Patent Publication Number: US-8974149-B2

Title: Method of joining two portions of an underwater pipeline for conducting fluids and/or gas

Description:
TECHNICAL FIELD 
     The present invention relates to a method of joining two portions of an underwater pipeline for conducting fluid and/or gas on the bed of a body of water. 
     BACKGROUND ART 
     For the purpose of the present invention, the term “underwater pipeline” is generally intended to mean a pipeline laid on the bed of a body of even deep water to conduct gas and/or fluid, in particular oil. 
     An underwater pipeline of the type described covers distances of hundreds of kilometers, is composed of pipes joined to one another on a laying vessel, is launched into the water off the laying vessel, and is laid on the bed of the body of water as it is assembled. 
     Each pipe is normally of 12-meter unit length, has a relatively large diameter ranging between 0.2 and 1.5 meters, and comprises a steel cylinder; a protective covering of polymer material contacting the steel cylinder to protect it from corrosion; and sometimes a heavy covering of concrete or Gunite contacting the protective covering to weigh the pipe down. 
     The pipes are joined at on-land installations into pipes of multiple unit length, and on laying vessels on which the pipes of unit or multiple unit length are joined to form the pipeline, which is then launched off the laying vessel onto the bed of the body of water. 
     The pipeline is assembled and launched off the laying vessel using one of two methods, depending on the depth of the body of water. 
     In a first method, the pipeline is formed on a launch tower comprising an assembly station, and is launched substantially vertically so that it assumes a J-shaped configuration between the laying vessel and the bed of the body of water. This method is particularly suitable for laying pipelines in very deep water. 
     In the second method, the pipeline is formed on a substantially horizontal assembly line, and is launched off a lay ramp which, in the work configuration, serves to guide and support the pipeline along a curved path having a first portion above water, and a second portion below water. Pipelines laid using this method assume an S-shaped configuration between the laying vessel and the bed of the body of water. 
     Close to coastlines and in shallow water, pipelines are normally buried in the bed to protect them against hydrodynamic stress, changes in temperature, and damage by foreign bodies. 
     Burying underwater pipelines in the bed is a common practice in shallow water, but is difficult to do and economically unfeasible in deep water. As a result, pipelines simply laid on the bed in deep water are exposed to blunt objects, such as inadvertently towed anchors, which literally “plough” the bed and may damage the pipeline, even to the point of ripping it apart. Incidents of this sort are relatively rare, but the damage caused by them is enormous, both in terms of pollution and the fact that many countries depend almost entirely on such pipelines for their energy supply. 
     When they do occur, therefore, steps must be taken immediately to repair, seal, and restore the mechanical characteristics of the pipeline. 
     Various methods of doing this have been proposed, some of which provide for carrying out all the repair work in the body of water, and others for performing part of the repair work above the body of water, and part in the body of water. 
     A repair method described in U.S. Pat. No. 5,437,517 comprises the steps of cutting out the damaged length of pipeline to form a first and second pipeline portion having a first and second end respectively; joining a first coupling head to the first pipeline portion in the body of water; joining a second coupling head to the second pipeline portion in the body of water; laying a telescopic sleeve, having a third and fourth coupling head, in the body of water, between the first and second coupling head; aligning the first pipeline portion, the second pipeline portion, and the telescopic sleeve in the body of water; adjusting the length of the telescopic sleeve in the body of water; and joining the telescopic sleeve to the first and second coupling head in the body of water. The telescopic sleeve, which comprises two sliding tubes, is then locked into position. All the above operations are performed in the body of water using underwater equipment controlled by ROVs (Remote Operated Vehicles) connected by cable (umbilical) to a laying vessel. 
     One of the most critical parts of the above method is aligning the first and second pipeline portion and the telescopic sleeve; and the deeper the water is, the more difficult alignment becomes. Adjusting the length of the telescopic sleeve is also a delicate operation, by having to be performed without moving the sleeve out of line with respect to the first and second coupling head. 
