Over the last 10 years Statoil has developed subsea remote hot tap technology. The first use of the remote hot tap technology was the Tampen Link hot tap in 2008. The hot tap cutting operation itself was performed without the use of divers; however, the preparatory works including hyperbaric welding of the hot tap tee was performed with saturation divers. The world’s deepest hot tap operations on a pressurized pipeline were performed on the Ormen Lange field in the Norwegian Sea in August 2009. Two Hot Taps were conducted in a water depth of 860 meters on pre-installed tees. The development of the Pipeline Repair System Remote Hot Tap equipment is the result of targeted research and development effort and extensive qualification work over many years. The Retrofit Tee remote installation, welding and cutting equipment has now been employed as part of a production installation: the Åsgard Subsea Compression project to extend the Åsgard gas-field lifetime.
This paper describes the dry hyperbaric GMA weld procedure development and qualification performed in the laboratory, using the Corrosion Resistant Alloy consumable filler material Alloy 59, for the Remote Hot Tapping application using the Retrofit Tee. Specific attention was paid to areas of concern prior to performing the formal Weld Procedure Qualification work, particularly with regard to the effects of moisture and temperature upon the resultant weld quality. Weld procedures developed in the laboratory were successfully tested subsea in representative environments using the Remote Tee Welding Tool (RTWT) equipment in the Sognefjord, Norway, with offshore tests performed at 265 and 350msw in 2011. Further tests were performed in 2012 at 265msw and in the Retrofit Tee itself at 316msw in the Nedstrandfjord.
The hyperbaric GMA weld procedures have now been applied for the production application for the Åsgard Subsea Compression project, with the installation of a Retrofit Tee, associated valve module and gooseneck spool to enable a cost-effective modification to the existing pipeline network without interfering with ongoing production. The Retrofit Tee will be connected with a Subsea Compressor station to extend the gas-field lifetime.
This milestone represents the world’s first application of diverless dry hyperbaric GMA welding for a subsea production application.