NL2006153C2

NL2006153C2 - Method and device for assembling or disassembling a structure under water.

Info

Publication number: NL2006153C2
Application number: NL2006153A
Authority: NL
Inventors: Guido Johannes Maria Ammerlaan
Original assignee: Heerema Marine Contractors Nl
Priority date: 2011-02-07
Filing date: 2011-02-07
Publication date: 2012-08-08
Also published as: GB2502489A8; NO20131209A1; GB2502489A; WO2012108765A1; US20140147217A1; GB201316002D0

Description

P30555NL00/WHA/BTA

Title: Method and device for assembling or disassembling a structure under water

Field of the invention

The present invention relates a method and a device for assembling or disassembling a structure which is at least in part submerged, in particular for disassembling a jacket structure.

5

Background of the invention and prior art

In the offshore industry, jacket structures (or jackets in short) are widely used to support and fix platforms above the sea surface. A jacket structure is generally positioned directly onto the seabed. A jacket comprises many tubulars which are interconnected and 10 form a lattice structure. The beams are generally made from steel. A jacket generally comprises a number of beams which are substantially upstanding and which extend from a base of the jacket to a top of the jacket. The upstanding beams are generally connected to one another via horizontal and diagonal cross-beams.

Once a jacket reaches the end of its economic or technical lifespan, it may need to 15 be removed. The required removal is dependent on local administrative requirements and can be in part or in full.

In a known method of removing a jacket, a heavy lift vessel is used to support a top part of the jacket. Subsequently, the jacket is cut at a certain distance above the seabed. The section above the cut is lifted and removed with the heavy lift vessel, and the section 20 below the cut remains on location. A further cutting and lifting operation may be required to remove a next part.

The cutting of the jacket generally is a time consuming and expensive operation. Generally, a large vessel with a crew is required in order to perform the cutting. Divers or one or more ROV’s and special cutting and lifting equipment are required for the actual 25 cutting itself. For the lifting operation, heavy lift capability is required, which is expensive.

The known removal operation has a further disadvantage in that bad weather can cause significant delays, which further increase the costs.

There is a need in the field of the art for more efficient and cost-effective way of removing jacket structures.

Object of the invention

It is an object of the invention to provide a method and device for removing in a reliable and efficient manner a large jacket structure which is at least partially submerged.

30 -2- 35 Summary of the invention

The invention provides a method of assembling or disassembling a structure which is located at least partially underwater, the method comprising: providing at least one movable arm, the movable arm comprising: at least a first segment and a second segment connected to one another via at 40 least a first hinge, a support connected to a proximal end of the first segment via at least one support hinge, the support being constructed to be mounted to the structure or to be placed on the seabed, a processing tool mounted to a distal end of the second segment, 45 at least one actuator configured to: o controllably move the first segment relative to the support, and to o controllably move the second segment relative to the first segment in order to position the processing tool at a target location in a working range of the arm, 50 a control device configured to control the at least one actuator and the processing tool during operation, performing a processing operation on the structure for assembling or disassembling the structure

With the present invention, a large jacket structure can be disassembled. It is 55 possible to disassemble a jacket structure of for instance 100 meter. The disassembling operation can be performed substantially independently by the movable arm. The movable arm can be connected to one or several umbilicals providing electrical and/or hydraulic power, communication cables, fibre optics and the like. The umbilical can extend to a vessel at the water surface or straight to shore.

60 It is also possible to disassemble the bottom part of a jacket after the top part has been removed with a heavy lift operation.

The movable arm has a substantial lifting capability, i.e. 10 tons or more. This is required to handle large tools and jacket segments. The movable arm thus does not need an extra under-water balloon to provide extra lifting capacity.

65 Under water cranes are known for other purposes. US4109480 discloses a submarine cherry picker constructed to be positioned on the seabed and suitable for repairing a pipeline underwater. This cherry picker is not suitable for disassembling a jacket structure, at least because the working range above the seabed is too limited. The cherry picker further lacks sufficient lifting capacity to handle parts without an extra balloon.

