Subsea actuator for operating a safety valve and related method

Abstract

An actuator (100) for operating a safety valve (200) between an active position and a fail- safe position in a subsea system (400) is disclosed. The safety valve (200) is operable between an active position and a fail-safe position and comprises a valve stem (210), a valve element (240) operated by the valve stem for controlling fluid flow through the safety valve, and biasing means (220) configured for biasing the safety valve towards the fail-safe position. The actuator is operable between a hold configuration, in which the actuator is configured to hold the safety valve in the active position, and a release configuration, in which the actuator is configured to allow the safety valve to return to the fail-safe position. The actuator comprises: an electric motor (120); a linkage mechanism (122) actuated by the electric motor (120); and an actuator stem (140) actuated by the linkage mechanism (122) in an axial direction (A). The actuator stem is configured to hold the safety valve in the active position by interacting with a safety valve stem to counteract a force applied by the biasing means. The actuator comprises a release mechanism (130) releasably connecting the actuator stem to the linkage mechanism. The release mechanism is configured to disconnect the actuator stem from the linkage mechanism upon the actuator being released from the hold configuration, thereby allowing the actuator stem free axial movement independent of the electric motor and the linkage mechanism.

Description

[0001] SUBSEA ACTUATOR FOR OPERATING A SAFETY VALVE AND RELATED METHOD

[0002] Technical Field

[0003] The present disclosure and invention relates to a subsea actuator for operating a safety valve in a subsea system. The present disclosure and invention also relates to a method of operating a safety valve in a subsea system.

[0004] In particular, the present disclosure and invention relates to an actuator and related method for operating a safety valve being biased to assume a fail-safe position.

[0005] Said subsea system may typically be a subsea hydrocarbon production and / or processing installation, e.g. a subsea well injection system.

[0006] Background

[0007] Within the art of subsea systems, in particular subsea hydrocarbon production and / or processing installations, it is known to operate valves to close and open fluid conduits. For example, such an actuator is disclosed in WO2019 / 141595A1, which publication discloses a subsea electric actuator operating a linear valve. The actuator has a roller-screw for translating a rotational movement of an electric motor to an axial movement of a gate rod operating the valve. The actuator has an override function allowing the gate rod to move in the axial direction relative the roller-screw part such that the linear valve can be operated by a ROV or diver independently of the motor.

[0008] However, particular considerations need to be considered when the valve to be operated is a safety valve being biased to assume a default position should the actuator operating the safety valve become de-energised. The present disclosure and invention is concerned with actuators configured to actuate this type of valves.

[0009] The default position of a safety valve may be closed or open. In particular, a fail-safe closed safety valve is typically configured to assume a closed position should the actuator operating the valve become de-energised, and a fail-safe open safety valve is typically configured to assume an open position in the same situation, i.e. when the actuator operating the valve become de-energised.

[0010] In the following, the term “fail-safe position” will be used to denote a default position of the safety valve, and the term “active position” will be used to denote a valve position being opposite the valve’s default position. In other words, the fail-safe position of a fail-safe closed valve is closed, whereas the active position of the fail-safe closed valve is open. Correspondingly, the fail-safe position of a fail-safe open valve is open, whereas the active position of the fail-safe open valve is closed.

[0011] A fail-safe valve may typically comprise a spring producing a biasing force biasing the safety valve towards the fail-safe position. In other words, in a spring-operated fail-safe closed valve such a spring typically operates to bias the safety valve towards a closed position. Correspondingly, in a spring-operated fail-safe open valve, the spring operates to bias the safety valve towards an open position. However, hydraulically biased safety valves are also known in the art, in which case a hydraulic pressure, e.g. originating from a hydraulic reservoir, is utilised to produce the biasing force. In some applications, hydraulic pressure originating from production or process pressure, e.g. hydrocarbon well pressure, may be utilised to produce the biasing force. In some applications, a combination of process or production pressure and spring operations may be utilised to produce the biasing force.

[0012] Electrically biased fail-safe valves are also known in the art, in which case electric power, e.g. originating from a battery internal or external to the fail-safe valve, may be utilised to produce the biasing force.

[0013] An actuator for operating a fail-safe valve is typically configured to produce an actuating force when energised, the actuating force being sufficient to counter the biasing force of the fail-safe valve such that the actuator, when energised, is capable to force the safety valve to its active position. As long as the actuator is energised, it will hold the fail-safe valve in the active position. When the fail-safe valve is to be brought to its fail-safe position, the actuator may be de-energised to reduce or completely cut-out the actuating force, thus allowing the biasing force of the safety valve to overcome the actuating force of the actuator to bring the safety valve to the fail-safe position. When the fail-safe valve is to be brought to its active position, the actuator is again energised to produce the actuating force such that the biasing force of the safety valve is overcome, thus forcing the safety valve to its active position.

[0014] This configuration of the actuator should allow a safe operation of the safety valve also if the actuator is de-energised in an uncontrolled manner, e.g. in an emergency situation, since a de-energisation of the actuator should automatically allow the fail-safe valve to return to its fail-safe position.

[0015] A problem with actuators operating safety valves is to ensure that the operated fail-safe valve always returns to the fail-safe position when the actuator is de-energised. This is particularly a problem in subsea systems in which the fail-safe valves may be kept at their respective active position for long periods of time, such may be the case for fail-safe valves in subsea hydrocarbon production and / or processing systems. In particular, even if the actuator has held the fail-safe valve in the active position continuously for an extended period of time, the actuator must allow the fail-safe valve to immediately return to its fail-safe position when de-energised. This is particularly important for actuators operating fail-safe closed shutdown valves, since a delayed or interrupted closure of such a valve may have serious consequences.

[0016] Consequently, one challenged associated with actuators operating fail-safe valves is to ensure that the fail-safe valve is brought to its fail-safe position when called upon. Another challenge associated with actuators operating fail-safe valves is to allow the failsafe valve, when called upon, to assume the fail-safe position in a timely manner, e.g. within a set time requirement.

