Abstract:
A hammer union comprises a thread end, a nut end and a hammer nut which, when cinched up, compresses a composite seal assembly thereby preventing leakage. The seal assembly comprises a metal insert of a size to pass into the seal groove of conventional hammer unions and a small seal acting between the insert, the thread end and the nut end. The small seal is conveniently an O-ring and is of a size that is compressed when the seal assembly is inserted into the thread end of the hammer union, thereby preventing the seal assembly from falling out of the threaded end when it is inverted. The metal insert provides another groove opposite the small seal to receive a second O-ring which acts as a spring to bias the small seal into sealing engagement, thereby allowing the new seal assembly to accommodate more variation in the length of the existing seal groove in prior art hammer unions.

Description:
[0001]    This application is an improvement over the invention disclosed in application Ser. No. 10/209,240, filed Jul. 31, 2002, entitled HAMMER UNION, SEAL THEREFOR AND METHOD.  
           [0002]    This invention relates to an improved technique for sealing between members of a hammer union and more particularly to an improved seal assembly that replaces the existing seal of a hammer union.  
         BACKGROUND OF THE INVENTION  
         [0003]    In the testing and production of hydrocarbon wells, specialized couplings are provided which incorporate seals to prevent leakage between the coupling components. One such coupling is known as a union and comprises a coarse male thread on one of the components which cooperates with coarse female threads on a collar to provide a quick connect/disconnect coupling.  
           [0004]    A more specialized quick connect/disconnect coupling is known as a hammer union which comprises four components: a thread end having coarse male threads on the exterior, a seal on the inside of the thread end, a nut end having a smooth nose abutting the seal and a hammer nut having coarse female threads on the interior and ears on the exterior which may be struck with a hammer to cinch up the coupling. Because hammer unions have the capability of being quickly connected and disconnected, they are widely used in temporary installations or in equipment which is expected to be disassembled periodically.  
           [0005]    Hammer unions have not been redesigned in many decades. The seal in a conventional hammer union is a large annular rubber seal that is basically rectangular in cross section. One of the coupling components provides a groove or rabbit receiving the annular rubber seal which is compressed between the coupling components when they are cinched up, thereby providing a seal. The rubber component is exposed to gases, fluids and abrasives flowing in the interior flow passage of the coupling. This conventional seal has withstood the test of time and has basically been unchanged for at least fifty years.  
           [0006]    One of the situations where hammer unions are widely used is in equipment to test gas wells after they are initially completed or after recompletion from one zone to another. Typically, regulatory agencies require that gas wells be tested to provide a measure of gas deliverability and pressure using chokes of several different size. To enforce these regulations, regulatory agencies often will not allow a well to be produced into a sales line before testing. Test equipment typically comprises a trailer having an inlet end for connection to the well head, a separator for separating gas and liquid, an orifice meter for measuring the gas from the well and an outlet for connection to a flow line leading to a flare.  
           [0007]    Many gas wells, particularly those completed at depth, do not produce commercial quantities of natural gas until they are fraced. It is a tribute to the research of major oil companies and major oil field service companies that modern frac techniques convert large numbers of conventionally completed uneconomic wells into economic ones. A typical current frac job injects a liquid or gel containing 500,000 or so pounds of sand or other proppant under pressure into a well to create, propagate and prop open a vertical fracture extending many hundreds of feet away from a well bore to provide a high permeability flow path from a relatively low permeability formation to the well bore.  
           [0008]    One of the facts of life of fracturing a well with a large quantity of sand or other proppant is that not all of the proppant stays in the hydrocarbon zone when the well is produced. When production starts, some of the proppant returns to the well bore and is produced at the surface.  
           [0009]    Hammer unions are also widely used on drilling rigs to make mud line connections, to make connections in cementing operations and to pump various liquids into a well bore during completion operations.  
