Patent Publication Number: US-9845801-B1

Title: Header ring for reciprocating pump

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 61/582,645, filed Jan. 3, 2012, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to seals and, more particularly, to a header ring for a reciprocating pump. 
     2. Description of the Prior Art 
     Hydraulic fracturing is used for removal of petroleum, natural gas, coal seam gas and other flowable substances from beneath the earth&#39;s surface. Highly pressurized fluid is forced into a wellbore to create new fractures in a rock layer. After creating the fracture it is desirable to maintain the fracture width since this increases extraction rates and recovery of fossil fuels. Thus, material such as sand, ceramic, or other particulate, which is known as proppant, is mixed with the fluid and forced under pressure into the fracture to keep it open. The abrasive nature of the particulates, however, wreaks havoc on the piston/cylinder assemblies of the high-pressure pumps used in “fracking.” 
     When the particulates are allowed between the walls of the bore/plunger assemblies, loss of pressure results. Keeping them from reaching between the bore and cylinder plunger, therefore, is essential for seal duration. Well service packing (WSP) is typically used to seal the gap and permit slidable engagement. The packing is a collection of ring-shaped seals contained in a bore, known in the art as a “stuffing box,” and arranged in order so as to incrementally ride against the wall of the plunger and seal it at the fluid end. The bore receives the reciprocating plunger making replacement of all of the seals, which often must be done in the field, more manageable and convenient. The seals typically comprise a header ring at the fluid end and at least a pressure ring behind it. The header ring is especially important in providing a good seal since it is toward the fluid end and bears much of the abuse. 
     At the time of this writing, frictional wear of the header ring is perhaps at its worst. This is because the proppant now preferred in frac jobs has become smaller and smaller in size. To make matters worse, the seal has to withstand a range of different fluid pHs, too. That is, the pressurized fluid may be cement (mildly acidic) instead of water (neutral), for example. The material from which the seals are made, therefore, must be matched with a set of desired physical properties. Prior seals are made from elastomeric composites, which can be abrasive to the stuffing box even if there is no proppant between the seal and box. The seals are subjected to extremely high pressures and a broad range of operating temperatures as well. Hence, wear and tear of the seals are constant concerns. 
     Besides problems caused by not properly cleaning the contacting surfaces when replacing seals in the field, sealing problems are exacerbated by the mechanics of the stuffing box. Packing is secured in the box mechanically and secured about the plunger with a gland nut. If the nut is too tight, the header ring, which may be formed from a compressible material, may be extruded back into the fluid end, and the seal will fail. Conversely, if the gland nut is too loose, the seal assembly will move back and forth in the stuffing box causing wear and eventual failure of the seal. Assuming the gland nut is properly secured, still, it may back off due to vibration of the pump. As a result, the contact load on the header ring is insufficient to adequately seal the fluid end of the wellbore. 
     There, therefore, remains a need for an improved header ring and sealing system for a reciprocating pump. The present invention is directed toward meeting this need. 
     SUMMARY OF THE INVENTION 
     The invention relates to a header ring for a reciprocating pump. The header ring includes a ring shaped body. The body has a side wall defining an open top and an open bottom and an inner wall portion with an inner wall surface for contacting a plunger. The inner wall portion includes an outwardly extending annular undercut, which defines an overhang. The inner wall portion includes an annular shoulder, an inwardly sloped portion and a flat portion. The header ring also has an outer wall portion with an outer wall surface for contacting a bore wall, which is typically a stuffing box containing sealing rings. The outer wall portion includes a bottom with an inwardly extending annular ledge. The outer wall portion is formed from a nonabrasive elastomer. 
     In another aspect of the invention, the inner wall includes an inwardly directed annular shoulder adjacently spaced from and in alignment with the undercut. The shoulder is located between the undercut and the top of the body. 
     In another aspect, the outer wall portion and the inner wall portion are each formed of an elastomer having a durometer of between about 70 and 95 Shore A. The inner wall portion is harder than the outer wall portion. 
     In still another aspect, the outer wall portion includes a flat upper portion, a flat lower portion, an outwardly sloped annular middle portion connecting the upper and lower portions. An inwardly extending annular ledge is formed in the bottom of the outer wall portion. 
     One object of the present invention is to provide an improved header ring for a reciprocating pump. Related objects and advantages of the invention will become apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of an embodiment of the header ring of the invention. 
