Abstract:
A coating for use in protecting surfaces susceptible to environmental degradation. The coating may be applied to metallic surfaces for providing a barrier against elements and/or ambient conditions that would otherwise degrade the surface material. The coating includes multiple layers, where a thermoplastic polymer is included, wholly or partly, within one or more of the layers. Example applications of the coating are for protecting valve seat seals and valve stem seals of a valve assembly used in conjunction with handling of fluids produced from a subterranean formation.

Description:
1. FIELD OF INVENTION 
       [0001]    This invention relates in general to gate valves used in the oil and gas industry, and in particular to a process for forming a coating on a surface, where the coating can withstand decompression without being damaged. 
       2. DESCRIPTION OF RELATED ART 
       [0002]    Thermoplastic materials are used to form various components used for the production of oil and gas. Seals within valves, such as gate valves, may be made wholly or partly from thermoplastics. A gate valve typically has a body with a cavity intersected by a flow passage. A gate in the gate valve moves in the cavity between a closed position, blocking flow through the flow passage and an open position, that allows flow through the flow passage. A stem engages an end of the gate, that when rotated in a particular direction, either raises or lowers the gate. The body of the gate valve generally includes a stem passage for which the stem to extend through. Stem seals are often provided between the stem and the stem passage, to seal therebetween and prevent leakage of pressure from the cavity. 
         [0003]    Leakage from the flow passage and into the cavity is typically addressed by annular seals disposed in the cavity and coaxially registered with flow passage. Springs are usually included for pushing the seal against the gate to maintain the fluid flow barrier across the seal and gate interface. Thermoplastics however lose their resiliency over time and after being subjected to the high temperatures of downhole fluids. 
       SUMMARY OF INVENTION 
       [0004]    Disclosed herein is a surface coating for protecting a material, such as a metal, from degradation due to ambient exposure. In an example embodiment disclosed is a valve assembly for use in handling fluids produced from a subterranean formation made up of components that are in sliding contact with one another and where a coating is on a surface of one of the components. The coating is made of a base layer on the surface having primer mixed with thermoplastic. Over the base layer is a thermoplastic layer, with an outer layer of thermoplastic and lubricant over the thermoplastic layer. In an example embodiment the primer includes a polymer, such as, a thermoplastic amorphous polymer, a polyimide, a polyamideimide, polyetheretherketone, or combinations of these. In an example embodiment the thermoplastic can be a polymer such as a polyetheretherketone, polyetherketoneketone, polyetherimide, polyethersulfone, chlorinated polyethylene, polyketone, or combinations thereof. In an example embodiment wherein the lubricant may be a polymer, such as, a fluoropolymer, polyvinylfluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, perfluoroalkoxy, fluorinated ethylene-propylene, ethylene tetrafluoroethylene, polytetrafluoroethylene, polyethylenechlorotrifluoroethylene, or combinations thereof. The primer can be polyamideimide and the thermoplastic can be polyetheretherketone (PEEK). In an example embodiment, the amount of polyamideimide in the base layer ranges from about 60% to about 90% by volume and the amount of PEEK in the base layer ranges from about 10% to about 40% by volume. In an example embodiment the thermoplastic includes polyether-etherketone (PEEK) and the lubricant includes polytetrafluoroethylene (PTFE). Optionally, the amount of PEEK in the outer layer ranges from about 10% to about 40% by volume and the amount of PTFE in the outer layer ranges from about 60% to about 90% by volume. In an example embodiment, surfaces of the components in sliding contact include metal and one of the components is a seal. 
         [0005]    Also disclosed herein is a method of coating a surface of a valve component. In an example embodiment the method includes applying a base layer of a mixture of a primer and a thermoplastic to the surface, cover the base layer with a thermoplastic layer; and adding an outer layer of thermoplastic and lubricant on the thermoplastic layer. The valve can be actuated so that the outer layer is in sliding contact with a metal surface. In an example embodiment, the base layer is bonded to the thermoplastic layer by melting the thermoplastic in the base layer. In an example embodiment the primer includes a polymer such as a thermoplastic amorphous polymer, a polyimide, a polyamideimide, polyetheretherketone, or combinations thereof. Optionally, the thermoplastic can includes polyetheretherketone, polyetherketoneketone, polyetherimide, polyethersulfone, chlorinated polyethylene, polyketone, or can be combinations thereof. In an example embodiment, the lubricant includes a fluoropolymer, polyvinylfluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, perfluoroalkoxy, fluorinated ethylene-propylene, ethylene tetrafluoroethylene, polytetrafluoroethylene, polyethylenechlorotrifluoroethylene, as well as combinations thereof. Alternatively, the primer includes polyamideimide and the thermoplastic includes polyetheretherketone (PEEK). In an example embodiment, the amount of polyamideimide in the base layer ranges from about 60% to about 90% by volume and the amount of PEEK in the base layer ranges from about 10% to about 40% by volume. In an example embodiment, the thermoplastic has polyetheretherketone (PEEK) therein and the lubricant includes polytetrafluoroethylene (PTFE). In an example embodiment, the amount of PEEK in the outer layer can be from about 10% to about 40% by volume and the amount of PTFE in the outer layer can be from about 60% to about 90% by volume. Optionally, the surface is on a metal seal. 
