Subsea electro-hydraulic actuator with accumulator

Abstract

It is described a subsea electro-hydraulic actuator (100) for operating a biased fail-safe safety valve (500) in a subsea hydrocarbon production and / or processing system, the safety valve (500) being operable between an active position and a fail-safe position, the actuator (100) comprising: - a piston assembly (200) comprising a piston rod (210) configured to operate the safety valve (500); - a hydraulic reservoir (110); - a hydraulic pump (130) being hydraulically connected to the hydraulic reservoir (110); - a check valve (140) being hydraulically connected, at first port (141), to the hydraulic pump (130) and being hydraulically connected, at a second port (142), to the piston assembly (200); - dump valve (150) being operable between an open position and a closed position and hydraulically connected, at first port (153), to the piston assembly (200) and, at a second port (154), to the hydraulic reservoir (110), the dump valve (150) comprising a solenoid (151), the solenoid (151) being configured, when energised, to hold the dump valve (150) in the closed position, and, when deenergised, to allow the dump valve (150) to be brought to the open position to allow the safety valve (500) to be brought to the fail-safe position; wherein an accumulator (300) is hydraulically connected to the second port (142) of the check valve (140) and to the first port (153) of the dump valve (150). It is further described a subsea assembly comprising a biased fail-safe safety valve (500) and the subsea electro-hydraulic actuator (100).

Description

[0001] SUBSEA ELECTRO-HYDRAULIC ACTUATOR WITH ACCUMULATOR

[0002] Technical Field

[0003] The present disclosure and invention relates to a subsea electro-hydraulic actuator for operating a biased fail-safe safety valve in a subsea hydrocarbon production and / or injection well and / or processing system, wherein the actuator comprises an accumulator for handling pressure variations in the actuator. In particular, the present invention relates to an apparatus according to the preamble of claim 1.

[0004] Background

[0005] The production from or injection into a subsea well is controlled by a number of valves that is assembled into a Christmas tree. The actuation of the valves is normally dependent upon hydraulic fluid to operate hydraulic actuators for the valves and is therefore entirely dependent upon an external source for the supply of hydraulic fluid. Hydraulic power is normally supplied through an umbilical running from a station located on a vessel on the surface or, less common, from a land based station. Usually the actuators are controlled by pilot valves housed in a control module located at or near the subsea installation, the pilot valves directing the supply of fluid to each actuator, as dictated by the need for operation. The pilot valves may be operated by electric means and such a system is therefore called an electro-hydraulic system.

[0006] The design of actuators and valves for subsea wells are dictated by stringent requirements because of the dangers of uncontrolled release of hydrocarbons. A typical requirement is that these valves must be failsafe closed, meaning that they must go to the safe state upon loss of power or control. The most common means today in subsea environments, is to use springs that are held in the compressed state by the hydraulic pressure, keeping the valve open, and which is released in the event of loss of hydraulic pressure, thus bringing the valve to safe state (i.e. open or close). The spring force needed to close a valve is dependent on both the well pressure and the ambient pressure, with larger ambient pressure demanding larger springs.

[0007] For the control of subsea wells, a connection between the well and a monitoring and control station must be established. This station can either be located in a floating vessel, platform standing on the seabed or on a land station a long distance away. Communication between the control station and the subsea installation is normally provided by installing an umbilical between the two points. The umbilical contains lines for the supply of hydraulic fluid to the various actuators in or by the well, electric lines for the supply of electric power and signals to various monitoring and control devices and lines for signals to pass to and from the well. This umbilical is expensive, costing several thousand dollars per meter.

[0008] It would therefore be cost-saving to be able to eliminate the umbilical. In the invention, the standard hydraulic lines can be eliminated while maintaining the standard hydraulic spring- operated failsafe system. WO 2015044441 A2 relates to an actuator for a valve in a subsea installation, the valve having a valve element that is movable between a first position and a second position and a spring biasing the valve element to the first position, the actuator comprising: an exchangeable actuator module comprising a hydraulic cylinder with a movable piston, the piston being in mechanical contact connected to said valve element through one or more rods, a fluid pump operatively connected to said hydraulic cylinder, said fluid pump is adapted to supply fluid through a first hydraulic line operatively connected between said hydraulic cylinder and said fluid pump, said first hydraulic line supplying a sufficient pressure to move the piston to cause the valve element to move to the second position, a reservoir for storing a quantity of hydraulic supply fluid, said fluid in said hydraulic fluid supply reservoir having a pressure that is less than said sufficient pressure, and a second hydraulic line providing a fluid passage between the first hydraulic line and said hydraulic fluid supply reservoir, a bypass control unit located in said second hydraulic line and having a movable element operating to open or close said fluid passage providing a failsafe function to the valve, and a first and second force generating means, both the first and second force generating means biasing the movable element to close the fluid passage, and a third force generating means biasing the movable element to open the fluid passage. During use, the third force generating means is a pressurized fluid, preferably originating from the first hydraulic line and the first force generating means is a solenoid, optionally in combination with a lever.

