Abstract:
A gate valve has a body, the body having a cavity and a flow passage intersecting the cavity. A seat fabricated from a ceramic and/or hardfacing alloy matrix composite substrate is mounted to the body at the intersection of the flow passage and the cavity. A gate fabricated from a ceramic and/or hardfacing alloy matrix composite substrate is installed at the cavity and has an engaging face that slidingly engages the seat while the gate is being moved between open and closed positions. The engaging faces of the gate and seats are coated with a low-friction material to facilitate sliding. The ceramic and/or hardfacing alloy matrix composite substrate construction of the gate and seats with low friction engaging surfaces enhances the gate valve&#39;s bearing stress capacity.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to valves, and in particular to a gate and/or a seat seal in a valve body with a substrate comprising a ceramic and/or hardfacing alloy matrix composite which allows for increased bearing stress capacity. 
     BACKGROUND OF THE INVENTION 
     Gate valves are typically used when a straight-line flow of fluid and minimum flow restriction are required. Typically, the gate has body with a cavity and a flow passage extending through the body and intersecting the cavity to allow flow through the valve. When the valve is wide open, the gate is drawn into an end of the valve cavity away from the flow passage. The flow passage is typically the same size as the pipe in which the valve is installed. 
     A typical gate valve used in connection with oil and gas production has a flow passage that intersects a central cavity in the valve. Seats are placed in counterbores formed in the flow passage at the intersection of the flow passage with the cavity. An obstruction or gate is moved past the seats between open and closed positions to seal the cavity from the passage. 
     The seats generally have seals which seal the seat to the counterbore of the flow passage. These seals prevent the entry of fluid from the central cavity or chamber of the body to the downstream flow passage. When the gate is opened, the seals perform no function. For gate valves designed with unidirectional sealing when the gate is closed, fluid will flow past the upstream seat into the chamber or cavity of the body. The fluid pressure in the chamber is sealed by the seal of the downstream seat formed between the gate and the seat. In addition, a sand screen may also be positioned in the seats to protect the valve from sand intrusion. For gate valves designed with bidirectional sealing when the gate is closed, fluid is maintained on one side of the gate and not allowed to flow into the chamber or cavity of the body. 
     When gate valves are subjected to high pressure environments, the bearing stress between the seat and the gate increases and thus gate valves must be able to tolerate the increased bearing stress. This is especially the case on the downstream side of the gate as the gate is forced onto the seat. This can often result in local deformation of the gate where it contacts the seat, making it more difficult or impossible to actuate the gate between open and closed positions. To counter this problem, the size of the valve, the actuators, and the tree may be increased, resulting in additional weight and expense. 
     One approach used to address this issue has been to coat the (metal) gate and seat with a thin coating composed of Tungsten Carbide particles with CoCr metal binder (WCCoCr coating) due to its hardness and low friction. Diamond-like Carbon (DLC) coatings have also been used on top of the WCCoCr coatings to lower the friction further. However, there is a limit to the bearing stress beyond which these coatings tend to locally deform or gall, creating stresses in the coatings and thus limiting bearing stress. Eventually leakage and difficulty in operating the gate valve may result. Another approach to control this bearing stress is to increase the surface area of the seat by increasing its diameter. However this also has the unintended effect of increasing the force applied due to the increased effective pressure-area. The return on controlling bearing stress with this method diminishes with higher pressure valves, resulting in even larger valves and the actuators needed to close and open them. Another approach has been to attempt solid ceramic or cemented carbide gates and seats to achieve a higher bearing stress capacity. The problem thus far is that the high temperatures required for sintering solid parts typically results in degraded carbide properties, which in turn result in a poor surface texture and high friction. 
     A need exists for a technique to increase bearing stress capacity in gate valves and minimize friction without an increase in the actuator size or production tree. 
