EP2770112B1 - Lifting device for offshore platforms - Google Patents

Description

The invention relates to a lifting device for an offshore platform and to methods for raising or lowering an offshore platform with the lifting device and method for raising and lowering a support leg of an offshore platform with the lifting device according to claims 1, 9, 10, 11 and 12 ,

From the US 2011/0305521 A1 is an offshore platform known that can be pulled by a barge on location. The offshore platform has four vertically movable support legs, each with a arranged at the sea bottom end foot. The support legs are moved relative to the platform by means of two pinions. Along the support legs racks are provided, in which engage the pinions. By driving the pinions, the support legs can first be placed on the seabed and the platform can be subsequently lifted out of the sea.

In the US 5,188,484 A a comparable lifting mechanism is disclosed in which an offshore platform comprises four support legs, along each of which a rack is arranged in the longitudinal direction and which is movable along the racks by means of engaging driven pinions.

In addition, jacking systems are known which allow a gradual lifting of the platform or a gradual lowering of the support legs by means of two relatively movable clamping rings.

The US 2,944,403 relates to a hydraulic jacking system with two clamping rings, each having a plurality of arranged along the clamping ring circumference clamping jaws which are pressed by means of hydraulic cylinders against the outer wall of the support leg.

The US 3,565,400 discloses a jacking system having two circumferential clamping rings divided by a longitudinally tapered contact surface which, by pulling force on the outer clamping ring member, increases the clamping force on the outer conversion of the support leg. The clamping rings are permanently closed around the support legs.

A disadvantage of the known systems is, on the one hand, that a lifting method by means of toothed racks and pinions requires relatively expensive and cost-intensive construction of the support legs, and, on the other hand, the known lifting devices by means of two clamping rings intended both for lifting and for permanently holding the platform. The clamping rings can disadvantageously not be subsequently installed around the support leg and also not subsequently removed from the support leg again. The known constructions are also usable only for limited support leg diameter.

In the GB 2 335 181 A discloses a clamping ring which can be solved by means of two actuators.

From the US 2,870,639 a clamping ring is known which has a plurality of ring elements. The ring elements are connected to each other by means of a wedge-shaped element. By moving the wedge-shaped element by means of a pressure cylinder, the circumference of the clamping ring can be changed. On the other hand arranged on two oppositely inclined surface pairs jaws, which cause in a vertical movement of the clamping ring in both directions an increase of the contact pressure against a leg wall. A disadvantage of the latter system is in particular that this can be applied only to a small span of different support leg diameter. This document is equivalent to the preamble of claim 1 and is considered to be the closest prior art.

It is therefore an object of the present invention to provide a lifting device that can be applied to support legs with a larger span of different diameters, as well as to provide a method that can also be applied to a larger span different support leg diameter.

It is an object of the invention to provide a device and method of the type mentioned, which reduce or avoid the above-mentioned disadvantages.

The object is achieved in its first aspect by an aforementioned lifting device having the features of claim 1 and in its second aspect by methods having the features of claims 11 to 14.

Preferred embodiments of the invention are subject of the dependent claims.

The lifting device according to the invention is intended for lifting and / or lowering an offshore platform along at least one support leg. Under a lifting device is here to understand both a lifting and a lowering device. For the sake of simplicity, it is only referred to as a lifting device. The platform is floating from a transport position in the water or on a barge in an operating position above the sea surface by means of at least one lifting device in an operating position raised. In the operating position, derricks, wind turbines, etc. can be placed on the platform. The lifting device is also suitable for lowering the support leg from a transport position into a contact position with the seabed having operating position.

Of course, the lifting device can also be used for lowering the platform from the operating position into the transport position and for lifting the support legs from the operating position into the transport position.

The lifting device comprises a plurality of segments connected together to form a closed clamping chain. The segments are preferably substantially identical, conveniently identical in construction. As a result, a cost-effective production of the clamping chains is possible. The clamping chain has a circumference and at least one radius, the clamping chain is in its circumference and at least one radius by the segmented design and the ability to insert additional segments and superfluous segments to remove, changeable. It is advantageously used for a wide range of support leg cross sections.

