Abstract:
An underwater support device and an installation method for initiating the buckling of a section of rigid underwater pipe ( 16 ) deployed on a seabed ( 14 ). The device has a longitudinal support ( 22 ) capable of being installed between the seabed and the section of rigid underwater pipe ( 16 ) in a transverse direction, in such a way as to be able to locally detach the section of rigid underwater pipe ( 16 ) from the seabed ( 14 ) and allow the rigid underwater pipe ( 16 ) to be moved relative to said longitudinal support ( 22 ) in the direction of the longitudinal support. The device also has a link member ( 36 ) to secure the rigid underwater pipe ( 16 ) and the longitudinal support ( 22 ) in such a way as to be able to install said longitudinal support ( 22 ) on the seabed ( 14 ) by deploying the section of rigid pipe ( 26 ) on the seabed ( 14 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a 35 U.S.C. §§371 national phase conversion of PCT/FR2014/050663, filed Mar. 21, 2014, which claims priority of French Patent Application No. 1352529, filed Mar. 21, 2013, the contents of which are incorporated by reference herein. The PCT International Application was published in the French language. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an underwater support device for initiating the lateral bucking of a section of rigid underwater pipe deployed on a seabed and a method for installing a rigid underwater pipe equipped with said device. 
     BACKGROUND OF THE INVENTION 
     One field of application envisaged is that of the underwater transport of hydrocarbons, of water, of gas or of mixtures thereof. The underwater hydrocarbon drilling wells are linked to underwater installations bearing on the seabed by the rigid underwater pipes for conveying the hydrocarbons. The latter are generally extracted at a high temperature relative to the seabed temperature, and the temperature variations of the hydrocarbons or else the pressure variations, even the service outages, consequently cause thermal variations of the rigid pipe. So, the latter tends to elongate and then shrink. In order to avoid these elongations causing high axial stresses on the rigid pipe likely to cause uncontrolled lateral buckling of the rigid pipe, buckling points are initiated, step by step, where the pipe moves away laterally from its initial position. Since the lateral buckling zones are predefined by the designers, it is possible to give the rigid pipe improved characteristics offering a greater resistance to the great deformations imposed by the lateral buckling. 
     For this, the idea has been devised of installing transversely, step by step under the pipe, longitudinal supports, each formed by a tubular element of circular section so as to locally detach the rigid pipe from the seabed surface. The tubular element is covered with a coating facilitating the sliding of the rigid pipe. In this way, in the vicinity of the tubular element, the rigid pipe is free relative to the seabed and, consequently, the latter offers no resistance to it. Thus, when the rigid pipe tends to elongate because the hot transported fluid causes it to expand, an axial stress occurs, and it thus provokes a buckling of the rigid pipe at the transverse tubular element. In this way, the axial stress disappears. 
     Thus, prior to the installation of a rigid pipe from a surface vessel, tubular elements are deposited on the seabed, step by step and along the predetermined path of the rigid pipe. Then, the rigid pipe is deployed from the surface vessel on the seabed by guiding it for it to be able to come to bear exactly on the tubular elements, orthogonally. 
     Such a mode of implementation requires both a pre-installation of the tubular elements on the seabed and then a real accuracy in the laying of the rigid pipe. Consequently, the laying time can vary according to the weather and sea conditions. 
     Therefore, the problem which arises and that the present invention seeks to resolve is how to provide an underwater support device for the rigid underwater pipe that makes it possible to facilitate and shorten the laying time thereof and avoid any underwater intervention prior to the installation of the rigid pipe. 
     SUMMARY OF THE INVENTION 
     To this end, according to a first aspect, the present invention proposes an underwater support device for initiating the lateral buckling of a section of rigid underwater pipe deployed on a seabed, said device comprising a longitudinal support capable of being installed bearing on said seabed, between said seabed and said section of rigid underwater pipe in a transverse direction relative to said section of rigid underwater pipe, so as to be able to locally detach said section of rigid underwater pipe from said seabed and allow the movements of said rigid underwater pipe relative to said longitudinal support in the direction of said longitudinal support. According to the invention, the device further comprises a link member for securing said rigid underwater pipe and said longitudinal support in such a way as to be able to install said longitudinal support on said seabed by deploying said section of rigid pipe on said seabed. 
     Thus, a feature of the invention lies in the possibility of securing the longitudinal support and the rigid underwater pipe, and thereby being able to bring the longitudinal supports onto the seabed at the time of the deployment of the pipe precisely where required. That is to say, spaced apart from one another by the desired distance and directly under the rigid pipe. As will be explained hereinbelow in more detail, the implementation of the underwater support device is done firstly from the surface. 