[0009] It is an objective of the invention to provide a subsea electro -hydraulic actuator which can comply with pressure variations originating from pressure drops, temperature variations and / or leaks in the actuator.

[0010] The present invention is directed to various apparatuses and methods that may solve or at least reduce at least one of the aforementioned problems or challenges.

[0011] Summary of the invention

[0012] The invention is defined in the attached claims.

[0013] According to a first aspect, it is disclosed a subsea electro-hydraulic actuator for operating a biased fail-safe safety valve in a subsea hydrocarbon production and / or injection well and / or processing system, the safety valve being operable between an active position and a fail-safe position, the actuator comprising:

[0014] - a piston assembly comprising a piston rod configured to operate the safety valve;

[0015] - a hydraulic reservoir;

[0016] - a hydraulic pump being hydraulically connected to the hydraulic reservoir;

[0017] - a check valve being hydraulically connected, at first port, to the hydraulic pump and being hydraulically connected, at a second port, to the piston assembly;

[0018] -a dump valve being operable between an open position and a closed position and hydraulically connected, at first port, to the piston assembly and, at a second port, to the hydraulic reservoir, the dump valve comprising a solenoid, the solenoid being configured, when energised, to hold the dump valve in the closed position, and, when deenergised, to allow the dump valve to be brought to the open position to allow the safety valve to be brought to the fail-safe position; wherein an accumulator is hydraulically connected to the second port of the check valve and to the first port of the dump valve.

[0019] The accumulator may comprise an accumulator spring.

[0020] The accumulator may comprise an accumulator piston and the accumulator spring may be arranged concentrically relative the accumulator piston. Thus, the accumulator spring may be arranged radially inwards of the accumulator piston or radially outwards of the accumulator piston.

[0021] The piston assembly may comprise a piston rod for actuating the safety valve, and the accumulator may be arranged inside the piston rod.

[0022] The accumulator may be a gas accumulator.

[0023] The dump valve may be hydraulically connectable, at a pilot port, to the hydraulic pump to allow hydraulic fluid from the hydraulic pump to operate the dump valve from the open position to the closed position.

[0024] The hydraulic actuator may comprise a directional valve hydraulically connectable, at a first port to the hydraulic pump and, at a second port to the first port of the check valve.

[0025] The directional valve may be a solenoid control valve.

[0026] The directional valve may comprise a third port connectable to the hydraulic reservoir and a fourth port connectable to the pilot port.

[0027] The actuator may comprise a second directional valve hydraulically connectable, at a first port to the hydraulic pump and, at a second port, to the pilot port.

[0028] The dump valve may be a 2-position, 2-way normally open directional control valve, a spring biasing the dump valve towards the open position and a solenoid biasing the dump valve towards the closed position when electrically energised.

[0029] The dump valve may be a 2-position, 2-way normally open directional control valve, a pilot line biasing the dump valve towards the open position and a solenoid biasing the dump valve towards the closed position when electrically energised.

[0030] The subsea electro-hydraulic actuator may comprise a first pressure relief valve hydraulically connectable, at a first port, to the hydraulic pump and, at a second port, to the hydraulic reservoir.

[0031] The subsea electro-hydraulic actuator may comprise at least one pressure relief function and may be either: - a first pressure relief valve hydraulically connectable, at a first port, to the second port of the check valve and, at a second port, to the hydraulic reservoir, and / or

[0032] - a second pressure relief valve hydraulically connectable, at a first port, to the second port of the check valve and, at a second port, to the hydraulic reservoir.