[0017] An object of the present disclosure and invention is to address these problems and challenges. In particular, an object of the present disclosure and invention is to provide an actuator and a related method that solve or at least reduce the aforementioned problems or challenges.

[0018] A further object of the present disclosure and invention is to provide an actuator and a related method for operating a safety valve in a subsea system which increases reliable operations of the safety valve.

[0019] Yet a further object of the present disclosure and invention is to provide a new type of actuator and a related method for operating a safety valve in a subsea system.

[0020] Summary

[0021] With the abovementioned problem and challenge and known solutions in mind, and according to a first aspect, the present disclosure provides an actuator for operating a safety valve in a subsea system, the safety valve being operable between an active position and a fail-safe position and comprising a valve stem, a valve element operated by the valve stem for controlling fluid flow through the safety valve, and biasing means configured for producing a force biasing the safety valve towards the fail-safe position.

[0022] The actuator is operable between a hold configuration, in which the actuator is configured to hold the safety valve in the active position, and a release configuration, in which the actuator is configured to allow the safety valve to return to the fail-safe position under the influence of the biasing means, e.g. biased by the biasing means.

[0023] The actuator comprises:

[0024] - an electric motor;

[0025] - a linkage mechanism actuated by the electric motor; and

[0026] - an actuator stem actuated by the linkage mechanism in an axial direction.

[0027] The linkage mechanism may comprise any configuration capable of transforming a rotational motion of the electric motor into an axial or translational motion of the actuator stem.

[0028] When the actuator is in the hold configuration, the actuator stem is configured to hold the safety valve in the active position by interacting with the safety valve stem to counteract said force applied by the biasing means. The linkage mechanism may comprise a self-locking mechanism or a break configured to prevent the actuator stem from yielding to the force applied by the biasing means onto the actuator stem in the hold configuration. The actuator comprises a release mechanism releasably connecting the actuator stem to the linkage mechanism, the release mechanism being configured to disconnect the actuator stem from the linkage mechanism upon the actuator being released from the hold configuration, thereby allowing the actuator stem free axial movement independent of the electric motor and the linkage mechanism.

[0029] The linkage mechanism may comprise:

[0030] - a rotatable element which is rotatably actuated by the electric motor; and

[0031] - a linearly actuated element which is linearly actuated by the rotatable element.

[0032] A gearbox may be arranged between the electric motor and the rotatable element.

[0033] The actuator stem may be releasably connected to linearly actuated element via said release mechanism.

[0034] The linearly actuated element may be at least partially enclosing the actuator stem in a radial direction.

[0035] The release mechanism may comprise a release element at least partially enclosing the linearly actuated element in a radial direction and being axially movable (i.e. in said axial direction) in relation to the linearly actuated element between a locked position and a released position.

[0036] The release mechanism may further comprise a solenoid configured to releasably hold the release element in the locked position. The release mechanism may also comprise a release spring biasing the release element towards the released position.

[0037] The release mechanism may further comprise at least one release mechanism assembly comprising:

[0038] - a through-opening arranged in the linearly actuated element;

[0039] - a first recess arranged in the release sleeve;

[0040] - a second recess arranged in the actuator stem; and

[0041] - at least one locking element arranged in the through-opening.

[0042] The release mechanism is configured such that, in said locked position, the through-opening and the second recess of each release mechanism assembly are aligned allowing the at least one locking element to provide a locking engagement between the linearly actuated element and the actuator stem. Also, the release mechanism is configured such that, in said released position, the through-opening and the first recess of each release mechanism assembly are aligned allowing the at least one locking element to evacuate the second recess and release said locking engagement between the linearly actuated element and the actuator stem.

[0043] The at least one locking element is accommodated in the through-opening such that it can move in the radial direction, i.e. in a direction which is orthogonal to an axial direction of the linearly actuated element. The at least one locking element may comprise or be a cylindrical roller or a spherical ball.

[0044] At least two locking elements may be arranged in each through-opening. The at least two locking elements may be stacked one on top of the other in an axial direction of the linearly actuated element.

[0045] The at least one release mechanism assembly may comprise a first release mechanism assembly and a second release mechanism assembly arranged opposite each other in the linearly actuated element. In other words, the first release mechanism assembly and the second release mechanism assembly may be arranged at a circumferential distance of 180 degrees from each other when viewed in the circumferential direction of the linearly actuated element.

[0046] The through-opening of the first release mechanism assembly and the through-opening of the second release mechanism assembly may be arranged in a first common plane orthogonal to the axis of the linearly actuated element.

[0047] The at least one release mechanism assembly may further comprise a third release mechanism assembly and a fourth release mechanism assembly arranged opposite each other in the linearly actuated element. In other words, the third release mechanism assembly and the fourth release mechanism assembly may be arranged at a circumferential distance of 180 degrees from each other when viewed in the circumferential direction of the linearly actuated element.

[0048] The first release mechanism assembly and the third release mechanism assembly may be arranged at a circumferential distance of 90 degrees from each other when viewed in the circumferential direction of the linearly actuated element. Also, the second release mechanism assembly and the fourth release mechanism assembly may be arranged at a circumferential distance of 90 degrees from each other when viewed in the circumferential direction of the linearly actuated element.

[0049] The through-opening of the third release mechanism assembly and the through-opening of the fourth release mechanism assembly may be arranged in any one of: said first common plane; and a second common plane being orthogonal to the axis of the linearly actuated element and being different from said first common plane.

[0050] As previously stated, the linkage mechanism may comprise any configuration capable of transforming a rotational motion of the electric motor into an axial or translational motion of the actuator stem. For example, the rotatable element may comprise or be a lead screw and the linearly actuated element may comprise or be a lead nut. Alternatively, the rotatable element may comprise or be a threaded shaft provided with a helical raceway for ball bearings and the linearly actuated element may comprise or be a ball screw.