           [0010]    Disclosures of some interest relative to this invention are U.S. Pat. Nos. 2,726,104; 3,140,107; 3,848,905; 4,930,791 and U.S. Patent Publication H945.  
         SUMMARY OF THE INVENTION  
         [0011]    In this invention, it is recognized that new gas wells, particularly those that have been fraced, produce high velocity streams of proppant laden gas and liquid. Because the proppants are sand or similar particles, they are quite abrasive. These high velocity abrasive well streams have the capability of cutting out the conventional seals used in many flow line connections, specifically hammer unions. This creates a dangerous and awkward situation where highly flammable well production, both liquid and gas, escapes from a flow line at a location where it is unexpected. Instead of the well contents being flared at a flare installation hundreds of feet from the well head or test rig, all of a sudden, well contents are escaping in the test rig, immediately adjacent the well head or some other equally unsuitable location. Well testers and others in the immediate area have to be vigilant to detect the onset of large leaks in flow lines and test equipment and be prepared to shut the well in. It is a scary thing to shut in a well producing a high velocity stream loaded with proppant because of the danger of cutting out valves on the well head, leaving the well uncontrollable.  
           [0012]    In this invention, flow line coupling seals, such as in hammer unions, are modified to provide a seal largely protected against the abrasive action of high velocity well contents. Specifically, the conventional all-rubber seal is removed and discarded. It is replaced by an annular metal insert or carrier having a small annular groove or rabbit receiving an O-ring or other much smaller seal. In this fashion, a seal protected against the action of abrasive high velocity well fluids is placed in the same groove as a conventional seal, meaning that the metal components of a conventional flow line coupling, such as a hammer union, do not have to be machined or otherwise modified to accommodate a seal providing a much longer useful life.  
           [0013]    There are situations where the seal receiving groove in existing hammer unions is slightly longer in the direction of flow than normal. This means there is occasionally inadequate sealing pressure between the O-ring and the seal seat which it seals against. This is overcome in this invention by using an additional compressible member on the opposite side of the annular metal insert from the sealing O-ring. In a preferred embodiment, this additional compressible member is an additional O-ring.  
           [0014]    It is an object of this invention to provide an improved method and apparatus sealing a flow line coupling.  
           [0015]    Another object of this invention is to provide an improved hammer union.  
           [0016]    A further object of this invention is to provide a technique for changing the seal of a flow line coupling without machining or otherwise modifying the permanent metal components of the coupling.  
           [0017]    These and other objects and advantages of this invention will become more apparent as this description proceeds, reference being made to the accompanying drawings and appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a side view of a conventional hammer union having a conventional seal assembly, certain parts being broken away for clarity of illustration;  
         [0019]    [0019]FIG. 2 is a partial broken side view, similar to FIG. 1, of a hammer union incorporating the seal assembly of this invention;  
         [0020]    [0020]FIG. 3 is an enlarged partial side view showing a seal assembly of this invention in position in a thread end of a hammer union;  
         [0021]    [0021]FIG. 4 is an isometric view of the seal assembly of this invention illustrating a metal insert and a resilient O-ring, certain parts being broken away for clarity of illustration;  
         [0022]    [0022]FIG. 5 is a view similar to FIG. 2 showing the improved seal assembly of this invention;  
         [0023]    [0023]FIG. 6 is a view similar to FIG. 3 showing the improved seal assembly of this invention;  
         [0024]    [0024]FIG. 7 is an exploded cross-sectional view of the annular metal insert, seal and compressible member of this invention;  
         [0025]    [0025]FIG. 8 is an enlarged partial view of the end of the metal insert shown in FIG. 7;  
         [0026]    [0026]FIG. 9 is a broken isometric view of the improved seal assembly of this invention; and  
         [0027]    [0027]FIG. 10 is a side view of the metal insert of FIG. 8. 
     
    
     DETAILED DESCRIPTION  
       [0028]    Referring to FIG. 1, there is illustrated a conventional hammer union  10  comprising as major components a thread end  12 , a nut end  14  and a hammer nut  16 .  
