GB2251907A - Power actuated releasable connector for pressure containing bores - Google Patents

Abstract

A releasable connector for pressure containing bores, particularly connections used for subsea drilling and oil or gas production, has independent, powered actuating mechanisms for its locking and pre-loading functions. The locking may be effected by locking dogs 6, collet fingers or a spring ring cooperating with a groove, and the pre-loading by tension bolts 7. Both mechanisms may be operated hydraulically, the locking using a low and the pre-loading a high pressure. For locking, the connector is first locked and then pre-loaded, for unlocking, the preloading is released first, but the unlocking mechanism has sufficient power to release the lock even if the pre-loading release mechanism fails. <IMAGE>

Description

CONNECTOR FOR PRESSURE CONTAINING BORES This invention relates to connectors for joining components of pressure containing bores. The term "connector" includes any form of pressure tight joint between components.

To make up joints for pressure containing bores quickly without the need for manual action, rotation or torque, various types of connectors have been devised. The need for effective connectors occurs particularly in the oil industry, especially for subsea drilling and oil or gas production.

Two types of connector are in common use. These are (a) hydraulic locking mechanisms that simultaneously apply a locking and pre-loading force on make up, and (b) flange systems that use hydraulic bolts.

These can be described as follows: Hydraulic Locking and Pre-Loading Connectors In this type of connector, the locking mechanism may be locking dogs or collet fingers or a spring ring driven hydraulically by a set of individual pistons or an annular piston. As the piston or pistons are energised the dogs, collet fingers or ring are latched.

The piston or pistons, which may be vertical or horizontal, drive against a tapered face giving a horizontal force on the dogs, collet fingers or ring pushing them into a tapered groove to effect locking. The use of a tapered groove means that, simultaneously, a vertical force is generated that pre-loads the connectors.

Advantages - One hydraulic action latches the connector and achieves a preloading locking force.

- Only a low hydraulic pressure (ca. 1,500 psi) is required.

- Only two hydraulic lines, a latch and lock line and a release line, are necessary, although, as a safety measure, a secondary line may be added to guard against control line failure.

Disadvantages - Although only a low hydraulic pressure is required, this, in turn, implies a large piston area and hence a large hydraulic cylinder volume.

- The pre-load force is dependent solely on the friction of the dog/collet/ring in the tapered groove and the piston action against the tapered face that energises the locking system.

- The friction force on the tapered face has to be relied on to hold the connector locked when the hydraulic pressure is released.

- If the friction alone is not considered satisfactory an additional locking system is required (eg a drilling connector could release due to drilling vibrations or a production connector due to the vibration when producing oil and gas).

Bolt Tensioning Systems These systems use the technique of tensioning a number of bolts hydraulically so that the nuts can be made up with a minimum of torque. When used underwater, divers have to be employed to tighten the nuts.

Once the nut is made up, the hydraulic piston unit used for tensioning is removed.

This type of system is commonly used for connecting pipeline flanges using divers and does not provide a quick-release connection.

Advantages - A pre-set uniform tension is applied to the bolts.

- A positive locked up clamping force is achieved.

Disadvantages - Each nut and bolt has to be tightened individually.

- Requires human assembly and adjustment.

Connector According To The Present Invention According to the present invention a connector for joining components of pressure containing bores, particularly connectors used for subsea drilling and oil or gas production, having both releasable locking and pre-loading functions is characterised in that the locking and pre-loading functions have independent, powered actuating mechanisms.

The releasable locking mechanism may comprise locking dogs, collet fingers or a locking spring ring on one component of the connector cooperating with a groove on the other component. The dogs, collet fingers or spring ring (hereafter called for convenience the locking latch,) may be actuated by a hydraulic.

cylinder and piston. A low hydraulic pressure (eg 500 to 4000 psi) should be adequate for this function.

Although a hydraulic pressure actuating system is preferred the actuation may be electrical, or electro-hydraulic (eg electrical actuation of a closed hydraulic system).

The actuating system may have a mechanical override, at least for unlocking, to guard against hydraulic (and/or electrical) failure.

The pre-loading function may comprise a set of tension bolts passing through the cap of the connector. The tensioning of the bolts is, according to the present invention, effected separately from the locking function and is power operated, thereby avoiding the need for manual diver operation which has been a drawback of other bolt tensioning systems.

