AU693574B2 - Device for laying flexible conduits from a floating support - Google Patents

Description

I APPARATUS FOR LAYING FLEXIBLE PIPES FROM A FLOATING

PLATFORM

The present invention relates to apparatus for laying, from a floating platform, flexible pipes including at least one accessory.

In the meaning of the present invention, the term "accessory" covers any accessory mounted on, or any member incorporated in the flexible pipe and constituting, relative to an ordinary portion of the flexible pipe, a special zone that temporarily prevents the laying operation being continued with the normal laying means used for driving the ordinary portion of the flexible pipe. In particular, accessories miy be rigid and have outside dimensions greater than the diameter of the flexible pipe, such as end fittings which are mounted at both ends of each section of flexible pipe, or the various accessories located on the periphery of the flexible pipe, such as collars, backbone-type bend limiters, stiffeners, anodes, buoys, etc. In the meaning of the invention, the term "accessory" also covers any accessory whose size does not exceed the outside diameter of the pipe, such as any member inside the wall of the flexible pipe, whenever such accessories or members give rise to local weakening of the mechanical strength of the pipe, in particular its crushing strength, of a kind to make it impossible locally for traction in the flexible pipe to be taken up by the tensioner means normally used for handling the ordinary portion of the pipe.

The present inveation relates more particularly to apparatus enabling flexible pipes to be laid vertically or at a small angle relative to the vertical, in which the diameter of the pipe can lie in the range a few centimeters to several tens of centimeters, and to do so in depths of water that may lie in the range a few tens of meters to several hundreds of meters, or even more than 1,000 meters.

P IImt fA1 NIaX 1,1 i' 1 -2- In document W091/15699, the Applicant company has described apparatus for laying flexible pipes in which the apparatus comprises main tensioner means of the linear winch type, and auxiliary tensioner means for lowering a length of flexible pipe including an accessory by gripping the accessory.

The main tensioner means are advantageously of the multiple ca -pillars type having two or more caterpillars which serve ±n a "closed" position to hold the outside surface 10 of the flexible pipe, while in an "open" position in which the caterpillars have been moved apart laterally, the caterpillars allow the section of pipe including an accessory to pass between them.

o In the embodiments described in the above-mentioned prior document, the auxiliary tensioner means comprise at least one moving elongate traction member such as a cable controlled by S, a winch. The cable is suitable for being connected to the accessory.

Since that accessory is necessarily of the rigid 20 accessory type having outside dimensions greater than the outside diameter of the flexible pipe, it is necessary to make it in such a manner as to be capable of withstanding the forces that correspond to the traction force in the flexible pipe that must be taken up by the elongate traction members via the accessory. In addition, the accessory must include means for securing it to the flexible pipe that enable the traction force of the flexible pipe corresponding to the resultant of the traction forces in the wires of the reinforcing layers of the flexible pipe to be transmitted to the accessory by means of a frictinCi effect that requires extremely tight clamping forces, which clamping forces must be distributed over a sufficient length of pipe for the crushing pressure to remain compatible with the mechanical strength of the pipe. Unfortunately, the axial foiris exerted on the flexible pipe by common accessories such as buoys have values of a few hundreds of kilograms force up to a few (metric) tons I IPI itn 4A1 A' GM 1, 7 AiS -3force, in practice less than 10 tons, while the traction force to which the flexible pipe is subjected and that must be taken up by the accessory and transmitted to the elongate traction members is several tens of tons, and may reach or exceed 200 to 300 tons. As a result it is necessary to reinforce the mechanical strength members of all the accessories considerably, thereby excessively increasing the cost thereof.

Also, the apparatus of document W091/15699 is not usable with ,*lo accessories that lie within the outside diameter of the 0 10 flexible pipe.

The present invention seeks to provide laying apparatus of the above-mentioned general type that is capable of L. obviating the need to reinforce the structure and the means for securing each accessory where accessories are of outside dimensions greater than the outside diameter of the flexible pipe, and also of enabling flexible pipe to be laid that includes at least one accessory of dimensions smaller than the outside diameter of the flexible pipe.

According to the present invention there is provided see 20 apparatus for laying, from a floating platform, flexible pipes including at least one accessory, said apparatus comprising a linear winch as main tensioner means for normal lowering of 00 the flexible pipe under tension, and further comprising 0.4 auxiliary tensioner means for lowering the flexible pipe under tension while the accessory is passing through the main tensioner means; wherein said main tensioner means has an axis that is substantially vertical; and wherein the auxiliary tensioner means include at least one moving elongate clamp support member actuated for vertical displacement by drive means, and connected at one end to a clamp suitable for being clamped around the flexible pipe.

Because of the presence of the clamping means of the invention, the auxiliary tensioner means hold the flexible pipe by clamping to a portion remote from its ends rather than to an accessory, thereby providing greater ease in implementation while laying is taking place and avoiding the I 0i1 It V yI I2V 7 51A -4above-mentioned need to reinforce the structure of accessories and the means for securing them.

