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Title:
METHOD FOR LIFTING AN OBJECT, ASSEMBLY FOR LIFTING AN OBJECT AND A GUIDING STRUCTURE FOR USE IN AN ASSEMBLY FOR LIFTING OBJECTS
Document Type and Number:
WIPO Patent Application WO/2021/230749
Kind Code:
A1
Abstract:
The invention relates to an assembly of a crane, an object having two tubular members, two lifting tools that are engageable with the tubular members and that are suspended from the crane by a flared rigging, and a guiding structure having a frame and a connector between each lifting tool and the frame, wherein in a first mode the lifting tools are above the jacket, the connectors are in an active state wherein the connectors determine the position of the lifting tools with respect to the frame, and the lifting tools are spaced apart by the guiding structure, and wherein in a second mode the lifting tools are engaged with the tubular members, the connectors are in an idle state, the lifting tools are spaced apart by the engaged object, and the object is suspended from the crane via the main slings.

Inventors:
TEN KLOOSTER ALBERT MARK (NL)
AARNOUDSE CORNELIS JOZUA (NL)
Application Number:
PCT/NL2021/050314
Publication Date:
November 18, 2021
Filing Date:
May 17, 2021
Export Citation:
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Assignee:
BOSKALIS BV BAGGERMAATSCHAPPIJ (NL)
International Classes:
B66C1/16; B63B27/16; B63B35/00; E02B17/02
Attorney, Agent or Firm:
GEURTS, Franciscus Antonius (NL)
Download PDF:
Claims:
C LA IM S

1. Assembly of a crane, an object to be lifted by the crane along a vertical lifting axis, a first lifting tool that is suspended from the crane by a first main sling and a second lifting tool that is suspended from the crane by a second main sling, wherein the first main sling and the second main sling form a flared main rigging, and a guiding structure that is suspended from the crane by an auxiliary rigging, wherein the object comprises a first tubular member that has a first top end and a second tubular member that has a second top end, wherein the first top end and the second top end are spaced apart from each other transverse to the lifting axis over a first distance, wherein the first lifting tool is engageable with the first top end and the second lifting tool is engageable with the second top end, wherein the guiding structure comprises a frame that extends transverse to the lifting axis, a first connector between the first lifting tool and the frame, and a second connector between the second lifting tool and the frame, wherein the assembly comprises a first mode and a second mode, wherein in the first mode the first lifting tool is above and spaced apart from the first top end in the direction of the lifting axis and the second lifting tool is above and spaced apart from the second top end in the direction of the lifting axis, the first connector and the second connector are in an active state in which the first connector determines the position of the first lifting tool with respect to the frame and the second connector determines the position of the second lifting tool with respect to the frame, and the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure, and wherein in the second mode the first lifting tool is engaged with the first top end and the second lifting tool is engaged with the second top end, the first connector and the second connector are in an idle state, the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the engaged object, and the object is suspended from the crane via the main slings.

2. Assembly according to claim 1, wherein in the first mode the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure over a second distance, and in the second mode the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the object over a third distance, and wherein the second distance differs from the third distance.

3. Assembly according to claim 2, wherein the second distance is smaller than the third distance.

4. Assembly according to claim 2 or 3, wherein the third distance is equal to the first distance.

5. Assembly according to any one of the preceding claims, wherein the first connector comprises a first connector cable between the frame and the first lifting tool, wherein in the first mode the first connector cable extends from the frame towards the lifting axis, wherein the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the frame and the tensioned first connector cable, and wherein in the second mode the first connector cable is slack.

6. Assembly according to claim 5, wherein the first connector comprises a pair of first connector cables between the frame and the first lifting tool, wherein the pair of first connector cables is spaced apart at the frame and the pair of first connector cables is proximate to each other at the first lifting tool to form a triangular configuration.

7. Assembly according to any one of the preceding claims, wherein the second connector comprises a second connector cable between the frame and the second lifting tool, wherein in the first mode the second connector cable extends from the frame towards the lifting axis, wherein the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the frame and the tensioned second connector cable, and wherein in the second mode the second connector cable is slack.

8. Assembly according to claim 7, wherein the second connector comprises a pair of second connector cables between the frame and the second lifting tool, wherein the pair of second connector cables is spaced apart at the frame and the pair of second connector cables is proximate to each other at the second lifting tool to form a triangular configuration.

9. Assembly according to any one of the preceding claims, wherein the first top end is a first open top end and the second top end is a second open top end, wherein the first lifting tool is a first internal lifting tool that mates with the first open top end and the second lifting tool is a second internal lifting tool that mates with the second open top end, and wherein the first internal lifting tool is engageable with the first open top end by inserting the first internal lifting tool into the first open top end and the second internal lifting tool is engageable with the second open top end by inserting the second internal lifting tool into the second open top end.

10. Assembly according to claim 9, wherein the first open top end and the second open top end have a circular cross section, and wherein the first internal lifting tool and the second internal lifting tool have a cylindrical shape that corresponds to the circular cross section of the first open top end and the second open top end respectively.

11. Assembly according to claim 9 or 10, wherein at least one internal lifting tool comprises a stabbing guide that extends downwards towards the corresponding open top end for initial entry thereof.

