Method and Apparatus for Assembling and Laying Underwater Pipeline

The invention refers to a method of and apparatus for assembly and laying of an undersea pipe constituted by a plurality of pipe sections which are fixed together.

Although the subsequent description of the invention refers particularly to the method of pipe laying known under the designation of `laying in a J`, that is to say, in which the slope of the pipe varies so as to impose upon it no point of inflection, it is in fact applicable to any method in which the end of the pipe on board a surface support such as a laying barge undergoes a displacement with respect to the support because of the pitching and pounding caused by the swell and bad weather.

One of the advantages of the method of laying in a J is that of avoiding the use of ramps of large dimensions, with well defined curvatures and of offering considerable security against accidental deformations because of the elimination of points of inflection along the curve formed by the pipe, the end of which is resting on the bottom. However, if experience has been able to show that by keeping the surface end of the pipe at a certain angle one was assured of its laying in position without accidental deformation, experience obtained hitherto has related only to pipes of small section, the diameter of the pipes employed being at most equal to about 25 cm, and in water of no great depth.

It has been observed, however, during the course of development of mathematical programmes of dynamic simulation for pipes of larger diameter and for pipe laying at any depth, that, whatever the slope given to the ramp bearing the end of the pipe, one could not avoid the appearance of waves of transverse deformation as soon as the tension applied to the end of the pipe was no longer greater than a certain critical tension, it being impossible to maintain the required known conditions because of the movements of the barge and especially its pounding.

It is an object of the present invention to provide a method of laying undersea pipe, in accordance with which the submerged portion of the pipe in course of being laid is always subjected to a force greater than the critical force below which waves of transverse deformation appear, by the employment of means for compensating for changes in the forces applied to the pipe portion because of the relative displacement of the surface support and the end of the pipe portion.

Another object of the invention is to provide apparatus for putting into effect the foregoing method, which comprises means for suspending the end of the submerged pipe portion from the surface support, which suspension means is connected to the surface support by a deformable and adjustable damping or compensation means.

By use of the above method and apparatus, whatever the movements of the surface support with respect to the end of the submerged pipe portion the appearance of any wave of deformation can be avoided, a hydropneumatic means, for example, being used to ensure a substantially constant tension in the submerged pipe portion greater than the limiting tension for the depth of lay and the diameter of the pipe.

The apparatus may include means connected to damping means for suspending a pipe section to be connected to the end of the portion already submerged, the two suspension means being connectable together by a device which ensures synchronization of the movements of the end of the submerged pipe portion and of the section to be connected.

By use of the above described apparatus a tension can be maintained which is greater than the critical tension, as well as the synchronization of the movement of the end of the submerged pipe portion and of the new pipe section to be connected thereto. It then becomes possible to employ any known means for connecting the section to the pipe portion whilst maintaining the required tensile force on the pipe portion.

In accordance with the method of laying in a J, the barge is displaced by a distance corresponding to the length of the new section, while progressively submerging the newly attached pipe section to bring the upper end of the section opposite the means of suspension of the submerged pipe portion.

The invention will be more fully understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings.

In the drawings:

FIG. 1 is a general diagrammatic view of an embodiment of apparatus according to the invention, partly cut away;

FIG. 2 is an enlarged view of part of the apparatus of FIG. 1; and

FIG. 3 is an enlarged view of another part of the apparatus of FIG. 1.

In the drawings, the laying barge 20, which may be any suitable surface support carries a laying ramp 1 the slope of which can be varied by rotation of the ramp about the shaft 5. A feed ramp 9, pivotable about a shaft 6 coaxial with shaft 5 enables a new section 14 of pipe to be brought into alignment with the last attached section 50 of the submerged pipe or pipe-line P.

The end of the last section 50 of the pipe P is held by a set of jaws 22 of any suitable type, which are mounted on a member or slide 2 which is displaceable longitudinally along the ramp 1 under the control of damping or compensation means in the form of a jack 42. For this purpose the end of the rod 43 of the jack 42 is connected to the slide 2, the body of the jack being fixed to the ramp 1. The control chamber of the piston of jack 42 is connected by a pipe 49 to two hydropneumatic accumulators 44.