The closed clamping chain can circulate in a cross section perpendicular to a longitudinal direction of the support leg exactly circular support leg, but also an elliptical support leg and even a triangular in cross-section, square or rectangular support leg.

The segments are spaced from each other along the circumference, and they have reciprocating jaws reciprocating in the radial direction, the clamping jaws of the segments form in their interaction from a variable in size clamping cross-section. Movable back and forth in the radial direction here means that at least one movement component of the movement of movement of the clamping jaws runs in exactly the radial direction.

In a preferred embodiment of the invention, the jaws are arranged movably on the segments by means of a self-locking mechanism and they each have at least one friction-enhancing element on their radially inner side. The self-locking mechanism makes it possible for the clamping jaws to reduce the clamping cross-section by virtue of the pulling force acting on the clamping chain caused by the dead weight of the platform and thus to clamp the clamping chain to the outer transformation of the support leg by self-locking. A self-locking mechanism is on the one hand maintenance friendly and therefore inexpensive, on the other hand, the self-locking is particularly safe, because no additional hydraulic to exercise a sufficient clamping pressure or clamping force is required. Even with a sudden failure of the hydraulic clamping pressure remains.

The self-locking mechanism preferably has a mechanical stoppage. The stoppage prevents unwanted turning of the jaws and thus a sudden loss of clamping force

Conveniently, the self-locking mechanism comprises at least one arranged on inner sides of segment bodies, at least one axis pivotable arm, wherein the pivot axes are preferably tangential to the circumferential direction. The at least one arm is articulated with its radially outer end on the inside of the segment body, preferably pivotably by means of a rotary joint. Conveniently, in each case a clamping jaw is arranged on the radially inner arm end, wherein the clamping jaw in turn preferably by a Swivel joint is articulated on the radially inner end of the arm. By pivoting the at least one arm of the clamping cross section is variable.

The clamping jaws preferably have on their radial inner side preferably separate friction-enhancing elements, in particular rubber elements. The friction-enhancing elements therefore prevent the slipping of the clamping chain on the outer wall of the support leg.

For safe release of the self-locking, it is beneficial to first trigger an initial inhibition of the clamping chain on the support leg. For this purpose, according to the invention, an actuator associated with each segment is provided, which is operatively connected to the at least one arm of the segment and pivots the arm so far that the clamping jaw presses on the outer wall of the support leg while exerting an initial pressure and prevents the clamping chain from slipping off the self-inhibition can ever trigger.

The actuator may be a controllable hydraulic cylinder or a spring. In the second case, it comes in case of failure of any control yet caused by the initiation safe self-clamping in any position on the support leg.

Preferably, a centering device is present. The centering device is conveniently detachable. The centering device concentrically positions the clamping chain around the support leg during the clamping process. As a result, the clamping jaws are charged equally, and it is in particular an unintentional turning over a further away from the outer wall of the support leg jaw prevented.

The centering device may be a mechanical spacer from the clamping chain to the support leg, preferably it may be formed as a centering ring surrounding the support leg, which is connected to the clamping chain with spacers. The centering ring is also stop for the jaws.

The centering device may comprise an angle measuring device of the arms relative to the segment or a distance measuring device to the outer wall of the support leg and a control of the actuator designed as a hydraulic cylinder.

Preferably, the connection between adjacent, preferably identical segments is detachably formed. This makes it possible to open the clamping chain after the platform has reached its operating position above the sea surface, and completely removed from the support leg. The platform is permanently attached to the support leg by means of bolted connections or other suitable connections without a lifting device.

In a further preferred embodiment of the lifting device longitudinally oriented lifting cylinders are provided with a platform-side and a clamping chain-side end, and both ends have fastening means for attachment to the platform or the clamping chain. The lifting cylinders make it possible to lift the platform with the clamping chain clamped in, by simultaneously retracting all lifting cylinders of the lifting device. The same applies to the lowering of the platform.