70 Furthermore, the cherry picker according to US4109480 is limited to lifting parts, and cannot -3- perform any other functionality than lifting, because only a hook 65 is provided at the end of the crane.

US6267037B1 describes a cutting tool for cutting an underwater pipeline. The tool comprises a cutting wire which is rotated to cut the pipeline. The tool has limited capabilities 5 and is not very versatile. A part which is cut from the structure is uncontrolled and drops to the seabed. The apparatus of US6267037B1 therefore is not suitable to disassemble a jacket independently or substantially independently.

In an embodiment, the processing tool comprises: a gripping tool for gripping a part of the structure and/or 10 - a cutting tool for cutting in the structure.

In an embodiment, the method comprises: - gripping a part of the structure with the gripping tool, cutting in the structure with the cutting tool such that said part becomes separated from the structure, 15 - moving the separated part away from the structure with the gripping tool.

In this way, the part can be removed in a simple and efficient manner.

In an embodiment, the method comprises simultaneously gripping the part with the gripping tool and cutting in the structure with the cutting tool, thereby preventing the part from falling when the part becomes separated from the structure. The capability of 20 simultaneous gripping in one location and cutting in another location allows safe removal of the parts, without dropping of the parts onto the seabed below.

In an embodiment, the cutting tool is movable relative to the gripping tool, allowing a part of the structure to be held by the gripping tool while the cutting tool cuts the structure in different positions which are required to separate the part from the structure, the method 25 comprising: gripping a part of the structure which is envisaged to be separated from the structure with the gripping tool, moving the cutting tool to different locations and cutting in the structure at the different locations for separating the part from the structure while maintaining the 30 grip on the part with the gripping tool.

Generally, a part such as a beam is connected to the rest of the structure at multiple locations. Generally, multiple cuts will have to be performed to separate the part completely from the structure. Because the cutting tool is movable relative to the gripping tool, a part of a substantial size can be separated from the structure. In an embodiment, the working range 35 of the cutting tool extends up to 5 meter from the gripping tool. In this way, parts of up to 10 meter can be removed from the structure.

In an embodiment, the method comprises: -4- providing a container at the seabed within a working range of the movable arm, - each time separating a part from the structure, placing the separated parts in the container by the arm, lifting the filled container to the water surface, 5 - transporting the container to a remote location with a vessel.

The parts can be conveniently collected in the container. Littering of parts on the seabed can be avoided, which results in a clean removal operation. The container can be hoisted with a cable by a vessel. A new, empty container may be put in place prior to the removal of the full container in order to enable a non-stop operation.

10 In an embodiment, the support comprises at least one clamp, the method comprising: clamping the structure at a first position, - removing at least one first part from the structure, and in particular as many parts as are within the working range of the movable arm at the first position, releasing the at least one clamp, 15 - moving the support to a second position on the structure and clamping the structure at the second position, removing at least one second part from the structure, and in particular as many parts as are within the working range of the movable arm at the second position, repeating these steps until the structure is substantially disassembled.

20 By starting at the top of the structure and moving downward, an efficient operation is possible. In case of a jacket which is wider than the working range of the movable arm, it is possible that the movable arm is positioned at several locations in one horizontal level before being moved downward to a next, lower horizontal level.

In an embodiment, the movable arm is moved in a downwards spiral along the outer 25 side of the structure for disassembling the structure.

In an embodiment, the method comprises clamping the at least one clamp to a vertical beam or substantially vertical beam of the structure and moving downwards along said beam from said first position to said second position and further downward until the structure is substantially disassembled.

30 The substantially vertical beam is a suitable location to support the movable arm and can function as a rail along which the support can move downward.

In an embodiment, an auxiliary rail is mounted to the support structure for supporting the arm, wherein the support of the movable arm is constructed to engage said rail and slide or roll along said rail. The rail has a vertical or substantially vertical orientation. The rail can 35 be mounted to the vertical or substantially vertical beam and extends substantially parallel to the vertical or substantially vertical beam.