Similarly the new pipe section 14 is held on a feed ramp 9 by jaws 12 mounted on a structure 11 mounted on a member or slide 10. The jaws 12 may be of any suitable type. The connection between the ramp 9 and the slide 10 is provided by damping or compensation means in the form of a jack 46, the control chamber of which is connected to hydropneumatic accumulators 48 by pipe 47. In order to facilitate the alignment of the new section 14 with the last section 50 of the pipe P, the section 14 is supported on the ramp 9 by adjustable rollers 13 and 13a. With the new and last pipe sections aligned, one can proceed to screw up the joint or, with bevels on the sections parallel, one can proceed to weld the joint.

Although slideways are provided for guiding the movable parts, e.g. jaws 12 and 22 and slides 2 and 10, these slideways have not been shown for greater clarity in the drawing.

The slope of the ramp 1 is controlled, in the embodiment illustrated, by a screw-and-nut telescopic system 38 of which one end is articulated at 37 to the surface support, the system being controlled, for example, by a geared motor 45. Displacement of the axis of a pin 33 at the other end of the telescopic system 38 brings about rotation of the ramp 1 about the shaft 5 through a connecting rod 36 hinged to the ramp at 32. The pin 33 is in addition connected to the surface support 20 by a connecting rod 34 pivoted on the surface support at 35.

Raising of the ramp 9 about the shaft 6 may be effected by means, for example, of a cable 30 and a winch 31 or by means of jacks arranged at suitable places. Locking means of any suitable kind, represented diagrammatically by hooks 52 and 53, the latter being controlled by a jack 58, ensure if required the locking together of the ramps 1 and 9, when aligned.

When the ramps 1 and 9 are aligned, the slides 2 and 10 may be locked together by means, for example, of a synchronization jack 8 which is fixed to the slide 10. The rod 55 of the jack 8 carries at its end a catcher device 7 which snaps onto the end 3 of an arm 54 which is fixed to the slide 2. Control of the locking or unlocking of the slides 2 and 10 may be effected by any suitable device and does not necessitate any great force by the jack 8 upon its rod 55. In this way the synchronization of the two slides 2 and 10 is ensured and if necessary the repositioning of the slide 10 with respect to the slide 2 after displacement of the rod 55 has been effected by the required distance and after the rod has been fixed. Thus the jack 8 plays the part of an adjustable-position coupling.

The surface support is provided with any suitable means for preserving a fixed position during the course of connecting the section 14 of the pipe P, and then for displacing the support by a distance equal or corresponding to the length of the new section, when the lower end of the pipe P is already resting on the bottom of the water. The slope of the ramp 1 is adjusted as a function of the depth of lay and the characteristics of the pipe P, particularly its diameter and weight 50 that the pipe has at any moment a position close to the required position, when the section 50 is being guided between the rollers 41 on the ramp 1.

Similarly the pressure in the accumulators 44 is adjusted so that for the given depth and pipe, it enables a force to be communicated to the slide 2 such that whatever the sea conditions the jaws 22 always exert on the section 50 a tensile force which avoids any wave of transverse deformation.

The pressure in the accumulators 48 is also regulated so that the slide 10 constantly balances the weight of the new section 14 lying out of the water.

Let us suppose that the bare end of the section 50 is being held by the jaws 22 supported by the ramp 1 but sliding on it through the slide 2 and that the ramp 9 is lying in the horizontal position. Then by any known means a new section 14 is loaded onto the rollers 13, counter-rollers 13a completing the hold on the section 14 during the course of the subsequent tilting of the ramp. The end of the section 14 is seized by the jaws 12. In this position the slide 10 is in its right-hand extreme position because of the pressure exerted by the accumulators 48 on the jack 46. Before tilting of the ramp 9 by means of the winch 31, a connector 15 is introduced into the section, which is attached to an electro-carrier cable 18 passing round a pulley 16 the spindle of which is carried by a unit 17 carried by the slide 10. The cable 18 passes over a pulley 45 on ramp 9, a pulley 24 mounted on the slide 2, and a pulley 25 which is mounted on the ramp 1, before being wrapped round a control winch 4. Thus when at the end of raising the ramp 9 the hooks 52 and 53 are locked together and the slides 2 and 10 are made one by means of the jack 8 the catcher device 7 of which attaches itself to the end 3 of the arm 54, displacements of the pulley 24 and 16 are synchronized. The result is that the connector 15 preserves its position with respect to the sections 50 and 14, whatever the pounding movements undergone by the surface support 20, if the winch 4 is not operated.

