Electromagnetically Actuated Pressure Relief Valve for Fracturing Systems

Abstract

Valves for relieving pressure from high-pressure fluid systems have a valve fitting and a valve actuator. The pressure relief valve is normally shut and is adapted to open at a relief fluid pressure. It comprises a valve fitting and an actuator. The actuator has a valve stem, a spring, and an electromagnet. The stem is coupled to a valve body and mounted for linear reciprocation. The spring applies a mechanical force that biases the stem to place the valve in a normally shut state, but allows the valve to open at a first fluid pressure below the relief pressure. The electromagnet applies a magnetic force that, together with the mechanical force, holds the valve in an operationally shut state at a second fluid pressure above the relief pressure. The valve may be opened at fluid pressures above the first fluid pressure by de-energizing the electromagnet at the relief pressure.

Claims

1. A pressure relief valve for high-pressure fluid transportation systems, said pressure relief valve being normally shut and adapted to open at a relief fluid pressure, said pressure relief valve comprising: (a) a valve fitting, said valve fitting comprising: i) a housing adapted for assembly into a high-pressure flow line, said housing having: (1) a fluid inlet; (2) a fluid outlet; and (3) a fluid flow path between said inlet and said outlet; ii) a valve seat in said flow path; iii) a valve body adapted to selectively seat on said valve seat, said valve body exposed to fluid pressure in said inlet; (b) a valve actuator coupled to said valve fitting; said valve actuator comprising: i) a bonnet coupled to said fitting housing; ii) a valve stem; said valve stem being: (1) coupled to said valve body; (2) mounted in said bonnet for linear reciprocation between a closed position, in which said valve body is seated on said valve seat to shut off flow through said flow path, and an open position, in which said valve body is unseated from said valve seat to allow flow through said flow path; iii) a resilient element applying a mechanical force biasing said valve stem in its said closed position and placing said valve in a normally shut state, said mechanical force allowing said valve stem to move to its open position and place said valve in an open state at a first fluid pressure in said inlet below said relief pressure; and iv) an electromagnet applying, when energized, a magnetic force biasing said valve stem in its said closed position, said magnetic force, together with said mechanical force, being sufficient to hold said valve stem in its said closed position and said valve in an operationally shut state at a second fluid pressure in said inlet above said relief pressure; (c) whereby said valve is placed in its open state at fluid pressures above said first fluid pressure by de-energizing said electromagnet at said relief pressure.

2. The pressure relief valve of claim 1, wherein: (a) said valve actuator comprises a ferromagnetic plate fixedly mounted on said valve stem; (b) said resilient element applies said mechanical force to said plate to bias said valve stem in its closed position; and (c) said electromagnet, when energized, applies said electromagnet force to said plate to bias said valve stem in its extended, closed position.

3. The pressure relief valve of claim 2, wherein said valve stem comprises an annular ferromagnetic plate mounted around said valve stem and extending radially therefrom.

4. The pressure relief valve of claim 3, wherein said electromagnet has a generally annular shape and is mounted around said valve stem of said valve actuator, said annular electromagnet and said annular plate having substantially equal diameters.

5. The pressure relief valve of claim 1, wherein a contact face of said ferromagnetic plate or said electromagnet is provided with a slight raised surface effective to create a narrow air gap between said contact faces.

6. The pressure relief valve of claim 1, wherein said electromagnet is a DC electromagnet.

7. (canceled)

8. The pressure relief valve of claim 1, wherein said resilient element is a spring and said valve comprises: (a) a first spring retainer slidably mounted around said valve stem between said electromagnet and a first end of said spring; (b) a second spring retainer slidably mounted around said valve stem adjacent a second end of said spring; and (c) an adjusting nut bearing on said second retainer, said adjusting nut adapted to position said second retainer along said valve stem and thereby adjust said biasing force of said spring.

9. The pressure relief valve of claim 1, wherein said valve seat is a cylindrical seat provided in a bore extending from either said inlet or said outlet and said valve body is a plug, said plug being adapted to extend into said cylindrical seat to shut off flow through said flow path and to retract from said cylindrical seat to allow flow through said flow path.

10. (canceled)

11. The pressure relief valve of claim 8, wherein said valve seat is a cylindrical sleeve insert carried within an enlarged diameter portion of said bore, said sleeve insert having a pressure seal mounted in its inner circumference.

12. The pressure relief valve of claim 1, wherein said valve body is replaceably coupled to said valve stem.

13. The pressure relief valve of claim 1, wherein: (a) said valve stem, in its said closed position, extends beyond said bonnet into said housing of said valve fitting; and (b) said valve actuator is provided with pressure seals between said valve stem and said bonnet to isolate said resilient element and said electromagnet from fluid in said flow path.

14. The pressure relief valve of claim 1, wherein said valve comprises: (a) a first bore extending along a primary axis of said valve; and (b) a second bore intersecting said first bore; (c) wherein: i) said valve seat is a cylindrical sleeve insert, wherein said sleeve insert: (1) is carried within an enlarged diameter portion of said first bore proximate to said intersection between said first bore and said second bore; and (2) has a pressure seal mounted in its inner circumference; ii) said valve body is a plug mounted on a distal end of said valve stem; iii) said valve stem, in its said closed position, extends across said intersection such that said plug extends into said sleeve insert; and iv) said valve stem, in its said open position, retracts into said bonnet such that said plug is withdrawn from said sleeve insert.

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. (canceled)

20. (canceled)

21. A pressure relief valve system for high-pressure fluid transportation systems, said valve system comprising a pressure relief valve of claim 1 and a control system for detection of said relief pressure and selectively energizing and de-energizing said electromagnet.