         [0006]    Yet further disclosed herein is a method of coating a surface of a metal seal of a valve component. In an example embodiment the method includes applying a base layer of a polyamideimide primer and a polyetheretherketone thermoplastic to the metal surface, on the base layer, applying a thermoplastic layer of polyetheretherketone, and applying an outer layer of about 10% to about 40% by volume of polyetheretherketone and about 60% by volume to about 90% by volume of polytetrafluoroethylene on the thermoplastic layer. The base layer is bonded with the thermoplastic layer by melting the polyetheretherketone in the base layer and the valve can be actuated so that the outer layer is in sliding contact with a metal surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a sectional view of a protective coating on a substrate in accordance with an example embodiment of the present invention. 
           [0008]      FIG. 2  is a sectional view of an example of a gate valve with seals having the protective coating of  FIG. 1 . 
           [0009]      FIG. 3  is an enlarged sectional view of the gate valve of  FIG. 2  with the coating of  FIG. 1  applied to surfaces of a valve seat. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0010]    Coatings are typically applied to metal surfaces for shielding against elements that can corrode, degrade, or otherwise be damaging when exposed to metal. Thus when choosing a coating, consideration is often given for the particular elements ambient to where the metal surface will be situation. Ambient conditions also factor into deciding on a coating as some materials degrade under high pressure and/or temperature. The operating range and rate of change of an operational environment may drive material selection as fluctuations in ambient conditions can damage a coating. 
         [0011]      FIG. 1  illustrates an example embodiment of a coating  10  protecting an underlying substrate  12 . The coating  10  is bonded to the substrate  12  along an interface  14  that defines the contact between the surface  12  and coating  10 . The coating  10  is shown made up of layers where the layer directly on top of the substrate  12  is referred to as a base layer  16 . In the embodiment of  FIG. 1 , the base layer  16  includes a mixture of a polymer primer. Examples of the polymer primer include thermoplastic amorphous polymer, a polyimide, a polyamideimide, polyetheretherketone, and combinations thereof. 
         [0012]    Particles of a thermal plastic compound can be disbursed within the primer  16 . Examples of thermal plastic compounds considered for use with the disclosure herein include, but are not limited to polyetheretherketone, polyetherketoneketone, polyetherimide, polyethersulfone, chlorinated polyethylene, polyketone, and combinations thereof. In example embodiments, the thermal plastic may make up from about 10% to about 40% by volume of the base layer  16 . As such, the primer  18  in the base layer  16  may make up from about 60% to about 90% by volume of the base layer  16 . On the side of the base layer  16  opposite the substrate  12  is a thermal plastic layer  20  that in an example embodiment can be substantially homogeneous and made of a single compound. In one example embodiment, the intermediate layer  22  is formed fully from a thermal plastic material and may be of the same material making up the thermal plastic  20  intermixed within the base layer  16 . 
         [0013]    An outer layer  24  is shown on a side of the intermediate layer  22  opposite the base layer  16 , wherein the outer layer is made up of a matrix material with particles interspersed therein. In the embodiment of  FIG. 1 , the matrix includes a thermal plastic  26 , which may be made of the same or similar to the thermal plastic  20 . The particles  28  shown intermixed within the thermal plastic  26  can be a lubricant, example lubricants include but are not limited to fluoropolymer, polyvinylfluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, perfluoroalkoxy, fluorinated ethylene-propylene, ethylene tetrafluoroethylene, polytetrafluoroethylene, polyethylenechlorotrifluoroethylene, and combinations thereof. One of the advantages of forming a protective layer  10  as illustrated in  FIG. 1  is when cured, such as by heating, the base layer  16  adheres to both the surface of the substrate  12  and the intermediate layer  22  by virtue of melting the thermal plastic  20  in the base layer  16 . By melting the thermal plastic  20  and allowing it to resolidify, bonding is realized between the base layer  16  and substrate  12  as well as the intermediate layer  22 . Moreover, the novel composition is resistant to explosive decompression that can be damaging to other coatings. Therefore, the coating  10  provides significant advantages when applied to surfaces of a valve that may be subjected to large pressure and/or temperature fluctuations that can produce explosive decompression. 
         [0014]    In one example of use, the layer  10  is shown applied to various components within a valve assembly  30 . In the example of  FIG. 2 , the valve assembly  30  includes a valve body in which is formed a cavity for allowing axial movement of a gate  36  therein. The gate  36  includes an opening  38  therethrough and may be moved axially within the cavity  34  by its connection to a stem  40 . The stem  40  is shown projecting upward from the gate  36  and through a stem passage  42 . On the lower end of the stem  40  is a lock nut  44  for securing the stem  40  to the gate  36 . An axial cavity  46  is provided in the gate  36  and in a portion adjacent the opening  38 , the cavity  46  provides a space in which the stem  40  may extend into as the gate  36  is actuated axially within the body  32 . 