[0033] The biased fail-safe safety valve may be a fail-safe closed safety valve, the safety valve may be operable between a closed position and an open position and may comprise a spring biasing the safety valve towards the closed position, and wherein, when the dump valve may be deenergised, the safety valve may be allowed to be brought to the closed position.

[0034] According to the first aspect, it is also disclosed a subsea assembly comprising:

[0035] - a biased fail-safe safety valve;

[0036] - a subsea electro-hydraulic actuator as defined above.

[0037] The safety valve is traditionally biased by springs but may also be biased using pressure of a process fluid or hydraulic fluid, respectively, or a combination of springs and pressure.

[0038] The subsea electro-hydraulic actuator described above depends on leak free, or at least almost leak free, valves, i.e. dump valves and check valves, therefore elastomeric seals are preferably used in these valves.

[0039] According to a second aspect it is disclosed a subsea electro-hydraulic actuator for operating a fail-safe closed safety valve in a subsea hydrocarbon production and / or injection well and / or processing system, the safety valve being operable between a closed position and an open position and comprising a spring biasing the safety valve towards the closed position, the actuator comprising:

[0040] - a piston assembly comprising a piston rod configured to operate the safety valve;

[0041] - a hydraulic reservoir;

[0042] - a hydraulic pump being hydraulically connected to the hydraulic reservoir;

[0043] - a check valve being hydraulically connected, at first port, to the hydraulic pump and being hydraulically connected, at a second port, to the piston assembly;

[0044] -a dump valve being operable between an open position and a closed position and hydraulically connected, at first port, to the piston assembly and, at a second port, to the hydraulic reservoir, the dump valve comprising a solenoid, the solenoid being configured, when energised, to hold the dump valve in the closed position, and, when deenergised, to allow the dump valve to be brought to the open position to allow the safety valve to be brought to the closed position; wherein an accumulator being hydraulically connected to the second port of the check valve and to the first port of the dump valve.

[0045] The accumulator may comprise a spring.

[0046] The accumulator can thus be a spring-loaded accumulator. The accumulator may comprise a piston rod and wherein the spring may be arranged concentrically relative the piston rod.

[0047] The spring can be arranged concentrically around a piston rod. Alternatively, the spring can be arranged inside a hollow piston rod.

[0048] The piston assembly may comprise a piston rod for actuating the safety valve, and the accumulator may be arranged inside the piston rod.

[0049] Alternatively, the accumulator may be arranged around the piston rod.

[0050] The accumulator may be a gas accumulator.

[0051] The accumulator can thus be a gas-loaded accumulator.

[0052] The dump valve may be hydraulically connectable, at a pilot port, to the hydraulic pump to allow hydraulic fluid from the hydraulic pump to operate the dump valve from the open position to the closed position.

[0053] The subsea electro-hydraulic actuator may comprise a directional valve hydraulically connectable, at a first port to the hydraulic pump and, at a second port to the first port of the check valve.

[0054] The directional valve may be solenoid control valve.

[0055] The solenoid control valve can be a so-called normally open solenoid control valve.

[0056] The directional valve may comprise a third port connectable to the hydraulic reservoir and a fourth port connectable to the pilot port.

[0057] The subsea electro-hydraulic actuator may comprise a second directional valve hydraulically connectable, at a first port to the hydraulic pump and, at a second port, to the pilot port.

[0058] The dump valve may be a 2-position, 2-way normally open directional control valve, a spring biasing the valve towards the open position and a solenoid biasing the valve towards the closed position when electrically energised.

[0059] The dump valve may be a 2-position, 2-way normally open directional control valve, a pilot line biasing the valve towards the open position and a solenoid biasing the valve towards the closed position when electrically energised.

[0060] The subsea electro-hydraulic actuator may comprise a first pressure relief valve hydraulically connectable, at a first port, to the hydraulic pump and, at a second port, to the hydraulic reservoir.

[0061] The subsea electro-hydraulic actuator may comprise at least one pressure relief function and may be either: - a first pressure relief valve hydraulically connectable, at a first port, to the second port of the check valve and, at a second port, to the hydraulic reservoir, and / or

[0062] - a second pressure relief valve hydraulically connectable, at a first port, to the second port of the check valve and, at a second port, to the hydraulic reservoir.

[0063] The present invention also relates to a subsea assembly comprising:

[0064] - a fail-safe closed safety valve;

[0065] - a subsea electro-hydraulic actuator as defined above.