The clamp may be of any appropriate type, having an open position enabling it to be placed around or disengaged from the flexible pipe, and a closed position having a central passage through which the flexible pipe passes, said clamp being suitable for sliding along the pipe and for being locked thereon in a clamping position at any location determined in such a manner as to exert sufficient clamping force on the 10 flexible pipe to take up the traction forces in the pipe. The clamp may be held by the elongate clamp support member(s) which may, for example, be constituted by a cable wound on a winch mounted on a support structure of the apparatus, or the rod of at least one actuator mounted on the support structure.

15 The support structure may be a derrick mounted on the floating platform for laying. The support structure is advantageously the same as that which supports the main tensioner means, and guide means such as a wheel or a groove bringing the flexible pipe that is to be laid into a substantially vertical 20 orientation above the main tensioner means.

The main tensioner means are designed to support all of the traction forces of the pipe during normal laying which is continued for as long as the length of pipe does not include an accessory, said main tensioner means then operating as a 25 simple tensioner. During the operation of causing an accessory to pass through the main tensioner means, at least a portion of the main tensioner means is opened and the traction forces are supported, at least in part, by the auxiliary tensioner means.

In a first embodiment, the main tensioner means constitute a single simple tensioner. While an accessory is passing through, the main tensioner means are completely open and all of the traction forces of the pipe are then supported by the auxiliary tensioner means, In a second embodiment, the main tensioner means comprise multiple tens- ners including at least two vertically spaced apart individual tensioners in axial alignment, each suitable for supporting only a portion of the traction forces of the pipe. When an accessory is passing through the main tensioner means, the individual tensioners are opened in succession, one by one, or several at a time, with the traction forces in the pipe being taken up by the auxiliary tensioner means operating in combination and synchronously with at least one of the individual tensioners.

In a variant, the apparatus of the invention includes stationary retaining means for suspending the flexible pipe without vertical displacement by means of the clamp, the clamp being supported by said stationary retaining means.

The stationary retaining means have an open central passage centered approximately on the axis of the main tensioner means, and they are preferably disposed beneath the main tensioner means.

In the open position, the central passage through the stationary retaining means is of transverse dimensions that are sufficient to allow an accessory to pass through.

In the clubed position, the transverse dimensions of the central passage are reduced, with its outline lying at least in part within the outside surface of the clamp.

The clamp can thus rest against the top surface of the stationary retaining means which can thus take up the traction force of the flexible pipe via the clamp. In this closed position, the central passage nevertheless remains large enough to allow the flexible pipe to pass through freely together, where appropriate, with an accessory, in particular when the accessory is not very bulky.

In particular, the retaining means of the invention may be in the form of a support-table as described in WO/15699.

Other advantages and characteristics of the invention appear on reading the description of nonlimiting and preferred embodiments given with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic elevation view of a ship for laying flexible tubular pipe and fitted with apparatus of the present invention; Figures 2a to 2h show, very diagrammatically, the stages of a first laying sequence implementing the present invention; Figures 3a to 3h show, very diagrammatically, the stages of a second laying sequence implementing the present invention; Figures 4a to 4h show, very diagrammatically, the stages of a third laying sequence implementing the present invention; Figures 5a to 5h show, very diagrammatically, the stages of a fourth laying sequence implementing the present invention; Figures 6, 7, and 8 are highly diagrammatic elevation views of variant embodiments of apparatus of the invention; 0 Figure 9 is a diagram showing a clamp usable in the apparatus of the invention; 0 Figures 10a, lla, and 12a are front views showing the Figure 9 clamp in three positions in the course of operation; and Figures 10b, llb, and 12b are end views showing the Figure 9 clamp in the operating positions corresponding to Figures 10a, lla, and 12a respectively.

Figure 1 shows a ship 1 for laying flexible pipe 2.

In particular, the flexible pipe 2 to be laid is of the type sold in long lengths by the Applicant company for conveying hydrocarbons produced in off-shore wells /.r0 b^^J3 oC^ P' I1 t fA 2Hx J i I 1 1 -7and having excellent mechanical strength properties, in particular for conveying fluids under pressure.

The apparatus of the invention may also be used for laying other elongate structures such as cables or umbilical lines.

The laying ship 1 is of the type fitted with dynamic positioning means 3 and a central well or "moon pool" 4 through which the pipe 2 is to be laid. Alternatively, the laying apparatus may be disposed, for example, at the stern of 10 the ship over a well, or it may be cantilevered outboard. It is also possible for the ship to be positioned merely by anchor lines.

The laying ship 1 also includes means for storing pipes, such as a vertical axis panier 5 from which a pipe Js paid out 15 and passes over guide means 6 such as a groove in the example shown so as to be disposed substantially vertically.

Other guide means, such as a wheel, could equally well be envisaged.

The guide means 6 are supported by a derrick type support structure 7 mounted on the laying ship 1 over the well 4, said support structure supporting main tensioner means and age a auxiliary tensioner means of the apparatus of the invention, as described below.

The main tensioner means shown diagrammatically at 8 are 25 of the linear winch type and they are disposed vertically, i.e. they have central axis coinciding with the axis of the pipe 2 which extends more or less vertically i.e. linearly through the main tensioner means as the pipe 2 is driven linearly by the main tensioner means during lowering.

