GB2336417A

GB2336417A - Fluid transfer arrangement

Info

Publication number: GB2336417A
Application number: GB9805455A
Authority: GB
Inventors: Baan Jacob De
Original assignee: Bluewater Terminal Systems NV
Current assignee: Bluewater Terminal Systems NV
Priority date: 1998-03-13
Filing date: 1998-03-13
Publication date: 1999-10-20
Anticipated expiration: 2018-03-13
Also published as: GB9805455D0; GB2336417B

Abstract

The present invention relates to apparatus for transferring fluid between two conduits, in particular between an offshore riser (4) and a tanker vessel (1). The apparatus consists of a stack of fluid swivels (7) providing fluid paths between the riser and the vessel. Each swivel (7) is also resiliently mounted on a support structure (9) so as to be movable axially relative to the structure. The configuration allows an individual swivel (7) to be removed from the stack without disassembling the whole stack. The swivel (7) concerned is detached from its neighbours and those above it are jacked up relative to the support structure (9) to create a gap sufficient to remove the swivel (7) laterally.

Description

2336417 FLUID TRANSFER ARRANGEMENT The present invention relates to an

improved arrangement for supporting an assembly comprising a large number of fluid swivel modules, such that the number of individual modules in the assembly can be increased without having a significant impact on the size of the individual modules, whilst also maintaining easy access to the modules for repair and replacement.

offshore oil production occurs in many areas of the world from floating vessels which usually anchor to the seabed by means of a so-called single point mooring system. One example of such a system can be found in US Patent No. 4,301,840, although many other examples are well known.

In such a system, the vessel is able to weathervane around the single point mooring, often over more than 3600. Consequently, a fluid transfer system for transferring fluids between the anchored part of the mooring system and the floating vessel is required which can cope with the weathervaning of the vessel. Normally, many separate fluid streams must be transferred and this has led to the development of socalled fluid swivel stacks where a number of identical or nearly identical swivel modules are stacked one on top of another. Each module represents an individual flow path and theoretically an unlimited number of modules could be stacked in one assembly. This type of assembly is described for example in US Patent No. 4,306,741 but other examples are also known.

As mentioned above, it is possible in theory to stack an unlimited numbor of more or less similar swivel modules one on top of another in order to create the number of individual flow paths which are required in a particular situation. In practice however there are limitations. The swivel assembly is mounted on a floating vessel and therefore such assembly is subject to accelerations due to motion of the vessel and this generates significant loads, particularly near to the base of the swivel assembly. High loads can lead to deformation and this contradicts the very nature of fluid swivels; they depend on good dimensional stability in order to perform their prime task of sealing the fluids against escape to the environment.

Large loads are also experienced, especially near to the base of the swivel assembly, due to torsional which are caused by the swivel modules being forced to rotate as the vessel weathervanes. The means of attachment of the base of the swivel to a supporting structure, and also the means of attachment of the swivel modules to each other, must be able to handle all of the loads described above.

Conventionally, this leads to the need to make the lower swivel modules larger in diameter than the upper modules. This creates a more costly design and the larger diameter makes it more difficult to achieve sealing of fluids in high pressure and/or high temperature applications. Larger diameters also make it more difficult to achieve the require machining tolerances.

A further problem of such swivel assemblies is the fact that replacement of an individual module, e.g due to failure of the sealing arrangement, becomes difficult because it requires removal of all the individual modules located above the one requiring replacement.

- 3 It is therefore an aim of the present invention to overcome the above described difficulties and to provide a practical solution for supporting a fluid swivel assembly.

Accordingly, the present invention provides apparatus for transferring fluid between first and second fluid conduits, comprising a stack of two or more fluid swivels operable to provide a fluid path between the first and second conduits, the stack defining a longitudinal axis, and means to mount each fluid swivel on a support structure, the mounting means operable to allow relative axial displacement of the fluid swivels.

Preferably this is achieved by the mounting means incorporating an extensible member.

Preferably the extensible means comprises a hydraulic plunger.

Advantageously the mounting further comprises resilient means.

The resilient means may comprise a spring or a block of resilient material.

Conveniently, each fluid swivel comprises an inner part and an outer part defining a fluid path therebetween and which are connected together to allow relative rotation, wherein the inner parts of adjacent fluid swivels are detachably fastened to each other.

The apparatus preferably further comprises removal means for removing a fluid swivel from the stack or inserting a fluid swivel into the stack.

- 4 The removal means preferably comprises an arm attachable to a fluid swivel and mounted on the support structure so as to be moveable towards and away from the stack.

The arm may also be mounted on the support structure so as to be moveable up and down the support structure.