[0051] According to yet an alternative, the rotatable element of the linkage mechanism may comprise or be a first roller screw part which is rotationally connected to the electric motor, and the linearly actuated element of the linkage mechanism may comprise or be a second roller screw part which is connected to the first roller screw part via threads allowing the first roller screw part to linearly actuate the second roller screw part when rotated by the electric motor.

[0052] As previously stated, the linkage mechanism may comprise a self-locking mechanism or a break configured to prevent the actuator stem from yielding to the force applied by the biasing means on the actuator stem in the hold configuration. For example, any one of the lead screw, lead nut, threaded shaft and roller screws may be provided with self-locking threads to prevent the linkage mechanism (and thus also the actuator stem) from yielding to the biasing force produced by the biasing means.

[0053] The release mechanism may be configured to disconnect the actuator stem from the linkage mechanism upon the actuator receiving a command to bring the safety valve to the fail-safe position.

[0054] According to a second aspect, the present disclosure provides subsea system, e.g. a subsea hydrocarbon production and / or processing system, comprising a fail-safe biased safety valve and an apparatus according to the first aspect configured for operating the fail-safe biased safety valve.

[0055] According to a third aspect, the present disclosure provides a method of bringing a safety valve operated by an actuator in a subsea system from an active position to a fail-safe position, wherein the safety valve comprises: a safety valve stem; and biasing means configured for producing a force biasing the safety valve towards the fail-safe position, wherein the actuator comprises: an electric motor; a linkage mechanism actuated by the electric motor; and an actuator stem actuated by the linkage mechanism; and wherein the actuator stem is configured to hold the safety valve in the active position by interacting with the safety valve stem to counteract said force applied by the biasing means.

[0056] The method comprises the step of releasing connection between the linkage mechanism and the actuator stem upon the actuator being released from the hold configuration, thereby allowing the actuator stem free axial movement independent of the electric motor and the linkage mechanism.

[0057] The linkage mechanism may comprise a rotatable element, e.g. a lead screw, which is rotatably actuated by the electric motor and a linearly actuated element, e.g. a lead nut, which is linearly actuated by the rotatable element, and the step of releasing connection between the linkage mechanism and the actuator stem may include the step of disconnecting a mechanical coupling between the linearly actuated element and the actuator stem, thereby allowing free axial movement of the actuator stem independent of the linearly actuated element. The actuator may comprise a release mechanism according to the first aspect and the step of releasing the mechanical coupling between the rotatable element and the linearly actuated element may comprise activating the release mechanism.

[0058] Above-discussed preferred and / or optional features of each aspect of the disclosure may be used, alone or in appropriate combination, in the other aspects of the disclosure.

[0059] The claimed invention is specified in the independent claims of this application. Advantageous adaptations and versions of the claimed invention are specified in the independent claims.

[0060] Description of the drawings

[0061] Following drawings are appended to facilitate the understanding of the claimed invention:

[0062] Fig. 1 schematically illustrates a subsea system in the form of a hydrocarbon production Christmas tree comprising a safety valve and an actuator operating the safety valve.

[0063] Fig. 2 is a cross-sectional view schematically illustrating the actuator of Fig. 1 in a first position.

[0064] Fig. 3 is a cross-sectional view schematically illustrating the actuator of Fig. 1 in a second position.

[0065] Figs. 4a-4d are cross-sectional views schematically illustrating the actuator of Fig. 1 in various positions during a release-to-hold operation.

[0066] Figs. 5a-5c are cross-sectional views schematically illustrating the actuator of Fig. 1 in various positions during a hold-to-release operation.

[0067] Fig. 6 schematically illustrates a cross-sectional view of the actuator of Fig. 1.

[0068] It should be understood, however, that the drawings are not intended to limit the claimed invention to the subject-matter depicted in the drawings.

[0069] In the drawings, like reference numerals have been used to indicate common parts, elements or features unless otherwise explicitly stated or implicitly understood by the context.

[0070] Detailed description

[0071] In the following, one or more specific embodiments of the invention will be described in more detail with reference to the drawings. However, it is specifically intended that the claimed invention is not limited to the embodiments and illustrations contained herein but includes modified forms of the embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation- specific decisions must be made to achieve the developer’s specific goals, such as compliance with system and / or business-related constraints, which may vary from one implementation of the invention to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication and manufacture for the skilled person having the benefit of this disclosure.

[0072] Fig. 1 schematically illustrates a subsea system 400 in the form of a subsea hydrocarbon production or processing system comprising a subsea hydrocarbon production Christmas tree 300. The installation 400 further comprises a safety valve 200 in the form of a fail-safe valve and an actuator 100 for operating the safety valve 200. The safety valve 200 is arranged in a production conduit 310 of the Christmas tree 300.

[0073] The safety valve 200 is operable between an active position, which in the present embodiment is an open position, and a fail-safe position, which in the present embodiment is a closed position. In other words, in the present embodiment the safety valve 200 is a failsafe closed valve.

[0074] The actuator 100 is operable between a hold configuration and a release configuration. In the hold configuration the actuator 100 is configured to interact with the safety valve 200 to hold or maintain the safety valve 200 in the active position. In the release configuration, the actuator 100 is configured to allow the safety valve 200 to return to the fail-safe position.

[0075] The safety valve 200 comprises a safety valve stem 210 and biasing means, in the present case a safety valve spring 220, configured for biasing the safety valve 200 towards the failsafe closed position. The safety valve 200 further comprises a valve element 240 operated by the valve stem 210. In the present embodiment the valve element 240 is arranged at a distal end of the valve stem 210, which valve element 240, in the active position of the safety valve 200, allows a production fluid to flow through the conduit 310 and, in the fail-safe position of the safety valve 200, prevents the production fluid from flowing through the conduit 310. The safety valve spring 220 is configured to bias the safety valve stem 210 and the valve element 240 towards a position in which the valve element 240 prevents the production fluid from flowing through the conduit 310, which position consequently corresponds to the closed, fail-safe position of the safety valve 200.