The linear winch may be implemented, in particular, in the form of a set of multiple caterpillars, comprising two or more caterpillars adapted to be moved together and apart radially relative to the central axis so that when actuated into the closed position as shown in Figure 1, they exert on the flexible pipe 2 both balanced clamping forces and an axial l.'4 drive force, enabling the pipe to be lowered vertically I f .il'iIA1 KM w 1 'I 1A" -8through the well 4.

Alternatively, the main tensioner means may comprise at least two motor-driven wheels, or preferably at least two wheel trains, the wheels in any one train being spaced apart vertically and lying in a common vertical plane containing the axis of the pipe, such that each wheel train can act on the pipe in a manner analogous to the endless caterpillar.

Two winches 9 are mounted at the top portion of the support structure 7, each serving to pay out and wind in a 10 respective clamp support member in the form of a cable having fixed to the bottom end thereof a clamp 11 described in greater detail below with reference to Figure 9.

As can be seen in Figure 1, the clamp 11 is dimensioned so that when in the closed position it holds and clamps onto 15 an ordinary portion of the flexible pipe 2.

As explained, the apparatus of the invention is designed to lay flexible pipe that includes accessories, and in particular rigid accessories having outside dimensions greater than the diameter of the flexible pipe, e.g. the end fittings 20 at each end of a length of pipe.

Various non-limiting laying sequences are shown in Figures 2 to Figures 2, 3, and 4 relate to passing an accessory 12, which is disposed in a portion of the flexible pipe remote 25 from its ends, through laying apparatus including simple main tensioner means constituted, in the examples shown, by a single tensioner comprising at least two endless caterpillars.

Alternatively, the simple tensioner means may comprise two or more individual tensioners of the linear winch type in alignment on a common vertical axis and all operating simultaneously during the stages of the laying operation, including when they are passing an accessory, such that the traction forces exerted by each of the individual tensioners are combined to take up the traction force of the flexible pipe 2.

9 Reference is made initially to Figures 2a to 2h.

Figure 2a shows a disposition in which apparatus of the invention is to be found when an accessory 12 mounted on the flexible pipe 2 reaches the vicinity of the main tensioner means 8. The accesEory 12 illustrated is of the rigid type and its outside dimensions are greater than the outside diameter of the pipe.

Until this stage, the main tensioner means 8 have been driving and holding the flexible pipe during laying.

In the position of Figure 2a, laying is interrupted by stopping the movement of the caterpillats of the main tensioner means 8 which remain clamped against the pipe 2 so as to take up the traction in the pipe. Depending on characteristics specific to each set of circumstances, the ship 2 may be stopped or it may continue under way, possibly at reduced speed.

As shown in Figure 2b, the clamp 11 for retaining the pipe 2 by means of its cables is placed around the pipe 2 upstream from the accessory 12.

In its closed position, the clamp 11 can thus pass into its clamping position so as to exert the necessary radial compression forces on the pipe 2 to ensure that it takes up the axial traction force.

By acting on the winches 9 controlling the cables 10, the cables are tensioned so as to transfer the laying tension from the main tensioner means 8 to the auxiliary tensioner means as constituted by the winches 9 and the cables 10 which retain the clamp 11.

As shown in Figure 2c, the main tensioner means 8 are opened and then, as shown in Figure 2d, the flexible tubular pipe is lowered again by paying out a sufficient length of the cables 10 to bring the accessory 12 and the clamp 11 downstream from the main tensioner means 8. If the ship is stopped to perform step 2b, it is possible, depending on the circumstances of the operation, to enable it to start again during step 2d.

-I I Once the clamp 11 has reached the desired position beneath the tensioner 8, it is held in place and the traction force in the pipe continues to be taken up by the winches. The ship may be stationary or, depending on circumstances it may continue to move forwards.

Thereafter, as shown in Figure 2e, the main tensioner means 8 are reclosed, thereby transferring the laying tension to said tensioner means 8. The cables 3 are relaxed, as shown in Figure 2f, after which the clamp 11 is opened as shown in Figure 2g, removed as shown in Figure 2h, and the normal laying operation is taken up again with the laying ship being put back into movement if it had been stopped during steps 2e and 2f.

The laying sequence shown in Figures 3a to 3h is very suLstantially similar to that described above with reference to Figures 2a to 2h, the essential difference lying in the fact that during the step shown in Figure 3b, the clamp 11 is put into place on the flexible tubular pipe 2 downstream from the accessory 12 but still upstream from the main tensioner means 8.

The laying sequence shown in Figures 4a to 4h is likewise very similar to those shown with Reference to Figures 2a to 2h and 3a to 3h, but it differs in that during the step shown in Figure 4b, the clamp 11 is put into place on the flexible pipe 2 downstream from the main tensioner means 8.

The laying sequence shown in Figures 5a to corresponds to implementing variant apparatus having multiple main tensioner means comprising, in the embodiment shown, two distinct multi-caterpillar sets 8a and 8b that are spaced apart vertically, each of which constitutes an individual tensioner of smaller capacity than that of the tensioners used in the preceding embodiments.