The power operation for tensioning is preferably hydraulic using a high pressure hydraulic supply (eg 7000-10000 psi). It may act on separate pistons fixed to one end of each bolt or it may act on a single annular piston fixed to all of the bolts. The power only has to pre-stress the bolts with minimal physical movement, so that only a small volume of high pressure hydraulic fluid will be required. The actuation may be by direct hydraulic pressure or an electro-hydraulic system.

Once tensioned the bolts may be locked up by rotating a tension screw. The system that carries out this operation may be powered by a hydraulic motor or actuated mechanically by a ROV and may comprise a gear or rotating ring driven by the power source, a drive gear, a clutch and a drive bushing The system may have both a hydraulic motor and a mechanical override operable by a ROV to guard against a malfunction of the hydraulic system.

The reason for a set of clutch nuts/bushings is to ensure that each tension bolt is made up to the same torque. When a tension bolt is made up to a pre-set torque, the clutch drive bushings will slip allowing the remaining bolts to reach their torque. (This is set by the properties of a clutch drive nut spring.) When all the torque screws reach their preset torque, all the clutch drive plates will slip resulting in the spinning of the rotation ring. Once this is achieved the power supply can be stopped and the hydraulic tensioning pressure released.

The locking operation comes first, followed by the tensioning operation, whereupon the connector is fully mechanically tensioned up and locked, irrespective of whether the power supply to either or both operations is maintained or not, eg whether the hydraulic pressure remains or is vented off. The system does not rely on any friction factor to remain locked.

As previously indicated, both the locking and pre-tensioning functions are releasable, and to unlock a connector the sequence is reversed, ie the tension is first released on the bolts and then the locking latch is unlocked.

The hydraulic tensioning system and mechanical transmission to lock up the bolts is, therefore, preferably reversible to release the tension, and the locking latch system also has to be capable of being reversed under power. Preferably, as a precaution, the effective power supply to unlock the latch system is such that the latch system can be unlocked even if the tension on the bolts has not been released, eg if there has been a failure in the power supply to the tensioning system. In the case of a hydraulic lock-unlock system there may be separate hydraulic pistons for the locking and unlocking actions. The unlock hydraulic piston may have a larger surface area than the lock hydraulic piston so that the force available for unlocking is sufficient even if the connector is still tensioned.Alternatively, there may be a secondary unlock piston in addition to the normal unlock piston, again with a surface area sufficient to permit unlocking even if the connector is still tensioned. Such a secondary unlock piston allows unlocking even if there has been damage to the normal lock-unlock hydraulic system and it may be actuated by a higher hydraulic pressure than the normal piston.

The invention is illustrated with reference to the accompanying drawings in which, Figure 1 is a part-sectioned view of the connector according to the present invention, the left hand side of the drawing showing the connector unlocked and untensioned, and the right hand side showing it locked and tensioned, Figure 2 is a half section along the line A-A of Figure 1, with, again, the left hand side showing, the connector unlocked and the right hand side showing it locked, Figure 3 is a flow diagram of a hydraulic system for use with the connector of Figures 1 and 2, and Figure 4 is a section through an accumulator and indicator for the hydraulic tensioning system of the connector of Figures 1 and 2.

Figures 1 & 2 show a typical hub and cap connector for an undersea well head, although it is to be understood that the present invention may be used to join any two components of pressure containing bores, eg hub and cap joints, flange joints, or any other form of joint.

In Figures 1 and 2, a hub 3 is shown as part of a well head with a releasable cap 4 positioned on it. Hub 3 has a groove 5 on its outer periphery and cap 4 has a series of locking dogs 6 capable of being moved horizontally into groove 5 to lock the cap to the hub.

A series of tension bolts 7 extend up through the cap, some of the bolts 7A being positioned between dogs 6 and some 7B passing through dogs 6, the passages 8 through the dogs being elongated to allow the dogs to move without affecting the bolts.

Hub 3 and cap 4 have the usual pressure seal 9 and seal retention piston 10 at the centre to seal the connecting bores, this being conventional and not forming part of the present invention.

Cap 4 has means for locking and unlocking dogs 6 in groove 5 and also means for tensioning bolts 7.

Describing first the dog lock-unlock mechanism, this has dog latching ring 11 with a stepped tapered interior face 12 capable of bearing on a corresponding stepped, tapered exterior face 13 of dogs 6 so that vertical downward movement of ring 11 effects horizontal inward movement of dogs 6. This arrangement of tapered surfaces does not, however, produce any tensioning of the connector as it does with the prior art combined locking and tensioning systems.