[0076] The actuator 100 comprises an actuator stem 140 configured to co-operate with the valve stem 210. The actuator stem 140 is operable between a first, retracted position (also see Fig. 3), corresponding to the closed, fail-safe position of the valve 200, and a second extended position (also see Fig. 2), corresponding to the open, active position of the valve 200.

[0077] The actuator 100 displays an axis A (see Figs. 2 and 3) and comprises a housing 110. The housing 110 is configured to be rigidly attached to the safety valve 200 at a first axial end 102. The actuator 100 further comprises an electric motor 120 and said actuator stem 140. The electric motor 120 is rigidly connected to the housing 110 inside the same. The actuator stem 140 is operated by the electric motor 120 via a linkage mechanism 122 and is configured to move in the axial direction A of the actuator.

[0078] The linkage mechanism 122 comprises a rotatable element 124 which is rotatably actuated by the electric motor 120. The linkage mechanism 122 also comprises a second, translationally or linearly actuated element 126 which is actuated by the rotatable element 124, i.e. it is connected to the rotatable element 124 such that a rotational motion of the rotatable element 124 is transformed to a linear motion of element 126. In the present embodiment the linearly actuated element 126 is configured to move linearly in the direction of the axis A of the actuator 100.

[0079] In one embodiment the rotatable element 124 may comprise a lead screw and the linearly actuated element 126 may comprise a lead nut. In another embodiment the rotatable element 124 may comprise a threaded shaft provided with a helical raceway for ball bearings and the linearly actuated element 126 may comprise a ball screw. According to yet another embodiment, the rotatable element 124 may comprise a first roller screw part which is rotationally connected to the electric motor, and the linearly actuated element 126 may comprise a second roller screw part which is connected to the first roller screw part via threads allowing the first roller screw part to linearly actuate the second roller screw part when rotated by the electric motor. However, any configuration of a rotatable element and a linearly actuated element capable of transforming a rotational motion into an axial or translational motion may be used.

[0080] In some embodiments a gearbox, schematically illustrated as 121 in Fig. 2, may be arranged between the electric motor and the linkage mechanism, e.g. between the electric motor 120 and the lead screw (if a lead screw configuration is utilised) or between the electric motor 120 and the threaded shaft (if a ball screw configuration is utilised).

[0081] In the following the linkage mechanism 122 will be assumed to be a lead screw configuration comprising a lead screw 124 and a lead nut 126. However, it is understood that a ball screw configuration, or indeed any other configuration capable of transforming a rotational motion into a transversal motion, may alternatively be used. The actuator stem 140 extends through an opening in the housing 100 at the first axial end 102. By operating of the electric motor 120 and the linkage mechanism 122, the actuator stem 140 can be brought from the first, retracted position, as is disclosed in Fig. 3, to the second, extended position, as is disclosed in Fig. 2. To this end, the lead screw 124 is connected to and rotatably actuated by the electric motor 120. The lead nut 126, in turn, is axially actuated by the lead screw 124, i.e. it is connected to the lead screw 124 such that a rotational motion of the lead screw 124 is transformed to an axial motion of the lead nut 126, i.e. a motion in the direction of the axis A of the actuator 100. The lead nut 126 comprises a threaded section 126a comprising inner threads (not disclosed) configured to interact with corresponding outer threads (not disclosed) of the lead screw 124. The lead nut 126 further comprises an annular sleeve section 126b in which the actuator stem 140 is arranged. The lead nut 126, and in particular the sleeve section 126b of the lead nut 126, radially encloses the actuator stem 140. In the axial direction A, the actuator stem 140 is slidably accommodated in the sleeve section 126b. In the present embodiment the actuator stem 140 displays a quadrangular cross section and the inner surface of the sleeve section 126b displays a corresponding quadrangular shape, e.g. corresponding to the embodiment disclosed in Fig. 6, thus allowing the actuator stem 140 to slide inside the sleeve section 126b in the axial direction A. In an alternative embodiment, the inner surface of the sleeve section 126b may be cylindrical and the actuator stem 140 may have a corresponding cylindrical outer surface, thus allowing the actuator stem 140 to be slidably accommodated in the sleeve section 126b. Consequently, the outer diameter of the actuator stem 140 may be slightly less than the inner diameter of the sleeve section 126b.

[0082] In the present embodiment, the lead nut 126 also comprises a distal annular protrusion or radially extending flange 126c, the function of which will be discussed in more detail below.

[0083] The sleeve section 126b of the lead nut 126 comprises through-openings 127 in which locking elements 138 are arranged. In the present embodiment, the through-openings 127 are arranged pairwise opposite each other, i.e. offset by 180 degrees when viewed in a plane orthogonal to axis A, e.g. as is disclosed in Fig. 6. For example, four through-openings 127 may be are arranged in the lead nut 126 at equidistance positions along the circumferential direction of the lead nut 126 (said circumferential direction being orthogonal to the axial direction A).

[0084] At least one locking element 138 is arranged in each through-opening 127 and accommodated in the through-opening such that it can move in the radial direction, i.e. in a direction which is orthogonal to the axial direction A.

[0085] The locking element 138 may be a cylindrical roller or a spherical ball.

[0086] At least two locking elements may be arranged in each through-opening 127, and the at least two locking elements may be stacked one on top of the other in the axial direction A of the linearly actuated element.