     According to a mode of implementation of the invention that is particularly advantageous, said longitudinal support has a groove forming a slide for slidingly receiving said link member. Thus, the longitudinal support comes to bear on the seabed substantially at right angles to the rigid pipe which comes to bear on the longitudinal support. Thus, the rigid pipe is locally detached from the seabed, and the link member which links the rigid pipe and the longitudinal support is translationally guided in the groove, when the rigid pipe tends to buckle laterally. 
     According to a preferred embodiment, said link member is mounted to rotate in said groove. Thus, the longitudinal support can be held in a fixed position folded back parallel to the rigid pipe so as to facilitate its routing from the surface to the seabed. 
     According to another embodiment, said link member has a cam to allow the rotation of said link member relative to said longitudinal support by a determined angular segment. The cam is rotationally secured to the rigid pipe, and it extends inside the groove. In this way, when the longitudinal support is deployed from a position in which it extends parallel to the pipe to a position substantially at right angles to the pipe, the opposite edges of the groove, initially free relative to the cam, come to bear against it in the latter right-angled position. Thus, the longitudinal support is immobilized in rotation relative to the pipe in a direction of rotation. 
     According to yet another embodiment, said groove is T-shaped so as to form a widened groove bottom, and said cam is engaged in said widened groove bottom. In this way, the cam is captive in the widened bottom of the groove in such way that the link member is itself captive to the longitudinal support. 
     Furthermore, said link member has a through orifice for receiving said section of rigid underwater pipe. Thus, on the opposite side, the link member is captive in turn to the rigid pipe. The longitudinal support is consequently totally secured to the rigid pipe and cannot be detached therefrom during its transfer from the surface to the seabed. 
     Advantageously, and as will be explained in the detailed description, immobilizing collars are installed on the pipe on each side of the link member so as to be able to translationally immobilize the latter relative to the rigid pipe. 
     In addition, said longitudinal support has two opposite ends and, advantageously, one of said ends has an attachment member to be able to attach said link member in a position situated close to said one of said ends. Thus, the link member is translationally immobilized in said groove at one of its ends, and consequently, it can easily be folded back toward the rigid pipe to be held there at the other of its ends. 
     Also, the underwater support device comprises an elastic return member stretched between said link member and the other of said opposite ends of said longitudinal support. In this way, when the link member is freed of said one of said ends of the longitudinal support, the elastic return member retracts and provokes the translational driving of the longitudinal support relative to the link member to a position situated substantially mid-way between the two ends of the longitudinal support. This operation is carried out in proximity to the seabed after the longitudinal support has been routed, in such a way as to be able to bring it to bear on the seabed in a transverse position relative to the rigid pipe. 
     According to another object, the present invention proposes a method for installing a rigid underwater pipe on a seabed from a surface, said method being of the type whereby: a surface vessel is provided with a rigid pipe stored on said surface vessel; said rigid pipe is paid out from said surface vessel for its deployment on said seabed as said surface vessel is driven in movement on said surface; and according to the invention, it further comprises the following steps: a plurality of underwater support devices as described above are provided; said plurality of underwater support devices are stored on said surface vessel; and the underwater support devices of said plurality of underwater support devices are secured to said rigid pipe, as said rigid pipe is paid out, so as to be able to drive said underwater support devices from said surface vessel to said seabed. 
     Thus, contrary to the prior art, where it was necessary to first deposit and align the longitudinal supports on the seabed before installing the rigid pipe thereon, by virtue of the subject of the invention, the longitudinal supports are transported directly from the surface to the seabed at the time of the deployment of the rigid pipe. They are thus situated directly in the alignment of the rigid pipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In addition, said underwater support devices are secured at a distance from one another on said rigid pipe. This distance can thus be determined on the surface by spacing them apart from one another at the desired pitch. 
       Other particular features and advantages of the invention will emerge on reading the following description of a particular embodiment of the invention, given as an indicative but nonlimiting example, with reference to the attached drawings in which: 
         FIG. 1  is a schematic view showing an installation method according to the invention; 
         FIG. 2  is a schematic view illustrating a detail of  FIG. 1  of an underwater support device in a first position; 
         FIG. 3  is a perspective schematic view of the underwater support device illustrated in  FIG. 2 , in a second position; 
         FIG. 4  is a straight cross-sectional schematic view of the underwater support device illustrated in  FIG. 3  along the plane VI-VI; 
         FIG. 5  is a detailed perspective schematic view of a linking device; and, 
         FIG. 6  is a perspective schematic view, of the underwater support device illustrated in  FIG. 3 , in a third position. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  illustrates a laying vessel  10  navigating on the surface  12  directly above a seabed  14 . The laying vessel  10  represented here installs a rigid underwater pipe  16  according to a so-called “rigid-unwound” method, in which the rigid pipe  16  is forcibly wound onto a drum  18 , and in which it is paid out through a well  20  in the laying vessel  10 , to then be submerged and deposited bearing on the seabed  14 . Furthermore the rigid underwater pipe  16  is equipped, on the laying vessel  10 , as it is unwound, with underwater support devices  22 . 