22. A pressure relief valve system for high-pressure fluid transportation systems, said valve system comprising: (a) the pressure relief valve of claim 1, and (b) a control system operatively connected to said valve, said control system comprising: i) a pressure sensor adapted to measure fluid pressure in said system; ii) an electro-mechanical switch controlling current to said electromagnet; and iii) a controller adapted to receive signals from said sensor and to generate control signals to said switch to selectively energize said electromagnet; (c) whereby: i) said valve is held in its operationally shut state at pressures below said relief pressure by closing said switch and energizing said electromagnet; and ii) said valve is opened by opening said switch and de-energizing said electromagnet in response to detection of said relief pressure.

23. The pressure relief valve system of claim 22, wherein said electromagnet is powered by DC current.

24. The pressure relief valve system of claim 23, wherein said controller is adapted to reduce the level and reverse the polarity of power energizing said electromagnet before de-energizing said electromagnet.

25. The pressure relief valve system of claim 24, wherein a contact face of said ferromagnetic plate or said electromagnet is provided with a slight raised surface effective to create a narrow air gap between said contact faces.

26. A flow line for a high-pressure fluid transportation system, said flow line comprising the pressure relief valve system of claim 22.

27. A high-pressure fluid transportation system, said system comprising the flow line of claim 26.

28. The system of claim 27, wherein said system is a system for fracturing a well.

29. A method for controlling flow through a high-pressure fluid transportation system, wherein said method comprises: (a) installing the pressure relief valve system of claim 22 in fluid communication with a fluid conduit in said system; (b) opening said valve upon detection of the relief pressure, thereby relieving excess pressure in said conduit.

30. The method of claim 29, the method comprising: (a) installing said valve of said pressure relief valve system in fluid communication with a fluid conduit in said system, said fluid pressure in said conduit being below said first fluid pressure such that said valve is in its normally shut state; (b) energizing said electromagnet to place said valve in its operationally shut state; (c) flowing fluids through said conduit at high pressures; and (d) de-energizing said electromagnet if said fluid pressure in said conduit is equal to or greater than said relief pressure.

31. The method of claim 30, wherein said electromagnet is energized with DC power and said method comprises reducing the level of said DC power and reversing its polarity immediately prior to de-energizing said electromagnet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] FIG. 1 (prior art) is a schematic view of a system 24 for fracturing a well and receiving flowback from the well, which system 24 includes a high-pressure flow line 14 feeding a zipper manifold 16 that can selectively divert fluid into three well heads 19.

[0064] FIG. 2 is an isometric view of a flowline assembly 25 incorporating a first preferred embodiment 30 of a pressure relief valve of the subject invention.

[0065] FIG. 3 is an isometric view of novel pressure relief valve 30 shown in FIG. 2.

[0066] FIG. 4 is an isometric, cross-sectional view of novel pressure relief valve 30 shown in FIGS. 2 and 3 in which valve 30 is shown in its shut state.

[0067] FIG. 5 is a cross-sectional view of novel pressure relief valve 30 in its shut state.

[0068] FIG. 6 is a cross-sectional view of novel pressure relief valve 30 in its open state.

[0069] FIG. 7 is an isometric, exploded view of internal components of novel pressure relief valve 30.

[0070] FIG. 8 is a schematic showing a control system 80 for a preferred embodiment 90 of the pressure relief valve systems of the subject invention.

[0071] In the drawings and description that follows, like parts are identified by the same reference numerals. The drawing figures are not necessarily to scale. Certain features of the embodiments may be shown in exaggerated scale or in somewhat schematic form. Some details of conventional design and construction may not be shown in the interest of clarity and conciseness.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0072] The subject invention, in various aspects and embodiments, is directed generally to pressure relief valves for flowlines, and especially for high-pressure flowlines. More particularly, it provides valves that are designed to provide reliable, accurate, precise, and rapid actuation to relieve excessive pressure even when used in fluid transportation systems, such as systems for fracturing oil and gas wells, that convey abrasive and corrosive fluids at high pressures and flow rates. Specific embodiments will be described below. For the sake of conciseness, however, all features of an actual implementation may not be described or illustrated. In developing any actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve a developer's specific goals. Decisions usually will be made consistent within system-related and business-related constraints. Specific goals may vary from one implementation to another. Development efforts might be complex and time consuming and may involve many aspects of design, fabrication, and manufacture. Nevertheless, it should be appreciated that such development projects would be routine effort for those of ordinary skill having the benefit of this disclosure.

[0073] Broad embodiments of the novel valves are directed to valves that may be tapped into flow lines. They are normally shut and are adapted to open at a threshold pressure in the flow line, what will be referred to as a predetermined relief pressure. The valves comprise a valve actuator. The valve actuator has a resilient member, such as a spring or a gas-charged bellows or piston, that applies a mechanical force to bias a reciprocating valve stem in a closed position. The actuator also has an electromagnet that, when energized, applies a magnetic force to the valve stem. The electromagnetic force also biases the valve stem in its closed position. The combined mechanical and magnetic force is sufficient to hold the valve stem in its closed position at pressures above the relief pressure. The mechanical force generated by the resilient member, however, is not sufficient alone to hold the valve stem in its closed position at the relief pressure. It allows the valve to open at pressures significantly below the relief pressure. Thus, the valve may be held in a normally-shut operational state by energizing the electromagnet. When the relief pressure is detected, the electromagnet can be deenergized to allow the valve stem to move to an open position, allowing the valve to open rapidly.

[0074] The novel pressure relief valves may be used in a variety of systems. They are particularly useful in high-pressure flow lines that are common in chemical and other industrial plants, on marine dredging vessels, strip mines, and especially in the oil and gas industry. Certain embodiments are particularly well suited as components of temporary pipe and flow line installations. Hydraulic fracturing systems, such as those shown in FIG. 1, are a very common application where pressure relief valves are a practical necessity. They may be tapped into the high-pressure side of a frac system. If operating pressures reach a specified maximum pressure, the relief pressure P.sub.R, the valve will open rapidly and divert fluid from, and reduce pressure in the high-pressure side before the relief pressure P.sub.R is exceeded.

