Jacking system and method for relative movement of a leg with respect to a platform

Abstract

 The invention relates to a jacking system (1) for a jacking platform (2), having a number of supporting legs (4), for relative movement of one of the legs (4) with respect to the platform (2), comprising a number of cross heads (7, 11). Each cross head (7, 11) is independently movable in longitudinal direction of the leg by means of at least one actuator (8, 12). Each cross head (7, 11) is provided with a leg engaging mechanism that is arranged to engage respectively disengage with the leg (4). A processor is arranged to control the cross heads (7, 11) such that the relative movement of the leg (4) is performed alternately by the cross heads (7, 11). The jacking system (1) according to the invention comprises two cross heads (7, 11) that are positioned opposite one another such that one cross head can be operated in pulling mode and the other cross head can be operated in pushing mode.
The invention also relates to a method for relative movement of a leg (4) with respect to a platform (2) using a jacking system (1) according to the invention.

Description

[0001] The present invention generally relates to a jacking system and a method for relative movement of a leg with respect to a platform.

[0002] Jacking systems are well known in the art and are used for raising and lowering supporting legs of a jacking platform, i.e. a type of mobile platform that is able to stand still on the (sea) floor resting on its supporting legs. Jacking platforms are specifically useful as a base for servicing other water structures, such as offshore wind turbines, long bridges and drilling platforms. The jacking platform can either be self propelled or towed to the structure to be serviced. Upon arrival at the location of the structure, the jacking system is used to jack down the legs onto the (sea) floor. Then "preloading" takes place, where the weight of the platform and additional ballast water are used to drive the legs securely into the (sea) bed so they will not penetrate further while operations are carried out. After preloading the jacking system can be used to raise the entire platform above the water level to a predetermined height or "air gap" so that wave, tidal and current loading acts only on the relatively slender legs and not on the hull. Once the services on the structure have been performed and the jacking platform is no longer needed, the jacking system pulls the legs out of the (sea) floor into a transport position. The jacking platform is then ready to be transported to another location.

[0003] It is noted that applicant already produces jacking systems for raising and lowering supporting legs of a main platform, such as a jack-up rig or a pontoon like structure, in which a fixed cross head is situated on deck of the platform and a travelling cross head is situated above or below the fixed cross head.

[0004] The present invention specifically relates to a jacking system for a jacking platform, having a number of supporting legs, for relative movement of one of the legs with respect to the platform, comprising a number of cross heads, wherein each cross head is independently movable in longitudinal direction of the leg by means of at least one actuator and wherein each cross head is provided with a leg engaging mechanism that is arranged to engage respectively disengage with the leg, and a processor arranged to control the cross heads such that the relative movement of the leg is performed alternately by the cross heads.

[0005] Such a jacking system is known from European patent application EP2221417. The known jacking system comprises three yokes that are operated in alternating mode, such that two yokes carry the load of the platform or the leg, while one yoke returns to its starting position.

[0006] The present invention has for its object to provide an improved jacking system in terms of load distribution and safety.

[0007] The jacking system according to the present invention is characterized in that the jacking system comprises two cross heads that are positioned opposite one another such that one cross head can be operated in pulling mode and the other cross head can be operated in pushing mode.

[0008] In the jacking system according to the invention the two cross heads are able to operate alternately in pulling mode and pushing mode, both in jacking the legs down onto the (sea) floor as well as in jacking the legs up out of the (sea) floor. This is an advantage since the actuators, for instance hydraulic cylinders, are able to provide more force in pushing mode than in pulling mode under the same conditions. The use of two crossheads or yokes doubles the jacking speed when compared to jacking systems having only one crosshead and allows the jacking system according to the invention to operate at a jacking speed that is comparable to the jacking speed of the known jacking system.

[0009] In a first preferred embodiment the processor is arranged to control the cross heads such that when one of the cross heads is operative in pulling mode or pushing mode, the other cross head returns to its starting position. Precious time can be saved due to the simultaneous operation of the two crossheads in working mode respectively non-working mode.

[0010] According to a further preferred embodiment the processor is arranged to control the cross heads such that the cross heads can assume a takeover position in which both leg engaging mechanisms engage with the leg. In this further preferred embodiment a stable takeover position is guaranteed.

[0011] According to a strong embodiment each crosshead essentially runs along the entire circumference of the leg to provide an optimal load distribution.

[0012] According to a practical embodiment each crosshead comprises three or more actuators, preferably six actuators. According to a further practical embodiment the leg engaging mechanism comprises at least two movable locking pins to be received in the holes of the leg. Suitable pin and hole leg engaging mechanisms are known per se in the art.

