Pipe joints or couplings – Combined
Patent
1994-07-28
1997-01-07
Arola, Dave W.
Pipe joints or couplings
Combined
285177, 285286, 285403, 4051683, F16L 5500
Patent
active
055909159
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved method of laying subsea pipeline from a reel vessel.
It is known to lay a subsea pipeline by welding pipe into long lengths at a shore base, spooling the pipe onto a reel on a vessel, and unspooling the pipe from the vessel at the desired location. The pipe undergoes plastic deformation on spooling, and on unspooling must be straightened and held in tension between the vessel and the seabed. See for example U.S. Pat. Nos. 4,157,023 and 4,230,421 which describe the construction and operation of the reelship "Stena Apache" (formerly "Apache").
This method has the benefit that most of the pipe preparation (welding, coating, testing) can be carried out ashore under cover in optimum conditions, and the vessel operation can be optimised for laying when on station. However, the vessel transit time between the shore base and the laying site is non-productive. It is therefore-important to load the vessel reel fully in order to minimise transit time.
There are instances where it is desired to lay pipelines of different diameters, each size being of a length less than the capacity of the reel. It may be uneconomic to transport such pipelines separately. If, however, the pipelines are simply secured end to end during spooling, then due to the difference in bending stiffness between the pipes an irreversible deformation is likely to occur as the join approaches the reel during spooling up.
An object of the present invention is to overcome or mitigate this problem.
From one aspect, the invention provides a method of spooling a first pipe of first diameter and a second pipe of second diameter onto a reel, the pipe being plastically deformed on spooling to conform to the reel, the method comprising spooling the first pipe onto the reel, spooling the second pipe onto the reel on top of the first pipe, and interconnecting the trailing end of the first pipe to the leading end of the second pipe via a transition joint at some time before said trailing end reaches the reel.
The transition joint may be an initially straight, generally tubular member having a bending moment equal to or greater than the difference in bending moment between the first and second pipes.
Preferably, the diameter of the first pipe is larger than the diameter of the second pipe.
Alternatively, the transition joint may comprise first and second pipe sections hingeably connected together and preformed to a radius conforming to that to which adjacent pipe is bent on the reel during spooling.
The invention, from another aspect, provides a transition joint for use in the foregoing method.
The joint may be a tapered member formed integrally or by a plurality of sections secured together. Preferably, the outer surface is smoothly tapered and the inner surface formed by conical and cylindrical sections.
Alternatively, the joint may comprise a series of pipe sections of reducing diameter. The sections may overlap, or may be joined by generally conical reducers.
In another form the joint comprises first and second pipe sections bent to a common radius and hingeably connected together.
Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which:
FIG. 1 is a schematic side view of a reel pipelay ship;
FIG. 2 is a diagrammatic illustration of pipe being spooled;
FIG. 3 illustrates the forces acting in FIG. 2; and
FIGS. 4-9 are diagrammatic cross-sectional side views of embodiments of transition pieces for use in the invention.
FIG. 1 shows a pipelay vessel 1 having a horizontal-axis reel 3 from which pipe 4 is unspooled for laying via a straightening and tensioning device 5 mounted on a pivotal take-off ramp 2.
FIGS. 2 and 3 illustrate the case where a smaller line 7 is being spooled on top of a larger line 6, with a transition zone 9. Owing to the difference in rigidity of the lines 6 and 7, a point of maximum bending occurs when the point 10 contacts the reel surface 3 (i.e. normally the surface formed by the underlying turns) and a buckled hinge is likely to occ
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Arola Dave W.
Stena Offshore Limited
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