[0066] Above-discussed preferred and / or optional features of each aspect of the invention / disclosure may be used, alone or in appropriate combination, in the other aspects of the invention / disclosure.

[0067] 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.

[0068] Description of the drawings

[0069] Following drawings are appended to facilitate the understanding of the claimed invention:

[0070] Fig. 1 discloses a subsea electro-hydraulic actuator and a fail-safe closed safety valve in a subsea hydrocarbon production and / or processing system, wherein the subsea electro-hydraulic actuator is shown with one directional valve and a spring-loaded accumulator;

[0071] Fig. 2 discloses a subsea electro-hydraulic actuator and a fail-safe closed safety valve in a subsea hydrocarbon production and / or processing system similar to the actuator in Fig. 1 except that the actuator comprises two directional valves and a spring-loaded accumulator;

[0072] Fig. 3 discloses a subsea electro-hydraulic actuator and a fail-safe closed safety valve in a subsea hydrocarbon production and / or processing system similar to the actuator in Fig. 2 except that the actuator comprises a gas-loaded accumulator;

[0073] Fig. 4A discloses subsea electro-hydraulic actuator and a fail-safe closed safety valve in a subsea hydrocarbon production and / or processing system as in Fig. 1, but where the spring-loaded accumulator is arranged inside a piston rod of a piston assembly;

[0074] Fig. 4B shows details of the piston assembly in Fig. 4A with the spring-loaded accumulator arranged therein, where the spring-loaded accumulator is in a noncompensating position;

[0075] Fig. 4C is a detailed view of section A in Fig. 4B; Fig. 4D shows details of the piston assembly in Fig 4A, where the spring- loaded accumulator is in a compensating position;

[0076] Fig. 4E is a detailed view of section B in Fig. 4D;

[0077] It should be understood, however, that the drawings are not intended to limit the claimed invention to the subject-matter depicted in the drawings.

[0078] 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.

[0079] Detailed description

[0080] 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 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.

[0081] Fig. 1 discloses a subsea electro-hydraulic actuator 100 and a fail-safe closed safety valve 500 in a subsea hydrocarbon production and / or processing system, wherein the subsea electro-hydraulic actuator 100 is shown with one directional valve 160 and a spring-loaded accumulator 300.

[0082] The safety valve 500 is mechanically in contact with a piston rod 210 of a piston assembly 200. In Fig. 1 the piston assembly 200 has operated the safety valve 500 to a closed position. The actuator 100 in Fig. 1 comprises a hydraulic pump 130. The hydraulic pump 130 is in fluid communication with a hydraulic reservoir 110. A first hydraulic line 400 extends from the hydraulic pump to a directional valve 160. The directional valve 160 in Fig. 1 is shown as a four port directional valve 160 and the first hydraulic line 401 is connectable to a first port 161 of the directional valve 160. The directional valve comprises a spring 166 biasing the directional valve towards an open position (as shown in Fig. 1) and a solenoid 165 biasing the directional valve 160 towards a closed position. A second hydraulic line 402 is connectable to a second port 162 of the directional valve 160 in one end and to a first port 201 of the piston assembly 200 in an opposite end. A check valve 140 is arranged inline in the second hydraulic line 402. The check valve 140 has a first port 141 and a second port 142. The piston assembly 200 is disclosed with a first chamber 204 and a second chamber 205 separated by a piston 203 connected to piston rod 210. The first port 201 is in fluid communication with the first chamber 204. A second port 202 of the piston assembly 200 is in fluid communication with the hydraulic reservoir 110 via a third hydraulic line 403.

[0083] A fourth hydraulic line 404 is connectable to the second hydraulic line 402 between the second port 142 of the check valve 140 and the first port 201 of the piston assembly 200 and is connectable to a first port 153 of the dump valve 150. The dump valve 150 is being operable between an open position and a closed position. In Fig. 1 the dump valve 150 is in the closed position. The dump valve 150 comprises a second port 154 which is connectable to a fifth hydraulic line 405. The fifth hydraulic line 405 is in fluid communication with the hydraulic reservoir 110. The dump valve 150 comprising a solenoid 151. The solenoid 151 being configured, when energised, to hold the dump valve 150 in the closed position, and, when deenergised, to allow the dump valve 150 to be brought to the open position to allow the safety valve 500 to be brought to the closed position. The dump valve is disclosed with a spring 155 biasing the dump valve 150 to its open position. The biasing force of the solenoid 151, when electrically energised, is larger than a biasing force of the spring 155 (and / or eventual pressure forces of process fluid or hydraulic fluid). Thus, when the dump valve 150 is in the closed position, the solenoid 151 maintains the dump valve 150 in the closed position until the solenoid 151 is switched off or the electrical current to the solenoid 151 is lost.

