GB2263256A

GB2263256A - A chain locker seal

Info

Publication number: GB2263256A
Application number: GB9300653A
Authority: GB
Inventors: Francis Lamond Crichton
Original assignee: HOULDER OFFSHORE ENGINEERING L
Current assignee: HOULDER OFFSHORE ENGINEERING L
Priority date: 1992-01-14
Filing date: 1993-01-14
Publication date: 1993-07-21
Also published as: GB9200718D0; GB9300653D0

Abstract

A chain locker seal (1) comprises sealing means (25) shaped to fit into sealing engagement with an anchor attachment means (55) and with a conduit (40) for the transfer of the anchor attachment means (55). The sealing means (25) thereby forms a substantially watertight seal between the anchor attachment means (55) and the conduit (40). Typically, the anchor attachment means may be a chain (55) and the conduit may be a spurling pipe (40). <IMAGE>

Description

"A Chain Locker Seal" This invention relates to a chain locker seal. In particular, the invention is applicable to the sealing of storage facilities for the anchor chains of a floating structure such as a semi submersible oil rig or a ship. These storage facilities are commonly known as chain lockers.

A conventional semi submersible oil rig relies on eight anchors (two at each corner) for maintaining its position relative to the well. These anchors are raised and lowered by windlasses on deck and the anchor chains are stored in a chain locker within each leg of the oil rig. The anchor chain is transferred from the chain locker to the windlass though a pipe commonly known as a spurling pipe, the opening of which at the windlass end is unprotected against water entry.

Therefore, any water entering the spurling pipe is transferred directly to the chain locker where it accumulates.

This causes problems of corrosion in the chain locker and more importantly, can adversely affect the stability of the oil rig since a leg with a chain locker partially filled with water will be heavier than one whose chain locker is empty, and may cause the rig to lean, thereby increasing the susceptibility of the partially filled leg to further water ingress. Thus the retention of water within a chain locker is highly undesirable.

According to the present invention there is provided a chain locker seal comprising a sealing means, shaped to fit closely with an anchor attachment means and with a conduit for the transfer of the anchor attachment means, thereby forming a substantially watertight seal between the anchor attachment means and the conduit.

The sealing means preferably comprises a rigid structure to which is most preferably attached a sealing material which may be deformable such as an elastomeric material although a non elastomeric material may alternatively be attached.

Typically, the sealing means comprises two such structures in the form of plates which preferably seal against opposite sides of the anchor attachment means.

The anchor attachment means is preferably a stud chain but alternatively may be a different shape of chain or steel hawser.

The conduit means for transfer of the anchor attachment means is preferably a spurling pipe.

Preferably, the sealing means is movable in and out of engagement with the anchor attachment means and conduit.

Preferably, the movement of the sealing means in and out of engagement with the anchor attachment means and the conduit is controlled by operation of means for moving the anchor attachment means, such as a windlass.

Hence, typically, the sealing means is out of engagement with the attachment means when attachment means is being moved and is in engagement with the attachment means when the attachment means is not being moved.

An example of a chain locker seal in accordance with the invention will now be described by way of example, with reference to the accompanying drawings in which: Fig. 1 is a half sectional elevation of a chain locker seal in a closed position; Fig. 2 is a plan view of the chain locker seal shown in Fig. 1; Fig. 3 is an end elevation of the chain locker seal shown in Fig. 1; Fig. 4 is a schematic diagram of a control system for the chain locker seal shown in Figs. 1 to 3; and Fig. 5 is an end elevation of a semi submersible oil rig showing some internal detail and embodying the chain locker seal shown in Figs. 1 to 3.

Figs. 1 to 3 show a chain locker seal 1 which comprises a housing 2 through which two shafts 5 extend. Each shaft 5 is connected to a torque unit 10 which powers its rotation and which is mounted on the external surface of the housing 2. From each shaft 5 extends a pair of cranks 15, each crank pair 15 being connected to a seal plate 25 by two connecting members 20, the joints between the connecting members 20 and the seal plates 25 and between the connecting members 20 and the cranks 15 allow rotation of the connecting members 20 relative to the seal plates 25 and the cranks 15 respectively. Each seal plate 25 comprises a generally rectangular plate 25 of stainless steel with a general semicircle of sponge rubber 30 attached thereto.

