METHOD AND APPARATUS FOR MECHANICAL CONNECTION BETWEEN AN OFFSHORE STRUCTURE AND A SUBSEA PILE

Abstract

A method for connecting an offshore structure (2) to a subsea pile (1) includes inserting a connecting portion (14) of the structure inside the subsea pile. The connecting portion (14) comprises a plurality of outwardly moveable clamping members (5). Moving each of the plurality of clamping members (5) into gripping contact with an inside surface of the subsea pile provides a mechanical connection. The method may also include a grouting step to make the connection permanent.

Claims

1. A method for connecting an offshore structure to a subsea pile, the method comprising: a) inserting a connecting portion of the structure inside the subsea pile, wherein the connecting portion comprises a plurality of outwardly moveable clamping members; and b) outwardly moving each of the plurality of clamping members into gripping contact with an inside surface of the subsea pile.

2. The method of claim 1 wherein the clamping members are retractable, to release the gripping contact.

3. The method of claim 1 wherein the clamping members are spaced apart on the connecting portion, so as to contact the inside surface of the pile at spaced apart locations about its circumference and/or at axially spaced locations along a length of the pile.

4. The method of claim 1 wherein the clamping members are distributed on the connecting portion so as to contact the inside surface of the pile at substantially equally spaced intervals around its circumference when operated.

5. The method of claim 1 wherein the clamping members are fitted to a connecting portion in opposed pairs, to produce diametrically opposed gripping forces acting on the inside surface of the subsea pile.

6. The method of claim 1 wherein the plurality of clamping members comprises a first and second group of clamping members, the first group provided on the connecting portion at one location along its length, and the second group provided at a different location along the length of the connecting portion.

7. The method of claim 6 wherein the members of each group of clamping members is arranged to contact the inside surface of a subsea pile at spaced apart locations about its circumference.

8. The method of claim 1 wherein the clamping members each comprise a contact surface for contacting the inside surface of the subsea pile, that is shaped to conform to the inside surface of the subsea pile.

9. The method of claim 1 wherein the clamping members each comprise a contact surface for contacting the inside surface of the subsea pile, that is textured.

10. The method of claim 1 wherein the clamping members each comprise a piston, that extends from a hydraulic piston in cylinder arrangement.

11. The method of claim 10 wherein at least one of the clamping members consists of, or consist essentially of, the piston of the respective piston in cylinder arrangement and an end of the piston contacts the inside surface of the subsea pile with gripping contact.

12. The method of claim 10 wherein at least one of the clamping members comprises a shaped and/or textured contact surface element for contacting the inside surface of the subsea pile with gripping contact.

13. The method of claim 10 wherein the pistons are double acting.

14. The method of claim 1 wherein at least two clamping members are provided in a clamping assembly; each clamping member comprises a piston, that extends from a hydraulic piston in cylinder arrangement; wherein each piston in cylinder arrangement is fitted to an end of a clamping assembly member and the pistons extend outwards from the assembly in opposite directions to provide diametrically opposed gripping forces acting on the inside surface of the subsea pile.

15. The method of claim 14 wherein the clamping assembly member is a cylindrical tube.

16. The method of claim 1 wherein clamping members are provided in a clamping assembly; each clamping member of the assembly comprises a piston, of a piston in cylinder arrangement; and wherein the clamping assembly comprises a single cylinder having a piston, extendable from each end, and the cylinder is divided by a wall between the two pistons into two chambers, to separate the hydraulic pressure experienced by each piston.

17. The method of claim 1 wherein the clamping members each comprise the screw of a screw jack arrangement.

18. The method of claim 1 wherein clamping members are provided in a clamping assembly; each clamping member of the assembly comprises a screw of a screw jack; wherein each screw jack is fitted to an end of a clamping assembly member and the screws extend outwards from the assembly in opposite directions to provide diametrically opposed gripping forces acting on the inside surface of the subsea pile.

19. The method of claim 1 further comprising inserting grout material into an annular space between the connecting portion and the inside surface of the pile when they are connected by the clamping members.

20. The method of claim 19 wherein the connecting portion and/or the inside surface of the subsea pile is/are provided with texturing along a length; wherein the plurality of clamping members comprises a first and second group of clamping members, the first group provided on the connecting portion at one location along its length, and the second group provided at a different location along the length of the connecting portion; and the first group of the plurality of clamping members is provided on the connecting portion above the surface texturing, and a second group of the plurality of clamping members provided below the surface texturing.

21. The method of claim 19, further comprising retracting the clamping members out of contact with the inside surface of the subsea pile after the grout has set.