         [0015]    A valve bonnet  48  is shown mounted on an upper end of the body  32  for housing the actuation mechanisms for the gate  36 . The upper end of the bonnet  48  narrows into a neck and through which the stem passage  42  is formed. Stem seals  52  are shown disposed within a widened portion of the stem passage  42  and provide a sealing function along the stem  40  to prevent pressure communication from the cavity  34  to external of the valve  30 . On the surface of the stem seals  52 , facing a moving portion of the stem  40 , is a protective coating  10  as described in conjunction with  FIG. 1 . By applying the coating  10  on the sliding contact surface of the stem seals  52 , the coating  10  protects the seals  52  from frictional damage. Moreover, as described above, the coating  10  will not suffer damage when exposed to pressure drops that may cause other such coatings to bubble and crack from explosive decompression. 
         [0016]    Also shown within the bonnet  48  is a back seat seal assembly  54  circumscribing a portion of the stem  40  and having a surface in contact with the inner surface of the bonnet  48 . A layer of coating  10  is shown on the surface of the back seat seal assembly  54  that contacts the bonnet  48 . As discussed above, with regard to the stem seals  52 , the coating  10  provides frictional protection for the back seat seal assembly  54  and without suffering the disadvantage of bubbling from explosive decompression. 
         [0017]    The embodiment of  FIG. 2  further includes a hand wheel  56  for actuating the gate  36 . A gear box mechanically connected with the hand wheel  56  provides a mechanical advantage for moving the gate  36 , where the gear box  58  is set on an annular collar  60  shown mounted on an upper end of the neck  50 . An output shaft  62  depends downwardly from the gear box  58  into coupling engagement with the upper end of the stem  40 . A bearing assembly  64  circumscribes the output shaft  62  and is mounted in an upper end of the inner portion of the collar  60 . 
         [0018]    Shown in cross-sectional view in  FIG. 3  is another application of the coating  10  in use with a valve assembly  30 . In this example, the valve body  32  is shown having a flow passage  66  that flows through the body  32  and intersecting the cavity  34 . In the example of  FIG. 3 , the gate  36  is positioned so that the opening  38  is registered with the passage  66 . As shown, a valve seat  68  is mounted in a body pocket  70  formed in a side of the body  32  facing the gate  36 . The valve seat  68  is an annular member and shown having a coating  10  on its face that is in contact with a side surface of the gate  36 . As is known, the gate  36  is axially actuated by movement of the attached stem  40  such that the gate  36  slides with respect to the face of the valve seat  68 . The coating  10  shown applied onto the sliding surface and adjacent outer surfaces of the valve seat  68  provides a surface that protects both the gate  36  and the valve seat  68  from damage due to the sliding contact; and as discussed above, the coating  10  is resistant to damage from decompression that damages other known coatings. Also illustrated in the example embodiment of  FIG. 3 , a spring  72  is shown in the end of the valve seat  68  nested in the body pocket  70 . Circumscribing the end of the valve seat  68  opposite its contact with the gate is a seal for sealing between the body pocket  70  and valve seat  68 . 
         [0019]    Shown in a side partial sectional view in  FIG. 4A  is one example embodiment of forming the coating  10  as described herein onto a component. In the example of  FIG. 4A , a spray nozzle  76  is shown having an exit directed towards the substrate  12 , wherein each layer is spray applied onto the substrate  12  and/or the preceding layers. The substrate  12  can be a surface of a component, where the component includes any part, including seals of a valve assembly. Exiting from the discharge of the spray nozzle  76  is a spray  78  representing the composition of each particular layer in a liquid form. Now referring to  FIG. 4B , the component having the substrate  12  and applied coating  10  is shown placed in a heated environment, such as an oven  80  where heat is applied so that the temperature is increased above the melting point of the thermal plastic within the base layer  16 . As described above, melting the thermal plastic and then allowing it to resolidify forms an improved bond between the base layer  16  and substrate  12  as well as between the intermediate layer  18  and base layer  16 . In example embodiments, the base layer  16  has a thickness of up to about 1 ml including thicknesses of around 0.5 ml and about 0.75 ml. In example embodiments, the intermediate layer  22  and outer layer  24  have thicknesses that may range from about 1 ml up to about 5 ml. Other example embodiments exist wherein the thicknesses of the intermediate layer  22  and outer layer  24  can be any value between 1 ml and 5 ml. Further optionally, the spray technique shown in  FIG. 4A  may include a liquid dispersion application. Optionally, an electrostatic application may be included for adhering the spray on particles to the substrate  12  or preceding layers. 
         [0020]    The present method described herein, therefore, is well adapted to carry out and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.