     An underwater pipeline repair method described in U.S. Pat. No. 4,304,505 comprises the steps of cutting out the damaged length of pipeline to form a first and second pipeline portion having a first and second end respectively; raising the first end onto a laying vessel; joining a first coupling head to the first pipeline portion; laying the first end and the first coupling head onto the bed of the body of water; raising the second end onto the laying vessel; joining a second coupling head to the second pipeline portion; laying the second end and the second coupling head onto the bed; laying a pipe section, having a third and fourth coupling head, in the body of water, between the first and second coupling head; aligning the first pipeline portion, the second pipeline portion, and the pipe section in the body of water; and joining the pipe section to the first and second coupling head in the body of water. 
     This method too involves a critical aligning stage, which is vital for achieving connections capable of restoring the mechanical characteristics and fluidtight sealing between the pipe section and the first and second pipeline portion. 
     Accurately aligning the first and second pipeline portion and the telescopic sleeve or pipe section calls for the use of an extremely complex aligning device designed to engage and align the first and second pipeline portion and the telescopic sleeve (or pipe section, in the case of the method described in U.S. Pat. No. 4,304,505). 
     DISCLOSURE OF INVENTION 
     It is an object of the present invention to provide a straightforward method of joining two portions of an underwater pipeline, with no need for complex, bulky equipment. 
     Another object of the present invention is to provide a method of joining two portions of an underwater pipeline that can be implemented on sloping and/or uneven beds. 
     According to the present invention, there is provided a method of joining two portions of an underwater pipeline for conducting fluid and/or gas on the bed of a body of water; the method comprising the steps of:
         joining a telescopic sleeve, having a first coupling head; to a first end of a first pipeline portion above the body of water;   positioning the first end, the telescopic sleeve, and the first coupling head in a first given position below the body of water;   joining a second coupling head to a second end of a second pipeline portion above the body of water;   positioning the second end and the second coupling head in a second given position, close to the first coupling head, below the body of water; and   connecting the first and second coupling head hermetically below the body of water.       

     The present invention makes the aligning step relatively easy, by only having to align the first and second coupling head in the body of water; all the other connections being made abovewater. 
     Another object of the present invention is to provide a method of repairing an underwater pipeline. 
     According to the present invention, there is provided a method of repairing an underwater pipeline, the method comprising the steps of cutting and removing a pipeline section from the pipeline below a body of water to form a first and second pipeline portion; raising the first and second pipeline portion partly above the body of water; and joining the first and second pipeline portion using the method described above for joining two portions of an underwater pipeline. 
     Another object of the present invention is to provide a method of laying an underwater pipeline. 
     According to the present invention, there is provided a method of laying an underwater pipeline, the method comprising the steps of laying a first and second pipeline portion along two respective converging paths by means of two respective laying vessels; and joining the first and second pipeline portion using the method described above for joining two portions of an underwater pipeline. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
         FIGS. 1 to 5  show side views, with parts removed for clarity, of an underwater pipeline lying in a body of water and at various stages in the underwater pipeline repair method according to the present invention; 
         FIG. 6  shows a larger-scale, partly sectioned side view, with parts removed for clarity, of a detail of a launching device employed in the method of joining two portions of an underwater pipeline according to the present invention; 
         FIGS. 7 to 9  show larger-scale, longitudinal sections, with parts removed for clarity, of one end of a pipeline portion at respective stages in the method of joining two portions of an underwater pipeline according to the present invention; 
         FIG. 10  shows a larger-scale, longitudinal section, with parts removed for clarity, of one end of a further pipeline portion at one stage in the method of joining two portions of an underwater pipeline according to the present invention; 
         FIGS. 11 and 12  show side views, with parts removed for clarity, of an underwater pipeline lying in a body of water and at different stages in the method of joining two portions of an underwater pipeline according to the present invention; 
         FIG. 13  shows a larger-scale, longitudinal section, with parts removed for clarity, of a telescopic sleeve welded to a pipeline portion and assembled to another pipeline portion in accordance with the method of joining two portions of an underwater pipeline according to the present invention; 
         FIG. 14  shows a larger-scale view in perspective, with parts removed for clarity, of a detail of a self-centring connecting assembly designed to implement the method of joining two portions of an underwater pipeline according to the present invention; 
         FIG. 15  shows a side view, with parts removed for clarity, of one stage in the method of laying an underwater pipeline according to the present invention; 
         FIG. 16  shows a view in perspective, with parts removed for clarity, of one stage in a first variation of the method according to the present invention; 
         FIG. 17  shows a longitudinal section of two pipeline portions fixed to a sleeve equipped with a coupling head, and to a coupling head respectively; 
         FIGS. 18 ,  19  and  20  show views in perspective, with parts removed for clarity, of successive stages in a further variation of the method according to the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Number  1  in  FIG. 1  indicates as a whole an underwater pipeline laid on the bed  2  of a body of water  3  to conduct fluid and/or gas, and in particular oil. 