In such an embodiment, not only can the capacity of each individual tensioner be lower than that required for retaining and lowering flexible tubular pipes, but also

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the assembly comprising the clamp and the auxiliary tensioner means can likewise be of smaller capacity.

As explained below, at all times the pipe is retained during lowering steps and during steps when lowering is stopped either by both main individual tensioners operating simultaneously in synchronism, in which case the traction force in the pipe corresponds to the sum of the retaining forces in the two individual tensioners, or else by simultaneous and synchronous operation both of one of the main individual tensioners and of the assembly comprising the clamp and the auxiliary tensioner means whose retaining force is added to that of the active individual tensioner to take up the traction force in the pipe.

As in the previous embodiments, lowering of the pipe 2 is interrupted whenever an accessory 12 comes to the upstream end of the upper main tensioner 8a.

As shown in Figure 5a, the clamp 11 is installed on the flexible tubular pipe 2 upstream from the accessory 12 which is itself upstream from the upper tensioner 8a, thereby enabling the clamp 11 to take up the tension previously exerted by the upper individual tensioner 8a.

As shown in Figure 5b, the upper tensioner 8a is opened and the lower tensioner 8b is caused to operate synchronously with the assembly comprising the clamp and the auxiliary tensioner means so as to lower the flexible pipe as represented diagrammatically by the vertical arrow.

In the position shown in Figure 5c, the clamp 11 and the accessory 12 have passed through the main tensioner 8a and are located in the empty gap between the individual tensioners 8a and 8b. At this stage, as shown in Figur; 5d, the upper tensioner 8a is closed so that the load constituted by the pipe 2 is taken up by the upper tensioner 8a and the assembly comprising the clamp and the auxiliary tensioner means.

T 06 As shown in Figure 5e, the lower tensioner 8b is closed and then, as shown in Figure 5f, the upper tensioner 8a and the assembly comprising the clamp and the auxiliary tensioner means are caused to operate synchronously so as to continue lowering the flexible pipe.

As shown in Figure 5g, once the clamp and the accessory have passed out from the bottom of the lower tensioner 8b, it is reclosed so as to cause the tension to be taken up by the two tensioners 8a and 8b, with tension on the clamp 11 being released, after which the clamp is dismantled as shown in Figure 5h. Thereafter normal laying is continued with the tensioners 8a and 8b.

The apparatus shown in Figure 5 operates analogously to that shown in Figure 2, the clamp 11 being clamped on the pipe 2 upstream from the accessory 12. It is also possible to implement apparatus with multiple main tensioner means, e.g. two individual tensioners operating on a principle analogous to that shown in Figure 3 in which the clamp 11 is put into place on the pipe 2 beneath the accessory 12, but still above the main tensioner means, and in particular above the upper individual tensioner 8a, with the successive steps of the operation being similar to those shown in Figure In both cases, i.e. when the clamp 11 is put into place on the pipe 2 upstream from the main tensioner means, the empty gap between the two adjacent individual tensioners is preferably large enough to be capable of containing the assembly constituted by the accessory 12 and the clamp 11, as shown in Figure 5c. However it is also possible to restrict this empty gap to the dimensions of the larger of those two objects, in particular by increasing the vertical distance between them so that said distance corresponds at least to about the total height occupied by the set of individual tensioners constituting the main tension'c means.

01 I II i It is also possible to implement apparatus with multiple main tensioner means operating on a principle analogous to that shown in Figure 4, the clamp 11 being put into place on the pipe 2 downstream from the main tensioner means, e.g. beneath the lower individual tensioner 8b if the apparatus has two individual tensioners. Under such circumstances, the empty gap between two adjacent individual tensioners is determined as a function of the dimensions of the accessory 12 on its own.

The various individual tensioners constituting the main tensioner means of the apparatus may all be of the same type, and in particular they may all have the same capacity in terms of maximum tractive force.

By increasing the number of individual tensioners constituting the main tensioner means, it is possible to reduce the capacity of the auxiliary tensioner means, i.e. to reduce the maximum retaining force as a function of which they are designed and dimensioned, and in particular the capacity of the clamp 11. For example, if the ma .n tensioner means comprise three identical multicaterpillar tensioners, then the capacity of the auxiliary tensioner means can be divided by three compared with that which would be required by the auxiliary tensioner means of laying apparatus capable of handling the same load but in which the main tensioner means are constituted by a single multi-caterpill.at unit whose capacity, under the same circumstances, would have to be three times greater than the capacity of each of the three multi-caterpillar units constituting the equivalent three-unit main tensioner means.

In another embodiment (not shown) in which the main tensioner means comprise at least three individual tens'.oners, the capacity of the auxiliary tensioner means is increased so as to correspond to the total capacity of two of the main tensioner units simultaneously or possibly more than two individual tensioners

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simultaneously. This makes it possible to open simultaneously two adjacent individual tensioners, with the main individual tensioners being opened in successive pairs starting from the top tensioner and going down to the bottom tensioner as the accessory and the clamp pass through the main tensioner means. At any instant during this passage, the accessory and the clamp are received in the space defined by two adjacent individual tensioners in the open position, which means that there is no need to provide any empty gaps between individual tensioners so they can be located close together. Since the clamp is also clamped to the flexible pipe in the vicinity of the accessory, this disposition makes it possible to reduce the total height occupied by the apparatus above the deck of the ship.