Preferably each fluid swivel is the same size and the first and second conduits each conduct a plurality of separate fluid streams and wherein each fluid stream is transferred through a respective fluid swivel.

The apparatus of the present invention is primarily intended for use o a floating vessel and in this case the vessel carries the second conduit, the support structure is secured to the vessel, a body rotatably attached to the vessel receives the first conduit, and the first conduit is connected to the stack of fluid swivels by flexible piping.

The present invention also provides a method for removing a fluid swivel from the apparatus described above, comprising the steps of disconnecting a fluid swivel to be removed from each adjacent fluid swivel; raising each fluid swivel positioned above the fluid swivel to be removed by adjustment of the mounting means to create a first separation between the fluid swivel to be removed and the upwardly adjacent fluid swivel; raising the swivel to be removed by adjustment of the mounting means to create a second smaller separation between the fluid swivel to be removed and the downwardly adjacent fluid swivel; and removing the fluid swivel from the stack.

The method may further comprise the steps of inserting a replacement fluid swivel into the space left by the removed fluid swivel; lowering the replacement fluid swivel by adjustment of the mounting means to bring it into contact with the downwardly adjacent fluid swivel; lowering the fluid swivels above the replacement fluid swivel by adjustment of the mounting means to bring the replacement fluid swivel into contact with the upwardly adjacent fluid swivel; connecting the replacement fluid swivel to the adjacent fluid swivels above and below.

The invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:

FIGURE 1 illustrates in schematic form a fluid swivel arrangement of the prior art;

FIGURE 2 illustrates in schematic form a fluid swivel support arrangement in accordance with one embodiment of the present invention; FIGURE 3a is an enlarged view showing the connection between inner parts of adjacent swivel modules; FIGURE 3b is similar to Figure 3a but shows an alternative mode of connection; FIGURE 4 shows one embodiment of a resilient connection between the outer parts of adjacent swivel modules; FIGURE 5 illustrates a step in the removal of one swivel module from the stack; FIGURE 6a is a side view of part of the stack supporting frame showing a removal arm in two positions; FIGURE 6b shows the apparatus for Figure 6a in the direction of arrows B; and FIGURE 6c is a plan view of the apparatus of Figure 6a.

A typical prior art fluid swivel stack assembly of the type described above is illustrated in Figure 1. Here, a floating vessel 1 is fitted with a structure such as a turret 2 which is anchored to the sea bed by means of anchor legs 3. The vessel 1 is able to rotate about the turret 2. Well fluids enter the turret 2 through flexible risers 4 and thence enter the fluid swivel assembly 5. Thereafter, the fluids are transferred via the fluid swivel assembly 5 to further piping and into the vessel's process plant 6.

The fluid swivel assembly 5 consists of a number of individual swivel modules 7 stacked one on top of is another. Typically each swivel module 7 consists of a radially inner part and a radially outer part which are rotatable relative to one another and which define a fluid passageway between them. The inner parts of the swivel modules 7 are connected to each other to build up a stack of fluid swivel modules 7 which is fitted on a base support 8 which is integrated with the turret 2. Thus, the inner parts of the modules in the stack rotate together with the turret 2 while the outer parts rotate with the vessel as it weathervanes around the turret 2.

A supporting frame 9 supports piping which exits the outer parts of the swivel modules 7 and directs the piping towards the process plant 6.

In this example, all the swivel modules 7 are shown the same diameter, although as referred to above, the diameter of the lower modules 7 may be increased in some applications to cope with the loads imposed.

Turning now to Figure 2 an embodiment of the - 7 present invention is illustrated, using like reference numerals where appropriate. As in Figure 1, a vessel 1 is rotatably fitted with a turret 2 which is anchored to the seabed by anchor legs 3 and receives well fluids through flexible risers 4. The risers 4 transmit well fluids via the turret 2 to the stack of fluid swivel modules 7. However, in this case, flexible steel piping 11 connects the base 8 of the swivel stack with the turret 2.

The inner parts 20 of the swivel modules 7 are connected to each other to build up the stack. Two examples of suitable types of interconnection are shown in Figures 3a and 3b.

In Figure 3a, the inner parts 20 of adjacent modules 7 are each provided with an annular groove 21. connecting pieces 22 of generally U-shaped cross section are fitted across the joint between adjacent inner parts 20, the arms of the U being seated in the grooves 21. Each connecting piece 22 is secured by a bolt 23.

In Figure 3b, the inner parts 20 have mating annular flanges 24 which are secured together around the circumference of the innerparts 20 by bolts 25.

The outer part 26 of each swivel module 7 is mounted by structures 10 to the supporting frame 9.