Conveniently, the lifting device comprises a further clamping chain, which is preferably arranged along the support leg between the platform-side clamping chain and the platform. The platform-side further clamping chain is arranged in a relatively fixed position to the platform during the lifting operation. The lifting device operates by successively clamping and releasing the two clamping chains, so that the support legs can be lowered in a Jacking- process until they have contact with the seabed and the platform can be lifted out of the water in a jacking process

The further clamping chain and the clamping chain are identical, in particular, the further clamping chain further actuators, which trigger an initial inhibition.

With regard to the second aspect of the invention, the object is achieved by a method for lifting as well as by a method for lowering an offshore platform, which are carried out with at least one of the abovementioned lifting devices.

The method for lifting the platform runs by the clamping chain is released in a first position on the support leg, preferably by extending the lifting cylinder and the clamping chain is initially inhibited at a second farther from the platform second position on the support leg, preferably by actuating the actuators. Subsequently, the further clamping chain is released in a third position along the support leg, and by releasing the further clamping chain in the second position, the initially inhibited clamping chain is clamped in the second position by self-locking. The lifting cylinders are retracted and the further clamping chain is initially inhibited in a fourth position on the outer wall of the support leg. Thereafter, the clamping chain is released in the second position and thereby clamped the initially inhibited further clamping chain in the fourth position by self-locking. The process then repeats itself from the first step and is carried out until the platform has reached the operating altitude above the seabed.

Preferably, the at least one support leg is initially placed vertically after transport to location. The platform may have a plurality of support legs, preferably three, but also four, six or eight support legs.

The offshore platform is brought to location by means of a barge or self-floating and the support legs lowered to location by means of the described lifting device until feet of the support legs make contact with the seabed. Thereafter, the lifting device is operated further and thus lifted the platform out of the water. The platform is raised above the surface of the water so that it is no longer exposed to waves in its operating position.

The method for lowering the platform by means of at least one lifting device runs according to and according to the features of claim 12.

Both in the method for lifting and for lowering the platform, the self-locking mechanism is designed so that it triggers by a force acting on the clamping chain to the seabed facing force, preferably the arms are inclined thereto from radially outward radially inward to the platform or the seabed ,

The invention also relates to a method for lowering and a method for lifting the support leg from the transport position to the operating position or vice versa, by first the self-locking mechanism of the clamping chain and the other clamping chain relative to the method for raising or lowering the platform is handled, so a force acting on the support leg and pointing to the seabed triggers the self-locking mechanism. For this purpose, in particular, the jaws are handled. The arms then extend from radially outward to radially inward inclined away from the platform.

The self-locking mechanism is different umschlagbar depending on the design of the clamping chains and the centering device. It can be handled by opening the clamping chain, turning over the clamping jaws and then closing the clamping chain. However, it is also conceivable to disengage the centering mechanism and to move the clamping chain relative to the support leg and then turn over the clamping jaws more distant from the support leg, the clamping chain in an eccentric movement to guide the support leg and successively turn over each of the most distant from the support leg jaws.

A method for lifting the support leg according to the features of claim 13, a method for lowering the support leg with the features of claim 14th

Fig. 1

eine perspektivische Ansicht einer plattformabseitigen Klemmkette einer erfindungsgemäßen Hebeeinrichtung,

Fig. 2

eine Seitenansicht der Hebeeinrichtung in Fig.1,

Fig. 3

eine Draufsicht der Hebeeinrichtung in Fig. 1.,

Fig. 4

eine perspektivische Innenansicht eines Segmentes der Klemmkette in Fig. 1

Fig. 5

eine perspektivische Außenansicht des Segmentes in Fig. 4.

The invention will be described with reference to an embodiment in five figures. Showing:

Fig. 1

a perspective view of a platform-side clamping chain of a lifting device according to the invention,

Fig. 2

a side view of the lifting device in Fig.1 .