     Pipeline  1  has a damaged area—in the example shown, a rip  4  caused accidentally—and is in need of repair. For the sake of simplicity in the description and drawings, bed  2  is flat, though pipeline  1  may lie on sloping or variously uneven beds. 
       FIG. 1  also partly shows the pipeline repair equipment employed, which comprises a laying vessel  5 ; underwater remote operated vehicles (ROVs)  6 , only one of which is shown in  FIG. 1 ; and two gantry cranes  7  which rest on bed  2  of the body of water  3  to raise and support the part of pipeline  1  containing rip  4  off bed  2 . 
     As shown in  FIG. 1 , gantry cranes  7  are positioned astride pipeline  1  and on either side of rip  4  to lift the part of pipeline  1  containing rip  4  off bed  2 . 
     The Laying Vessel 
     Laying vessel  5  is designed to assemble pipelines on board and launch pipelines into the body of water  3 . In this particular case, laying vessel  5  is used to repair pipeline  1  lying on the bed of body of water  3 . 
     Laying vessel  5  comprises a semisubmersible  8 ; and a launch rig  9  which, in the example shown, is a launch tower which extends in a substantially vertical launch direction D 1 , is hinged to semisubmersible  8 , and is designed to J-launch the pipeline onto bed  2  of body of water  3 . Though shown in a substantially vertical position, launch rig  9  can be tilted to an angle of 30° with respect to the vertical at the launch stage. 
     Launch rig  9  is substantially defined by an elongated trestle structure, and comprises a top portion housing an assembly station  10 ; an intermediate portion housing a gripping fixture  11  comprising a crawler gripping device  12  ( FIG. 6 ) for selectively gripping pipeline  1 ; and a bottom portion housing a step feed device  13  comprising jaws  14  fixed to the trestle structure ( FIG. 6 ), and movable jaws (not shown) movable along the trestle structure. 
     Laying vessel  5  is equipped with at least one crane  15  for lowering into the water and recovering underwater vehicle  6 , gantry cranes  7 , and other equipment used to repair pipeline  1 ; and a winch  16  fitted to launch rig  9  to recover and hoist parts of pipeline  1  off bed  2  of body of water  3  and partly into launch rig  9 , at assembly station  10 , and to lower them into body of water  3 . 
     The Underwater Vehicle 
     Underwater vehicle  6  is controlled from laying vessel  5  over an umbilical  17 , and comprises a frame  18 ; a pontoon  19 ; television cameras (not shown); a propeller assembly (not shown); at least one manipulator arm  20 ; and a docking station  21  which docks with respective docking stations of underwater equipment for carrying out operations as described below. 
     Depending on the operations performed in body of water  3 , one or more underwater vehicles  6  may be used to speed up repair of pipeline  1 . 
     The Gantry Crane 
     Each gantry crane  7  comprises two gantry structures  22  connected rigidly by cross beams  23 ; a powered carriage assembly  24  connected to two jaws  25  for gripping pipeline  1 , and which moves jaws  25  along a system of cartesian axes xyz inside gantry structures  22 ; and a docking station (not shown) which docks with docking station  21  of underwater vehicle  6 , which thereby controls operation of powered carriage assembly  24  and jaws  25 . 