[0075] A first preferred embodiment 30 of the novel pressure relief valves is shown in FIGS. 2-7. Pressure relief valve 30 may be incorporated, for example, in the frac system 24 shown in FIG. 1 as part of a flowline assembly 25. Flowline assembly 25 is shown in FIG. 2. As shown therein, flowline assembly 25 includes a plug valve 26, a first adapter fitting 27, a 90 elbow 28, a second adapter fitting 29, and novel pressure relief valve 30, all connected in series. Flowline assembly 25 may be tapped into a high-pressure conduit in frac system 24, such as flow line 14 which runs from frac manifold 9 to goat head 15. A tee fitting may be used to connect a tap line from flow line 14 to plug valve 26 in flowline assembly 25. Plug valve 26 will be open during operations, but it may be closed to take valve 30 offline for servicing or replacement. Pressure relief valve 30 may be connected at its downstream end to a bleed-off line. The bleed-off line typically discharges any flow released by pressure relief valve 30 into a tank or pit, such as flowback tanks 21. Valve 30 will open if excess pressure is detected in flow line 14 allowing flow to be diverted. Once the conditions giving rise to the excess pressure have been corrected, valve 30 may be closed to resume fracturing.

[0076] When novel pressure relief valve 30 is assembled into a frac system it preferably will be rated for high pressures, that is, rated pressures of at least about 6,000 psi. For many frac jobs, it may have to be rated for pressures of 10,000 psi, 15,000 psi, or even 20,000 psi. Pressure relief valve 30 and other embodiments of the novel pressure relief valves, however, may be rated for low pressure service (from about 1,000 to about 2,000 psi) or for medium pressure service (from about 2,000 to about 6,000 psi) and used in lower pressure systems. It will be appreciated, however, that what is characterized as low-pressure in frac systems, is actually extremely high pressure as compared to many common fluid transportation systems, such as those that transport water and steam.

[0077] Frac systems are intended for temporary use and will be assembled and disassembled at different well sites as needed. Thus, they are assembled on site from a large number of individual frac iron components and subassemblies of individual components. The components, including valves and other flow control devices, typically will be assembled with various types of unions. Unions allow the components to be connected (made up) and disconnected (broken down) relatively quickly, more quickly than threaded connections that may be preferred for permanent installations.

[0078] The three types of unions commonly used in frac systems are hammer (or Weco) unions, clamp (or Greyloc)) unions, and flange unions. Though spoken of in terms that may imply they are discreet components, unions are actually interconnected subassemblies of the components joined by the union. One sub will be on one component, and a mating sub will be on the other. The subs then will be connected to each other to provide the union. The novel valves preferably are provided with such unions to facilitate their installation in a frac system.

[0079] For example, as may be seen in FIG. 3, novel pressure relief valve 30 generally comprises a valve fitting 34 and a valve actuator 36. Valve fitting 34 comprises a housing 41 that is provided with hammer union subs. One end of housing 41 is provided with a male hammer union sub 42 and another end is provided with a female hammer union sub 43. As is typical, male hammer union sub 42 has a large wing nut 44 carried on housing 41 around a segmented collar 45. A union will be made up by threading wing nut 44 onto external threads on a female hammer union sub of another flowline component, such as an upstream shut-off valve in a tap line running from high-pressure flow line 14. Tightening wing nut 44 will cause the ends of the mated components to bear on and seal against each other. Female hammer union 43 will be assembled in a like manner to a male hammer union sub of a downstream flowline component, such as a bleed-off line.

[0080] Hammer unions subs 42 and 43 are of conventional design. Preferably, they are constructed as disclosed in U.S. Pat. No. 10,808,871 to Duy D. Nguyen, but other conventional designs may be used. Likewise, if desired, the novel pressure relief valves may be assembled into flow lines by conventional clamp or flange unions, by threaded connections, welding, or by other conventional methods and apparatus. It also will be appreciated that the figures illustrate the novel valves as oriented horizontally. That will be the orientation in which they typically will be installed in a system, but they may be installed with a vertical orientation as well.

[0081] As best appreciated from FIGS. 4-7, valve fitting 34 of novel pressure relief valve generally comprises fitting housing 41, a valve seat 51, a valve body 52, and a flowpath wear sleeve 54. Fitting housing 41 comprises the major portion of valve fitting 34 and defines many of its features. It is the primary structure to which other flowline components in frac system 24 will be connected, for example, through hammer union subs 42 and 43 as described above. It also provides the structure in which the other components of valve fitting 34 are assembled and the structure to which valve actuator 36 will be mounted. Given that valve 30 preferably is designed for high-pressure applications, fitting housing 41 will be fabricated with relatively thick walls from high-tensile material.

[0082] In particular, as seen in the figures, fitting housing 41 provides a valve inlet 46, a valve outlet 47, and a receptacle 48 in which valve actuator 36 is mounted. A bore 56 extends from inlet 46 along a secondary axis normal to a primary axis X of valve 30. Inlet bore 56 provides a conduit for fluids entering valve 30. Another bore 57 extends from outlet 47 along primary axis X. It intersects with bore 56 extending from inlet 46 and provides a conduit for fluids to exit valve 30. Bores 56 and 57, as is typical, are generally cylindrical and to a great extent uniformly so. They usually will have a diameter generally equal to the flow line in which valve 30 is tapped. That will help minimize erosion in and pressure drop through valve 30. Conduits with other geometries and sizes may be used, however, if desired.

