WO2015163767A1

WO2015163767A1 - Actuator for use in subsea installations

Info

Publication number: WO2015163767A1
Application number: PCT/NO2015/000007
Authority: WO
Inventors: Svein Lilleland
Original assignee: Subsea Chokes International As
Priority date: 2014-04-25
Filing date: 2015-04-24
Publication date: 2015-10-29

Abstract

Actuator for use in subsea installations. The actuator comprises a pressure compensator (D) for limitation of temperature-induced pressure increase in a closed hydraulic system in the actuator. The pressure compensator comprises a piston (14) arranged movable within a cylinder. The piston exhibits a first end having a first area (Al), and a second end having a second area (A2). The first area (Al) is connected to a first port (1) connected to a supply pressure (PI). The second area (A2) is connected to a second port (2) connected to a closed hydraulic system having pressure (P2). The first area (Al) is larger than the second area (A2). If the pressure P2 rises, the piston will start to move toward the first port (1) when the pressure (P2) reach a value equal to the ratio between (A1/A2) and then limit the pressure (P2) to the supply pressure (PI) x ratio between (Al) and (A2).

Description

Actuator for use in subsea installations

[0001] The invention concerns a device for limiting temperature-induced pressure increase in closed hydraulic systems in subsea installations. The invention also concerns use of a pressure compensator in an actuator. Background

[0002] Hydraulic systems is an extensively used technology in numerous fields, e.g., hydraulic presses. Another example is valve control in process plants and control of equipment down i wells in offshore installations, where force from hydraulic fluid at high pressure is transformed into mechanical power or movement, for example for rotating a valve disc to control a fluid flow. [0003] Hydraulically operated actuators are used in subsea installations, e.g., for valve control. However, actuators of this type are subjected to large temperature variations. In a closed compartment, the pressure in a hydraulic fluid will increase proportionally by a temperature rise. This pressure increase is produced by the liquid bulk modulus and the liquid expansion coefficient. Typical values based on bar, liters and °C are: · Bulk modulus: 20 000 bar

• Thermal expansion coefficient: 0.0005 cm³/cm³/°C

[0004] Both of these parameters will vary slightly by, among others, liquid type, but only marginally. Then, the pressure increase coefficient typically becomes 20 000 * 0.0005 = 10 bar/°C. This will be a practical value for most calculation purposes. [0005] For subsea installations offshore, temperature increase from 4 to up to 200 °C may be encountered. This may produce a potential pressure increase from, e.g. 200 bar to about 2200 bar. This is an unbearable situation and may result in leakage and breakdown. A conceivable way of solving an excessive pressure increase could be to install a safety valve in a subsea hydraulic system to relieve pressure. However, safety valves a subject to leakage and do sooner or later have to be repaired or replaced. There is also a risk that the safety valve fails to close completely when the pressure decreases, and becomes stuck almost fully closed. Another alternative would have been to use explosive ink in the closed hydraulic circuit, but this has to be replaced after a burst. However, replacement of subsea valves and replacement of explosive ink in offshore installations requires tripping out the subsea Christmas tree. However, replacement of subsea valve in offshore installations is a very expensive operation, tripping out a subsea Christmas tree to retrieve a safety valve in the hydraulic system typically cost 3.8 million USD. Safety valves are therefore not any real alternative. Accordingly, there are no reliable devices available to handle temperature induced pressure increase in actuators having a closed hydraulic system.

Object [0006] Accordingly, there is a need for an actuator capable of limiting temperature-induced pressure increase in a closed hydraulic circuit in actuators of this type that overcomes the disadvantages of prior art solutions that leak or need periodical replacement.

The invention

[0007] These objects are achieved by an actuator in accordance with the characterizing part of patent claim 1 including use of a pressure compensator. Further advantageous features appear from the dependent claims.

[0008] A pressure compensator is in accordance with the invention arranged in the actuator, within the hydraulic circuit of the actuator, to limit temperature-induced pressure increase in the hydraulic circuit. The pressure compensator exhibits a piston accommodated in a cylinder. The piston and the cylinder are formed with a larger area at the low pressure side than the area at the high pressure side. A pressure increase in the hydraulic circuit at the high pressure side will result in a pressure increase to a limit value determined by the area ratio between the end faces of the piston, among other things, whereupon the piston starts to move in direction of the low pressure side. After this point in time, the pressure will remain constant even though the temperature increases, provided that the piston does not meet physical resistance in the cylinder in the pressure compensator. This arrangement enables the actuator to continue operation in a safe manner, even at highly increased temperatures. The pressure compensator of the actuator is described in further details below.