Fig. 3

a top view of the lifting device in Fig. 1 .,

Fig. 4

an interior perspective view of a segment of the clamping chain in Fig. 1

Fig. 5

an external perspective view of the segment in Fig. 4 ,

Offshore platforms are self-swimming with support legs 2 or floating on a barge in the sea on location spent. There, the raised during transport support legs 2 are lowered to the seabed and the platform then lifted out of the sea or from the barge and permanently locked in an operating position.

In the figures, a part of a lifting device 1 is shown, which serves on the one hand to lower one of the support legs 2 of the offshore platform from the raised state for transport state until it has contact with a seabed. Each of the support legs is associated with the identical lifting device 1. On the other hand, the platform can then be lifted further out of the sea into the operating position with the simultaneous use of all lifting devices 1. There it is located at a distance from sea level and above sea level. In the operating position, the platform without the lifting device 1 can be locked.

Fig. 1 shows a portion of the support leg 2 of the platform (not shown). The platform would be at the bottom of the picture Fig. 1 arranged. Through the platform are in this embodiment, four perpendicular to the plane of the platform in a longitudinal direction L movable support legs 2 passed. Of course, it is also conceivable to provide platforms with three, six, eight or a different number of support legs 2.

The platform of the illustrated embodiment is buoyant together with the four retracted support legs 2. It can therefore be pulled by a ship offshore on location, the support legs 2 are raised during transport.

The support legs 2 of the platform moved to location are identified by means of an in Fig. 1 shown platform-side clamping chain 3 is first lowered until at the sea bottom side end of the support legs 2 arranged (not shown) support feet have contact with the seabed. In the seabed, the support feet can be anchored in various ways, for example, with suction devices such as suction or by or through elephant feet. The easiest way is to press a seabed-side closed tubular support leg 2 into the seabed.

After the support legs 2 are anchored on their support feet in the seabed, the platform is lifted out of the water by means of the lifting devices 1 and vertically along the longitudinal direction L of the support legs 2 until the operating height is reached, in which the platform is no longer the wave is exposed.

The complete lifting device 1 comprises the platform-side clamping chain 3 and a structurally identical platform-side clamping chain according to FIG Fig. 1 , which are arranged one above the other along the longitudinal direction L of the support leg 2 and respectively circulate the support leg 2 concentrically. In the Fig. 1 shown further spaced from the platform clamping chain 3 is hereinafter referred to as platform off-side clamping chain 3. The more tightly mounted on the platform clamping chain is hereinafter referred to as a platform-side clamping chain. The components assigned to the platform-side or platform-side clamping chain are accordingly referred to as platform-side or platform-side.

The platform-side clamping chain 3 comprises eight segments 6. One of the segments 6 is in Fig. 1 hidden by the support leg 2. Each segment 6 has two longitudinally L mounted on one another segment body 7, 8. A platform-side segment body 7 and a platform-side segment body 8 are connected to one another via a connecting flange screwed. From each of the platform-side segment body 8 is a longitudinally extending lifting cylinder 9 from the platform down.

The platform-side clamping chain 3 has a diameter substantially constant along the circumference, and it orbits the support leg 2 substantially concentrically.

The lifting cylinder 9 has a chain-side end and a platform-side end, which are each articulated via a bolt connection to one of the platform-side segment body 8 of the platform-side clamping chain 3 or on the platform. The clamping-chain-side lifting cylinder end has a clamping chain-side tab 11 that protrudes in the longitudinal direction L and that engages in a fork 13 projecting from the platform-side segment body 8 and is articulated by means of a bolt arranged in the circumferential direction of the platform-side clamping chain 3. A protruding from the platform-side lifting cylinder end in the longitudinal direction L tab 12 engages in a corresponding, with the sea side platform side firmly connected (not shown) fork.