[0083] In any event, fitting housing 41 thus defines a flow path through valve 30 between inlet 46 and outlet 47. As described further below, fluid may flow in either direction through the flow path in valve 30. Thus, the designations of inlet and outlet are in a sense arbitrary and are made for convenience in describing the novel valves. Valve 30 may be tapped into, for example, flow line 14 with the end designated as outlet 47 serving as the inlet for fluid. The other end designated as inlet 46 will provide the valve outlet.

[0084] Fluid flowing through valve 30 will have an erosive and corrosive effect. Such effects are most pronounced where flow is turbulent, such as at the intersection of inlet bore 56 and outlet bore 57. Thus, as exemplified, replaceable wear sleeve 54 is mounted in the flow path at the bores' intersection. As best appreciated from FIG. 7, wear sleeve 54 has a generally open-cylindrical configuration providing a central conduit. A circular opening extends through the side of wear sleeve 54. The opening allows fluid from inlet bore 56 to flow into the central conduit and thence into outlet bore 57. In the event of excessive wear, sleeve 54 may be replaced.

[0085] A mechanism preferably is provided to make it easier to position wear sleeve 54 in the intersection so that its side opening is properly aligned with inlet bore 56. For example, as appreciated from the cross-sectional views of FIGS. 5-6 and parts view of FIG. 7, wear sleeve 54 may be provided with a slot extending across its upper surface. A pin may be mounted, for example, in a bottomed hole in housing 41 such that it extends into the intersection. The pin is located such that when the slot in wear sleeve 54 is aligned with the pin as wear sleeve 54 is installed, the side opening in wear sleeve 54 will be precisely aligned with inlet bore 56. Other alignment mechanisms may be used. Likewise, if desired, a replaceable wear sleeve may be omitted from the novel pressure relief valves.

[0086] Valve actuator 36, as may be seen in FIGS. 4-6, generally comprises a bonnet 61, a valve stem 71, a spring 72, an electromagnet 73 (simplified depiction), a ferromagnetic plate 74, spring retainers 77, and an adjusting nut 78. Bonnet 61 comprises the major portion of valve actuator 36 of relief valve 30. It is the primary structure in which the other components of valve actuator 36 will be assembled. Bonnet 61 also provides the structure by which valve actuator 36 will be assembled to valve fitting 34.

[0087] For example, bonnet 61 comprises the assembly of two subs, a nipple 61a and a main sub 61b. Both nipple 61a and main sub 61a have a profiled, generally open-cylindrical configuration. Nipple 61a has a generally cylindrical passage in which valve stem 71 is carried. The passage extends along primary axis X of valve 30. The inner end of nipple 61 is provided with an annular flange 63. Flange 63 allows nipple 61a to be connected to bonnet main sub 61b, for example, by threaded connectors extending through flange 63 and into main sub 61b. Flange 63 on nipple 61a and main sub 61b define a generally cylindrical, central chamber 66 through which valve stem 71 extends. Spring 72, electromagnet 73, and ferromagnetic plate 74 are mounted inside chamber 66 and around valve stem 71.

[0088] The outer circumference of the distal end (left side in the figures) of nipple 61a is profiled to allow it to fit closely within housing receptacle 58 of valve fitting 34. The central portion of nipple 61a tapers inward toward a reduced diameter portion. The tapered portion of nipple 61a bears on a mating taper provided in housing receptacle 48, while the reduced diameter portion fits closely within receptacle 48. Nipple 61a thus may be inserted into housing receptacle 48, allowing valve actuator 36 to be assembled to valve fitting 34 by a hammer-type union. Preferably, as shown, static pressure seals, such as elastomeric O-rings, square cut rings, or lobed rings, are provided between the outer circumference of nipple 61a and housing receptacle 48.

[0089] More specifically, receptacle 48 of fitting housing 41 is provided with external threads like those of female hammer union sub 43 on inlet 47 of fitting housing 41. A hammer-type union male sub 62 is provided on the distal end of nipple 61a. Bonnet wing nut 64, similar to wing nut 44 of male hammer union sub 42 on outlet 47 of fitting housing 41, is carried loosely around the central portion of nipple 61a. A segmented collar 65, similar to segmented collar 45 in hammer union sub 42, is assembled outward of wing nut 64, but behind an annular, radially-extending boss, by sliding bonnet wing nut 64 inward. Wing nut 64 then is slipped over segmented collar 65 and engaged with the external threads of receptacle 48 on fitting housing 41. As wing nut 64 is tightened, the distal end of nipple 61a will be drawn into receptacle 48 and valve actuator 36 secured to valve fitting 34.

[0090] Valve seat 51 is mounted in the flow path through valve 30. Valve body 52, as described further below, is selectively seated on valve seat 51 to either open or shut off flow through valve 30. A cylindrical valve seat may be formed in housing 41 of valve fitting 34 as an integral feature, for example, of outlet bore 57. As noted, however, fluid flowing through valve 30 has an erosive and corrosive effect on valve 30 after extended service. Thus, valve seat 51 preferably, as shown, is a separate, replaceable component.

[0091] For example, valve seat 51 is an insert, such as a cylindrical, sleeve insert. It is carried within an enlarged diameter portion of outlet bore 57. Preferably, radial pressure seals, such as elastomeric O-rings, square cut rings, or lobed rings, are provided between the outer circumference of valve seat 51 and the inner circumference of the enlarged diameter portion of bore 57. For example, a pair of O-rings may be mounted in annular glands provided in the outer circumference of valve seat 51. When valve actuator 36 is assembled to valve fitting 34, valve seat 51, as well as wear sleeve 54 will be secured in fitting housing 41. That is, the distal end of nipple 61a of valve actuator 36 bears on and captures wear sleeve 54, which in turn bears on and captures valve seat 51.