As described above, the main tensioner means may be constituted by at least two trains of motor-driven wheels, each wheel train comprising at least two wheels lying in a common vertical plane, so as to present at least two superposed levels of wheels, there being at least two wheels at each level, which wheels are regularly distributed around the pipe 2 so as to be capable of clamping against it in balanced manner. In such apparatus, the main tensioner means may advantageously be implemented in such a manner as to be capable of moving the wheels at a given level in radial directions on a level-by-level basis, with each level being independent of the others, thereby enabling the wheels on any one level to be moved apart or towards the pipe 2 in order to clamp against it. It should be understood that such a set of motor-dzJ.ven wheel trains constitutes, in the meaning of the invention, multiple main tensioner means, with each of the levels of wheels whose radial displacements can be controlled independently constituting an individual tensioner as described above.

II II i'r 'It KAI 9' 1I I I I tji As shown in Figures 2 to 5, the winches 9 may be disposed above the main tensioner mrlans, e.g. they may be supported by the top portion of the derrick 7.

Alternatively, the winches 9 may be disposed beneath the main tensioner means, e.g. they may be mounted on the deck of the ship 1, with the cables 10 passing over return sheaves mounted at the top of the derrick 7 above the main tensioner means.

Instead of winches 9, it is also possible to envisage 04eo 10 using capstans, chain windlasses, or combinations of the above-described elements.

Figures 6, 7, and 8 show non-limiting variants of the auxiliary tensioner means.

In the embodiment of Figure 6, a single winch 9a is 15 provided whose drum carries two cables In the embodiment of Figure 7, a single winch 9b is provided carrying a single cable 10b connected at its bottom end by a spreader 13 to two cables 14 which are in turn connected to the clamp 11.

In the embodiment of Figure 8, two long-stroke actuators are provided whose clamp support members are actuator rods 16 connected to the clamp 11.

The actuator rods 16 may be directed either downwards, as shown in Figure 8, in which case the actuator cylinders are 25 mounted at the top of the derrick 7, or else they may be directed upwards with the actuator cylinders being carried by the deck of the ship, and with the actuatory rods working in compression.

Naturally, numerous 'her auxiliary tensioner means can be designed without going beyond the ambit of the invention.

It is thus possible to envisage a single actuator whose rod is connected to a spreader, as in the embodiment of Figure 7, with the spreader being connected in turn to the clamp 11 by two cables.

It is also possible to design a set of two actuators pulling on cables that are reeved in order to reduce 16 their stroke, or an actuator associated with a reeved cable and a spreader.

The members which enable the flexible pipe 2 to be gripped by the main tensioner means and constituting the active portion thereof, such as caterpillars fitted with pads, or wheels or wheel trains, are disposed around the vertical axial passage occupied by the pipe so as to leave at least two empty gaps between said gripping members and along the full height thereof for the purpose of allowing elongate handling members to pass such as the cables 10 or the actuator rods 16. It is thus possible to clamp the gripping means onto the pipe 2 without being impeded by the cables or the actuator rods.

Reference is now made to Figures 9 and 10a to 12b.

These figures show a non-limiting example of a clamp 11 usable in the invention.

In general, the clamp 11 comprises at least two moving gripping elements having an internal surface and a general configuration that are designed to enable them to clamp against the flexible pipe in balanced manner, the section of the pipe being circular or of some special non-cylindrical shape as applies, for example, to a multi-line connection of the umbilical type. In addition, the clamp includes positioning means that act on the gripping elements so as to move them, in particular in a radial direction, relative to the axis of the pipe, and to provide the necessary clamping forces.

Thus, in one direction, the gripping elements can move away from the pipe 2, with the clamp taking up its relaxed position, while in the other direction they can press against the pipe and exert sufficient radial compression force thereon to enable the clamp to take up the axial traction force in the pipe, with the clamp then being in its clamping position.

In a first embodiment, the positioning means are simply constituted by a special configuration of certain members associated with the gripping elements, so that 1, 'IVT J the clamping force is created by the traction force in the pipe itself and increases as a function of the traction force. This constitutes a self-locking or selfblocking clamp, e.g. by means of the wedge effect in application of a mechanical principle that is very widely used.

In a second embodiment, the positioning means may be of the actuated type, e.g. by means of radially-acting hydraulic actuators which determine the position of the gripping elements relative to the pipe 2 and, in particular, develop the radial compression forces that are exerted by the gripping elements on the pipe.

Figures 9 to 12 show a variant of the wedge effect self-locking clamp. The clamp shown comprises a main frame 20 housing two wedge-shaped moving jaws 21, the frame 20 being closed by a door 22 and suspended from handling members 23 which may, for example, be cables such as the cables 10, 10a, and 14 described with reference to Figures 1 to 7, or the rods 16 of the actuators described with reference to Figure 8.