In an embodiment, the control device comprises cameras.

-5-

In an embodiment, the control device comprises: - a data processing device comprising a memory configured for storing: geometrical data relating to the initial form of the structure, and disassembly data relating to the progress of disassembling the 5 structure and the current form of the structure, - one or more sensors constructed for determining a current position of the arm and of the processing tool relative to the structure, and wherein the method comprises: loading the geometrical data into the memory, 10 - determining a part to be removed from the structure and determining a target position of the processing tool on the basis of the geometrical data and the disassembly data, moving the processing tool to the target position, removing a part from the structure by gripping the part, cutting in the structure 15 until the part is separated and moving the part away from the structure, updating the disassembly data with data on the removed part, repeating the steps until the structure is disassembled.

With this embodiment, feed forward control and feedback control can be combined for an efficient removal process. With the geometrical data and the disassembly data, a next 20 part which is to be removed can be determined. It can also be determined how the movable arm can reach said part. If the support needs of the movable arm to be repositioned at another support location, this can be performed prior to the cutting operation. The support may need to be replaced vertically or horizontally. Next, the part is gripped and cuts are made in the structure. Next, the part is removed and the disassembly data are updated with 25 the removed part.

The sensors provide data for accurate positioning. Although in theory the complete form of the structure is known from the geometrical data, in practice unknown obstacles may be present, due to an incomplete or inaccurate drawing. With the sensors, the actual data can be used for accurate positioning.

30 In an embodiment, the method comprises: - cutting the structure at a cutting point, wherein a top part of the structure is separated from a bottom part of the structure, lifting the top part of the structure with a lifting device on a vessel and removing the top part from the location with the vessel, 35 - disassembling the bottom part of the structure according to the method of claim 1.

-6-

In some situations, it is more efficient to remove a top part of the jacket with a lift operation. Only the bottom part may then be disassembled with the movable arm. This will speed up the total disassembly time and will allow the movable arm to work at a depth below the water surface where there is no influence from waves.

5 In an embodiment, the method comprises: providing a first of said movable arm, providing a second of said movable arm, gripping a part of the structure with the gripping tool of the first movable arm, cutting in the structure with the cutting tool of the second movable arm such that 10 said part becomes separated from the structure, moving the separated part away from the structure with the first movable arm.

With a pair of arms, it is possible to speed up the operation. Moreover, some parts may need to be supported in more than one location. This can be performed with two or more arms.

15 In an embodiment, the method comprises: gripping the first movable arm with the gripping tool of the second movable arm, releasing the support of the first movable arm from the structure, - moving the first movable arm with the second movable arm, such that the support of the first movable arm is moved from a first support position to a second 20 support position, thereby changing the working range of the first movable arm.

One arm can be used to efficiently replace another arm. This allows easy repositioning of the arms.

The present invention further relates to a movable arm for disassembling or assembling a structure extending at least partially under water, the movable arm comprising: 25 - at least a first segment and a second segment connected to one another via at least a first hinge, - a support connected to a proximal end of the first segment via at least one support hinge, the support being constructed to be mounted to the structure or to be placed on the seabed, 30 - a processing tool mounted to a distal end of the second segment, - at least one actuator configured to: o controllably move the first segment relative to the support, and to o controllably move the second segment relative to the first segment in order to position the processing tool at a target location in a working 35 range of the arm, - a control device configured to control the at least one actuator and the processing tool during operation.

-7-

The movable arm provides substantially the same advantages as described in relation to the method above.

In an embodiment, the cutting tool is movable relative to the gripping tool, allowing a part of the structure to be held by the gripping tool while the cutting tool cuts the structure in 5 different positions which are required to separate the part from the structure.

In an embodiment, the cutting tool is connected to the gripping tool or to the movable arm via a movable cutting arm which provides the cutting tool with a working range which extends around the gripping tool.

In an embodiment, the support comprises a clamping device which comprises 10 clamping members constructed to clamp to a vertical or substantially vertical beam of the structure. The clamp comprises clamping members which have substantially vertically extending gripping surfaces.