       FIG. 2  illustrates an underwater support device  22  with which a portion of rigid pipe  16  to which it is secured is equipped. The underwater support device  22  is thus installed along the rigid pipe  16 , on the laying vessel  10 , as the pipe  16  is unwound. 
     The underwater support device  22  comprises two opposite ends, a securing end  24  and an attachment end  26 , spaced apart from one another by a distance of between  5  and  10  meters, for example. The securing end  24  has a heavy flange  28  while, at the opposite end, the attachment end  26  has a stop flange  30 . Furthermore, the longitudinal support  22  is equipped with two structural rods  32 ,  34  that appear in  FIG. 2  through transparency and which extend to protrude from the stop flange  30  in the attachment end  26 . 
     The longitudinal support  22  is secured to the rigid pipe  16  via a link member  36  that will be described in more detail hereinbelow and which makes it possible to translationally immobilize it relative to the rigid pipe  16 . Furthermore, at the opposite end, at the attachment end  26 , the longitudinal support  22  is held along the rigid pipe  16  by means of a securing collar  38  which encircles the rigid pipe  16  and the structural rods  32 ,  34  extending to protrude from the stop flange  30 . 
     Furthermore, the link member  36  that passes through a portion of rigid pipe  16  is held in translation by means of two stop collars  40 ,  42  installed on each side, around the rigid pipe  16 . In this way, the longitudinal support  22  is held in a fixed position along a portion of the rigid pipe  16 . On the other hand, the rotation about the pipe is allowed so as to ensure that the underwater device is always under the rigid pipe, even if the latter was made to turn about its axis. 
     A plurality of longitudinal supports  22  are supplied and stored on the laying vessel. Thus, the longitudinal supports  22  are installed on the rigid pipe  16  so as to be able to be routed to the seabed  14 , as the rigid pipe  16  is deployed. 
     On approaching the seabed  14 , the securing collar  38  is translationally driven in a direction opposite to the link member  36  so as to free the structural rods  32 ,  34  protruding from the stop flange  30 , to also free the attachment end  26  of the rigid pipe  16 . Also, the longitudinal support  22  will be able to pivot about the link member  36  to a position substantially at right angles to the rigid pipe  16  as illustrated in  FIG. 3 , by virtue of means that will be described hereinbelow. 
     This  FIG. 3  shows the longitudinal support  22  and the link member  36  which links it to the rigid pipe  16 . A T-shaped longitudinal groove  44  can be seen in this  FIG. 3 , formed in the top wall  45  of the support  22 , from the securing end  24  to the attachment end  26 . The T-shaped longitudinal groove  44  forms a slide for the link member  36 . 
     The link member  36  will be described in detail first of all with reference to  FIG. 5 , where it is illustrated by a three-quarter underside view. It comprises a plate  46  separating a head  48  from a foot  50 . The head  48  is passed right through by a through orifice  52  suitable for receiving the rigid pipe  16 . Furthermore, it is divided into two parts, a bottom part secured to the plate  46  defining a hemicylindrical bottom part of the through orifice  52 , and a top part defining a hemicylindrical top part. The two parts are linked together by two screws, screwed respectively from each side of the hemicylindrical parts. 
     Opposite, relative to the plate  46 , the foot is equipped with a cam  54 . The latter, of generally square form, extends radially relative to the foot  50  and it has two rounded opposite corners  56 ,  58 . Furthermore, it has two first opposite bearing edges  60 ,  62 , for transportation, and two second opposite bearing edges  64 ,  66 , for service. It will be observed that the two first opposite bearing edges  60 ,  62  extend substantially parallel to the axis of the through orifice  52 . Furthermore, the foot  50  has a recess  68  situated close to the plate  46 . 