12. Assembly according to any one of the preceding claims, wherein the assembly comprises a third lifting tool that is suspended from the crane by a third main sling, wherein the first main sling, the second main sling and the third main sling form the flared main rigging, the object comprises a third tubular member that has a third top end that is spaced apart from the first top end and the second top end transverse to the lifting axis, wherein the third lifting tool is engageable with the third top end, wherein the guiding structure comprises a third connector between the third lifting tool and the frame, wherein in the first mode the third lifting tool is above and spaced apart from the third top end in the direction of the lifting axis, the third connector is in an active state in which the third connector determines the position of the third lifting tool with respect to the frame, the third lifting tool is spaced apart from the first lifting tool and the second lifting tool transverse to the lifting axis by the guiding structure, and wherein in the second mode the third lifting tool is engaged with the third top end, the third connector is in an idle state, and the third lifting tool is spaced apart from the first lifting tool and the second lifting tool transverse to the lifting axis by the engaged object.

13. Assembly according to claim 12, wherein the assembly comprises a fourth lifting tool that is suspended from the crane by a fourth main sling, wherein the first main sling, the second main sling, the third main sling and the fourth main sling form the flared main rigging, the object comprises a fourth tubular member that has a fourth top end and that is spaced apart from the first top end, the second top end, and the third top end transverse to the lifting axis, wherein the fourth lifting tool is engageable with the fourth top end, wherein the guiding structure comprises a fourth connector between the fourth lifting tool and the frame, wherein in the first mode the fourth lifting tool is above and spaced apart from the fourth top end in the direction of the lifting axis, the fourth connector is in an active state in which the fourth connector determines the position of the fourth lifting tool with respect to the frame, the fourth lifting tool is spaced apart from the first lifting tool, the second lifting tool, and the third lifting tool transverse to the lifting axis by the guiding structure, and wherein in the second mode the fourth lifting tool is engaged with the fourth top end, the fourth connector is in an idle state, and the fourth lifting tool is spaced apart from the first lifting tool, the second lifting tool, and the third lifting tool transverse to the lifting axis by the engaged object.

14. Assembly according to any one of the preceding claims, wherein the object is an offshore jacket, the first tubular member is a first jacket leg, the second tubular member is a second jacket leg, and wherein the offshore jacket comprises jacket braces between the first jacket leg and the second jacket leg that space apart the first jacket leg and the second jacket leg transverse to the lifting axis.

15. Method for lifting an object by means of an assembly of a crane, the object to be lifted by the crane along a vertical lifting axis, a first lifting tool that is suspended from the crane by a first main sling and a second lifting tool that is suspended from the crane by a second main sling, wherein the first main sling and the second main sling form a flared main rigging, and a guiding structure that is suspended from the crane by an auxiliary rigging, wherein the object comprises a first tubular member that has a first top end and a second tubular member that has a second top end, wherein the first top end and the second top end are spaced apart from each other transverse to the lifting axis over a first distance, wherein the first lifting tool is engageable with the first top end and the second lifting tool is engageable with the second top end, wherein the guiding structure comprises a frame that extends transverse to the lifting axis, a first connector between the first lifting tool and the frame, and a second connector between the second lifting tool and the frame, wherein the assembly comprises a first mode and a second mode, wherein in the first mode the first lifting tool is above and spaced apart from the first top end in the direction of the lifting axis and the second lifting tool is above and spaced apart from the second top end in the direction of the lifting axis, the first connector and the second connector are in an active state in which the first connector determines the position of the first lifting tool with respect to the frame and the second connector determines the position of the second lifting tool with respect to the frame, and the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure, wherein in the second mode the first lifting tool is engaged with the first top end and the second lifting tool is engaged with the second top end, the first connector and the second connector are in an idle state, the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the engaged object, and the object is suspended from the crane via the main slings, wherein the method comprises the steps of moving the first lifting tool above and spacing it apart from the first top end in the direction of the lifting axis, and moving the second lifting tool above and spacing it apart from the second top end in the direction of the lifting axis, aligning the first lifting tool with the first top end and aligning the second lifting tool with the second top end, in the first mode engaging the first lifting tool with the first top end and engaging the second lifting tool with the second top end, and in the second mode lifting the object along the vertical lifting axis.

16. Method according to claim 15, wherein in the first mode the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure over a second distance, and in the second mode the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the object over a third distance, wherein the second distance differs from the third distance, wherein the step of engaging the first lifting tool with the first top end and engaging the second lifting tool with the second top end comprises moving the first lifting tool with respect to the second lifting tool transverse to the lifting axis.

17. Method according to claim 16, wherein the second distance is smaller than the third distance, and wherein moving the first lifting tool with respect to the second lifting tool transverse to the lifting axis comprises moving the first lifting tool away from the second lifting tool transverse to the lifting axis.

18. Method according to any one of the claims 15- 17, wherein the first connector comprises a first connector cable between the frame and the first lifting tool, wherein in the first mode the first connector cable extends from the frame towards the lifting axis, wherein the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the frame and the tensioned first connector cable, and wherein in the second mode the first connector cable is slack.

19. Method according claim 18, wherein the first connector comprises a pair of first connector cables between the frame and the first lifting tool, wherein the pair of first connector cables is spaced apart at the frame and the pair of first connector cables is proximate to each other at the first lifting tool to form a triangular configuration.

20. Method according to any one of the claims 15- 19, wherein the second connector comprises a second connector cable between the frame and the second lifting tool, wherein in the first mode the second connector cable extends from the frame towards the lifting axis, wherein the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the frame and the tensioned second connector cable, and wherein in the second mode the first connector cable is slack.

21. Method according to claim 20, wherein the second connector comprises a pair of second connector cables between the frame and the second lifting tool, wherein the pair of second connector cables is spaced apart at the frame and the pair of second connector cables is proximate to each other at the second lifting tool to form a triangular configuration.