[0084] An accumulator 300 is arranged in the second hydraulic line 402 and is hydraulically connected to the second port 142 of the check valve 140 and to the first port 153 of the dump valve 150.

[0085] The dump valve 150 comprises a pilot port 152 biasing the dump valve 150 towards the closed position (i.e. working in the same direction as the solenoid 151). The pilot port 152 being hydraulically connectable to the hydraulic pump 130 via a sixth hydraulic line 406 to allow hydraulic fluid from the hydraulic pump 130 to operate the dump valve 150 from the open position (as shown in Fig. 1) to the closed position. It should be noted that, in order to be able to connect the hydraulic pump 130 to the pilot port 152, the directional valve 160 needs to be in the other position compared to the position shown in Fig. 1.

[0086] The actuator 100 may comprise a first pressure relief valve 180 and / or a second pressure relief valve 190.

[0087] The first pressure relief valve 180 may be arranged in a seventh hydraulic line 407 and may be hydraulically connectable, at a first port 181, to the second port 142 of the check valve 140 and, at a second port 182, to the hydraulic reservoir 110.

[0088] The second pressure relief valve 190 may be arranged in an eight hydraulic line 408 and may be hydraulically connectable, at a first port 191, to the second port 142 of the check valve 140 and, at a second port 192, to the hydraulic reservoir 110. Alternatively, the second pressure relief valve 190 may be arranged as an integral part of the dump valve 150 having a spring between the solenoid 151 and the valve member (movable part of the valve).

[0089] The directional valve 160 comprises a third port 163 connectable to the hydraulic reservoir 110 via a ninth hydraulic line 409.

[0090] A subsea assembly is defined by the components forming part of the actuator 100 and the safety valve 500.

[0091] When operating the dump valve 150 from the open position in Fig. 1 such as to able to perform a controlled opening of the safety valve 500 from the closed position in Fig. 1, this may be done by performing the following steps:

[0092] Turn on solenoid 165 to change position of the directional valve 160 to open for fluid communication from the first hydraulic line 401 to the sixth hydraulic line 406,

[0093] Turn on the hydraulic pump 130 to change the position of dump valve 150 to an open position,

[0094] Turn on solenoid 151 to hold the directional valve 150 in the closed position,

[0095] Optional: Turn off the hydraulic pump 130,

[0096] Turn off solenoid 165 in the directional valve 160 to change position of the directional valve 160 to open for fluid communication from the first hydraulic line 401 to the second hydraulic line 402,

[0097] (Optional: If hydraulic pump 130 has been turned off, turn on hydraulic pump 130)

[0098] Use the hydraulic pump pressure to operate the piston assembly 200 to operate the safety valve 500 to an open position,

[0099] (Optional: Turn off solenoid 165 to change position of the second three port directional valve 160),

[0100] Turn off the hydraulic pump 130.

[0101] Fig. 2 discloses a subsea electro -hydraulic actuator 100 and a fail-safe closed safety valve 500 in a subsea hydrocarbon production and / or processing system similar to the actuator 100 in Fig. 1 except that the actuator 1 comprises two directional valves 120; 170 and a spring- loaded accumulator 300.

[0102] The directional valve with reference number 120 is a first three port directional valve 120 and the directional valve with reference number 170 is a second three port directional valve 170. The two three port directional valves 120 and 170 are identical and together perform the same function as the directional valve 160 in Fig. 1 and are shown as solenoid control valves.

[0103] The first three port directional valve 120 is hydraulically connectable via the first hydraulic line 401, at a first port 121 to the hydraulic pump 130 and, at a second port 122 to the first port 141 of the check valve 140. A third port 173 of the first three port directional valve 120 is hydraulically connectable to the hydraulic reservoir 110 via line 413.