22. The method of claim 21 wherein voids left after retracting the clamping members are filled.

23. A method for grouting an offshore structure to a subsea pile, the method comprising: a) inserting a connecting portion of the structure inside the subsea pile, wherein the connecting portion comprises a plurality of outwardly moveable clamping members; b) outwardly moving each of the plurality of clamping members into gripping contact with an inside surface of the subsea pile; c) inserting a grout material into the annular space between the connecting portion and the inside surface of the pile; and d) allowing the grout material to set.

24. A method for connecting a structure to a pile, the method comprising: a) inserting a connecting portion of the structure inside the pile, wherein the connecting portion comprises a plurality of outwardly moveable clamping members; and b) outwardly moving each of the plurality of clamping members into gripping contact with an inside surface of the pile.

25. A clamping assembly for use in the method of claim 1, the clamping assembly comprising two clamping members, each comprising a piston that extends from a hydraulic piston in cylinder arrangement; wherein each piston in cylinder arrangement is fitted to an end of a clamping assembly member and the pistons extend outwards from the assembly in opposite directions in use.

26. The clamping assembly of claim 25 wherein the clamping assembly member is a cylindrical tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 Shows one possible arrangement of subsea piles 1 and support structure 2 in place on the seabed 3;

[0052] FIG. 1a shows in cross section schematic detail a prior art subsea pile and structure connection;

[0053] FIG. 2 Shows a cross section of a pile 1 and part of a structure 2 with a single pair of opposed clamping members 5 extended across the annular gap 4;

[0054] FIG. 3 Shows a pair of hydraulic cylinders incorporated into an intermediate structure 7 to form a clamping assembly 8;

[0055] FIG. 4 Shows an illustration of a pile and part of a structure with multiple clamping assemblies 8 arranged at different distances from the top of the pile and at different orientations relative to the longitudinal axis of the pile;

[0056] FIG. 5 Shows an illustration of a pile and part of a structure with multiple clamping assemblies 8 arranged at different distances from the top of the pile and at different orientations relative to the longitudinal axis of the pile as viewed from one end of the pile (i.e. a cross section view);

[0057] FIG. 5a shows an illustration similar to that of FIG. 5 but where the structure and pile are eccentric;

[0058] FIG. 6 Shows a cutaway illustration of a pile and clamping member with the end of the clamping member shaped to interface with the pile internal surface as viewed from one end of the pile;

[0059] FIG. 7 Shows an illustration of 3 possible different methods for shaping the end of the clamping member that makes contact with the pile, ridges 10, protrusions 11 and the interface formed from a separate piece of material 12 which is then connected to the clamping member 5; and

[0060] FIG. 8 shows in schematic cross section detail a subsea pile and structure connection in accordance with the invention.

SHORT SUMMARY OF THE INVENTION WITH REFERENCE TO THE DRAWINGS

[0061] The method of the present invention provides an improved means of limiting movement between the structure 2 and the pile 1 (FIG. 1) by acting directly at the most critical areas. The present invention also removes the need for the complex fabrications required in existing designs.

[0062] The present invention functions (FIG. 2) by acting outwards from the element of the structure 2 that extends inside the pile 6 and interfaces with the inside surface of the pile. In this way the clamping members 5 that provide the mechanical connection are not limited in position to being at the top of the pile and can be located lower down and act directly at the most critical areas.

[0063] The present invention may comprise two clamping members 5 which are positioned at opposite ends of a simple structure 7 in an extended state (FIG. 3). This unit is passed through holes in the part of the structure 2 that is intended to protrude down inside the pile 1 and securely fixed in place.

[0064] Once the structure is in place relative to the pile, the clamping members are extended across the annular gap 4 to exert force in an outwards direction to act on the inner surface of the pile. This has the advantage that the structure 7 between the clamping members 5 is mainly in compression and consequently can be of a simple construction.

[0065] The clamping members are preferably hydraulic cylinders which are operated either remotely or locally to the device. These hydraulic cylinders can be incorporated into an intermediate structure 8 such as a tubular construction so that they form a clamping assembly (FIG. 3).

[0066] Multiples of these assemblies 8 can be installed at different heights (FIG. 4) and radial angles (FIG. 5) to suit the specific requirements of the overall installation.

[0067] When multiples of these assemblies are employed in a single situation the relative positions of the pile and structure can be maintained within a small margin even in opposition to the forces acting on the structure from multiple directions.

[0068] The ends 9 of the clamping members 5 which contact with the inner surface of the pile may be shaped such as to facilitate an even distribution of the force exerted by the member onto the pile (FIG. 6).