Downward movement of ring 11 to lock the connector is effected by latching piston 14 bearing in the top of ring 11, the piston in its turn being moved by hydraulic pressure applied to its top through inlet 15. The space between the main body 16 of cap 4 and a surrounding cylindrical outer plate 17 forms a hydraulic cylinder 18.

Upward movement of ring 11 to unlock the connector is effected by a second dog retracting piston 19 which bears through its extension 20 on the underside of ring 11.

Upward movement of retracting piston 19 is effected by hydraulic pressure applied to the underside of piston 19 through inlet 21. Hydraulic cylinder 22 within which piston 19 slides is bounded by lower body 23 of the cap and cylindrical outer plate 17.

A further secondary unlock piston 24 is positioned within cylinder 22 below retracting piston 19 with a further inlet 25 below it.

It will be seen that the surface area of retracting piston 19 is considerably greater than that of latching piston 14 so that, for the same hydraulic pressure a much greater unlocking force can be applied. As will be discussed hereafter the tensioning system is capable of being released before unlocking, but the surface area of retracting piston 19 is such that dogs 6 could be unlocked even if the tension on the connector had not been released. Secondary unlock piston 24 is similar in size to retracting piston 19. Its separate inlet 25 allows it to be subjected to a greater hydraulic pressure than piston 19 (eg the high pressure hydraulic supply described hereafter for the tensioning system) thereby further increasing the potential force available for unlocking in the event of a failure to release the tensioning system.

The fact that faces 12 and 13 are both tapered and stepped means that latching ring 11 only has to be forced up by one vertical step against the tension in the connector to remove this pre-load tension and free latching dogs 6. Thereafter a normal unlock hydraulic pressure will be sufficient to complete the upward movement of latching ring 11 and complete the freeing of latching dogs 6.

All the moving parts of this lock-unlock hydraulic system and any potential points of leakage have seals indicated in the drawing by solid shading, the type and number of seals following recommended conventional practice for the hydraulic pressure involved, which may be moderate, eg 1000 psi for the normal unlock system. The pressure on secondary unlock piston 24 may be up to 10,000 psi with correspondingly stronger seals.

Finally, in the lock-unlock system dog latching ring 11 may have an external indicator rod 26 attached to it so that the position of the ring and hence whether the connector is locked or unlocked can be monitored by, eg, an underwater TV camera on a ROV.

Alternatively an electrical sensing system could be used for monitoring.

Turning now to the tensioning system, bolts 7 extend up from lower body 23 of cap 4 to the main body 16. The inner surface of lower body 23 contacts hub 3 vertically and the main-body 16 contacts the top of hub 3 vertically through pressure seal 9. These two contact points provide lower and upper guidance surfaces between hub 3 and the lower and main bodies of cap 4. The top of bolts 7 have an annular tension piston 27 fixed to them, this piston being within an annular hydraulic cylinder 28 bounded by main body 16 of the cap and tension plate 29. There is a hydraulic inlet to cylinder 28 (not shown) below tension piston 27 and seal 30 around bolt 7 prevents leakage and hydraulic fluid down the bolt. Other seals are indicated by solid shading in the drawing to ensure that the hydraulic tensioning system is fluid tight.

Latching dogs 6 are between lower body 23 and main body 16 of the cap, the two bodies being separate but held together by tension bolts 7. It will be seen, therefore, that upward hydraulic pressure on tension piston 27 will tend to move lower body 23 upwardly to squeeze latching dogs 6 and force their upper surfaces firmly against the underside of groove 5. The top inner face of groove 5 is tapered to conform with conventional systems and to ease the release of dogs 6, but it is the tension in bolts 7 which provides the pre-loading force and not just the functional force between dogs 6 and groove 5.

Although a single annular piston 27 attached to each bolt 7 is shown, it will be appreciated that this single annular piston could be replaced by separate pistons for each bolt, each separate piston having its own separate hydraulic cylinder.

Tension piston 27 has internally screw threaded holes in its top into which fit externally screw threaded locking bolts 31.

There is a hole and locking bolt 31 above each tension bolt 7.

Locking bolt 31 may be rotated by a clutch drive mechanism indicated generally at 32.