The complete lifting device 1 additionally has, for each of the support legs 2, the platform-side clamping chain (not shown) which, in contrast to the platform-side clamping chain 3, is connected directly to the platform via bolt connections. There are no lifting cylinders between the platform-side clamping chain and the platform provided.

The individual segments 6 are aligned in the longitudinal direction L and arranged equidistant from each other along the circumference of the support leg 2. The segments 6 are connected to each other on both sides with adjacent segments 6 via two groups of four connecting lugs 16, 17. The platform-side group of connection tabs 16 is laterally connected to platform-side segment bodies 7 and the platform-side group of connection tabs 17 is laterally hingedly connected to platform-side segment bodies 8 via a bolt connection with longitudinal bolt L extending longitudinally.

Each of the segments 6 comprises two clamping jaws 18, 19 which are provided one above the other in the longitudinal direction L and which are arranged on radially inner sides of the platform-side or platform-side segment body 7, 8 via a respective arm 21, 22 which is inclined in the radial direction. Each of the two arms 21, 22 of a segment 6 is connected via a rotary joint to the radial inner side of a platform-side or platform-side segment body 7, 8 and via a further rotary joint hingedly connected to a radial outer side of the platform-side or platform-side clamping jaws 18, 19. The hinges of both arms 21, 22 are each rotatable about an axis extending tangentially to the circumferential direction.

Fig. 2 shows the arrangement of Fig. 1 in a side view. The same reference numerals as in the other figures denote the same components as in the Fig. 1 , Each segment 6 has in the longitudinal direction L superimposed platform-side and platform-side segment body 7, 8, which are in the circumferential direction on both sides with four connecting straps 16, 17 with an adjacent segment body 7, 8 in articulation. The two segment body 7, 8 and the respective segment 6 associated lifting cylinder 9 are arranged exactly in the longitudinal direction L one above the other. A stroke direction of the lifting cylinder 9 runs parallel to the longitudinal direction L.

Fig. 3 shows a plan view of the platform-side clamping chain 3 in Fig. 1 and Fig. 2 , The platform-side jaws 18 and the platform-side clamping jaws 19, not shown, of the platform-side clamping chain 3, are in contact with an outer wall of the circular cross-section support leg 2. The jaws 18, 19, which are dimensioned in their entirety, the entire platform weight distributed on four support legs 2 and four lifting devices 1, each exert a clamping force on the outer wall of the support leg 2. After the platform is lifted out of the water and has reached its operating position by means of the lifting devices 1, the platform is permanently locked by means not shown holding means to the support legs 2. The platform-side clamping chains 3 of the lifting devices 1 are then released at bolt connections of certain platform-side and platform-side tabs 16, 17 on one of the segments 6 and completely removed. The same applies to the platform-side clamping chains.

Fig. 4 shows one of the six segments in a view obliquely radially from inside to outside. In Fig. 4 the operation of a self-locking mechanism is recognizable.

The self-locking mechanism is doubled here per segment 6. The required number of clamping jaws 18, 19 depends on the coefficient of friction and the permissible surface pressure of the friction-enhancing material on the outer wall of the support leg 2. A platform-side part of the self-locking mechanism includes the inclined platform-side arm 21 which is rotatably supported on the platform-side segment body 7 around the rotation axis extending in the circumferential direction of the platform-side clamping chain 3. The platform-side clamping jaw 18 is another one in Circumferentially guided circumferential direction of the further clamping chain 3 extending axis of rotation on platform off-side arm 21.

For a platform-side part of the self-locking mechanism of the segment 6 applies the same, it comprises the tilted in a foot angle platform side arm 22, in turn via a bolt connection with the platform-side jaw 19 of the same segment 6 about a parallel to the other axis of rotation of the first part of the self-locking mechanism hinged in Connection and which is articulated on the platform-side segment body 8 about a parallel to the axis of the first part of the self-locking mechanism. Inner sides of the clamping jaws 18, 19 overlie a clamping cross-section. The size of the clamping cross section varies with the size of the adjusting angle of the arms 21, 22nd

Since the platform-side arms 21 and the platform-side arms 22 are arranged to slope down parallel to each other and radially inward towards the platform, a movement of the lifting device 1 in FIG Fig. 1 from top to bottom by a force acting on the lifting cylinder weight self-locking of the clamping chain 3 on the support leg 2, because the clamping cross-section decreases.