22. Method according to any one of the claims 15- 21, wherein the first top end is a first open top end and the second top end is a second open top end, wherein the first lifting tool is a first internal lifting tool that mates with the first open top end and the second lifting tool is a second internal lifting tool that mates with the second open top end, wherein the first internal lifting tool is engageable with the first open top end by inserting the first internal lifting tool into the first open top end and the second internal lifting tool is engageable with the second open top end by inserting the second internal lifting tool into the second open top end, wherein the step of engaging the first lifting tool with the first top end and engaging the second lifting tool with the second top end comprises, lowering the first internal lifting tool, the second internal lifting tool and the guiding structure towards the object, and inserting the first internal lifting tool into the first open top end and inserting the second internal lifting tool into the second open top end.

23. Method according to claim 22, wherein the first open top end and the second open top end have a circular cross section, and wherein the first internal lifting tool and the second internal lifting tool have a cylindrical shape that corresponds to the circular cross section of the first open top end and the second open top end respectively.

24. Method according to claim 22 or 23, wherein at least one internal lifting tool comprises a stabbing guide that extends downwards towards the corresponding open top end for initial entry thereof, and wherein the step of aligning the first lifting tool with the first top end and aligning the second lifting tool with the second top end comprises aligning the stabbing guide of the at least one internal lifting tool with the corresponding at least one open top end.

25. Method according to any one of the claims 15- 24, wherein the assembly comprises a third lifting tool that is suspended from the crane by a third main sling, wherein the first main sling, the second main sling and the third main sling form a flared main rigging, the object comprises a third tubular member that has a third top end that is spaced apart from the first top end and the second top end transverse to the lifting axis, wherein the third lifting tool is engageable with the third top end, wherein the guiding structure comprises a third connector between the third lifting tool and the frame, wherein in the first mode the third lifting tool is above and spaced apart from the third top end in the direction of the lifting axis, the third connector is in an active state in which the third connector determines the position of the third lifting tool with respect to the frame, the third lifting tool is spaced apart from the first lifting tool and the second lifting tool transverse to the lifting axis by the guiding structure, wherein in the second mode the third lifting tool is engaged with the third top end, the third connector is in an idle state, and the third lifting tool is spaced apart from the first lifting tool and the second lifting tool transverse to the lifting axis by the engaged object, wherein the step of moving the first lifting tool above and spacing it apart from the first top end in the direction of the lifting axis, and moving the second lifting tool above and spacing it apart from the second top end in the direction of the lifting axis comprises moving the third lifting tool above and spacing it apart from the third top end in the direction of the lifting axis, the step of aligning the first lifting tool with the first top end and aligning the second lifting tool with the second top end comprises aligning the third lifting tool with the third top end, and the step of engaging the first lifting tool with the first top end and engaging the second lifting tool with the second top end comprises engaging the third lifting tool with the third top end.

26. Method according to claim 25, wherein the assembly comprises a fourth lifting tool that is suspended from the crane by a fourth main sling, wherein the first main sling, the second main sling, the third main sling and the fourth main sling form a flared main rigging, the object comprises a fourth tubular member that has a fourth top end and that is spaced apart from the first top end, the second top end, and the third top end transverse to the lifting axis, wherein the fourth lifting tool is engageable with the fourth top end, wherein the guiding structure comprises a fourth connector between the fourth lifting tool and the frame, wherein in the first mode the fourth lifting tool is above and spaced apart from the fourth top end in the direction of the lifting axis, the fourth connector is in an active state in which the fourth connector determines the position of the fourth lifting tool with respect to the frame, the fourth lifting tool is spaced apart from the first lifting tool, the second lifting tool, and the third lifting tool transverse to the lifting axis by the guiding structure, wherein in the second mode the fourth lifting tool is engaged with the fourth top end, the fourth connector is in an idle state, and the fourth lifting tool is spaced apart from the first lifting tool, the second lifting tool, and the third lifting tool transverse to the lifting axis by the engaged object, wherein the step of moving the first lifting tool above and spacing it apart from the first top end in the direction of the lifting axis, moving the second lifting tool above and spacing it apart from the second top end in the direction of the lifting axis, and moving the third lifting tool above and spacing it apart from the third top end in the direction of the lifting axis comprises moving the fourth lifting tool above and spacing it apart from the fourth top end in the direction of the lifting axis, the step of aligning the first lifting tool with the first top end, aligning the second lifting tool with the second top end, and aligning the third lifting tool with the third top end comprises aligning the fourth lifting tool with the fourth top end, and the step of engaging the first lifting tool with the first top end, engaging the second lifting tool with the second top end, and engaging the third lifting tool with the third top end comprises engaging the fourth lifting tool with the fourth top end.

27. Method according to any one of the claims 15- 26, wherein the object is an offshore jacket, the first tubular member is a first jacket leg, the second tubular member is a second jacket leg, and wherein the offshore jacket comprises jacket braces between the first jacket leg and the second jacket leg that space apart the first jacket leg and the second jacket leg transverse to the lifting axis.

28. Guiding structure for use in an assembly according to any one of the claims 1-14 or for use in a method according to any one of the claims 15-27.

-o-o-o-o-o-o-o-o-

JP/FG

Description:
Method for lifting an object, assembly for lifting an object and a guiding structure for use in an assembly for lifting objects

BACKGROUND

The invention relates to a method for lifting offshore structures, in particular for lifting offshore jackets, an assembly for lifting offshore structures and a guiding structure for use in an assembly for lifting offshore structures.