The door 22 and the jaws 21 are preferably actuated by hydraulic actuators (not shown) or by any other mechanism suitable for causing them to change position.

In the position shown in Figures 10a and 10b, the door 22 is open and the jaws 21 are in the high, open position enabling the clamp to be put into place around the flexible pipe 2.

It should be observed that in Figure 10a the door 22 is omitted for reasons of clarity, and that it is represented only by dashed lines in Figures Ila and 12a.

In the position of Figures Ila and llb, the door 22 is closed and the Jaws 21 are in the high position so as to allow the clamp to move in translation along the flexible pipe 2, the clamp thus being in a closed but unclamped position.

In the position of Figures 12a and 12b, the Jaws 21 are in a closed and low position, thereby clamping around 18 the flexible pipe in order to enable the flexible pipe 2 to be gripped and to enable laying traction forces to be transmitted to the handling members 23.

It may be observed that the clamp can be made in such a manner that the contribution of the hydraulic actuators actuating on the jaws 21 to the compression forces exerted on the pipe 2 is practically negligible, said forces being created almost entirely by the wedging effect from equal and opposite forces applied to the pipe 2 and to the clamp 11, as a function of the angle between the axis of the pipe 2 and the parallel surfaces presented by the outside walls of the jaws 21 and the inside walls of the frame 20 forming the housing for the jaws. The facing parallel surfaces of the jaws 21 and of the frame 20 are implemented in such a manner as to be capable of operating as slideways. They may thus be plane, prismatic, or indeed cylindrical.

In the variant shown, thi walls of each of the two jaws 21 forming contact beJth o.urfaces with the pipe 2 are cylindrical in shape cor2-s ,.nding to the cylindrical outside surface of the pipe. The substantially cylindrical contact surfaces of the jaws can be dimensioned as a function of the characteristics of the flexible pipe 2 so that a small amount of clearance remains, in the clamping position, between the two facing faces of the two jaws on either side of the pipe.

The height of the jaws 21, corresponding to the length of the generator lines of the cylindrical surfaces formed by the contact bearing surfaces of the jaws for engaging the pipe must be sufficient, as a function of the length of the jaws, to ensure that the radial compression force exerted by the jaws on the pipe is compatible with the crushing strength of the flexible pipe, with the intensity of the radial compression forces being itself determined as a function of the characteristics of the pipe so that the traction force can be trantsmitted by friction through the wall of the

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19 pipe from the mechanical reinforcement that withstands the axial load in the pipe to the jaws 21 which constitute the gripping means of the clamp.

Alternatively, the number of jaws may be greater than two, with the jaws preferably being identical and regularly spaced apart around the central vertical axis of the clamp.

The inside surface of each jaw that bears against the flexible pipe may be plane or it may be concave facing the axis of the pipe, being polygonal or rounded in shape. In particular, it may be cylindrical in shape as shown in Figures 9 to 12.

Instead of having a frame 20 closed by a door 22, as shown in Figures 9 to 12, the clamp 11 may be made so as to be generally in the form of an opening collar, like a hinged clamp, with two jaws that are hinged to each other about a vertical axis at one of their ends, and that are capable of being closed and clamped against each other at their opposite ends by a closure member such as a catch, preferably actuated by a hydraulic actuator. In the closed position, the two jaws define a central passage for receiving the flexible pipe 2, and the inside walls of the jaws may, in particular, present sloping surface elements forming slideways on which the jaws can bear, the necessary clamping forces thus being obtained by a wedging effect in the same manner as in the variant illustrated in Figures 9 to 12.

The clamp 11 may also be implemented in various other known forms.

It may thus have the general configuration of an opening collar comprising three hinged-together elements.

Two jaws pivot in a horizontal plane about two axes carried by a central element so as to be capable of closing completely around the flexible pipe. The inside faces of the hinged elements may have sloping surfaces for receiving the jaws so as to act in the same manner as the two-jaw clamp described above.

uj eI a, In the case (not shown) of a clamp 11 fitted with actuated positioning means, such as hydraulic actuators acting radially on the gripping elements, such as the Jaws, the apparatus may operate by the actuators applying thrust forces of an intensity that can reach a determined value, set in advance as a function of the traction force and of the characteristics of the flexible pipe.

Alternatively, the positioning means may operate at given displacement, with the contact-bearing surfaces of the jaws being forced by the actuators to reach a position that is fixed relative to the axis of the pipe.

The embodiments described with reference to Figures 2, 3, 4, and 5 correspond to passing an accessory 12 that is situated in the ordinary portion of the flexible pipe 2.

Naturally, the apparatus of the present invention can be implemented for passing end fittings serving to enable two successive lengths of flexible pipe to be connected together. These end fittings are referenced 12a and 12b in Figure i.

Such a connection can be made either at the top of the apparatus or else on the deck of the laying ship i.