Furthermore, the self-locking mechanism is coupled with an initial locking mechanism. The latter comprises a platform-side lever 40 and a platform-side actuator 41 acting on it.

The platform-side lever 40, which is guided on the platform-side segment body 7, is connected to the platform-side arm 21 radially on the inside and to the platform-side actuator 41 radially on the outside. The platform-side actuator 41 drives the platform-side lever 40 and pivots over the platform-side lever 40, the platform-side arm 21. The platform-side and the platform-side arm 21, 22 are connected to each other via a bolt connection. The platform-side actuator 41 can thus pivot both clamping jaws 18, 19 of the segment 6 together in a circular motion simultaneously in the radial direction and in the longitudinal direction L.

Due to the radial component of the circular movement of the clamping jaws 18, 19, opposite clamping jaws 18, 19 of the clamping chain 3 move slightly toward one another and thus reduce the clamping cross section between the clamping jaws 18, 19 and allow an initial clamping of the clamping chain 3 on the outer wall of the supporting leg 2.

The force acting on the support leg 2 of the initial inhibition is lower than that of the self-locking. The platform-side actuators 41 serve to exert an initial pressure on the outer wall of the support leg 2, which presses the jaws 18, 19 so strong on the outer wall that slipping of the clamping chain 3 is prevented in the construction of the self-locking. For this, at least the gravity of the jaw n 18, 19 must be overcome.

Fig. 5 shows segment 6 in FIG Fig. 4 in a view from radially outside to radially inside. The platform-side actuator 41 is formed as a hydraulic differential cylinder. The stroke of the cylinder is 200 mm, the capacity between 50 - 100 kN. The hydraulic cylinders 9 have a capacity of 1,000 kN and a stroke of 1,500 mm. Segment 6 weighs about 2.5 t. These are only exemplary values.

In principle, each of the clamping chains 3 can be expanded by inserting further segment bodies 7, 8 with associated arm 21, 22 and associated clamping jaw 18, 19 in the longitudinal direction L around a further part of a self-locking mechanism.

Fig. 4 shows the radial inner side of the two jaws 18, 19, each with six arranged on the inside rubber pads 50 with a support surface of 110 x 250 mm, which are arranged in two aligned in the longitudinal direction L three-arrays, the two sets of three separated from each other by a guide rail 51 are.

The subsequent position indications refer to a position along the lengthwise direction of the support leg, with a third position closest to the platform, a fourth position closest second, a first position farthest second, and a second position farthest from the platform is.

