Abstract:
A swivel for placing utility product with horizontal directional drilling techniques comprising a head piece and a tail piece rotationally mounted on the head piece. A bearing assembly of oppositely disposed units with high thrust capacity and self-alignment properties is mounted on a stub shaft integral with the head piece and enclosed by a shell body associated with the tail piece. A gap between the head piece and shell body is sealed with a metal face seal assembly. A juncture between the shaft and main part of the head piece is shaped to avoid a stress riser condition and a thrust washer has a configuration complimentary to the juncture to transmit forces between the head piece and bearing assembly. A joint between the tail piece and shell body is locked with a weld bead technique that enables the unit to be refurbished with reduced labor.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to improvements in swivels for connecting utility products to pipe strings in horizontal directional drilling operations.  
           [0002]    Horizontal direction drilling is increasingly popular because of increased demand for placement of utility product such as communications cable, power cable or conduit, infrastructure that obstructs traditional trenching methods, and technological advances in horizontal directional drilling. Activity in this field has demonstrated a need for a reliable coupling device to connect a drill or pipe string to a product line such as conduit for fiber optic cable. Typically, the product is installed by pulling the drill or pipe string back through the bore that has been created by various drilling and reaming methods. Coupling devices, commonly known as swivels, have been introduced to the industry. These swivels are intended to allow a pipe string to rotate while pulling the product without requiring the product to rotate. Rotation of the product could damage it. Existing swivel designs are prone to failure because of the harsh environment and high forces that are experienced in typical product installations. More specifically, the bore may be exposed to drilling fluid such as a mixture of water, bentonite and polymers known in the industry as “mud”. This liquid is used as coolant for the cutting tools, holding the drilled hole or bore open and to lubricate the product being installed.  
           [0003]    This liquid or mud can be destructive of the bearing seals and bearings typically found in commercially available swivels. Bearings may fail, not only from degradation or loss of lubrication due to seal failure, but also from heavy bending force loads on the swivel which the bearing structure is not capable of sustaining. Another significant problem with prior art swivels is their tendency to break under combined cyclic tensile and bending stresses that typically occur in use. These bending forces occur as the pipe string, swivel and product pass along a bore that deviates from a straight line such as where a hard formation or other obstruction or resistance may have been encountered during drilling operations. The nature of the work limits the physical size of the componentry in a swivel making it difficult to achieve satisfactory strength and durability.  
         SUMMARY OF THE INVENTION  
         [0004]    The invention provides a swivel for use with horizontal directional drilling equipment for product installation that has improved performance, durability and maintenance characteristics. A swivel constructed in accordance with the invention has extended bearing life by inclusion of a type of bearing assembly that tolerates practical dimensional tolerances and inevitable bending deflections in the swivel components during use. The swivel incorporates a metal face seal between the rotating and non-rotating parts of the swivel to exclude solid and liquid contaminanats from the interior and to retain lubricant therein.  
           [0005]    A cantilever or stub shaft supporting the bearing structure in the swivel has a large smooth fillet at its base to significantly reduce stress riser effects at this cross-section transition area. This area is capable of sustaining substantial tensile and compressive forces as well as large cyclical bending forces without failure in an extended service life. The swivel achieves a desired compactness by arranging the seal assembly around the shaft transition area. These elements, consequently, do not separately add to the necessary length of the swivel. Moreover, the seal assembly uses parts of the structure of the swivel itself to eliminate the need to make an outside diameter of the swivel larger than is required. The disclosed swivel is retained in an assembled state by a unique welding technique that is simple, reliable and avoids complicated and/or tedious labor when the swivel is disassembled and reassembled for regular maintenance and/or inspection and refurbishment.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a cross-sectional view of a swivel of the invention taken in a longitudinal or axial plane;  
         [0007]    [0007]FIG. 1A is an enlarged cross-sectional fragmentary view of a seal area of the swivel; and  
         [0008]    [0008]FIG. 2 is an end view of the product end of the swivel taken from the reference direction indicated by the arrows  2 - 2  in FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]    Referring now to the figures, there is shown a swivel assembly  10  for coupling a drill or pipe string to a product such as a communications cable, power cable or conduit for the same. Typically, a pipe string will be positioned in a bore or hole with horizontal directional drilling techniques. At the down hole end of the drill string, the swivel can be connected between the drill string and the lead end of a product to enable it to pull the product back through the bore.  
         [0010]    The swivel  10  includes a head piece  11 , a shell body  12  and a tail piece  13  which are primarily round bodies that, in assembly, are all concentric with a common axis  14 . Disposed within these bodies are a seal assembly  16 , a thrust washer  17 , bearing assemblies  18  and a nut  19 , all concentric about the common axis  14 .  
         [0011]    The illustrated swivel assembly  10  is rated at 30 tons. The head piece  11  has an internally threaded bore  21  or “box end” with 2-⅞ API (American Petroleum Institute) threads, for example, to enable it to be coupled with the end of a drill string. Flats  22  on the exterior of a solid circular mid-section  23  of the head piece  11  enable it to be held or turned with a wrench. Extending axially from the mid-section  23  is a cylindrical stub shaft or pin  24 . At its distal or free end, the shaft  24  has external machine threads  26 . At its fixed end where it is joined with the mid-section  23 , the shaft  24  has a large radius, smooth fillet  27  that, as will be discussed, serves to avoid the existence of a stress riser at this juncture. The thrust washer  17  has a bore  28  that slips over the shaft  24  and a throat area  29  that closely compliments the shaft fillet  27 . The thrust washer  17  has a radial face  30  on its side opposite the throat  29 . An annular skirt or collar  31  extends axially from the mid-section  23  concentrically about the shaft fillet  27 . The collar  31  is machined or otherwise formed with an annular pocket  32  with an inside surface  33  that is slightly conical, increasing in diameter with increasing distance from the mid-section  23 . Each end of the pocket  32  has a radial shoulder  34 ,  36 .  
