GB2363814A

GB2363814A - Support construction for a ballastable topsides transporter

Info

Publication number: GB2363814A
Application number: GB0115249A
Authority: GB
Inventors: Geir Rolfsnes
Original assignee: Marine Shuttle Operations AS
Current assignee: Marine Shuttle Operations AS
Priority date: 2000-06-23
Filing date: 2001-06-21
Publication date: 2002-01-09
Anticipated expiration: 2021-06-21
Also published as: GB2363814B; NO311969B1; GB0115249D0; NO20003308L; NO20003308D0

Abstract

A support construction is provided for a ballastable topsides transporter 1 comprising pontoons 6 defining a moonpool 4 and structural elements (7, 8, 9 and 28) which interconnect the pontoons and the support construction above the moonpool. The support construction comprises rocker arms 10 supported by the structural elements in rocker bearings 11 with horizontal rocker axes 13. The rocker arms have first ends 14 adapted to engage the topsides 2 and hydraulic cylinders 5 extending between the structural elements and the rocker arms for controlling the rocking movement of the rocker arms. Each rocker arm is provided with at least one hinge (25, 26, Fig 6) with a vertical hinge axis (21, 22, Fig 6) positioned between the rocker bearing and the first end of the arm to allow horizontal positioning of the first end.

Description

2363814 I Support construction for an offshore platform topsides The

invention relates to a support construction for an offshore platform topsides, which support construction forms part of a ballastable transporter comprising pontoons which define a moonpool and structural elements which interconnect the pontoons and the support construction above the pontoons, for supporting the topsides above the moonpool, wherein the topsides can be lowered onto or lifted up from a substructure or barge located in the moonpool by lowering or raising the transporter by ballasting or deballasting.

The installation of an offshore platform topsides on a substructure is of relevance in connection with the development of offshore oil and gas fields The installation of the platform topsides on the substructure can be done by placing the topsides on a support construction on the transporter of the above mentioned kind, move the transporter to the substructure, locate the transporter around the substructure, i e the substructure is located in the moonpool, and then transfer the topsides to the substructure by ballasting the transporter, which causes the topsides to be lowered onto the substructure.

The removal of offshore platforms, including removal of the topsides from the substructure, is a field which will become increasingly important in the years to come, as a number of offshore platforms will be taken out of service Removal of a platform topsides from a substructure can be done by locating a transporter with a moonpool around the substructure, i e the substructure is located in the moonpool, bring support constructions on the transporter in engagement with the platform topsides, lift the topsides up from the substructure by deballasting the transporter, and then bring the transporter with the topsides to a receiver, e g a barge The transfer of the topsides from the transporter to the barge can be done similarly to the transfer from the transporter to the substructure, as described above.

The sea is almost always in motion, and a transporter will therefore almost always be in motion This motion is a combination of vertical and horizontal movements and rotations, and is partly translatory and partly oscillating It is possible to control some of this motion by correct sizing, tugboats, moorings, thrusters or other arrangements, but the motion of the transporter due to the motion of the sea can never be totally eliminated.

A substructure, e g a jacket, is, however, fixed to the sea floor, and will consequently be almost at rest.

When ballasting a transporter carrying a topsides during the transfer of the topsides to a substructure which is located in the moonpool of the transporter, there is then some uncontrolled relative motion between the topsides and the substructure In order to guide the topsides to the correct location on the substructure, the topsides and substructure may have corresponding trunnions and apertures, or other stationary guiding arrangement This might be sufficient to control the motion of the transporter with the topsides in calm sea, but at an offshore location stationary guiding arrangements are usually not sufficient to control the motion of the transporter This motion may then cause collisions and damage to the topsides and the substructure.

A similar problem exists when lifting a platform topsides from a substructure by deballasting a transporter which is embracing the substructure, the problematic relative motion then being between the stationary topsides and the moving transporter.

NO 160 424 describes a device with adjustable buoyancy for lifting and transport during operations at sea The device consists of floats which together form an oblong, ballastable structure with a U-shaped cross section and an opening in the bottom.

After ballasting of the device, a barge with a platform topsides can be brought into the opening, whereupon when the device is deballasted, gripping devices in the device's long sides are caused to lift the platform topsides from the barge After moving the device to a position where a jacket is located in the opening, the device is ballasted, with the result that the topsides is lowered onto the jacket.