In an embodiment, the support comprises: a first clamp, 15 - a second clamp spaced apart from the first clamp, and at least one support beam connecting the first and second clamp to one another, wherein the first segment is connected to said support beam via the support hinge.

In an embodiment, the control device comprises: 20 - a data processing device comprising a memory configured for storing: geometrical data relating to the form of the structure, assembly data or disassembly data relating to the individual steps of assembling or disassembling the structure, one or more sensors constructed for determining a current position of the arm 25 and of the processing tool relative to the structure, and

The present invention further relates to an assembly for disassembling a structure extending at least partially under water, the assembly comprising: at least one movable arm according to the invention, and at least one container for accommodating removed parts from the structure.

30

Brief description of the drawings

The previous and other features and advantages of the present invention will be more fully understood from the following detailed description of exemplary embodiments with reference to the attached drawings.

Figure 1A shows a schematic side view of the movable arm according to the invention comprising a cutting tool.

35 -8-

Figure 1B shows a schematic side view of the movable arm according to the invention comprising a gripping tool.

Figure 2A shows an orthogonal view of an embodiment of the movable arm in a first operational step.

5 Figure 2B shows an orthogonal view an embodiment of the movable arm in a next operational step.

Figures 3-8 show schematic side views of respective steps of the method according to the invention.

10

Detailed description of the figures

Turning to Figure 1A, a movable arm 20 according to the invention is shown. The movable arm 20 comprises a support 22 having two clamps 24A, 24B. The two clamps 24A, 24B are connected to the support 22 or one another via two intermediate beams 26A, 26B, 15 which are preferably adjustable in length.

The movable arm 20 is mounted on a turret 63. The turret 63 comprises a pivot 61 via which the arm 20 is rotatable relative to the support 22 about rotation axis 62.

A proximal end 34 of a first segment 28A is connected to the turret 63 via a hinge 27.

20 The arm comprises a first segment 28A and a second segment 28B. The first and second segments are connected to one another via a hinge 29. The movable arm may comprise additional segments, i.e. three or four segments.

The movable arm 20 comprises a number of actuators 33 with which the movable arm can be moved. The actuators 33 can be electric or hydraulic. A power cable 35 is 25 provided which extends between the movable arm 20 and an auxiliary vessel for providing power to a motor 31 of the movable arm 20.

A processing tool 30 is provided at a distal end 36 of the second segment 28B. The processing tool 30 comprises for instance a cutting tool 51, but may also be another type of equipment such as like a gripping tool 50, a tool for drilling, grinding and the like. The cutting 30 tool 51 may be a saw, a flame cutting tool, a welding tool, a laser device or a different kind of cutting tool. In an embodiment, the cutting tool comprises a wrench for connecting or disconnecting bolts.

The rotation axis 62, the hinge 27 and the hinge 29 provide the segment 28b with three degrees of freedom relative to the support 22.

35 The processing tool 30 is rotatable relative to segment 28B about three independent axes of rotation 80, 81,82 via a hinge 84. This provides the cutting tool 30 with six degrees of freedom. The six degrees of freedom allow the rotation tool 30 to be -9- positioned in any position within the 3D working range and have any orientation in that position.

The cutting tool 51 is provided with a rotating cutting wire 109. In use, the rotating cutting wire 109 cuts through steel tubulars in a practical manner.

5 Turning to figures 2A and 2B, a jacket 10 which is to be removed comprises a plurality of substantially vertical (or upstanding) beams 2. The beams may be oriented at an angle of 0-8 degrees to the vertical. The jacket 10 comprises a grid of 4 by 2 upstanding beams 2. The jacket further comprises horizontal cross-beams 4 which extend between the upstanding beams 2 and diagonal beams 6, which also extend between the diagonal 10 beams. The beams 2, 4, 6 are connected to one another at joints 7 and form a lattice structure.

The jacket 10 may also comprise ducts 9 and other equipment which is mounted to the lattice structure.