[0104] A first port 171 of the second three port directional valve 170 is hydraulically connectable via an inlet line 410 the hydraulic pump 130 (i.e. via first hydraulic line 401).

[0105] A second port 172 of the second three port directional valve 170 is hydraulically connectable to the pilot port 152 via inlet / outlet line 411.

[0106] A third port 173 of the second three port directional valve 170 is hydraulically connectable to the hydraulic reservoir 110 via outlet line 412.

[0107] When operating the dump valve 150 from the open position in Fig. 2 such as to able to perform a controlled opening of the safety valve 500 from the closed position in Fig. 2, this may be done by performing the following steps:

[0108] Turn on solenoid 175 to change position of the second three port directional valve 170 to open for fluid communication from the first hydraulic line 401 to the inlet / outlet line 411,

[0109] Turn on the hydraulic pump 130 to change the position of dump valve 150 to an open position,

[0110] Turn on solenoid 151 to hold the directional valve 150 in the closed position,

[0111] Optional: Turn off the hydraulic pump 130,

[0112] Turn off solenoid 175 to change position of the second three port directional valve 170 to the closed position,

[0113] Turn on solenoid 125 to change position of first three port directional valve 120 to open for fluid communication from the first hydraulic line 401 to the second hydraulic line 402,

[0114] (Optional: If hydraulic pump 130 has been turned off, turn on hydraulic pump 130),

[0115] Use the hydraulic pump pressure to operate the piston assembly 200 to operate the safety valve 500 to an open position,

[0116] (Optional: Turn off solenoid 125 to change position of the second three port directional valve 120),

[0117] Turn off the hydraulic pump 130. Fig. 3 discloses a subsea electro-hydraulic actuator 1 and a fail-safe closed safety valve 500 in a subsea hydrocarbon production and / or processing system similar to the actuator 1 in Fig. 2 except that the actuator 1 comprises a gas-loaded accumulator 300.

[0118] Although it is mentioned in relation to Figures 1-3 that the actuator 100 is for operating a safety valve 500 which is a fail-safe closed safety valve 500, it is clear that the actuator 100 is equally configured to operate a fail-safe open safety valve 500.

[0119] Fig. 4A discloses subsea electro-hydraulic actuator 100 and a fail-safe safety valve 500 in a subsea hydrocarbon production and / or injection well and / or processing system as in Fig. 1, but where the spring-loaded accumulator 300 is arranged inside a piston rod 210 of a piston assembly 200. Similar to the relative positions of the components of the actuator 100 in Fig. 1, the safety valve 500 is mechanically in contact to a piston rod 210 of a piston assembly 200 and the piston assembly 200 has allowed the safety valve 500 to be operated to the closed position.

[0120] Arrow F indicates the force F exerted from the safety valve 500 on the piston rod 210 of the piston assembly 200 biasing the piston rod 210. When the force F is larger than the pressure (times piston area) in the first chamber 204, the safety valve 500 is in the closed position. And when the force F is smaller than the pressure times piston area in the first chamber 204, the safety valve 500 is in the open position.

[0121] Fig. 4B shows details of the piston assembly 200 in Fig. 4A with the spring-loaded accumulator 300 arranged therein, where the spring-loaded accumulator 300 is in an empty position. The piston assembly 200 is disclosed with a first chamber 204 and a second chamber 205 separated by a piston 203 connected to a piston rod 210. The first port 201 is in fluid communication with the first chamber 204. The accumulator 300 is arranged inside the piston rod 210 and comprises an accumulator piston 302 and an accumulator spring 301. The accumulator spring 301 is arranged radially outwards of the accumulator piston 302 and encircles a part of the length of the accumulator piston 302.

[0122] The accumulator piston 302 is movable from the end position shown in Figs. 4B and 4C where a flange 303 of the accumulator piston 302 is in contact with the piston 203 of the piston assembly 200, and to the end position shown in Figs. 4D and 4E where a second end face 302" of the accumulator piston 302 is in contact with the internal wall of the piston rod 210' of the cylinder / piston assembly 200. The piston 203 is provided with a through-going opening 206 for receiving an end of the accumulator piston 302.

[0123] The accumulator spring 301 biases the accumulator piston 302 towards the piston 203. As seen in Figs. 4B and 4C, a first end face 302’ of the accumulator piston 302 is flush with a surface of the piston 203 facing the first chamber 204, while a second end face 302”, on an opposite longitudanl end of the accumulator piston 302 relative to the first end face 302’, is at a distance D from an inner end 210’ of the piston rod 210.

