Abstract:
A method of treating a valve with a coating, such as hardfacing, that includes depositing the coating with a spray stream that is oriented perpendicular to the surface being treated. The method further includes applying a coating of uniform thickness onto lateral surfaces of a valve seat, a portion of the valve seat bore, and the interface between a valve seat lateral surface and the valve seat bore. The valve seat bore can include an annular recess formed to receive a layer of coating.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/049,571, filed May 1, 2008, the full disclosure of which is hereby incorporated by reference herein. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates in general to gate valves used in the oil and gas industry, and in particular to a process for coating the inner rim of a gate valve seat. 
       Description of Related Art 
       [0003]    Referring to  FIGS. 1 and 2 , a standard gate valve  10  as used in the oil and gas production industry according to the prior art is illustrated. Valve  10  has a body  12  with a generally flow passage  14  extending there through. A pair of ring-shaped seats  16  rest in recesses formed in body  12 . Seats  16  each have a front face  18  and a back face  19  and contain an annular bore  20 . The bore  20  has a wall  22  with an inside diameter that is approximately equal to the flow passage  14  inside diameter. A chamfered edge or curved surface is formed on each seat  16  where the front face  18  joins the inner wall  22 . Each seat  16  has an outer rim  25  at the junction of front face  18 . A gate  26  is positioned between the seats  16 . Gate  26  has a solid portion  28  with a hole  30  shown registering with the bore  20  allowing flow through the valve  10 . The hole  30  has an inside diameter that is approximately equal to the inside diameter of the bore  20  in the seats  16 . 
         [0004]    The gate  26  is movable relative to the front faces  18  of the seats  16 . Shown in  FIG. 2 , the gate  26  has moved with respect to its position in  FIG. 1 , talking the hole  30  out of registration with the bore  20  to close the valve. When the valve  10  is in the closed position, the gate  26  and the seat front faces  18  are in contact and held closely together to prevent fluid leakage. Over time, as the gate  26  moves repeatedly between the open and closed positions, wear and friction occur at the areas of contact between the solid portion  28  and the front faces  18 . These wear surfaces can be treated by applying a coating  32  or “hardfacing,” for example tungsten carbide to the contacting surfaces of at least one of the gate  26  and the seats  16 . 
         [0005]    Depicted in  FIG. 3  is a valve  10  having a coating  32  applied to the seat front face  18  downstream of the gate  26 . Damage is most prevalent along the front face  18  and wall  22  boundary because the gate  26  elastically bows into the seat bore  20  under a pressure load. When the gate  26  is moved to open the valve, the deflected portion of the gate  26  applies concentrated forces onto the seat  16  which can result in damage. 
         [0006]    Typically, a thermal spray or vapor gas deposition processes have been used to apply the coating  32  to the seat  16 . A thermal spray gun  34  according to the prior art is illustrated in  FIG. 4  applying a coating to a valve seat  16 . A robotic arm  36  is attached to the gun  34  and programmed to direct the movement of the gun  34 . A fine metallic powder, for example, a member of the tungsten carbide-cobalt family, is introduced into the barrel of the gun at an entry point  38 . Oxygen and fuel gas, for example, propane, propylene, hydrogen, or some hydrocarbon, are fed into the barrel of the gun at entry points  40  and  42 . Purge gas may be introduced into the barrel at entry point  46 . The fuel gas is ignited, and the resulting hot, high-pressure gas heats the powder and forces it out of the nozzle  44  of the gun barrel as a beam  45  for use as coating  32 . The coating  32  may be dispensed through the nozzle  44  in the form of a continuous stream, or alternatively, it may be dispensed in intermittent pulses, with nitrogen gas used to purge the barrel after each pulse. 
         [0007]    To apply coating  32  to a valve seat  16 , as illustrated in  FIGS. 4 and 5 , the seat  16  is affixed to a base  48 . The robotic arm  36  positions the spray gun  34  so that the nozzle  44  is directed towards the front face  18  of the seat  16 . There is preferably a fixed distance between the end of the nozzle  44  and the front face  18  of the seat  16  in order to produce a beam  45  with optimum strength and a coating  32  with optimum bond integrity. The coating  32  is applied to the front face  18  of the seat  16  along the radius  50  of the seat  16  along axis A. The gun  34  points a beam  45  initially at the outer rim  25  of the seat  16  on a point on axis A, and then moves the beam  45  to apply coating  32  from the outer rim  25  of the seat  16  to the inner rim  24  of the seat  16 . Beam  45  remains perpendicular to Plane A at all times. Once the gun  34  reaches the bore  20 , it reverses course and retraces its path along A to apply coating  32  from the bore  20  of the seat  16  to the outer rim  25  of the seat  16 . As shown, the beam  45  contacts the seat  16  normal to the front face  18 . 