     SUMMARY OF THE INVENTION 
     A gate valve having a substrate of a ceramic and metal matrix composite material with increased stiffness and hardness, relative to the current metals used in gates and seats, above which a low-friction coating is applied. An example of a ceramic and/or hardfacing alloy matrix composite substrate is Tungsten Carbide in a cobalt matrix. The greater stiffness and hardness of the ceramic and metal matrix composite material substrate supports the coatings and increases the net bearing stress capacity and thus the efficiency of the valve. In previous efforts, local deformations of the softer metal under a harder, thin layer of coating caused premature failure of the coating. With a substrate below the coating of greater hardness and stiffness than the underlying metal, this can be avoided. Using a substrate of greater stiffness and hardness, the bearing stress capacity of the same coating, which was previously applied directly to the metal, will therefore be increased. This combination of substrate and coating will allow the seat to have a smaller sealing diameter and the gate to be less wide due to the reduced requirement for bearing support area. As a result, the net force and friction between the seat and gate are lessened; reducing the force and energy requirement on the valve&#39;s hydraulic actuator. This can be achieved in three primary ways, with multiple combinations deriving from those three. 
     In a first embodiment of the invention, a gate valve has a body with a cavity and a flow passage intersecting the cavity. Seats are mounted in the body at the intersection of the flow passage and the cavity. A gate in the cavity has an engaging face that slidingly engages the face of each seat while being moved between open and closed positions. Both the seats and the gate are constructed from a ceramic and/or hardfacing alloy matrix composite substrate having a greater hardness and stiffness than the metal of the gate, such as Inconel. A low-friction coating may be applied to one or both of thesubstrates, the gate substrate and the seat substrate. 
     In a second embodiment of the invention, a gate valve has a body with a cavity and a flow passage intersecting the cavity. Metal seats are mounted in the body at the intersection of the flow passage and the cavity. A ceramic and/or hardfacing alloy matrix composite seat ring is mounted in each seat and has an engaging face which is coated with a low-friction material A gate in the cavity has an engaging face that slidingly engages the face of each seat while being moved between open and closed positions. The gate is composed of a metal base sandwiched between two ceramic and/or hardfacing alloy matrix composite plates, whose outer surfaces are coated with a low-friction material. 
     In a third embodiment of the invention, a gate valve has a body with a cavity and a flow passage intersecting the cavity. Metal seats are mounted in the body at the intersection of the flow passage and the cavity. A gate in the cavity has two engaging faces that slidingly engages the face of each seat while being moved between open and closed positions. A ceramic and metal matrix composite hardfacing of about ⅛ inch thickness or less is applied by a welding, powder metallurgy or thermal spray technique on the engaging surfaces of the gate and two seats. The gate is composed of a metal base sandwiched between two ceramic and/or hardfacing alloy matrix composite hardfacings, whose outer surfaces are coated with a low-friction material. The seat is composed of a metal base with the engaging surface coated with a ceramic and/or hardfacing alloy matrix composite hardfacing and then coated with a low-friction material. This hardfacing technique may be utilized in each of the embodiments presented as an alternative to using a ceramic and/or hardfacing alloy matrixsubstrate to provide a stiffer surface. 
     Any combination of the previously described seat and gate substrate configurations is also possible. For instance, one valve design may favor a hardfaced metal seat with a solid ceramic gate, while another valve may be better suited to use a metal seat/ceramic seat ring with a hardfaced gate configuration. 
     An added benefit for all configurations described is that the potential for a cutting function exists. In some gate valves, a requirement is that hardware such as cables, tooling, etc. left in the open bore of the valve must able to be sheared clear by the gate and still allow the valve to close and seal. In these configurations, the gate and/or seat are typically fitted with some sort of extra-hard and possibly sharp edges on their inner diameters&#39; engaging perimeters. In many cases this blade/edge is ceramic. The proposed configurations require minimal, if any, modification to perform this function since the interfacing surfaces are already made of ceramic or cemented carbide, or equipped with a ceramic or cemented carbide plate or cemented carbide-hardfaced surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical partial sectional view of a gate valve, in accordance with an embodiment of the invention. 
         FIG. 2  is a sectional view of a portion of a valve body shown in  FIG. 1 , in accordance with an embodiment of the invention. 
         FIG. 3  is an enlarged sectional view of the coated seat and gate shown in  FIG. 2 , in accordance with an embodiment of the invention. 
         FIG. 4  is a sectional view of an alternative embodiment of the flow path of the valve shown in  FIG. 1 , in accordance with an embodiment of the invention. 