Offshore jackets are generally known as steel supporting structures for offshore oil and gas production platforms. In recent years offshore jackets are also used to support wind turbines and converter stations of offshore wind farms. The jackets are steel tubular space frames that generally comprise three or four vertical or slightly oblique jacket legs that are interconnected by lateral braces.

For transportation, offshore installation and offshore removal of the jacket it is often lifted by a heavy lift crane. In a known lifting method for jackets use is made of internal lifting tools (ILT's). In this lifting method the internal lifting tools are connected to the crane hook of the heavy lift crane by lifting slings and are inserted into the top of the jacket legs to grip the inner wall thereof. The jacket is then lifted by the heavy lift crane and after lifting of the jacket the internal lifting tools are released from the jacket legs. SUMMARY OF THE INVENTION

In the known lifting method the internal lifting tools are inserted one by one into the respective jacket legs. After insertion of each internal lifting tool the respective lifting sling is temporarily disconnected from the crane hook and placed on the jacket. When all the internal lifting tools are in place all the lifting slings are connected to the crane hook of the heavy lift crane and the jacket is lifted. After the jacket has been lifted the lifting slings are disconnected from the crane hook and the internal lifting tools are removed from the jacket legs one by one. A disadvantage of the method is that handling the internal lifting tools one by one is time consuming. A further disadvantage is that inserting and removing the internal lifting tools and connecting and disconnecting the lifting slings requires personnel to be present on the jacket to handle the heavy lifting equipment. Therefore the method is potentially dangerous for the personnel.

Often a dedicated platform is temporarily installed on top of the jacket to allow personnel to access the jacket and to prepare the lifting operation in a more safe manner. Especially in decommissioning projects where a jacket has to be removed from an offshore location, installing a temporary platform on the jacket often is difficult, expensive and risky.

It is an object of the present invention to provide a method for lifting offshore jackets, an assembly for lifting offshore jackets and a guiding structure for use in an assembly for lifting offshore jackets that address at least one of the problems described above

According to a first aspect, the invention provides an assembly of a crane, an object to be lifted by the crane along a vertical lifting axis, a first lifting tool that is suspended from the crane by a first main sling and a second lifting tool that is suspended from the crane by a second main sling, wherein the first main sling and the second main sling form a flared main rigging, and a guiding structure that is suspended from the crane by an auxiliary rigging, wherein the object comprises a first tubular member that has a first top end and a second tubular member that has a second top end, wherein the first top end and the second top end are spaced apart from each other transverse to the lifting axis over a first distance, wherein the first lifting tool is engageable with the first top end and the second lifting tool is engageable with the second top end, wherein the guiding structure comprises a frame that extends transverse to the lifting axis, a first connector between the first lifting tool and the frame, and a second connector between the second lifting tool and the frame, wherein the assembly comprises a first mode and a second mode, wherein in the first mode the first lifting tool is above and spaced apart from the first top end in the direction of the lifting axis and the second lifting tool is above and spaced apart from the second top end in the direction of the lifting axis, the first connector and the second connector are in an active state in which the first connector determines the position of the first lifting tool with respect to the frame and the second connector determines the position of the second lifting tool with respect to the frame, and the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure, and wherein in the second mode the first lifting tool is engaged with the first top end and the second lifting tool is engaged with the second top end, the first connector and the second connector are in an idle state, the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the engaged object, and the object is suspended from the crane via the main slings.

When the object is embodied as an offshore jacket and the first tubular member is a first jacket leg of the jacket and the second tubular member is a second jacket leg, in the first mode the lifting tools are spaced apart by the guiding structure in accordance with the mutual spacing of the top ends of the jacket legs of the jacket. Therefore, the lifting tools can be aligned with and inserted into the corresponding leg top ends all at the same time in a single lift. This may save time during the lifting operation of the jacket. As the main slings remain connected to the crane hook of the crane in both the first mode and the second mode of the assembly there is no need for personnel to handle the heavy main slings during the lifting operation. Therefore, less or no personnel needs to be present on the jacket so that the lifting operation is less dangerous for the personnel. Furthermore, no dedicated platform is required on top of the jacket when personnel does not have to access the jacket to prepare the lifting operation. Thus, without the need to install a temporary platform on the jacket the lifting operation can be less difficult, less expensive and less risky.

Due to the flared configuration of the main rigging the slings will have a horizontal force component at or near the lifting tools as a result of the suspended load. The horizontal force component is proportional to the weight of the suspended load. In the second mode the lifting tools and the heavy jacket are suspended from the main rigging which results in a big horizontal force component. In the second mode the connectors are in the idle state and the flared main rigging can transfer no or at least limited forces to the frame of the guiding structure as the frame is idle with respect to the main slings. The lifting tools are spaced apart by the engaged jacket and therefore the big horizontal force component will be induced thereto as a compression force. In the first mode the relatively light lifting tools are suspended from the main rigging which results in a smaller horizontal force component as compared to the horizontal force component in the second mode. In the first mode the connectors are in the active mode and the lifting tools are spaced apart by the guiding structure and therefore the smaller horizontal force component will be induced through the connectors to the frame as a compression force. The frame of the guiding structure may thus be dimensioned to resist the smaller compression forces that are induced by the main rigging in the first mode. The frame may therefore be designed slimmer and lighter and therefore in an economically advantageous manner.

In an embodiment in the first mode the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure over a second distance, and in the second mode the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the object over a third distance, wherein the second distance differs from the third distance. In an embodiment the second distance is smaller than the third distance. In an embodiment the third distance is equal to the first distance. Due to the differing second distance and third distance the lifting tools move with respect to the frame during engagement of the lifting tools with the jacket legs. This movement causes the connectors to transfer from the active state to the idle state when the lifting tools are lowered by the crane. No further external actions are required and therefore the lifting operation can be executed in a straightforward and quick manner.