         [0008]    Referring now to  FIG. 5 , the seat  16  is rotated about axis B while coating  32  is applied to the front face  18  of the seat  16  back and forth between bore  20  and outer rim  25 . Obtaining a constant coating  32  thickness can be achieved by timing seat  16  rotation and the gun  34  emissions rate. When the gun  34  sprays coating  32  near the bore  20 , some overspray may enter the bore  20  but it is kept minimal by perpendicular path of the beam  45  to plane A. Moreover, the minimal overspray does not significantly attach itself as coating  32  to the inner wall  22  of the bore  20 . 
         [0009]    Enlarged for clarity in  FIG. 6 , depicted in a side sectional view is a closed valve  20  with its gate  26  wedged by fluid pressure (represented by arrows) against a seat  16 . The fluid pressure bows the gate  26  in its middle concentrating force along an interface  21  between the front face  18  and the bore wall  22 . The bowing is exaggerated in  FIG. 6 . Present coating processes leave a reduced thickness feathered end  33  at the interface  21 . Thus hardfacing  32  along the interface  21  is vulnerable to fracturing due to the concentrated stress combined with the decreased thickness hardface coating at the feathered end  33 . 
       SUMMARY OF INVENTION 
       [0010]    Disclosed herein is a method of treating a valve seat having a bore, a seat face, and a chamfered edge joining the bore and seat face. In one example the method includes forming a counter bore from the seat face into the bore that defines a recess, and directing a metal coating spray stream at chamfered edge, so that a metal coating is applied on the chamfered edge, the seat face, and into the recess. 
         [0011]    The present disclosure also include a valve that includes a valve body, an axial passage formed through the body, a valve gate having an aperture selectively registerable with the passage, an annular valve seat having a lateral side in contact with the valve gate and a bore registered with the passage, a chamfered edge on the valve seat spanning from a seat face into the bore, and a metal coating on the seat side, the chamfered surface, and along the bore wall past the chamfered edge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]      FIG. 1  is a sectional view of a typical gate valve according to the prior art with the gate in an open position. 
           [0013]      FIG. 2  is a sectional view of the gate valve of  FIG. 1  with the gate in a closed position. 
           [0014]      FIG. 3  is an enlarged view of the downstream side of the gate valve of  FIG. 1  with a prior art coating applied to the top surface of the valve seat. 
           [0015]      FIG. 4  is a side view of a thermal spray gun and robotic arm for applying coating to a valve seat of the gate valve of  FIG. 1  in a prior art method. 
           [0016]      FIG. 5  is a top view of a valve seat of the gate valve of  FIG. 3 . 
           [0017]      FIG. 6  is an enlarged side view of the valve seat of the gate valve of  FIG. 3 . 
           [0018]      FIG. 7  provides a side view of a thermal spray gun and robotic arm for applying coating to a valve seat of a gate valve according to an embodiment of the present disclosure. 
           [0019]      FIG. 8  is an enlarged side view of the valve seat of a gate valve as coating is being applied according to an embodiment of the present disclosure. 
           [0020]      FIG. 9  schematically illustrates a side sectional view of a valve treated as disclosed herein included with a production tree with a wireline through the valve. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0021]    Disclosed herein is a process for treating a downhole component. In an example the component parts may also be treated. The thermal spray gun  34  ( FIG. 4 ) orientation can be advantageously changed during the coating process to apply a coating  32  having a uniform composition and thickness that bonds to the article being treated, including curved surfaces on the article. In one example, a valve seat  16  can be treated by coating one of its lateral faces, i.e. inner or outer face  18 ,  19 , as well as the bore inner wall  22  of the valve seat  16  ( FIG. 3 ). 
         [0022]    Referring now to  FIG. 7 , depicted in a side view is an example of a thermal spray gun  34  coating a valve portion. In the example illustrated, the beam  45  is angled oblique, rather than normal, to the plane A containing the inner face  18 . A controller  37 , shown in communication with the arm  36 , can be included and programmed to control the robotic arm  36 . The arm  36  is shown tilting the gun  34  with respect to the plane A as the beam  45  is directed at the seat  16  from the nozzle  44 . The arm  36  can manipulate the gun  34  so that the nozzle  44  moves back and forth between the seat  16  outer rim and its bore  20  without changing the oblique angle to the plane A. This can be accomplished by maintaining the gun  34  tilt constant while moving it along the path. Alternatively, the controller  37  may swivel the gun  34  so its tilt angle changes as the nozzle  44  moves along a path. Coating  32  can be applied directly along the seat outer rim  25 , the bore inner wall  22 , and/or other areas of the seat  16 . Optionally, the robotic arm  36  and spray gun  34  can be held stationary and instead, the base  48  securing the seat  16  may be tilted. In an alternative embodiment, the process may be used to provide a coating  32  to other components of the valve  10 , for example, certain areas of the solid portion  28  of the gate  26 . 
