This invention relates to a power screw mechanism. The invention also relates to a remotely operated vehicle comprising a power screw mechanism, and a method of operating a power screw mechanism.
Power screw mechanisms are commonly used in a subsea environment for operations relating to the operation of underwater hydrocarbon extraction facilities. For example, a power screw mechanism may be used by a remotely operated vehicle (ROV) for the mating of a recoverable half multiple quick connection (MQC) plate (e.g. a stabplate), for example, bearing hydraulic and electrical power and chemical injection feeds, for a subsea well to a fixed reciprocal half multiple quick connection plate (e.g. a stabplate) mounted on a subsea tree. Typically, a screw mechanism is operated by the ROV to force the two plates to mate and to lock them together. The mating and locking screw mechanism is, typically, part of the recoverable half multiple quick connection plate connection and remains subsea during the operation of the well. De-mating of the multiple quick connection plate connection for maintenance/repair purposes involves an operation by an ROV of unscrewing the screw mechanism, which is designed to force the mated plates apart.
However, during the screwing or unscrewing process, the screw mechanism may become seized causing the recoverable half multiple quick connection plate to become stuck to the fixed reciprocal half multiple quick connection plate.
The conventional way to release the recoverable half multiple quick connection plate in such a situation is to have shear pins placed within the mechanism in a cam and slot arrangement. If the mechanism becomes seized the drive screw is rotated with the now seized main shaft and the shear pins are sheared allowing the two seized items to be placed into a position where the recoverable half multiple quick connection plate can be removed.
However, the use of shear pins has a number of known drawbacks. For example, the mechanism has a tendency to shear the pins prematurely if the main shaft is not fully landed out and a torque is applied to the drives screw, since the main shaft is prevented from rotating and the applied torque is taken by the shear pins.
Additionally, when the shear pins fail they can become jammed between mating surfaces. This can make it more difficult to place the seized mechanism in the recoverable half multiple quick connection plate into a position where it can be removed.
The present invention aims to overcome the drawbacks associated with prior art drive screw mechanisms by eliminating the requirement for shear pins.
In accordance with a first aspect of the present invention there is provided a power screw mechanism comprising: a drive screw; a main shaft; and a clutch disposed between the drive screw and the main shaft, wherein the clutch is configured to provide a frictional engagement between the drive screw and main shaft within a first range of torques applied to the drive screw, such that rotation of the drive screw causes rotation of the main shaft over the first range of torques, and the clutch is further configured to slip out of frictional engagement between the drive screw and main shaft within a second range of torques applied to the drive screw, such that rotation of the drive screw does not cause rotation of the main shaft over the second range of torques, wherein the second range of torques is greater in magnitude than the first range of torques.
The main shaft could comprise an axially extending cutout along a portion of its length, said cutout comprising first and second opposing ends. The power screw mechanism could further comprise a first rotation key within the cutout, wherein axial movement of the main shaft in a first direction is prevented when the first end of the cutout contacts the first rotation key. The power screw mechanism could further comprise a second rotation key within the cutout, wherein axial movement of the main shaft in a second direction, opposite the first direction, is prevented when the second end of the cutout contacts the second rotation key.
The main shaft could also comprise an axially and radially extending cutout along a portion of its length, said cutout comprising first and second opposing ends and clockwise and anticlockwise opposing ends. The power screw mechanism could further comprise a matched position pair of rotation keys within the cutout, wherein the axial and or radial movement of the main shaft is prevented when the respective end of the cutout contacts the pair of rotation keys.
The main shaft could comprise a tri-probe.
The clutch could circumferentially surround the drive screw.
A remotely operated vehicle could comprise a power screw mechanism as described above, as could a multiple quick connection plate, and a subsea control module.
In accordance with a second aspect of the present invention there is provided a method of operating a power screw mechanism, the power screw mechanism comprising a drive screw and a main shaft, the method comprising the steps of: providing a clutch between the drive screw and the main shaft, the clutch being configured to provide a frictional engagement between the drive screw and main shaft within a first range of torques applied to the drive screw, such that rotation of the drive screw causes rotation of the main shaft over the first range of torques, and the clutch being further configured to slip out of frictional engagement between the drive screw and main shaft within a second range of torques applied to the drive screw, such that rotation of the drive screw does not cause rotation of the main shaft over the second range of torques, the second range of torques being greater in magnitude than the first range of torques; and rotating the drive screw within one of the first and second ranges of torques.