[0092] Valve body 52, as described further below, is operationally coupled to reciprocating valve stem 71 of valve actuator 36. Thus, as may be seen by comparing FIGS. 5-6, valve body 52 may be selectively seated on valve seat 51 to either open or shut off flow through valve 30. Valve body 52, for example, is a generally cylindrical plug that is sized to fit closely within valve seat 51. Thus, when it is extended into and within valve seat 51, valve body 52 will place valve 30 in a shut state in which the flow path through fitting housing 41 is blocked such that fluid cannot flow through valve 30.

[0093] A radial pressure seal 55, such as an elastomeric O-ring, square cut ring, or lobed ring, preferably is provided between valve seat 51 and valve body 52 to minimize leakage through the clearance between valve seat 51 and valve body 52. For example, as seen best in FIGS. 5-6, an elastomeric O-ring 55 may be mounted in an annular gland on the inner circumference of valve seat 51. Other types of conventional seals and annular packings are known and may be used if desired. A hard seal ring made, for example, from engineering plastics such as polyether ether ketone (PEEK) may be used. Back up rings also may be used with elastomeric seal rings.

[0094] Valve body 52 preferably, as shown, is releasably coupled to the distal end of valve stem 71, that is, the end of valve stem 71 that is extendable beyond bonnet 61 of valve actuator 36 and into valve fitting 31. For example, the distal end of valve stem 71 has a short, axially extending cylindrical boss. A skirt on the mating end of valve body 52 fits closely around the boss on valve stem 71 and is releasably coupled thereto, for example, by a threaded fastener. In the event valve body 52 suffers excessive wear, it may be replaced. Of course, other coupling designs may be used or, if desired, valve body 52 need not be replaceable. It may be an integral feature of valve stem 71.

[0095] Likewise, if desired, other conventional valve seat and body designs may be utilized in the novel pressure relief valves. For example, the valve seat and valve body may be provided with facing, radially extending beveled or flat annular seal surfaces similar to the valving surfaces provided in globe valves. Globe-type facing valving surfaces may be provided in lieu of, or in addition to the bore and plug design of valve seat 51 and valve body 52. In such designs, the seal surface on the valve body will bear axially on the seal surface of the valve seat.

[0096] As will be appreciated by comparing FIGS. 5 and 6, valve stem 71 is mounted in valve actuator 36 for linear reciprocation between an extended, closed position and a retracted, open position. In its closed position, valve stem 71 seats valve body 52 on valve seat 51 to shut off flow through the flow path and place valve 30 in its shut state. When valve stem 71 is in its open position, valve body 52 is retracted and unseated from valve seat 51. Fluid can flow through the flow path and valve 30 is in its open state.

[0097] More specifically, valve stem 71 extends axially through and, when extended, beyond bonnet 61 of valve actuator 36. It fits closely within the axial passage provided in nipple 61a. The passage in nipple 61a is aligned axially with bore 57 extending from outlet 47 and guides valve stem 71 as it reciprocates. Preferably, guide rings are provided within the passage to increase the ease and reliability with which valve stem 71 reciprocates. Pressure seals also preferably are provided between the passage walls and valve stem 71 to minimize, if not eliminate leakage of fluid from valve fitting 31 into valve actuator 36.

[0098] For example, as may be seen best in FIGS. 5-7, valve actuator 36 is provided with a pair of stem guide rings 75a/b and a stem pressure seal 76a at the distal end of nipple 61a and a stem guide ring 75c and a stem pressure seal 76c near the flanged-end of nipple 61a. Stem guide rings 75 are mounted, for example, in annular rabbets provided in the walls of the axial passage in nipple 61a. Stem seals 76 preferably are radial, reciprocating dynamic pressure seals, such as elastomeric cup-style seal rings having an integral backup ring to minimize extrusion of the seal under excessive pressure. Other seal designs and backup rings, however, may be used that provide a pressure seal and tolerate reciprocation of valve stem 71. Stem guide rings 75b/c on the low-pressure side of seals 76a/c also assist in further minimizing extrusion of seals 76a/c.

[0099] When in its extended, closed position, valve stem 71 extends beyond bonnet 61 and across the intersection of inlet bore 56 and outlet bore 57 in valve fitting 34. Valve body 52 is thereby inserted into valve seat 51 and engages pressure seal 55 therein to shut off flow through valve 30. When valve stem 71 is in its retracted, open position, valve stem is withdrawn fully into bonnet 61 such that it is not exposed to the corrosive and erosive effects of fluid flowing through valve 30. Valve body 52 also is largely clear of the intersection, thereby reducing constriction of flow through the intersection. It will be appreciated, however, that valve 30 may be configured such that valve body 52 is fully retracted into bonnet 61. In that event, flow through valve seat 51 and the flow path in valve 30 is substantially unrestricted by valve body 52. The sealing surfaces of valve body 52 also would be protected from fluid flowing through valve 30.

[0100] Spring 72 and electromagnet 73 of valve actuator 36 cooperate to control the reciprocation of valve stem 71 and, in turn, opening and shutting of valve 30. Spring 72 applies a mechanical force that biases valve stem 71 in its extended, closed position. Electromagnet 73, when energized, applies a magnetic force that also biases valve stem 71 in its extended, closed position. The mechanical and electromagnet forces are coordinated and controlled to ensure that valve 30 will remain in its shut state at desired operating pressures, what will be referred to as its operationally shut state, but will open reliably and rapidly if pressure within the system meets or exceeds the predetermined relief pressure P.sub.R.

[0101] For example, as best appreciated from FIG. 7, electromagnet 73 has a generally annular configuration. It is mounted inside chamber 66 in main sub 61b of bonnet 61 and secured to flange 63 on nipple 61a, for example, by threaded fasteners extending through flange 63 and into the base of electromagnet 73. Valve stem 71 extends through and reciprocates within the central passage in electromagnet 73.