         [0029]    The thread end  12  includes a short conduit  18  adapted to connect to a conduit or pipe, as by providing relatively fine exterior threads  20 , such as machine threads or eight round threads. Very coarse exterior threads  22  are provided on the end opposite the threads  20 . On the inside, the thread end  12  includes a flow passage  24  and an annular groove or rabbit  26  communicating with the passage  24  for receiving a large rubber seal  28 . Typically, the groove or rabbit  26  includes an enlarged rim  30  for receiving a bulge  32  on the rubber seal  28  to assist keeping the seal  28  in the groove  26 . The seal  28  is an annular member made of a rubber or rubber like material. The threaded end  12  terminates in a more-or-less frustoconical seat  34  which may be straight or slightly concave.  
         [0030]    The nut end  14  includes a short conduit  36  adapted to connect to a pipe or conduit having relatively fine exterior threads  38 , such as machine threads or eight round threads. On the inside, the nut end  14  includes a flow passage  40  communicating with the passage  24  providing a passage through the hammer union  10 . The nut end  14  terminates in a nose  42  having a more-or-less frustoconical face  44  mating with the seat  34  and providing a seal seat  46  perpendicular to an axis of flow  48  through the hammer union  10 .  
         [0031]    The hammer nut  16  comprises a collar  50  of sufficient internal diameter to pass over the nut end  14  and the thread end  12  so the internal threads  52  mate with the coarse external threads  22 . The hammer nut  16  includes a rim or shoulder  54  which engages a similar exterior shoulder  56  on the nut end  14  thereby closing up the gap between the thread end  12  and the nut end  14  upon threading the collar  50  onto the coarse threads  22 . The dimensions of the thread end  12  and the nut end  14  are selected such that cinching up the hammer nut  16  causes the seal seat  46  to compress the seal  28  thereby preventing leakage between the thread end  12  and the nut end  14 . The hammer nut  16  also includes a series of ears or projections  58  which may be manually grasped and turned or struck with a hammer to cinch up the thread and nut ends  12 ,  14 . Cooperation between the coarse threads  22 ,  52  provides a quick connect/disconnect feature for the hammer union  10  and also allows easy connection between the thread and nut ends  12 ,  14  even when the conduits  18 ,  36  are not perfectly aligned. Those skilled in the art will recognize the hammer union  10  to be a typical prior art hammer union which has been manufactured and used in the drilling and production of hydrocarbon wells for many decades.  
         [0032]    The problem is that the seal  28  is exposed to liquids and gases passing through the flow path provided by the hammer union  10 . When the hammer nut  16  cinches up the thread end  12  and the nut end  14 , there is a tendency to compress the rubber seal  28  so it bulges out into the flow passage  24 . When using a hammer union  10  in a situation where the flow contents are high velocity abrasive laden liquids or gases, there is a tendency for the seal  28  to be eroded or cut out by the abrasives, particularly when it bulges out into the flow passage  24 . When the high velocity flow stream is a hydrocarbon liquid or gas, there is a significant hazard because the leaking flow stream is highly flammable and is easily ignited.  
         [0033]    Referring to FIGS.  2 - 4 , this invention is illustrated. In FIG. 2, the standard hammer union  10  has been modified by removing the conventional seal  28 , as with a screw driver, awl or other pointed instrument, and replaced with a seal assembly  60  of this invention. The seal assembly  60  comprises an annular metal insert or carrier  62  and a seal  64 , typically an O-ring, much smaller than the seal  28 . The seal assembly  60  is designed to provide a suitable resilient seal between the thread and nut ends  12 ,  14  and protect the seal  64  from abrasion due to a high velocity well stream flowing through the passages  24 ,  40 , preferably without modifying the metal components of the hammer union  10 . This feature is important because it is much easier to simply replace the seal  28  with the seal assembly  60  than it is to remove an existing hammer union from service, take it to a machine shop and have it machined in some manner, and then return it to service, bearing in mind that the hammer union may be installed in a location many miles from the nearest machine shop.  