[0124] Fig. 4C is a detailed view of section A in Fig. 4B The empty position of the spring-loaded accumulator 300 in Figs. 4B and 4C is illustrated in that the flange 303 of the accumulator piston 302 is in contact with the piston 203 of the piston assembly 200, thereby there is no hydraulic energy stored.

[0125] Fig. 4D shows details of the cylinder / piston assembly 200 in Fig 4A, where the spring-loaded accumulator 300 is in a filled position. When comparing the relative position of the accumulator piston 302 in Figs. 4B and 4C relative to the the accumulator piston 302 in Figs. 4D and 4E, it can be seen that the accumulator piston 302 has moved towards, and into contact with, the inner end 210’ of the piston rod 210 (i.e. towards right in the Figures). The position in Figs. 4D and 4E, where the second end face 302” of the accumulator piston 302 is in contact with the inner end 201’ of the piston rod 210 and the flange 303 of the accumulator piston 302 is not in contact with the piston 203, is referred to as filled posisiotn or compensating position. The volume of the accumulator 700 is indicated by the dotted lines surrounding ref. no 700 and is defined by cross-sectional area of the through-going opening 206 multiplied by the distance D (the distance D is the travel distance for the accumulator piston 302 between the position in Figs. 4B / 4C relative to the position in Figs. 4D / 4E).

[0126] The safety valves and the hydraulic valves described above are traditionally biased by springs but may also be biased using pressure of a process fluid or hydraulic fluid, respectively, or a combination of springs and pressure.

[0127] 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.

[0128] LIST OF REFERENCE NUMBERS

[0129] 100 hydraulic system

[0130] 110 hydraulic reservoir

[0131] 120 directional valve / first three port directional valve

[0132] 121 first port of first three port directional valve

[0133] 122 second port of first three port directional valve

[0134] 123 third port of first three port directional valve

[0135] 125 solenoid

[0136] 126 spring

[0137] 130 hydraulic pump

[0138] 140 check valve

[0139] 141 first port of check valve

[0140] 142 second port of check valve

[0141] 150 dump valve

[0142] 151 solenoid

[0143] 152 pilot port

[0144] 153 first port of dump valve

[0145] 154 second port of dump valve

[0146] 160 directional valve

[0147] 161 first port of directional valve

[0148] 162 second port of directional valve

[0149] 163 third port of directional valve

[0150] 164 fourth port of directional valve

[0151] 170 second three port directional valve

[0152] 171 first port of second three port directional valve

[0153] 172 second port of second three port directional valve

[0154] 173 third port of second three port directional valve

[0155] 175 solenoid

[0156] 176 spring

[0157] 180 first pressure relief valve

[0158] 181 first port of first pressure relief valve

[0159] 182 second port of first pressure relief valve

[0160] 190 second pressure relief valve

[0161] 191 first port second pressure relief valve

[0162] 192 second port second pressure relief valve

[0163] 200 piston assembly

[0164] 201 first port of piston assembly

[0165] 202 second port of piston assembly

[0166] 203 piston of piston assembly

[0167] 204 first chamber of piston assembly

[0168] 205 second chamber of piston assembly

[0169] 206 through-going opening

[0170] 210 piston rod of piston assembly

[0171] 210’ inner end of piston rod 210

[0172] 300 accumulator

[0173] 301 accumulator spring

[0174] 302 accumulator piston

[0175] 302’ first end face

[0176] 302” second end face 303 flange of piston rod

[0177] 401 first hydraulic line

[0178] 402 second hydraulic line

[0179] 403 third hydraulic line

[0180] 404 fourth hydraulic line

[0181] 405 fifth hydraulic line

[0182] 406 sixth hydraulic line

[0183] 407 seventh hydraulic line

[0184] 408 eight hydraulic line

[0185] 409 ninth hydraulic line

[0186] 410 inlet line

[0187] 411 inlet / outlet line

[0188] 412 outlet line

[0189] 413 line

[0190] 500 safety valve

[0191] 700 compensation volume A section AB section B F Arrow (force)

