Shearing gate valve

This application claims the benefit of U.S. provisional application Serial No. 60/143,858, filed Jul. 15, 1999.

TECHNICAL FIELD

This invention relates in general to gate valves, and in particular to a gate valve having an asymmetrical gate that allows shearing of a wireline while maintaining post-shear seal integrity.

BACKGROUND ART

In the prior art, two types of coatings are generally used on valve gates. Some gates are coated with a layer of very hard material such as a carbide material. A coating of very hard material offers great durability. However, use of this type of coating on gates that are used to shear a wireline is not recommended. A coating of very hard material is generally brittle, thereby being inherently subject to chipping. Also, this type of coating is generally thin, averaging between 0.003 inches and 0.005 inches, and incapable of holding an edge while cutting. Furthermore, since this coating is not metallurgically bonded to the substrate material, high shear stresses that arise at the coating-substrate interface promote cracking of the coating. Cracking or chipping of the coating is not desirable because it reduces sealing efficiency, thereby requiring replacement of the gate more frequently.

Since coatings of very hard materials, such as carbides, are not ideal for wireline cutting applications, wireline shearing gates have been typically hardfaced with a second type of coating. The type of coating that is more suitable for wireline cutting operations is a hard ductile material such as Stellite® or Colmonoy® to provide protection against chipping when used for shearing. However, sometimes it is difficult to coat larger areas with these materials without cracking of the coating. Also, such ductile materials have markedly inferior wear characteristics compared to carbides and are easily scratched or otherwise damaged.

Because of the above problem with coating or hardfacing gates with either only an extremely hard material or only a more ductile material, prior art gate valves have not been suited for shearing wireline while retaining post-shear seal integrity.

Also, prior art seat seals have used PTFE (Polytetrafluoroethylene) jackets energized with a stand off ring that inserts within an opening in the seat seals. The openings in the seat seals have traditionally faced towards the gate of the gate valve. A problem with this configuration is that while pressure acting on the downstream seal acts to force the seal open, thereby energizing the seal, pressure on the upstream side of the gate acts to compress the seal, which results in leakage around the seal.

SUMMARY OF THE INVENTION

In this invention, the single shear gate of a gate valve is coated with a combination of materials to achieve a gate capable of shearing wireline while retaining seal integrity. The asymmetrical gate allows for shearing wireline in a single location, thereby eliminating a slug of shearable material. Since ductility is desired at the shearing edge of the gate, and extreme hardness is desired at the sealing surfaces of the gate, this invention strategically locates materials having appropriate characteristics.

The shearing edge is constructed of an inlay of a hard ductile material that provides protection against chipping. The sealing surfaces, on the other hand, are coated with an extremely hard material that provides durability to the sealing surface. Extremely hard sealing materials are very brittle and may crack and chip if subjected to the high shearing stresses encountered during shearing. However, cracking and chipping is prevented by providing inlays of a more ductile material located at the shearing edges that isolate the brittle sealing material from the majority of the shearing stresses.

Valve seats surrounding the gate of the gate valve have seals provided to seal between the valve seat and the valve body. The seals are energized with a standoff ring. The upstream seal is reversed from the traditional orientation such that the standoff ring engages the valve body and the seal opening faces upstream, which results in pressure energizing the seal, thereby preventing leakage.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIG. 1

is a sectional view illustrating a typical gate valve that also has features constructed in accordance with this invention.

FIG. 2

is an enlarged view of the gate and seat portion of

FIG. 1

, showing the gate in an open position.

FIG. 2

a

is an enlarged view of the upstream seat seal of FIG.

2

.

FIG. 2

b

is an enlarged view of the downstream seat seal of FIG.

2

.

FIG. 3

is an enlarged view of the gate and seat portion of

FIG. 1

, showing the gate in a closed position.

FIG. 4

is a top view of the gate of the gate valve of FIG.

1

.

FIG. 5

is a sectional view of the gate shown in

FIG. 4

taken along the line

6

—

6

in FIG.

4

.

FIG. 6

is a sectional view of the seat shown in FIG.

2

.

FIG. 7

is the same sectional view shown in

FIG. 6

, but showing a different arrangement of the inlay and the coating of the seat.

FIGS. 8A-8D

are parts of a sectional view taken along the line

10

—

10

in FIG.

4

and showing the steps used in connecting the inlay to the gate.

FIG. 9

is an enlarged view of the gate and seat portion of

FIG. 1

, showing the shearing of a wireline.