[0102] Ferromagnetic plate 74 has a generally annular, disc shape. It is fixedly mounted on and around valve stem 71, for example, by threaded connectors, and is positioned axially on valve stem 71 such that when it bears on electromagnet 73, valve body 52 is seated on valve seat 51. Thus, when electromagnet 73 is energized, ferromagnetic plate 74 will be attracted to it, thereby generating a magnetic force biasing valve stem 71 in its extended, closed position.

[0103] Preferably, ferromagnetic plate 74 has a generally smooth, circular face oriented toward electromagnet 73, and its radius approximates the radius of electromagnet 73. That will maximize the attractive force generated when electromagnet 73 is energized. The face of plate 74 also preferably is provided with a very slight raised surface or surfaces that extend a slight axial distance away from the major surface of the face. The face of ferromagnetic plate 74 may be machined, for example, with a narrow, circular boss. A suitable circular boss, for example, would be virtually imperceptible at the scale of the figures referenced herein. The raised surface creates a very narrow, but extensive air gap between the face of ferromagnetic plate 74 and the face of electromagnet 73. The air gap will not significantly reduce the holding force created by electromagnet 73, but will allow ferromagnetic plate 74 to release from electromagnet 73 more rapidly when it is deenergized. Alternately, a narrow air gap may be provided by a slight, raised surface provided on the contact face of electromagnet 73 or by thin spacers.

[0104] Spring 72 is mounted around valve stem 71 on the other side of ferromagnetic plate 74 and between a pair of spring retainers 77. Valve stem 71 extends through central passages in retainers 77. One spring retainer 77a is mounted on ferromagnetic plate 74. The other spring retainer 77b is slideably carried around valve stem 71 and within a minor diameter portion of bonnet main sub 61b. Adjusting nut 78 is threaded into a threaded hole at the end of main sub 61b of bonnet 61 and bears on spring retainer 77b. As its name implies, adjusting nut 78 is used to adjust the axial position of spring retainer 77b within bonnet 61 and thus the compression applied to spring 72.

[0105] Spring 72 thus applies (through spring retainer 77a) a mechanical force on ferromagnetic plate 74 that biases valve stem 71 in its extended, closed position. Spring 72 will be selected, primarily in respect to its spring rate and force, so that when electromagnet 73 is not energized, the force generated by spring 72 will be sufficient to cause ferromagnetic plate 74 to bear on electromagnet 73 at pressures in frac system 24 below a seating pressure Ps. Valve stem 71 thus will be placed in its closed position, with valve body 52 seated on valve seat 51 and valve 30 placed in its normally shut state. Spring 72 also will be selected such that it allows valve stem 71 to fully retract.

[0106] Importantly, however, spring 72 will be selected and tuned such that the mechanical force applied by it is not sufficient to hold valve 30 in its shut state at operating pressures approaching relief pressure P.sub.R if electromagnet 73 is not energized. That is, pressure P.sub.1, the pressure above which spring 72 allows valve stem 71 to retract and open valve 30, is below and, preferably, well below the predetermined relief pressure P.sub.R. If electromagnet 73 is not energized, therefore, spring 72 will allow valve 30 to open at pressure P.sub.1 well below the predetermined relief pressure P.sub.R. If electromagnet 73 is energized, however, valve 30 will not open unless a pressure P.sub.2, a pressure above and preferably well above relief pressure P.sub.R, is exceeded.

[0107] While the resilient member of the novel valves preferably is a spring, such as spring 72, it will be appreciated that other resilient members may be used if desired. For example, conventional automatic check valves may use a gas-charged bellows or gas-charged piston to bias the valve stem. Such designs also may be used in the novel pressure relief valves.

[0108] Actuation of electromagnet 73 and opening of valve 30, for example, to relieve excess pressure in frac system 24, may be described in further detail by reference to FIG. 8. FIG. 8 shows schematically a preferred pressure relief valve system 90 comprising novel pressure relief valve 30 and a preferred system 80 for controlling and operating valve 30. Control system 80 is an electronically controlled system and generally comprises a controller 81, a pressure sensor 92, and a switch 93.

[0109] Controller 81 may be a printed circuit board controller. Preferably, however, it is a programmable logic controller or other programmable digital computer such as a laptop. Such controllers typically comprise a central processing unit (CPU), power supply, programming device, and input and output (I/O) modules. Sensor 82 is a pressure transducer or other conventional sensor for measuring fluid pressure. It is mounted in flow line 14 and connected to controller 81. Controller 81 controls switch 83 to energize and deenergize electromagnet 73.

[0110] Switch 83 may be, for example, a low-voltage electromechanical switch having a normally open relay, such as a mini ISO (cube) relay or a solenoid switch that is rated for continuous use. Switch 83 is installed in the line from power source 84 providing power to electromagnet 73. It may be installed proximate to electromagnet 73 or in a remote control booth or doghouse. Switch 83 is triggered by controller 81 in response to input from pressure sensor 92. Preferably, as incorporated into control system 80, a second, manual switch 85 is provided to control switch 83 at the discretion of the operator.

[0111] Electromagnet 73 may be energized by an AC power source. An AC electromagnet can provide extremely rapid release of ferromagnetic plate 74. Its holding power, however, may suffer if it is energized for extended periods of time. Thus, power source 84 preferably provides DC power and electromagnet 73 will be a DC electromagnet. Other factors being equal, a DC electromagnet will provide a stronger magnet. A DC electromagnet, however, will have a residual electromagnetic field after it is de-energized and will create induced magnetism in ferromagnetic materials. Such effects vary depending, for example, on the ferromagnetic core of the electromagnet, the ferromagnetic material attracted to the electromagnet, the energizing power applied to the electromagnet, and the duration of energization. In any event, such effects can cause ferromagnetic plate 74 to stick briefly to electromagnet 73 after it is de-energized and delay opening of valve 30.