WO 99/06270 describes a transporter for removal of an offshore platform topsides from an associated jacket, comprising an oblong, ballastable structure consisting of two long sides, an intermediate underside and an opposite open upper side At one end the underside has a moonpool which can contain the jacket when the transporter is located with the underside horizontally down in the sea, and on the sides of the moonpool the long sides have contact sections which, when the transporter is deballasted, can be brought into abutment against the platform topsides and lift it, thus transferring it to the transporter.

A known support construction for a transporter for carrying a topsides comprises support arms which are supported by structural elements of the transporter and have ends which project above a moonpool for the location of a substructure Each support arm has two hinges with vertical hinge axes, and each arm thus consist of two rotatable sub-arms The total length of the arm can be adjusted by rotating the sub- arms in the hinge axes The rotational movement of each sub-arm can be controlled by a hydraulic cylinder which is fixed to the transporter.

In this way horizontal movement can be allowed for Vertical movements, which often are relatively large, can however not be allowed for in this way.

The object of the invention is to provide a support construction for an offshore platform topsides which allow vertical relative motions between a topsides and a substructure when transferring the topsides from a transporter to the substructure, and vertical relative motions between a topsides and a transporter when transferring the topsides from a substructure to the transporter The object is further also to allow horizontal relative motions between the topsides and the substructure when transferring the topsides from the transporter to the substructure, and horizontal relative motions between the topsides and the transporter when transferring the topsides from the substructure to the transporter.

The objects are achieved with a support construction of the type mentioned in the introduction which are characterized by the features which are stated in the claims.

The invention thus relates to a support construction for an offshore platform topsides, which support construction forms part of a ballastable transporter comprising pontoons which define a moonpool and structural elements which interconnect the pontoons and the support construction above the pontoons, for supporting the offshore platform topsides above the moonpool, wherein the platform topsides can be lowered onto or lifted up from a substructure or barge located in the moonpool by lowering or raising the transporter by ballasting or deballasting The support construction comprises rocker arms which are supported by the structural elements in rocker bearings with horizontal rocker axes, the rocker arms have first ends which are adapted to engage the platform topsides, and hydraulic cylinders extend between the rocker arms and the structural elements for controlling the rocking movement of the rocker arms.

The invention will now be explained in more detail in association with a description of individual specific embodiments, and with reference to the drawings, in which:

fig 1 is a perspective view of a transporter with support constructions according to the invention, fig 2 is a plan view of the transporter in fig 1, fig 3 is a side view of the transporter in fig 1 in the process of removing a platform topsides from a substructure, fig 4 and 5 are fractional views corresponding to fig 3, illustrating vertical motion of the transporter, and fig 6 is a detailed perspective view of a rocker arm according to the invention.

Fig 1 is a perspective view of a ballastable transporter 1 comprising lower pontoons 6 which define a moonpool 4 and upper girders 7 which are located above and are parallel to the pontoons 6 and define an opening 18 above the moonpool 4 The moonpool 4 and the opening 18 essentially correspond to each other, thereby forming a vertical recess through the transporter 1, which recess is horizontally accessible from one side of the transporter The transporter 1 also comprises structural elements which interconnect the pontoons 6 and the girders 7 In the illustrated embodiment the structural elements are columns 8 which are perpendicular to the pontoons 6 and the girders 7 A support bridge 29 interconnects the girders 7.

For ballasting purposes the pontoons 6 has ballasting chambers Additionally the structural elements, i e the columns 8, may also comprise ballasting chambers In the 1 0 illustrated embodiment the girders 7 are cylindrical, and may also comprise ballasting chambers.

The transporter 1 floats in the sea, with the pontoons 6 down and the columns 8 vertical References to "upper", "lower", "above", "below", "vertical" etc in this patent application refers to the way the transporter floats in the sea.

The transporter 1 may be used for installation of a platform topsides 2 on a substructure, or removal of a topsides 2 from a substructure.

Fig 2 is a plan view of the transporter I 1 A topsides 2, illustrated by its lower frame only, is located above the opening 18 and the moonpool 4 The topsides 2 is supported by a support construction which in turn is supported by the structural elements of the transporter I 1 The support construction, which will be discussed in more detail later, comprises rocker arms 10 with first ends 14 which are adapted to engage the platform topsides 2 The first ends 14 of the rocker arms 10 project from the girders 7, and are located in the opening 18 above the moonpool 4.

