GB2154276A

GB2154276A - Ball and socket joint for joining a tower carrying a surface platform to a foundation on the ocean floor

Info

Publication number: GB2154276A
Application number: GB08503100A
Authority: GB
Inventors: Heinz Gerhard Butt; Michael Vogt
Original assignee: Bilfinger und Berger Bau AG
Current assignee: Bilfinger SE
Priority date: 1984-02-17
Filing date: 1985-02-07
Publication date: 1985-09-04
Also published as: GB8503100D0; NO850602L; DE3405716C2; GB2154276B; SE8500734L; SE8500734D0; DE3405716A1

Abstract

A ball and socket joint for joining a tower carrying a surface platform to a foundation on the ocean bed has a bearing ring 10 having a tin-lead-bronze alloy as the sliding surface. The joint also has a torsion preventer in the form of a torsion-resistant pipe 8 extending through the joint inner area linked to an arrangement comprising fitted pins 14 with sliding pads 15 guided in slide chairs 9. The arrangement prevents any rotary movement of the tower base, but allows sloping positions. <IMAGE>

Description

SPECIFICATION Ball and socket joint for joining a tower carrying a surface platform to a foundation on the ocean floor The invention relates to a ball and socket joint, for joining a tower carrying a surface platform to a foundation on the ocean floor, the joint having a lower spherical cap ring fixed to a stop plate and an upper spherical cap ring mounted thereon and whose joint collar is embedded in the tower, the vertical and horizontal forces acting on the tower being transferred to the foundation by a spherical cap-like bearing ring arranged between the spherical cap rings.

Such joints are known inter alia from German Patent 2,549,859, where a PTFE layer is arranged in the contact region between the two joint parts. Despite the extra pressure lubrication provided, the PTFE sliding elements are subjected to wear making it necessary to periodically change the sliding elements a number of times during the life of the joint. The constructional measures for replacing the sliding elements and the actual replacement of said elements are very complicated.

According to German Patent 2,549,859, DE-OS 2,755,592 and DE-OS 3,132,711, the PTFE sliding elements of ball and socket joints are provided with an extreme pressure lubricating requiring the continuous operation of a lubricator which requires maintenance and the consumption and storage of a large amount of lubricant.

All three joints described in the aforementioned specifications are only able to remove moments around the vertical axis of the tower to a limited extent as a result of their design.

Moments of a considerable magnitude occur around the vertical axis as a result of the different application directions of wind, current and wave forces, non-uniform flow-round, unavoidable eccentric position of the centre of gravity of the operational means of the tower and the deck, together with possible eccentrically applied mooring forces.

Therefore, the present invention seeks to provide a ball and socket joint for joining a tower carrying a surface platform to a foundation on the ocean bed, which is relatively free from maintenance, which requires no permanently operating mechanical auxiliary means for the operation thereof and which can also transfer large forces and torsional moments.

According to the invention, we provide a ball and socket joint, for joining a tower carrying a surface platform to a foundation on the ocean floor, the joint having a lower spherical cap ring fixed to a stop plate and an upper spherical cap ring mounted thereon or therein and whose joint collar, in use, is embedded in the tower, the vertical and horizontal forces acting on the tower being transferred to the foundation by a spherical cap-like bearing ring arranged between the upper and lower spherical cap rings, the moments around the vertical axis acting on the tower being also transferred into the foundation by a torsion preventer arranged in the interior of the ball and socket joint level with the equator, in the form of pins with sliding pads guided in slide chairs, all the sliding faces which slide upon one another being provided with the same pairing of sliding materials formed by a low-friction tin-lead-bronze alloy produced by casting with incorporated solids agglomerates on one side and a stainless, polished material on the other side, the torsion preventer having a torsion resistant pipe connected to the joint collar and either the pipe carries the pins and the slide chairs are connected to the stop plate or the pipe carries the slide chairs and the pins are connected to the stop plate.

Further advantageous features of the invention can be gathered from the following description and claims.