         FIG. 5  is an enlarged sectional view of the coated seat ring and gate plate interface shown in  FIG. 4 , in accordance with an embodiment of the invention. 
         FIG. 6  is an alternative embodiment of a coated seat ring and gate interface, in accordance with an embodiment of the invention. 
         FIG. 7  is an alternative embodiment of a coated seat and gate plate interface, in accordance with an embodiment of the invention. 
         FIG. 8  is an alternative embodiment of a hardfaced and coated seat and gate shown, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an example embodiment of a gate valve  10  is shown. The gate valve  10  has a body  11  and a flow passage  12  that extends transversely through body  11 . Valve  10  has a gate  14  with an opening  16  therethrough. A gate  14  is shown in the open position with the opening  16  registered with the passage  12 . The gate  14  travels within a cavity  18  in the body  11  that is transversal to and intersected by the passage  12 . The term “substrate” is used throughout to describe either a plate affixed to an underlying structure, a layer welded onto an underlying structure, or a solid structure, wherein the plate, layer, or solid structure comprises a ceramic and/or hardfacing alloy matrix composite. 
     Referring to  FIGS. 2 and 3 , enlarged and more detailed illustrations of an example embodiment of the gate valve  10  of  FIG. 1  are shown for clarity and to better explain the invention. Ring-shaped valve seats  20  seal against counterbores  24  formed on the body  11 . The seats  20  have openings that circumscribe the passage  12  on opposing sides of the gate  14 . The gate  14  is in contact with the seats  20  in both the open and closed positions. In this embodiment, the seats  20  and the gate  14  are formed from a ceramic and/or hardfacing alloy matrix composite, such as Tungsten Carbide with a Cobalt or Nickel binder. The hardness of the cemented carbide may vary between Rockwell C 72-73, which is approximately twice as hard as the average 36 Rockwell C of the existing standard Inconel 718 material typically used in fabricating these parts. Further, the modulus of elasticity of the ceramic and/or hardfacing alloy matrix composite may be on the order of 48,000 KSI, making it approximately 65% stiffer than the standard Inconel 718 metal alloy, which has modulus of elasticity of 29,000 KSI. Material properties may be altered with heat treatments. Various compositions of ceramic and/or hardfacing alloy matrix composite compounds may be utilized for the seat  20  and the gate  14 , however, one material candidate, which the invention is not limited to, is a 86% WC10% Co4% Cr grade. 
     In an example of operation, a stem  17  ( FIG. 2 ) connected to the gate  14  moves the gate  14  to the open position and registers the opening  16  of the gate  14  with flow passage  12  of the valve  10 , thereby allowing flow through the valve  10 . When the gate  14  is closed, the opening  16  no longer registers with the flow passage  12  and thus flow is stopped. The gate  14  has an engaging face  26  on each side that interfaces with a seat face  28  on each of the seats  20 . To minimize friction when actuating the gate  14 , the interfacing surfaces  26 ,  28  between the seats  20  and the gate  14  are coated with low-friction coatings  30 ,  32 , such as a Diamond-like Carbon (DLC) coating. The DLC coating  30 ,  32  may be deposited onto the faces  26 ,  28  at a lower temperature than the temperature used during the fabrication of the ceramic and/or hardfacing alloy matrix composite parts, the seat  20  and gate  14  in this embodiment. This results in the coatings  26 ,  28  having a higher quality, lower friction surface than the ceramic and/or hardfacing alloy matrix composite parts themselves. 
     Continuing to refer to  FIGS. 2 and 3 , while gate  14  is open, fluid is flowing through the flow path  12 . When the gate  14  is closed the pressure increases upstream of the gate  14 , resulting in an increase in the bearing stress on the seat  20  and the gate  14 . As explained earlier, in existing configurations, the increased bearing stress could cause local deflection of the metallic seats and the gate. However, the significantly harder and stiffer ceramic making up the seats  20  and the gate  14 , in this embodiment, help prevent local deflection and associated stress accumulation associated with softer metals. 