Fig 3 is a side view of the transporter 1 in the process of removing a platform topsides 2 from a substructure 3 The illustrated substructure is a jacket, i e a steel trusswork, which rests on the seabed 15 The substructure 3 and the topsides 2, which is a steel construction comprising one or more decks and equipment which is necessary for the intended purpose, together form an offshore platform.

In fig 3 the transporter I is floating besides the substructure 3, with the substructure located in the vertical recess formed by the moonpool 4 and the opening 18 The draft of the transporter 1 has been adjusted such that the first ends 14 of the rocker arms are lower than the underside of the topsides 2, which has been achieved by filling the ballasting chambers of the transporter 1 with a suitable amount of sea water The first ends 14 of the rocker arms 10 are brought into engagement with corresponding elements of the topsides 2.

The transporter 1 is then deballasted, which leads to a reduced draft and a raising (not illustrated) of the topsides 2, up from substructure 3 The transporter 1 with the topsides 2 is then free to move away (not illustrated) from the substructure 3 The removal of the topsides 2 from the substructure 3 is then completed.

Installation of a topsides is the reverse process Similarly a topsides may be raised from or lowered onto a barge or a jetty at a construction yard by deballasting or ballasting the transporter.

Further, not illustrated, the transporter comprises piping, valves, pumps with motors and control equipment for performing the ballasting/deballasting The transporter may be manned or unmanned In the first case the transporter also comprises at least one control room for the personnel In the second case the ballasting/deballasting is remotely controlled by means of not shown communication equipment.

Ballasting/deballasting may also be carried out by an umbilical which contains both pressurised water for ballasting and pressurised air for deballasting, together with pressurised fluid for operation and control of the valves In a preferred embodiment a hydraulic power pack, i e a hydraulic pump driven by a diesel engine, is located on a vessel nearby, and pressurized hydraulic fluid is supplied through the umbilical for energising hydraulically driven ballast water pumps and air-compressors for deballasting located on the transporter.

The transporter may be equipped with a propulsion machinery, or the transporter may be moved with tugs.

As discussed in the general part of the description, at an offshore location there will almost always be some relative motion between a floating transporter and a stationary substructure, which in the above described removal of the topsides 2 from the substructure 3 by the transporter 1 means that there will be some relative motion between the transporter 1 and the topsides 2, which relative motion might cause collisions and damage during mating A similar problem exists when lowering a topsides from a transporter onto a substructure during an installation at an offshore location, the relative motion then being between the topsides and the substructure.

Generally the motions of the sea is a combination of translatory and rotational motion in all directions A major component, however, is the vertical motion, known as the heave motion.

According to the invention the rocker arms 10 of the support construction are supported by the structural elements in rocker bearings 11 with horizontal rocker axes 13, which can be seen in fig 2 and 3.

Fig 3 illustrates that the rocker bearings 11 are located on support beams 28, which are supported by the pontoons 6 via inclined struts 9 The support beams 28 are also supported by the girders 7 via tie-backs 12 The weight of the platform topsides 2 is transferred from the rocker arms'10 first ends 14, which support the topsides 2, through the rocker arms 10, through the rocker bearings 11, through the support beams 28, through the inclined struts 9, to the pontoons 6 The transfer of the weight of the topsides 2 through the inclined struts 9 results in tension forces in the tie-backs 12, which are transferred to the girders 7 located above the pontoons 6.

According to the invention, the rocking movement of the rocker arms 10 are controlled by hydraulic cylinders which extend between the rocker arms 10 and the structural elements In one embodiment, which is not illustrated, at least one hydraulic cylinder extends between the structural elements and the rocker arm 10 in an area of the rocker arm 10 between the rocker bearing 11 and the first end 14 of the rocker arm 10 With reference to fig 3, this could be realised by hydraulic cylinders between the first end 14 of the rocker arm 10 and the support beam 28.

In a preferred embodiment, at least one hydraulic cylinder 16 extends between the structural elements and the rocker arm 10 in an area of the rocker arm 10 between the rocker bearing 11 and a second end 24 of the rocker arm 10 opposite the first end 14.