[0087] In the present embodiment, the locking elements 138 are in the form of right-cylindrical metal rollers, and two equally sized rollers 138 are arranged in each through-opening 127. Each roller 138 has a diameter which is larger than the thickness of the sleeve section 126b. In the present embodiment each roller 138 has a diameter which is approximately twice the thickness of the sleeve section 126b. The height and width of each through-opening, i.e. the extent of the through-opening 127 in the axial direction and the circumferential direction of the load nut 126, respectively, is such that the through-opening 127 can movably accommodate two rollers 138a, 138b aligned in the axial direction A, i.e. stacked one on top of the other in the axial direction A. In other words, the height of each through-opening 127 (in the axial direction A) may be slight larger than two roller diameters, i.e. two times the diameter of each roller 138. The width of each through-opening 127 (in the circumferential direction of the lead nut 126) is sufficient to accommodate the rollers aligned orthogonal to the axial direction A, e.g. being slight larger than the length of a roller.

[0088] In an alternative embodiment (not disclosed), the locking elements 138 may be in the form of spherical metal balls, i.e. each locking element having a spherical shape, and each through-opening 127 may be configured to accommodate two balls stacked one on top of the other in the axial direction A.

[0089] Providing the locking elements 138 as right-cylindrical rollers or spherical balls one stacked on top of the other in the axial direction A allows for a low-friction operation of the locking elements, as will be discussed in more detail below.

[0090] Aligned with each through-opening 127 in the axial direction A, the cylindrical outer surface of the actuator stem 140 comprises a recess 141. Similar to the through-openings 127, the recesses 141 are arranged pairwise opposite each other, i.e. offset by 180 degrees along the circumferential direction of the actuator stem 140 when viewed in a plane orthogonal to axis A, e.g. corresponding to the embodiment disclosed in Fig. 6. The depth of each recess 141 approximately corresponds to a roller radius, thus allowing each recess 141, when aligned with a through-opening 127, to accommodate a part of the rollers 138 (e.g. see Fig. 2). In the axial direction A of the actuator stem 140, each recess 141 is delimited by an upper support surface 141a and a lower support surface 141b (see Fig. 3). Each recess 141 has a height (in the axial direction A of the actuator stem 140) which approximately corresponds to four roller diameters, and a width (in the circumferential direction of the actuator stem 140) being sufficient to accommodate the rollers.

[0091] Consequently, the release mechanism comprises opposing release mechanism assemblies 131, wherein each assembly comprises a through-opening, a first recess, a second recess, and at least one locking element arranged in the through-opening. In each release mechanism assembly 131, the through-opening, first recess, and second recess are movable in relation to each other in the axial direction A but aligned in the circumferential direction (i.e. in the direction orthogonal to the axial direction A).

[0092] In the present embodiment the release mechanism comprises opposing first 131a and second 131b release mechanism assemblies and opposing third 131c and fourth 13 Id release mechanism assemblies, as is illustrated in Fig. 6. In the present embodiment the through- openings of all release mechanism assemblies 131a, 131b, 131c, 13 Id are arranged in a common plane being orthogonal to the axis A. However, in other embodiments the through- openings of the first and second release mechanism assemblies 131a, 131b may be arranged in a first plane, and the through-openings of the third and fourth release mechanism assemblies 131c, 13 Id may be arranged in a second plane which is different from the first plane. In some embodiments the release mechanism may comprise only one pair of opposing release mechanism assemblies, and in some embodiments the release mechanism may comprise more than two pairs of opposing release mechanism assemblies.

[0093] In yet some embodiments the release mechanism may comprise only one release mechanism assembly.

[0094] The actuator 100 further comprises a solenoid 132 and a release element 134. The solenoid 132 is fixedly arranged inside the housing 110 at a second axial end 104 thereof. The release element 134 displays a generally cylindrical outer surface and is slidably arranged inside the housing 110. The release element 134 comprises a first, upper section 134a displaying a generally planar surface facing the solenoid 132. The release element 134 further comprises a second, annular section 134b radially enclosing the lead nut 126. The inner surface of the annular section 134b is cylindrical and the lead nut 126, by virtue of displaying an outer cylindrical surface having a diameter which is slightly less than the inner diameter of the annular section 134b, is slidably accommodated in the annular section 134b in the axial direction A.

[0095] The release element 134 also comprises a distal annular protrusion or radially extending flange 134c configured for co-operating with release springs 136 which are arranged inside the housing 110 and bias the release element 134 towards the first axial end 102 of the housing 110, i.e. downwards in Figs. 2 and 3.

[0096] The release element 134 is made from an electromagnetic material allowing the solenoid 132, when energised, to electromagnetically lock to the release element 134 in a manner which will be explained in more detail below. In a preferred embodiment, the release element 134 is made from soft magnetic iron.

[0097] Aligned with each through-opening 127 in the circumferential direction, the cylindrical inner surface of the annular section 134b comprises a recess 135. Consequently, similar to the through-openings 127 and the recesses 141, the recesses 135 are arranged pairwise opposite each other, i.e. offset by 180 degrees when viewed in the circumferential direction, i.e. in a plane orthogonal to axis A. Similar to the recesses 141, the depth of each recess 135 approximately corresponds to a roller radius, thus allowing each recess 135, when aligned with a through-opening 127, to accommodate a part of the rollers 138 (e.g. see Fig. 3). Each recess 135 has a length (in the axial direction A of the release element 134) which approximately corresponds to two roller diameters and a width (in the circumferential direction of the release element 134) allowing the recess 135 to accommodate the rollers 138. Consequently, each recess 135 is capable of part-accommodating two rollers 138 aligned in the axial direction A.

[0098] Since the rollers 138 have a diameter that is larger than the wall thickness of the load nut 126, the rollers 138 will extend either into the recesses 135, as is disclosed in Fig. 3, or into the recesses 141, as is disclosed in Fig. 2, depending on how the actuator stem 140, the lead nut 126 and the release element 134 are aligned.