[0013] The invention also relates to a jacking system for relative movement of a leg with respect to a platform, comprising a number of cross heads, wherein each cross head is independently movable in longitudinal direction of the leg by means of at least one hydraulic cylinder and wherein each cross head is provided with a leg engaging mechanism that is arranged to engage respectively disengage with the leg, and a processor arranged to control the cross heads, characterized in that, the at least one hydraulic cylinder of each cross head is connected to a fluid reservoir such that a predetermined amount of hydraulic fluid can flow to the reservoir in the engaged position of the cross head to provide a damping effect when the leg touches the seabed.

[0014] According to the invention the jacking system provides a damping effect when one of the legs of the jacking platform absorbs a shock, for instance when the leg hits the (sea) floor in a critical touchdown. All known jacking systems using hydraulic cylinders can profit from such a damping system. Only in a preferred embodiment the jacking system is the jacking system as described above.

[0015] The present invention further relates to a method for relative movement of a leg with respect to a jacking platform comprising the steps of:

a) Providing a jacking system according to the present invention on a jacking platform having a plurality of legs;

b) Controlling one cross head to engage on one of the legs and to operate in pulling mode or pushing mode;

c) Simultaneously with step b) controlling the other cross head to return to its starting position;

d) Subsequently controlling the cross heads to assume a takeover position in which both leg engaging mechanisms engage with the leg;

e) Controlling the other cross head to engage on the leg and to operate in opposite pushing mode or pulling mode;

f) Simultaneously with step e) controlling the one cross head to disengage from the leg to return to its starting position;

g) Repeat steps b) through f) until the desired relative position of the leg with respect to the platform is reached.

[0016] The invention will now be described in more detail with reference to the drawings, in which:

Figure 1 shows a preferred embodiment of a jacking system according to the invention in a first position;

Figure 2 shows the jacking system according to the invention in a second position;

Figure 3 shows the jacking system according to the invention in a third position;

Figure 4 shows the jacking system according to the invention in a fourth position;

Figures 5A and 5B show part of the jacking system according to the preferred embodiment in cross section in different positions;

Figures 6A and 6B show another part of the jacking system according to figures 1-4 in cross section in different positions;

Figure 7 shows the jacking system according to the invention provided with a first damping system and;

Figure 8 shows the jacking according to the invention provided with a second damping system.

[0017] Figure 1 shows a jacking system 1 for a jacking platform 2, such as a jack-up mono hull, having a jacking tower 3 attached to the platform 2 in which a supporting leg 4 is movable.

[0018] Each leg 4 is provided with a number of leg engaging holes 21 that are arranged to receive a locking pin or locking shaft, like locking pins 10 respectively 14 present on crosshead 7 respectively 11 as will be described herein below.

[0019] According to the invention the jacking system 1 further comprises two travelling crossheads 7, 11 that are each movable with respect to the jacking tower 3 in longitudinal direction of the leg 4 by means of jacking cylinders 8 respectively 12. Travelling crosshead 7 is denoted herein as upper crosshead 7 whereas travelling crosshead 11 is denoted herein as lower crosshead 11.

[0020] According to the invention the jacking system 1 further comprises a processor (not shown) arranged to control the cross heads 7, 11 such that the relative movement of the leg 4 is performed alternately by the cross heads 7, 11.

[0021] Each cross head 7, 11 is provided with a leg engaging mechanism that is arranged to engage respectively disengage with the leg 4. The engaged, respectively disengaged positions of the crossheads are shown in figures 5A, 5B, 6A and 6B. In figures 5A, 5B a preferred embodiment of upper crosshead 7 is shown. In figures 6A and 6B a preferred embodiment of lower crosshead 11 is shown in cross section.

[0022] In figure 5A locking pins 10 are disengaged from holes 21 of leg 4. In this disengaged position the travelling upper crosshead 7 is freely movable with respect to leg 4.

[0023] In figure 5B the locking pins 10A, 10B and 10C are each actuated by the associated actuator 9A, 9B and 9C towards the engaged position in which the upper cross head 7 is fixed to leg 4. In the engaged position the upper cross head 7 is bearing the load of the leg 4 or of (part of) the platform 2.

[0024] In figure 6A locking pins 14 are disengaged from holes 21 of leg 4. In this disengaged position the travelling lower crosshead 7 is freely movable with respect to leg 4.