The jacket 10 which is shown in figures 2A, 2Bis only a part of the original jacket. It 15 is the bottom part, and the top part of the jacket is already removed, for instance via a heavy lift operation.

Returning to figure 1 A, the clamps 24A, 24B are constructed to be connected to the vertical beams 2. To this end, the clamps comprise clamp members 23 which have substantially vertically extending gripping surfaces. The gripping surface 23 are pivotable 20 relative to the intermediate beams 26A, 26B such that they gripping surfaces can be aligned with the intermediate beams. This allows the intermediate beams 26A, 26B to be oriented substantially parallel to an upstanding beam 2 of the jacket. See also figure 4

Turning to Figure 1B, a gripping tool 50 is connected to the distal end of the second segment 28B. The gripping tool comprises fingers 101 which are movable relative to one 25 another for gripping a part of the structure.

The arm 20 may comprise both a gripping tool 50 and with a cutting tool 51, only a gripping tool, 50, or only a cutting tool 51.

If the arm 20 comprises both a gripping tool 50 as a cutting tool 51, a movable cutting arm (not shown) may be provided which provides the cutting tool 51 with a working 30 range about the gripping tool 50. The movable cutting arm is equipped with an actuator, so that the cutting tool 51 can be controllably positioned around the gripping tool.

The movable clamp arm comprises at least one actuator and the actuator is coupled to a control unit 60.

In an embodiment, the control unit 60 comprises a data processing device. The 35 data processing device comprises a memory configured for storing geometrical data relating to the initial form of the structure, and disassembly data relating to the progress of disassembling the structure and the current form of the structure.

-10-

The geometrical data may be obtained from measurements or a computer file which was used to design the jacket, an AutoCAD file or similar file from another design program.

The disassembly data may comprise a sequence of removal operations according to which the structure is to be disassembled. In the sequence, the structure may be divided 5 into separate parts which are to be removed in sequence.

In an embodiment, the movable arm comprises several sensors 102 which are used for determining a current position of the movable arm and of the processing tool relative to the structure. These sensors may be ultrasonic sensors, video cameras and/or touch sensors which register an engagement of the movable arm with the structure.

10 Other sensors are also provided, such as a current sensor 104 for measuring the current, a weight sensor 103 for measuring the weight of the part 32 which is lifted.

Operation

With reference to figure 3, the movable arm 20 according to the invention operates 15 as follows. When a jacket 10 needs to be removed, an auxiliary vessel 110 is positioned at the water surface 111 nearby. An ROV 112 which is connected to the auxiliary vessel via an umbilical 114 is used to make a cut in the jacket 10, dividing the jacket in a bottom part 10A and a top part 10B.

Turning to figure 4, two movable arms 20A, 20B are subsequently positioned on the 20 jacket 10. The movable arms 20 are positioned on the jacket 10 from the vessel 110, for instance by lowering the movable arms 20A, 20B with a hoisting system from the vessel.

The clamps 24A, 24B are clamped onto one of the upstanding beams 2, see figure 1. The movable arms 20A, 20B may also start the operation at a position which is above the water level, however this is less preferred.

25 One movable arm 20A comprises at least a gripping tool 50, and one movable arm 20B comprises at least a cutting tool 51. In one embodiment, both arms 20A, 20B comprise both a gripping tool 50 and a cutting tool 51.

Two containers 40 are positioned at the seabed 100, within working range of the movable arms 20. The containers comprise one ore more connectors 41 for connecting a 30 cable to the container 40. The containers comprise a bottom and side walls and are open at the top, so that a part can be placed in the container with relative ease.

Turning to figure 5, a heavy lift vessel 120 is positioned at the jacket 10. The heavy lift vessel 120 comprises a crane 122 and lifts the top part 10B of the jacket 10. The bottom part 10B remains on the seabed 100.

35 With reference to figure 6, the movable arms 20A, 20B then start with the operation of cutting a part 32 from the jacket 10. The part will generally be a beam 2, 4, 6 or a part of a beam, but may also be a joint 7 or a beam in combination with a joint 7.

