Apparatus and method for installation and protection of sub sea cables

Abstract

An apparatus for installation and protection of subsea cables comprises at least a first tubular member (1) and at least a second tubular member (2). Both these are arranged to be installed subsea with a subsea foundation (3). This allows passage of cable (29) through it. The first tubular member (1) is arranged telescopically within the second tubular member (2) so as to extract outwardly towards seabed (5) from an end portion (7), with respect to the second tubular member (2), only up to a prefixed length. This ensures that a continuous conduit for the cable is obtained through the scour protection of the foundation (3). The present invention also includes a methodology for installation of the apparatus and a method for installing a cable through the scour protection of the foundation, by using the apparatus.

Claims

1. An apparatus for installation and protection of subsea cables from a seabed unit, said seabed unit being of the type which is adapted to be landed on a seabed and stabilized by scour protection, said apparatus having an installation mode before said seabed unit has been landed on said seabed, and an installed mode after said seabed unit has landed on said seabed, said seabed unit having a first end portion adapted to extend above a water surface and a second end portion adapted to rest on said seabed, said apparatus comprising: a first tubular member; a second tubular member; said first tubular member comprising a first end and a second end; said second tubular member comprising a first end and a second end; said first tubular member being arranged telescopically on an inside of said second tubular member; a part of said second tubular member comprises a curved shape extending between a vertical direction and a horizontal direction, said curved shaped part being situated within outer constraints of the seabed unit, wherein in said installation mode: said first end of said second tubular member resides within said first end portion; said second end of said second tubular member resides at or close to said second end portion; said first end of said first tubular member resides within said second tubular member; and said second end of said first tubular member resides at or close to said second end of said second tubular member so that said first tubular member in said installation mode resides within said second tubular member; wherein in said installed mode: said second tubular member remains stationary with respect to said seabed unit; said second end of said first tubular member is at a distance from said second end of said second tubular member; said first end of said first tubular member remains inside said second tubular member: said first tubular element is lying flat on said seabed outside of said seabed unit; said second tubular member extends through a desired zone for said scour protection; and said first and second tubular members together form a conduit for at least one cable to be fed therethrough.

2. The apparatus according to claim 1, wherein in said installation mode, said second end of said first tubular member coincides with said second end of said second tubular member.

3. The apparatus according to claim 1, wherein said first tubular member is a flexible protective pipe and said second tubular member is a non-flexible J-shaped tube.

4. The apparatus according to claim 3, wherein a movement restrictor is provided in close proximity to said second end of said second tubular element, said movement restrictor being selectively adapted to prevent unwanted extraction or retraction of said protective pipe.

5. The apparatus according to claim 4, wherein the movement restrictor comprises a plate provided near said second end of said second tubular element, said plate being slidably received in guides, said plate being adapted for engagement with a selected one of complementary grooves in an outer surface of said protective pipe, and said grooves being provided at selected points along said protective pipe.

6. The apparatus according to claim 4, wherein the movement restrictor comprises at least one restraining line for arresting said protective pipe from being extracted outwards from said second tubular element after a certain length.

7. The apparatus according to claim 4, wherein the movement restrictor comprises a clamp for arresting said protective pipe from being retracted back into said second tubular element once said protective pipe is extracted to a desired length.

8. The apparatus according to claim 7, wherein a friction clamp is adapted to be operated by a remotely operated vehicle (ROV) and is pre-installed at said second end of said second tubular element, said friction clamp upon actuation clamping said protective tube relative to said second end of said second tubular element.

9. The apparatus according to claim 3, wherein a pull-out handle is fixed to the protective tube at said second end thereof for horizontally pulling the protective tube to a pre-determined length from the second tubular element through the desired zone of scour protection before scour protection is applied so that the second end of the protective tube is outside the scour protection.

10. The apparatus according to claim 9, wherein the pull-out handle is adapted for attachment to a pull line for providing said horizontal pulling force, and an opposite end of said pull line is adapted to be attached to a constant tension winch placed on a vessel floating on said water surface through a pulley resting on said seabed.

11. The apparatus according to claim 3, wherein a sacrificial hold back sling is provided to prevent said protective tube from sliding outwards from said second tubular element during towing out and installation of said seabed unit.