An example of the support structure 10 is shown in Figure 4. Each resilient support structure 10 includes an extensible component 12, the length of which can be latered to allow each swivel module 7 to be displaced along the vertical axis of the fluid swivel stack 5. These components 12 are typically hydraulically activated plunger devices of known type.

The support structure 10 also comprises a resilient means 13, such as metal springs or blocks of rubber. These resilient means 13 are required to overcome fabrication and assembly tolerances between like faces on the outer parts 26 of the modules 7 in the swivel stack 5, since the inner parts 20 are directly connected together.

Figure 5 shows a step in the method of removing any individual swivel module 7a from within the fluid swivel stack, without having to remove the swivel modules adjacent to it. This is achieved by first disconnecting the inner part 20 of the module 7a to be removed from the adjacent modules and then jacking upwards the support structures 10 of all the swivel modules 7 above the module 7a to be removed, so as to create a gap G as shown.

Following this step, the module 7a to be removed is also raised, but to a lesser extent, to create another smaller gap G' between it and the f luid swivel beneath. The module 7a can now be moved out of the stack in a horizontal plane, free of interference with adjacent modules 7. The swivel modules below the module 7a. to be removed are not jacked up.

As shown in Figure 6, means to remove an individual module from the assembly 5 are preferably installed on a permanent basis on the support frame 9 and may consist of an apparatus 14 which can be moved vertically up and down the support frame 9 and secured at desired locations level with the various swivel modules in the stack. This apparatus 14 may typically be provided with a pivoting arm 15 which can be locked on to the swivel module 7a to be removed. The module 7a is then rotated out of the assembly 5 in a horizontal plane in the direction of arrows R.

The apparatus 14 is subsequently moved down the frame 9 together with the swivel module 7a to land the swivel module 7a on a landing area 9a at the base of the frame 9. From this landing area 9a the ship's crane can remove the module 7a for transport to e.g a repair shop.

Re-installation of the repaired module, or a new module, is effected by the same apparatus 14,15 in reverse order to the steps described above.

The support frame 9 is preferably also fitted with working platforms (not shown) so that each individual module can be visited for general inspection and maintenance work.

Thus, the present invention provides an improved fluid swivel arrangement for transferring fluids provides for ease of access each swivel to facilitate maintenance procedures, thus improving efficiency and reducing costs. The arrangement of the present invention also allows all the swivel modules to be identical, making the assembly simpler and cheaper. Nevertheless, modules of different size or other parameters could be used if desired to suit a particular application. It will be apparent to those skilled in the art that a number of variations and modifications are possible to the particular arrangement described above without departing from the scope of the invention.

- 10

Claims

CLAIMS:

is 1. Apparatus for transferring fluid between first and second fluid conduits, comprising a stack of two or more fluid swivels operable to provide a fluid path between the first and second conduits, the stack defining a longitudinal axis, and means to mount each fluid swivel on a support structure, the mounting means operable to allow relative axial displacement of the fluid swivels.
2. Apparatus as claimed in claim 1, wherein the mounting means incorporates an extensible member.
3. Apparatus as claimed in claim 2, wherein the extensible means comprises a hydraulic plunger.
4. Apparatus as claimed in any preceding claim, wherein the mounting means further comprises resilient means.
5. Apparatus as claimed in claim 4, wherein the resilient means comprises a spring.
6. Apparatus as claimed in claim 4, wherein the resilient means comprises a block of resilient material.
Apparatus as claimed in any preceding claim, wherein each fluid swivel comprises an inner part and an outer part defining a fluid path therebetween and which are connected together to allow relative rotation, wherein the inner parts of adjacent fluid swivels are detachably fastened to each other.
8. Apparatus as claimed in any preceding claim, further comprising removal means for removing a fluid swivel from the stack or inserting a fluid swivel into the stack.
9. Apparatus as claimed in claim 8, wherein the removal means comprises an arm attachable to a fluid swivel and mounted on the support structure so as to be moveable towards and away from the stack.

