SYSTEM AND METHOD FOR LAYING AN UNDERWATER PIPELINE ON A BED OF A BODY OF WATER

Abstract

A system for laying an underwater pipeline on a bed of a body of water has a construction site to form a string of an underwater pipeline, the string being defined by a curved portion shaped substantially like a portion of the bed of the body of water characterized by an abrupt change in slope; at least two vessels to transfer, in the body of water, the string from the construction site to a laying site in the body of water and substantially on the vertical of a path along which to lay the string; and a plurality of floating devices configured to be coupled to the string and so as to selectively support and sink the string in the body of water, and progressively lay the string along the path on the bed of the body of water.

Claims

1-21. (canceled)

22. An underwater pipeline laying system comprising: a plurality of floating devices configured to be coupled to a string of an underwater pipeline formed at a construction site by joining together a curved portion of pipe and two straight portions of pipe such that the string includes a curved portion having a shape corresponding to a portion of a bed of a body of water including an escarpment, wherein the string is transferred, in the body of water, from the construction site to a laying site in the body of water via at least two vessels, said laying site being aligned with a path on the bed of the body of water along which to lay the string, each floating device configured to: selectively support the string in the body of water, selectively sink the string in the body of water, and progressively lay the string along the path on the bed of the body of water; and a stabilizer device configured to be coupled to the curved portion of the string to stabilize the curved portion of the string.

23. The underwater pipeline laying system of claim 22, wherein a first of the two vessels includes a first traction element configured to be connected to a first end of the string and a second of the two vessels includes a second traction element configured to be connected to a second, opposite end of the string.

24. The underwater pipeline laying system of claim 22, wherein a first of the two vessels includes a first winch configured to be connected to a first end of the string and a second of the two vessels includes a winch element configured to be connected to a second, opposite end of the string.

25. The underwater pipeline laying system of claim 22, wherein each floating device has a variable buoyancy.

26. The underwater pipeline laying system of claim 22, wherein each floating device is configured to be selectively uncoupled from the string.

27. The underwater pipeline laying system of claim 22, wherein each floating device is configured to vary a distance with the string.

28. The underwater pipeline laying system of claim 22, wherein each floating device is controllable independently of the other floating devices.

29. The underwater pipeline laying system of claim 22, which includes a further vessel including a traction element connectable to the curved portion of the string.

30. The underwater pipeline laying system of claim 29, wherein the further vessel includes a further winch connectable to the curved portion of the string.

31. The underwater pipeline laying system of claim 20, which includes a remotely operated underwater vehicle connected to the further vessel and configured to control a laying operation of the string on the bed of the body of water.

32. The underwater pipeline laying system of claim 22, wherein said laying site is vertically aligned with the path along which to lay the string.

33. The underwater pipeline laying system of claim 22, wherein the stabilizer device is configured to prevent a deformation of the curved portion of the string.

34. A method for laying an underwater pipeline on a bed of a body of water, the method comprising: assembling a string of an underwater pipeline at a construction site by joining together a curved portion of pipe and two straight portions of pipe such that the string includes a curved portion having a shape corresponding to a portion of the bed of the body of water including an escarpment; transferring, in the body of water, the string from the construction site to a laying site in the body of water, said laying site being aligned with a path on the bed of the body of water along which to lay the string; sinking the string in the body of water; laying the string along the path on the bed of the body of water; and coupling the curved portion of the string to a stabilizer device configured to stabilize the curved portion of the string.

35. The method of claim 34, wherein during the transfer step, the string lies in the body of water substantially in a horizontal plane within a designated distance of a free surface of the body of water.

36. The method of claim 34, further comprising rotating the string in the body of water at the laying site to arrange the string substantially along a vertical plane.

37. The method of claim 34, wherein laying the string on the bed of the body of water comprises arranging, in succession on the bed of the body of water, the curved portion and progressively two straight portions arranged on opposite sides of the curved portion.

38. The method of claim 34, further comprising connecting the string to a plurality of vessels.

39. The method of claim 38, further comprising connecting one end of the string to one of the vessels and connecting an opposite end of the string to another one of the vessels.

40. The method of claim 38, further comprising connecting the string associated with the curved portion to a further vessel.

41. The method of claim 34, further comprising coupling a plurality of floating devices to the string.

42. The method of claim 41, further comprising varying the buoyancy of each floating device independently of the other floating devices.

43. The method of claim 41, further comprising uncoupling each floating device from the string independently of the other floating devices.

44. The method of claim 41, further comprising varying a distance of each floating device from the string independently of the other floating devices.

