Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Reexamination Certificate
2002-04-30
2004-05-04
Lagman, Frederick L. (Department: 3673)
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
C405S166000
Reexamination Certificate
active
06729803
ABSTRACT:
The present invention relates to holding a pipe under tension sore particularly, the present invention relates to a clamp system installed on a floating support enabling a pipe to be held under tension and locked in position. The present invention also relates to a floating support including a device for connecting together and laying successive portions of an off-shore pipe from said floating support.
The present invention thus applies to holding a substantially vertical pipe in suspension, and also to any type of duct for conveying a fluid, electricity, optical signals, or information, and in particular rigid or flexible tubular pipes, umbilical cords, and electric cables. It applies in particular to off-shore pipes handled from a ship performing installation operations, in particular over very great depths, i.e. in depths of about 1000 meters (m) or more.
Drilling operations are performed from a derrick fitted with a winch and tackle for handling a string of rods. As drilling progresses, the string is lengthened by adding rods, in general in unit lengths that are multiples of
12
m, corresponding to the height available under the hook of the derrick. Said unit length is generally assembled by screwing the new length to the already-assembled string of rods that is held in suspension from the rotary table, using a clamp system of the type having self-locking wedges that leave bite marks.
In the same manner, off-shore pipes are laid in very great depth from floating supports fitted with handling means constituted by an optionally-articulated tower, possessing handling functions similar to those of a derrick. At great depths, laying is said to be “J-laying” since the portion of the pipe between the level of the ship and its point of contact on the sea bed is J-shaped. During laying, successive pieces of pipe are connected end to end, and this requires the already-immersed portion of pipe to be held so that the end of this portion can be presented to the new piece of pipe, then to operate assembly tools, and then to guide the pipe so as to lay it in the sea. The use of clamps with marking wedges made of steel for holding the suspended portion of pipe suffers from the drawback of leaving traces on the outside of the pipe, and above all of damaging its anticorrosion coating. Numerous other types of clamp have been developed, based essentially on toggle-hinge systems or on cam-locking systems, with the movements of engaging and of disengaging a clamp often being driven by hydraulic actuators.
Such clamps are well adapted for loads that are small, but in very great depths, e.g. 2500 m, the weight of a pipe can exceed 500 (metric) tonnes and it is necessary to guarantee an extremely high level of safety whatever the type of pipe, during each stage of end-to-end connection, where a cycle can last for 15 minutes to 45 minutes, or indeed in the event of operations being interrupted for a variety of reasons such as an accident with the equipment or a storm, which might last for several days. If there is no need to ensure that the outer coating of the pipe is preserved undamaged, then clamps with marking wedges of the kind described above are entirely suitable for performing the function of holding the pipe, even if it presents irregularities in diameter, but if said coating is fragile, that type of clamp should not be used.
Numerous solutions have been developed to avoid damaging the outsides of pipes, but they are not adapted to extreme loads since they present the drawback of not guaranteeing positive safety in the event of slip phenomena starting, thereby running the risk of giving rise to severe accidents, not only to the equipment, but also to personnel.
The problem of the present invention is thus to be able, with a maximum level of safety and under extreme levels of loading, both to retain a pipe that presents an outside surface that has the reputation of being fragile, and to ensure that operation can be performed safely, even in the event of small dimensional variations in the outside shape of the pipe or its outer coating.
To do this, the present invention provides a clamp system installed on a floating support, enabling a pipe to be held under tension and comprising:n
a tubular element suitable for containing said pipe coaxially and secured to said floating support at the level of its assembly plane;
said tubular element containing a plurality of friction shoes;
each of said shoes being mounted on the end of a piston of a preferably-hydraulic actuator;
said actuators and shoes being disposed in a plurality of planes of said tubular element along the longitudinal axis of said tubular element, and being distributed in each of said planes around said pipe, preferably symmetrically about said longitudinal axis of the tubular element; and
said pistons moving in translation in a directions perpendicular to said longitudinal axis of said tubular element, whereby:
said friction shoes are in a clamping position against said pipe when said pistons are in an extended position, and said shoes are in a position disengaging and releasing said pipe when the pistons are in a retracted position; and
each actuator being provided with means for locking said piston in the extended position. When a hydraulic actuator is used, hydraulic pressure can be relaxed while still keeping said piston in its position clamped against said pipe.
The clamp system of the invention ensures that the pipe is retained with a high level of safety since it enables the loads to be spread over a broad zone of the pipe both within a given plane and also between different planes.
While the shoes are being clamped against the pipe, it is possible to modulate the pressure applied on the shoes so that they flatten and distribute the compression force on the pipe in a manner that is substantially uniform. In addition, it is possible to apply pressures that are different between the various planes, or indeed between the various shoes within the same plane, depending on the type of pipe and on the type of outer coating.
The tubular element preferably comprises at least two, and preferably at least four shoes in each of said planes. Said tubular element comprises at least three planes, and preferably at least nine planes. Said tubular element can have 30 or even 50 friction shoes.
The pressure with which said shoes are clamped against said pipe can be adapted plane by plane or within a given plane, actuator by actuator.
Increasing the number of planes thus makes it possible to achieve the desired retaining force, insofar as the flexible elements as constituted by the friction shoes absorb displacements of the pipe.
In the clamp of the invention, the actuator may be a mechanical actuator with a lockable drive shaft or it may be a hydraulic actuator, in particular one having a leaktight check valve provided with an accumulator using a diaphragm or a piston, in particular for compensating losses through gaskets, and of a volume that is determined as a function of expected rates of leakage for the maximum length of time the clamp might need to be in operation.
Said means for locking said piston is preferably constituted by motorized screw-driving means, said piston being secured to a nut which co-operates with a motor-driven screw so as to move in translation and lock said piston in its extended position by blocking the screw.
Each of the actuators is thus provided with a motor-driven screw-and-nut device allowing the rod to be actuated into its position where it is clamped against the pipe. The screw can be blocked either by mechanically locking the rotary element, or by means of an irreversible gearing device, or indeed by mechanically locking the drive shaft since the amount of torque required for holding it is small.
Mechanical and hydraulic actuators are known to the person skilled in the art in the fields of mechanical and hydraulic engineering and they are not described in greater detail herein.
In a preferred embodiment:
said actuator comprises a hollow actuator body secured to said tubular element constituting the clamp s
Bouygues Offshore
Cohen & Pontani, Lieberman & Pavane
Lagman Frederick L.
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