The race has been on to create a mechanically-lined pipe that can be installed using reel-lay. Now it’s been done, and the method is taking off. Elaine Maslin provides an overview.
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BUTTING’s own-brand BuBi-Pipe in manufacturing. Photos from Butting. |
An increasing amount of corrosive substances are flowing through today’s subsea oil and gas pipelines, generating greater demand for corrosion-resistant materials.
To overcome the corrosion caused by such substances, corrosion resistant alloy (CRA) pipes (e.g. 316L, 904L, 825, or 625), metallurgically bonded clad pipes and mechanically lined pipes have been developed.
Subsea pipeline installation firms have been paying particular attention to how to manufacture, handle and install mechanically lined pipe by reel-lay – a method which would speed up installation times, as well as reduce materials costs. Installation by reel lay also enables contractors to lay longer sections of pipe, without having to weld large numbers of stands while offshore.
Mechanically lined pipe uses a combination of carbon steel outer pipe with a corrosion resistant alloy liner. The CRA liner is hydraulically assembled inside the carbon steel pipe, creating an interference stress between the carbon steel host pipe and the CRA pipe.
According to German pipe manufacturer BUTTING, which produces BuBi-Pipe, its own-brand mechanically lined pipe, the benefits of mechanically lined pipe over clad pipe is a 40-60% reduction in cost, depending on diameter and grade.
BUTTING’s BuBi-Pipe is a bimetallic pipe, which is telescopically aligned inside a pipe in carbon-manganese material and the tight mechanical bond between the pipes is achieved in a hydroforming facility.
BUTTING has been producing its own-brand BuBi-Pipe since June 1994, including for offshore use, as pipelines, riser pipes and SCR-pipes. But, until its use on the Guará-Lula NE project, by Subsea 7, offshore Brazil, in 2013, no one had deployed mechanically lined pipe – either from BUTTING or anywhere else – by reel lay, largely due to some of the issues around internal buckling of the liner during the laying process.
“Most projects have been installed by S-Lay, followed by Bundle,” says Brigitte Blechinger, Senior Sales Manager Oil & Gas at BUTTING. “Reeling seems to be coming up as a new method, as it is a cost effective solution compared to the others. Further, a shorter installation period is required and the majority of welding and inspection can be done onshore. Vessels are flexible and they can quickly be mobilized to global locations. In the end reeling has a positive cost and time impact on offshore development projects.”
Reels can be loaded at a spoolbase, where the pipe is spooled onto reels on the vessel, or, as with EMAS AMC’s Lewek Constellation, they can be taken on the reel to the pipelay vessel on a barge and be lifted in to place, replacing empty spools, without the vessel having to return to a spoolbase.
According to Brigitte Blechinger, manufacturing output of BUTTING’s BuBi-Pipe is also 3-4 times higher than output for clad pipes, further speeding up the process – BUTTING can produce a lot more BuBi-Pipes within a certain time frame than e. g. metallurgically clad pipes.
“The manufacturing process used is economically superior and strictest tolerances can be gained, using specialized production for both carbon steel and CRA material,” Blechinger says. “In addition, variable combinations of materials can be used, freeing the manufacturer from as many raw material supply constraints.”
The move to develop mechanically lined pipe for reel-lay began in the late 2000s, led by Subsea 7 and Technip.
BUTTING has been working with Subsea 7 to qualify its BuBi-Pipe for flowlines and low-fatigue riser applications by reel lay and since 2008 exclusively on BuBi-Pipe with 3mm liner. BuBi-Pipe ranges from 4in to 28in. outside diameter and up to 24m-long, produced in accordance with API, ASTM, DNV or ISO and suitable for S-Lay, J-Lay, bundle or reel-lay.
Subsea 7 was the first to install mechanically lined pipe by reel-lay on Petrobras’ pre-salt Guará-Lula NE project in Brazil’s Santos Basin, using the Seven Oceans pipelay vessel. Some 70km of BuBi-Pipe SCRs were installed by reel-lay in 2100m water depth. Subsea 7 is already also lining up its next job, on Statoil’s Aasta Hansteen development offshore Norway for which BUTTING has already delivered the BuBi-Pipe. For the development in the Norwegian Sea about 19km of 12in BuBi-Pipe will be installed by reel-lay.
Subsea 7 says the main challenge associated with BuBi-Pipe by reeling was to demonstrate that the inner pipe, or liner, did not suffer from local buckling during the spooling process. “Equally important was to demonstrate the integrity of the weld joining the liner pipe to the outer pipe at the ends of each joint or seal weld,” said Subsea 7 last year [2014].
Technip’s first reel lay with mechanically lined pipe is due to be on Deep Gulf Energy’s Kodiak project in the Gulf of Mexico. The job is also BUTTING’s next BuBi-Pipe project for reel lay, under a contract with Tenaris. Technip is the installation contractor with installation expected in 2015.
Kodiak is in Mississippi Canyon Blocks 727 and 771, in the Gulf of Mexico, in 1472-1710m water depth. The project is a subsea tie-back to the Devils Tower Truss Spar in Mississippi Canyon Block 773. To withstand Kodiak field’s high-temperature and pressure, as well as extremely corrosive production fluids, mechanically lined pipe was chosen. It will be installed using the Deep Blue deepwater pipelay and subsea construction vessel.
“Generally, BuBi-Pipes are qualified for reeling by DNV GL and other accreditation societies and in case of e. g. Guará-Lula by our customers Subsea 7 and Petrobras,” Blechinger said. Subsea 7 is also further developing the uses for BuBi pipe, specifically around its potential to be used for fatigue-sensitive applications, such as steel catenary risers.
With an order backlog for BuBi-Pipe for reel lay in place, BUTTING says demand for the pipe is growing. “Currently a lot of projects are tendering mechanically lined pipes where installation shall be made by reeling,” Blechinger says.
Technip, which installed the first reeled steel catenary riser in 2001, has said its design, endorsed by DNV in 2011, allows reel-lay at atmospheric pressure. Technip also had a fitness for service certificate from DNV in August 2012 for a dynamic mechanically lined SCR for reel-lay.
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