     Each gantry structure  22  is equipped with supporting plates  26  which are embedded in bed  2  to define a precise position of gantry crane  7 . 
     The Underwater Pipeline 
     With reference to  FIG. 7 , pipeline  1  comprises a metal cylinder  27 , and a protective covering  28  of deformable polymer material about metal cylinder  27 . In other words, protective covering  28  is more deformable than metal cylinder  27 . 
     The term “protective covering” includes relatively thin (a few millimeters thick) PP (polypropylene) or PE (polyethylene) corrosion-proofing coverings, as well as lagging which, in addition to corrosion-proofing, also provides for thermal insulation, may be as much as a few tens of a mm in thickness, and is normally made of solid PU (polyurethane) or multilayer PP (polypropylene). 
     Pipeline  1  also has a concrete or Gunite covering on top of protective covering  28  to weigh the pipeline down. 
     With reference to  FIG. 1 , rip  4  has compromised the integrity of metal cylinder  27  ( FIG. 7 ), resulting in oil leakage into body of water  3  and water flow into pipeline  1 . The method according to the present invention provides for repairing pipeline  1  to restore the mechanical characteristics and fluidtight sealing of the pipeline as laid down by current safety standards. 
     Pipeline  1  is flexible enough to extend along curved paths. 
     Pipeline Repair Method Including the Method of Joining Two Portions of an Underwater Pipeline 
     The repair method comprises moving laying vessel  5  and the other repair equipment to the accident site, and lowering underwater vehicle  6  and gantry cranes  7  into the water using crane  15 . Correct positioning of gantry cranes  7  on either side of rip  4  and astride pipeline  1  is controlled by underwater vehicle  6 , which is connected to each gantry crane  7  by docking station  21 , and remains connected to gantry crane  7  to control gripping and raising of pipeline  1  by means of jaws  25 . 
     The above operations are performed for each gantry crane  7 . 
     In an embodiment not shown, gantry cranes  7  may be more than two in number, the number substantially depending on the type of pipeline  1 , the type of gantry crane  7 , and the type of bed  2 . 
     Similarly, more than one underwater vehicle  6  may be employed. In a preferred operating mode, two underwater vehicles  6  are employed to operate at least two gantry cranes  7  simultaneously. 
     When raised by both gantry cranes  7 , pipeline  1  assumes the configuration shown in  FIG. 1 . 
       FIG. 2  shows the step of cutting pipeline  1 , which comprises making two cuts crosswise to pipeline  1  on opposite sides of rip  4 , so as to divide pipeline  1  into a portion  30  containing the damaged area, i.e. rip  4 , and two pipeline portions  31  and  32 , as shown in  FIG. 3 . 
     With reference to  FIG. 2 , the portion of pipeline  1  eventually defining portion  30  is connected to a float  33 , and underwater vehicle  6  is connected to a cutter  34  which, in the preferred embodiment, is defined by a wire cutter with which to make the cuts in pipeline  1  as described above. 
     With reference to  FIG. 3 , portion  30  is lifted onto laying vessel  5  by means of float  33 , underwater vehicle  6 , and crane  15 . 
     The two portions  31  and  32  of the pipeline thus have respective ends  35  and  36 , and extend along respective axes A 1  and A 2 . 
     The length of the recovered portion  30  is measured to determine the distance between ends  35  and  36 . 
     With reference to  FIG. 4 , winch  16  lowers a cable  37  connected to a gripping head  38  which, in the example shown, is an expansion head which is inserted into end  35  of pipeline portion  31  and subsequently expanded to grip end  35  of pipeline portion  31  from the inside. 
     Insertion and expansion of gripping head  38  inside end  35  are controlled by underwater vehicle  6 . 
     With reference to  FIG. 5 , pipeline portion  31  is raised partly by winch  16  and gripping head  38 , and inserted partly inside launch rig  9 , as shown in  FIG. 6 . Inside launch rig  9 , crawler gripping devices  12  and jaws  14  grip pipeline portion  31 , and gripping head  38  is released from end  35  of pipeline portion  31 . End  35  is raised as far as assembly station  10 , where weigh-down covering  29  and protective covering  28  are removed from end  35 , and end  35  is bevelled to form a suitable edge on metal cylinder  27 . More specifically, in the example shown, the work carried out on end  35  at assembly station  10 , above body of water  3 , transforms end  35  from the  FIG. 7  to the  FIG. 8  configuration. 