The main shaft could comprise an axially extending cutout along a portion of its length, said cutout comprising first and second opposing ends. The power screw mechanism could further comprise a first rotation key within the cutout, wherein axial movement of the main shaft in a first direction is prevented when the first end of the cutout contacts the first rotation key. The power screw mechanism could further comprise a second rotation key within the cutout, wherein axial movement of the main shaft in a second direction, opposite the first direction, is prevented when the second end of the cutout contacts the second rotation key.
The main shaft could also comprise an axially and radially extending cutout along a portion of its length, said cutout comprising first and second opposing ends and clockwise and anticlockwise opposing ends. The power screw mechanism could further comprise a matched position pair of rotation keys within the cutout, wherein the axial and or radial movement of the main shaft is prevented when the respective end of the cutout contacts the pair of rotation keys.
The main shaft could comprise a tri-probe.
The clutch could circumferentially surround the drive screw.
The step of rotating the drive screw within one of the first and second ranges of torques could be performed by a remotely operated vehicle.
The invention will now be described by way of example with reference to the accompanying drawings, in which:
With the shear pins 4 sheared from the main shaft 2, it is possible to disengage the seized drive screw 3 and main shaft 2. However, as described in the introduction above, the sheared shear pins 4 can become jammed between the main shaft 2 and the housing, ultimately preventing rotation of the drive screw 3 and main shaft 2 and thus separation of the mechanism.
The power screw mechanism 5 comprises a drive screw 6 and a main shaft 7. The main shaft comprises a tri-probe 8, which may be used in the mating/de-mating of a multiple quick connection plate at an underwater structure in an underwater hydrocarbon extraction facility.
The main shaft 7 comprises of a pair of cutouts 9 which extend along a portion of its length. The cutout 9 has first and second opposing ends connected by first and second sidewalls. The power screw mechanism 5 further comprises a pair of rotation keys 10a, 10b. These act to limit the rotational movement of the main shaft 7 when the pair of rotation keys 10a, 10b contacts a sidewall of the cutout 9. In the embodiment of
A clutch 11 is disposed between the drive screw 6 and the main shaft 7. The clutch 11 provides a frictional engagement between the drive screw 6 and main shaft 7 within a first range of torques applied to the drive screw 6, such that rotation of the drive screw 6 causes rotation of the main shaft 7 over the first range of torques. A typical example of a torque applied to the drive screw 6 during mating/de-mating operations is approximately 5 Nm. Therefore, the first range of torques may be, for example, approximately 0 Nm to 5 Nm.
The clutch is further configured to slip out of frictional engagement between the drive screw 6 and main shaft 7 within a second range of torques applied to the drive screw 6, such that rotation of the drive screw 6 does not cause rotation of the main shaft 7 over the second range of torques. The exact value of the second range of torques is unimportant, save that the lower end of the range should be greater than the upper end of the first range. Therefore, the second range of torques may be, for example, approximately 5.5 Nm to 500 Nm.
The clutch can be adapted to provide a frictional engagement and to slip out of frictional engagement as appropriate depending on the specific application at hand. As an alternative, the first range of torques may fall within 0.1 to 300 Nm, and the second range of the torques may fall within 0.2 to 6000 Nm.
When a torque is applied to the drive screw 6 in the second range of torques, the clutch will simply slip over the drive screw 6 and the frictional engagement between the drive screw 6 and the main shaft 7 will be lost. This will allow the main shaft 7 to be either extended or retracted if, for example, the main shaft 7 is not fully landed out or an axial load between the main shaft 7 and its mating reciprocal half prevents rotation during a mating/de-mating process. If this is the case the main shaft 7 will experience a large degree of resistance to its rotation. This in turn increases the torque on the drive screw 6, and can move the torque from a value within the first range to a value within the second range. The same process occurs when a sidewall of the cutout 9 contacts one of the rotation keys 10a, 10b.
Further features of the power screw mechanism 5 are visible in
Also shown in
In
In
In
In
If the drive screw 6 is seized to the main shaft 7, then the main shaft 7 (and hence the tri-probe 8) will still rotate with rotation of the drive screw 6. The tri-probe can therefore be rotated to the disengaged orientation and achieve secondary release without the need for shear pins. In other words, the rotation clutch 11 does not hinder the rotation of the seized main shaft 7 and drive screw 6.
The invention is not limited to the specific embodiments disclosed above, and other possibilities will be apparent to those skilled in the art.
Number | Date | Country | Kind |
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1703183.2 | Feb 2017 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/054813 | 2/27/2018 | WO | 00 |