[0099] As previously stated, the actuator 100 is actuatable between a hold configuration and a release configuration. Fig. 2 shows the actuator 100 in the hold configuration, whereas Fig. 3 shows the actuator 100 in the release configuration. Operation of the actuator 100 from the release configuration to the hold configuration will now be described in more detail with reference to Figs. 4a-4d, where Fig. 4a shows the actuator 100 in the release configuration, in which the actuator stem 140 is in the first, retracted position (corresponding to the closed, or fail-safe, position of the safety valve 200) and Fig. 4d shows the actuator 100 in the hold configuration, in which the actuator stem 140 is in the second, extended position (corresponding to the open, or active, position of the safety valve 200). Figs. 4b and 4c show the actuator 100 in intermediate positions between the release and hold configurations.

[0100] In the release configuration disclosed in Fig. 4a, the actuator stem 140 is in the retracted position and, consequently, the safety valve 400 is in the fail-safe position, i.e. closed in the present embodiment. In this position of the actuator 100, the release springs 136 are acting on the distal annular protrusion 134c of the release element 134 to bias the release element 134 towards the first axial end 102 of the actuator 100 (also see Fig. 3). Also, the distal annular protrusion 134c of the release element 134 is acting on the distal annular protrusion 126c of the lead nut 126 to bias the lead nut 126 towards the first axial end 102 of the actuator 100 to bring the distal annular protrusion 126c to rest on an inner end surface 106 of the actuator 100.

[0101] In the release configuration (Fig. 4a), each through-opening 127 is aligned with the respective recess 135 but not with the recess 141. Consequently, in this position the actuator stem 140 is allowed free axial movement independent of the lead nut 126. However, due to the biasing force F from the safety valve 400, the actuator stem 140 is forced to the retracted position, as is also disclosed in Fig. 3. Stops 128 may be arranged, e.g. in the inside wall of the lead nut 126, defining the retracted position of the actuator stem 140.

[0102] In order to bring the actuator 100 to operate the safety valve 400 from the fail-safe position to the active position, the electric motor 120 is activated to bring the lead screw 124 to rotate in a first direction. This rotation of the lead screw 124 will bring the lead nut 126 to move axially towards the second axial end 104 of the actuator, i.e. upwards in Fig. 4b. In Fig. 4b this is illustrated by the pair of shorter arrows in the figure. Since the distal annular protrusion 126c of the lead nut 126 is acting on the distal annular protrusion 134c of the release element 134, the axial movement of the lead nut 124 will bring the release element 134 also to move towards the second axial end 104 of the actuator. In Fig. 4b this is illustrated by the pair of longer arrows in the figure. Consequently, at this stage of the operation of the actuator 100, the release element 134 and the lead nut 124 are brought to move axially towards the second axial end 104 of the actuator 100 in unison. Also, at this stage of the operation of the actuator 100, the release springs 134 are compressed. The actuator stem 140, however, will remain immobile during this stage of the operations.

[0103] The rotation of the lead screw 124 in the first direction is continued until the upper section 134a of the release element 134 is brought into contact with the solenoid 132, as is illustrated in Fig. 4b. Also, at this point of the operation, the though-openings 127 in the lead nut 126 have become aligned with the upper part of the recesses 141 of the actuator stem 140, as is also illustrated in Fig. 4b.

[0104] When the upper section 134a of the release element 134 has been brought into contact with the solenoid 132, the solenoid 132 is energised and the release element 134 is electromagnetically locked to the solenoid 132.

[0105] The rotation of the electric motor 120 is then reversed, bringing the lead screw 124 to rotate in a second direction which is opposite the first direction. The reversed rotation of the lead screw 124 will bring the lead nut 126 to move axially towards the first axial end 102 of the actuator 100, i.e. downwards in the figures. However, the solenoid 132, when energised, is configured to produce a retaining force acting upon the release element 134 which is larger than the biasing force produced by the compressed release springs 136. Consequently, the release element 134 will not follow the lead nut 126 in this downward axial movement but will remain electromagnetically locked to the solenoid 132. This is illustrated by the pair of arrows in Fig. 4c.

[0106] The actuator stem 140 will initially remain immobile also during this stage of the operations by virtue of the biasing force F of the safety valve 400 keeping the actuator in the first, retracted position. However, since the release element 134 is electromagnetically locked to the solenoid 132, the though-openings 127 in the lead nut 126 will eventually be brought out of alignment with the recesses 135 of the release element 134, and the rollers 138 will be forced out of the recesses 135 and into recesses 141, as is illustrated in Fig. 4c. At this point of operations, the actuator stem 140 is no longer allowed free axial movement independent of the lead nut 126.

[0107] The actuator stem 140 will remain immobile until the rollers 138 are brought into contact with the lower support surfaces 141b of the recesses 141 (see Fig. 3), as is also illustrated in Fig. 4c. At this point of operations, the lead nut 126 will start to impart an axial, downward force onto the actuator stem 140, overcoming the biasing force F imparted by the valve stem 210 (see Fig. 1).

[0108] The rotation of the lead screw 124 in the second direction is continued until the actuator stem 140 is fully extended, as is illustrated in Fig. 4d, and the safety valve 400 has been brought to the active, open, position.

[0109] Consequently, the lead screw 124 and the lead nut 126 form part of a linkage mechanism 122 (see Fig. 2) which is actuated by the electric motor 120 to bring the actuator stem 140 to the extended position. In Fig. 4d, the actuator stem 140 is acted upon by the valve stem 210 (not disclosed in Fig. 4d but indicated in Fig. 2 by force F). The actuator stem 140, in turn, imparts an axial force upon the lead nut 126 via the rollers 138, which mechanically locks the actuator stem 140 to the lead nut 126. The lead nut 126 is prevented from moving upwards in the axial direction A by the holding power of the linkage mechanism 122, which holding power prevents the lead screw 124 from rotating. For example, the lead screw 124 (or the threaded shaft - if a ball screw configuration is used) may be locked in rotation, e.g. using a self-locking thread or any other type of brake or lock. In other words, Fig. 4d shows the actuator 100 in a hold configuration in which the holding power of the linkage mechanism 122 prevents the actuator stem 140 from yielding to the biasing force F produced by the safety valve spring 220.

