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.
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.
HOW does it work
Shutting off an oil and gas flow to connect new pipes would entail significant costs and other complications. Therefore, hot-tapping has been performed for years on oil and gas pipelines in full operation: A ship designed for subsea operations lowers various machines and equipment down to the seabed.
What happens first is that a seabed excavator digs out the part of the pipe where the intervention will take place. The pipe’s protection, which could be concrete and epoxy coating, is then removed using a 1200 bar pressure pressure washer. The T-section is then lowered and bolted in place.
The welding robot then arrives and blows the branch pipe on the T-section dry using argon gas. The area is then dried and heated using induction-based heating coils. The robot then welds an internal seal weld between the inside of the branch pipe and the pipe to be hot-tapped. Then the isolation valve is installed. The tapping machine is lowered and drills at overpressure on the branch pipe side, extracts the drill and coupon through the valve and closes it. The new tie-in point is then ready for use and can be connected using one ofmany types of remotely operated tools available for pipe tie-ins.
WHAT is it
Remote hot-tapping of live pipelines at water depth of 2000 metres amounts to a revolution as regards utilising the network of oil and gas pipelines on the seabed. This applies particularly to new development projects that want to tie in to existing pipeline systems.
The method can also be used for converting oil-producing fields to gas production, introducing gas lift in oil fields, installing subsea compression plants and by-passing in the event of pipeline damage.
“This way of doing it has been both costly and risky, considering that people were doing the job on the seabed. The depth restriction has also been a considerable disadvantage. With the new technology, the entire operation is performed by remote control from a boat on the surface”, says project manager Kjell Edvard Apeland.
FUTURE potential
Hot tap technology is a technological breakthrough, and a door opener for developing marginal fields, as well as extending the lifetime of other fields.
The ability to connect anywhere on a pipeline, without stopping production, yields considerable flexibility and significant savings.
We can tie in anywhere, and we can better utilise the many thousand kilometres of pipeline already on the seabed. We can tie in new fields or new and improved production solutions to existing infrastructure where this is most optimal.
Facts about hot tap
The very first operation was performed in connection with preparations for Åsgard subsea gas compression in the Norwegian Sea last year. A tie-in point was welded on to the Åsgard B production flowline at a water depth of 265 metres. After ten days on the field, the hot-tap operation team on board the Technip-owned vessel Scandi Arctic could confirm success in the pioneering operations.
Hot tap: hot operations on the seabed
Statoil is behind the development of new technology that makes it possible to tie in to a pipe on the seabed, while it is in operation, without divers and without preparing the pipe for it.
Remotely Welded Retrofit Subsea Hot Tap Tee
A remote-controlled hot tap operation consists of a robot welding a T-piece on to the pipe, while gas is flowing through it. Afterwards a remote-controlled drilling machine will drill holes in the producing pipeline, with no effect on pressure and production.
The technology is this week awarded The OTC spotlight on technology-award during the Offshore Technology conference in Houston, US.The technology has been developed in Statoil’s pipeline technology environment at Killingøy in Haugesund. Norway’s expertise within tie-in and repair of pipelines is gathered here.
Application
Part of the gas export solution from the Johan Sverdrup field, the assignment will take about two years to complete. Work starts immediately.
“We’re pleased to award the contract to IKM Ocean Design,” says Svein Birger Thaule, executive vice president for asset management at Gassco.
“We believe this supplier will help us put in place a good and safe gas export solution for the field. The project will moreover be extremely important in ensuring gas deliveries for our Kårstø processing plant.”
Johan Sverdrup lies in the Norwegian North Sea, about 40 kilometres south of Grane, 65 kilometres north of Sleipner and 140 kilometres west of Stavanger.
Its gas will be exported to Kårstø via a new 18-inch pipeline, tied into the Statpipe rich-gas leg from Statfjord with the aid of hot tapping and connection to a 30-inch retrofit tee.
Installation will be diverless, using hot tapping equipment from the pipeline repair system (PRS) base in Haugesund.
Johan Sverdrup is one of the five largest oil fields on the Norwegian continental shelf. With estimated resources of 1.7 to three billion barrels, it will rank as one of Norway’s most important industrial projects over the next half-century.
The field is due to come on stream in December 2019, and to continue producing for 50 years.
Gassco will serve as the operator and technical manager of the 156-kilometre pipeline from the riser platform on Johan Sverdrup to the Statpipe rich-gas leg once the field comes on stream. Statoil is the development operator.
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