Abstract:
A method of forming a protection system and a protection system for a secondary conduit adapted to be coupled to a main conduit is disclosed. The main conduit and the secondary conduit are for installation below the sea surface. The method includes spooling onto a reel an elongate member in a first configuration for transportation and/or storage until such a time that it is ready to be deployed. The first configuration is a substantially planar configuration. The method also includes paying the elongate member out from the spool and causing or allowing the elongate member to adopt a second configuration and form the protection system for the secondary conduit. The second configuration is a substantially non-planar configuration. The elongate member is coupled to an external surface of the main conduit.

Description:
This Application is the U.S. National Phase of International Application Number PCT/GB2010/052119 filed on Dec. 16, 2010, which claims priority to Great Britain Application Number 0921946.0 filed on Dec. 16, 2009. 
     BACKGROUND OF THE INVENTION 
     (1) Field of Invention 
     The present invention relates to an apparatus and method for protecting a conduit which may be a cable to be installed subsea and particularly but not exclusively relates to a method and apparatus for protecting a cable such as a Direct Electrical Heating (DEH) cable that is attached to fluid flowline (in a manner known in the art as “piggybacked”) that is to be installed subsea. 
     (2) Description of Related Art 
     Conventionally, fluid flowlines such as oil flowlines are arranged to transport oil from subsea wellheads and/or from offshore production platforms to oil and gas storage facilities and refineries onshore, and such flowlines are conventionally installed subsea in a reeled pipe lay operation from a flowline installation vessel such as a reel lay vessel such as the Seven Oceans operated by the present applicant Subsea 7. 
     In a lot of oil wells, the oil is relatively highly viscous and the viscosity increases the lower the temperature of the oil drops. Accordingly, it is conventional to heat the oil flowing through the flowlines in order to prevent the viscosity rising by using either induction heating or trace heating. In either case, electrical cables need to be run to provide the closed circuit required. In the induction heating case, the return cables are the DEH cables. 
       FIG. 4  shows a conventional prior art DEH cable  1  which is arranged to provide electrical power to wire heating elements (not shown) installed at two or more longitudinally spaced apart locations in the side wall of a conventional steel flowline  3 . As can be seen in  FIG. 3 , the flowline  3  is provided with suitable rigid insulation  5  in a conventional manner. 
     When installing flowlines  3  and DEH cables  1  on the sea bed, it is important to provide a Mechanical Protection System (MPS) for them in order to protect them (and particularly the otherwise exposed DEH cable  1 ) from dropped objects, fishing nets, anchors etc. as such objects can do great harm to DEH cables  1  and flowlines  3  which may result in the need to replace the whole flowline  3 . 
     One such conventional MPS  10  that is not in accordance with the present invention is shown in  FIGS. 1 to 4 , in which: 
       FIG. 1  is a cross sectional view of a cover section  14  being brought toward a gutter section  12  of the conventional MPS  10 ; 
       FIG. 2  is a perspective side view of a number of gutter sections  12  of the conventional MPS  10  in a stacked configuration for transportation and/or storage; 
       FIG. 3  is a perspective view of a number of cover sections  14  of the conventional MPS  10  in a stacked configuration for transportation and/or storage; and 
       FIG. 4  is a cross sectional end view of the conventional MPS  10  of  FIG. 1  shown in its in use configuration piggybacked on a flowline  3  with a DEH cable  1  being located in the cylindrical throughbore of the MPS  10  and being protected thereby. 
     As best seen in  FIG. 4 , the conventional MPS  10  comprises a main body  12  in the form of a gutter section  12  and an upper cap  14  in the form of a cover section  14  and which are shown in more detail and in isolation in  FIG. 1 . The main body  12  and the upper cap  14  comprise a suitable key  13  and slot  15  which, when mated, realisably secure the upper cap  14  to the main body  12  such that the structure of the upper cap  14  and main body  12  when coupled provide a protective structure around a cylindrical through bore  11  which in use forms a protective cylindrical chamber  11  suitable for protecting the DEH  1 . 