[0025] In figure 6B the locking pins 14A, 14B and 14C are each actuated by the associated actuator 13A, 13B and 13C towards the engaged position in which the lower cross head 11 is fixed to leg 4. In the engaged position the lower cross head 11 is bearing the load of the leg 4 or of (part of) the platform 2.

[0026] Preferably crossheads 7 and 11 are identical. In the preferred embodiment crosshead 7, 11 is provided with three locking pins 10A, 10B, 10C respectively 14A, 14B, 14C. Each locking pin is driven by an actuator 9A, 9B, 9C respectively 13A, 13B, 13C.

[0027] In the preferred embodiment the shape of crosshead 7, 11 is generally hexagonal. It is noted that the shape is adaptable to the shape of the jacking tower 3 and/or the leg 4 and can be any other geometrical shape, f.i. a circular or rectangular shape.

[0028] Jacking tower 3 is further provided with a fixed crosshead 5 having locking pins 6 that can be received by leg engaging holes 21 for fixing the leg 4 to the tower 3.

[0029] Referring to figures 1 through 4 showing the jacking system according to the invention in four different positions the movement of the leg 4 relative to the platform 2 is described. The described and shown movement relates to a downward movement of the leg 4 relative to the platform 2, f.i. when the leg 4 is jacked down onto the seabed. This movement corresponds to an upward movement of the platform 2 relative to the leg 4, f.i. when the platform 2 is climbing up the leg 4 to rise above sea level.

[0030] The method according to the invention comprises the following steps

a) Controlling one cross head 7, 11 to engage on one of the legs 4 and to operate in pulling mode or pushing mode;

b) Simultaneously with step b) controlling the other cross head 7, 11 to return to its starting position;

c) Subsequently controlling the cross heads 7, 11 to assume a takeover position in which both leg engaging mechanisms engage with the leg 4;

d) Controlling the other cross head 7, 11 to engage on the leg 4 and to operate in opposite pushing mode or pulling mode;

e) Simultaneously with step d) controlling the one cross head 7, 11 to disengage on the leg 4 to return to its starting position;

f) Repeat steps a) through e) until the desired relative position of the leg 4 with respect to the platform 2 is reached.

[0031] The four positions corresponding to these method steps are shown in figures 1-4.

[0032] In figure 1 cross head 7 operates in pushing mode whereas cross head 11 operates in pulling mode. Cross head 7 is in its starting position wherein upper crosshead locking pins 10 engage into holes 21, whereas cross head 11 is in the end position wherein lower crosshead locking pins 14 disengage from holes 21.

[0033] In figure 2 the jacking cylinders 8 move to perform a working stroke in the direction of the downward arrows to push leg 4 downwards. Simultaneously jacking cylinders 12 perform a non-working stroke (return stroke) in the direction of the upwards arrows to allow the lower cross head 11 to return to its starting position.

[0034] In figure 3 the jacking system takes up its takeover position. In this takeover position both locking pins 10 and 14 engage into holes 21 of leg 4.

[0035] In figure 4 upper crosshead locking pins 10 disengage from holes 21. Next jacking cylinders 12 are actuated to perform a working stroke in the direction of the downward arrows. During the working stroke the jacking cylinders 12 pull leg 4 downwards. Simultaneously the jacking cylinders 8 perform a non-working or return stroke in the direction of the upper arrows. The upper cross head 7 returns to its starting position.

[0036] The jacking system 1 then returns to the first position shown in figure 1. The jacking system next assumes a takeover position in which all locking pins 10 and 14 engage into holes 21.

[0037] The jacking system 1 repeats the sequence shown in figures 1 through 4 until the legs 4 are jacked down onto the seabed and/or the platform 2 has reached a safe position above sea level.

[0038] Each crosshead 7, 11 is provided with a leg guide support 19 for guiding the leg 4. The leg guide support has a shape corresponding to the shape of leg 4.

[0039] Inside tower 3 a leg guide support 20 is present for guiding the leg 4. The jacking tower 3 is further provided with a guide frame 17 for guiding the upper crosshead 7 and a guide frame 18 for guiding the lower crosshead 11. In the preferred embodiment shown three guide frames are present. The number of guide frames can however differ depending on the circumstances.