In an embodiment the first connector comprises a first connector cable between the frame and the first lifting tool, wherein in the first mode the first connector cable extends from the frame towards the lifting axis, wherein the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the frame and the tensioned first connector cable, and wherein in the second mode the first connector cable is slack. In an embodiment thereof the first connector comprises a pair of first connector cables between the frame and the first lifting tool, wherein the pair of first connector cables is spaced apart at the frame and the pair of first connector cables is proximate to each other at the first lifting tool to form a triangular configuration.

In an embodiment the second connector comprises a second connector cable between the frame and the second lifting tool, wherein in the first mode the second connector cable extends from the frame towards the lifting axis, wherein the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the frame and the tensioned second connector cable, and wherein in the second mode the second connector cable is slack. In an embodiment thereof the second connector comprises a pair of second connector cables between the frame and the second lifting tool, wherein the pair of second connector cables is spaced apart at the frame and the pair of second connector cables is proximate to each other at the second lifting tool to form a triangular configuration.

The connector cables are a robust and straightforward manner to provide a connector that is in an active state in the first mode and that is in an idle state in the second mode. The cable is in the first mode kept tensioned as the lifting tools are urged towards the lifting axis by gravity. In the second mode the lifting tools are fixated by the jacket so that the lifting tools are closer to the frame and the cable is slack. Due to the triangular configuration of the pair of connector cables the lifting tools can be kept in a fixed position with respect to the frame and with respect to each other so that the lifting tools may not swing as a result of crane motions or other external factors. Keeping the lifting tools in a substantially fixed mutual position makes inserting the lifting tools into the jacket legs easier.

In an embodiment the first top end is a first open top end and the second top end is a second open top end, wherein the first lifting tool is a first internal lifting tool that mates with the first open top end and the second lifting tool is a second internal lifting tool that mates with the second open top end, and wherein the first internal lifting tool is engageable with the first open top end by inserting the first internal lifting tool into the first open top end and the second internal lifting tool is engageable with the second open top end by inserting the second internal lifting tool into the second open top end. In an embodiment thereof the first open top end and the second open top end have a circular cross section, and wherein the first internal lifting tool and the second internal lifting tool have a cylindrical shape that corresponds to the circular cross section of the first open top end and the second open top end respectively. In an embodiment at least one internal lifting tool comprises a stabbing guide that extends downwards towards the corresponding open top end for initial entry thereof.

Internal lifting tools are well known tools that are widely used and which provide a reliable engagement or connection between the main slings and the jacket legs. Using a stabbing guide increases the accuracy of inserting the lifting tools into the jacket legs.

In an embodiment the assembly comprises a third lifting tool that is suspended from the crane by a third main sling, wherein the first main sling, the second main sling and the third main sling form the flared main rigging, the object comprises a third tubular member that has a third top end that is spaced apart from the first top end and the second top end transverse to the lifting axis, wherein the third lifting tool is engageable with the third top end, wherein the guiding structure comprises a third connector between the third lifting tool and the frame, wherein in the first mode the third lifting tool is above and spaced apart from the third top end in the direction of the lifting axis, the third connector is in an active state in which the third connector determines the position of the third lifting tool with respect to the frame, the third lifting tool is spaced apart from the first lifting tool and the second lifting tool transverse to the lifting axis by the guiding structure, and wherein in the second mode the third lifting tool is engaged with the third top end, the third connector is in an idle state, and the third lifting tool is spaced apart from the first lifting tool and the second lifting tool transverse to the lifting axis by the engaged object. In an embodiment the assembly comprises a fourth lifting tool that is suspended from the crane by a fourth main sling, wherein the first main sling, the second main sling, the third main sling and the fourth main sling form the flared main rigging, the object comprises a fourth tubular member that has a fourth top end and that is spaced apart from the first top end, the second top end, and the third top end transverse to the lifting axis, wherein the fourth lifting tool is engageable with the fourth top end, wherein the guiding structure comprises a fourth connector between the fourth lifting tool and the frame, wherein in the first mode the fourth lifting tool is above and spaced apart from the fourth top end in the direction of the lifting axis, the fourth connector is in an active state in which the fourth connector determines the position of the fourth lifting tool with respect to the frame, the fourth lifting tool is spaced apart from the first lifting tool, the second lifting tool, and the third lifting tool transverse to the lifting axis by the guiding structure, and wherein in the second mode the fourth lifting tool is engaged with the fourth top end, the fourth connector is in an idle state, and the fourth lifting tool is spaced apart from the first lifting tool, the second lifting tool, and the third lifting tool transverse to the lifting axis by the engaged object. The assembly may comprise any object or jacket having two or more tubular members or jacket legs, and/or two or more lifting tools. The assembly and more specifically the guiding structure will then function in an equivalent manner as described above.

In an embodiment the object is an offshore jacket, the first tubular member is a first jacket leg, the second tubular member is a second jacket leg, wherein the offshore jacket comprises jacket braces between the first jacket leg and the second jacket leg that space apart the first jacket leg and the second jacket leg transverse to the lifting axis.