[0110] In order to bring the safety valve 200 back to the fail-safe position in a controlled manner, the operations of the actuator 100 discussed above in relation to Figs. 4b and 4c can simply be reversed. In particular, staring from the actuator state disclosed in Fig. 4d, the electric motor 120 can be activated to bring the lead screw 124 to rotate in the first direction, which rotation of the lead screw 124 will cause the lead nut 126 and the interconnected actuator stem 140 to move jointly axially towards the second axial end 104 of the actuator 100, i.e. upwards in Fig. 4d. The rotation of the lead screw 124 in the first direction can then be continued until the actuator 100 assumes the state illustrated in Fig. 4b, at which point the actuator stem 140 has again assumed the retracted position and the safety valve the fail-safe position.

[0111] However, the actuator 100 provides an alternative way of bringing the safety valve 200 from the active position to the fail-safe position. In the following, this alternative operation will be described in more detail with reference to Figs. 5a-5c.

[0112] Fig. 5a shows the actuator 100 in the same hold configuration as in Fig. 4d, i.e. with the actuator stem 140 held in the extended position by the holding power of the electric motor 120. In this position the release element 134 is electromagnetically locked to the solenoid 132 and the energised solenoid 132 ensures that the recesses 135 in the release element 134 are kept out of alignment with the through-openings 127. This, in turn, ensures that the rollers 138 extend into the recesses 141 of the actuator stem 140 and mechanically locks the actuator stem 140 to the lead nut 126. As previously discussed, this allows the holding power of the linkage mechanism 122 to prevent the actuator stem 140 from yielding to the biasing force F produced by the safety valve spring 220, thus keeping the safety valve 200 in the active, or open, position.

[0113] By de-energising the solenoid 132, however, the electromagnetic lock between the solenoid 132 and the release element 134 can be broken, thereby allowing the release spring 136 to bring the release element 134 from the electromagnetically locked position disclosed in Fig. 5a to a released position disclosed in Fig. 5b, thus bringing the recesses 135 of the release element 134 into alignment with the through-openings 127 in the lead nut 126. This will release the rollers 138 from the recesses 141 in the actuator stem 140 and allow the biasing force F produced by the safety valve spring 220 to bring the actuator stem 140 from the extended position disclosed in Fig. 5b to the retracted position disclosed in Fig. 5c without interference from the lead nut 126, the lead screw 124 and the electric motor 120.

[0114] In other words, the solenoid 132, the release element 134, the release springs 136, the through-openings 127, the recesses 135 and 141 and the rollers 138 act as a release mechanism 130 (see Fig. 2) that allows the mechanical coupling between the actuator stem 140 and the linear actuator 120 to be released quickly and efficiently, thus allowing the safety valve 200 to go to the fail-safe position without interference from the electric motor 120 and the linkage mechanism 122. In this regard, the configuration of arranging the rollers 138 one on top of the other in the axial direction A is particularly advantageous, since this allows for low-friction transfer of the rollers 138 from the recesses 141 to the recesses 135 when the solenoid is de-energised. Consequently, the release mechanism 130 dispenses with the need to release the holding power of the linkage mechanism 122 prior to bringing the safety valve 200 to the fail-safe position. Thus, the release mechanism 130 allows the safety valve 200 to be brought to the fail-safe position independent of the working condition or status of the linkage mechanism 122 and the electric motor 120.

[0115] Consequently, the actuator 100 is operable between a hold configuration, in which the actuator 100 is configured to hold the safety valve 200 in the active position, and a release configuration, in which the actuator 100 is configured to allow the safety valve 200 to assume the fail-safe position and the release mechanism 130 releasably connects the actuator stem 140 to the linkage mechanism 122 and allows the linkage mechanism 122 to be disconnected from the actuator stem 140 upon the solenoid 132 becoming de-energised, thereby allowing the actuator stem 140 free axial movement independent of the electric motor 120 and the linkage mechanism 122 when moving from the extended position (corresponding to the active position of the safety valve) to the retracted position (corresponding to the fail-safe position of the safety valve).

[0116] The solenoid 132 becoming de-energised can result from an operator sending a command to the actuator 100 to de-energise the solenoid 132. Alternatively, de-energisation of the solenoid 132 can result from the actuator becoming de-energised in an un-supervised manner, e.g. as a result of an emergency shut-down command automatically being generated within the subsea system. In such a situation, the safety valve can rapidly assume the failsafe position by virtue of the biasing force F having to shift only the actuator stem 140 and not the linkage mechanism 122 in order to bring the safety valve to the fail-safe position. This may be beneficial since the forces required to shift a linkage mechanism that have not be operated for an extended period of time may be considerable, and in some situations the forces required may be so great that safe operations of the safety valve may be jeopardised.

[0117] Fig. 6 schematically illustrates, in a cross-sectional view, the release mechanism of the actuator of Fig. 1. As previously discussed, the release mechanism comprises opposing release mechanism assemblies 131a, 131b, 131c, 13 Id, wherein each assembly comprises a through-opening in which locking elements, i.e. the rollers 138a, 138b, 138c, 138d in the present embodiment, are arranged.

[0118] In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to person skilled in the art to which the disclosed subject-matter pertains, are deemed to lie within the scope of the present invention as defined by the following claims. For example, it is understood that the biasing means configured for biasing the safety valve towards the failsafe position may not necessarily be a spring. In other embodiments the biasing means may comprise a hydraulic pressure source hydraulically biasing the safety valve stem. The hydraulic pressure source may for example comprise a hydraulic reservoir or an accumulator. In other embodiments still, the hydraulic pressure source may comprise process or production fluid. In other words, necessary hydraulic pressure for biasing the safety valve stem towards the fail-safe position may be received from process or production fluid in the subsea hydrocarbon production or processing system.