[0069] Depending on the requirements of the specific installation it may also be advantageous to shape the ends of the clamping members that contact the pile to be a series of protrusions 11 or ridges 10 such as to increase the coefficient of friction between the clamping member and pile and so resist movement in a direction other than along the primary axis of the member (FIG. 7). Depending on the specific materials employed in the manufacture of the clamping member and pile it may also be advantageous to create this shaped interface from a separate piece of material 12 (FIG. 7) which is then attached to the member. In this manner the properties of different materials can be exploited to further increase the coefficient of friction between the clamping member and pile.

[0070] Once the gap 4 has been filled with a suitable medium and that medium has become solid the invention may include a means of withdrawing the clamping members 5 so that they can be retracted to ensure that there is no electrical connection between the pile and structure which could lead to undesired galvanic corrosion.

[0071] The invention may also be described as in the following non-limiting numbered clauses.

[0072] Numbered Clauses

[0073] 1) a method of mechanical connection between an offshore structure and subsea pile that acts on the inside surface of the pile in order to resist relative movement between the structure and the pile.

[0074] 2) a method of mechanical connection between an offshore structure and pile as set out in clause 1, such that the method of connection is achieved by the use of hydraulic cylinders.

[0075] 3) a method of mechanical connection between an offshore structure and pile as set out in clause 2, such that the hydraulic cylinders are incorporated into the element of the structure that extends down within the pile.

[0076] 4) a method of mechanical connection between an offshore structure and pile as set out in clause 2, wherein the hydraulic cylinders are incorporated into opposing ends of a intermediate structure.

[0077] 5) a method of mechanical connection between an offshore structure and pile as set out in clause 3, such that the ends of the rods of the hydraulic cylinders are shaped to match the internal surface of the pile.

[0078] 6) a method of mechanical connection between an offshore structure and pile as set out in clause 3, such that the external ends of the cylinder rods are shaped in such a way as to present multiples of ridges or protrusions that will contact the inner surface of the pile when the cylinder is extended so as to increase the friction between the cylinder rod end and the inner surface of the pile.

[0079] 7) a method of mechanical connection between an offshore structure and pile as set out in clause 3, such that the external ends of the cylinder rods are terminated by an additional piece of material that is shaped in such a way as to result in multiples of ridges or protrusions that will contact the inner surface of the pile when the cylinder is extended so as to increase the friction between the cylinder rod end and the inner surface of the pile.

[0080] 8) a method of mechanical connection between an offshore structure and pile as set out in clause 4, wherein multiple such assemblies are attached to the main structure.

[0081] 9) a method of mechanical connection between an offshore structure and pile as set out in clause 8, such that the multiple assemblies are positioned at different heights and angles relative to the main axis of the part of the structure to which they are attached.

DETAILED DESCRIPTION OF THE DRAWINGS

[0082] FIG. 1 shows a schematic view of a three legged structure 2 (a jacket assembly) with each leg fitting to a pile 1 that has previously been driven into the seabed 3.

[0083] As shown in schematic cross section detail FIG. 1a, the leg of the structure 2 has a connecting portion 14 that fits into the interior of the pile 1. In this example the connecting portion 14 is an end of the leg.

[0084] The annular space 4 between the connecting portion 14 and the inner surface of the pile 1 can be filled with a grout, for example along a length suggested by double headed arrow L. On setting the grout layer provides a permanent connection between the structure 2 and the pile 1. To ensure good connection with the layer of grout filling annular space 4 a number of grooves and/or ridges 16 are provided along a length of the inside surface of the pile 1 and along a length of the outside surface of the connecting portion 14.

[0085] To obtain a strong connection, movement between the connecting portion 14 and the pile 1 during the insertion of the grout and its setting must be prevented as far as possible. The prior art method clamps leg of structure 2 to the outside of pile 1, at or near its top, as suggested by arrows C. Clamping at the top of the pile 1 may be ineffective in preventing motion of the connecting portion 14 at a lower position within the pile 1 if the structure 2 is subject to strong forces e.g. from wave or tidal motion.

[0086] FIG. 2 shows in schematic perspective a connection arrangement similar to that of FIG. 1 except that a mechanical connection has been made between the connecting portion 14 and the inside surface of the pile 1, before grouting operations commence. The mechanical connection has been made by outward movement of clamping members, which in this example are the pistons 5 of hydraulic cylinder arrangements 18. Two hydraulic cylinder arrangements 18 are shown in FIG. 2, with pistons 5 acting in diametrically opposed directions to give diametrically opposed gripping forces between the inside surface of the pile 1 and the connecting portion of the structure 2.

