GB2307940A - Subsea clamp - Google Patents

Abstract

A subsea clamp comprises a male drive member 1 with a housing 3 for attachment to a first subsea structure and a receptacle attachment member 2 for location on a second subsea structure. The drive member 1 and attachment member 2 are locked together by rotating a drive nut 5 so that a clamp nut 8 moves longitudinally and locks a resilient collet 12 against a ridge 18 of the attachment member 2. Further rotation of the drive nut 5 causes the housing 3 and the top of the attachment member 2 to be brought into contact. A fine guide pin 15 is provided on the first subsea structure being attached for engagement with an aperture on the second subsea structure.

Description

SUBSEA CLAMP This invention relates to clamps and especially to clamps for retaining deployed packages on subsea structures.

In various subsea systems it is necessary to secure packages such as control modules to an existing structure and make hydraulic and/or electrical couplings. It is desirable to be able to release the clamps for subsequent removal of the modules, perhaps a significant time later. Therefore the clamps need to constitute a mechanism for both bringing together the module and subsea structure against resistive forces and also for separating the module and subsea structures.

An existing clamp for this purpose comprises a receptacle mounted on the subsea structure which engages with a splined cruciform end of a bolt assembly. The bolt assembly has a nut which can be screwed along a thread on the bolt shaft urging a yoke, and any attached module, closer to or away from the cruciform end of the bolt. To engage the end of the bolt in the receptacle the splined end is passed all the way through a cruciform aperture in an anchor plate on the receptacle and the splined end is then rotated 450 to prevent withdrawal. The ends of the splines bear against the anchor plate in a load bearing arrangement as the nut is tightened to clamp the module.

A disadvantage with such an arrangement is that it can be difficult to align the cruciform splines and plate, and once the splines are in engagement with the underside of the plate there is a limited load bearing area. It is also necessary to rotate the bolt assembly for engagement and disengagement of the splines and apertured plate.

The present invention is directed towards providing a clamp assembly that is simple to engage and simpler to manufacture.

Accordingly the invention provides a clamp for clamping subsea structures, the clamp comprising a drive member for mounting to a first subsea structure an attachment member for mounting on a second subsea structure, and a locking member disposed such that it is releasably engageable between the drive member and attachment member by a relative longitudinal movement with respect to the drive member.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-sectional diagram of an embodiment of a clamp according to the present invention positioned adjacent a receiving receptacle immediately prior to commencement of a clamping operation; Figure 2 shows the clamp of Figure 1 at a first stage of the clamping operation; Figure 3 shows the clamp of Figure 1 at a second stage of the clamping operation with the clamp fully inserted into the receptacle; Figure 4 shows the clamp of Figure 1 at a third stage of the clamping operation when active manipulation of the clamp assembly is commenced; Figure 5 shows the clamp of Figure 1 at a fourth stage of the clamping operation; Figure 6 shows the clamp of Figure 1 in a fully clamped position;; Figure 7 shows an alternative embodiment of a clamp according to the invention with the clamp fully inserted into the receptacle; and Figure 8 shows the clamp of Figure 7 in the fully clamped position.

In the following description a clamp is described in a vertical position, which means that downward movement is gravity aided. In other orientations the clamp operates similarly but the clamp mechanism provides force instead of, or to counter, gravity aided movement.

Referring to Figure 1, a clamp assembly comprises a male clamp part 1 which can be engaged into a receptacle part 2.

The male clamp part 1 is generally attached via a clamp housing 3 to a package which is to be deployed. When deployed the package is secured to a subsea structure which carries the receptacle 2.

The male clamp part 1 comprises an elongate drive rod 4 which engages at its upper end with a drive nut 5 via a thread 6 and drive pin 7 and at its lower end with a clamp nut 8 via a thread 9. Attachment of the clamp part 1 to the housing 3 is via a bearing 10 in which the drive nut is rotatably journalled. An anti-rotation pin 11 interconnects the housing 3 and the clamp nut 8 so that when the drive nut is rotated the drive rod 4 rotates with respect to the clamp nut and the clamp nut 8 is effectively screwed up or down along the drive rod 4.

Externally of the clamp nut 8 there is a collet 12, the lower end of which is turned outwardly and is free to spring inwardly and outwardly and the upper end of which carries a locking or detent arrangement, such as detent balls 13 which engage in sockets inside the housing 3.

The lower end of the clamp nut 8 is provided with a conical nose 14 which acts as a coarse guide for locating the clamp into the circular opening of receptacle 2. A fine guide pin 15 is provided on the package which can subsequently engage into an aperture on the subsea structure as the clamp is tightened to align connectors and couplings 16, 17 on the package and subsea structure.

Starting with the position shown in Figure 1, the sequence of operation to tighten the clamp and secure the package to the subsea structure will now be described. The package and clamp are lowered into the position shown in Figure 1 with the clamp nose 14 locating in the upper end of the receptacle 2 and by virtue of its conical shape centring the male part of the clamp in the receptacle and aligning the fine guide pin with its aperture.

As the package continues to be lowered to the position shown in Figure 2, the clamp nut 8 enters the receptacle 2 and the leading edge of the outwardly flared end of the collet 12 engages with an inward chamfer 20 on the receptacle opening and springs the leaves of the collet inwardly so that they can slide past an upper retaining ridge 18 on the receptacle 2 and spring outwardly below the ridge 18 as shown in Figure 3. At this point the nose 14 has come to rest on the lower profile of the receptacle and the fine alignment pins have entered the guide apertures on the subsea structure. The connectors and couplings have not yet engaged and the drive nut has not yet been rotated.

Progression from the position in Figure 3 to the position in Figure 4 in which the outwardly flared end of the collet has moved down to abut a correspondingly shaped profile 21 on the clamp nut is achieved by clockwise rotation of the drive nut. The drive nut rotation causes the projecting end of the drive rod 4 to extend further through the clamp nose 14 with the clamp nut engaging further up the thread 9. This reduces the length between the housing 3 and the receptacle 2 which does several things. First, the package is lowered further so that the connectors and couplings 16, 17 start to engage. In the vertical orientation gravity helps lower the package, in say a horizontal orientation the tightening of the clamp would urge the two parts together.Second, as the housing 3 is lowered with respect to the clamp nut 8, the collet which is attached to the housing via engagement of detent balls 13 is also lowered until the lower end of the collet engages with the correspondingly configured contour on the clamp nut, which then prevents the collet from flexing inwardly. Just as this latter engagement of the collet takes place, the detent balls are released by virtue of a retaining large diameter portion 19 on the upper end of the clamp nut moving upwardly and out of engagement with the balls. It will be appreciated from this that the collet is essentially a floating collet that is releasably held in turn by its lower then upper end as rotation of the drive nut retracts the clamp nut and housing towards one another.

Further rotation of the drive nut retracts the housing and clamp nut more towards one another as shown in Figure 5. By this time the connectors and couplings 16, 17 have commenced joining and there is some resistance to overcome, hence the clamp nose lifts upwardly from the lower profile of the receptacle and the collet, held by the engaging surface of the clamp nut, bears against the lower chamfer of the receptacle retaining ring 18. This position is retained as the rotation of the drive nut is continued to the final position shown in Figure 6 where the housing 3 abuts the receptacle and the couplings and connectors are fully engaged.

In the event that descent of the package is not gravity aided, for example in a horizontal orientation, then the clamp nut may move to the Figure 5 position abutting the collet against the retaining ring 18 without the collet moving first to the Figure 4 position.

The release mechanism is a simple reversal of the clamping steps. Anti-clockwise rotation of the drive nut and drive rod commences pushing the clamp nut downwardly to engage again on the lower profile of the receptacle as shown in Figure 4. This releases the anchoring of the lower end of the collet, the detent engages and as the package is pulled upwardly the collet can flex inwardly to enable the male part of the clamp to be released from the receptacle.

In some instances the subsea environment or the length of time that a package is installed may give rise to situations where the drive nut and clamp seize together. In this situation rotation and over torque of the drive nut 5 will cause the drive pin 7 to shear. Rotation of the drive nut will then extend the siezed together drive rod and clamp nut, pushing apart the package and the structure, releasing the collet. The package may then be lifted away from the structure.

It will be appreciated that the drive rod of the described embodiment could be modified to comprise a hollow shaft and the receptacle could be replaced by a mounting that locates within a clamp nut arrangement.

An alternative embodiment of the invention is shown in Figures 7 and 8. In this embodiment when the drive nut is rotated to bring the housing and receptacle towards one another the projecting end of the rod 4 is taken up at the housing end of the rod rather than at the receptacle end projecting through the clamp nut. This is achieved by the top end of the drive rod threadingly engaging within an axial bore 22 in the drive nut which screws the rod up into the bore as the nut is rotated. The lower end of the drive rod is configured the same as the clamp nut of the first embodiment with a clamp nose portion 14 and a profile 21 for engaging detent 13 and no separate clamp nut is provided.

When the drive nut is screwed to move the housing towards the receptacle as in Figures 4 to 6, instead of the rod 4 projecting downwardly through the clamp nut and receptacle, in this embodiment the rod moves upwardly into the drive nut bore. The profiled clamp nose end of the drive rod moves and cooperates with the floating collet and the receptacle in the same way as described for the clamp nose of the previous embodiment.

In both the described embodiments the collet acts as a floating locking member constrained to move between a first position in which lateral motion with respect to the clamp nose and receptacle is permitted, and a second position in which lateral motion is restricted. The collet slides from the first to second position after the clamp nose engages with a stop surface in the receptacle, the collet and clamp nose then moving in unison to abut a second stop surface on the receptacle which prevents the abutting collet and clamp nose from being withdrawn any further from the receptacle.

Claims (11)

1. A clamp for clamping subsea structures, the clamp comprising: a drive member for mounting to a first subsea structure; an attachment member for mounting on a second subsea structure; and a locking member disposed such that it is releasably engageable between the drive member and attachment member by a relative longtudinal movement with respect to the drive member.

2. A clamp according to claim 1 in which the drive member is a drive rod and clamp nose, the attachment member is a receptacle that engages with the clamp nose via the locking member which is adapted to wedge between the clamp nose and receptacle.

3. A clamp according to claim 2 in which the locking member is longitudinally movable between a first position in which it does not wedge between the clamp nose and receptacle and a second wedging position.

4. A clamp according to claim 3 in which the locking member is held in the first position until the clamp nose abuts a stop surface in the receptacle, the locking member then being released to move relative to the clamp nose and into the wedging position with the clamp nose.

5. A clamp according to claim 4 in which the clamp nose and locking member move in unison into wedging engagement with a second stop surface on the receptacle.

6. A clamp according to claim 1 in which the drive member has a clamp nose with an enlarged portion and the locking member comprises a collet longitudinally movable between a first position in which its effective outward projection is no greater than that of the enlarged portion and a second position in which its effective outward projection is greater than that of the enlarged portion.

7. A clamp according to claim 1 in which the locking member comprises a portion which is inwardly deflectable when the locking member is in a first position and upon said relative longitudinal movement with respect to the drive member is restrained from deflection.

8. A clamp according to claim 1 in which the drive member comprises a drive rod rotatable within a sleeve that is attachable to the first subsea structure and the attachment member comprises a receptacle having a substantially circular opening with an inwardly chamfered edge, the drive rod having a conical clamp nose portion which locates on the chamfered edge as it is inserted into the receptacle.

9. A clamp according to claim 4 in which the receptacle has a profiled inner surface with a first abutment surface at its inward end and a second inwardly facing abutment surface at its opening, and the locking member longitudinally moves from a first position with respect to the drive member to a second position once the drive member abuts the first abutment surface, subsequent relative longitudinal movement of the drive member and receptacle bringing the locking member into contact with the second abutment surface where it wedges the drive member within the receptacle.

10. A clamp according to claim 2 in which the drive rod is integrally formed with the clamp nose.

11. A clamp according to claim 2 in which the clamp nose is part of a threaded nut on the drive rod.