Preferably the hydraulic cylinder 16 is located in the second end 24 of the rocker arm This is illustrated in fig 1 and 3, in which two hydraulic cylinders 16 extend between support runners 5, which are integral with the girders 7, in each second end 24 of the rocker arms 10.

According to the laws of mechanics, the magnitude of a force in an end of a rocker arm in equilibrium is in inverse proportion to the distance from the rocker bearing to the end of the rocker arm Due to the arrangement with the inclined struts 9, the rocker bearings 11 are located above the moonpool 4, vertically offset from the pontoons 6, which is favourable with respect to having a short distance from the rocker arms'10 first ends 14, which support the topsides 2, to the rocker bearings 11.

In the embodiment with one or more hydraulic cylinders 16 in the second end 24 of the rocker arm 10, preferably the distance 1, between the rocker bearing 11 and the second end 24 of the rocker arm 10 (see fig 3) is longer than the distance 12 between the rocker bearing 11 and the first end 14 of the rocker arm 10, which causes the total force to be taken up by the total number of hydraulic cylinders 16 to be less than the weight of the topsides 2.

In the removal of the platform topsides 2, prior to the mating between the first ends 14 of the rocker arms 10 and the topsides 2, the rocker arms 10 can be moved in counter-phase with the heave-motion of the transporter 1, i e the first ends 14 of the rocker arms are kept essentially at a constant elevation, while approaching the corresponding elements of the topsides 2 The first ends 14 of the rocker arms 10 are then mated with the corresponding elements of the topsides 2 The pressure in the hydraulic cylinders 16 are then relatively low, in order not to introduce any big forces between the first ends 14 of the rocker arms 10 and the corresponding elements of the topsides 2.

Preferably both a spring-function and a damper function is included in the hydraulic circuits for the hydraulic cylinders 16 The spring function can be realised by a chamber containing a pressurized, compressible gas, and the damper function can be realised by a throttle valve Such a spring-function and damper-function are both known technology The hydraulic circuits are controlled by an electronic controller, which is also known technology.

In the first time after the mating between the first ends 14 of the rocker arms 10 and the topsides 2, the hydraulic circuits provide no or only small resistance to the relative motion between the topsides 2 and the transporter 1 Then the pressure of the hydraulic cylinders 16 are gradually increased, the transporter is gradually deballasted, and the weight of the topsides 2 is gradually transferred to the transporter 1 Relative vertical motion between the transporter 1 and the topsides 2 is, however, allowed while transferring the weight of the topsides 2 from the substructure to the transporter This is illustrated in fig 3, 4 and 5 In fig 3 the rocker arms 10 are in a middle position, and the stroke of the hydraulic cylinders 16 are at their middle, In fig 4 the transporter 1 has moved upwards in the sea, i e the transporter is raised relative to the sea surface 19 and the substructure 3, which is fixed to the sea bed 15 The stroke of the hydraulic cylinders 16 are here at their maximum In fig 5 the transporter 1 has moved down in the sea, i e the transporter is lowered relative to the sea surface 19 and the substructure 3, and the stroke of the hydraulic cylinders 16 are at their minimum.

Finally the topsides 2 is raised from the substructure 3, and the movement of the hydraulic cylinders between the rocker arms 10 and the structural elements of the transporter 1 is locked The transfer of the topsides 2 from the substructure 3 to the transporter 1 is then completed.

Fig 6 is a detailed perspective view of a rocker arm 10 As discussed, the rocker arm is supported in a rocker bearing 11 with a horizontal rocker axis 13 The rocker bearing 11 is supported by the support beam 28, which is supported by the inclined strut 9 and the tie-back 12 Two hydraulic cylinders 16 are arranged between the second end 24 of the rocker arm 10 and a support runner 5 which is integral with the girder 7 The first end 14 of the rocker arm 10 is provided with a fork element 17 for engagement with a corresponding trunnion 20 The trunnion 20 is a part of the platform topsides 2, and is also illustrated in fig 1 and 2.