We have found that as a result of the invention, all the kinetically functioning parts of the torsion preventer of the ball and socket joint can be continuously monitored in the dry and under atmospheric pressure, that larger horizontal vertical forces and torques around the vertical axis can be transferred than in the case of known joints, that the joint can be produced less expensively as a result of the simplified construction and that through the pressure adaptation in the interior of the ball and socket joint, no mechanical packings are required for normal operation.

The invention is described by way of example in greater detail hereinafter with reference to the drawings, wherein: Figure 1 is a perspective view of an embodiment of the invention; and Figure 2 a section through the embodiment according to Fig. 1 with a protective cylinder.

The ball and socket joint shown in Fig. 1 has a joint lower part 1, joined in fixed or uncouplable manner via a stop plate 3 to a foundation of a tower carrying a surface platform and located on the ocean floor. The stop plate 3 carries a cylinder 4 or a frustum having a lower sperical cap ring 5.

A joint upper part 2 and a joint collar 7 joined in shear-proof manner to the tower or are embedded in the tower base 20 in the manner visible from Fig. 2. The joint upper part 2 is formed from a spherical cap ring 6, which is connected to the joint collar 7. At the top, joint collar 7 is terminated by a not shown, pressure-proof manhole with a docking means 33 for a personnel lock or for a decompression or transfer chamber. At the bottom, the joint collar 7 is continued by a torsion-proof pipe 8, which passes into a widened base 34, which carries pins 14 form ing part of a torsion preventer assembly 13.

The pins 14 are arranged on diametrically facing points of the pipe base 34 and are shaped, inserted or screwed thereon, or are placed from above with the aid of mating parts in pin holders provided for this purpose.

The outer ends of the pins 14 remote from the torsion-resistant pipe 8 are introduced into sliding pads 15, which can be moved vertically up and down in fork-like slide chairs 9, but are secured by the latter against rotary movements about the vertical axis of pipe 8 and the joint collar 7. Thus, in the represented embodiment are provided two slide chairs 9, which diametrically face one another with respect to the base 34 and which are carried by stop plate 3 and are fixed thereto.

In another, not shown embodiment, the slide chairs are directly jointed to the lower part of the joint.

The bearing region 10 removing the horizontal and vertical forces is arranged on the lower spherical cap ring 5 above the ball and socket joint equator. It is formed by a lowfriction tin-lead-bronze alloy produced by casting and with incorporated solids agglomerates and which can contain an additional lubrication system suitably with silicone-free lubricants on one side and a stainless polished material on the other side.

Preferably the low-friction tin-leadbronze alloy is mounted on plates, which may suitably be of metal or plastics. The sliding material may be arranged on wedge-shaped plates with interchangeable parts.

The bearing surface is defined by the circumference and the height of the bearing region determined from the load. The bearings can optionally be adjusted by mechanical devices or hydraulically supported. In addition, the bearing can either be statically or hydrostatically constructed. The bearing ring 10 may be in one piece or comprise a plurality of segments which segments may be supported by interconnected hydraulic lift elements.

For the exceptional operating case of inspecting the joint inner area 19 under atmospheric conditions, a known paacking 11 is fitted above the bearing ring 10 to the lower spherical cap ring 5, and seals the latter against the upper spherical cap ring 6. Such stuffing box packings have already been tried out under offshore conditions and can be repacked by adjustment. Below the bearing ring 10, an expandable packing 12 is fitted to the lower spherical cap ring 5 and can be put into operation from the joint inner area 19, if working in the latter is to take place under atmospheric pressure, which is well below the external water pressure and is e.g. adapted to the air pressure on the earth's surface. For this purpose, the expandable packing can be proven multi-stage or redundant elements.

As has already been stated, the torsion preventer 13 has pins 14 arranged in the joint inner area 19 and which are positioned level with the equator of the spherical cap rings 5 and 6.

These pins 14 carry sliding pads 15 displaceable along the pin axis and which, even when the tower slopes, transfer forces to the slide chairs 9 and consequently to the stop plate 3 to which they are connected in torsion resistant manner.

Due to the torsion preventer 13, the pins 14 are stressed in single shear manner by the slide chairs 9. In another embodiment, in which a support is additionally provided and which is supported on stop plate 3, it is also possible to achieve double shear stressing of pins 14.