Claims

Claims1. A subsea electro-hydraulic actuator (100) for operating a biased fail-safe safety valve (500) in a subsea hydrocarbon production and / or injection and / or processing system, the safety valve (500) being operable between an active position and a fail-safe position, the actuator (100) comprising:- a piston assembly (200) comprising a piston rod (210) configured to operate the safety valve (500);- a hydraulic reservoir (110);- a hydraulic pump (130) being hydraulically connected to the hydraulic reservoir (HO);- a check valve (140) being hydraulically connected, at first port (141), to the hydraulic pump (130) and being hydraulically connected, at a second port (142), to the piston assembly (200);- dump valve (150) being operable between an open position and a closed position and hydraulically connected, at first port (153), to the piston assembly (200) and, at a second port (154), to the hydraulic reservoir (110), the dump valve (150) comprising a solenoid (151), the solenoid (151) being configured, when energised, to hold the dump valve (150) in the closed position, and, when deenergised, to allow the dump valve (150) to be brought to the open position to allow the safety valve (500) to be brought to the fail-safe position; characterised by an accumulator (300) being hydraulically connected to the second port (142) of the check valve (140) and to the first port (153) of the dump valve (150).

2. The subsea electro-hydraulic actuator (100) according to claim 1, wherein the accumulator (300) comprises an accumulator spring (301).

3. The subsea electro-hydraulic actuator (100) according to claim 2, wherein the accumulator (300) comprises an accumulator piston (302) and wherein the accumulator spring (301) is arranged concentrically relative the accumulator piston (302).

4. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the piston assembly (200) comprises a piston rod (210) for actuating the safety valve (500), and wherein the accumulator (300) is arranged inside the piston rod (210).

5. The subsea electro-hydraulic actuator (100) according to claim 1, wherein the accumulator (300) being a gas accumulator.

6. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the dump valve (150) being hydraulically connectable, at a pilot port (152), to the hydraulic pump (130) to allow hydraulic fluid from the hydraulic pump (130) to operate the dump valve (150) from the open position to the closed position.

7. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the hydraulic actuator (100) comprising a directional valve (160) hydraulically connectable, at a first port (161) to the hydraulic pump (130) and, at a second port (162), to the first port (141) of the check valve (140).

8. The subsea electro-hydraulic actuator (100) according to claim 7, wherein the directional valve (160) being solenoid control valve.

9. The subsea electro-hydraulic actuator (100) according to claim 7 or 8, wherein the directional valve (160) comprises a third port (163) connectable to the hydraulic reservoir (110) and a fourth port (164) connectable to the pilot port (152).

10. The subsea electro-hydraulic actuator (100) according to claim 7 or 8, wherein the actuator comprises a second directional valve (170) hydraulically connectable, at a first port (171) to the hydraulic pump (130) and, at a second port (172), to the pilot port (152).

11. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the dump valve (150) being a 2-position, 2- way normally open directional control valve, a spring (155) biasing the dump valve (150) towards the open position and a solenoid (151) biasing the dump valve (150) towards the closed position when electrically energised.

12. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the dump valve (150) being a 2-position, 2- way normally open directional control valve, a pilot line biasing the dump valve (150) towards the open position and a solenoid (151) biasing the dump valve (150) towards the closed position when electrically energised.

13. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the actuator (100) comprises a first pressure relief valve (180) hydraulically connectable, at a first port (181), to the hydraulic pump (130) and, at a second port (181), to the hydraulic reservoir (110).

14. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the actuator (100) comprises at least one pressure relief valve (180;190), being either:- a first pressure relief valve (180) hydraulically connectable, at a first port (181), to the second port (142) of the check valve (140) and, at a second port (182), to the hydraulic reservoir (110), and / or- a second pressure relief valve (190) hydraulically connectable, at a first port (191), to the second port (142) of the check valve (140) and, at a second port (192), to the hydraulic reservoir (110).

15. The subsea electro-hydraulic actuator (100) according to any of the preceding claims, wherein the biased fail-safe safety valve (500) is a fail-safe closed safety valve (500), the safety valve (500) being operable between a closed position and an open position and comprising a spring biasing the safety valve (500) towards the closed position, and wherein, when the dump valve is deenergised, the safety valve (500) is allowed to be brought to the closed position.

16. A subsea assembly comprising:- a biased fail-safe safety valve (500);- a subsea electro -hydraulic actuator (100) according to any of the preceding claims 1- 15.

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