Fig 6 also illustrates that the rocker arm 10 comprises two hinges 25, 26 with a vertical hinge axis 21, 22 respectively, located between the rocker bearing 1 1 and the first end 14 of the rocker arm 10 Further the rocker arm 10 comprises a hinge 27 with a vertical hinge axis 23 above the rocker bearing 11 By means of these hinges, see also fig 2, it is possible to vary the horizontal location of the first end 14 of the rocker arm 10 relative to the support beam 28 and the girder 7 in all horizontal directions Preferably there is also at least one hydraulic cylinder (not illustrated) for controlling the movement of the vertical hinges 25, 26, 27 When mating the transporter 1 and the topsides 2 during a removal of the topsides from the substructure, relative horizontal motions between the topsides and the transporter is allowed in a similar manner as discussed above with respect to the relative vertical motion.

The combination of the rocker bearings 1 1 and the hinges 25, 26, 27 provides a favourable support construction which allow both vertical and horizontal relative motions Although the illustrated number of three hinges 25, 26, 27 in each rocker arm 10 is preferred, the number of hinges may be different.

It should be understood that the above considerations related to the relative vertical and horizontal motion between the topsides and the transporter during a removal of the topsides from the substructure is equally applicable to a relative vertical and horizontal motion between the topsides and the substructure when transferring the topsides from the transporter to the substructure during an installation of the topsides on the substructure.

Claims

CLAIMS:

1 A support construction for an offshore platform topsides ( 2), which support construction forms part of a ballastable transporter ( 1) comprising pontoons ( 6) which define a moonpool ( 4) and structural elements ( 7, 8, 9, 28) which interconnect the pontoons ( 6) and the support construction above the pontoons ( 6), for supporting the topsides ( 2) above the moonpool ( 4), wherein the topsides ( 2) can be lowered onto or lifted up from a substructure ( 3) or barge located in the moonpool ( 4) by lowering or raising the transporter ( 1) by ballasting or deballasting, the support construction is characterized by comprising rocker arms ( 10) which are supported by the structural elements ( 7, 28) in rocker bearings ( 11) with horizontal rocker axes ( 13), the rocker arms ( 10) having first ends ( 14) which are adapted to engage the platform topsides ( 2), and hydraulic cylinders ( 16) extending between the rocker arms ( 10) and the structural elements ( 5, 7, 28) for controlling the rocking movement of the rocker arms ( 10), each rocker arm ( 10) comprises at least one hinge ( 25, 26) with a vertical hinge axis ( 21, 22) located between the rocker bearing ( 11) and the first end ( 14) of the rocker arm ( 10).

2 A support construction according to claim 1, characterized by that at least one hydraulic cylinder extends between the structural elements ( 5, 7, 28) and the rocker arm ( 10) in an area of the rocker arm ( 10) between the rocker bearing ( 11) and the first end ( 14) of the rocker arm ( 10).

3 A support construction according to claim 1 or 2, characterized by that at least one hydraulic cylinder ( 16) extends between the structural elements ( 5) and the rocker arm ( 10) in an area of the rocker arm ( 10) between the rocker bearing ( 11) and a second end ( 24) of the rocker arm ( 10) opposite the first end ( 14), and that the hydraulic cylinder ( 16) is preferably located in the second end ( 24) of the rocker arm ( 10).

4 A support construction according to claim 3, characterized by that the distance (li) between the rocker bearing ( 11) and the second end ( 24) of the rocker arm ( 10) is longer than the distance ( 12) between the rocker bearing ( 11) and the first end ( 14) of the rocker arm ( 10).

A support construction according to any of the preceding claims, characterized by that the first end ( 14) of the rocker arm ( 10) is provided with a fork element ( 17) for engagement with a corresponding trunnion ( 20) of the platform topsides ( 2).

6 A support construction according to any of the preceding claims, characterized by that the rocker arm ( 10) comprises a hinge ( 27) with a vertical hinge axis ( 23) above the rocker bearing ( 11).

7 A support construction according to any of the preceding claims, characterized by at least one hydraulic cylinder for controlling movement of the vertical hinges ( 25, 26, 27).

8 A support construction according to any of the preceding claims, characterized by that the rocker bearings ( 11) are located above the moonpool ( 4), vertically offset from the pontoons ( 6), and that the weight of the platform topsides ( 2) is transferred from the rocker bearings ( 11) to the pontoons ( 6) via inclined struts ( 9).

9 A support construction according to claim 8, characterized by that forces resulting from the transfer of the weight of the topsides ( 2) via the inclined struts ( 9) are transferred from the rocker bearings ( 11) to girders ( 7) located above the pontoons ( 6) via tie-backs ( 12).