Definitions [0009] The term "actuator" as used herein, is meant to comprise a closed hydraulic circuit, a hydraulic piston connected with the hydraulic circuit, a directional control valve or control valve controlling the pressure to one or the other side of the hydraulic piston, to control a device connected to the actuator, e.g. a valve. The actuator do also in accordance with the invention comprise a "pressure compensator" to limit temperature-induced pressure increase in the closed hydraulic circuit. The pressure compensator is described in further details below. [0010] The terms "hydraulic fluid" and "liquid" as used herein, is meant to identify fluids substantially comprising liquid, such as water, liquid hydrocarbons, hydraulic liquid but not gas. A particularly preferred flowing medium is hydraulic liquid arranged in hydraulic systems to control mechanical components in subsea installations for oil and gas production. [0011] The term "pressure compensator" as used herein, is meant to identify a device for limitation of temperature-induced pressure increase in the closed hydraulic circuit in the actuator. Details of the pressure compensator is described in further details below.

General description

[0012] In the actuator as defined above, a pressure compensator is arranged in the circuit in the closed liquid- or hydraulic system in the actuator. The pressure compensator comprises a closed housing having a first port, a second port, and a substantially cylindrically shaped bore in flow connection with the first and second port. The first port is connected with supply system for a pressurized liquid medium at a pressure P₁₍ whereas the second port is connected with a closed system at a second pressure P₂. A piston is accommodated in the bore and may move axially within the cavity between the respective ports as a result of pressure difference between the ports. The piston has a length which is shorter than the bore in the housing and do accordingly create a first and second free space or compartment in the recess in which the piston can move. The piston exhibits a first end facing the first port having a first surface area Ai which is exposed to the supply pressure Pi and a second end facing the second port having a second area A₂ which is smaller than the first area Ai and which is exposed to the pressure P₂ in the closed liquid system. The piston exhibits an annular space between the first and second end of the piston, in which the piston can move and is in flow connection with the surrounding pressure.

[0013] If the pressure P₂ in the closed system increases, the pressure P₂ in the closed system will increase to a level corresponding to the area ratio between the first and second end of the piston. Should the pressure P₂ increase further, the piston will start to move in direction of the first port in the device and limit the pressure P₂. The pressure P₂ in the closed system will then remain substantially constant even though for example the temperature should increase further.

[0014] The size of the first and second compartments in the bore between first end of the cylinder and first port, and between second end of the cylinder and second port (the stroke length of the piston) and the size ratio between the first and second area A_x and A₂, respectively, will vary with the system the pressure compensator is going to be used in, such as surrounding pressure and expected pressure increase. [0015] For example, is the pressure Pi = 200 bar and the area ratio between Ai and A₂ is 1.1, the pressure P₂ is 200 bar and the liquid is an ordinary hydraulic liquid, the pressure P₂ will increase to 200 bar * (A- A₂) = 220 bar at temperature increase, whereupon the piston starts to move in direction of the first port in the pressure compensator and limit the pressure P₂ to 220 bar. In a closed cylinder having a first and second free compartment in which the piston can move, there is of course a limit of how much the pressure compensator is able to limit. However, a person skilled in the art may, with support in the present description and his/hers skill in the art, easily be able to dimension a pressure compensator in accordance with prevailing pressure and expected pressure/volume variations in the system in which the actuator according to the present invention is going to be utilized.

Drawings

[0016] In the following, the invention is described in further details with reference to drawings, where

Fig. 1 illustrates a schematic flow sheet of a hydraulic circuit in an actuator in accordance with the present invention, and

Fig. 2 illustrates a principle drawing of the pressure compensator in the actuator in accordance with the present invention, viewed in a schematic cross-section.