DETAILED DESCRIPTION OF THE INVENTION

Referring to

FIG. 1

, valve

11

is a standard gate valve except for features in accordance with this invention. Valve

11

has a body

13

, and a flow passage

15

that extends transversely through body

13

. Valve

11

has a gate

17

with a hole

19

therethrough. Gate

17

is located in a sealed chamber

14

in body

13

and is shown in the open position in FIG.

1

. Actuator pistons

16

connect to opposite ends of gate

17

to stroke gate

17

between its open and closed positions. Alternatively, a threaded rod may be used to move the gate. Also shown in

FIG. 1

are ring-shaped valve seats

20

mounted in body

13

, which have holes

21

that register with the flow passage

15

of the valve.

When gate

17

is in the open position (FIG.

2

), the hole

19

of gate

17

registers with flow passage

15

of the valve

11

thereby allowing flow through the valve. When gate

17

is closed (FIG.

3

), hole

19

no longer registers with the flow passage

15

. Instead, the solid portion of gate

17

registers with the flow passage

15

and comes into contact with seats

20

.

Referring to

FIGS. 2 and 3

, seat

20

rests in recess

23

formed in valve body

13

. Each seat

20

is biased towards gate

17

by seat springs

25

. Upstream seals

27

and downstream seals

29

prevent leakage around valve seats

20

. As shown in

FIGS. 2

a

and

2

b

, each seal

27

,

29

is an elastomeric ring

31

having an annular cavity

33

. Elastomeric ring

31

is preferably constructed of PTFE. A standoff ring

35

has a protruding rim

37

that inserts within cavity

33

to energize seal

27

,

29

. Protruding rim

37

of standoff ring

35

engages cavity

33

, which forces elastomeric ring

31

to expand, thereby effecting an improved seal. The downstream seal

29

on the downstream side of gate

17

(

FIG. 2

b

) is oriented such that pressure leaking around downstream seat

20

energizes the seal

29

and causes it to expand. Standoff ring

35

is thus on the upstream side of downstream seal

29

with its head in abutment with downstream seat ring

20

. The end of elastomeric ring

31

of downstream seal

29

that is opposite the cavity

33

abuts a shoulder in body

13

. Similarly, the elastomeric ring of upstream seal

27

on the upstream side of gate

17

(

FIG. 2

a

) is oriented such that pressure leaking around seat

20

energizes upstream seal

27

and causes it to expand. The head of standoff ring

35

in upstream seal

27

engages body

13

. The end of elastomeric ring

31

of upstream seal

27

opposite cavity

33

engages a shoulder on seat ring

20

.

FIG. 4

shows gate

17

in more detail. The gate

17

shown in

FIG. 4

is for a rising-stem type valve. According to this invention, gate

17

has an inlay

39

along its shearing edge. Inlay

39

is formed of a hard ductile material. The hardness is desirable to facilitate shearing of a wireline

41

(shown in FIG.

9

). The harder the material, the better it will shear the wireline. However, extremely hard materials, such as carbides, are also very brittle. Brittleness is not desired because chipping occurs, thereby reducing the sealing capability of the gate. Some ductility is desirable because it prevents chipping. The preferred embodiment of the invention uses Stellite®. Stellite® is a hard ductile material. It is hard enough to allow shearing of the wireline, but is more ductile than carbide materials, thereby preventing chipping.

The inlay

39

of Stellite® is applied to gate

17

as shown in

FIGS. 8A-8D

. Before machining hole

19

(FIG.

4

), a groove

43

(

FIG. 8A

) is machined into gate

17

. The groove

43

extends straight from one side of gate

17

to the other side of gate

17

and intersects what will later become hole

19

. Still referring to

FIGS. 8A-8D

, groove

43

has a bottom surface

45

, and an inclined wall

47

. Inclined wall

47

can be either perpendicular to bottom surface

45

, thereby creating a 90-degree angle between the bottom surface

45

and the inclined wall

47

, or it can be inclined at some other angle, such as the 45-degree angle shown in FIG.

8

A. Groove

43

extends from one side of gate

17

to the other side of gate

17

for ease of manufacture. The groove

43

could have a different configuration as long as it allows a shearing edge to be formed around at least a portion of hole

19

.

After groove

43

is machined into gate

17

, groove

43

is welded full with Stellite® to form inlay

39

. The welding process results in the Stellite® protruding above surface or face

49

of gate

17

, as shown in FIG.

8

B. Surface

49

is the surface which is later coated with the very hard material.

Referring now to

FIG. 8C

, the inlay

39

is ground down to leave a rectangular notch

51

of Stellite® protruding above surface

49

. The Stellite® inlay material

39

around the rectangular notch

51

is ground down flush with the surface

49

of gate

17

.

Before the extremely hard coatings are applied to the gate, hole

19

is machined into gate

17

as shown in FIG.