After the four support legs 2 are placed on the seabed, the lifting method for lifting the platform out of the water basically in the following successive steps: The platform downstream clamp chain 3 is initially in a first position along the support leg 2. The platform-side clamping chain 3 is released and the hydraulic cylinders 9 of the platform-side clamping chain 3 are extended and then the platform-side actuators 41 of the platform-side clamping chain 3 retracted and thus the clamping cross-section between the clamping jaws 18, 19 is reduced until an initial inhibition of the jaws 18, 19 on the outer wall of the support leg 2 occurs. The initial inhibition prevents slipping of the jaws 18, 19 along the outer wall of the support leg 2 in the next step. After the establishment of the initial inhibition, the lifting cylinder 9 are retracted again, thereby the platform-side clamping chain 3 is increasingly burdened with the load of the platform and built the self-locking platform-side clamping chain 3 and the platform-side clamping chain dissolves. By extending the platform-side actuators, the jaws of the platform-side clamping chain are completely detached from the outer wall of the support leg 2 in a third position. The platform-side clamping chain 3 is now clamped in a second position. The lifting cylinders 9 are retracted and the platform raised by the stroke of the lifting cylinder 9. Then, the platform-side clamping ring is initially inhibited on the outer wall of the support leg 2 in a fourth position. After the platform-side clamping ring is initially inhibited, the platform-side actuators 41 are actuated and the self-locking of the platform-side clamping chain 3 is released. As the self-locking of the platform-side clamping chain is released, the self-locking of the platform-side clamping chain builds up in the fourth position. As a result, the overlying load is displaced from the platform-side clamping chain 3 to the platform-side clamping chain. The platform-side clamping chain 3, after the load is completely on the platform-side clamping chain, be released from the support leg 2. The lifting cylinders 9 are then extended again, and the platform-side clamping chain 3 is again clamped in the extended state of the lifting cylinder 9, in turn, by means of initial inhibition and subsequent self-locking on the outer wall of the support leg 2. Thereafter, the platform-side clamping chain is released again by the platform-side actuators are extended. To the extent that the self-locking of the platform-side clamping chain is released, the self-locking of the platform-side clamping chain 3 builds up until the full load is again on the platform offset side chain 3. The process is repeated until the platform has reached its operating altitude above sea level. Throughout the lifting process, the platform-side clamping chain 3 and the platform-side clamping chain are concentrically positioned around the support leg 2 by means of a centering device (not shown).

In the operating position, the platform is permanently locked to the support legs 2, preferably by means of bolt connections. The lifting device 1 can be completely opened in the operating state of the platform by releasing the connecting straps 16, 17 and completely removed from the support leg 2. The lifting device 1 is only again required, for example, when the platform must be lowered for disassembly. The procedure for lowering the platform runs accordingly.

LIST OF REFERENCE NUMBERS

1

lifter

2

outrigger

3

Platform-side clamping chain

6

segments

7

platform-side segment body

8th

Platform-side segment body

9

lifting cylinder

11

clamp chain side tab

12

platform-side tab

13

fork

16

Platform-side connection tabs

17

platform-side connecting straps

18

Platform-side jaw

19

platform-side jaw

21

platform-side arm

22

platform-side arm

40

platform-side lever

41

platform-side actuator

50

rubber Reinforcement

51

guide rail

L

longitudinal direction

Claims (13)