Claims

Claims1. An actuator (100) for operating a safety valve (200) in a subsea system (400), the safety valve (200) being operable between an active position and a fail-safe position and comprising a valve stem (210), a valve element (240) operated by the valve stem (210) for controlling fluid flow through the safety valve (200), and biasing means (220) configured for producing a force biasing the safety valve (200) towards the fail-safe position, the actuator (100) being operable between a hold configuration, in which the actuator (100) is configured to hold the safety valve (200) in the active position, and a release configuration, in which the actuator (100) is configured to allow the safety valve (200) to return to the fail-safe position under the influence of the biasing means (220), the actuator (100) comprising:- an electric motor (120);- a linkage mechanism (122) actuated by the electric motor (120); and- an actuator stem (140) actuated by the linkage mechanism (122) in an axial direction (A), the actuator stem (140) being configured, when the actuator (100) is in the hold configuration, to hold the safety valve (200) in the active position by interacting with the safety valve stem (210) to counteract said force applied by the biasing means (220), characterised by the actuator (100) comprising a release mechanism (130) releasably connecting the actuator stem (140) to the linkage mechanism (122), the release mechanism (130) being configured to disconnect the actuator stem (140) from the linkage mechanism (122) upon the actuator (100) being released from the hold configuration.

2. The actuator (100) according to claim 1, characterised by the linkage mechanism (122) comprising:- a rotatable element (124) which is rotatably actuated by the electric motor (120); and- a linearly actuated element (126) which is linearly actuated by the rotatable element (124), the actuator stem (140) being releasably connected to the linearly actuated element (126) via said release mechanism (130).

3. The actuator (100) according to claim 2, characterised by the linearly actuated element (126) at least partially enclosing the actuator stem (140) in a radial direction.

4. The actuator (100) according to any one of claims 2-3, characterised by the release mechanism (130) comprising:- a release element (134) at least partially enclosing the linearly actuated element (126) in a radial direction and being axially movable in relation to the linearly actuated element (126) between a locked position and a released position;- a solenoid (132) configured to releasably hold the release element (134) in the locked position; and- a release spring (136) biasing the release element (134) towards the released position.

5. The actuator (100) according to claim 4, characterised by the release mechanism (130) comprising at least one release mechanism assembly (131) comprising:- a through-opening (127) arranged in the linearly actuated element (126);- a first recess (135) arranged in the release sleeve (134);- a second recess (141) arranged in the actuator stem (140); and- at least one locking element (138) arranged in the through-opening (127), wherein, in said locked position, the through-opening (127) and the second recess (141) are aligned allowing the at least one locking element (138) to provide a locking engagement between the linearly actuated element (126) and the actuator stem (140), and wherein, in said released position, the through-opening (127) and the first recess (135) are aligned allowing the at least one locking element (138) to evacuate the second recess (141) and release said locking engagement between the linearly actuated element (126) and the actuator stem (140).

6. The actuator (100) according to claim 5, characterised by the at least one locking element (138) comprising a cylindrical roller or a spherical ball.

7. The actuator (100) according to any one of claims 5 and 6, characterised by at least two locking elements (138a, 138b) being arranged in each through-opening (127) and being stacked one on top of the other in an axial direction (A) of the linearly actuated element (126).

8. The actuator (100) according to any one of claims 5-7, characterised by said at least one release mechanism assembly (131) comprising a first release mechanism assembly (131a) and a second release mechanism assembly (131b) arranged opposite each other in the linearly actuated element (126).

9. The actuator (100) according to claim 8, characterised by the through-opening (127) of the first release mechanism assembly (131a) and the through-opening (127) of the second release mechanism assembly (131b) being arranged in a first common plane orthogonal to the axis (A) of the linearly actuated element (126).

10. The actuator (100) according to any one of claims 8 and 9, characterised by said at least one release mechanism assembly (131) comprising a third release mechanismassembly (131c) and a fourth release mechanism assembly (13 Id) arranged opposite each other in the linearly actuated element (126).

11. The actuator (100) according to claim 10, characterised by the through-opening (127) of the third release mechanism assembly (131c) and the through-opening (127) the fourth release mechanism assembly (13 Id) being arranged in any one of: said first common plane; and a second common plane being orthogonal to the axis (A) of the linearly actuated element (126) and being different from said first common plane.

12. The actuator (100) according to any one of claims 2-11, characterised by the rotatable element (126) being a lead screw and by the linearly actuated element being a lead nut.

13. The actuator (100) according to any one of claims 2-11, characterised by the rotatable element (126) being a threaded shaft provided with a helical raceway for ball bearings and by the linearly actuated element being a ball screw.

14. The actuator (100) according to claim any one of the preceding claims, characterised by the release mechanism (130) being configured to disconnect the actuator stem (140) from the linkage mechanism (122) upon the actuator (100) receiving a command to bring the safety valve (200) to the fail-safe position.

15. A subsea system (400) comprising a fail-safe biased safety valve (200) and an apparatus (100) according to any one of the preceding claims.

16. A method of bringing a safety valve (200) operated by an actuator (100) in a subsea system (400) from an active position to a fail-safe position, the safety valve (200) comprising a safety valve stem (210) and biasing means (220) configured for producing a force biasing the safety valve (200) towards the fail-safe position, the actuator (100) comprising:- an electric motor (120);- a linkage mechanism (122) actuated by the electric motor (120); and- an actuator stem (140) actuated by the linkage mechanism (122), the actuator stem (140) being configured to hold the safety valve (200) in the active position by interacting with the safety valve stem (210) to counteract said force applied by the biasing means (220), the method comprising the step of releasing connection between the linkage mechanism (122) and the actuator stem (140) upon the actuator (100) being released from the hold configuration, thereby allowing the actuator stem (140) free axial movement independent of the electric motor (120) and the linkage mechanism (122).

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