Thus, the connection between an end fitting 12a terminating a first section of flexible pipe and an end fitting 12b mounted at the beginning of a second section of pipe which needs to be lowered to the bottom can be achieved above the main tensioner means, with the accessory that needs to pass through the main tensioner means by implementing the apparatus of the invention thus being constituted by the assembly of the two coupledtogether end fittings.

The coupling step is advantageously preceded by a step consisting in installing a temporary support around the first section of pipe, e.g. a fork-shaped member that is supported laterally by the derrick 7 and that serves to support the top end of the first section of pipe, e.g.

via a shoulder constituting the bottom edge of its end fitting. Since the traction force continues to be taken up by the main tensioners 8, the force which the temporary support nee's to withstand is restricted to the relatively very small weight of the end fitting itself together with the top portion of the first section of pipe located above the main tensioners 8.

The clamp 11 can be installed either on the second section of pipe in a variant analogous to the procedure shown in Figures 2 or 5, or else on the first section of pipe, in which case either it is installed above the main tensioner means 8 in a variant that is analogous to the procedure shown in Figure 3, or else it is installed beneath the main tensioner means 8 in another variant analogous to the procedure shown in Figure 4.

When the clamp 11 is installed not on the second section of pipe, but on the first section, it is possible to couple the two end fittings together beneath the main tensioner means 8, e.g. on the deck of the ship, thereby making the operation easier to perform.

In a first stage of the operation, the first section of pipe is lowered in accordance with the invention, while supported by the clamp 11 so that its end fitting is located beneath the main tensioner means, the clamp 11 having been disposed on the first section of pipe either above the main tensioner means, in a procedure similar to that illustrated in Figure 3, or else beneath the main tensioner means 8, in a procedure corresponding to the case shown in Figure 4. The end fitting is then in a position analogous to those illustrated in Figures 3d or 4d.

The second stage of the operation begins by bringing the second section of pipe so that it passes through the guide means 6 and comes down through the main tensioner means 8 that have been left open until the end fitting of the second section of pipe comes level with the end fitting of the first section. After the end fittings have been coupled together, the main tensioner means 8 jl l.A j I I I t, I 4 22 are closed on the second section of pipe. The laying apparatus is then in a situation analogous to that shown in Figures 3e or 4e.

The traction force in the two coupled-together sections of pipe is then taken up by the main tensioner means 8 and it is possible to disengage the clamp 11 and return to normal laying operation.

It should be observed that in this variant implementation, the two end fittings constitute, in the meaning of the present invention, two separate accessories which are mounted at respective ends of two different sections of flexible pipe and which pass through the main tensioner means separately and successively prior to being coupled together.

Preferably, the first stage of the method described above includes an additional step consisting in putting a temporary support into place around the top portion of the first section of pipe so as to support said section as its end fitting passes through the main tensioner means 8.

Advantageously, the temporary support is put into place as soon as the section of pipe stops being lowered for the purpose of putting the clamp 11 into place. In simple manner, the bottom edge of the end fitting of the first section of pipe can have a shoulder that bears against the temporary support. By way of example, the temporary support may be in the form of a fork or of an opening collar and it can be moved in various manners so as to accompany the end fitting while it passes through the main tensioner means 8, e.g. by retaining it using cables wound on the winches, or by securing it to a motor-driven carriage that moves along a vertical rail, or merely by causing it to be carried by the clamp 11 put into place above the main tensioner means 8 a little below the end fitting in apparatus operating in the manner shown in Figure 3.

23 It should be observed that the load supported in this way by the temporary support which corresponds merely to the weight of the end fitting and the top portion of the first section of pipe is very small and quite unlike the considerable traction force that is supported by the main tensioner means 8 and by the clamp 11, which traction force corresponds to the total weight of the portion of pipe that is suspended between the surface and the bottom of the sea.

In variant implementations (not shown), fixed retaining means may be provided that are preferably disposed beneath the main tensioner means, e.g. a support-table comprising two moving portions capable of being displaced in an approximately horizontal plane on either side of the vertical axis end of the main tensioner means, between an open position and a closed position.

The support-table which is mounted, in particular, o, the work deck of the laying ship has an open central passage between its two moving portions, which passage is substantially centered on the axis of the main tensioner means, thereby allowing the flexible pipe to pass freely in the open position together with any accessories that may be mounted thereon.

The use of the support-table is compatible with the various laying sequences described above.

Thus, for example in the laying sequence described with reference to Figure 3, the steps up to and including that of Figure 3d are implemented without any change.

After the accessories 12 have gone through the open main tensioners 8, as shown in Figure 3d, the table is closed, assuming that it was open during the preceding stages of the operation.

The flexible pipe continues to be lowered until the clamp comes to rest on the closed table.

It is then possible to relax the cables 10 and to VA detach them from the clamp 11 so as to be able to I I I 24 withdraw them by winding them onto the winches 10 (the proced re is analogous if actuators are used instead of cablas arid w4.nches), the flexi.le pipe then being supported by the table and the main tensioner means can remain opan. It should be Observed that when a support table is not used (Figure it is necess--y to close the main tensioner means on the flexible piae (Figure 3e) before lowering the cables 10 (Figure 3f).