     As can be seen in  FIG. 4 , the DEH piggyback cable  1  is loosely installed inside the inner bore provided by the MPS  10 , and can thus move freely inside the MPS  10  to accommodate flowline  3  thermal differential expansion and flexing of the two relative to each other that might occur during their installation and handling. 
     The conventional MPS  10  of  FIGS. 1 to 4  is assembled as follows. The flowline  3  and its insulation  5  are pulled off the reel on the flowline installation vessel (not shown). An engineer  17  either manually picks up or with the use of a crane or the like lifts a main body  12  and rests it on top of the insulation  5  of the flowline  3 . Each main body  12  is in the region of 2.6 meters or so long and can weigh in the region of 17 to 26 kg each. 
     The DEH cable  1  is then pulled off its own reel (not shown) by a suitable machine and is placed into the semi-circular lower through bore portion  19  of the main body  12  such that it rests therein and one length of upper cap  14  is manually picked up by the engineer  17  or can be lifted with a crane or the like and manipulated such that the key  13  is brought towards and is fitted into the slot  15  (it being shown in  FIG. 1  as being brought toward). A metal band  16  is then manually applied around the outer surface of the upper cap  14  and the main body  12  and also the outer surface of the insulation  5  such that the metal banding  16  ensures that the MPS  10  is held securely against the flowline  3 . The MPS  10  thereby provides a protective chamber within or in the form of its cylindrical throughbore  11  for the DEH cable  1 . 
     However, such a conventional MPS  10  suffers from several disadvantages. For instance, the main body or gutter section  12  and also the upper cap or cover section  14  are typically 2.6 meters long. Therefore, for a typical 11 km length of flowline  3 , 4230 gutter sections  12  and 4230 cover sections  14  would be required. These would typically be supplied to the flowline installation vessel on wooden pallets and typically 100 such pallets would be required and these would be supplied within 40 containers which would take up the available deck space on an installation vessel many times over. Accordingly, the flowline installation vessel would need to be supplied on a regular basis with for example 3 or 4 containers per supply run. Consequently, the transportation/supply costs are very expensive. Furthermore, such a conventional MPS  10  heavily relies on manual handling of 8460 gutter and cover sections in total for a typical 11 km length of flowline  3  and this therefore poses a significant safety risk to the engineers  17  involved. Furthermore, the assembly of the gutter  12  and cover  14  sections, particularly because of the manual assembly, is very time consuming. 
     It is an object of embodiments of the present invention to mitigate such disadvantages with the conventional MPS  10  but still provide a reliable and an assured protection system for a DEH cable  1 . 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided a protection system for a secondary conduit adapted to be coupled to a main conduit, wherein both the main conduit and the secondary conduit are for installation below the sea surface, the protection system comprising:
         an elongate member adapted to be spooled onto a reel for transportation and/or storage.       

     In accordance with the present invention there is provided a method of forming a protection system for a secondary conduit adapted to be coupled to a main conduit, wherein both the main conduit and the secondary conduit are for installation below the sea surface, the method comprising:
         spooling an elongate member onto a reel for transportation and/or storage until such a time that it is ready to be deployed; and   paying the elongate member out from the spool such that it forms the protection system for the secondary conduit.       

     The elongate member may be coupled to an external surface of the main conduit. The elongate member may be coupled to the main conduit in a piggyback manner. The external surface of the main conduit may be a layer of insulation. The elongate member may be coupled to the external surface of the main conduit using securing means, the securing means comprising a strap and/or band. The band may be a metal band. 
     The securing means may include a fixing member, the fixing member housing at least a portion of the elongate member; the fixing member may have a shape that compliments the external surface of the main conduit to which the fixing member is secured using the strap. 
     There may be more than one securing means attached to the main conduit. The securing means may be attached to the main conduit at intervals of between 4 and 5 meters along the longitudinal axis of the main conduit. 
     The securing means may further include a piggyback block; typically the piggyback block is U-shaped. The strap normally extends around an outer surface of the piggyback block and the external surface of the main conduit. The piggyback block normally extends around an outer surface of the elongate member and may be interposed between the outer surface of the elongate member and an inner surface of the strap. 