         FIG. 2  is a partial cross sectional view that shows an exemplary down hole packing set in horizontal showing a prior art header ring and other seals in the casing contacting the plunger on the interior and the bore or stuffing box wall on the exterior. The packing set includes a junk ring a, a header ring b, a pressure ring c, and a top adaptor ring d, which is partially cut away; 
         FIG. 3  is an enlarged cutaway cross sectional view of the prior art header ring shown in  FIG. 2 ; 
         FIG. 4  is an enlarged cutaway cross sectional view of the header ring of the invention taken along lines  4 - 4  of  FIG. 1 ; and 
         FIG. 5  is a partial cross sectional view like the one of  FIG. 1  with the new header ring of the invention substituted for the prior art header ring. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring to the Figures, one embodiment of the invention provides a header ring  10  for a reciprocating pump. The ring shaped body  20  has a side wall  22  that defines an open top  24  and an open bottom  26 . The cross section, ( FIG. 4 ) shows an inner wall portion  30  with an inner wall surface  32  for contacting a plunger pump  12 . The inner wall portion  30  includes an annular undercut  34  angled upward and outward that defines an overhang  35 . The undercut has a radial portion  37  that connects the undercut with the pedestal or foot of the bottom  26  of the body  20 . 
     An inwardly directed annular shoulder  33  is adjacently spaced from the undercut  34  and radial portion  37 . The shoulder may be shaped so as to be in direct alignment with the undercut  34 , the radial portion  37 , or both the undercut  34  and the radial portion  37 , like the embodiment of  FIG. 4 . The shoulder  33  is located between the undercut and the top  24  of the body. The inner wall portion  30  also has an inwardly sloped portion  36  and a flat portion  38 . The flat portion  38  is shown in  FIG. 4  as substantially parallel with the vertical, but in another embodiment, the flat portion may be formed inwardly or outwardly at an angle of between about minus 15 degrees (−15°) and fifteen degrees (15°) relative to the vertical (0°). In more preferred embodiments the flat portion  38  is formed in a manner such that it is angled inwardly (relative to the vertical showing in  FIG. 4 ) toward the plunger wall  12  ( FIG. 5 ) to between about zero (0°) and fifteen degrees (15°). 
     The body  20  includes an outer wall portion  50  with an outer wall surface  52  for contacting a bore wall  40 , which in typical applications is the wall of a stuffing box. Both the outer wall portion  50  and the inner wall portion  30  may be thicker or thinner than depicted in  FIG. 4 . The outer wall portion has an outwardly and downwardly directed sloped top portion  54 , a flat upper portion  51 , a flat lower portion  56 , and an outwardly sloped annular middle portion  58  connecting the upper and lower portions  51 ,  56 . In the embodiment illustrated in  FIG. 5 , the outer wall portion  50  includes a bottom  57  with an outwardly extending annular ledge  60 . 
     In some embodiments, the outer wall  50  and the inner wall  30  may be formed as a homogeneous elastomer ring. The body  20  can be made from a number of different natural or synthetic rubbers as, for example, nitrile or butadiene rubber, with a desired degree of hardness depending upon the use to which the plunger pump  12  is exposed. The outer wall  50  and the inner wall  30  may each be formed from an elastomer having a durometer of between about seventy (70) and ninety-five (95) Shore A. In another embodiment, the inner wall  30  and the outer wall  50  are formed from different materials, and the inner wall is harder than the outer wall. 
     In some embodiments, the header ring  10  or at least a portion thereof is formed from ultra-high-molecular-weight polyethylene (UHMWPE), e.g., perfluoroalkoxy (PFA), polyurethane, and/or other thermo or thermoset plastics. In other embodiments, the header ring or at least a portion thereof is formed from a fluorinated polymer, e.g., polytetrafluoroethylene (PTFE)-based material, fluorinated ethylene propylene (FEP). 
     In yet another embodiment the header ring  10  or at least a portion thereof is formed from a rigid and/or nonrigid composite elastomer using known means. Some portions and parts of the header ring  10  may, in some embodiments, be harder than others and/or have various values of hardness and include materials, such as fiber, filler or elastomer coated fabric, for example, to yield desirable physical properties driven by the particular environment of the application, such as ambient temperatures, pressures or pHs. In one embodiment, the header ring  10  or at least a portion thereof is formed from a fluorocarbon. 