Detailed description

[0017] With reference to Fig. 1, a flow sheet is shown, illustrating a hydraulic system in an actuator in accordance with the present invention, having a hydraulic cylinder 4 to control, for example, valves in subsea installations. Other details of an actuator of this type has been omitted for simplicity. The hydraulic system is connected to a hydraulic source 10 for supply of hydraulic fluid at a pressure PI. The pressure compensator in the actuator in accordance with the present invention to limit pressure, is designated generally at reference character D. The pressure compensator D is in flow connection with the hydraulic source 10 via conduit 12. The pressure compensator D exhibits a first port 1 connected to the hydraulic source 10 and a second port 2 connected to a hydraulic volume at pressure P₂. Pressure fluctuations arising in this hydraulic volume is to be limited. The pressure compensator D exhibits a first area Ai exposed to the hydraulic source 10 at pressure P_x and a second area A₂ exposed to a hydraulic volume at pressure P₂ to be limited in case of temperature increase. [0018] Still referring to Fig. 1, the second port 2 of the pressure compensator D is connected to an ordinary hydraulic cylinder 4 which accommodates a piston 5 arranged axially movable in the cylinder and being provided with a piston rod 6, thus forming a first compartment 7 and a second compartment 8 in the hydraulic cylinder. This piston and this cylinder do not have to be mistaken by piston and cylinder described in connection with Fig. 2 related to the pressure compensator. The respective compartments of the hydraulic cylinder 4 is connected with a directional control valve 9 to direct the pressure to the first 7 or second compartment 8 in the hydraulic cylinder 4, thus moving the piston 6 in one direction or the other, and then perform mechanical opening or closing of a connected component in a subsea installation, such as a valve (not shown). The direction of movement of the piston is indicated by the arrow B in Fig. 1 in a case where the hydraulic source 10 provides the first compartment 7 with hydraulic fluid at the pressure PI. At this point in time, the pressure P_x equals the pressure P₂. The position of the directional control valve 9 is indicated by the dots figure 9A. Then the second compartment 8 in the hydraulic cylinder 4 is in flow connection with the surrounding pressure indicated by reference numeral 11. In a subsea installation down in a deep water well, the surrounding pressure may for example be 300 bar. The dotted lines in Fig. 1 indicated by reference character 9B, illustrates a situation where the hydraulic source 10 provides the second compartment 8 in the hydraulic cylinder 4, thus moving the piston 5 to the left in the drawing, and in a direction toward the arrow B, for example to close or open a connected component (not shown) opposite the first situation described above. When the directional control valve 9 is in an intermediate position as shown in Fig. 1, the valve has little or no leakage from compartments 7 and 8 to the environments 11, and if the cylinder is heated the pressure P₂ will increase.

[0019] Now referring to Fig. 2, an illustration is provided of an example of the pressure compensator D itself in the actuator of the present invention, in a highly schematic cross-section. Mutual dimensions of piston, cylinder and cylinder volume is solely provided as illustration and is not to be interpreted as any exact measures of the device.

[0020] The pressure compensator comprises a closed housing 3 having a first port 1, a second port 2 and a cylindrical bore 15 in flow connection with the first port and the second port 2. A piston 14 is arranged within the cylindrical bore 15 and is movable axially in the bore 15 between the first port 1 and the second port 2. The direction of movement of the piston 14 is indicated by the dotted line C in the center of the housing 3.

[0021] The bore 15 exhibits a first diameter Dl at the first port 1 which is larger than the second diameter D2 at the second port 2. The transition between the first and second diameter Dl and D2 is formed by a flange 17, which is described in further details below. A port 16 is formed in the end of the cylinder having the first (and largest) diameter Dl by the flange 17 and is in flow connection with the surrounding pressure, as described above.

[0022] The piston 14 exhibits equivalently a first diameter DS1 at the first end 13 which is equal to or slightly smaller than the cylinder diameter Dl. The length LSI of the piston 14 having diameter DS1 is shorter than the length LSI of the cylinder 15 having the largest diameter Dl. Moreover, the second end 20 of the piston 14 exhibits a second diameter DS2 which is equal to or slightly less than the second diameter D2 of the cylinder 15. The length LS2 of the piston 14 having diameter DS2 is larger than or equal to the length LS2 of the cylinder 15 at the second port 2 plus the longitudinal extension of the port 16 arranged at the flange 17.

[0023] The cylinder 15 and the piston 14 do in this way form an annular space 18 between the cylindrical part having largest diameter Dl and the piston part having smallest diameter DS2. The port 16 is also located within this annular space 18. Moreover, a first free space or compartment Si is formed between the first end 13 of the piston, having the largest diameter DS1 and the first port 1, and a second free space or compartment S₂ between the second end 20 of the piston, having the smallest diameter DS2 and the second port 2.

[0024] Moreover, the piston is provided with gaskets indicated at reference numeral 19, to prevent liquid from flowing in the clearance between the cylinder 15 and the piston 14. Relative dimensions between cylinder and piston including dimensioning and localization of gaskets 19 is not described in further detail, since it is considered to be within the reach of a person having ordinary skill in the art and with support in the present description.

[0025] Moreover, Fig. 2 illustrates the pressure compensator in a situation where the pressure P₂ in the closed hydraulic system has been limited towards the supply pressure Pi by a magnitude represented by the volume of the free space S₂, provided that the initial situation of the piston was a position where the second end 20 was localized adjacent to the second port 2 having a free space S₂ substantially equal to zero. Moreover, the device of Fig. 2 is capable of limiting the pressure P₂ in the closed hydraulic system by a volume represented by the free space Si between the first end 13 of the piston 14 and the first port 1 toward the supply pressure Pi.