According to a second aspect, the invention provides a method for lifting an object by means of an assembly of a crane, the object to be lifted by the crane along a vertical lifting axis, a first lifting tool that is suspended from the crane by a first main sling and a second lifting tool that is suspended from the crane by a second main sling, wherein the first main sling and the second main sling form a flared main rigging, and a guiding structure that is suspended from the crane by an auxiliary rigging, wherein the object comprises a first tubular member that has a first top end and a second tubular member that has a second top end, wherein the first top end and the second top end are spaced apart from each other transverse to the lifting axis over a first distance, wherein the first lifting tool is engageable with the first top end and the second lifting tool is engageable with the second top end, wherein the guiding structure comprises a frame that extends transverse to the lifting axis, a first connector between the first lifting tool and the frame, and a second connector between the second lifting tool and the frame, wherein the assembly comprises a first mode and a second mode, wherein in the first mode the first lifting tool is above and spaced apart from the first top end in the direction of the lifting axis and the second lifting tool is above and spaced apart from the second top end in the direction of the lifting axis, the first connector and the second connector are in an active state in which the first connector determines the position of the first lifting tool with respect to the frame and the second connector determines the position of the second lifting tool with respect to the frame, and the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the guiding structure, wherein in the second mode the first lifting tool is engaged with the first top end and the second lifting tool is engaged with the second top end, the first connector and the second connector are in an idle state, the first lifting tool and the second lifting tool are spaced apart from each other transverse to the lifting axis by the engaged object, and the object is suspended from the crane via the main slings, wherein the method comprises the steps of moving the first lifting tool above and spacing it apart from the first top end in the direction of the lifting axis, and moving the second lifting tool above and spacing it apart from the second top end in the direction of the lifting axis, aligning the first lifting tool with the first top end and aligning the second lifting tool with the second top end, in the first mode engaging the first lifting tool with the first top end and engaging the second lifting tool with the second top end, and in the second mode lifting the object along the vertical lifting axis.

According to a third aspect, the invention provides a guiding structure for use in an assembly or for use in a method according to any one of the aforementioned embodiments.

The method and its embodiments and the guiding structure relate to the practical implementation of the assembly according to any one of the aforementioned embodiments and thus have the same technical advantages, which will not be repeated hereafter.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:

Figure 1A is an isometric view of an assembly for lifting offshore jackets according to an embodiment of the invention;

Figure IB shows an isometric view of a guiding structure of the assembly of figure 1A;

Figure 2 is a section view of the guiding structure of figure IB in a first mode, and;

Figure 3 is a section view of the guiding structure of figure IB in a second mode.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1A shows an assembly 1 of a crane 20 on a vessel 10, an object 3 that protrudes from the water surface of a sea 2, four internal lifting tools 40a-d (ILT's) that are suspended from the crane 20 and a guiding structure 50 that is suspended from the crane 20. The vessel 10 comprises a hull 11 with a bow 12, a stern 13, a main cabin 14 at the bow 12, a deck 15 between the main cabin 14 and the stern 13, and a crane pedestal 16 on the deck 15 that supports the crane 20. The crane 20 is used to lift the object 3, in this example to remove the object 3 from the seabed at an offshore location and to place it on the deck 15 of the vessel 10 as part of a decommissioning operation. The crane 20 may also be used to, amongst others, install the object 3 onto the seabed or to lift the object 3 from a quay onto the deck 15 or vice versa.

The crane 20 in this example comprises a crane base 21 that is rotatable with respect to the crane pedestal 16, a crane boom 22 that is hingeable with respect to the crane base 21, and a crane suspension point or crane hook 23 that is suspended from the crane boom 22 by a hoisting cable 24. The crane 20 is operable to move the crane hook 23 along a vertical lifting axis L in order to lift the object 3. As best shown in figure IB, in this example the object 3 is embodied as an offshore jacket 30 that has a space frame configuration comprising steel tubular members, and that comprises a first jacket leg 31a, a second jacket leg 31b, a third jacket leg 31c, a fourth jacket leg 31a, and multiple lateral jacket braces 32 between the jacket legs 31a-d that interconnect and space apart the jacket legs 31a-d. Each jacket leg 31a-d comprises a central leg axis P that is orientated substantially vertical and an open leg top end 33a-d that has a circular cross section. Depending on the space frame configuration of the jacket 30 the jacket legs 31a-d and therewith the central leg axes P may be orientated slightly oblique towards each other.

It is to be understood that the object 3 may also be embodied as, for instance, a subsea template or a topside of an offshore platform. The object 3 at least comprises a first tubular member 31a that has a first top end 33a and a second tubular member 31b that has a second top end 33b. The first top end 33a and the second top end 33b are spaced apart from each other transverse to the lifting axis L. The first top end 33a and the second top end 33b may, for instance, be spaced apart by braces 32, the topside construction or other structural parts.

The four lifting tools 40a-d correspond to the four jacket legs 31a-d of the jacket 30. The lifting tools 40a-d comprise a generally cylindrical shaped gripper body 41 having a central lifting tool axis T, a top cap 42 at one end of the gripper body 41, a padeye 43 on the top cap, a tapered stabbing end 44 opposite to the top cap 42, multiple stiffening ribs 45 around the circumference of the gripper body 41 that extend between the top cap 42 and the stabbing end 44, and multiple teeth or grippers 46 that are arranged between the stiffening ribs 45 and that extend between the top cap 42 and the stabbing end 44. In this example each lifting tool 40a-d is suspended from the crane 20 by a corresponding main lifting sling 47a-d that is connected to the crane hook 23 and that is connected to the padeye 43 of the lifting tool 40a-d by a shackle 48. The main lifting slings 47a-d diverge from each other from the crane hook 23 towards the lifting tools 40a-d to form a flared main rigging for the lifting tools 40a-d. The lifting tools 40a-d comprise a stabbing guide 49 at the stabbing end 44 that is in this example embodied as a substantially triangular steel plate that extends downwards from the stabbing end 44 parallel to the lifting axis L and towards the open leg top ends 33a-d for initial entry thereof.

