GB2188998A - Modular swivel - Google Patents

Abstract

A modular swivel comprises at least two pivoted plates mounted in stepped relationship, the pivots being situated at the extremities and mid points of the plates. Each plate has at least one associated channel, the upper section of the channel in the lower plate communicating with the lower section of the channel in the upper plate through a swivel joint so that a clear path is formed through the swivel. The plates pivot on an axis which is coaxial with the axis of the swivel joint. The swivel may be used on mooring and loading buoys for tankers. <IMAGE>

Description

SPECIFICATION Modular swivel This invention relates to a modular, multipath, pressure swivel for use in connection with loading buoys.

Offshore loading buoys have been developed to allow a vessel to approach in any direction and to secure it to the buoy from the bows. The vessel is connected to the buoy by hoses through which it is either loaded or discharged, the vessel being able to revolve around the buoy.

Many offshore oilfields, and probably more in the future, will rely on subsea wellhead equipment with well production being taken via a loading buoy to a tanker.

In order to permit motion of a tanker relative to the buoy, such as weathervaning, or, conversely, driving back to a heading, it is necessary to provide swivels in the system.

Current swivels are bulky (up to 2.2 m in diameter), difficult to maintain and/or remove or replace. There are also problems with the seals of such units and these problems are likely to intensify since requirements are increasing for higher pressure capability, above 200 bar, and for gas handling. Their major advantage is that they allow full 3600 rotation and any multiple of this.

Alternative systems are possible using flexible hoses, or chicksan type pipework, etc.

These are smaller and easier to maintain and or replace than the above. They suffer from limited rotational capability, however, always less than 3600.

We have now devised a modular swivel in which the rotational capability is dependent on the number of modules present. Three or more gives a capability greater than 3600.

Thus according to the present invention there is provided a modular swivel comprising at least two pivoted plates mounted in stepped relationship, the pivots being situated at the extremities and the mid points of the plates, each plate having at least one associated channel, the upper section of the channel in the lower plate communicating with the lower section of the channel in the upper plate through a swivel joint so that a clear path is formed through the swivel, the plates pivoting on an axis which is coaxial with the axis of the swivel joint.

When only two plates are present the potential rotation will be somewhat less than 3600. When three or more plates are present, the potential rotation will be in excess of 3600.

More than one channel can be fitted into or onto each plate, the total number being limited by the space available in the plates and the corresponding number of swivel joints.

The pivoted plates may carry support wheels or rollers to assist in bearing their weight, thus removing much of the load from the swivels.

Associated pipework may be supported by a framework attached to the pivots with the swivel plates arranged along the centre line such that they can be maintained or replaced on an individual basis.

As a contingency measure, additional plates can be installed and locked in place by a quick disconnection system such as explosive bolts so that if a section jams, they can be brought into use.

The swivel possesses the following advantages when compared with previous swivels: 1. The seal area on the swivel joints is considerably reduced from greater than 1 metre to approximately pipe diameter.

2. Removal of#each swivel component can be achieved without removal of the others, or the whole unit, as at present.

3. It is possible to pig the lines if allowance is made for swept bends.

4. Current large diameter swivels are designed for up to 200 bar internal pressure, with considerable problems in trying to develop them to 350 bar.

The proposed system, with relatively small diameter swivels is capable of being designed for pressures of 350 bar and greater.

The novel swivel needs power assistance from the floating facility, or the assistance of another vessel to rotate it back to its heading and "unwind" the system when at the extent of its rotation. This is not seen as a major disadvantages, however.

The invention is illustrated with reference to Figs. 1 to 3 of the accompanying drawings, wherein Fig. 1 is a schematic diagram of a multi-path modular swivel, Fig. 2 is a detail of the swivel arrangement and Fig. 3 is a section of one type of swivel joint.

A multi-path modular swivel is built up from three plates 1, 2 and 3. Plate 1 is pivoted at pivots 4, 5 and 6, plate 2 at pivots 5, 6 and 7 and plate 3 at pivots 6, 7 and 8. In effect, plate 2 is hinged to both plates 1 and 3.

Plates 1, 2 and 3 support corresponding channels 9 and 10, 11 and 12, and 13 and 14 respectively. These meet at swivel joints 15, 16, 17, 18, 19 and 20.

The plates carry support wheels W1-W6 to assist in bearing their weight.

The diameter of the swivel is related to the pressure piping and its pressure rating, 30 cm being a typical figure.

The arrangement shown provides + 1 full - 2 full revolutions, i.e., three full revolutions in total.

A space 27, shown in Fig. 2, may be left between pairs of swivel joints such as 15 and 16 to provide access for maintenance.

The swivel joint illustrated in Fig. 3 comprises an upper section 21, and a lower section 22 with a bearing 23 between them so that one section can rotate relative to another.

An internal sleeve 24 retained in position by seals 25 provides a passageway between the entry line 26 and the exit line 27. A removable cap 28 is fitted to section 21 to provide access to the sealing assembly 24 and 25.

Claims (5)

1. A modular swivel comprising at least two pivoted plates mounted in stepped relationship, the pivots being situated at the extremities and mid points of the plates, each plate having at least one associated channel, the upper section of the channel in the lower plate communicating with the lower section of the channel in the upper plate through a swivel joint so that a clear path is formed through the swivel, the plates pivoting on an axis which is coaxial with the axis of the swivel joint.

2. A modular swivel according to claim 1 comprising three or more pivoted plates.

3. A modular swivel according to either of the preceding claims wherein two or more channels are fitted into or onto each plate.

4. A modular swivel according to any of the preceding claims wherein the pivoted plates carry support wheels or rollers.

5. A modular swivel as hereinbefore described with reference to Figs. 1-3 of the accompanying drawings.