12. The apparatus according to claim 1, wherein said first tubular member is a stiff protective pipe.

13. The apparatus according to claim 1, further comprising a pull line extending through said first and second tubular elements, said pull line being adapted for attachment to one end of said at least one cable.

14. A method for installing a subsea cable from a seabed unit, the method comprising: a) pre-installing a second tubular member and a first tubular member within the seabed unit so that the first tubular member is arranged telescopically inside the second tubular member; b) installing the unit in a seabed while retaining the first tubular member relative to the second tubular member; c) releasing the first tubular member from the second tubular member; d) pulling the first tubular member outwardly from the second tubular member, so that the first tubular member extends outwardly essentially along the seabed to a location outside a desired scour protection zone; e) pre-installing or passing a cable pull-in line through the second tubular member and the first tubular member, so that the pull-in line with a first end extends out from an outer end of the first tubular member and with a second end extending out from an end opposite of the first tubular member of said second tubular member; f) attaching a cable to be installed to the first end of the pull-in line; g) pulling the line pull-in line with the cable trailing; and h) before steps f) and g), applying scour protection around the seabed unit and on a part of the first tubular member.

15. The method of claim 14, wherein the step of retaining the first tubular member relative to the second tubular member after the first tubular has been extended to the desired length prevents the first tubular member from retracting back relative to the second tubular member.

16. The method of claim 15, wherein the step of predetermining the desired length of extraction of the first tubular member by a movement restrictor.

17. An apparatus for installation and protection of subsea cables from a seabed unit, said seabed unit being of the type which is adapted to be landed on a seabed and stabilized by scour protection, said apparatus having an installation mode before said seabed unit has been landed on said seabed, and an installed mode after said seabed unit has landed on said seabed, said seabed unit having a first end portion adapted to extend above a water surface and a second end portion adapted to rest on said seabed, said apparatus comprising: a first tubular member; a second tubular member; said first tubular member comprising a first end and a second end; said second tubular member comprising a first and a second end; said first tubular member being arranged telescopically on an inside of said second tubular member; a part of said second tubular member comprises a curved shape extending between a vertical direction and a horizontal direction, said curved shaped part being situated within outer constraints of the seabed unit, wherein in said installation mode: said first end of said second tubular member resides within said first end portion; said second end of said second tubular member resides at or close to said second end portion; said first end of said first tubular member resides within said second tubular member; and said second end of said first tubular member resides at or close to said second end of said second tubular member so that said first tubular member in said installation mode resides within said second tubular member; wherein in said installed mode: said second tubular member remains stationary with respect to said seabed unit; said second end of said first tubular member is at a distance from said second end of said second tubular member; said first end of said first tubular member remains inside said second tubular member; said first tubular element is lying flat on said seabed outside of said seabed unit; said second tubular member extends through a desired zone for said scour protection; and said first and second tubular members together form a conduit for at least one cable to be fed therethrough wherein a movement restrictor is provided in close proximity to said second end of said second tubular element, said movement restrictor being selectively adapted to prevent unwanted extraction or retraction of said first tubular element from said second tubular element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Having described the main features of the invention above, a more detailed and non-limiting description of a n exemplary embodiment will be given in the following with reference to the drawings.

(2) FIG. 1 shows the general arrangement of a foundation in a bottom-fixed condition together with the J-tube and the protective pipe, according to a preferred embodiment of the present invention, with the J-tube yet to be installed on seabed.

(3) FIGS. 2a, 2b, 2c, 2d show in detail the structure and working of a preferred embodiment of the stopping means according to the present invention, where FIG. 2a shows the stopping means out of engagement with the pipe in a elevation view, FIG. 2b shows the situation in FIG. 2a in a plan view, FIG. 2c shows the stopping means in engagement with the pipe in a elevation view, FIG. 2d shows the situation in FIG. 2c in a plan view.

(4) FIG. 3 shows a detail of the outer end of the pipe and the J-tube with another preferred embodiment of the stopping means of the present invention.

(5) FIGS. 4a and 4b show detail views of the clamp shown in FIG. 3.