45. The method of claim 34 wherein said laying site is vertically aligned with the path along which to lay the string.

46. The method of claim 34, further comprising causing the stabilizer device to prevent a deformation of the curved portion of the string.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Further characteristics and advantages of the present disclosure will become clear from the description below of certain embodiments, with reference to the figures in the accompanying drawings, in which:

[0042] FIG. 1 is an elevation view, with parts shown schematically and parts removed for clarity, of a system configured to lay an underwater pipeline positioned in an operating field;

[0043] FIG. 2 is a side elevation view, with parts removed for clarity; of an underwater pipeline lying on the bed of a body of water;

[0044] FIGS. 3 to 6 are plan views, in a reduced scale with parts removed for clarity, of a construction site of a string of the underwater pipeline;

[0045] FIG. 7 is a plan view, with parts removed for clarity, of a transfer step of the string in the body of water;

[0046] FIGS. 8 to 12, are side elevation views, with parts in section and parts removed for clarity, of successive steps of laying the string on the bed of the body of water; and

[0047] FIG. 13 is a side elevation view, with parts removed for clarity and parts in section, depicting the string laid on the bed of the body of water.

DETAILED DESCRIPTION

[0048] Referring now to the example embodiments of the present disclosure illustrated in FIGS. 1 to 13, referring to FIG. 1, a system 1 is shown, as whole, for laying an underwater pipeline 2 on a bed 3 of a body of water 4 along a predefined path 5.

[0049] With reference to the case shown in FIG. 2, the bed 3 of the body of water 4 comprises an escarpment 6, which has an upper edge 7 characterized by an abrupt change in slope. The system 1 is configured to form a string 8 of the underwater pipeline 2, lay the string 8 and successively complete the underwater pipeline 2.

[0050] The string 8 includes a curved portion 9 shaped substantially like a portion of the bed 3 of the body of water 4 characterized by an abrupt change in slope. In the case shown, the curved portion 9 is shaped to substantially follow the abrupt change in slope of the bed 3 at the upper edge 7 of the escarpment 6. In the case shown, the string 8 comprises two straight portions 10 joined to the curved portion 9 on opposite sides. The portions 10 are defined “straight” because they are made straight. However, the straight portions 10 have a certain flexibility that enable them to assume curved configurations with broad radii of curvature so as not to cause plastic deformation of the string 8. As such, once laid on the bed 3 of the body of water 4, the straight portions 10 follow the profile of the bed 3 without exceeding the permissible deformation values and may also bend without exceeding the deformation limits in the transfer and laying steps.

[0051] Referring to FIG. 1, the system 1 comprises a construction site 11, where the curved portion 9 (FIG. 2) and straight pieces of pipe (not shown in the accompanying figures) are joined together to form the string 8 (FIG. 2). The joining operations envision preparation of the ends, welding and the application of a protective coating on the weld (i.e., field joint coating). The construction site 11 thus comprises an assembly line 12 and can be positioned on shore or in the body of water 4 close to the shore or part on shore and part in the body of water 4. Referring to FIG. 3, the assembly line 12 is positioned on shore, while, during construction, the string 8 leaving the assembly line 12 is positioned in the body of water 4.

[0052] Referring to FIG. 1, the system 1 comprises a laying site 13, which is located in the body of water 4 over the path 5 wherein it is intended to lay the string 8.

[0053] The transfer of the string 8 from the construction site 11 to laying site 13 is carried out in the body of water 4. The construction and transfer of the string 8 envision vessels 14 that are connected to the string 8. The system 1 also comprises floating devices 15 configured to be distributed along the string 8 and to selectively support and sink the string 8 in the body of water 4.

[0054] Referring to FIGS. 5 to 7, the system 1 comprises a stabilizer device 16 configured to be coupled to the curved portion 9 of the string 8 and to prevent deformation along the curved portion 9 of the string 8. In certain embodiments, the stabilizer device 16 comprises a stay wire that defines a chord of the curved portion 9 and is connected to the string 8. In particular, the stay wire comprises at least one steel or textile cable or at least one bar or chain and is connected to the curved portion 9 by constraints, such as clamps or eyebolts.

[0055] In particular, in the step of transferring the string 8, two vessels 14 are connected by respective traction elements 17 to the opposite ends of the string 8. The two vessels 14 comprise respective winches 18 configured to control the respective traction elements 17.

[0056] In the step of rotating the string 8, a further vessel 14 is connected to the curved portion 9 of the string 8 by a traction element 17. The traction element can be connected to the same constraints to which the stabilizer device 16 is connected. The further vessel 14 comprises a further winch 18 to control the traction element 17.

[0057] The floating devices 15 have variable buoyancy so as to be able to vary the position of the string 8 in the body of water.

[0058] The floating devices 15 can be selectively uncoupled from the string 8.

[0059] In particular, each floating device 15 can be controlled independently of the other floating devices 15. In practice, the buoyancy of each floating device 15 is controlled independently of the other floating devices 15.

[0060] Furthermore, the release of each floating device 15 from the string 8 can also be controlled and performed independently of the other floating devices 15.