     Reference will be made to  FIG. 4  illustrating in detail how the link member  36  cooperates, on the one hand with the rigid pipe  16  and on the other hand with the longitudinal support  22 . This  FIG. 4  clearly illustrates the T-shaped longitudinal groove  44 , which has a widened bottom  70  forming two opposite parallel edges  72 ,  74  and two corresponding shoulders  76 ,  78 . Thus, the foot  50  of the link member  36  is fitted into the T-shaped groove and  44 , is fitted into the cam  54  inside the widened bottom  70 . The cam  54  is then able to come to bear against the shoulders  76 ,  78  while the plate  46  comes to bear against the top wall  45  of the longitudinal support  22 . In this way, the link member  36  is captive to the T-shaped longitudinal groove  44 . 
     Furthermore, the two second opposite bearing edges  64 ,  66  are respectively in contact with the two opposite parallel edges  72 ,  74  of the widened bottom  70  of the T-shaped longitudinal groove  44 . It will then be understood that, initially, when the support  22  extends along the rigid pipe  16 , the two first opposite bearing edges  60 ,  62  are respectively in contact against the two opposite parallel edges  72 ,  74 , and that, by forcibly rotating the longitudinal support  22 , the two opposite parallel edges  72 ,  74  of the widened bottom  70  of the T-shaped longitudinal groove  44  are respectively driven around the two rounded opposite corners  56 ,  58 . By virtue of the two other corners, not rounded, the longitudinal support  22  is immobilized in rotation in the same direction in a position substantially at right angles to the rigid pipe  16 . 
     Thus,  FIG. 3  illustrates the longitudinal support  22  and the rigid pipe  16  in this substantially right-angled position, and in which the link member  36  is held on the one hand at the securing end  24  of the longitudinal support  22  by means of a strap  80  which encircles the foot  50  of the link member  36  and which emerges through slots  82 ,  84  formed in the heavy flange  28 , and on the other hand by a stretched elastic member  86 , which encircles the foot  50 , in the recess  68 , and which extends longitudinally in the T-shaped groove  44  to be attached to the attachment end  26 . 
     It will be observed that, when the rigid pipe  16  is deployed by caternary means, and when the securing collar  38  releases the structural rods  32 ,  34 , on the one hand the longitudinal support  22  extends by its own weight below the rigid pipe  16 , and on the other hand, in a substantially horizontal direction by virtue of the heavy flange  28  which rebalances the distribution of the weights relative to the body of the longitudinal support  22 . Thus, as represented in  FIG. 3 , the longitudinal support  22  will be able to come to bear on the seabed  14  during the deployment of the rigid pipe  16 . 
     Once all is laid on the seabed, the strap  80  is removed so as to release the link member  36 , as illustrated in  FIG. 6 . Consequently, the elastic member  86  tends to retract and thereby drives the longitudinal support  22  in translation relative to the link member  36  to an intermediate position in which the link member  36  is situated mid-way between the heavy flange  28  and the stop flange  30 . In this way, by continuing the deployment of the rigid pipe  16 , the longitudinal support  22  is made to bear on the seabed, while the rigid pipe  16  is locally detached from this seabed. Similarly, the collars  40  and  42  are removed for the pipe to be able to be displaced along its axis without risking displacing the underwater support device. 
     Furthermore, the link member  36  is now free in translation in the T-shaped longitudinal groove  44  of the longitudinal support  22 . 
     Also, when commissioning the rigid pipe  16 , its longitudinal extension due to the thermal or internal pressure variations quite naturally provokes the buckling thereof at the longitudinal support  22  and thereby slidingly drives the link member  36  toward the end  26 , relative to its initial position between the two ends  24 ,  26  of the longitudinal support  22 . 
     Also, as illustrated in  FIG. 1 , the invention relates also to a method for installing a rigid underwater pipe and longitudinal supports  22  on a seabed  14  from a surface  12 . The rigid pipe  16  and the longitudinal supports  22  are initially stored on the laying vessel  10 . The rigid pipe  16  is either forcibly pre-wound on a drum, as illustrated in  FIG. 1 , or obtained from an assembly of sections directly on the laying vessel  10 . 
     During the paying out of the rigid pipe  16  for its deployment on the seabed  14 , the longitudinal support  22  are installed at the points determined in the in-situ analysis of the rigid pipe, in the configuration as represented in  FIG. 2 . For this, the pipe is installed inside the hemicylindrical bottom part of the bottom part of the head  48  of each of the longitudinal supports  22 , then the top part is added and screwed on to keep the pipe captive between the two parts. The two stop collars  40 ,  42  are then installed on each side of the head  48 . 
     It is only when the longitudinal supports  22  come to approach the seabed  14  that they are adjusted in position, for example by means of an underwater robot, for them to be then able to come to bear on the seabed  14 .