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self-contained laybarge to store pipe (with additional supply
barges, as required). Some laybarges use anchored mooring system
to mantain position, such as the Castoro 10 (at this time, owned by
Saipem); others use thrusters in the dynamically positioned
station-keeping mode.
Station-keeping is very important during pipelay, since
unexpected movement away from the planned laying route may
severely bend the pipeline either in a sagbend or in an overbend,
and the pipe may buckle or kink. The Allseas S-lay barge Lorelay
was first to apply dynamic positioning system to pipelay. The
McDermott DB50 (J-lay) is also dynamically positioned. Both
vessels use an integrated control system, which tracks the relative
position of the touchdown point and the vessel.
At the time of this writing, the Canyon Express flowlines in
the Gulf of Mexico achieved the world's deepest pipeline
installation. which took place in the Summer 2002 at a maximum
water depth of 7300 ft or 2225 m [de Reals, et a1 2003; Nogueira
and Stearns, 2003]. This successful project consisted of 110 miles
of 12 in. pipe, with a number of in-line structures, which had to
land at precise locations on the seabed, with tight tolerances.
Previously, the Blue Stream pipeline at 7050 ft (2150m)
water depth was installed across the Black Sea [McKeehan and
Kashunin, 1999] consisting of about 390 km of 24 in. pipe. The
installation contractor, Saipem, used the J-lay vessels during the
installation of these projects: the Canyon Express project was
installed with the vessel FDS and the Blue Stream project used the
semi-submersible S-7000.
The Horn Mountain 10-in. pipeline has been installed by
Allseas, using the S-lay method with the vessel Solitaire, during
the Winter 2002 in the Gulf of Mexico at a water depth of about
5500 ft. Allseas was able to achieve an impressive maximum lay
rate of 5.6 miles in one day. The interested reader may consult
Langner (2000) for a more comprehensive description of recent
projects installed in the Gulf of Mexico.
For the offshore pipeline engineer. it is interesting to know
the availability of the vessel fleet, as well as its pipe storage
capacity and lay rates. This information is important to help
establish the potential cost of a project and, therefore, its
feasibility.
J -lay Installation Method
The J-lay installation method is a relatively new type of
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