4

. Gate

17

has an upstream side

53

and a downstream side

55

(FIG.

5

). Downstream side

55

is preferably coated with a coating

57

, which is a hard material such as tungsten carbide. Hole

19

in gate

17

is tapered such that the opening on the upstream side

53

is larger than the opening on the downstream side

55

. The opening on the upstream side

53

is irregularly shaped. A taper

59

may be provided around a perimeter of the upper portion of upstream opening

61

. Beginning at leading edge

60

of the upstream surface

53

, the lower surface of hole

19

tapers upward and towards downstream side

55

, forming first lower surface

63

. The lower surface then tapers more steeply upwards, forming second lower surface

65

. Second lower surface

65

terminates at third lower surface or shearing surface

67

, which extends with a less steep upward slope to the downstream side

55

to form leading edge

68

of downstream side

55

. The result is a single shearing surface

67

. The single shearing surface

67

significantly reduces the force necessary to shear shearable media, such as wireline

41

(FIG.

9

), as compared to gates having two shearing surfaces.

As can be seen in

FIGS. 4 and 5

, shearing surface

67

is coextensive with a portion of inlay

39

. Once hole

19

has been machined and inlay

39

has been prepared as described above, surface

49

and the portions of inlay

39

that have been ground flush with surface

49

can be coated with an extremely hard material or coating

57

such as tungsten carbide, preferably having a thickness between 0.003 and 0.007″. Coating

57

is deposited by a conventional high energy deposition technique such as Praxair's LW-45. The coating

57

, deposited onto surface

49

and the portion of inlay

39

that is flush with surface

49

, will form the sealing surface that will contact against seat

20

. During opening and closing of the valve, coating

57

is subject to scratching and other damage which must be prevented if the seal integrity of the valve is to be preserved. Therefore, it is desirable for coating

57

to be very durable. Because tungsten carbide is an extremely hard material, it affords great durability. Portions of surface

49

that do not perform any sealing function need not be coated. In the case that portions of surface

49

are not coated, then these portions should be made to be flush with coating

57

on surface

49

and flush with the rectangular notch

51

of inlay

39

.

The above process will result in the shearing surface

67

of hole

19

having reinforcements of Stellite® as shown in

FIG. 5

along a portion of the circumference of hole

19

on the downstream side

55

. Since only a portion of this circumference acts as a shearing edge, only that portion of the circumference needs to have the Stellite® shearing edge. However, the Stellite® shearing edge can extend completely around the circumference, if desired.

The above description discusses improvements only to the downstream side

55

of gate

17

. Since only the downstream side

55

functions as the shearing surface, only one side of each gate

17

needs to be improved. The upstream side

53

need not be reinforced with Stellite®, since the upstream side

53

performs no shearing functions.

In the preferred embodiment of this invention, at least downstream seat

20

has an inlay

69

of a hard ductile material that forms a shearing edge (FIG.

6

). The hardness is desirable to facilitate shearing of the wireline

41

. The harder the material, the better it will shear the wireline

41

. However, some of the very hard materials are also very brittle. Brittleness is not desired because chipping occurs thereby reducing the sealing capability of the seat

20

. Some ductility is desirable because it prevents chipping. The preferred embodiment of the invention uses Stellite® for inlay

69

.

In the preferred embodiment, inlay

69

is applied to seat

20

by a process similar to the process used for applying inlay

39

to gate

17

. Referring to

FIG. 6

, a groove is machined into the circumference defined by the intersection of hole

21

and of sealing surface

71

of the seat

20

. The Stellite® inlay

69

is then welded into the groove and machined to remove the excess portions of inlay

69

. The remainder of surface

71

is then coated with a coating

73

of an extremely hard material such as tungsten carbide. The coating

73

is deposited so that coating

73

and the outward surface of the inlay

69

are flush, thereby providing a smooth sealing surface. Tungsten carbide is an extremely hard material that affords great durability. Since the coating

73

deposited onto surface

71

will form the sealing surface that will contact against the sealing surface of gate

17

, this coating needs to be very durable to preserve the integrity of the seal. Tungsten carbide provides such durability.

Although the seat described above has both Stellite® inlay

69

and tungsten carbide coating

73

, it would also be feasible to use only a Stellite® inlay

69

that extends across the entire surface

71

of seat

20

, as shown in FIG.

7

.