The outer diameter of the gripper body 41 of the lifting tools 40a-d substantially corresponds to or mates with the internal diameter of the leg top ends 33a-d with a positive tolerance. When the lifting tools 40a-d are stabbed into the corresponding leg top ends 33a-d the top caps 42 abut the leg top ends 33a-d. The grippers 46 can be outwardly expanded to bring them in abutment with the inside wall of the jacket legs 31a-d. The grippers 46 then grip the inside wall of the jacket legs 31a-d so that the lifting tools 40a-d are securely connected to or engaged with the leg top ends 33a-d of the jacket legs 31a-d. The grippers 46 can be inwardly retracted to detach them from the inside wall of the jacket legs 31a-d in order to remove or release the lifting tools 40a-d from the jacket legs 31a-d.

In this example the guiding structure 50 comprises a rigid, cross shaped frame 58 that has two pairs of steel tubular main girders 51 as its legs. The main girders 51 of each pair of main girders 51 extend parallel to each other and are spaced apart by multiple steel tubular cross braces 52 that extend transverse between the main girders 51. The pairs of main girders 51 are orientated transverse to each other and intersect each other near the middle of the main girders 51.

The frame 58 comprises four pairs of girder suspension points 53a-d at the main girders 51 at about two thirds of the length of the main girders 51 between the center and the distal end thereof. The frame 58 is suspended from the crane hook 23 by an auxiliary rigging 59 that, in this example, comprises four pairs of auxiliary lifting slings 54a-d that are connected to the crane hook 23 and to the corresponding pairs of suspension points 53a- d. The auxiliary rigging 59 keeps the frame 58 of the guiding structure 50 at a fixed distance from the crane hook 23 along the lifting axis L so that the frame 58 extends horizontally and substantially transverse to the lifting axis L.

The guiding structure 50 comprises a lifting tool suspension point 55a-d at each distal end of the main girders 51 of the frame 58 so that each pair of main girders 51 comprises a pair of spaced apart lifting tool suspension points 55a-d at each distal end thereof. The guiding structure 50 comprises a first connector 56a between the first pair of lifting tool suspension points 55a and the first lifting tool 40a, a second connector 56b between the second pair of lifting tool suspension points 55b and the second lifting tool 40b, a third connector 56c between the third pair of lifting tool suspension points 55c and the third lifting tool 40c, and a fourth connector 56d between the fourth pair of lifting tool suspension points 55d and the fourth lifting tool 40d.

In this example each connector 56a-d comprises a pair of corresponding connector cables 57a-d of which each connector cable 57a-d is connected between one of the respective lifting tool suspension points 55a-d and the padeye 43 of the lifting tool 40a-d. Thus, each pair of connector cables 57a-d is spaced apart from each other at the frame 58, is proximate to each other at the corresponding lifting tool 40a-d and therefore has a V- shaped or triangular configuration towards the lifting tool 40a-d. Each connector cable 57a-d extends from the lifting tool suspension point 55a-d at the distal end of one of the main girders 51 obliquely downwards away from the crane hook 23, obliquely towards the lifting axis L and obliquely towards the opposite parallel main girder 51 of the pair of main girders 51.

Figures 2 and 3 are a side section view of the guiding structure 50 through the lifting axis L, the first lifting tool 40a and the second lifting tool 40b. This section view is chosen to clearly show the mutual distances between the components of the assembly 1. In the description below the arrangement and the functioning of the assembly 1, in particular of the guiding structure 50, is explained by sometimes referring to the first and second member of the components of the assembly 1 only. This is done for clarity reasons only and it is to be understood that the description equivalently applies to any other pairs or groups of members of the components concerned.

In figure 2 the assembly 1 is shown in a first mode in which the lifting tools 40a-d are above and spaced apart from the corresponding jacket legs 31a-d in a direction along the lifting axis L. The first jacket leg 31a and the second jacket leg 31b are spaced apart transverse to the lifting axis L over a first distance A and the first lifting tool 40a and the second lifting tool 40b are spaced apart from each other transverse to the lifting axis L by the guiding structure 50 over a second distance B that is smaller than the first distance A. The lifting tool axes T are orientated substantially parallel to the lifting axis L and both lifting tools 40a-b are positioned with their stabbing guide 49 at least partly within the circumference of the corresponding leg top ends 33a-b when looked at from above along the lifting axis L.

The lifting tools 40a-d are suspended below the frame 58 of the guiding structure 50. The configuration of the connectors 56a-d between the frame 58 and the lifting tools 40a-d substantially determines the position of the lifting tools 40a-d with respect to the frame, keeping the lifting tools 40a-d at a predetermined position and orientation with respect to the frame 58 and therewith with respect to each other. The pairs of connector cables 57a-d keep the lifting tools 40a-d spaced apart from the lifting axis L, therefore the main lifting slings 47a-d extend obliquely away from the crane hook 23 and the lifting axis L, hence the flared main rigging. The guiding structure 50 resists compression forces that are induced by the oblique main lifting slings 47a-d. These compression forces are proportional to the weight of the object that is suspended by the main lifting sings 47a-d. In the first mode the compression forces are relatively low as only the lifting tools 40a-d are suspended from the main lifting slings 47a- d.