         [0034]    To these ends, the insert  60  is made of any suitable metal such as one comparable to the thread and nut ends  12 ,  14 . The thickness of the insert  60 , i.e. the dimension parallel to the flow axis  48 , is approximately the same as, or slightly less than, the compressed conventional rubber seal  28 . In this manner, the dimensional design of the conventional hammer union  10  is unaffected because the seat  34  and face  44  engage and stop movement of the thread and nut ends  12 ,  14 . The internal diameter of the metal insert  62  is substantially the same as the diameters of the flow paths  28 ,  40 .  
         [0035]    The external diameter of the metal insert  62  is more difficult to select, mainly because there is some variation in the diameter of the groove  26  from manufacturer to manufacturer and in unions of the same manufacturer. It will be recollected that the prior art seal is a large rubber member capable of accommodating grooves of somewhat different diameter. Accordingly, the diameter of the groove  26  has not been tightly controlled in the past, mainly because there was no reason to.  
         [0036]    If one were adapting a single hammer union, the external diameter of the insert  62  has to be smaller than the measured diameter of the groove  26 . If one were adapted a large number of hammer unions of the same nominal size, the external diameter of the insert  62  would have to be smaller than all or a very large percentage of existing hammer unions. Thus, one should select an outside diameter of the insert  62  that is considerably smaller than a large fraction of the grooves  26  of existing hammer unions. This means the seal  64  has to be relatively large and/or relatively compressible to accommodate the gaps that occur between the insert  60  and the groove  26 .  
         [0037]    The requirement that the insert  60  fit a large proportion of existing hammer unions introduces another problem. If the insert  60  is made small enough in diameter to fit most existing hammer unions of the nominal size under consideration, there is the tendency for the seal assembly  60  will fall out of the thread end  12  if it is handled with the threads  20  up. This is not fatal but it is very aggravating for the seal assembly  20  to fall in the mud when the hammer union  10  is being assembled. Accordingly, the seal  64  is selected so its external diameter is noticeably larger than the largest groove  26  so that when the insert  62  and seal  64  are placed in the groove  26 , the seal assembly  60  is wedged in place by the seal  64 . In other words, the seal  64  wedges the seal assembly  60  in place before the seal  64  is compressed by the seal seat  46  of the nut end  16 .  
         [0038]    To these ends, the insert  62  comprises an annular metal member  66 . The insert  62  might have separate grooves on its side and end but it is much preferred to provide a rabbit or groove  68  on an exterior edge facing the seal seat  46  and the groove  26 . The groove  68  accordingly includes an annular face  70  parallel to the flow axis  48  and a annular shoulder or face  72  perpendicular to the flow axis  48 . The groove  68  accordingly opens through the outside diameter of the insert  62  to face the thread end  12  and opens through the a rim or shoulder  74  to face the seal seat  46 . The groove  68  is typically a small fraction of the cross-sectional size of insert  60 . A butt end  76  of the insert  62  abuts the groove  26  and prevents movement of the insert  62  away from the seal seat  46  in a cinched up position of the thread and seal ends  12 ,  14 .  
         [0039]    The seal  64  may be of any suitable cross-sectional shape, such as square, polygonal or of compound shape but is preferably round, i.e. an O-ring. The seal  64  is preferably conventional rubber or rubberoid material, which is used herein to mean that the seal has the characteristics of rubber, i.e. it is resilient, tolerant of high temperatures and pressures and relatively chemically inert to compounds typically found in hydrocarbon well streams. A preferred O-ring seal  64  is made of Buna rubber and is available from any automotive supply store or any industrial supply house.  
         [0040]    After the old seal  28  has been removed, the metal insert  62  is dropped into the groove  26  and the seal  64  is stretched over the shoulder  76  by inserting part of the O-ring  64  into the groove  68  and progressively pushing or rolling the O-ring  64  around the shoulder  76  and into the groove  68 .  
         [0041]    The single most common size hammer union is of a nominal 2″ internal diameter has a nominal groove diameter of 2{fraction (11/16)}″. In fact, upwards of 80% of all existing hammer unions are of 2″ nominal diameter. Thus, making a seal assembly which may be used in all 2″ hammer unions, without having to machine any of the existing parts is a particularly appealing feature of this invention. Thus, all of the dimensions below relate to 2″ hammer unions.  
         [0042]    Hammer unions are made by a number of manufacturers, including FMC Corporation of Houston, Tex. The seal groove of a 2″ hammer union is stated to be 2{fraction (11/16)}″ but measuring a large number of 2″ hammer unions showed something slightly different. The largest measured groove diameter was 2.687 inches and the smallest measured groove diameter was 2.660 inches. In order to make a seal assembly that fits all existing hammer unions without machining existing parts, the metal insert  62  of this invention is selected to be small enough to fit in the smallest measured conventional hammer union and accordingly has a maximum size of 2.650 inches, including any tolerances, in diameter. Thus, the maximum size of the metal insert  62  is selected to be 2.650 inches and a tolerance of plus zero, minus 0.005 inches.  
         [0043]    The minimum diameter of the metal insert  62  depends on the size, design and compressibility of the seal  64 . Because high pressure on the inside of the hammer union  10  produces an axial force and a radial force tending to press the seal  64  into the corner between the hammer nut  16  and the nose  42 , it is easy to make the seal  64  perform satisfactorily. Thus, the metal insert  62  may have a loose tolerance on the small side. The minimum diameter of the metal insert is presently unknown because no attempt has been made to make an insert  62  of minimum diameter. However, a preferred minimum diameter is 2.535 inches which is the minimum measured diameter of 2.660 inches less twenty five thousandths of an inch. Although it is believed that much smaller minimum diameters are feasible because the O-ring seals may be made larger than stated below, a practical minimum size is on the order of 2.250 inches.  
         [0044]    The thickness of the metal insert  62 , i.e. the distance from the rim  74  to the butt end  76  is also capable of substantial variation. The measured distance of a number of nominal 2″ diameter hammer unions, with the groove  26  empty but with the hammer nut  16  made up, showed that the groove  26  was more-or-less consistent at about 0.470 inches in length parallel to the flow axis  48 . It is preferred that the nut end  14  and the thread end  12  abut, or nearly abut, to provide a closed corner into which the seal  64  is compressed. Thus, the maximum thickness of the metal insert  62  is on the order of 0.470 inches and a preferred metal insert is on the order of about 0.450 inches thick.  
         [0045]    In a manner analogous to the selection of the minimum diameter of the metal insert  62 , the minimum thickness of the metal insert  62  is subject to wide variation because the seal  64  may be selected to be larger than the preferred dimension stated herein. No attempt has been made to make a satisfactory metal insert with a minimum thickness but a practical minimum thickness is on the order of about 0.30 inches.  
         [0046]    The groove  68  cut into the metal insert  62  is sized to receive a suitably sized seal, i.e. a seal that is large enough to seal against the thread end  12  and the nut end  14  in their made up condition. Although the groove  68  may be of any suitable size, in a preferred design for a nominal 2″ hammer union, the groove  68  is 0.165 inches on a side, i.e. the sides  70 ,  72  are 0.165 inches each. The seal  64  is selected to be of a size suitable for an insert  62  of the selected diameter and a groove  69  of the selected size. Although the seal  64  may vary considerably, an O-ring having a nominal diameter of {fraction (3/16)}″, which in reality has a diameter of about 0.210 inches, has proved suitable. Thus, an O-ring  64  suitable for this size insert is 2{fraction (11/16)} inches in outside diameter. A typical O-ring seal used in this invention is placed in the groove  68  by placing one section of the circumference of the O-ring over the rim  74  and rolling the balance of the O-ring into the groove  68  with the thumbs.  