[0061] Each floating device 15 is connected to the string 8 by a stay wire, the length of which can be selectively varied, independently of the other floating devices 15, from a remote location. In accordance with a variant that is not shown, the floating devices are directly coupled to the string, in particular by clamps or bands.

[0062] The system 1 comprises an ROV 19 connected to the further vessel 14 and configured to control the operations of laying the string 8 on the bed 3 of the body of water 4.

[0063] The information transmitted by the ROV 19 enables controlling the step of laying the string 8 and governing the position of the vessels 14, the winches 18 and the operations of the floating devices 15.

[0064] From the operational viewpoint, the system 1 provides for laying a string 8 on the bed 3 of the body of water 4 on an edge 7 of an escarpment 6 and subsequently completing the underwater pipeline 2 by joining pieces of pipe (not shown in the accompanying figures) to the string 8 to complete the underwater pipeline 2. The completion of the underwater pipeline 2 can be performed, for example, by a laying vessel (not shown in the accompanying figures) which recovers an end of the string on board for performing the subsequent steps of assembly and laying.

[0065] Conversely, the string 8 is prefabricated on the assembly line 12 and progressively set afloat in the body of water 4, as shown in FIG. 3. The prefabrication of the string 8 provides the assembly and setting afloat in succession of a first straight portion 10, the curved portion 9 (FIG. 5), and a second straight portion 10 (FIG. 6). The floating devices 15 are coupled to the string 8 as the string 8 is assembled. In a similar manner, the stabilizer device 16 is coupled to the curved portion 9.

[0066] A vessel 14 is connected to the free end of the first straight portion 10 by a traction element 17 and the winch 18. The vessel 14 keeps the first straight portion 10 in a straight position so as to maintain the string 8 in tension during the assembly step and advances in direction D as the length of the first straight portion 10 grows.

[0067] Once the first straight portion 10 has been completed and the curved portion 9 has been joined to the first straight portion 10, the first straight portion 10 is inclined in a horizontal plane with respect to direction D, as shown in FIG. 4. The entity of the inclination is a function of the angle between the two straight portions 10 of the string 8 and, consequently, of the curved portion 9. In particular, the curved portion 9 is made by joining straight pieces with the ends opportunely shaped so as to approximate the curve with a polygonal shape. Then, the stabilizer device 16 and a vessel 14 are coupled to the curved portion 9. Both vessels 14 are advanced in direction D as the second straight portion 10 is assembled and increases in length, as shown in FIGS. 5 and 6.

[0068] Once assembly of the second straight portion 10 is completed, the free end of the second straight portion 10 is also secured to a vessel 14, as shown in FIG. 7. The straight portions 10 may also deform provided that such deformation does not exceed certain threshold values.

[0069] Once completed, the string 8 is supported by the floating devices 15 and by the vessels 14, and is transported in the body of water 4 by the vessels 14 to the laying site 13, as show in FIG. 8. In this step, due to the support provided by the floating devices 15, the string 8 lies in the body of water 4 substantially on a horizontal plane in proximity of the free surface of the body of water 4.

[0070] In the next step, the string 8 is rotated so as to arrange the string 8 substantially on a vertical plane above the path 5. The rotation is performed by the selective and differential sinking of the string 8, and by the action of the vessel 14 connected to the curved portion 9.

[0071] In the case shown in FIG. 9, rotation of the underwater pipeline 2 is made possible by the varying of distance between the underwater pipeline 2 and the floating devices 15. In practice, each floating device 15 is capable of varying the length of its stay wire in a remotely-controlled manner.

[0072] Alternatively, the same operation is possible by varying the buoyancy of each floating device. In particular, rotation of the string 8 is made possible by a defined sequence of varying the buoyancy or flooding of selected floating devices. The sequence enables keeping induced strain on the string 8 within acceptable limits. In certain embodiments. the shape of the string 8 is monitored during the rotation step to avoid excessive deformation. The control tools that can be used to perform this checking are acoustic instruments and structural simulation software.

[0073] Then, the string 8 is sunk so as to progressively move the string 8 closer to the path 5. This step is performed by reducing the buoyancy of the floating devices 15, which start to sink, as shown in FIG. 10.

[0074] The sinking of the string 8 is selective and performed so as to initially arrange the curved portion 9 in contact with the edge 7 and successively the straight portions 10, as shown in FIGS. 11 and 12. The stabilizer device 16 is removed before the curved portion 9 touches down. As the string 8 is gradually laid, the floating devices 15 are uncoupled from the string and recovered, as shown in FIGS. 12 and 13.

[0075] Finally, it is evident that variants can be made to the present disclosure with respect to the embodiments described with reference to the accompanying drawings without departing from the scope of the appended claims. Accordingly, various changes and modifications to the presently disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.