Valves and valve actuation – Electrically actuated valve – Rotary electric actuator
Reexamination Certificate
1999-08-26
2001-07-10
Shaver, Kevin (Department: 3754)
Valves and valve actuation
Electrically actuated valve
Rotary electric actuator
C251S129040, C166S363000
Reexamination Certificate
active
06257549
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a actuation module, and in particular to a valve actuation module for actuating valve elements, such as a gate valve slab, needle stem, ball valve sphere or a choke cage or plug, on a subsea wellhead, but can equally be applied to other devices that require operating in a subsea environment.
Currently perceived wisdom is that subsea wellheads should have hydraulically operated valves which are provided with a fail-safe mechanism in the form of a large spring arranged to push the valve element into a safe position upon loss of hydraulic pressure. Generally speaking, it is possible to use the well pressure to assist in this movement of the valve element. However, for safety reasons it is still necessary to have a spring which is large enough that it will close the valve without assistance from the well pressure or in the reverse situation where external pressure is higher than well pressure.
With the current trend to deeper water wells, there is an increase in hydrostatic pressure but a possible decrease in well pressure. Thus, the net pressure differential can work against fail safe forces on the stem to close the valve. In this situation, the spring must be designed to be large enough to overcome the friction between the valve elements, the housing seals, and to overcome the hydraulic forces to expel the hydraulic control fluid to close the valve against the hydrostatic pressure and low internal well pressure. It can be readily appreciated from this that at increasing water depths, the size of the spring must be greatly increased thereby increasing the size and cost of the system. Further, the size of the force delivered by the spring has an adverse effect on the high power required for each operation and on its sensitivity.
An alternative approach is disclosed, for example, in U.S. Pat. Nos. 4,920,811 and 5,195,721 in which the valve elements are electrically operated by powerful electrical motors using considerable electrical power. This would require immense storage capacity if not directly supplied by the umbilical from the remote installation. In both cases, a clutch is provided to disconnect the valve element in the event of a loss of power, thereby allowing the spring to move the valve into a fail-safe position. In this case, although it is no longer necessary for the spring to overcome hydraulic control fluid pressure being electric, a large spring is required to overcome the valve friction and the hydrostatic pressure. Furthermore, the clutch mechanism needed to disengage the valve element results in an unnecessarily costly and complicated structure.
The inventor has appreciated that the above problems can be overcome by the revolutionary new approach of operating the devices, not by a hydraulic actuator, with a fail safe return spring, but by means of a rotary actuator driven by an electric motor which is normally energised from an external source through an umbilical. The necessary fail safe condition is achieved by providing the motor with a local backup power source which, in the event of loss of primary power, is sufficient to drive the motor to return the device to a safe position.
SUMMARY OF THE INVENTION
In accordance with the present invention, therefore, an actuation module for actuating a device in a subsea wellhead assembly comprises a housing containing a rotatable actuator which is, or is arranged to be, coupled to a rotatable part of the device, whereby, in use, rotation of the part by the actuator causes an element of the device to move between operating positions; an electric motor for rotating the actuator; an input for receiving primary power and/or a control signal from an external source for energising and/or controlling the motor; an electrical storage unit for providing a back-up secondary power source; and a controller for responding to a loss of primary power and/or control signal and thence causing the motor to be energised if necessary from the electrical storage unit so that the motor causes the element to move to one of the operating positions representing, in use, a safe mode.
With this arrangement, the coupling, which only transmits rotary motion between the actuator and the part of the device, is unaffected by hydrostatic pressure and a spring is not required. Thus the electric power to operate the device is much reduced as all that is required is sufficient power to overcome the friction between the device element and housing seals. Further, because each actuator can be provided with its own self contained back-up power source, each device has individual fail-safe control.
Although the module may be a permanent fixture on the wellhead assembly, it may from time to time require replacement. For this reason the module is preferably arranged to be coupled to, and decoupled from, the wellhead assembly by, for example, a diver or ROV. In this case, the coupling between the rotatable actuator and the rotatable part of the device will be a torque-transmitting interface, such as a splined or keyed coupling, which can be engaged and disengaged by relative axial movement.
The backup secondary power source is most simply a battery. The primary power source, connected to the module through an umbilical, may be connected through the backup source to maintain this fully charged, any surplus power being available to energise the motor. This ensures that whenever there is a loss of primary power, the backup source will always be fully charged for operating the motor.
The controller could be a simple solenoid switch or, for more sophisticated applications, an intelligent programmed processor.
There may be more than one of the actuators and respective motor and backup secondary power source, for operating a respected number of wellhead assembly devices, in the same housing. This avoids the primary power umbilical having to have suitably sized core to carry the power for each actuator, which would make it very costly and bulky. By providing a local storage unit and a local processor for allocating power to the respective actuators, the umbilical can be reduced to a single power core and a signal line. The signal line will instruct the processor and controller as to which actuators are to be operated. The processor must then be capable of detecting either a loss of primary power or a loss of remote signal, and in either case cause the respective actuator to be operated to bring the respective device into a safe mode.
REFERENCES:
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patent: 4667736 (1987-05-01), Rumbaugh et al.
patent: 4886114 (1989-12-01), Perkins et al.
patent: 4920811 (1990-05-01), Hopper
patent: 5166677 (1992-11-01), Schoenberg
patent: 5195721 (1993-03-01), Akkerman
patent: 5588637 (1996-12-01), Carsten et al.
patent: 5704392 (1998-01-01), Frew
Bielinski Peter J.
Cooper Cameron Corporation
Hartman Michael P.
Keasel Eric
Shaver Kevin
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