(6) FIG. 5a is a view of the detail arrangement of the protective pipe according to the present invention, prior to its pull-out.

(7) FIG. 5b is a view of the details of a hinged pull-out bar according to FIG. 5a.

(8) FIG. 5c is a view of the details of a friction clamp shown in FIG. 5a.

(9) FIG. 6 is a view which explains the method of pulling out the HDPE/protective pipe from the J-tube.

(10) FIG. 7 is a view of a stage when the HDPE pipe has been pulled out of J-tube, awaiting dumping of filter bags.

(11) FIG. 8 is a view which shows filter bags that have been placed over the HDPE pipe after extraction and it is ready for the scour protection system to be installed.

(12) FIG. 9 is view of a stage when scour protection has been completed and the cable is to be installed.

DETAILED DESCRIPTION OF THE INVENTION

(13) The following describes a preferred embodiment of the present invention which is purely exemplary for the sake of understanding the invention and non-limiting to the protective scope.

(14) In all the figures, like reference numerals represent like features. Further, when in the following it is referred to top, bottom, upward, downward, above or below and similar terms, this is strictly referring to an orientation with reference to the seabed, where the seabed is horizontal and at the bottom.

(15) It should also be understood that the orientation of the various components may be otherwise than shown in the drawings, without deviating from the principle of the invention.

(16) Additionally, the present invention is explained with reference to a J-tube, within which there is a protective tube, which is telescopically movable with respect to the J-tube. This protective tube is essentially an HDPE tube, but can consist of other suitable materials. It should be understood, that the present invention embraces all such arrangements of two or more tubular members which are capable of being arranged telescopically for forming a continuous conduit for a subsea cable to pass through.

(17) The cables which are proposed to be installed and protected by the apparatus of the present invention, essentially extend from other offshore or on-shore structure(s), on or embedded into the seabed near a foundation resting on the seabed, then into the foundation and up to the structure supported by the foundation.

(18) In most of the figures only one J-tube and one protective tube are shown for the sake of convenience. There can be a plurality of such J-tubes and protective tubes within the foundation according to the present invention. This is true for the various other associated components described. The J-tube and the protective tube may each be a single tube or each may be a number of tubes, attached together to form a J-tube and a protective tube of the present invention.

(19) FIG. 1 is a view of the general arrangement of major components of the apparatus when the protective pipe 1 has not been extracted out to the seabed 5 from the J-tube 2, but still resides within the outer J-tube 2. It shows the foundation 3, which in this example is a gravity based structure (GBS) resting on the seabed 5. The foundation 3 supports a topside structure (not shown) at its top end 4. The topside structure may be a windmill extending upwards from the water surface 31.

(20) Within the foundation 3 is already pre-installed the apparatus of the present invention, which is now to be described. In this example it is a J-tube 2, preferably made of a non-flexible material, such as steel, glass fibre reinforced plastic (GRP), carbon fibre reinforced resin or other suitable material, extending downwards from the top end 4. The J-tube has a conical portion 2b and a curved portion 2a, which has a greater diameter than an upper straight portion 2c. The protective pipe 1 is accommodated within the curved portion 2a of the J-tube 2, between the end 7 of the J-tube and its conical portion 2b. The protective pipe 1 is slidable with respect to the J-tube 2. Thus, it is a telescopic assembly and the protective pipe 1 can be pulled out of the J-tube 2 beyond the end portion 7, by a horizontal pulling force.

(21) The protective pipe 1 is generally made of a somewhat flexible material like High Density Polyethylene (HDPE) which allows it to be inserted into and bent according to the shape of the J-tube 2 and will below sometimes be referred to as HDPE pipe 1. Other materials, such as carbon fibre reinforced resins may also be used.

(22) The FIG. 1 also shows the end portion (bell mouth 30) of the retracted HDPE pipe 1, which is seen coinciding with the end portion 7 of the J-tube 2. A stopping means 6 (explained in detail below) can also be seen which prevents the HDPE pipe from being inadvertently extracted, or retracted once it is installed on the seabed 5. This stopping means 6 is provided in close proximity to the end portion 7. The conical section 2b forms a transition between the curved portion 2a and the straight portion 2c, with a smaller diameter than the curved portion 2a, of the J-tube 2.