     Removal of protective covering  28  may also include grit blasting the exposed part of metal cylinder  27 . 
     A telescopic sleeve  39  with a coupling head  40  is then joined to pipeline portion  31  at assembly station  10 , above body of water  3 . More specifically, telescopic sleeve  39  has an axis A 3  and is welded to metal cylinder  27 , with axes A 1  and A 3  aligned, to form the structure shown in  FIG. 9 . 
     The weld area may subsequently be covered with a protective joint  41  at assembly station  10 . 
     Pipeline portion  31 , telescopic sleeve  39 , and coupling head  40  are then laid on bed  2  of body of water  3  by winch  16  and gripping head  38 . Alternatively, winch  16  may be connected directly to telescopic sleeve  39 . 
     In the same way as for pipeline portion  31 , pipeline portion  32  is inserted partly inside launch rig  9 , coverings  28  and  29  are removed, the edge of metal cylinder  27  is bevelled, portion  32  is joined to a coupling head  42 , and the joint is covered with a protective covering  41 , as shown in  FIG. 10 . 
     Once these operations are completed, underwater vehicle  6  lays pipeline portion  32  on bed  2  of body of water  3 , so that coupling head  42  is positioned close to and facing coupling head  40 . Gantry cranes  7  are positioned along respective pipeline portions  31 ,  32  as shown in  FIG. 11 , and respective jaws  25  grip respective ends  35 ,  36  of portions  31 ,  32  to produce the configuration shown in  FIG. 11 . 
     At this stage, the two gantry cranes  7  are preferably controlled simultaneously by respective underwater vehicles  6  to align coupling heads  40  and  42  faster. To align them, each coupling head  40 ,  42  is equipped with a signal transmitter which indicates the position of the respective coupling head and transmits it to the respective underwater vehicle  6  controlling respective gantry crane  7 ; and gantry cranes  7  move the ends of pipeline portions  31  and  32  and coupling heads  40  and  42  to align axes A 3  and A 2  roughly, with a margin of error of a few millimeters. 
     Before being welded to end  35  of pipeline portion  31 , telescopic sleeve  39  is adjusted in length on board laying vessel  5 , above body of water  3 . This rough adjustment is based on the distance determined between ends  35  and  36 , and the length of coupling heads  40  and  42 . Theoretically, the length of telescopic sleeve  39  and the lengths of coupling heads  40  and  42  should total the length of portion  30  removed from pipeline  1 . For easy manoeuvring, however, the length of telescopic sleeve  39  is preferably adjusted to leave a gap of a few decimeters between coupling heads  40  and  42  when they are aligned in body of water  3 . 
     When aligned roughly by gantry cranes  7 , coupling heads  40  and  42  are separated a few decimeters apart, and axes A 2  and A 3  are also most likely offset a few millimeters. 
     Coupling heads  40  and  42  are connected hermetically by a clamping device  43  which, together with coupling heads  40 ,  42 , forms part of a self-centring connecting assembly  44  which, at the clamping stage, aligns axes A 3  and A 2  and extends telescopic sleeve  39  simultaneously. 
     With reference to  FIG. 14 , clamping device  43  comprises two annular jaws  45  connectable to each other by threaded bars  46  and nuts  47 ; and each annular jaw  45  comprises two half-rings  48  connected by a hinge  49 , so jaw  45  can be opened and placed about one of pipeline portions  31 ,  32 . 
     With reference to  FIG. 13 , coupling head  40  comprises a tubular portion  50  joined to telescopic sleeve  39 ; a flange  51  with a front face  52  perpendicular to axis A 3  and facing coupling head  42 ; a truncated-cone-shaped projection  53  extending about axis A 3 ; a lateral face  54 ; and a rear face  55  sloping with respect to axis A 3 . 