All the movable parts of the torsion preventer 13 can be inspected in the dry and/or under atmospheric pressure. According to another embodiment, the sliding pads 15 can act directly in the cylinder 4 of the joint lower part 1, so that there are no separate slide chairs 9 of the type shown in Fig. 1.

In another embodiment (not shown), the slide chairs are shaped onto the pipe base 34 or are positively connected thereto, whilst the cyliner 4 of the joint lower part 1 carries the pins provided with the sliding pads level with the equator of the spherical cap rings 5. 6.

However, for the satisfactory operation of the torsion preventer 13, it is always necessary for the axis of pins 14 to be in the equatorial plane of the spherical cap rings 5 or 6 in the normal state.

In a further embodiment (not shown), a press can be fitted in each slide chair 9 and is supported against the particular sliding pad 15. As a result, the ball and socket joint can be locked in the manner required in certain construction phases.

For the protection of any free sliding face of the joint upper part 2, the ball and socket joint is surrounded by a protective cylinder 21 according to Fig. 2, which is embedded in the normally concrete tower base 20, which is also connected to the joint upper part 2. In practice, the latter has additional shear ribs 35, which improve the force transfer from the tower base 20 to the joint upper part 2. In the perspective view of Fig. 1 the shear ribs 35 have been omitted so as to overburden the drawing.

The protective cylinder 21 shown in Fig. 2 extends from the lower edge of the tower base 20 in a downwards direction to about the equatorial plane of the ball and socket joint and in the vicinity of its lower edge carries a first circular flange 25, which is used for fixing the outer edge of a membrane 22.

The inner edge of the membrane 22 is fixed to a second circular flange 28, which is fitted to cylinder 4 and which is also located in the equatorial plane of the ball and socket joint.

Therefore, an inner space 32 is formed be tween the tower base 20 and the membrane 22 on the one hand and between the joint lower part 1 and the protective cylinder 21 on the other and is sealed against the sea water present beneath membrane 22 in Fig. 2. For example, for this purpose membrane 22 is a profiled steel sheet or made from reinforced rubber.

Protective cylinder 21 contains at least one underpressure valve 23 and at least one overpressure valve 24, which either ventilate or vent the inner area 32. The setting of the under or overpressure valves 23 and 24 can be selected in such a way that the pressure in inner area 32 is just above, just below or precisely level with the surrounding external water pressure. Moreover, inner area 32 an be filled with another suitable medium other than air, which obtains its necessary pressurization from the compressed air from the joint inner area 19.

In order to protect the portion of the joint lower part 1 which is in constant contact with the sea water, its cylinder 4 is corrosively protected by a protective coating 31 of an elastic material, such as e.g. rubber. For this purpose, the protective coating 31 extends over the outer wall of cylinder 4 from circular flange 28 to stop plate 3.

The inner area 19 of the ball and socket joint is constantly filled with compressed air during operation and its pressure corresponds to the external water pressure level with the equator of the joint. As a result, the external water pressure and the internal air pressure are in equilibrium. Mechanical packing members are not necessary for maintaining operation. Access to the joint inner area 19 is ensured by mans of a personnel lock, a decompression chamber of a transfer chamber through docking means 33 and whilst maintaining atmospheric pressure.

For operational reasons, it can occasionally be advantageous to fit the ball and socket joint in the reverse position. In this case, the external spherical cap ring is connected to the base member and the internal spherical cap ring to the rising structure, whilst all the other joint parts correspondingly change their position. As the construction of such a ball and socket joint is obvious to the expert as a result of the above description, there is no need to give any further explanation in this connection.

Claims

1. A ball and socket joint, for joining a tower carrying a surface platform to a foundation on the ocean floor, the joint having a lower spherical cap ring fixed to a stop plate and an upper spherical cap ring mounted thereon or therein and whose joint collar, in use, is embedded in the tower, the vertical and horizontal forces acting on the tower being transferred to the foundation by a spherical cap-like bearing ring arranged between the upper and lower spherical cap rings, the moments around the vertical axis acting on the tower being also transferred into the foundation by a torsion preventer arranged in the interior of the ball and socket joint level with the equator, in the form of pins with sliding pads guided in slide chairs, all the sliding faces which slide upon one another being provided with the same pairing of sliding materials formed by a low-friction tin-lead-bronze alloy produced by casting with incorporated solids agglomerates on one side and a stainless, polished material on the other side, the torsion preventer having a torsional resistant pipe connected to the joint collar and either the pipe carries the pins and the slide chairs are connected to the stop plate or the pipe carries the slide chairs and the pins are connected to the stop plate.