The main lifting slings 47a-d extend centrally between the main girders 51 of the pairs of main girders 51 near the distal end thereof. Gravity causes the lifting tools 40a-d towards the lifting axis L and therefore assures that the pairs of connector cables 57a-d are under tension in an active state in which the connector cables 57a-d structurally couple the lifting tools 40a-d and the frame 58 of the guiding structure 50. As the connector cables 57a-d are under tension they have a fixed length. By the V-shaped configuration of the connector cables 57a-d the lifting tools 40a-d are kept in the predetermined position in a horizontal plane that is transverse to the lifting axis L. By adjusting the length of the connector cables 57a-d the predetermined position of the lifting tools 40a-d can be adjusted while using the same frame 58.

In figure 3 the assembly 1 is shown in a second mode in which the lifting tools 40a-d are engaged with the leg top ends 33a-d of the jacket legs 31a-d and the jacket 30 is suspended from the crane 20 via the main slings 47a- d. The first lifting tool 40a and the second lifting tool 40b are spaced apart from each other transverse to the lifting axis L by the jacket 30 over a third distance C that is equal to the first distance A. The jacket 30 resists the compression forces that are induced by the oblique main lifting slings 47a-d. In the second mode the compression forces are relatively high as the lifting tools 40a-d and the heavy jacket 30 are suspended from the main lifting slings 47a-d.

The distance between the crane hook 23 and the first lifting tool 40a and the distance between the crane hook 23 and the second lifting tool 40b is the same in the first mode and in the second mode due to fixed length of the respective main slings 54a-b. The distance between the pair of first lifting tool suspension points 55a and the pair of second lifting tool suspension points 55b is the same in the first mode and in the second mode due to the rigid main girders 51. The distance between the frame 58 of the guiding structure 50 and the crane hook 23 is the same in the first mode and in the second mode due to fixed length of the auxiliary slings 54a-d. Because the third distance C between the first lifting tool 40a and the second lifting tool 40b in the second mode is larger than the second distance B between the first lifting tool 40a and the second lifting tool 40b in the first mode, in the second mode the distance between the pairs of lifting tool suspension points 55a-b and the corresponding lifting tools 40a-b is smaller than the length of the pairs of connector cables 57a-b, and therefore the connector cables 57a-b are slack or in an idle state.

As the connector cables 57a-d are slack the lifting tools 40a-d or the main lifting slings 47a-d are free to move with respect to the main girders 51. The lifting tools 40a-d or the main lifting slings 47a-d are structurally uncoupled from the main girders 51 and can transfer no or at least limited forces to the main girders 51 of the frame 58 of the guiding structure 50. The main girders 51 are structurally disconnected from the lifting tools 40a-d so that the compression forces that are induced by the oblique main lifting slings 47a-d are not or at least limited transferred thereto. The lifting tools 40a-d and the guiding structure 50 are independently of each other suspended by the main lifting slings 47a-d and the auxiliary lifting slings 54a-d respectively.

To lift the offshore jacket 30 the vessel 10 moves close to the jacket 30 so that the jacket 30 is within reach of the crane 20. The crane 20 moves the crane hook 23 with the guiding structure 50 and the internal lifting tools 40a-d above the jacket 30 so that the lifting axis L passes through the footprint of the jacket 30, more specifically the lifting axis L passes through the center of gravity of the jacket 30. Subsequently the lifting tools 40a-d are aligned with but spaced apart from the corresponding leg top ends 33a-d of the jacket 30 so that the assembly 1 is in the first mode as described above. This may be achieved by using tugger winches that are connected to the guiding structure 50 or to the lifting tools 40a-d.

Subsequently the crane 20 lowers the guiding structure 50 and the internal lifting tools 40a-d towards the jacket 30. The lifting tools 40a-d are inserted into the open leg top ends 33a-d, when necessary the lifting tools 40a-d are guided into the leg top ends 33a-d by the stabbing ends 44 and/or by the stabbing guides 49. When the lifting tools 40a-d are inserted into the jacket legs 31a-d the lifting tool axes T are aligned with the leg axes P and eventually coincide therewith. During the insertion of the lifting tools 40a-d the lifting tools 40a-d move away from the lifting axes L and towards the corresponding pairs of lifting tool suspension points 55a-d in a direction transverse to the lifting axis L. As a result the pairs of connector cables 57a-d become slack or idle. When the lifting tools 40a-d are fully inserted in the jacket legs 31a-d the top caps 42 abut the leg top ends 33a-d and the assembly 1 is in the second mode as described above.

Thereafter the lifting tools 40a-d are operated connect to or to grip the jacket legs 31a-d by outwardly expanding the grippers 46 and bring them in abutment with the inside wall of the jacket legs 31a-d. Once all the lifting tools 40a-d are securely connected to the jacket 30 the crane 20 raises the crane hook 23 to lift the jacket 30. As the connector cables 57a-d are idle the lifting tools 40a-d or the main lifting slings 47a-d transfer no or at least limited forces to the main girders 51 of the frame 58 of the guiding structure 50.

When the jacket 30 is moved to the required position the crane 20 lowers the crane hook 23 to set down the jacket 30. Subsequently the lifting tools 40a-d are operated to release the jacket legs 31a-d and the crane hook 23 is slowly and carefully raised to remove the lifting tools 40a-d from the leg top ends 33a-d. During the removal of the lifting tools 40a-d they move towards the lifting axes L and away from the lifting tool suspension points 55a-d in a direction transverse to the lifting axis L, and the connector cables 57a-d become tensioned. When the lifting tools 40a-d are removed from the leg top ends 33a-d the assembly 1 is back in the first mode as described above. Subsequently the crane 20 moves the crane hook 23 with the guiding structure 50 and the internal lifting tools 40a-d away from the jacket 30 and the vessel 10 moves away from the jacket 30.

It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention.