GB2319052A

GB2319052A - A latching system

Info

Publication number: GB2319052A
Application number: GB9622792A
Authority: GB
Inventors: Adrian Paul Willams
Original assignee: BRISCO ENG Ltd
Current assignee: BRISCO ENG Ltd
Priority date: 1996-11-01
Filing date: 1996-11-01
Publication date: 1998-05-13
Anticipated expiration: 2016-11-01
Also published as: GB9622792D0; GB2319052B

Abstract

A latching system for releasably securing a subsea control module 2 to a mounting base 8 comprises at least one spigot 26 on one of the module 2 or the mounting base 8, a fixed inner mounting collar 18 on the other, and an outer locking ring 20. The collar 18 has a slot 28 for receiving each spigot 26, and the locking ring 20 has a cam or ramp surface 30 for each spigot 26 arranged to act on the spigot 26 when the spigot 26 is journalled in the slot 28. Rotation of the locking ring 20 in one sense progressively urges the spigot 26 along the slot 28 towards the mounting base 8, and rotation of the locking ring 20 in the opposite sense progressively urges the spigot 26 along the slot 28 away from the mounting base 8.

Description

A LATCHING MECHANISM The present invention relates to a latching mechanism for a system for controlling and/or monitoring processes in subsea oil or gas wells.

In a subsea oil or gas well, wellhead valves for controlling the flow of production fluids are conventionally mounted on a stub pipe standing up from the sea bed, often referred to as a Christmas tree. A subsea control module is used to open and close gate valves on a Christmas tree, and to monitor operational parameters such as temperatures, flow rates, and valve positions.

The subsea control module (SCM) contains all the hydraulics, electronics, and chemical distribution means to carry out the control and monitoring functions required of it. The SCM is mounted on a mounting base which is mounted on a Christmas tree or other subsea structure.

Because some subsea wells are below practical diving depth, the SCM is typically mounted on the mounting base by means of a Remotely Operated Vehicle (ROV) which is controlled by an operator on the surface. The ROV is provided with one or more robot arms, typically two arms, for grabbing and manipulating objects.

If a problem occurs with any function of the SCM it is usually necessary for the SCM to be removed from the Christmas tree or other subsea structure and brought up to the surface for work to be done on it. The SCM is liable to remain mounted on the mounting base for a considerable period of time at the bottom of the sea. Under such conditions sedimentation or other effects of sea water may tend to cause the SCM to become stuck to the mounting base, making it difficult to release from the base even when the mounting means have been released by the ROV.

It is an object of the present invention to provide a latching mechanism for releasably securing a subsea control module to a mounting base which reduces the above problem.

According to the present invention there is provided a latching mechanism for releasably securing a subsea control module to a mounting base, the latching mechanism comprising at least one spigot on one of the module or the mounting base, a fixed inner mounting collar on the other, having a slot for receiving each spigot, and a rotatable outer locking ring which has a cam or ramp surface for each spigot arranged to act on the spigot when the spigot is journalled in the slot, whereby rotation of the locking ring in one sense progressively urges the spigot along the slot towards the mounting base, and rotation of the locking ring in the opposite sense progressively urges the spigot along the slot away from the mounting base.

This mechanism allows quick and easy latching and release of the SCM. Because turning of the locking ring not only releases the SCM from the mounting base, but also urges the SCM and the mounting base apart, unlatching of the SCM also separates the SCM from the mounting base.

Preferably the spigot is provided on the SCM, and the mounting collar and locking ring are provided on the mounting base, but this arrangement could be reversed.

The same latching mechanism may also be used for connecting or disconnecting control jumpers or the like from the subsea system, so as to reduce the number of different types of operation which an ROV is required to carry out. This allows a simpler ROV to be used and/or an ROV which needs fewer tools.

The SCM may house all of the control hydraulics and electronics for the well, or there may be a plurality of SCMs, each of which houses some of the control means.

The invention will now be further described, by way of example, with reference to the following drawing in which: Figure 1 shows a conventional SCM mounted on a Christmas tree; Figure 2 is an exploded view of a latching mechanism for releasably securing an SCM to a mounting base in accordance with one embodiment of the present invention; Figure 3 is a side elevation view of an SCM secured to a mounting base by a latching mechanism in accordance with another embodiment of the invention; Figure 4 is a part sectional view of a module latched to a mounting base in accordance with one aspect of the present invention; Figure 5 is a part sectional view of the module and mounting base of Figure 4, in an unlatched, separated condition; and Figures 6 to 9 are perspective views of the module and mounting base of Figures 2 to 5 in various stages of latching or unlatching.

Figure 1 shows a Christmas tree 4 mounted on a guide base 14 of a subsea wellhead (not shown). The Christmas tree 4 has welded or bolted to it a mounting base 8 for a conventional SCM 2. The SCM 2 contains means for controlling the opening and closing of gate valves on the Christmas tree 4, and for monitoring the pressure, temperature and flow rate of production fluids. The SCM 2 has a handle 10 for use in its tranportation by an ROV.

The mounting base 8 is provided with an interface 16 through which the operation of the SCM 2 is controlled by means of a control jumper 12.

The SCM 2 is secured to the mounting base 8 by means of clamps 6 which can be removed by a modified ROV prior to removal of the SCM from the mounting base. However after removal of the clamps 6 the SCM may remain stuck to the mounting base 8 because of the effects of long exposure to sea water.

The SCM 2 shown in Figure 2 has a latching mechanism in accordance with the present invention. The mounting base 8 is provided with a fixed mounting collar 18 and a rotatable locking ring 20. The collar 18 has vertical slots 28, and the locking ring 20 has corresponding arcuate slots 30. The SCM 2 is provided with a spigot 26 for each pair of slots 28, 30, and a handle 10 to enable it to be held and moved by a manipulator arm of an ROV.

To latch the SCM 2 to the mounting base 8 the inner and outer slots 28, 30 are aligned so that the slots are in register with each other at the top of the collar 18. The SCM 2 is lowered into the mounting collar 18 so that each spigot 26 is journalled in the slots 28, 30. The locking ring 20 is then turned clockwise (viewing from above) so that the camming action of the walls defining the arcuate slot 30 urges the spigot 26 progressively downwards to the bottom of the inner slot 28. At this point the SCM 2 is securely latched to the mounting base 8, and hydraulic and/or electrical connections are automatically made between the SCM and pipes or circuits within the mounting base by means of self-sealing couplings, as best shown in Figures 4 and 5. Such self-sealing couplings, for example electrical couplings 34, and hydraulic couplings 32, are well known in the art, and need no further description here. To release the SCM, the above process is reversed, with the locking ring 20 being turned counterclockwise and the spigot 26 being urged progressively away from the bottom of the inner slot 28. The mounting collar 18 may optionally be provided with a profiled upper circumference 22, as shown in Figure 3, to help guide the SCM 2 into the mounting collar 18. Also illustrated in Figure 3 is a turning member 24 provided on the locking ring 20. The turning member 24 comprises a ring with an internal screw thread, mounted on the locking ring 20. To turn the locking ring 20 the manipulator arm of the ROV is provided with a torque tool which is located on the turning member 24 and turned so that the screw threaded member causes rotation of the locking ring 20. About 30 to 400 of turn are needed to fully latch or unlatch the SCM.

Any connector or control jumper which is connected to the subsea system may also be connected and disconnected by a similar latching mechanism, thereby reducing the number of different operations which the ROV is required to carry out.

Figures 6 to 9 shows various stages of the latching process. In Figure 6, which corresponds with the sectional view shown in Figure 5, the SCM is being guided into the mounting collar 18, which has an upper circumferential surface which is profiled so as to guide the SCM into position. The spigots 26 are not yet engaged with the slots 28, 30. Figures 8 and 9 show a spigot 26 journalled in the slots 28, 30. The SCM is unlatched and ready to be removed from the mounting base, or to be fully latched. Finally, Figure 7, which corresponds with the sectional view shown in Figure 4, shows the latching mechanism fully engaged, after rotation of the locking ring 20 from its position as shown in Figures 8 and 9.

The spigot 26 is secured at the lowest point in the slot 28 in the mounting collar, and at the lowest point in the slot 30 in the locking ring 20.

Claims

1. A latching mechanism for releasably securing a subsea control module to a mounting base, the latching mechanism comprising at least one spigot on one of the module or the mounting base, a fixed inner mounting collar on the other, having a slot for receiving each spigot, and a rotatable outer locking ring which has a cam or ramp surface for each spigot arranged to act on the spigot when the spigot is journalled in the slot, whereby rotation of the locking ring in one sense progressively urges the spigot along the slot towards the mounting base, and rotation of the locking ring in the opposite sense progressively urges the spigot along the slot away from the mounting base.

2. A latching mechanism as claimed in Claim 1, wherein the spigot is provided on the SCM, and the mounting collar and locking ring are provided on the mounting base.

3. A latching mechanism as claimed in Claim 1 or Claim 2, wherein the locking ring is provided with a screw threaded member whereby the locking ring can be made to turn about the mounting collar by mating of the screw thread with a complementary screw thread and rotation of that complementary screw thread.

4. A latching mechanism for releasably securing a subsea control module to a mounting base substantially as herein described with reference to any one of Figures 2 to 9 of the drawing.

5. A system for controlling and/or monitoring the flow of production fluids in a subsea oil or gas well, the system comprising a mounting base for securing in relation to a subsea wellhead, and at least one subsea control module provided with means for controlling or monitoring at least one process in the well, wherein the or each subsea control module is secured to the mounting base by means of a latching mechanism as claimed in any one of the preceding claims.