     In another embodiment, illustrated in  FIGS. 4 and 5 , ring-shaped valve seats  40  seal against a counterbore  24  formed on the body  11 . As in the previously described embodiment, the seats  40  have openings that circumscribe the passage  12  on opposing sides of the gate  14 . A gate  42  is composed of a metallic material located between two ceramic and metal composite plates  44 , whose outer surfaces are coated with a low-friction material coating  46 , such as tungsten carbide in a cobalt matrix having a DLC coating. In the embodiment shown, the plate  44  is bonded to the gate  42 , for example, through soldering, brazing, or welding. As shown in  FIG. 5 , seat rings  48  are shown on a side of the seats  40  facing the upstream and downstream side of the gate  14 . The plate or substrate  44  of the gate  42  is on both the upstream and downstream sides. The seat ring  48  fits within an annular recess or pocket  50  formed on the seat  40 . The outer periphery of the recess  50  is set radially inward from the outer diameter of the seat  40  and forms a rim  52  along the outer periphery of the recess  50 . The seat ring  48  may be bonded to the seat  40  or may be allowed to self-seal against the seat  40  and plate  44  on the gate  42 . The plates  44  can vary in thickness from ⅛″ to ½″ depending on the pressure environment and has a face  54  that selectively engages an engaging face  56  of the seat ring  48 . In an example embodiment, face  27  and face  28  lie in substantially parallel planes that are transverse to the passage  12 . The engaging face  54  of the plate  44  is coated with the low-friction coating  46  and the engaging face  56  of the seat ring  48  may also be coated with a low-friction material coating  58 . The gate  42  can be thinner than existing gates in order to accommodate the plates  44 . Both the seat ring  48  and the plate  44  may be formed from a ceramic and/or hardfacing alloy matrix composite, such as Tungsten Carbide with a Cobalt or Nickel binder. The hardness of the cemented carbide may be approximately Rockwell C 72-73. The seat  40  and gate  42  material can be made from corrosion resistant steel alloys such as one of the following: Inconel (a nickel-chrome alloy); high quality low alloy steel; stainless steel; combinations thereof; or another suitable metal material. Inconel 718, for example, typically has a Rockwell Hardness Number (HRN) in the C scale between 32 and 40. Material properties can be altered by the heat treatment process. Thus, example embodiment of the cemented carbide plate  44  and seat ring  48  can be approximately twice as hard as Inconel 718 material. Further, the modulus of elasticity of the cemented carbide plate  44  and seat ring  48  is approximately 65% stiffer than the standard Inconel 718. As in the first embodiment, various compositions of ceramic and/or hardfacing alloy matrix composites may be utilized for the substrate  44  and seat ring  48 . 
     In an example of operation for this embodiment, the stem  17  moves the gate  42  to the open position and registers the opening  16  of the gate  42  registers with flow passage  12  of the valve  10 , thereby allowing flow through the valve  10 . When the gate is closed, the opening  16  no longer registers with the flow passage  12  and thus flow is stopped. As previously explained, when the gate  42  is closed the pressure increases upstream of the gate  42 , resulting in an increase in the bearing stress on the seat  40  and the gate  42 . As explained earlier, in existing configurations, the increased bearing stress could cause local deflection of the seat  40  and the gate  42 . However, the significantly harder and stiffer cemented carbide making up the seat rings  48  and the plates  44  on the gate  14  help prevent local deflection, and associated stress accumulation, associated with the softer metal of the seat  40  and gate  42 . Prevention of local deflection, along with the low friction coatings  46 ,  58  on the plates  44  and seat ring  48  results in less energy being required to actuate the valve, potentially eliminating the need for larger actuators. 
     In another embodiment, illustrated in  FIG. 6 , a combination of the previously discussed embodiments is shown. Ring-shaped valve seats  60  seal against a counterbore  24  formed on the body  11 . As in the previously described embodiment, the seats  60  have openings that circumscribe the passage  12  on opposing sides of the gate  14 . A gate  62  is composed of a cemented carbide material such as Tungsten Carbide with a Cobalt or Nickel binder and has an engaging face  64 . The engaging face  64  is coated with a low friction material coating  66 , such as a DLC coating or other suitable material. A seat ring  68  is located between the seat  60  and the gate  62  on both the upstream and downstream sides. The seat ring  68  fits within an annular recess or pocket  70  formed on the seat  60 . The outer periphery of the recess  70  is set radially inward from the outer diameter of the seat  60  and forms a rim  72  along the outer periphery of the recess  70 . 