[0026] However, the pressure compensator of the present invention is not limited to the embodiment shown schematically in Fig. 2, but can be formed with different geometries and components, provided that is has a movable piston-like means having a surface area at the supply pressure side which is larger than the surface area of the piston-like means facing the closed liquid system in which temperature-induced pressure increase is to be limited by the supply pressure, arranged in a housing in flow connection with the supply pressure and the closed hydraulic circuit of the actuator, respectively.

[0027] Accordingly, the present invention contributes to the use of an actuator to control components in subsea installations, in that the disclosed pressure compensator is capable of limiting temperature-induced pressure increase and secure a reliable operation and decreased need for maintenance of the components. A pressure compensator of this type has not been described before.

Claims

1. Actuator for controlling components in subsea installations, said actuator comprising a housing, a closed hydraulic circuit, a hydraulic piston (5, 6, 7), a directional control valve (9) to control hydraulic pressure to the hydraulic piston (5, 6, 7), characterized in that the actuator comprises a device (D) for limiting temperature-induced pressure increase in the closed hydraulic circuit, said device comprising a housing (3) having a first port (1) for connection to a system (10, 12) for supply of hydraulic fluid at a supply pressure (Pi), a second port (2) for connection to a closed liquid system (4, 5, 6, 8, 9, 11) in which undesired pressure increase (P₂) is to be limited, a closed cylinder (15) formed within the housing (3) in flow connection with the first port (1) and the second port (2), a piston (14), having a first end (13) and a second end (20), accommodated inside the cylinder (15) arranged movable along the longitudinal axis (C) of the cylinder, whereby the longitudinal extension of the piston (14) is less than the longitudinal extension of the cylinder (15) and defines a first compartment (Si) located between the first port (1) and the first end (13) of the cylinder (15), and a second compartment (S₂) located between the second port (2) and the second end (20) of the cylinder (15) in flow isolation from the first compartment (Si), an annular space (18) formed between the cylinder (15) wall and a part of the piston (14), whereby the annular space (18) is in flow connection with surrounding pressure via an intermediate port (16) in the housing (3), whereby the area (Ai) of the first end (13) of the cylinder (15) which is exposed to the supply pressure (Pi) is larger than the area (A₂) of the second end (20) of the cylinder (15) which is exposed to the pressure (P₂) to be equalized.

2. The actuator of claim 1, characterized in that the piston (14) is formed with a first diameter (DSl) from the first port (1) along a distance (LSI) toward the second port (2) and with a second diameter (DS2) along a distance (LS2) toward the second port (2), where the first diameter (DSl) is larger than the second diameter (DS2) and that the cylinder (15) exhibits a first diameter (Dl) at the first port (1) and a second diameter (D2) at the second port which is smaller than the first diameter (Di) of the cylinder (15).

3. The actuator of claim 2, characterized in that the length (LS2) of the piston (14) having the smallest diameter (DS2) is slightly longer than the length of the corresponding part of the cylinder (15) having a corresponding diameter (D2).

4. The actuator of claim 3, characterized in that the port (16) in the annular space (18) between a part of the piston (14) and the cylinder (15) wall is arranged at a flange (17) formed in the cylinder (15) and forms the transition between largest diameter (Dl) and smallest diameter (D2) of the cylinder (15).

5. Use of the device to limit temperature-induced pressure increase according to one of the claims above, in an actuator to limit temperature-increased pressure increase in the closed hydraulic circuit in the actuator.

6. Use of a device (D) comprising a housing (3) having a first port (1) for connection to a system (10, 12) for supply of hydraulic fluid at a supply pressure (Pi), a second port (2) for connection to a closed liquid system (4, 5, 6, 8, 9, 11) in which undesired pressure increase (P₂) is to be limited, a closed cylinder (15) formed within the housing (3) in flow connection with the first port (1) and the second port (2), a piston (14) having a first end (13) and a second end (20), accommodated inside the cylinder (15) arranged movable along the longitudinal axis (C) of the cylinder, whereby the longitudinal extension of the piston (14) is less than the longitudinal extension of the cylinder (15) and defines a first compartment (Si) located between the first port (1) and the first end (13) of the cylinder (15), and a second compartment (S₂) located between the second port (2) and the second end (20) of the cylinder (15) in flow isolation from the first compartment (Si), an annular space (18) formed between the cylinder (15) wall and a part of the piston (14), whereby the annular space (18) is in flow connection with surrounding pressure via an intermediate port (16) in the housing (3), whereby the area (A^ of the first end (13) of the cylinder (15) which is exposed to the supply pressure (Ρ_χ) is larger than the area (A₂) of the second end (20) of the cylinder (15) which is exposed to the pressure (P₂) to be equalized, in an actuator for controlling components in subsea installations to limit temperature-induced pressure increase in a closed hydraulic circuit in the actuator.