(23) FIGS. 2a, 2b, 2c and 2d are detailed views of the end portion 7 of the J-tube 2, showing a preferred embodiment of the stopping means 6. The stopping means 6 prevents extraction or retraction of the protective tube 1 beyond a certain pre-defined limit. It comprises a plate 8a provided near said point of exit, which can slide along vertical stands 8b for engagement with complementary grooves 9 in the outer surface of the protective tube. The grooves 9 are provided at specific points on the protective pipe 1 where it is desired to retain it with respect to the J-tube 2. When the pipe 1 has been pulled out the desired length, the sliding plate 8a, whose rounded profile matches with the diameter of the groove 9, can be inserted into the appropriate groove 9 and lock the movement of the pipe 1.

(24) The sliding plate 8a may fall into the groove 9 by gravity or by spring force or may be operated manually by a remotely operated vehicle (ROV) or an actuator (not shown). With this mechanism, the pipe 1 is locked in position with the J-tube 2 and can neither move forward or backward. This would be particularly clear from the front views 2a and 2c which shows two consecutive stages, in the first stage the sliding plate 8a is approaching the grooves 9 but is yet to become engaged. In FIG. 2c the two are in engagement with each other. This would be clear from FIG. 2d as well, of which FIG. 2c is a front view. It shows clearly the engagement between the grooves 9 and the sliding plate 8a. Disposition of grooves 9 along various lengths of the pipe 1 provides the option to selectively predetermine the length of the pipe 1 that will be extracted out of the J-tube. In a separate detail view in FIG. 2c, the plate 8a is shown separated from the rest of the stopping mechanism.

(25) FIG. 3 shows another embodiment of the stopping means 6. This comprises a restraining wire 10 is attached to a ring 35 attached to the protective pipe 1. The ring is in turn connected to a cover 18 by a connection wire 36. The cover 18 prevents entry of unwanted material like soil or small rocks into the pipe 1 during installation. The restraining wire 10 is at its opposite end secured to a pad eye 19 fixed to the foundation 3. The restraining wire 10 restrains the protective pipe 1 from extracting out of the J-tube 2. A safety wire 12 is also connected between the ring 35 and the pad eye 19. The safety wire has a length corresponding with the desired extraction length of the pipe 1.

(26) FIG. 3 also shows a clamp 11 near the protective pipe 1 for clamping the same in order to prevent the pipe from retracting into the J-tube when it has been extracted to the desired length. FIG. 4a is an enlarged view of the clamp 11 which is of the hinged type, having a hinge 16. FIG. 4b is an enlarged view of the clamp 11 in operation which shows a T-bar 17a for engagement by an ROV, a right hand thread bar 17b, a stopper plate 17c welded to the thread bar 17b, a plate 17d with an oblong hole (not shown) to allow the thread bar to pass through, and a left hand thread bar 17e.

(27) Referring back to FIG. 3, the cover 18 is equipped with a handle 14 for attachment by a pull-out line (to be explained later) for pulling out the protective pipe 1. FIG. 3 also shows a pull-in line 13, which is used to pull in a cable inside the fully extracted protective pipe 1, as will be explained later, and a monkey fist ROV grab 15 attached to the outer end of the pull in line 13.

(28) FIGS. 5a and 5b show another alternative embodiment of the stopping means as well as a different embodiment of the means for extracting the pipe 1. Here a friction clamp 20 is preinstalled at the outer end 7 of the J-tube and adapted to clamp the pipe 1, to ensure that after the pipe 1 has been extracted to a desired length, it does not retract back inside J-tube, particularly when the cable 29 (shown in FIG. 9) is pulled in through the protective pipe 1. The clamp 20 is explained in detail in FIG. 5c.

(29) FIGS. 5a and 5b also shows a hinged pull-out bar 21 that is attached to the outer end of the pipe 1 and is to be used for pulling out pipe 1. The hinged pull-out bar 21 is attached to the pipe 1 in close proximity to the end portion 7, and just behind the bell mouth 30. It also shows the cable pull-in wire 13, which in this embodiment is attached to the hinged pull-out bar 21 by a sacrificial wire sling 23. The overall length of the pull-in wire 13, which is, e.g., 20 to 25 meters, may be arranged on a bracket reel (not shown) located at the upper end of the J-tube.

(30) A restraining wire sling 10 is connected to the end portion 7 of the protective pipe 1 to prevent the pipe 1 it from accidentally sliding out during transport and installation of the structure 3. A safety wire 12 is secured to the pad eye 19 fixed to the foundation 3 and is also connected to the pull-out bar 21. The safety wire has a length corresponding with the desired extraction length of the pipe 1. Once fully extracted, through the possible zone of scouring for the foundation 3, the protective pipe 1 cannot retract into the J-tube 2 as it is arrested by the friction clamp 20.

(31) FIG. 5c is a close view of the friction clamp 20 that is used to arrest the motion of the pipe 1 after it has been pulled out. This is actually a tong like arrangement with friction linings on the inner faces. The two arms 20a and 20b are hinged at one end 20c and at the other end threaded bar and nut arrangement 20d are provided for closing the two arms 20a, 20b. This threaded bar and nut arrangement 20d can be operated by an ROV. On activation, the device firmly clamps the pipe 1, without damaging it.

(32) FIG. 6 shows an exemplary arrangement to facilitate the pull-out of the protective pipe 1 from the J-tube 2. It shows two sets of J-tubes 2 and protective pipe 1 within the foundation. In practice, there can be several J-pipes, as explained above. A sling wire 24 is attached to the hinged pull-out bar 21 (shown in FIGS. 5a and 5b) or to the handle 14 of the cover 18, which is fixed to the pipe 1 near the outer end thereof, and is passed through a pulley held near the seabed with a clump weight 25.

(33) The pulling wire 24 is attached to a constant tension winch 26 placed on a vessel 27 on the water surface 31. The pulling wire 24 can thus provide a substantially horizontal pull to the hinged bar 21 and thus to the pipe 1 for smooth extraction from the J-tube 2.

(34) FIG. 7 is a view of a stage when the protective pipe 1 has been pulled out of the J-tube 2 awaiting placement of sand bags, filter bags or other types of relatively soft material that is able to protect the pipe 1 from the rocks of the scour protection.

(35) FIG. 8 is a view of the stage subsequent to what is shown in FIG. 7. Filter bags 27 have been placed over the protective pipe 1 and is now awaiting application of scour protection. It also shows the bell opening 30 of the fully extracted protective pipe 1 which is outside the possible zone of scour protection. Now scour protection for the foundation 3 is next to be applied.

(36) FIG. 9 is a view of a stage when scour protection 28 has been applied and the cable 29 is about to be pulled into the bell mouth 30 with the help of the cable pull-in wire 13 (shown in FIGS. 3 and 5a).

(37) The above figures are again referred to now for the purpose of explaining the operation of installation of the apparatus and the cables so that the functioning of each component, as described hereinbefore is understood.

(38) At the first stage on-shore preparation of foundation 3 for offshore installation is done. First, the protective pipe 1 is inserted into the J-tube 2 and placed within the foundation 3. In this configuration, the protective device 1 is itself protected and does not get in the way of marine operations. This arrangement is shown in FIG. 1. The components shown in FIG. 1 have been explained in detail before with reference to FIG. 1 and are not repeated.

(39) The foundation 3 with the J-tube 2 and protective pipe 1 so installed are now towed to the offshore location. The sacrificial hold back sling 23, connected to the end portion of the protective pipe 1 shown in FIG. 3 or 5a, ensures that the protective pipe 1 does not accidentally slide out of the J-tube 2 during towing. The foundation 3 is thereafter suitably installed on the seabed 5. The installation of the foundation will not be described in detail here, as this procedure is known to persons skilled in the art.