Clutch drive mechanism 32 has hollow tension plate 29 within which is a floating socket or drive bushing 33 surrounded by coil spring 34. Spring 34 forces socket 33 into contact with planet gear 35 through slip clutch 36. Surrounding the planet gears 36, of which there is one for each tension bolt 7, is a circular ring forming a sun gear ring 37, the inner gear teeth of which mesh with the external teeth of each planet gear 35. The gears are protected by a cover plate 38. The sun and planet gears may be immersed in oil and gear cover plate 38 has a connection 39 for a pipe leading to an accumulator to take the oil which will be displaced when bolts 7 are tensioned. This accumulator and its use as a tension indicator will be described in more detail hereafter with reference to Figure 4.

Sun gear 37 can be driven through angled gearing within casing 40 on top of cover plate 38, this gearing being driven by a hydraulic or electric motor (not shown) or manually by a ROV (not shown).

Figures 1 and 2 show the main features of the connector.

Additional items which may be desirable but are not shown are: - A hydraulic or electric drive motor for the clutch drive mechanism.

- A mechanical unlock override system that connects onto dog latching ring 11, driven by a screw drive rod using an ROV torque spigot.

In operation, cap 4 is placed over hub 3 with the parts in the positions shown on the left hand side of Figure 1. As previously indicated the hub and cap may form part of any desired connector but, typically, the hub may be part of a sub-sea well head and the cap part of a drilling or oil or gas production module sitting on the well head.

With the hub and cap properly positioned the locking sequence is initiated by admitting hydraulic fluid at eg 1000 psi through inlet 15 to cylinder 18 to force down latching piston 14 onto latching ring 11, which is moved downwardly so that its tapered, stepped face 12 acts on the tapered, stepped faces 13 of latching dogs 6 pushing them into groove 5. Any hydraulic fluid in cylinder 22 can be vented back to the control system. It will be noted that the locking movement of piston 14 is downward while the tensioning movement of piston 27 is upward. Latching pressure remains during tensioning and is unaffected by it.

Dogs 6 will be positioned within groove 5 and the hydraulic pressure is maintained to hold them there.

The tensioning of bolts 7 is then effected by admitting hydraulic fluid under high pressure, typically 7500 psi, to the bottom of cylinder 28 and the underside of tension piston 27. This draws lower body 23 up towards main body 16 squeezing dogs 6 and forcing their top faces firmly against the underside of groove 5.

The tapered top surface of groove 5 will force dogs 6 firmly against latching ring 11, which will act as a collar due to the vertical portions of the tapered, stepped faces of the dogs 6 and the latching ring 11. The dogs 6 are thus firmly locked prior to locking up tensioning bolts 7. The high hydraulic pressure is maintained to hold the tension and bolts 7 are then locked up. Sun gear ring 37 is rotated through gearing within casing 40 either mechanically by a ROV or hydraulically by a hydraulic motor, which may be driven from the low pressure hydraulic system used to move latching dogs 6. Alternatively an electric motor could be used.

Rotation of sun gear 37 rotates planet gears 35, which, in turn, through slip clutches 36 rotate floating sockets 33 and locking bolts 31, screwing these down into tension piston 27. The high hydraulic pressure is holding tension bolts 7 under tension so the torque required is governed by the strength of coil spring 34 which is compressed as floating socket 33 rotates. Only a relatively low torque will be required, the main purpose of the slip clutches 36 being to ensure that the same torque is applied and each tension bolt is under the same tension. Each clutch 36 will slip when the required torque has been reached. Bolts 7 will then be firmly held by tension plate 29 through locking bolt 31 and tension piston 27.

When all the tension bolts 7 have been locked up uniformly the high hydraulic pressure to the tension bolts and the low hydraulic pressure to the latching dogs can be released. The fully locked and tensioned connector is as shown on the right hand side of Figure 1.

For unlocking the sequence is reversed. High pressure, typically 10,000 psi, is applied again to cylinder 28 and the bottom of tension piston 27 relieving the load in the locking bolts 31.

Sun gear 37 is rotated in the opposite direction to that for tensioning to unscrew locking bolts 31 to their unlocked position.

Pressure in cylinder 28 can now be released, allowing tension piston 27 to move down and release the tension in bolts 7. Once the tension has been relieved in all the bolts, low hydraulic pressure, typically 1000 psi, can be applied to the underside of retracting piston 19 through inlet 21, so that piston extension 20 pushes on latching ring 11 and moves it to its unlocked position. The top side of retracting piston 19 is angled with a profile 41 corresponding to the underside of each latching dog. The profile of the retracting piston contacts the latching dogs as the piston reaches the top of its travel and frees the dogs from groove 5. The cap components have thus been returned to their unlocked positions allowing the module containing the cap to be lifted from the hub module.

If by any chance there is a failure of the high pressure hydraulic supply or a failure of any part of the clutch drive mechanism 26 so that bolts 7 cannot be untensioned, retracting piston 19 can still be pushed up by the low pressure hydraulic system lifting latching ring 11 and bringing piston 19 into contact with the underside of latching dogs 6. The surface area of piston 19 is chosen such that, at the hydraulic pressure used, the force is sufficient to move dogs 6 free of groove 5 against the tensioning force of bolts 6. The module containing the cap can thus still be lifted off, but there may be some risk of damage to the dogs so this procedure should only be used in an emergency.

If there is a failure of the low pressure hydraulic supply and/or a failure of part of the tensioning system, then secondary unlock piston 24 can be brought into play by applying high hydraulic pressure through inlet 25. A very powerful force is available to unlock the connector even if the tensioning system remains locked, but again, such a procedure should only be used in an emergency because of the risk of damage. As previously explained, the fact that faces 12 and 13 of latching ring 11 and dogs 6 are both tapered and stepped, means that latching ring 11 only has to be forced up by one vertical step against the tension. Thereafter normal unlock pressure will be adequate.

Figure 3 shows the main items of the cap of Figures 1 and 2 diagrammatically and the hydraulic and mechanical systems for locking and unlocking the connector both in normal operation and in any emergency.

Parts already described in Figures 1 and 2 have the same reference numerals. Additional parts not previously described are inlet 42 to tension cylinder 28 to apply pressure to the underside of tension piston 27, hydraulic motor 43 for actuating tensioning mechanism 32 (on the left of the drawing) and a mechanical override 44 for mechanism 32 operably by a ROV (on the right of the drawing).

The hydraulic system is shown diagrammatically on the far left of the drawing. In practice this will be in the running tool for landing the module having cap 4 which is to be locked to the module having hub 3. The hydraulic fluid supply may be through an umbilical 45 with two low pressure hydraulic lines 46, 47 leading respectively to cylinder 18 holding latch piston 14 and to cylinder 22 holding retracting piston 19 and two high pressure lines 48, 49 leading respectively to cylinder 28 and tension piston 27 and to inlet 25 below secondary unlock piston 24. The secondary unlock cylinder may also have an inlet 50 (see right hand side of drawing) allowing high pressure hydraulic fluid to be supplied directly to the underside of secondary unlock piston 24 by a ROV.

A branch 51 for latch piston line 46 and a branch 52 from retracting piston line 47 lead through pressure control valves 53, 54 to either side of hydraulic motor 43. Motor 43 can be driven in either direction, line 51 driving it to make up locking bolts 31 and line 52 to release them.

The method of locking and unlocking the connector has already been described with reference to Figures 1 and 2 and Figure 3 shows how the various hydraulic pressures are supplied and coordinated.

For locking, low pressure fluid is supplied through line 46 with line 47 being vented so that dogs 6 can be moved into groove 5. No fluid flows down branch line 51 until a set pressure is reached in line 46. This is only achieved when latching piston 14 has been fully stroked and the volume of fluid is fixed. High pressure fluid through line 48 then tensions bolts 7. Pressure control valve 53 in branch line 1 is set so that a step increase in the low pressure fluid supply operates motor 43 and drives clutch drive mechanism to take up the slack unlocking bolts 31 and thus to hold the tension in bolts 7. The high and low fluid pressures can then be released.

For normal unlocking, high pressure fluid through tension line 48 holds the tension bolts 7 allowing low pressure fluid through line 52 and control valve 54 to rotate motor 43 in the opposite direction and hence release drive mechanism 32 and also through line 47, to move latch ring 11 and release dogs 6.

Figure 3 also shows the variety of safety mechanisms to ensure that the connector can be locked and, more particularly, unlocked in the event of failure of different parts of the system. Tension in bolts 7 can be released mechanically by a ROV using mechanical override 44. If such a mechanical release is impractical, unlocking can proceed against the retained tension in bolts 7 using secondary unlock piston 25 and high pressure fluid through line 49 or in the ultimate by high pressure fluid supplied directly via an ROV through inlet 50.

There is considerable movement of latching ring 11 during the locking and unlocking of dogs 6 in groove 5 so a simple indicator rod 26 is sufficient to monitor the position of ring 11 and hence whether the connector is locked or unlocked.

The movement of tension bolts 7 is quite small, however, as between their tensioned and untensioned states, so monitoring of the tension in bolts 7 can be effected using an accumulator for the oil in which drive mechanism 32 is immersed. Figure 1 shows connection 39 in gear cover plate 38 leading to an accumulator which is shown in Figure 4.