[0112] Thus, control system 80 preferably is adapted to automatically switch the polarity of, and reduce the power energizing electromagnet 73 prior to de-energizing it. Controller 81, for example, preferably comprises circuits controlling the polarity and levels of power provided to electromagnet 73. Prior to de-energizing electromagnet 73, controller 81 thus will be able to lower and reverse the polarity of power energizing electromagnet 73 to minimize the effects of residual and induced magnetism once electromagnet 73 is de-energized. Properly controlled, ferromagnetic plate 74 may tend to pop off electromagnet 73. In any event, such control circuits will enable valve 30 to open more quickly. Seating pressure P.sub.S of spring 72 also may be set closer to relief pressure P.sub.R as any tendency to stick is reduced.

[0113] Prior to commencement of fracturing operations, valve 30 will be in its normally shut state by virtue of the biasing force of spring 72. It can be placed in its operationally shut state by closing switch 83 to energize electromagnet 73. Switch 83 may be closed by the operator using manual switch 85 or by controller 81 in response to signals from sensor 82 indicative of specified pressure conditions in frac system 24. For example, controller 81 may trigger switch 83 and energize electromagnet 73 when pressures as detected by sensor 82 fall below seating pressure P.sub.S at which the mechanical force applied by spring 72 is sufficient to place valve 30 in its shut state. In any event, once switch 93 is closed, electromagnet 73 will hold valve stem 71 of valve actuator 36 in its closed position and valve body 52 on valve seat 51, thus placing valve 30 in its operationally shut state. When valve 30 is in its operationally shut state, unless electromagnet 73 is de-energized, the combined mechanical and electromagnetic biasing forces will hold valve 30 in its shut state beyond relief pressure P.sub.R, that is, up to pressure P.sub.2.

[0114] Once fracturing commences, signals from pressure sensor 92 will be monitored by controller 81 and compared to the predetermined relief pressure P.sub.R. Relief pressure P.sub.R can be the pressure rating of flow line 14. Operators, however, typically will assemble frac system 24 such that its rating is comfortably above the pressures they anticipate will be required to fracture well 1. Relief pressure P.sub.R thus may be set at a desired maximum operating pressure for flow line 14 below the rated pressure for flow line 14. For example, if flowline 14 and the high-pressure side of frac system 24 is rated for 15,000 psi, relief pressure P.sub.R may be set at 15,000 psi or somewhat below that, such as 14,250 psi.

[0115] In any event, when pressure in excess of relief pressure P.sub.R is detected, controller 81 will de-energize switch 93, allowing it to return to its normally open state. In turn, electromagnet 73 will be de-energized. Fluid pressure in inlet 46 of valve 30 at that point will be well above pressure P.sub.1 at which spring 72 allows valve 30 to open. Fluid pressure will easily and rapidly push valve body 52 and valve stem 71 beyond the intersection of inlet bore 56 and outlet bore 57 and back to its retracted position. Valve 30 will open fully and rapidly to relieve excess pressure in frac system 24.

[0116] Once pressure in frac system 24 drops below seating pressure P.sub.S, spring 72 will return valve 30 to its normally shut state. Assuming the circumstances causing the unwanted increase in pressure have been addressed, and operations otherwise are ready to be restored, valve 30 again may be placed in its operationally shut state. Switch 93 will be closed to energize electromagnet 73 as described above.

[0117] Operators may have divergent preferences in selecting an appropriate seating pressure P.sub.S, pressure P.sub.1, pressure P.sub.2, and relief pressure P.sub.R. Spring 72 may be selected and tuned with adjusting nut 78, and electromagnet 73 selected in accordance with such preferences. For example, some operators may prefer to relieve only a few hundred psi of pressure to minimize disruption to fracturing operations. Seating pressure P.sub.S and pressure P.sub.1 will be relatively high. Other operators may prefer to vent more pressure, perhaps down to approaching zero psi. More fluid necessarily is diverted. Seating pressure P.sub.S and pressure P.sub.1 will be relatively low.

[0118] As noted above, valve 30 may be assembled into flow line 14 with either of its ends serving as the inlet and the other as outlet. Valve 30 has been exemplified with the end extending along the secondary axis normal to primary axis X serving as inlet 46. As such, an annular shoulder provided by a reduced diameter portion at the end of valve body 52 is exposed to pressure in flowline 14. When valve 30 is assembled such that outlet 47 (the end extending along primary axis X) serves as the inlet, the outer face of valve body 52 is exposed to pressure within flowline 14.

[0119] The surface area of the outer face being greater than that of the shoulder, the force generated against valve body 52 at a given pressure will be greater when outlet 47 serves as the inlet. Valve 30, therefore, will open somewhat more rapidly than when inlet 46 in fact is the inlet. On the other hand, when inlet 46 serves as the inlet, the magnetic force required to hold valve 30 in its operationally shut state need not be as great. Smaller, less powerful electromagnets, therefore, may be used. In turn, the overall size of the valve may be reduced.

[0120] It also will be appreciated as exemplified, again because of the difference in force generated against the shoulder versus the valve body face, seating pressure P.sub.S for valve 30 will be significantly lower than opening pressure P.sub.1. For example, if opening pressure P.sub.1 is set at 3,000 psi, valve 30 will not start to close again under the force generated by spring 72 alone until the pressure is approximately 600 psi. On the other hand, if valve 30 is assembled such that inlet 46 serves as the outlet and outlet 47 serves as the inlet, seating pressure P.sub.S will be substantially equal to opening pressure P.sub.1.