(40) After installation of the foundation 3 on the seabed 5, the hold back sling 23 is cut (preferably by an ROV). Now one end of the sling wire 24 is attached to the hinged pull-out bar 21 or the handle 14. The bar 21 or the handle 14 is fixed to the pipe 1 (as shown in FIGS. 3 and 5a) close to the end thereof. The other end of the sling wire 24 is passed through a pulley held near the seabed with a clump weight 25 and attached to a constant tension winch 26 placed on a vessel 27 on the water surface 31. This provides a substantially horizontal pull to the pipe 1, so that the pipe 1 is smoothly extracted from J-tube 2.

(41) As shown in FIG. 7, the pipe 1 is pulled out in the direction of the arrowhead along the seabed 5. FIG. 8 shows the bell mouth 30 of the fully extracted protective pipe 1. The bell mouth 30 is now outside the application zone of scour protection. Further, it would be clear from FIG. 7 and also from FIGS. 8 and 9, that the J-tube 2 and the fully extracted protective pipe 1 form a continuous conduit for cables from the top portion 4 of the foundation 3 to the seabed, through the zone of scour protection. For that purpose, it is vital that the length of extraction of the protective pipe 1 is predetermined accurately.

(42) On reaching the desired length of pull-out, the protective pipe 1 is locked in position by suitable stopping means 6, as explained with reference to FIGS. 2a, 2b, 2c, 2d, 5a and 5c. This stopping means 6 ensures that once the maximum length of extraction of the protective pipe 1 is reached, it neither retracts back, say during cable pull-in through the extracted protective pipe 1 and J-tube 2, nor accidentally slides further out of the J-tube.

(43) It needs to be explained further with reference to the pull-out of the protective pipe 1 as explained in the preceding paragraphs, that while the pipe 1 is pulled beyond the intended scour protection area on the seabed 5, it simultaneously pulls the cable pull-in wire 13 along with it. The cable pull-in wire 13 is attached to the hinged pull-out bar 21 with a sacrificial sling 23 as shown in FIG. 5a or is prevented to escape into the pipe 1 by the cover 18, as shown in FIG. 3. The cable pull-in wire 13 thereby passes through the J-tube 2 and protective pipe 1. Actually prior to pull-out of the pipe 1, this wire 13 is made to pass through the J-tube 2 and the pipe 1 such that one end of this wire extends out of the outer end of the pipe 1 while the other end extends out of the J-tube at its upper end.

(44) After the scour protection 28 is applied, the cable 29, which may already be placed near the bell mouth 30, may be inserted into the bell mouth 30. For that purpose, the pull-in wire 13 is attached to the cable 29 and pulled in through the bell mouth 30 through the extracted protective pipe 1 and up the J-tube 2, pulling the cable 29 with it.

(45) Thus cable installation is achieved after the scour protection has been applied. The need for removal of scour protection is effectively eliminated. This is possible because the protective tube can be pulled out of the J-tube to a pre-determined length. This length is so adapted that the end with the bell mouth 30 of the extracted pipe 1 is beyond the scour protection 28. At this length the pipe 1 will be locked relative to the J-tube.

(46) Thus it is always ensured that the pull-out of the pipe 1 is always unidirectional and maintains the desired, pre-calculated length. Further, as the HDPE pipe 1 is pre-installed in the J-tube 2 and both are installed on the seabed 5 along with the foundation 3, the entire operation is very weather robust.

(47) The present invention has been described with reference to a preferred embodiment and some drawings for the sake of understanding only and it should be clear to persons skilled in the art that the present invention includes all legitimate modifications within the ambit of what has been described hereinbefore and claimed in the appended claims.

(48) As an alternative to the relatively flexible pipe 1, the pipe may also be stiff but curved to correspond with the curvature of the curved portion 2a of the J-tube 2. This means that the pipe 1 will curve upwards when it has been extracted. However, after full extraction, the pipe may be rotated through 90 so as to lay flat on the seabed. This will require a somewhat longer pipe 1, as the pipe will extend in a curve through the scour protection zone.

(49) It is also conceivable to have the pipe 1 telescopically received on the outside of the J-tube 2 Instead of on the inside.

(50) It is also evident that other means for preventing the pipe 1 from sliding inadvertently out of or into the J-tube 2 may be used. Instead of ROV operated means, remotely operated actuators may be attached to the foundation, pipe 1 and J-tube 2.