is
10. Apparatus as claimed in claim 9, wherein the arm is mounted on the support structure so as to be moveable up and down the support structure.
11. Apparatus as claimed in any preceding claim, wherein each fluid swivel is the same size.
12. Apparatus as claimed in any preceding claim, wherein the first and second conduits each conduct a plurality of separate fluid streams and wherein each fluid stream is transferred through a respective fluid swivel.
13. A floating vessel including a fluid transfer apparatus as claimed in any preceding claim mounted thereon.
14. A floating vessel as claimed in claim 13, wherein the vessel carries the second conduit, the support structure is secured to the vessel, a body rotatably attached to the vessel receives the first conduit, and the first conduit is connected to the stack of fluid swivels by flexible piping.
15. A method for removing a fluid swivel from the apparatus as claimed in any preceding claim, comprising the steps of: disconnecting a fluid swivel to be removed from each adjacent fluid swivel; raising each fluid swivel positioned above the fluid swivel to be removed by adjustment of the mounting means to create a first separation between the fluid swivel to be removed and the upwardly adjacent fluid swivel; raising the swivel to be removed by adjustment of the mounting means to create a second smaller separation between the fluid swivel to be removed and the downwardly adjacent fluid swivel; and removing the fluid swivel from the stack.
16. A method as claimed in claim 15, further comprising the steps of: inserting a replacement fluid swivel into the space left by the removed fluid swivel; lowering the replacement fluid swivel by adjustment of the mounting means to bring it into contact with the downwardly adjacent fluid swivel; lowering the fluid swivels above the replacement fluid swivel by adjustment of the mounting means to bring the replacement fluid swivel into contact with the upwardly adjacent fluid swivel; connecting the replacement fluid swivel to adjacent fluid swivels above and below.
17. Apparatus for transferring fluid substantially as hereinbefore described with reference to Figures 2-6.
18. A method substantially as hereinbefore described with reference to Figures 2-6.

12-37 SEM AC: SPECS

18. A method substantially as hereinbefore described with reference to Figures 2-6.

Amendments to the claims have been filed as follows l. Apparatus for transferring fluid between first and second fluid conduits, comprising a stack of two or more fluid swivels detachably secured to one another and operable to provide a fluid path between the first and second conduits, the stack defining a longitudinal axis, and means to mount each fluid swivel on a support structure, the mounting means operable to allow axial displacement of each fluid swivel relative to the support structure.

2. Apparatus as claimed in claim 1, wherein the mounting means incorporates an extensible member.

is 3. Apparatus as claimed in claim 2, wherein the extensible member comprises a hydraulic plunger.

4. Apparatus as claimed in any preceding claim, wherein the mounting means further comprises re silient means.

5. Apparatus as claimed in claim 4, wherein the resilient means comprises a spring.

6. Apparatus as claimed in claim 4, wherein the resilient means comprises a block of resilient material.

7. Apparatus as claimed in any preceding claim, wherein each fluid swivel comprises an inner part and an outer part defining a fluid path therebetween and which are connected together to allow relative rotation, wherein the inner parts of adjacent fluid swivels are detachably fastened to each other.

1 4L - 8. Apparatus as claimed in any preceding claim, further comprising removal means for removing a fluid swivel from the stack or inserting a fluid swivel into the stack.

is 9. Apparatus as claimed in claim 8, wherein the removal means comprises an arm attachable to a f luid swivel and mounted on the support structure so as to be moveable towards and away from the stack.

10. Apparatus as claimed in claim 9, wherein the arm is mounted on the support structure so as to be moveable up and down the support structure.

Apparatus as claimed in any preceding claim, wherein each fluid swivel is the same size.

12. Apparatus as claimed in any preceding claim, wherein the first and second conduits each conduct a plurality of separate fluid streams and wherein each fluid stream is transferred through a respective fluid swivel.

13. A floating vessel including a fluid transfer apparatus as claimed in any preceding claim mounted thereon.

14. A floating vessel as claimed in claim 13, wherein the vessel carries the second conduit, the support structure is secured to the vessel, a body rotatably attached to the vessel receives the first conduit, and the first conduit is connected to the stack of fluid swivels by flexible piping.

15. A method for removing a fluid swivel from the 1 is - i 5 - apparatus as claimed in any preceding claim, comprising the steps of: disconnecting a fluid swivel to be removed from each adjacent fluid swivel; raising each fluid swivel positioned above the fluid swivel to be removed relative to the support structure by adjustment of the mounting means to create a first separation between the fluid swivel to be removed and the upwardly adjacent fluid swivel; raising the swivel to be removed relative to the support structure by adjustment of the mounting means to create a second smaller separation between the fluid swivel to be removed and the downwardly adjacent fluid swivel; and removing the fluid swivel from the stack.

16. A method as claimed in claim 15, further comprising the steps of:

inserting a replacement fluid swivel into the space left by the removed fluid swivel; lowering the replacement fluid swivel by adjustment of the mounting means to bring it into contact with the downwardly,adjacent fluid swivel; lowering the fluid swivels above the replacement fluid swivel by adjustment of the mounting means to bring the replacement fluid swivel into contact with the upwardly adjacent fluid swivel; connecting the replacement fluid swivel to the adjacent fluid swivels above and below.

!7. Apparatus for transferring fluid substantially as hereinbe-fore described with reference to Figures 2-6.