WO2001081163A1

WO2001081163A1 - Floating vessel with pipeline attachment apparatus

Info

Publication number: WO2001081163A1
Application number: PCT/EP2001/003853
Authority: WO
Inventors: Jacob De Baan
Original assignee: Bluewater Terminal Systems, N.V.
Priority date: 2000-04-20
Filing date: 2001-04-04
Publication date: 2001-11-01
Also published as: AU6585901A; GB0009949D0; GB2361459A

Abstract

A floating vessel (10) is disclosed which includes dynamic positioning means operable to adjust the position of the vessel (10) in response to the action of wind, wave and current in order to substantially maintain a desired position. The vessel (10) also includes apparatus (11) for connecting the vessel (10) to a pipeline (18). The apparatus (11) comprises a connection member (12) attached to the vessel (10) and displaceable relative thereto. The connection member (12) is connectible to an end of the pipeline (18) to provide a fluid path between the pipeline (18) and the vessel (10). The connection member (12) is displaced in response to relative movement between the pipeline (18) and the vessel (10) to minimise loads imposed on the pipeline.

Description

FLOATING VESSEL WITH PIPELINE ATTACHMENT APPARATUS

The present invention relates to a floating vessel, such as an oil tanker, having improved apparatus for attaching a pipeline to the vessel for transmission of fluid between the vessel and the pipeline .

In UK patent application no. 9905617.8 an apparatus is disclosed which allows a floating vessel to move on the surface of the sea, only restrained by its anchoring system, such that it can never exert an unacceptably high strain on a flexible riser pipeline rising from the seabed and is attached to the vessel. This is achieved by placing an apparatus on the seabed to which a movable member is connected. A free end of the movable member is connected to a lower end of the flexible riser and the other end of the movable member, which is attached to the seabed apparatus, is connected to a seabed pipeline. The movable member shifts in position in response to loads placed on the flexible riser to increase the overall flexibility of the riser system and prevent the riser from being stretched beyond its design limits.

The disadvantage of this system is that because the apparatus is placed on the seabed its installation, maintenance, inspection and repair is complicated and expensive and the apparatus is only a cost effective solution in particularly shallow waters .

Accordingly, there is a need to provide some apparatus for connecting a riser to a vessel which limits the loads applied to the riser whilst making the apparatus easier to install and maintain.

There is also a need to provide a connection system which is suitable for so-called dynamically positioned vessels. Such vessels, as is well known in the art, have control and thrust means allowing the vessel to maintain a substantially constant position even under the action of varying wind, wave and current conditions. However, such dynamically positioned vessels are nevertheless prone to excursion drive-offs in heavy seaways as a result of power or propulsion failures. In such circumstances, the vessel can easily drift beyond the natural flexibility of the riser arrangement before power can be restored. Furthermore, when certain water depth/wave height ratios arise, it is impossible for a dynamically positioned vessel to maintain position within the design flexibility limits of the riser system unless an extremely expensive, and thus totally impractical, power and propulsion system is used.

The present invention provides a floating vessel comprising dynamic positioning means operable to adjust the position of the vessel in response to the action of wind, wave and current in order to substantially maintain a desired position, and apparatus for connecting a pipeline to the vessel, wherein the apparatus comprises a connection member attached to the vessel for displacement relative thereto, the connection member being connectable to an end of the pipeline to provide a fluid path between the pipeline and the vessel, wherein the connection member is displaced in response to relative movement between the pipeline and the vessel to minimise loads imposed on the pipeline. The connection member may be freely displaceable in response to relative movement of the vessel and the pipeline .

Alternatively, drive means may be provided, powered by sources on the vessel itself, to drive the displacement of the connection member.

In a first embodiment, the connection member comprises an arm having a first end rotatably mounted to the vessel and a second end protruding from the vessel for connection to the pipeline, whereby the arm is rotatable in response to movement of the vessel.

