Hyperbaric tie-in and repair welding of pipelines at the seabed is performed as full penetration TIG butt welding. Variations in pipe end fit-ups make the root pass welding challenging with relatively low robustness. The present investigation concerns with exploiting copper backing to increase the root pass welding robustness. Initial welding experiments are performed at 15.4bara ambient pressure with the TIG process based on the technique and procedures used by the Statoil PRS (Pipeline Repair System). The results demonstrate that significant increase in robustness can be achieved, which can be an important contribution in the strive for cost reductions. Mechanical testing and microstructure examination of the weld metal revealed no negative influence of the copper backing. Initial MIG root pass welding experiments at 11bara are also performed as a part of the development of hyperbaric MIG butt welding of pipelines. These results are promising and demonstrate that by exploiting copper backing can robust procedures be developed, which opens for deep water MIG butt welding in the future.

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