2. Joint according to claim 1, wherein the sliding material of the sliding material pair contains an additional lubrication system with lubricants.

3. Joint according to claim 2, wherein the lubricants are silicone-free.

4. Joint according to any one of the claims 1 to 3, wherein the sliding material formed from the tin-lead-bronze alloy produced by casting is mounted on plates.

5. Joint according to claim 4, wherein the plates are made from metal or plastics.

6. Joint according to any one of the claims 1 to 3, wherein the sliding material is arranged on wedge-shaped plates and has interchangeable parts.

7. Joint according to any one of the claims 1 to 6, wherein the torsion-resistant pipe is either connected in a fixed, nonpositive and gas-tight manner with the upper spherical cap ring or is connected to said upper spherical cap ring in a positive, but gastight manner as a result of the fitting of a packing.

8. Joint according to any one of the preceding claims wherein the slide chairs are integrated into the spherical lower cap ring.

9. Joint according to any one of claims 1 to 7, wherein for better definition of the forces to be removed and the resulting stresses, the slide chairs are installed as independent components on the stop plate.

10. Joint according to any one of the claims 1 to 9, wherein the sliding pads and the pins can be removed from the construction.

11. Joint according to any one of the claims 1 to 10, which can be sealed against the foundation and against the tower in gastight and pressure-proof manner and is accessible via a personnel lock connectable to a manhole, or a decompression or transfer chamber.

12. Joint according to any one of the claims 1 to 11, wherein during operation in the interior thereof, a pressure may be applied which corresponds to the external water pressure, a monitoring system for checking the pressure level being installed and an automatically controlled supply system for compressed air being provided.

13. Joint according to any one of the claims 1 to 12, wherein for exceptional operating states and for redundancy, above the bearing ring is provided a packing and below the bearing ring is provided an expandable packing.

14. Joint according to any one of the claims 1 to 13, wherein the bearing ring is connected to the lower spherical cap ring and is jointly spherically worked therewith.

15. Joint according to any one of the claims 1 to 14, wherein the pins can be locked in the slide chairs by means of hydraulic presses set in slideways of the slide chairs.

16. Joint according to any one of the claims 1 to 15, wherein the spherical capshaped bearing ring is in one piece.

17. Joint according to any one of the claims 1 to 16, wherein the bearing ring comprises a plurality of segments.

18. Joint according to claim 17, wherein the segments of the bearing ring are supported by interconnected hydraulic lift elements.

19. Joint according to any one of the claims 1 to 18, wherein if required, the connection of stop plate to the foundation can be broken and restored again.

20. Joint according to any one of the claims 1 to 19, wherein in order to additionally protect the joint against continuous contact with sea water, a protective cylinder secured in the tower base is arranged concentrically round and in a spaced manner from the joint and is connected to the latter level with its equator by means of a flexible membrane, for example formed from shaped sheet steel or reinforced rubber and is filled with compressed air, which is freely linked with the compressed air in the interior of the joint.

21. Joint according to claim 20, wherein the pressure in the inner area between the inner wall of the protective cylinder, the outer wall of the joint and the tower base as well as the membrane is kept just above, just below or precisely level with the surrounding exter nal water pressure by overpressure or under pressure valves.

22. Joint according to claim 21, wherein the said inner area is filled with another suitable medium other than air and its necessary pressurization is obtained from the com pressed air from the interior of the joint.

23. Joint according to any one of the claims 1 to 22, wherein the remaining portion of the joint which is in constant contact with the sea water is protected against corrosion by a protective coating of elastic material, such as e.g. rubber.

24. A ball and socket joint, for joining a tower carrying a surface platform to a foundation on the ocean floor, substantially as shown in the accompanying drawings and described herein with reference thereto.