     Likewise, coupling head  42  comprises a tubular portion  56  welded to pipeline portion  32 ; a flange  57  with a front face  58  perpendicular to axis A 2  and facing coupling head  40 ; a truncated-cone-shaped recess  59  extending about axis A 2  and complementary in shape and size to projection  53 ; a lateral face  60 ; and a rear face  61  sloping with respect to axis A 2 . 
     Each jaw  45  has a seat defined by two faces  62  and  63  designed to mate respectively with rear face  55  and lateral face  54 , or with rear face  61  and lateral face  60 . In other words, each jaw  45  has a seat designed to form a joint with flange  51  or flange  57 . 
     When the two jaws  45  are tightened one against the other, telescopic sleeve  39  is extended, and projection fits inside recess  59  to accurately align coupling heads  40  and  42  until front faces  52  and  58  come into contact with each other. 
     With reference to  FIG. 12 , jaws  45  are positioned about respective coupling heads  40 ,  42  and clamped by means of a dedicated clamping unit  64  controlled by underwater vehicle  6 . 
     With reference to  FIG. 13 , telescopic sleeve  39  is locked into position by deforming one wall by means of a known hydroforming process, which deforms an inner tube  65  against an outer tube  66  with annular ribs  67 . 
     The method according to the present invention is extremely straightforward and requires no bulky equipment. 
     Method of Laying an Underwater Pipeline 
     The method described of joining two underwater pipeline portions may be used to advantage for repairing pipelines, particularly in deep water. The pipeline joining method forming part of the repair method described above, however, may also be employed as part of a method of laying an underwater pipeline  1  as shown in  FIG. 15 , in which two laying vessels  5  and  68  lay two underwater pipeline portions  31  and  32  extending along respective converging paths P 1  and P 2  and fitted respectively with a telescopic sleeve equipped with a coupling head, and with a coupling head. The two coupling heads are of the type described above, and are connectable in deep water in accordance with the method of joining two pipeline portions. 
     This application of the method of joining two underwater pipeline portions provides for simultaneously laying two underwater pipeline portions, each possibly hundreds of kilometers in length, and so greatly reducing overall laying time. 
     First Variation of the Method 
     A first variation, shown roughly in  FIG. 16 , employs a device  69  designed to rest on bed  2  of body of water  3  to support ends  35  and  36  of pipeline portions  31  and  32  and sleeve  39  in respective given positions. 
     The steps in the method described above remain the same, except that coupling heads  40 ,  42  and sleeve  39  are laid on device  69 , which serves to guide coupling heads  40 ,  42  accurately into respective given positions in which coupling heads  40 ,  42 , i.e. axes A 2  and A 3 , are substantially aligned. Once substantially aligned, coupling heads  40  and  42  are first moved into contact with each other, thus completing the alignment, and then clamped as described above. 
     Once coupling heads  40  and  42  are connected hermetically, pipeline  1  can be raised, and device  69  removed and raised on board laying vessel  5  (not shown in  FIG. 16 ). 
     In the  FIG. 16  example, device  69  comprises a base  70  defining a supporting base on bed  2 ; and a cradle  71  fitted to base  70  and comprising a flared seat  72  designed to guide telescopic sleeve  39  into a given position, and a flared seat  73  designed to guide coupling head  42  into a given position. Device  69  is designed to operate with an actuating device  74  for moving coupling heads  40  and  42  towards each other. 
     Base  70  is substantially flat, and cradle  71  is connected to base  70  by elastic joints (not shown in  FIG. 16 ) allowing adjustment of cradle  71  with respect to base  70 , in particular in a direction crosswise to pipeline  1 . Alternatively, cradle  71  is connected to base  70  on slides running along guides (not shown). 
     Actuating device  74  comprises a yoke  75  for engaging coupling head  42 ; a yoke  76  for engaging coupling head  40 ; and preferably hydraulic actuators  77  connecting yokes  75  and  76  and controlled to selectively bring coupling heads  40  and  42  into contact with each other. From this point on, the coupling heads are joined as described in the preceding method. 
