GB2125864A

GB2125864A - Seabed anchorage means of an offshore structure

Info

Publication number: GB2125864A
Application number: GB08318379A
Authority: GB
Inventors: Werner Rank
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1982-08-20
Filing date: 1983-07-07
Publication date: 1984-03-14
Also published as: NL8302379A; NO832995L; DE3230937C1; JPS5934396A; GB8318379D0; FR2569155A2

Abstract

A pedestal joint (3) for the connection of a supply tower (1) of an offshore structure with a foundation (2) anchored in or at the seabed comprises an inner ball element (4) and an outer socket (6). The ball element (4) is firmly connected by way of a neck (5) with the tower (1) and is mounted on support bearings (11) in the socket (6). The sealing of the ball element (4) relative to the socket (6) is effected by means of a stuffing box (19). A seal (31) is additionally arranged at the upper end of the collar (13) and comes into effect through upward displacement of the ball element (4). A pressure lock (33) arranged at the neck (5) enables inspection of a space (32), filled with compressed air, underneath a bell (20) fastened to the neck (5). <IMAGE>

Description

SPECIFICATION Seabed anchorage means of an offshore structure The present invention relates to seabed anchorage means of an offshore structure, and has particular reference to a pedestal joint for the connection of a movable supply tower of an offshore structure with a component which is constructed as foundation and anchored in or at the sea bed.

The interior of a pedestal joint described in German (Fed. Rep.) Patent Application P 31 32 711.7-24 is protected against influences at the seabed by a diving bell, which is arranged in its upper region and which, in conjunction with a collar of a cover ring of a socket of the joint and an air cushion present between the bell and the collar, forms a water barrier. The sealing of the air space, which stands under a pressure corrsponding to the water depth, is provided by a readjustable stuffing box arranged between a movable spherical part of the joint and the stationary cover ring. A complete renewal of the stuffing box packing is not possible, as the air cushion would then be lost and water wouid flow in. There is therefore scope for increase in the operational reliability through improved possibilities of maintenance and inspection.

According to the present invention there is provided seabed anchorage means of an offshore structure, comprising a ball element connected by a neck to the foot of a support tower of the structure, a socket receiving the ball element to be angularly movable in all directions relative thereto and comprising a casing provided with a base plate mounted on a foundation and with a part-spherical collar extending around the ball element at a spacing therefrom, bearing means arranged in the socket to slidably support the ball element, coupling means intercoupling the ball element and socket, the coupling means being movable in all directions about the centre of the ball element and adaptable to permit upward displacement of the ball element relative to the socket, first sealing means to close off the interior of the casing from the space between the collar and the ball element, second sealing means arranged at the upper end of the collar and effective to close off said space when the ball element is upwardly displaced, and a bell extending around part of the ball element to provide an air space therebetween accessible from within the anchorage means.

In a preferred embodiment, a ball joint is arranged between the foot of the tower and the foundation, is pivotable to all sides and is sealed off against ingress of water. The ball element which is fastened in or at the foot of the tower by way of the neck, of this joint is mounted in the socket, which is firmly anchored on the foundation, and is held together with the socket by means of a tension member movable to all sides about the centre of the ball joint The socket is constructed as cylindrical casing shell with a foot plate firmly connected with the foundation, and several support bearings are arranged within the casing, the ball element sliding on the bearings.Arranged on the casing shell is a cover ring with a collar, which is constructed as a spherical zone and closes off the ball joint except for a residual gap which is sealed off from the interior of the casing by a stuffing box. The gap between the ball element and the collar is additionally closable by means of a seal arranged at the upper end of the collar and through displacement of the spherical joint part in its vertical axis upwardly against the seal, and the space between the spherical joint part and the bell, which partially encompasses the ball joint, is accessible from the inside. For inspection and for maintenance of the stuffing box, the ball element can be displaced through resetting of the tension member in its longitudinal direction and through adjusting the bearings until the ball element bears against the seal.In order to assure the functional capability of this seal even during pivotal movement of the ball element, it is advantageous if an encircling guide ring, in which a sealing ring consisting of resilient material and resistant to sea water is securely mounted against displacement, is arranged at the collar. The space, standing under air pressure, between the ball element and the bell is conveniently accessible to a diver through a pressure lock present at the neck underneath the connection of the bell.

An increase in the operational reliability of such an anchorage means may result from the fact that the space between the spherical joint part and diving bell is now accessible and a second sealing means is present. The sealing ring of this sealing means consists of a finite profile and can therefore be readily exchanged by contrast with known infinite hollow body seals.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a sectional view of a pedestal joint embodying the invention.

Referring now to the drawings, there is shown anchorage means in the form of a pedestal joint 3 which consists of an inner spherical part 4 and an outer socket 6. The part 4 is firmly connected by neck 5 with a supply tower 1 of an offshore structure and is mounted in the socket 6 on support bearings 11. The socket 6 consists of a cylindrical casing shell 8, which is connected by a foot plate 9 with a foundation 2, and a cover ring 12 with an adjoining collar 1 3. Connection of the part 4 to the socket 6 is effected by way of a tension member 7, which is anchored at one end to the base plate 9 on the foundation 2 and fastened at the other end in the foot of the supply tower 1 to be displaceable in its longitudinal direction.

Sealing of the part 4 relative to the socket is primarily effected by means of a stuffing box 1 9.

In addition, a seal 31, which comes into effect on upward axial displacement of the part 4, is arranged at the upper end of the collar 13. The displacement of the part 4 takes place through resetting the tension member 7 and adjusting the support bearings 11, which have bearing shells which are hydraulically adaptable so as to always contact the surface of the part 4 with the same contact pressure. Consequently, the functional capability of the entire bearing system is not interrupted at any instant and maintenance of the stuffing box 19 can be performed when the seal 31 is effective.

A bell 20 is connected to the neck 5 and partially encompasses the part 4 and the collar 13 so as to provide a space 32, which is accessible for inspection purposes by a diver, access being by way of a pressure lock 33 in the wall of the neck 5.

Claims

1. Seabed anchorage means of an offshore structure, comprising a ball element connected by a neck to the foot of a support tower of the structure, a socket receiving the ball element to be angularly movable in all directions relative thereto and comprising a casing provided with a base plate mounted on a foundation and with a part-spherical collar extending around the ball element at a spacing therefrom, bearing means arranged in the socket to slidably support the ball element, coupling means intercoupling the ball element and socket, the coupling means being movable in all directions about the centre of the ball element and adaptable to permit upward displacement of the ball element relative to the socket, first sealing means to close off the interior of the casing from the space between the collar and the ball element, second sealing means arranged at the upper end of the collar and effective to close off said space when the ball element is upwardly displaced, and a bell extending around part of the ball element to provide an air space therebetween accessible from within the anchorage means.

2. Anchorage means as claimed in claim 1, the second sealing means comprising a guide ring encircling the ball element, and a sealing ring mounted in the guide ring to be secure against displacement relative thereto and comprising a resilient material resistant to salt water.

3. Anchorage means as claimed in either claim 1 or claim 2, comprising a pressure lock arranged in the neck below a connection of the bell to the neck and operable to enable access to the air space.

4. Seabed anchorage means of an offshore structure, the anchorage means being substantially as hereinbefore described with reference to the accompanying drawing.