The desired thicknesses in the preferred embodiment for inlays

39

and

69

and for coatings

57

and

73

are as follows. After grinding, the Stellite® inlays

39

and

69

should preferably be about 0.080 inches. However, thicknesses between 0.060 inches and 0.100 inches have also been found to be acceptable. Thicker inlays should also be theoretically acceptable, however, most of the processes used to apply the Stellite® to the gate limit the maximum thickness to about 0.100 inches. The preferable thickness of carbide coatings

57

and

73

is 0.005 inches. However, thicknesses between 0.003 inches and 0.006 inches have also been found to be acceptable.

As described above, the preferred embodiment uses Stellite® for inlays

39

and

69

and tungsten carbide for coatings

57

and

73

. However, different materials, having similar characteristics could also be used. The following criteria should be used in selecting appropriate materials. The material used for coatings

57

and

73

should be a very hard, wear resistant material. The preferred embodiment uses tungsten carbide for coatings

57

and

73

. The hardness of the tungsten carbide coatings of the preferred embodiment is in excess of

65

on the Rockwell C hardness scale. Such hardness is sufficient to provide a wear resistant sealing surface that is not easily scratched.

The material for inlays

39

and

69

should be hard material that is relatively ductile when compared to the material used for coatings

57

and

73

. The material selected for inlays

39

and

69

must be sufficiently hard to allow shearing of wireline

41

extending through the valve

11

, but must also be sufficiently ductile so that a small deformation will not cause fracture of the material. The preferred embodiment uses Stellite® for inlays

39

and

69

. The hardness of the Stellite® used in the preferred embodiment is in the range of about 40 to 50 on the Rockwell C hardness scale. This hardness is sufficient to allow shearing of wireline

41

. However, Stellite® was also selected for the preferred embodiment because it is relatively ductile when compared to the material used for coatings

57

and

73

, and will not chip or fracture when subjected to the deformations caused during shearing of a wireline.

In operation, while in the open position shown in

FIG. 2

, upstream seat

20

will not seal against gate

17

because its diameter is less than the diameter of hole

19

on the upstream side. Flow pressure communicates to the chamber

14

of body

13

that contains gate

17

. Seals

27

,

29

and downstream seat

20

perform no sealing function while gate

17

is open. In the closed position shown in

FIG. 3

, the downstream side of gate

17

will seal against the downstream seat ring

23

. The upstream seat ring

23

contacts the upstream side of gate

17

, but not any portion of hole

19

. Pressure in body chamber

14

will energize downstream seal

29

, pressing the legs apart. Sealing also occurs on the upstream contact of the upstream seat ring with the solid surface of gate

17

. Upstream seal

27

is energized by pressure in bore

15

, which forces the legs apart to seal. Even if the downstream sealing surface of gate

17

or downstream seat ring

23

is damaged, the upstream side of gate

17

and upstream seat ring

23

will still seal to block flow through bore

15

.

Referring now to

FIG. 9

, wireline

41

is shown extending through seats

20

and gate

17

. Gate

17

is shown in a nearly closed position. If gate

17

were in its open position, the downstream opening of hole

19

would be aligned with the flow passages defined by holes

21

of seats

20

. If gate

17

were in its closed position, then coating

57

would be completely obstructing the flow passage defined by holes

21

. As shown in

FIG. 9

, gate

17

is moving from its open position to its closed position as indicated by the arrow.

As gate

17

continues its movement from the open position to the closed position, wireline

41

will eventually come into contact with inlay

39

on third lower surface

67

of gate

17

and with inlay

69

on downstream seat

20

. As increasing force is applied to gate

17

, there will be a shearing action between inlay

39

and inlay

69

. This shearing action will result in the shearing of wireline

41

. Once wireline

41

is sheared, gate

17

will be able to continue to its closed position.

Once gate

17

is in its closed position, and assuming that pressure is higher at upstream seat

20

than at downstream seat

20

, then coating

57

will come into contact with coating

73

, and possibly inlay

69

, thereby creating a seal that will prevent flow through the valve

11

.

Since the shearing edge is formed by Stellite® inlays

39

, the shear stresses will mainly be bom by that edge, thereby insulating the carbide coatings

57

and

73

from the high shear stresses developed by the shearing of the wireline

41

. Since coatings

57

,

73

will not have encountered the high shearing stresses, chipping of those coatings will not occur, and the sealing integrity of the seal will have been preserved.

The invention is advantageous because it allows for the shearing of large diameter thick-walled coiled tubing. The asymmetrical gate, having a shearing surface on one edge only, assures that no slug of the media is produced, which may fall into the valve cavity and adversely affect performance. The single rather than double shearing action permits tubing to be sheared by the downstream interface only. Such an action substantially reduces the force necessary to shear the media. Additionally, reversing the seat seal on the upstream side of the valve gate allows the upstream seat to seal in the event of damage to the downstream sealing surface.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.