     This first variation of the method has the advantage of automatically aligning the coupling heads by means of the seats in the cradle. The coupling heads and respective pipeline portions are lowered into the cradle using systems similar to those employed to lower and recover the pipeline, and with the aid of underwater vehicles  6  (not shown) to roughly centre the seats in the cradle. The first variation of the method also speeds up connection by eliminating the need to align the coupling heads, and by involving only one connection below water. 
     Second Variation of the Method 
     In a second variation of the method, a telescopic sleeve  78  and coupling heads  79  and  80  are preferably substituted for telescopic sleeve  39  and coupling heads and  42 , as shown in  FIG. 17 . More specifically, telescopic sleeve  78  and coupling head  80  have substantially the same outside diameter, and coupling heads  79  and  80  have no flanges. Telescopic sleeve  78  is locked using the same system as for telescopic sleeve  39 , and coupling heads  79  and  80  are joined by inserting coupling head  79  inside coupling head  80  and deforming coupling head  79 . More specifically, coupling head  79  has a thin outer wall  81  and a thick inner wall  82  separated by a gap into which pressurized fluid is fed to deform the outer wall against coupling head  80  and so join coupling heads  79  and  80  hermetically. 
     This second variation of the method comprises substantially the same steps as the first variation, except that telescopic sleeve  78  is fitted to a cradle  83  above body of water  3 ; and cradle  83 , together with telescopic sleeve  78  and coupling head  79 , is laid on bed  2  of body of water  3 , as shown in  FIG. 18 . 
     With reference to  FIG. 18 , cradle  83  is substantially defined by a cylindrical half-shell, which is bound or otherwise fixed to telescopic sleeve  78  using means not shown in the drawings, and has a free portion projecting beyond coupling head  79 . 
     In the event the diameter of telescopic sleeve  78  is not constant along its whole length, spacers  84  are inserted between cradle  83  and telescopic sleeve  78 , so that the respective longitudinal axes of telescopic sleeve  78 , coupling head  79 , and the cradle are substantially aligned. Cradle  83  is attached accurately above body of water  3 , on board laying vessel  5 ; and cradle  83 , telescopic sleeve  78 , coupling head  79 , and pipeline portion  31  are then laid on bed  2  of body of water  3  using a pipeline lowering and recovery system, of which  FIG. 18  shows a cable  37 , and a harness  85  connected to cable  37  and telescopic sleeve  78 . 
     Portion  32  of pipeline  1  is then raised above body of water  3 ; coupling head  80  is joined to end  36 ; and coupling head  80  and pipeline portion  32  are then lowered into body of water  3  and into cradle  83 , as shown in  FIG. 19 . 
     Coupling head  80  is seated inside cradle  83 , facing coupling head  79 . At this point, coupling head  79  is inserted inside coupling head  80  by the actuating device described with reference to  FIG. 16 ; and an underwater vehicle  6  (not shown in  FIG. 19 ) then injects pressurized fluid to join coupling heads  79  and  80 . 
     With reference to  FIG. 20 , underwater vehicle  6  injects pressurized fluid into the gap in telescopic sleeve  78  to lock telescopic sleeve  78  in a given position. 
     This second variation of the method provides for easy, low-cost alignment of the coupling heads, and also has additional advantages over the first variation: the thinness of the cradle imposes no sharp bends in the pipeline close to the cradle; the cradle can be left on the bed and connected to the pipeline to act as a stiffener at the joint between the two pipeline portions; and the cradle is extremely simple to make and handle. 
     In another variation, not shown, the cradle may be connected to the coupling head without the telescopic sleeve, and the telescopic sleeve may be laid on the cradle together with the other coupling head. 
     The variations of the method described obviously also apply to both repairing damaged pipelines, and joining independently laid underwater pipeline portions. 
     Though the above description refers specifically to a laying vessel equipped with a J-launch tower, the methods according to the present invention also apply to vessels equipped with substantially horizontal assembly lines and S-launch ramps. 
     Clearly, changes may be made to the embodiments described of the present invention without, however, departing from the scope of the accompanying Claims.