500 (20″) 7.8 mm (0.307″) pipe. Throughout the operations, the pipe was pressurized with hydrogen at 99.5% purity and pressures ranging from 60 to 66 bar (870 to 957 psi). Equipment compatibility with hydrogen was carefully evaluated, leading to the use of sour service plugging heads for the isolation operation, while all other equipment remained consistent with natural gas conditions. Welding procedures were adjusted to limit the inside wall temperature to 700°C (1292°F). Of paramount importance was the inerting procedure, ensuring the absence of any explosive atmosphere at any stage of the operation, which proved to have the most significant impact. The HyTap experiment, conducted with these adaptations, successfully demonstrated that, with modifications to existing natural gas procedures, hydrogen lines can be welded, hot tapped, and isolated while in service.