     The method of forming a protection system may include the use of one or more shock absorbing means formed on at least one of its inner and outer surface. The elongate member may be coupled to the main conduit using securing means; the securing means may comprise a strap. 
     Preferably, the elongate member is adapted to be transformable between at least two configurations:
         a first configuration being a substantially planar configuration in which the elongate member is either spooled on or is suitable to be spooled on to the reel; and   a second configuration being a substantially non-planar configuration in which the elongate member has been payed out from the reel and in which the elongate member has been at least substantially enveloped around the secondary conduit to provide protection thereto.       

     Preferably, the main conduit is a conduit through which fluid may flow and more preferably is an oil flowline. Typically, the secondary conduit is a cable and more preferably is a DEH cable used to provide electrical power to one or more trace heating mechanisms of the main conduit. 
     Typically, the elongate member is manufactured and more preferably is extruded in the second configuration and is biased to return to the second configuration if permitted. Preferably, when the elongate member is in the second configuration, the elongate member comprises a throughbore within which the secondary cable may be placed or inserted for protection. Preferably, when the elongate member is in the second configuration, the elongate member comprises a substantially cylindrical or tubular body substantially or wholly surrounding the throughbore. The elongate member may comprise one or more shock absorbing means, which may additionally or alternatively function as centralising means, formed on either and more preferably both of its inner and outer surface. The shock absorbing and/or centralising means are preferably one or more circumferentially spaced apart ribs which project substantially radially inwards or outwards respectively. Most preferably, the inwardly projecting ribs formed on the inner surface are staggered from and therefore are not radially aligned with the outwardly projecting ribs formed on the outer surface. 
     Preferably, when the elongate member is in the substantially planar configuration, it comprises a pair of edges which are arranged parallel to its longitudinal axis. More preferably, the elongate member is transformed from the substantially planar configuration to the substantially non-planar configuration by causing or allowing the edges to move from the planar configuration in which they are on opposite sides of the central longitudinal axis of the elongate member but lying on substantially the same plane to meet and preferably butt against one another. Typically, the elongate member is transformed from the substantially non-planar configuration to the substantially planar configuration by pulling the edges away from one another until they lie on the same plane as the central longitudinal axis of the elongate member. 
     Preferably, the elongate member is biased towards or into the non-planar configuration and more preferably, the elongate member is formed from a resilient material, and is preferably an elastomeric material, that will naturally return to a substantially cylindrical or tubular configuration in the absence of external forces acting to prevent such return. More preferably, the elongate member is formed in an extrusion process such that it is extruded in the substantially cylindrical or tubular configuration and more preferably, is cut through its sidewall to create the said pair of edges or is extruded with such edges already formed. 
     The elongate member is preferably an MPS and the main conduit is typically a flowline for carrying oil and the secondary conduit is typically an electrical cable such as a DEH cable to provide power to a trace heating system of the main conduit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a cover section  14  being brought toward a gutter section  12  of the conventional MPS  10 ; 
         FIG. 2  is a perspective side view of a number of gutter sections  12  of the conventional MPS  10  in a stacked configuration for transportation and/or storage; 
         FIG. 3  is a perspective view of a number of cover sections  14  of the conventional MPS  10  in a stacked configuration for transportation and/or storage; 
         FIG. 4  is a cross sectional end view of the conventional MPS  10  of  FIG. 1  shown in its in use configuration piggybacked on a flowline  3  with a DEH cable  1  being located in the cylindrical throughbore of the MPS  10  and being protected thereby; 
         FIG. 5  is a perspective side view of a first and preferred embodiment of MPS in accordance with the present invention; 