         [0023]    An enlarged view of the coating process of  FIG. 7  is shown in a partial sectional side view in  FIG. 8 . In this example coating  32  is being applied along the boundary  27  between the front face  18  and the bore inner wall  22  where the boundary  27  is on a chamfered edge  29 . The chamfered edge  29  includes a curved surface on its outer periphery with a radius R. In the example of  FIG. 8 , the beam  45  is oriented substantially normal to the chamfered edge  29  at and around the boundary  27 . For the purposes of discussion herein, substantially normal to the chamfered edge  29  (including any other curved surface) can mean substantially perpendicular to a tangent line  53  shown where a curved surface is being contacted by the beam  45 . When normal to the line  53 , the beam  45  may also coincide with the line representing the surface radius R and thus may also point at the origin  0  of the radius R. In one example of use, the boundary  27  may be roughly at the mid-point of the chamfered edge  29 . In this example, material being deposited on the chamfered edge  29  at the boundary  27  flows respectively along the front face  18  and towards the bore inner wall  22  to form the coating  32 . 
         [0024]    In another example of use, the coating process includes adjusting the beam  45  angle (either stepwise or continuously) with respect to the plane A so that the beam  45  remains normal to the chamfered edge  29  at or around the boundary  27 , irrespective of where on its curved surface the beam  45  contacts the chamfered edge  29 . Thus the orientation of the gun  34  can change as it directs the beam  45  on the chamfered edge  29  along both sides of the boundary  27  between the bore wall  22  and inner surface  18 . The orientation change can be performed manually or by the controller. 
         [0025]    In the valve  10  embodiment of  FIG. 8 , a counter bore  54  is provided at an end of the bore  20  adjacent the face  18 . A transition  55  on the bore wall  22  defines an end of the counter bore  54 . The transition  55  is shown disposed where the bore wall  22  is cylindrical and no longer tapered or conical. The coating  32  of hardfacing (shown in dashed outline) applied to the seat  16  extends to the transition  55 , having an outer surface shown generally coplanar with the bore wall  22 . Strategically locating the transition  55  a distance inward from the plane A provides a sufficient space to receive the hardfacing without it flowing onto the bore inner wall  22  and protruding into the bore  20 . 
         [0026]    After being applied, the coating  32  may be ground to provide a curved surface with a radius R C . Optionally, the radius R C  can extend from the same origin O as the curved surface radius R. Grinding can also smooth the surface and so that the coating  32  has a uniform desired thickness and contact stress capacity for maximum resistance and sealing capability. As illustrated in  FIG. 8 , the coating  32  thickness is substantially the same along the front face  18  and the counter bore  54 . 
         [0027]    The application of coating  32  using a spray gun  34  with multiple degrees of movement according to the present invention increases the likelihood that a significant layer of coating  32  of uniform composition, thickness and bond integrity will attach and form along the front face  18 . Additionally, any coating  32  that is applied along the counter bore  54  will provide added support for the section of the coating  32  at the curved surface along the wall  22  and face  18  boundary that is tapered off and has reduced thickness and integrity. Thus valves treated with the present method can withstand greater loading and more loading cycles. 
         [0028]    Shown in a schematic view in  FIG. 9  is an example of a valve  74  with components, such as a valve gate, coated as described above. The valve  74  is disposed in a line  72  attached to a wellhead assembly  70 . The wellhead assembly  70 , which can be subsea or on land, is disposed over a well  76  bored through a formation  78 . A wireline  80  is inserted through the line  72  and valve  74 . The coating on the valve gate and valve seat increases their strength and cutting ability so the valve  74  can be closed onto and more easily sever the wireline  80  (including slickline, and/or tubing) with less susceptibility to damage than untreated valves. 
         [0029]    The method described herein can coat a surface or object using a thermal spray or cold spray process, including any other method or technique for applying and/or depositing material onto a surface. Additionally, a vapor gas deposition process can be employed with the present method. In an example, the seat  16  is heated to high temperature in a vapor chamber and controlled amounts of tungsten and carbon gases released into the chamber. The gases contact the seat  16  and form a thin layer of coating  32  on the surface of the seat  16 . Since no spraying is involved, the coating thickness will be substantially uniform on the front face  18 , inner wall  22 , and the chamfered edge  29  along where the face  18  and wall  22  join. The coating  32  can then be ground to a desired thickness. 
         [0030]    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.