- 11 -

Each part 32 is gripped with a gripping tool 50. The movement of the gripping tool to the part 32 and the subsequent gripping of the part 32 by the gripping tool may be performed manually or automatically. In the case of a manual movement, an operator may be present above the water surface in the auxiliary vessel 110, and control the movement of 5 the movable arm 2 via a connection such as a cable 35.

The part 32 is firmly held by the gripping tool 50. While the part 32 is held by the gripping tool 50, the cutting tool 51 makes cuts 55 in the jacket 2 with the cutting wire 109, so that part 32 becomes separated.

If the operation is carried out with a single arm 20, the processing tool 30 comprises 10 a cutting tool 51 which is movable independently from the gripping tool 50 and which has a three-dimensional working range 52 around the gripping tool 50. Thus, while the gripping tool 50 holds the part 32, the cutting tool 51 moves to the locations where the cuts 55 need to be made and makes the cuts.

If the operation is carried out with two arms 20A, 20B as is shown in figures 5 and 15 6. the arms 20A, 20B may cooperate. One arm 20A may hold the part 32 with the gripping tool while the other arm 20B cuts the part 32

When the part 32 is disconnected from the jacket 2, the movable arm moves the part 32 away from the jacket. The movable arm moves the part 32 toward the seabed and places the part 32 in the container 40. The gripping tool 50 then releases the part 32. The 20 movable arm 20 then continues with another part 32.

When all removable parts 32 within the working range of the movable arm 20 have been removed and put in the container, the movable arm 20 may need to be repositioned to another position. It is possible that the movable arm 20 is positioned at another location at a same horizontal level. For instance, the movable arm 20 may be repositioned on a different 25 upstanding beam 2 at the same level.

In one embodiment, this repositioning operation is carried out with a crane positioned on board the working vessel 110. A cable is connected to the movable arm 20. The clamps 24A, 24B are released from the structure 10 and the movable arm may is repositioned at a new location.

30 In another embodiment, the movable arm 20 has a capability of relocating itself.

The movable arm comprises multiple clamps. Two clamps are shown, 24A, 24B, but more than two is also possible. These clamps are mounted on movable clamp arms 26. Each clamp is mounted at an end of a movable clamp arm.

In another embodiment, two movable arms 20A, 20B are provided. Both movable 35 arms 20 comprise clamps 24A, 24B via which the structure is gripped. A first movable arm can move the second movable arm by gripping the second movable arm with its gripping tool 50. The second movable arm then releases its clamps 24A, 24B from the structure. The - 12- first movable arm moves the second movable arm to another location, where the clamps of the second movable arm clamp the structure again. The operation may also be performed the other way around, i.e. the second movable arm may move the first movable am. Thus, when the movable arms are operated in tandem, the disassembly is performed relatively 5 fast, and the repositioning of the movable arms is relatively simple.

When all removable parts 32 within the working range of the movable arm have been removed, the movable arm 20 is lowered, to a new lower position. For instance, the movable arm 20 can be repositioned on the same upstanding beam 2, but at a lower position. When the movable arm is repositioned to a lower location, the working range is 10 also lowered and the jacket structure can be further disassembled.

Turning to figures 7 and 8, when a containers 40 is full, the container is lifted to the surface by a vessel 120 and transported to shore. This can be a crane vessel or any other vessel with sufficient hoisting capacity to lift the loaded containers 40. A crane vessel can also lift the containers from the seabed and load them on a transportation barge. An empty 15 container may replace the full container. When the disassembly operation is completed, all the containers 40 are lifted to the surface.

In an embodiment, the processing tool 30 comprises a hoisting device with a winch. If the jacket is very large, the movable arm may not be able to position a part of the structure on the seabed, because the arm is too short and the working range too limited. The 20 removed part may then be lowered to the seabed with the hoisting device.

In an embodiment the movable arm is equipped with tracks to allow movement around and positioning on the seabed 100.

