Jan Olav Berge

Increased Robustness in Hyperbaric Welding of Subsea Pipelines by Introducing Copper Backing

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.Copyright

Deep Water Remote Pipeline Repair Using Welded Sleeve Technique

A technique for sub-sea pipeline repair using remote welding without the use of diverse has been developed. The technique involves the installation of an oversized pipe segment (sleeve) over the join by threading the pipe ends through the sleeve and performing a sub-sea fillet weld between the pipe and sleeve on each end. Current traditional welding techniques use pipe end butt to butt welding performed with the aid of divers in a habitat and are therefore depth limited. This technique is fully remote controlled and has been proven by simulating conditions in a hyperbaric chamber to work down to at least 2500 msw represented by 250 bar. This paper describes the technique, the structural considerations, and the equipment currently being built to perform this task, which will be in test in the second half of 2004 with sub-sea trials to follow. This paper compliments the paper IPC04-0630 “Diverless underwater GMA welding for pipeline repair using a fillet welded sleeve” [2], in which the welding procedural development is described. When compared with traditional welding or mechanical options (in particular for large pipes), the technique provides a much cheaper repair option.© 2004 ASME