     The above materials, compositions, and/or constituent elements forming the particular plastics discussed and their corresponding physical properties, however, should not be construed as limiting. Other materials, compositions, and/or constituent elements forming rigid and non-rigid materials or plastics possessing the physical properties useful in a manner as herein described may be appropriately desirable and availed using different materials, compositions, and/or constituent elements without undue experimentation and should be considered to fall within the scope of Applicants&#39; innovative header ring. 
     In more preferred embodiments, the inner wall portion  30  is formed from a high wear resistance/self-lubricated fluoroelastomer (FKM (FPM by ISO)) having a coefficient of friction between about 0.05 to 0.10, e.g., VITON®, and which may withstand pressure cycles of up to 20,000-30,000 psi; and the outer wall portion  50  is formed from a nonabrasive elastomer preferably containing graphite and/or rubber constituents, e.g., Hydrogenated Nitrile Butadiene Rubber (HNBR). A softer outer wall  50  substantially reduces the wear on the wall of the stuffing box  14  and prolongs the life of the seal  10  as a result. The softer outer wall  50  also produces inward radial force against the plunger  12  pump so that the inner wall surfaces  32 ,  38 ,  35 ,  34  and  37  define the self-sealing mechanism described below. 
       FIG. 2  shows an example of a prior well service sealing system or packing set illustrating diagrammatically different ring components (in cross section) a-d contained in a stuffing box  14 . The pump plunger  12  travels through the bore defined by the seals a,  10 ′ and b-d. The header ring  10 ′ shown in  FIGS. 2-3  is a prior art device and has a curved inner wall surface  15 ′ that is made to press against the plunger wall  12  to form a seal and a flat outer wall, as best seen in  FIG. 2 . Skilled artisans are familiar with the limited effective sealing life of the system created between the prior ring  10 ′ and the plunger  12  on the one side, and the ring  10 ′ and the wall  40  of the stuffing box  14  on the other. Regardless of the direction (in or out) of the plunger, sealing action delivered by the prior homogeneous elastomer ring  10 ′ against the respective surfaces of the plunger and stuffing box are the same in each direction. As a result, seal life is not optimal. 
     Referring to  FIGS. 4-5 , the automatic cleaning function of the ring  10  is described. When a sealing system or “packing” that includes the new header ring  10  is installed into the stuffing box, the unique geometry of the softer outer wall  50 , specifically the flat lower portion  56  and annular ledge  60  compresses against and automatically wipes/cleans the wall  40  of the stuffing box  14 . The wall  40  of the box is thus kept clean and sealed as these surfaces  56 ,  60 , unlike the plane surface of the outer wall of the prior ring  10 ′, provide different sealing actions against the wall of the stuffing box  14  when they are made to agitate (“washboard”) coincident with in/out motion of the plunger  12  pump. 
     Additionally, the compressive force to the softer outer wall  50  produces an inward radial force against the inner wall  30  that significantly improves seal function and duration. Flat portion  38  compresses radially against the wall of the plunger  12 . The amount of surface area of flat portion  38  made to contact the plunger wall  12  and hence, the effectiveness of the seal, is determined by the angle of flat portion  38  relative to the vertical, as described above. The radial force is transferred to portion  38 , overhang  35 , undercut  34  and radius  37 , which together form a self-sealing function between the ring  10  and the plunger  12  pump. Compression force on portion  38  causes the inner wall  30  to give slightly at radius  37  causing the wiper or sharp-edged overhang  35  and portion  38  to firmly seal with more or less force against the plunger  12 . Thus, a sharp wiping with less surface area contact or a full flat portion  38  optimal surface area contact may be used as desired. 
     On the upward stroke of plunger  12 , the overhang  35 , undercut  34  and radius  37  wipe and guide dirt and debris from the plunger keeping it free of silica, ceramic or other particulate that may cause leaks or damage to the packing. The new header ring  10  makes replacement of the packing more convenient because the “wipers”  60 ,  35  make walls  40 ,  12 , self-cleaning. That is, workers don&#39;t have to wrestle with cleaning the stuffing box and plunger in the field when replacing the packing. 
     For the purposes of promoting an understanding of the principles of the invention, specific embodiments have been described. It should nevertheless be understood that the description is intended to be illustrative and not restrictive in character, and that no limitation of the scope of the invention is intended. Any alterations and further modifications in the described components, elements, processes, or devices, and any further applications of the principles of the invention as described herein, are contemplated as would normally occur to one skilled in the art to which the invention relates.