The skilled person will understand that the present invention may also be used for assembling a structure underwater. The opposite procedure will then be followed. The parts 25 will be provided in a container at the seabed. The movable arm will be positioned at a first position near the seabed. Each time a part will be picked from the container by the movable arm and the part will be connected to the parts which are already in place. In this way, a complete jacket can be erected. When the jacket 10 becomes so tall that the movable arm 20 cannot reach the upper end, the support 22 of the movable arm is repositioned at a 30 higher position.

It will be obvious to a person skilled in the art that the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention and the scope of the claims.

Claims

A method for assembling or disassembling a structure (10) that is at least partially submerged in water, the method comprising: providing at least one movable arm (20), the movable arm comprising: at least a first segment (28A) and a second segment (28B) connected to each other via at least a first hinge (29), a support structure (22) connected to a proximal end (34) of the first segment via at least a support hinge (27, 61) wherein the support structure is constructed to be attached to the structure 10 (10) or to be placed on the sea bed (100), a processing apparatus (30) attached to a distal end (36) of the second segment, at least one actuator (33) arranged to: o move the first segment relative to support structure in a controlled manner, and to move the second segment relative to the first in a controlled manner to move the segment in order to position the processing device at a target location in a working area of the arm, a control device (56) which is adapted to control the at least one actuator and the processing device during operation, to perform a processing operation of a structure for assembling or disassembling the structure.

The method of claim 1, wherein the processing apparatus comprises: a gripping device (50) for gripping a part of the structure and / or a cutting member (51) for cutting into the structure

Method according to claims 1 or 2, wherein the processing operation comprises: 30. grasping a part of the structure with the gripping device, cutting into the structure with the cutting device (51) in such a way that said part is separated from the structure, moving the separated part away from the structure with the aid of the gripping device. - 14-

Method according to claims 1-3, comprising simultaneously gripping a part with the gripping device (50) and cutting into the structure with the cutting device (51), wherein the part falls after the part is separated from the construction is prevented. 5

A method according to any one of claims 1-4, wherein the cutting device is movable relative to the gripping device, so that it is possible that a part of the structure is held by the gripping device while the cutting device cuts at different positions that necessary to separate the part of the structure, the method comprising: 10. gripping a part of the structure to be separated from the structure with the gripping device, moving the cutting device to different locations and cutting in the structure at the different locations to separate the part from the structure, while in the meantime the grip on the part is maintained by the gripping device. 15

Method according to any of claims 1-5, comprising: providing a container (40) on the seabed in a working area of movable arm, separating part of the structure in each case, 20. placing the separated parts in the container through the at least one arm, lifting the filled container up to the water surface (111), transporting the container to a remote location by means of a vessel (120; 130).

The method of any one of claims 1 to 6, wherein the support structure comprises at least one clamp (24A, 24B), the method comprising: clamping the support structure (22) on the structure in a first position, removing at least one at least a part of the structure, and in particular as many parts as there are in the working area of the movable arm in the first position, 30. releasing the structure by the at least one clamp, moving the support structure (22) to a second position on the structure and clamping the structure in the second position, removing at least a second part of the structure, and in particular as many parts as there are in the working area of the movable arm in the second position, repeating these steps until the structure is substantially disassembled. - 15-

A method according to claim 7, comprising clamping the at least one clamp to a vertical or substantially vertical beam (2) of the structure and moving down said beam from said first position to said second position and further downward until the structure is substantially disassembled. 5

9. Method as claimed in claim 1, wherein the control device comprises: a data-processing unit which comprises a memory for storing: geometric data relating to the initial form of the structure, the disassembly data relating to the progress of the disassembly of the structure and the current shape of the structure, one or more sensors constructed to determine a current position of the arm and of the processing device relative to the structure, the method comprising: 15. loading the geometric data in memory, determining a portion to be removed from the structure and determining a target position of the processor based on the geometric data and the disassembly data, moving the processor to the target position, 20. removing a part of the structure for gripping the part, cutting the con structure until the part is separated from the structure and moving the part away from the structure, updating the disassembly data with data on the removed part, 25. repeating the steps until the structure is disassembled.