     The seat ring  68  has an engaging face  74  with a low-friction coating  76  to facilitate sliding between the gate  62  and the seat ring  48 . As in previously discussed embodiments, the ceramic and/or hardfacing alloy matrix composite gate  62  and seat ring  68  help prevent local deflection and associated stress accumulation associated with the softer metals. The net bearing stress may thus be increased and ultimately, less energy is required to actuate the valve, potentially eliminating the need for larger actuators. 
     In yet another embodiment, illustrated in  FIG. 7 , a combination of the previously discussed embodiments is shown. Ring-shaped valve seats  80  seal against a counterbore  24  formed on the body  11 . As in the previously described embodiment, the seats  80  have openings that circumscribe the passage  12  on opposing sides of the gate  14 . The seats  80  are fabricated from a ceramic and/or hardfacing alloy matrix composite, such as Tungsten Carbide with a Cobalt or Nickel binder. A gate  82  is composed of a metallic material located between two ceramic and/or hardfacing alloy matrix composite plates  84 , whose engaging surfaces  87  are coated with a low-friction material coating  86  or other suitable material. As previously discussed, in an example embodiment shown, the plate  84  is bonded to the gate  82 , for example, through soldering, brazing, or welding. The seat  80  has an engaging face  88  that is also coated by a low-friction coating  90  to facilitate sliding between the gate  82  and the seat  80 . As in previously discussed embodiments, the ceramic and/or hardfacing alloy matrix composite plate  84  of the gate  82  and seat  80  help prevent local deflection and associated stress accumulation associated with the softer metals. The net bearing stress may thus be increased and ultimately, less energy is required to actuate the valve  10 , potentially eliminating the need for larger actuators. 
     In yet another embodiment, illustrated in  FIG. 8 , a hardfacing alternative is shown. Ring-shaped valve seats  100  seal against a counterbore  24  formed on the body  11 . As in the previously described embodiments, the seats  100  have openings that circumscribe the passage  12  on opposing sides of the gate  102 . A ceramic and/or hardfacing alloy matrix composite hardfacing layer  104 ,  105  of about ⅛ inch thickness or less is applied by welding, the ceramic and/or hardfacing alloy matrix composite onto the engaging surfaces  106 ,  108  of at least one of the two seats  100  (one shown) or the gate  102 . Welding the ceramic and/or hardfacing alloy matrix composite onto the engaging surface may produce a series of beads that may be removed by grinding to form a flat surface. However, methods other than welding may be used to produce the hardfacing layer. In this embodiment, the seats  100  are composed of metallic material and a low friction coating  110  is applied to the hardfacing layer  104  applied to the seat  100 . The low friction coating may be a WCCoCr coating or other suitable material. An optional DLC coating may also be used together with the WCCoCr coating. A low friction coating  112  is also applied to the hardfacing layers  105  of the gate  102 . As with previously described embodiments, the ceramic and/or hardfacing alloy matrix composite hardfacing layers  104 ,  105  of the seats  100  and the gate  102  helps prevent local deflection and associated stress accumulation associated with the softer metals. The net bearing stress may thus be increased and ultimately, less energy is required to actuate the valve  10 , potentially eliminating the need for larger actuators. The hardfacing technique may be utilized in each of the embodiments presented above as an alternative to using a ceramic and/or hardfacing alloy matrix compsite plate to form the substrate to provide a stiffer surface. 
     The combinations of ceramic and/or hardfacing alloy matrix composite plates, seat rings, hardfacing, metal gate and seats described above provide increased hardness and stiffness to the gate and seat to reduce the possibility of performance degrading local deflection in the gate and seat of a valve. The embodiments described thus result in enhanced bearing stress capacity in gate valves and smaller, less expensive valves and actuators due to decreased energy requirements to actuate the valve. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These embodiments are not intended to limit the scope of the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.