         FIG. 6  is a cross sectional end view of the MPS of  FIG. 5 ; 
         FIG. 7  is a perspective side view of two reels side by side; 
         FIG. 8  is a perspective side view of a conventional reel; 
         FIG. 9  is a perspective end view of the MPS of  FIG. 5 ; 
         FIG. 10(   a ) is a more detailed end view of the MPS of  FIG. 9 ; 
         FIG. 10(   b ) is another more detailed perspective side view of the MPS of  FIG. 9 ; and 
         FIG. 11  is an end view of an alternative embodiment of an MPS. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments in accordance with the present invention will now be described, by way of example only, in which: 
       FIG. 5  is a perspective side view of a first and preferred embodiment of MPS in accordance with the present invention after having been pulled off or payed out from a reel and having been allowed or forced to transform from a flat configuration to its in use cylindrical configuration around a DEH cable (although the DEH cable is not shown in  FIG. 5 ); 
       FIG. 6  is a cross sectional end view of the MPS of  FIG. 5  after it has been allowed or forced into its cylindrical in use protection configuration (although the DEH cable is not shown); 
       FIG. 7  is a perspective side view of two reels side by side, each reel having the MPS of  FIG. 5  being provided thereon in its flat configuration; 
       FIG. 8  is a perspective side view of a conventional reel holding a conventional DEH cable for use with the MPS of  FIG. 5 ; 
       FIG. 9  is a perspective end view of the MPS of  FIG. 5  piggybacked to a flowline and exiting the lay tower; 
       FIG. 10(   a ) is a more detailed end view of the MPS of  FIG. 9  piggybacked to a flowline in the form of a twelve inch production pipeline; 
       FIG. 10(   b ) is another more detailed perspective side view of the MPS of  FIG. 9  in the piggybacked in-use configuration and as installed on a flowline which is a twelve inch production pipeline; and 
       FIG. 11  is an end view of an alternative embodiment of an MPS to that shown in  FIG. 5 , piggybacked to a flowline in the form of a twelve inch production pipeline. 
       FIG. 5  and  FIG. 6  show a first and preferred embodiment of an MPS  30  in accordance with the present invention. The MPS  30  is formed from an extruded resilient material such as a suitable rubber or other type of elastomer such as a suitable grade of polyurethane, or a composite material formed from recycled and reconfigured elastomers of suitable properties (rubber tyres etc.). Additional mechanical properties can be added to the extrusion by incorporating composite fibres such as glass, polyester or Kevlar—aramid fibres which would increase the tensile strength, stiffness and cut resistance of the MPS  30 . 
     The MPS  30  is extruded in the closed circular conduit arrangement shown in cross section in  FIG. 6  and comprises a cylindrical body  32  which therefore forms a lengthy tubular or conduit as shown in the lower half of  FIG. 5 . The MPS  30  also comprises a number of outer ribs  34  which are substantially equi-spaced around the outer circumference of the cylindrical body  32  and which project radially outwardly therefrom such that there are annular gaps  35  formed between each pair of adjacent outer ribs  34 . The ribs  34 ,  36  act to absorb the impact of any dropped objects or fishing nets or dragged anchors that may strike the MPS  30  and therefore act to protect a DEH cable  60  that resides within the MPS in use, as will be described subsequently. 
     The MPS  30  further comprises a plurality of inner ribs  36  which are substantially equi-spaced around the inner circumference of the cylindrical body  32  such that there are annular gaps  37  between each pair of adjacent inner ribs  36 . As can be seen in  FIG. 6 , each of the inner ribs  36  project radially inwardly from the inner surface of the cylindrical body  32  to the same depth into the cylindrical throughbore  38  of the MPS  30  such that the inner end faces  39  of the inner ribs  36  will collectively form an inner circumference (albeit a staggered inner circumference  39 ) and which will support the outer surface of a DEH cable  60  as will be described subsequently. 
     Conveniently and preferably, the inner ribs  36  are offset or staggered with respect to the outer ribs  34  such that an inner rib  36  is radially aligned with an annular gap  35  on the outer surface and an outer rib  34  is radially aligned with an annular gap  37  on the inner surface and this has the advantage that the respective ribs  34 ,  36  will lie in the respective annular gaps  35 ,  37  of the adjacent upper and lower layers of MPS  30  when the MPS  30  is in the flat configuration and is rolled or spooled onto a reel  50  as will be described subsequently. 