In a second embodiment, the connection member comprises a body mounted on the vessel for linear translation relative thereto. Such linear translation may be along one or more rails or tracks fitted to the vessel .

The body may have a first end translatably mounted to the vessel and a second end protruding from the vessel for connection to the pipeline.

Alternatively, the body may be mounted for translation within a slot extending substantially vertically through the hull of the vessel, whereby, in use, the pipeline rises up through the slot for connection to the body.

Preferably, the vessel further includes a disconnect facility between the connection member and the pipeline to allow for quick and easy connection and disconnection.

In a further embodiment, the connection apparatus may be combined with a swivel assembly operable to allow the vessel to align itself with the prevailing wind, wave and/or current conditions, in addition to relative displacements between the connection member and the vessel.

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

FIGURE 1 shows a first embodiment of the present invention;

FIGURE 2 shows a second embodiment of the present invention;

FIGURE 3 shows a third embodiment of the present invention; and

FIGURE 4 shows a further development of the first embodiment .

Figure 1 shows a typical dynamically positioned vessel 10, such as a oil tanker. As is well known in the art, the vessel 10 is provided with a control and propulsion system operable to selectively move the vessel 10 in the direction of arrows A and B in order to maintain the vessel in a nominally constant position despite the action of wind, wave and current which tends to shift the vessel to other positions.

In accordance with the present invention, the vessel 10 is also fitted with a connection means 11 for attaching a pipeline tothe vessel. In this first embodiment, the connection means 11 comprises an outrigger arm 12 extending laterally from the side of the vessel 10. In the figure, it is shown fitted approximately half way along the port side of the vessel but it will be clear to those skilled in the art that alternative locations are possible. The inboard end 14 of the outrigger arm 12 is rotatably connected to the vessel 10 for rotation about a substantially vertical axis in the direction of arrows C. The outboard end 16 of the outrigger arm 12 is connected to the upper end of a flexible pipeline 18, which in this example rises up from a seabed installation such as a well head 20. The outboard end 16 of the outrigger arm 12 is essentially aligned with the centre of the main upwardly extending part of the flexible pipeline 18. Depending on the amount of the displacement of the vessel 10, in spite of it trying to minimise this displacement by use of the dynamic positioning system, the outrigger arm 12 can rotate relative to the vessel 10 so as to keep the outboard end 16 substantially aligned with the flexible pipeline arrangement 18. In this way, the upper part of the pipeline 18 falls substantially vertically from the outrigger arm 12 and the loads imposed on the pipeline 18 do not exceed its design limits.

The outrigger arm 12 may be freely rotatable, within certain limits, in response to movement of the vessel relative to the pipeline 18. Alternatively, additional drive means, powered from the vessel, may be provided.

Figure 2 shows a second embodiment of the invention. In this embodiment, the rotating outrigger arm 12 is replaced by a sliding body 22 which is able to displace linearly in the direction of arrows D along a track or rail running along part of the deck of the vessel 10. A single rail 24 is shown in this case but two or more parallel rails, or any other convenient guide arrangement, could be used. The sliding body 22 has an inboard end mounted on the rail 24 and an outboard end protruding from the side of the vessel to which the upper end of the pipeline 18 can be connected. As before, the body 22 is displaced back and forth along the rail 24 in response to movement of the vessel 10 relative to the pipeline 18 so that the outboard end of the body 22 is maintained substantially coaxial with the pipeline 18. As in the first embodiment, the body 22 may be displaceable freely or with power assistance, and the position of the rail 24 on the vessel may be other than that illustrated.

Figure 3 shows a third embodiment of the present invention, having a similar principle to the second embodiment shown in Figure 2. However, in this case the sliding body 26 is displaceable within a slot 28 which extends substantially vertically right through the hull 30 of the vessel 10. In this case, a pair of parallel rails 24 is shown although once again any convenient guide arrangement may be used. In this case, the upper end of the pipeline 18 is not required to protrude above the surface of the water adjacent the vessel 10 but instead enters the slot 28 in the hull 30 beneath the vessel 10 and the water surface. This embodiment is particularly advantageous in ice covered water where otherwise the upper end of the pipeline 18 protruding from the surface of the water runs the risk of being damaged by floating ice.

