Subsea pipeline tie-ins and repair have been in focus for 20 years. The first welding operation offshore with PRS (Pipeline Repair System), a tie-in of a 28-inch pipeline, was performed in 1988 at Oseberg A in the North Sea. Since then, about 74 offshore hyperbaric welded tie-ins have been performed. Welded pipeline tie-ins and repairs offshore have so far taken place in water depths accessible to divers using either manual or semi-automated welding methods. Existing equipment is capable of undertaking pipeline repair welds over the diver accessible range and such systems have successfully been employed at depths to ~250m (820ft). Statoil has due to risk for divers health decided to introduce a diving depth limit of 180 m.
Other diving limits, defined by other companies, exist but diving deeper than 300 m is seldom done. New oil and gas fields and pipelines on the Norwegian continental shelf and world wide are very often located in areas beyond diving depth. All previous tie-ins and repairs have been done using the tungsten inert gas (TIG) welding process, which under the prevailing circumstances is not suitable for fully remote control operations.
Today, there is need for a fully remote-controlled welding technique that can be developed for use in deep waters, where diver support is impossible. So far, there is no existing technology for larger pipe diameters; smaller pipes are joined by mechanical couplings, but the technique is far too expensive for larger pipes.