     The MPS  30  is manufactured in a continuous manner such that each MPS  30  may be manufactured in either 5.5 km lengths if to be wound onto two reels  50  as shown in  FIG. 7  or, if to be wound onto one giant reel, may be manufactured in one 11 km length. During manufacture, a radially extending cut  40  is formed all the way through the side wall of the cylindrical body  32  at one point on its circumference and furthermore is formed all the way along the entire length (i.e. 5.5 km or 11 km length) of the MPS  30  such that the MPS  30  is now no longer wholly cylindrical but has a first  40 A and a second  40 B side edge. The cut  40  may be formed in any suitable manner such as by a blade, saw or the like, during manufacture. 
     In order to wind the MPS  30  onto a reel for storage and transportation prior to installation subsea, each circular side edge  40 A,  40 B is grabbed by a suitable machine (not shown) or a splaying device (not shown) and is opened outwards such that the MPS  30  is transformed from a cylindrical body shape as shown in  FIG. 6  to a flat body shape as shown in the upper half of  FIG. 5  such that the body  32  all lies on the same plane and the side edges are now pointing away from one another and are also lying on the same plane as the central longitudinal axis of the elongated MPS  30 . The first end  30 E out of the extrusion machine is then secured into a MPS end holder (not shown) provided at the very centre of a reel  50  and the reel is then rotated at the same speed as the extruded MPS  30  is manufactured such that the MPS  30  is wound flat onto the reel  50 . As shown in  FIG. 7 , two reels  50  have been wound, each with their own flattened MPS  30 F. As the flattened MPS  30 F is wound onto a reel  50 , the inner ribs  36  of the present layer of MPS  30 F are arranged to lie into the annular gaps  35  of the next inner most layer of flattened MPS  30 F such that each layer of flattened MPS  30 F takes up less radial space on the reel  50  than would otherwise occur. 
     Once a reel  50  has been provided with its predetermined length of flattened MPS  30 F, it can be transported to the flowline installation vessel and can be safely stored thereon whilst taking up significantly less space than a conventional MPS paleted system (e.g. such as the prior art system shown in  FIGS. 2 and 3 ). 
     When it is desired to install a flowline  64  with outer insulation  62  as shown in  FIG. 9  subsea such as on the subsea surface (i.e. the seabed bottom), the outer most end  30   g  (that is the end  30   g  that was wound onto the reel  50  last) is taken in its flattened form and is held securely in its flattened form and is presented into the lay tower using a loading tugger line (not shown) from the work station on the installation vessel and is presented into close proximity to the outer most end  60 G of the DEH cable  60  which is held on a separate reel  61 . The end  60 G of the DEH cable  60  is pulled off its storage reel  61  using the same loading tugger line as used for the end  30 G of the MPS  30  such that the end  60 G is pulled into close proximity with the end  30 G of the MPS  30 . The 2 paths of the ends  60 G and  30 G are combined into one by directing and guiding them together and the two combined paths of the ends  30 G and  60 G are passed through a “zip up” station which is set up between the two storage reels  50 ,  60 . Within the zip up station (not shown), the end  30 G of the flattened MPS  30  is allowed to return to its original round or cylindrical shape as shown in the lower half of  FIG. 5  or in the end view shown in  FIG. 6  whilst the DEH cable  60  is inserted therein. Indeed, the flattened MPS  30  will try to return to its original round or cylindrical shape as shown in the lower half of  FIG. 5  or in the end view shown in  FIG. 6  because it is resilient by manufacture to the cylindrical shape. Accordingly, the two ends  40 A,  40 B close around the DEH cable  60  such that the DEH cable  60  is located within the cylindrical throughbore  38  of the now circular MPS  30  and is therefore substantially or more preferably entirely enveloped by the side wall of the cylindrical body  32  of the now circular MPS  30 . Furthermore, because the MPS  30  is preferably formed from a material that is resilient and is therefore biased into the circular configuration shown in  FIG. 6 , it naturally wishes to return to that position and therefore does not require much if any energy to move it from the flattened configuration to the cylindrical configuration. 
     Now that the DEH cable  60  is surrounded by the MPS shroud  30 , the combined shrouded cable  30 ,  60  is passed over the aligner wheel piggyback gutter as it would be in a normal piggyback operation, and the gutter can be enlarged if required. 