[0121] It will be appreciated that the novel combination of various features in the pressure relief valves and valve systems of the subject invention retain important benefits of conventional pressure relief valves while providing significant advantages. Like conventional valves with automatically controlled actuators, the novel valves may be opened and shut. The novel valve systems also may be adjusted on the fly to accommodate different working or rated maximum pressures. For example, controller 81 may be reprogrammed with a new relief pressure P.sub.R, and control system 80 will open valve 30 at the new relief pressure P.sub.R. No changes in valve 30 are required. Like conventional designs, the novel valves also may be actuated in response to highly accurate pressure detectors. They will allow the system to be run safely at pressures approaching the specified relief pressure P.sub.R. Unnecessary interruptions may be minimized, while at the same time minimizing the risk of having to scrap expensive flow iron because the valve did not open until the relief pressure P.sub.R was exceeded.

[0122] On the other hand, the novel valves and valve systems provide import advantages over valves with conventional, automatically controlled actuators. Though they can be controlled with precision and accuracy, conventional automatic actuators are relatively slow to open, that is, to place the valve is a fully open state in which flow through the valve is minimally restricted. In contrast, the novel valves can fully open near instantaneously after their electromagnet is de-energized. The pressure P.sub.1 at which the mechanical force of spring 72 holds the valve shut may be set well below the relief pressure P.sub.R allowing the resistance of spring 72 to be easily and rapidly overcome.

[0123] Moreover, the novel pressure relief valves avoid problems inherent in conventional self-actuating pressure relief valves that rely on a resilient member, such as a spring-loaded or gas-charged valve stem. Spring and gas loaded valves are extremely difficult to calibrate. They also are affected by the temperature at which the valve operates. Unlike those conventional valves, the mechanical force provided by the resilient member in the novel valves is not required to hold the valve closed until pressures reach the relief pressure P.sub.R while at the same time allowing the valve to open at, not above the relief pressure P.sub.R. Opening pressure P.sub.1 may be set well below relief pressure P.sub.R. Operation of the novel valves at pressure P.sub.1 typically will not be nearly as critical as ensuring that the valve opens at, and not below or above the relief pressure P.sub.R. Thus, the spring or other reliant member need not be tuned with the same effort and precision as for conventional pressure relief valves. An acceptable margin of error in the biasing force of the resilient member will be much greater.

[0124] Moreover, conventional check valves can tend to flutter or partially open at pressures approaching the relief pressure. Such effects can allow excessive pressure to persist in the system. In contrast, the novel pressure relief valves can more rapidly reduce pressure in the system. They not only open near instantaneously, but they remain fully open until pressure in the system has dropped significantly below the relief pressure P.sub.R, that is, until pressure in the system approaches seating pressure P.sub.S.

[0125] The terms axial, radial, and forms thereof as used herein reference primary axis X of preferred valve 30 along which valve stem 71 reciprocates unless otherwise specified. For example, axial movement or position refers to movements or positions generally along or parallel to the primary axis. Radial will refer to positions or movement toward or away from the primary axis.

[0126] In general, the novel pressure relief valves may be fabricated from materials and by methods typically used in pressure relief valves and in frac iron generally. Given the extreme stress and the corrosive and abrasive fluids to which they may be exposed, especially those designed for high-pressure flow lines, suitable materials will be hard and strong. For example, mainly excepting their seals, the components of novel pressure relief valves may be fabricated from 4130 and 4140 chromoly steel or from somewhat harder, stronger steel such as 4130M7, high end nickel alloys, and stainless steel. The plug and seats preferably will be fabricated from stainless steel or the other harder steels. The components may be made by any number of conventional techniques, but typically and in large part will be made by forging, extruding, or mold casting a blank part and then machining the required features into the part.

[0127] Seals suitable for use in the novel pressure relief valves are commercially available from many manufacturers. Suitable rotary pressure seals include, depending on the application, X-Pac loaded U-cup seals (VT90 FKM (Viton) available from Martin Fluid Power Company, Inc. (MFP Seals) (www.mfpseals.com); urethane loaded lip seals available from Power Supply Components (powersupplyseals.com), and H2155 Hytrel/N6014 NBR polyseals available from MFP Seals. Suitable static pressure seals include Viton, HNBR, and Buna O-rings available from Parker Hannifin Corp. (www.parker.com). Workers in the art will be able to select an appropriate seal and design a corresponding gland in accordance with conventional design criteria.

[0128] Guide rings and seal backup rings also are commercially available from many manufacturers. They may be made of a hard material, such as steel, brass, and other metals, or from engineering plastics, such as polycarbonates, Nylon 6, Nylon 66, and other polyamides, including fiber reinforced polyamides such as Reny polyamide, polyether ether ketone (PEEK), and polyetherimides such as Ultem.

[0129] Systems for controlling operation of the novel pressure relief valves may be assembled from conventional components. Suitable controllers, sensors, switches, and other control system components are well known and readily available from many commercial sources.

[0130] Finally, pressure relief valve 30 has been exemplified in the context of frac systems, such as frac system 24 shown in FIG. 1. It has been exemplified specifically as installed in flow line 14 that feeds fluid into zipper manifold 16. The novel pressure relief valves, however, may be used elsewhere, or in multiple locations in conventional frac systems, for example, in missile 13 of frac manifold 9. Although particularly designed for use on the high-pressure side of frac systems, they may find use in the low-pressure side as well. Likewise, the novel pressure relief valves may be used in other conventional fluid transportation systems, whether temporary or permanent, especially when abrasive or corrosive liquids will be transported at high pressure or high flow rates.

[0131] While this invention has been disclosed and discussed primarily in terms of specific embodiments thereof, it is not intended to be limited thereto. Other modifications and embodiments will be apparent to the worker in the art.