Figure 4 shows that the accumulator is a simple cylinder 55 containing a piston 56. Oil from the drive mechanism 32 passes through connector 39 to the bottom of cylinder 55 and the underside of piston 56 through a further connection 57. The top of piston 56 carries an indicator rod 58 and there is a vent port 59 at the top of cylinder 55.

When bolts 7 are tensioned, oil in which drive mechanism 32 is immersed flows through connections 39 and 57 to the accumulator moving piston 56 and indicator rod 58 upwards, vent port 59 ensuring that there is no fluid lock. The size of the accumulator in relation to the volume of oil displaced when bolts 7 are tensioned can be designed to give a sufficient movement of piston 56 and indicator rod 58 to allow the rod's position to be monitored by an underwater TV camera operated by a ROV or by an electrical sensor.

The principal features of the invention and its advantages can be summarised as follows: (a) It is a connector that uses two discrete functions to achieve a lock and then to generate a pre-load.

(b) The lock function can use low pressure hydraulic fluid to carry out the relatively long stroke travel necessary to energise the lock (c) The pre-load function can use high pressure hydraulic fluid that only has to pre-stress the system and therefore does not require a high supply volume.

(d) The connector when made up is mechanically locked-up irrespective of whether the hydraulic pressure used for locking and pre-loading remains or is vented off. The system does not depend on any friction face factor to remain locked.

(e) The connector can be given a set pre-determined pre-load that is directly proportional to the high pressure supply. It does not rely on an assumed friction factor (which can alter due to the use of different lubricants or by the age of the connector since it was last serviced) to achieve a pre-load.

(f) The use of a high-pressure supply to achieve the pre-load reduces the need for large piston areas compared with low pressure connectors. This allows a more compact connector to be designed.

(g) The locking dogs are positively locked or unlocked using a full retract wedge profile system. The dogs do not rely on a tapered angle and its friction factor to remain in the locked position.

(h) All tie bolts are made up to the same tension.

(i) Long tie bolts mean that a larger elastic work envelope is generated so that the system is not sensitive to bore temperature or pressure changes.

Claims (13)

Claims

1. A connector for joining components of pressure containing bores having both releasable locking and pre-loading functions characterised in that the locking and pre-loading functions have independent, powered actuating mechanisms.

2. A connector as claimed in claim 1 wherein the locking and pre-loading actuating mechanisms are powered by hydraulic fluid pressure, the locking using a low pressure and the pre-loading a high pressure.

3. A connector as claimed in claim 1 or 2 wherein the locking mechanism comprises locking dogs or collets or a spring ring cooperating with a groove and the pre-loading mechanism comprises tension bolts.

4. -A connector as claimed in claim 3 which is a hub and cap connector, the locking dogs, collets or spring ring being on the cap between upper and lower bodies of the cap and the tension bolts extending between the upper and lower bodies, so that on tensioning the bolts the dogs, collets or spring rings are compressively loaded in the groove which is on the hub.

5. A connector as claimed in claim 3 or 4 wherein the tension bolts are locked in tension by a clutch drive mechanism.

6. A connector as claimed in claim 5 wherein the clutch drive mechanism is driven by a hydraulic or electric motor or by an ROV.

7. A connector as claimed in claim 5 wherein the clutch drive mechanism comprises a driven rotating ring, a drive gear, a clutch, and a drive bushing.

8. A connector as claimed in claims 5, 6 or 7 wherein the clutch drive mechanism rotates a locking screw threaded into a tension piston attached to a tension bolt.

9. A connector as claimed in claim 2 wherein the low pressure hydraulic locking mechanism has separate lock and unlock pistons.

10. A connector as claimed in claim 9 wherein the unlock piston surface area is sufficient to generate a force, at the hydraulic pressure applied, to unlock the mechanism against the force of the pre-loading mechanism.

11. A connector as claimed in claim 9 wherein there is a secondary unlock piston in addition to the normal unlock piston, the secondary unlock piston surface area being sufficient to generate a force, at the hydraulic pressure applied, to unlock the mechanism against the force of the pre-loading mechanism.

12. A connector as claimed in any of claims 1 to 8 wherein the powered locking actuating mechanism and/or the powered pre-loading mechanism has a mechanical overide for actuation in the event of power failure.

13. A connector as claimed in claim 1 substantially as described with reference to the drawings.