Synchronization of the slides 2 and 10 is effected progressively by means of the synchronization jack 8 as soon as the device 7 has latched onto the end 3 of the arm 54, recentering the operating travel of the slide 2 with respect to the travel of the slide 10 and then locking the jack 8 in this position. The jacks 42, 46 and 8 preferably have identical throws C.

Inside the pipe P a device 29 may be arranged for checking the gauge of the pipe. The device may be similar to that described in the French patent application No. 73.30931 which can lock itself in a watertight manner into the tube even in the event of the gauge not being true and may be drawn by a cable 28 carrying a source 27 for radiographic checking of successive pipe sections as well as a fixing-device 19 equipped with a set of jaws 21 for bearing against the inner wall of the section 50, seals which may be inflatable preventing any penetration of water inside the pipe P. The end of the device 19 has catching means capable of being connected to or disconnected from the connector 15 controlled by the electrocarrier cable 18.

Thus after synchronising displacements of the slides 2 and 10, it is sufficient to operate the winch 4 so as to lower the electro-carrier cable 18 until the connector 15 locks onto the fixing device 19 which is supporting by the cable 28 the source 27 and the gauging device 29. After releasing the jaws 21 of the device 19, the new section 14 is lowered by translation of the jaws 12 controlled by jacks 56, the alignment of the sections 14 and 50 being adjusted when the pipes are to be screwed together or the parallelism of the bevels being adjusted when the pipes are to be welded. This adjustment may be effected, for example, by making the rollers 13 adjustable in two different directions. After sliding of the tube 14 over the device 19 the jaws 21 are again tightened against the inner wall of this section.

Welding of the section 14 to the end section 50 of the pipe P is effected by employing a work-platform 39 which is displaced with the slide 2 so that during the whole of the welding operation the platform is fixed with respect to the pipe. At the end of welding the fixing device 19 is unlocked from the section 50 of the pipe by freeing the jaws 21 and the source 27 is brought into the plane of weld by winding up the electro-carrier cable 18 on the winch 4. The internal jaws 21 are then brought into action again in this new position.

The winch 4 is brought progressively under tension so as to take up through the cable 18 the weight of the pipe as completed by the section 14. After release of the jaws 22 and 12, the winch 4 enables the plane of weld to be lowered to the level of a second work-platform 40 where wrapping of the joint and the bared portions of the new section 14 is carried out. After this last operation the surface support 20 is displaced by the length of the section 14 to its new fixed point, the pipe being progressively lowered along the ramp under the control of the winch 4. The speed of unwinding of the winch is regulated so as to keep a correct operating region of the two slides in order that, during the whole of the movement, the slide always exerts a tensile force on the end of the pipe. When the surface support reaches the new fixed point the top end of the connected section 14 which constitutes the end of the pipe P is stopped at the level of the jaws 22 of the ramp 1. The internal jaws 21 of the fixing device 19 are unlocked and this device is raised again by means of the winch 4 in order to be ready to receive a new section. The electro-carrier cable 18 controls the release of the connector 15 which is freed from the device 19. After freeing of the locking means 52, 53 the ramp 9 is brought back to the horizontal to receive a new pipe section after unlocking the connector 7 from the jack 8.

Although the structure and the method described are particularly well adapted for the laying of pipes of any size at any depth, numerous modifications might be made to the various parts of the structure or to the various phases of the method. Thus instead of synchronizing the movements of the slides 2 and 10 by the jack 8 the pressures in the jacks 42 and 46 may be controlled after tilting of the ramp 9 so as to let the whole of the weight be supported by the slide 2. Similarly displacement of the slide 2 may be measured so as to bring under control the end of an auxiliary jack subsidiary to the slide 10 so that it follows the movement of the slide 2, a mechanical locking of some kind integrating the two slides after synchronization. One can employ, for example, the jaws of the fixing device 19.

Similarly the telescopic system 38 for the control of the slope of the ramp 1 may be replaced by an arm of fixed length, the position of its bearing point 37 varying along the surface support by means of a slideway.

As to the various jaws employed, e.g. jaws 12 or 22, they may be of a conventional type employed in drilling operations and appear in the form of a housing containing clamping wedges manipulated by any motive device.