Movement of each seal plate 25 is powered by rotation of the shafts 5 by the torque units 10 and is transmitted by the cranks 15 and the connecting members 20. The movement of each seal plate 25 is restricted by tracks 85 which guide it from an open position (not shown) to a closed position as shown in Figs 1 and 2.

In use, the chain locker seal 1 is disposed across the diameter of a conventional spurling pipe 40 in a semisubmersible rig 60 (see Fig. 5). An aperture 45 is cut in the spurling pipe 40 to facilitate mounting of the chain locker seal 1. When a windlass 50 (see Fig. 5) is selected for use during raising or lowering of an anchor and a chain 55 is to be moved within the spurling pipe 40, the seal plates 25 are drawn back along the tracks 35 to the open position (not shown) such that the movement of the chain 55 relative to the seal plates 25 is unhindered by the seal plates 25.

When the rig 60 is anchored or underway and the chain 55 is stationary within the spurling pipe 40, the seal plates 25 are moved into a closed position as shown in Figs 1 and 2. The downward and inward movement of the seal plates 25 on-the tracks 35 forces the sponge rubber 30b against the lower edge 45b of the aperture 45 in the spurling pipe 40 and forces the sponge rubber 30a against a stud 55a of the chain 55. Additionally, in the closed position, the sponge rubber semicircles 30 on both seal plates 25 adjoin at 26; hence a substantially watertight seal is formed at the seal plates 25 and water ingress into the lower portion 40a of the spurling pipe 40 and the chain locker 70 is prevented. Water entering the upper portion 40b of the spurling pipe 40 drains through outlets 75 and is discharged overboard via a valve 80.

Operation of the chain locker seal 1 is controlled by a control system (see fig. 4). The power for the operation of the torque units 10 is provided by a compressed air supply 90 which is directed by solenoid valves 1001 The solenoid valves 100 are actuable from a switch 105 in a windlass control cabin 110 such that selection of the windlass 50 for use automatically closes switch 105 causing activation of the torque units 10 and opening of the seal plates 25.

Conversely, deselection of the windlass 50 causes closure of the seal plates. In the event of a main power supply failure, and the necessity for manual release of the anchor chain 55, switch 106 can be closed to power the solenoid valves 100 from an emergency source and air can be supplied from a standby air reservoir 91. Testing of the seal without operation of the windlass 50 can be carried out by closing switch 106 and operating switch 107.

Although the example of the invention described above is for use in semi-submersible rigs, the invention could also be used in any other floating structure such as ships, or other vessels.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1. A chain locker seal comprising a sealing means, to fit closely with an anchor attachment means and with a conduit for the transfer of the anchor attachment means, thereby forming a substantially watertight seal between the anchor attachment means and the conduit.

2. A chain locker seal according to Claim 1, wherein the sealing means comprises a rigid structure and a deformable sealing material mounted on the rigid structure.

3. A chain locker seal according to Claim 2, wherein the deformable sealing material comprises an elastomeric material.

4. A chain locker seal according to any of the preceding Claims, wherein the sealing means comprises two opposing sections which seal against opposite sides of the anchor attachment means.

5. A chain locker seal according to any of the preceding Claims, wherein the anchor attachment means comprises a chain.

6. A floating structure comprising a chain locker seal according to any of the preceding Claims, wherein the sealing means is movably mounted on the structure to move into and out of sealing engagement with the anchor attachment means and the conduit, and the anchor attachment means and the conduit being mounted on the floating structure

7. A floating structure according to Claim 6, and further comprising a control system to control movement of the sealing means into and out of sealing engagement with the conduit and the anchor attachment means.

8. A floating structure according to Claim 7, and further comprising drive means to move the anchor attachment means, the drive means controlling the control system.

9. A chain locker seal as hereinbefore described with reference to the accompanying drawings.

10. A floating structure as hereinbefore described with reference to the accompanying drawjn