GB2333139A - Fluid transfer apparatus - Google Patents

Abstract

The apparatus, for transferring fluid between first and second conduits, e.g. between a flexible riser (4) and piping on board a floating vessel (1), comprises two or more fluid swivel assemblies (13) operable to provide a fluid path between the riser (4) and the onboard piping. Each fluid swivel assembly (13) comprises at least one fluid swivel (7). The first swivel assembly (13) is secured to a body (2) rotatably attached to the vessel (1). The body (2) receives the riser (4). The or each other swivel assembly (13) is mounted to a respective support structure (9) secured to the vessel (1). Flexible piping (10) connects each fluid swivel assembly (13) to its neighbour to ensure continuity of the fluid path.

Description

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 number 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.

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 wherein the second conduit is mounted on a floating vessel, the apparatus comprising two or more fluid swivel assemblies , each assembly comprising at least one fluid swivel operable to provide a fluid path between the first and second conduits, wherein the first fluid swivel assembly is secured to a body which is rotatably connected to the vessel and which receives the first fluid conduit and the or each other fluid swivel assembly is rotatably mounted on a respective support structure which itself is secured to the vessel so as to transmit loads thereto and wherein each fluid swivel assembly is connected to the adjacent fluid swivel assembly by at least one flexible pipe operable to provide a fluid path between the fluid swivels of respective assemblies.

Preferably each fluid swivel assembly comprises two fluid swivels to maximise ease of access to the swivels.

The apparatus may further comprise a linkage between adjacent fluid swivel assemblies to maintain rotational alignment therebetween Preferably, the fluid swivel assemblies are mounted one on top of another.

Conveniently, each fluid swivel is the same size.

Typically, the first and second conduits each conduct a plurality of separate fluid streams and each fluid stream is transferred through a respective fluid swivel.

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 3 is an enlarged view of one sub-assembly of the arrangement shown in Figure 2; FIGURE 4 is a perspective view of part of a linkage between adjacent sub-assemblies.

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 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 7 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 there is illustrated an embodiment of the present invention, which uses like reference numerals where appropriate. As in Figure 1, there is shown a vessel 1 rotatably fitted with a turret 2 which is anchored to the sea bed by anchor legs 3 and receives well fluids through flexible risers 4. The risers 4 transmit well fluids via the turret 2 to the fluid swivel modules 7. The lowermost swivel module 7 is secured to a base support 8 integrated with the turret 2 as before. However, in this embodiment the overall fluid swivel assembly is separated into four sub-assemblies 13.

Each sub-assembly 13 consists of two individual fluid swivel modules 7. Each sub-assembly 13 is rotatably mounted by means of a bearing 12 (best seen in Figure 3) on a load bearing supporting framework 9 which is itself secured to the vessel deck.

Continuity in the fluid path is assured by fitting flexible piping 10 between the sub-assemblies 13 to transmit the various fluid streams from the risers 4 to the relevant fluid swivel 7. By way of example, the flexible piping 10 may take the form of steel piping with a U-bend as shown in Figure 2, or a flexible hose, or some form of articulated pipe assembly.

A linkage such as a torsional driver assembly 11 may also be fitted between the sub-assemblies 13 in order to maintain rotational alignment between the inner parts of adjacent swivel modules 7, although depending upon the stiffness of the flexible piping 10 this is not always necessary. One example of a torsional driver assembly 11 is shown in Figure 4, although modifications to its precise configuration and alternative linkages are possible. In the Figure, the flexible piping 10 is omitted for clarity.

As is clear from Figure 2, with the arrangement of the present invention it is much simpler to access individual swivel modules for repair and replacement without disturbing the surrounding sub-assemblies. It will also be clear that swivel assembly inertia loads, caused by motion of the vessel, are not transferred down the stack to the lower modules but instead transferred directly to the supporting framework 9 which is secured to the vessel deck. The supporting frame 9 is a structure which can be easily and cheaply designed to cater for these large loads and to suit the environmental conditions, spatial constraints and so on of the situation in which it is to be used.

Whilst Figure 2 shows two individual swivel modules 7 in each sub-assembly 13, it is of course possible to have an individual module 7 supported by an individual frame 9. Likewise, more than two modules may be used in each sub-assembly although the benefits of easy access to individual modules 7 of course decline if many modules are used.

The arrangement of the present invention also allows all the swivel modules 7 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.

Thus, the present invention provides an improved fluid swivel arrangement for transferring fluids which simplifies design of the assembly and provides for ease of access to facilitate maintenance procedures, thus improving efficiency and reducing costs. It will be apparent to those skilled in the art that a number of variations and modifications are possible to the arrangement described above without departing from the scope of the invention.

Claims (8)

CLAIMS:

1. Apparatus for transferring fluid between first and second fluid conduits wherein the second conduit is mounted on a floating vessel, the apparatus comprising two or more fluid swivel assemblies , each assembly comprising at least one fluid swivel operable to provide a fluid path between the first and second conduits, wherein the first fluid swivel assembly is secured to a body which is rotatably connected to the vessel and which receives the first fluid conduit and the or each other fluid swivel assembly is rotatably mounted on a respective support structure which itself is secured to the vessel so as to transmit loads thereto and wherein each fluid swivel assembly is connected to the adjacent fluid swivel assembly by at least one flexible pipe operable to provide a fluid path between the fluid swivels of respective assemblies.

2. Apparatus as claimed in claim 1, wherein each fluid swivel assembly comprises two fluid swivels.

3. Apparatus as claimed in claim 1 or claim 2, further comprising a linkage between adjacent fluid swivel assemblies to maintain rotational alignment therebetween

4. Apparatus as claimed in any of claims 1 to 3, wherein the fluid swivel assemblies are mounted one on top of another.

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

6. 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.

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

8. Apparatus for transferring fluid substantially as hereinbefore described with reference to Figures 2-4.