Figure 4 shows the first embodiment as seen in Figure 1 with the additional feature of a disconnect facility 32 introduced between the connection member 11 and the pipeline 18. Any suitable disconnection facility may be used, preferably allowing simple, straightforward and fast connection and disconnection for maximum efficiency. The disconnect facility 32 is shown for use with the outrigger arm arrangement 12 but is of course equally applicable to the linearly displaceable connection members shown in Figures 2 and 3.

In a further embodiment of the invention (not shown) , the connection means may be combined with a fully revolving swivel assembly, as is well known in the art, such that the vessel may align itself with the prevailing wind, wave and/or current conditions, in addition to allowing relative displacement between the vessel and the connection means.

It will be apparent to those skilled in the art that by utilising the arrangement of the present invention a number of important issues can be resolved. Firstly, the power levels required to dynamically position a vessel in a given sea state can be reduced and, conversely, existing dynamically positioned vessels are enabled to work in much worse weather conditions, since the invention provides an improved degree of flexibility before unacceptably high loads are imposed on the riser pipeline 18. Secondly, since the connection means is mounted on the vessel itself it is much easier and cheaper to install, inspect and maintain.

Thirdly, a disconnect facility can be easily introduced between the connection member and the top of the flexible pipeline, which is above the water level, and hence it is easier to access, allowing speedy and simple connection and disconnection. This can be of particular interest in iceberg areas.

The skilled reader will appreciate that a number of modifications and variations to the precise details described could be incorporated in the present invention without departing from the scope of the invention.

Claims

CLAIMS :

1. A floating vessel comprising dynamic positioning means operable to adjust the position of the vessel in response to the action of wind, wave and current in order to substantially maintain a desired position, an apparatus for connecting a pipeline to the vessel, wherein the apparatus comprises a connection member attached to the vessel for displacement relative thereto, the connection member being connectable to an end of the pipeline to provide a fluid path between the pipeline and the vessel, wherein the connection member is displaced in response to relative movement between the pipeline and the vessel to minimise loads imposed on the pipeline.

2. A floating vessel as claimed in claim 1, wherein the connection member is freely displaceable relative to the vessel in response to relative movement of the vessel and the pipeline.

3. A floating vessel as claimed in claim 1, further comprising drive means to drive displacement of the connection member in response to relative movement of the vessel and the pipeline.

4. A floating vessel as claimed in any of claims 1-3, wherein the connection member comprises an arm having a first end rotatably mounted to the vessel and a second end protruding from the vessel for connection to a pipeline, whereby the arm is rotatable in response to relative movement of the vessel and the pipeline.

5. A floating vessel as claimed in any of claims 1-3, wherein the connection member comprises a body mounted on the vessel for linear translation relative thereto.

6. A floating vessel as claimed in claim 5, wherein the body is translatable along one or more rails or tracks.

7. A floating vessel as claimed in claim 5 or claim 6, wherein the connection member has a first end translatably mounted on the vessel and a second end protruding from the vessel for connection to a pipeline .

8. A floating vessel as claimed in claim 5 or claim 6, wherein the connection member is mounted for translation within a slot extending substantially vertically through the hull of the vessel, whereby, in use, the pipeline rises up through the slot for connection to the connection member.

9. A floating vessel as claimed in any preceding claim, further comprising a disconnect facility between the connection member and the pipeline .

10. A floating vessel as claimed in any preceding claim, further comprising swivel assembly in combination with the connecting apparatus, operable to allow the vessel to align itself with the dominating wind, wave and/or current conditions in addition to relative displacement between the connection member and the vessel.