         [0047]    The diameter of the groove face  70  is, analogous to the external diameter of the insert  62 , subject to variation because the internal diameter of the seal may vary substantially. For a nominal 2″ diameter hammer union with an O-ring seal  64  of {fraction (3/16)}″ nominal thickness and 2{fraction (11/16)}″ nominal outside diameter, the diameter of the groove face  70  is conveniently about 2.313 inches with a small tolerance.  
         [0048]    Referring to FIGS.  5 - 7 , the improvement of this invention is illustrated. In FIG. 5, the standard hammer union  10  has been modified by removing the conventional seal  28 , as with a screw driver, awl or other pointed instrument, and replaced with a seal assembly  80  of this invention. The seal assembly  80  comprises an annular metal insert or carrier  82 , a seal  84 , typically an O-ring, much smaller than the seal  28  and a compressible member  86  that accommodates oversize variations in the length of the groove  26  in the direction of the flow axis  48 . The seal assembly  80  is designed to provide a suitable resilient seal between the thread and nut ends  12 ,  14  and protect the seal  84  from abrasion due to a high velocity well stream flowing through the passages  24 ,  40 , preferably without modifying the metal components of the hammer union  10 . This feature is important because it is much easier to simply replace the seal  28  with the seal assembly  80  than it is to remove an existing hammer union from service, take it to a machine shop and have it machined in some manner, and then return it to service, bearing in mind that the hammer union may be installed in a location many miles from the nearest machine shop.  
         [0049]    To these ends, the insert  80  is made of any suitable metal such as one comparable to the thread and nut ends  12 ,  14 . The thickness of the insert  82 , i.e. the dimension parallel to the flow axis  48 , is approximately the same as, or slightly less than, the compressed conventional rubber seal  28 . In this manner, the dimensional design of the conventional hammer union  10  is unaffected because the seat  34  and face  44  engage and stop movement of the thread and nut ends  12 ,  14 . The compressible member  86  accommodates more variation in the length of the seat  26 , parallel to the flow axis  48 , meaning that the seal assembly  80  is more nearly a universal replacement for the prior art seal  28 . The internal diameter of the metal insert  82  is substantially the same as the diameters of the flow paths  28 ,  40 .  
         [0050]    The external diameter of the metal insert  82  is selected in the same manner as the external diameter of the metal insert  62 . To these ends, the insert  82  comprises an annular metal member  88 . The member  88  provides a first rabbit or groove  90  including an annular face  92  parallel to the flow axis  48  and an annular shoulder or face  94  perpendicular to the flow axis  48 . The groove  90  accordingly opens through the outside diameter of the insert  82  to face the thread end  12  and opens through the a rim or shoulder  96  to face the seal seat  46 . The groove  90  is typically a small fraction of the cross-sectional size of insert  82 . The member  88  provides a second rabbit or groove  98  including an annular face  100  parallel to the flow axis  48  and an annular shoulder or face  102  perpendicular to the flow axis  48 .  
         [0051]    The compressible member  86  resides in the second groove  98  and may be of any suitable type. Preferably, the compressible member  86  is an O-ring and is ideally the same size and type as the O-ring  84  so that an uninformed or unobservant user cannot put the wrong O-ring in the wrong groove. Thus, the seal assembly  80  is preferably symmetrical so it can be installed with either side providing the seal against the seal seat  46 . This makes the seal assembly  80  as fool proof as possible.  
         [0052]    After the old seal  28  has been removed, the compressible member  86  is stretched over the metal insert  82 , the metal insert  82  is dropped into the groove  26  and the seal  84  is stretched into the groove  90  by inserting part of the O-ring  84  into the groove  90  and progressively pushing or rolling the O-ring  84  over the shoulder  96  into the groove  90 .  
         [0053]    Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.