1. Lifting device for lifting an offshore platform along at least one support leg (2) with a plurality of segments (6) connected to one another to form a closed clamping chain (3), wherein the clamping chain (3) has a circumference and at least one radius,
   clamping jaws (18, 19) projecting from the segments being arranged at a distance from one another along the circumference and being able to move back and forth in the radial direction, which clamping jaws (18, 19) together form a clamping cross-section of variable size, wherein the clamping jaws (18, 19) are arranged in a movable manner on the segments (6) by means of a self-locking mechanism and the clamping jaws (18, 19) have at least one friction-increasing element (50) on their inner side,
   characterized by arms (21, 22) which are arranged on the segment inner sides and which are in each case pivotable about an outer axis running in the circumferential direction, on the inner arm ends of which arms there is arranged in each case one of the clamping jaws (18, 19), wherein the clamping cross-section can be varied by pivoting the arms (21, 22).
2. Lifting device according to claim 1, characterized by a centring device of the clamping chain (3) relative to the support leg (2).
3. Lifting device according to at least one of claims 1 to 2, characterized by an actuator (41) which is assigned to one segment (6) in each case and which is operatively connected to the respective arm (21, 22) of the segment (6) and can pivot the arm (21, 22) in order to trigger, in the state of use, an initial locking of the clamping chain (3) on the support leg (2).
4. Lifting device according to at least one of claims 1 to 3, characterized in that at least one further segment (6) can be inserted in an articulated manner between two separate segments (6) in order to enlarge the clamping cross-section.
5. Lifting device according to at least one of claims 1 to 4, characterized in that different segments (6) of the clamping chain (3) are structurally identical.
6. Lifting device according to at least one of the preceding claims, characterized by lifting cylinders (9) which act in the longitudinal direction (L) and are arranged on a platform side of each of the segments, the platform-side end of which lifting cylinders has a fastening means for fastening to the platform.
7. Lifting device according to at least one of the preceding claims, characterized by a further clamping chain which in the installed state is arranged along the at least one support leg (2) between the clamping chain (3) and the platform and which is arranged in a fixed position relative to the platform during the lifting process.
8. Lifting device according to claim 7, characterized by a control means for the lifting cylinders (9) and the actuators (41) as well as further actuators assigned to further segments of the further clamping chain.
9. Method for lifting an offshore platform with a lifting device (1) according to at least one of claims 1 to 8,
   wherein the offshore platform has at least one support leg (2),
   in that a clamping chain (3) in a first position on the at least one support leg (2) is released, lifting cylinders (9) are extended and the clamping chain (3) is initially locked on the at least one support leg (2) at a second position which is further away from the platform than the first position,
   a further clamping chain in a third position along the at least one support leg (2) is released and, as a result, the clamping chain (3) is securely clamped in the second position by self-locking,
   the lifting cylinders (9) are retracted,
   the further clamping chain is initially locked in a fourth position which is further away from the platform than the third position,
   the clamping chain (3) in the second position is released and, as a result, the further clamping chain is securely clamped in the fourth position by self-locking.
10. Method for lowering an offshore platform with a lifting device (1) according to at least one of claims 1 to 8,
    wherein the offshore platform has at least one support leg (2),
    in that a clamping chain (3) in a second position on the at least one support leg (2) is released,
    lifting cylinders (9) are retracted and the clamping chain (3) is initially locked on the at least one support leg (2) at a first position which is closer to the platform than the second position, a further clamping chain in a fourth position along the at least one support leg (2) is released and, as a result, the clamping chain (3) is securely clamped in the first position by self-locking,
    the lifting cylinders (9) are extended,
    the further clamping chain is initially locked in a third position which is closer to the platform than the fourth position,
    the clamping chain (3) in the first position is released and, as a result, the further clamping chain is securely clamped in the third position by self-locking.
11. Method for lifting a support leg (2) with a lifting device (1) according to at least one of claims 1 to 8,
    in that the self-locking mechanism is tripped,
    a clamping chain (3) in a second position on a support leg (2) is released,
    lifting cylinders (9) are retracted and the clamping chain (3) is initially locked on the support leg (2) at a first position which is closer to the platform than the second position,
    a further clamping chain in a fourth position along the support leg (2) is released and, as a result, the clamping chain (3) is securely clamped in the first position by self-locking,
    the lifting cylinders (9) are extended,
    the further clamping chain is initially locked in a third position which is closer to the platform than the fourth position,
    the clamping chain (3) in the first position is released and, as a result, the further clamping chain is securely clamped in the third position by self-locking.
12. Method for lowering a support leg (2) with a lifting device (1) according to at least one of claims 1 to 8,
    in that the self-locking mechanism is tripped,
    in that a clamping chain (3) in a first position on a support leg (2) is released,
    lifting cylinders (9) are extended and the clamping chain (3) is initially locked on the support leg (2) at a second position which is further away from the platform than the first position,
    a further clamping chain in a third position along the support leg (2) is released and, as a result, the clamping chain (3) is securely clamped in the second position by self-locking,
    the lifting cylinders (9) are retracted,
    the further clamping chain is initially locked in a fourth position which is further away from the platform than the third position,
    the clamping chain (3) in the second position is released and, as a result, the further clamping chain is securely clamped in the fourth position by self-locking.
13. Method according to any of claims 9 to 12, characterized in that the clamping chain (3) or further clamping chain is initially clamped or released respectively by clamping jaws (18) or further clamping jaws (19) initially being pressed or released respectively by means of actuators (41) or by means of further actuators on the outer wall of the support legs (2).

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