     As shown in  FIG. 9 , the piggybacked DEH cable  60  and MPS  30  are then strapped to the flowline  64  (more accurately are strapped to its insulation  62 ) by metal banding  63  which is conveniently placed every 4 to 5 meters or so along the length of the flowline  64 . The metal banding  63  is strapped around the outer surface of the insulation  62  on a plane that is perpendicular to the longitudinal axis of the flowline  64 . However, a piggyback block  65  is placed around the outer surface of the MPS  30  and the metal banding  63  is run around the outer surface of the piggyback block  65  such that the piggyback block is interposed between the outer surface of the reel-able MPS  30  and the inner surface of the metal banding  63 . The piggyback block  65  is substantially U shaped in profile and comprises a number of slots formed around its inner central portion where the slots are suitable shaped to accommodate the outer ribs  34  of the reel-able MPS  30  such that the piggyback block  65  will assist in keeping the reel-able MPS  30  in a secured position in a piggyback manner on the flowline  64 . The piggyback blocks  65  are preferably formed from a resilient elastomeric material such that they will also absorb the impact of any dropped objects or fishing nets or dragged anchors that may strike the piggyback blocks  65 . As can be seen in  FIG. 9 , the piggyback blocks  65  and then the metal banding have been applied to the outer surface of the reel-able MPS  30  and the outer surface of the insulation  62 , where the piggyback block  65  are typically spaced apart every 4 to 5 meters and depending on the MPS  30  material and content stiffness, may be spaced apart every 6 to 12 m or so along the entire length of the flowline  64 . The reel-able MPS  30  is therefore brought together with the flowline  64  in the lay tower work station such that the two are combined with the piggyback block  65  and the metal banding strap  63  and the combined apparatus as shown in  FIG. 10  can then be laid into the sea as required to install the flowline  64  on the subsea surface. 
     The outer ribs  34  and inner ribs  36  also function to absorb the shock of any object striking or hitting the reel-able MPS  30  and therefore act to protect the DEH cable  60 . 
     As shown in  FIG. 7 , the flat reel-able MPS  30 F can be conveniently stored on two reels such that when the flat reel-able MPS  30 F of the first reel  50 A has been fully unwound, it is a straightforward task to feed the outer most end  30   g  of the second length of flat reel-able MPS  30  from the second reel  50 B into the lay tower using the loading tugger line from the work station in a similar manner to that previously described. 
     An alternative embodiment of MPS  70  is shown in  FIG. 11  and comprises only inwardly projecting ribs  36  such that the body  72  comprises a smooth outer surface to the outer environment. This may be preferable when using conventional piggyback installation techniques and conventional piggyback blocks  74  with the same metal banding strap  63  as previously described but this embodiment does have the disadvantage that it will likely take up more space on the reel  50  than the preferred first embodiment of MPS  30 . 
     Accordingly, embodiments of the present invention have the advantage that they can be supplied on one or two conventional reels such as 9.2 meter diameter reels and can therefore take up significantly less deck space which will provide significant cost savings and also time savings in subsea laying operations. Furthermore, embodiments of the present invention provide safety enhancements to such installation jobs because there is no or only minimal manual handling required in that the MPS  30 ,  70  is located on a reel and is therefore reel  50  deployed. Furthermore, embodiments of the present invention will provide significant time savings and the cost savings associated therewith in relation to the installation time for flowlines to be installed subsea, due to the reel mounted nature of the MPS  30 ,  70 . 
     Individual lengths of the reelable MPS  30 ,  70  can be joined together using suitable fasteners (not shown) or bonded together without detracting from the shape and protection offered by the system  30 ,  70 . 
     An alternative location of the zipping-up station can be provided in the lay tower above the piggyback block  65 ,  74  installation station. This could allow the reelable MPS  30 ,  70  to be transported to the installation site using conventional rollers and conveyor belt or transmission belt technology, from the storage reel or carousel somewhere on deck or below the main deck, in the hold. 
     Modifications and improvements may be made to embodiments of the present invention as here and before described without departing from the scope of the invention.