This releases access to the accessory 12 in the space situated inside the main tensioners above the deck of the ship, thereby making it possible to take all of the actions required on the accessory as may be necessary as a function of the way in which the laying operations are progressing.

In a particular variant, it is also possible, while implementing a procedure in compliance with the above description, to connect the end fitting 12a of the first length 2a of the flexible pipe (held in the table by means of the clamp 11) to the first end fitting 12b of a second length 2b of flexible pipe passing via the guide means 6 and lowered through the still-open main tensioners 8. Once the end fitting 12b has been lowered in this way down to the end fitting 12a, the two end fittings can be coupled together.

After action has been taken on the accessory 12, or after the end fittings 12a and 12b have been connected together, depending on requirements, the main tensioner means 12 are closed about the second length 2b of flexible pipe so as to take up the traction exerted by the flexible pipe 2a "b.

The clamp 11 is removed.

The table is opened (except if the accessory 12 or -the end fittings 12a and 12b are of small transverse dimensions and can pass tnrough the central passage of the table, in which case it can be left closed).

The laying of the flexible pipe can be restarted, with traction being taken up by the main tensioner means.

L

I' 0ll'l KA1 k28900 95i 25 711W It will be understood that laying apparatus in accordance with the invention and that includes multiple main tensioner means, e.g. two individual main tensioners, could alternatively operate in conventional manner, i.e. without using the clamp with which it is fitted to allow an accessory to pass through the main tensioner means whenever it turns out that for a given operation the traction force in the flexible pipe is relatively small, e.g. less th2,n half the maximum capacity of the equipment, when the unit weight of the pipe 10 and/or the depth of the water are well below the maximum values for which the apparatus is designed.

meet The accessory can then be caused to pass through each of the two individual tensioners in succession by opening that one of the tensioners through which the accessory is to pass, 15 with the pipe continuing to be held by the other tensioner, such as laying procedure being described in FR-A-1 417 989.

Naturally, instead of being used for lowering and laying flexible pipes on the bottom, the apparatus of the invention can also be used for raising and storing on board the ship a 20 flexible pipe that has previously been laid on the bottom, e.g. for the purpose of recovering the pipe and laying it again on another site.

Although the invention is described above with reference to particular implementations, it is clear that the invention 25 is not limited in any way thereto, and that numerous variants and modifications can be provided without thereby going beyond the scope of the invention.

Throughout this specification and the claims which follow, unless the context reqiiires otherwise, the word "comprise", and variations such as "uomprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (9)

1. Apparatus for laying, from a floating platform, flexible pipes including at least one accessory, said apparatus comprising a linear winch as main tensioner means for normal lowering of the flexible pipe under tension, and further comprising auxiliary tensioner means for lowering the flexible pipe under tension while the accessory is passing through the main tensioner means; wherein said main tensioner means has an 10 axis that is substantially vertical; and wherein the auxiliary tensioner means include at least one moving elongate clamp support memnar actuated for vertical displacement by drive means, and connected at one end to a clamp suitable for being S, clamped around the flexible pipe.

2. Apparatus according to claim 1, wherein said clamp is arranged to be clamped around a portion of said flexible pipe remote from the ends of the pipe. 0a 20

3. Apparatus according to claim 1 or 2, wherein the clamp support member is a cable moved vertically by a winch.

4. Apparatus according to claim 1 or 2, wherein the clamp support member is a movable rod of at least an actuator.

5. Apparatus according to claim 3 or 4 comprising a support structure supporting the main tensioner means, the auxiliary tensioner means, and guide means bringing the flexible pipe into a substantially vertical direction over the main tensioner means.

6. Apparatus according to any one of the preceding claims, further comprising stationary retaining means.

7. Apparatus according to claim 6, wherein the stationary retaining means comprise a support-table. I I II IP uill i'RA1 x) 9 U2I5 12V9 -27-

8. Apparatus according to claim 6 or claim 7, wherein said stationary retaining means are disposed beneath the main tensioner means and have an open first position allowing the flexible pipe to pass together with any accessories mounted thereon, and a closed second position in which it takes up traction force from the flexible pipe by retaining the clamp.

9. Apparatus for laying, from a floating platform, flexible pipes including at least one accessory, such apparatus being 10 constructed and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings. *e 15 DATED this 7th day of May, 1998 COFLEXIP By its Patent Attorneys Davies Collison Cave *Oa a 1 I I I I I 4 28 ABSTRACT APPARATUS FOR LAYING FLEXIBLE PIPES FROM A FLOATING PLATFORM Apparatus for laying, from a floating platform, flexible pipes including at least one accessory, said apparatus comprising main tensioner means of the linoaL winch type for normal lowering of the flexible pipe, and auxiliary tensioner means for lowering the flexible pipe while the accessory is passing through the main tensioner means, said main tensioner means having an axis that is substantially vertical. The auxiliary tensioner means (11, 9, 10) include at least one moving elongate handling member (10) actuated in vertical displacement by drive means, and connected at one end to a clamp (11) suitable for being clamped around the flexible pipe .1 ~NT_9