[0087] Schematic cross section FIG. 3 shows a convenient arrangement that may be used, for example in fitting to a tubular connecting portion such as that depicted in FIG. 2. The clamping assembly 8 comprises a tubular structure 7 to which are fitted two opposed hydraulic cylinder arrangements 18. Each hydraulic cylinder arrangement 18 has a hydraulic cylinder 20 mounting piston 5 as a clamping member. The hydraulic cylinders 20 may be screw fitted into tubular structure 7. In this example the pistons 5 are double acting and can be retracted from the outwardly extended position shown by pumping fluid into a small annulus 24 between the piston and cylinder walls. Hydraulic lines for a hydraulic circuit are not shown in these drawings, for clarity.

[0088] FIG. 4 illustrates the use of clamping assemblies 8 of the form shown in FIG. 3. A structure 2 is shown fitted to a pile 1. The connecting portion 14 inside pile 1 is shown in ghost. A number of clamping assemblies 8 are shown fitted through the diameter of the connecting portion 14 to allow connection to the inside surface of pile 1.

[0089] The operation of the clamping assemblies 8 can be seen more clearly in plan view FIG. 5. The clamping assemblies 8 are each fitted across a diameter of the connecting portion 14 of structure 2. Ends of the assemblies 8, for example ends 22 of tubular structures 7, can be welded to the wall of the connecting portion 14 to provide a strong fitting.

[0090] As depicted in FIG. 5 the connecting portion 14 is centred inside pile 1 and each of the piston 5 (clamping members) has been extended into gripping contact with the inside surface of the pile 1. The pistons 5 are spaced at equal intervals around the circumference of the connecting portion in this example, providing relatively evenly disposed gripping forces between pile 1 and structure 2. Arrangements where the pistons are not at equal spacings are also contemplated. The annulus 4 can then be filled with grout to form a permanent connection if required.

[0091] FIG. 5a shows the same view as FIG. 5 except that the connecting portion 14 of the structure 2 is not centred in the pile 1. This situation may occur where a structure 2 connects to more than one pile, such as the three legged jacket arrangement shown in FIG. 1. Small errors in positioning of the piles in the seabed may be expected, leading to off centre positioning of the connecting portions within the piles. As can be seen from FIG. 5a the pistons 5 can extend to different extents to form a secure connection between the structure 2 and the pile 1. As with the arrangement of FIG. 5 the annulus 4 may be filled with grout to form a permanent connection.

[0092] FIG. 6 shows in schematic detail part of the wall of a pile 1 with an approaching piston 5 as a clamping member. The end 9 of the piston 5 may be shaped or textured to improve engagement with the inside surface of the pile 1. FIG. 7 shows some options for texturing the contact surface of a clamping member (e.g. the end of a piston 5).

[0093] A series of protrusions 11 or ridges 10 can be used to increase the coefficient of friction between the clamping member and pile and so resist movement in a direction other than along the primary axis of the member. Depending on the specific materials employed in the manufacture of the clamping member and pile it may also be advantageous to create this shaped interface from a separate piece of material 12 which is then attached to the clamping member body (piston 5). In this manner the properties of different materials can be exploited to further increase the coefficient of friction between the clamping member and pile.

[0094] FIG. 6 shows in a cross section view similar to that of FIG. 1a, the use of the methods and apparatus of the invention. The jacket leg of a structure 2 has an end, acting as a connecting portion 14 fitted inside a seabed pile 1. The inside surface of pile 1 and the outside surface of connecting portion 14 are provided with grooves and/or ridges 16 along a length L1 to act as keys for grout. Two groups of clamping assemblies 8 are provided, one above length L1 and one below length L1. Each group of clamping assemblies 8 take the form of those depicted in FIGS. 3 to 5a, having pairs of diametrically opposed hydraulic cylinders 20 with pistons 5 (as clamping members) acting outwardly.

[0095] In the method, the pistons 5 grip the inside surface of the pile 1 with a substantial force applied by hydraulic pumping. Once a secure connection has been made between the pile 1 and the structure 2, the annulus 4 between them may be filled with grout. After the grout has set (typically 24 hours or more) the pressure in the hydraulic system may be relaxed as the solid grout now provides secure mechanical connection. Alternatively, the hydraulic cylinders may be retracted to leave only a grout connection between pile and structure. Voids left in the grout layer by retracting pistons may be filled with e.g. fluid, such as hydraulic fluid fed from small ports (not shown) in assemblies 8.