[0040] Figures 7 and 8 relate to a damping safety system that is suitable for any jacking system. In figures 7 and 8 the preferred embodiment of the jacking system 1 according to the invention is provided with such a damping safety system. The damping safety system according to the invention comprises a hydraulic fluid reservoir or accumulator 15 that is coupled to upper crosshead 7, more specifically coupled to jacking cylinders 8 of upper crosshead 7. The damping safety system is arranged such that when a hydraulic pressure in the jacking cylinders reaches a predetermined threshold value, hydraulic fluid is allowed to flow into reservoir or accumulator 15. This allows the jacking cylinders to move over a certain distance denoted as X. The jacking cylinders are then able to absorb a shock that may occur when the leg 4 touches the seabed in a critical touchdown. Preferably each travelling crosshead is provided with its own hydraulic fluid reservoir or accumulator. In figure 8 therefore lower crosshead 11, more specially jacking cylinders 12 of lower crosshead 11 are hydraulically coupled to a hydraulic fluid reservoir or accumulator 16.

[0041] It is noted that either one larger accumulator may be used per cross head or one smaller accumulator may be used per cylinder. Suitable accumulators are available on the market. However in applicants view the use of such accumulators for providing a damping safety system relating to jacking cylinders forming part of a jacking system is novel in the art and solves the problem of absorbing the shock related to a critical touchdown of one of the legs of a jacking platform. The damping safety system according to the invention will attribute to a longer lifecycle of vital components of each jacking system known in the art.

[0042] The invention is of course not limited to the described and shown preferred embodiment. The invention relates generally to any embodiment falling within the scope of protection as defined in the claims and as seen in the light of the foregoing description and accompanying drawings.

Claims

1. Jacking system (1) for a jacking platform (2), having a number of supporting legs (4), for relative movement of one of the legs (4) with respect to the platform (2), comprising a number of cross heads (7, 11), wherein each cross head (7, 11) is independently movable in longitudinal direction of the leg by means of at least one actuator (8, 12) and wherein each cross head (7, 11) is provided with a leg engaging mechanism that is arranged to engage respectively disengage with the leg (4), and a processor arranged to control the cross heads (7, 11) such that the relative movement of the leg (4) is performed alternately by the cross heads (7, 11), characterized in that, the jacking system (1) comprises two cross heads (7, 11) that are positioned opposite one another such that one cross head can be operated in pulling mode and the other cross head can be operated in pushing mode.

2. Jacking system according to claim 1, wherein the processor is arranged to control the cross heads (7, 11) such that when one of the cross heads (7, 11) is operative in pulling mode or pushing mode, the other cross head returns to its starting position.

3. Jacking system according to claim 1 or 2, wherein the processor is arranged to control the cross heads (7, 11) such that the cross heads (7, 11) can assume a takeover position in which both leg engaging mechanisms engage with the leg (4).

4. Jacking system according to claim 1, 2 or 3, wherein each cross head (7, 11) essentially runs along the entire circumference of the leg (4).

5. Jacking system according to claim 4, wherein each cross head (7, 11) comprises three or more actuators (8, 12), preferably six actuators (8, 12).

6. Jacking system according to one or more of the preceding claims, wherein the leg engaging mechanism comprises at least two movable locking pins (9, 13) to be received in holes (21) of the leg (4).

7. Jacking system for relative movement of a leg (4) with respect to a platform (2), comprising a number of cross heads, wherein each cross head is independently movable in longitudinal direction of the leg by means of at least one hydraulic cylinder (8, 12) and wherein each cross head is provided with a leg engaging mechanism that is arranged to engage respectively disengage with the leg, and a processor arranged to control the cross heads, characterized in that, the at least one hydraulic cylinder (8, 12) of each cross head is connected to a fluid reservoir (15, 16) such that a predetermined amount of hydraulic fluid can flow to the reservoir in the engaged position of the cross head (7, 11) to provide a damping effect when the leg (4) touches the seabed.

8. Jacking system according to claim 7, wherein the jacking system is the jacking system (1) according to one or more of claims 1-6.

9. Method for relative movement of a leg (4) with respect to a platform (2) comprising the steps of

a) Providing a jacking system (1) according to one or more of claims 1-6 on a jacking platform (2) having a plurality of legs (4);

b) Controlling one cross head (7, 11) to engage on one of the legs (4) and to operate in pulling mode or pushing mode;

c) Simultaneously with step b) controlling the other cross head (7, 11) to return to its starting position;

d) Subsequently controlling the cross heads (7, 11) to assume a takeover position in which both leg engaging mechanisms engage with the leg (4);

e) Controlling the other cross head (7, 11) to engage on the leg (4) and to operate in opposite pushing mode or pulling mode;

f) Simultaneously with step e) controlling the one cross head (7, 11) to disengage on the leg (4) to return to its starting position;

g) Repeat steps b) through f) until the desired relative position of the leg (4) with respect to the platform (2) is reached.

Drawing