A method according to any of claims 1-9, comprising: cutting the structure at a cutting level, wherein an upper part of the structure is separated from a lower part of the structure, 30. lifting the upper part of the structure construction by means of a hoisting device on a vessel, moving the upper part from the location today, disassembling the lower part of the construction according to the method according to claim 1. 35

The method of claim 10, wherein the upper portion is removed by the vessel. - 16-

12. Method according to claim 10 or 11, wherein the upper part is removed on a floating transport bin.

A method according to any of claims 10-12, wherein the upper part is suspended from the hoisting device during the removal step.

A method according to any of claims 10-13, wherein the disassembled parts of the lower part are collected in at least one container on the seabed. 10

The method of claim 14, wherein the filled containers are removed from the sea bed by a hoisting device on a vessel.

A method according to any of claims 1-15, comprising: 15. providing a first said movable arm, providing a second said movable arm, gripping a part of the structure with the gripping device of the first movable arm cutting the structure with the cutting device of the second movable arm in such a way that said part is separated from the structure, moving the separated part away from the structure with the aid of the first movable arm.

17. Method as claimed in claim 16, comprising: 25. gripping of the first movable arm of the gripping device by the second movable arm, releasing the structure through the support construction of the first movable arm, moving the first movable arm, such that the support structure of the first movable arm is moved from a first support position to a second support position, the working area of the first movable arm being changed.

18. Movable arm (20) for disassembling or assembling a structure that extends at least partially under water, the movable arm comprising: - at least a first segment (28A) and a second segment ( 28B) connected to each other with at least a first hinge (29), a support structure (22) connected to a proximal end (34) of the first segment via at least one support hinge (27, 61), the support structure is constructed to be mounted on the structure or to be placed on the sea bed (100), a processing device (30) mounted on a distal end (36) of the second segment, at least one actuator (33) which is configured to: move the first segment relative to a support structure in a controlled manner, and to move the second segment relative to the first segment in a controlled manner in order to move the processing device at a target location in a working area of the arm, a control unit (56) adapted to control the at least one actuator and the processing device during operation.

The movable arm of claim 18, wherein the processing device comprises: 20. a gripping device (50) for gripping a part of the structure, and / or a cutting device (51) for cutting into the structure.

20. A movable arm according to claim 18 or 19, wherein the cutting device is movable relative to the gripping device, so that it is possible that a part of the structure is retained by the gripping device while the cutting device cuts the structure at different positions. required to separate the part of the structure.

21. A movable arm according to claim 18 or 20, wherein a distal end (36) of the movable arm has three degrees of freedom with respect to the support structure (22) of the movable arm so that the distal end (36) is in any position. the working area of the movable arm can be positioned, and wherein the processing device (30) is pivotable about three independent axes of rotation with respect to the distal ends, so that it becomes possible to orient the processing device in said direction in any direction.

A movable arm as claimed in any one of claims 18 to 21, wherein the cutting device is connected to the gripping device or to the movable arm via a movable cutting arm which provides the cutting device with a working area that extends around the gripper in direction . - 18-

The movable arm of any one of claims 18-22, wherein the support structure comprises a clamping device that includes clamping members that are constructed to clamp a vertical or substantially vertical beam of the structure. 5

The movable arm of any one of claims 1 to 23, wherein the support structure comprises: a first clamp (24A), a second clamp (24B) spaced from the first clamp, and - at least one support beam ( 26A, 26B) connecting the first and second clamp to each other, the first segment being connected to said support beam via at least one support hinge (27,61).

The movable arm of claim 10, wherein the control unit comprises: 15. the data processing device comprising a memory adapted to store: geometric data relating to the shape of the structure, assembly data or disassembly data relating to the individual steps for assembling or disassembling the structure, one or more sensors (102, 103, 104) constructed to determine a current position of the arm and of the processing device relative to the structure.

An assembly for disassembling a structure that extends at least partially under water, the assembly comprising: at least one movable arm according to claim 18, and at least one container for accommodating removed parts of the structure. 30