         [0012]    The bearing assemblies  18  are assembled on the shaft  24  facing in opposite directions. Preferably, these assemblies  18  are essentially identical to afford both high tensile and compressive bearing strength and economies of standardization. Each bearing assembly  18  is of the spherical roller thrust bearing type with rollers  41 , inner races  42  and outer races  43  each having respective spherical surfaces  44 ,  45  and  46 . The bearing assemblies  18  are retained axially on the shaft  24  by a hex nut  48  threaded onto the threads  26 . A washer  49  with an internal key  51  that fits into an axial slot  52  along the threads  26  is interposed between a radial face  53  of the inner race  42  and the nut  48  to prevent the nut from unintentionally loosening. The radial face  53  of the inner race  42  of the other bearing assembly  18  abuts the radial face  30  of the thrust washer  17 .  
         [0013]    The shell body  12  has the general form of a cylindrical tube. At an end  51  adjacent the head piece collar  31 , the shell body  12  is machined or otherwise formed with an annular pocket  52  having a slightly tapered conical surface  53  increasing in diameter in the direction towards the collar  31  and two generally radial shoulders  54 ,  55  facing one another.  
         [0014]    A radial hole or port  57  is drilled through the wall of the shell body  12  and is provided with tapered pipe threads to receive a socket head pipe plug  58 . Blind holes  59  are formed in the outer surface of the shell body  12  to enable it to be gripped by a suitable wrench or similar device to turn it or prevent it from turning during refurbishment. At its mid-length, the shell body  12  has an internal shoulder  61  with oppositely facing radial abutment surfaces  62 ,  63  that abut respective radial faces  64  of the outer races  43  of the bearing assemblies  18 . The shell body  12  is proportioned so that when the bearing assemblies  18  are adequately restrained by tightening of the nut  19  on the shaft threads  26 , there is a small clearance gap  66  between the shell body  12  and collar  31 .  
         [0015]    At its opposite end, the shell body  12  has internal machine threads  67  to receive complimentary external threads  68  on an extension  69  of the tail piece  13 .  
         [0016]    In assembly, the tail piece extension  69  is tightened into the threads  67  until respective radial faces  71 ,  72  of the shell and tail piece abut. At the periphery of these faces, the shell body  12  and tail piece  13  are chamfered so as to form a small, shallow circumferential groove  73  around the surfaces. The extension  69  surrounds the shaft nut  19  so that, in effect, the nut and part of the shaft  24  nest in a blind cavity within the extension. Wrenching flats  74  are formed on the exterior of the tail piece  13 . A pair of spaced supports  76  extend axially from a main portion of the tail piece  13 . The supports  76  have aligned holes  77  perpendicular to the axis  14  such that the supports  76  form a clevis to receive a pin  78 . Between the clevis supports  76 , the main portion of the tail piece  13  has a through hole  79  with female pipe threads to accept a grease fitting or a relief valve  81 .  
         [0017]    The metal face seal assembly  16  seals the gap  66  between the head piece  11  and shell body  12  while allowing relative rotation between these members. The seal assembly  16  comprises a pair of matched metal sealing rings  87  and two elastomeric load rings or O-rings  88 . Tapered surfaces  33 ,  53  in the head piece collar  31  and shell body, respectively, and tapered surfaces  89  of the rings  87  bias the elastomeric rings  88  towards their respective seal rings  87  and the seal rings together so that their radial faces  90  provide a dynamic or rotational seal between these rings. The elastomeric load rings  88  provide a static seal between the rings and the head piece  11  and shell body  12 . The metal rings  87  and elastomeric load rings  88  can be of a type marketed by Caterpillar, Inc.  
         [0018]    With the parts assembled as shown in FIG. 1, the tail piece  13  and shell body  12 , which are preferably fabricated from suitable steel, are mutually interlocked by tack welding these members together. This can be accomplished, for example, by laying three equally spaced weld beads  91  of 308 stainless filler of an approximate length of 12 mm in the peripheral groove  73  formed by their respective bevels or chamfers. Any excessive bead height beyond the periphery of these members can be ground off.  
         [0019]    The bearing cavity, existing primarily within the shell body  12 , and to a limited degree the head piece collar  31  and tail piece extension  69  is filled with suitable grease through a grease fitting threaded into the hole  79 . The head piece  11  is rotated relative to the tail piece  13  while grease is injected. When grease exits the port  57  without air, the port is plugged with the plug  58  and the grease fitting is replaced by a suitable commercially available relief valve  81 . The relief valve  81  can be provisionally covered with a vent plug inserted into the axial hole  79  after assembly of the relief valve.  
         [0020]    In use, the swivel assembly  10  couples a pipe string, threaded into the head piece, to a product coupled to the tail piece  13  by the pin  78 . The product, which can be a communications cable, power cable, gas line, or conduit, for example, is installed by pulling the pipe string back out of the hole. This action often involves high tensile forces because of drag on the product line. The hole often deviates from a straight line because of obstacles in the original path of the drill. These deviations or turns in the hole can result in very high bending force loads being imposed on the swivel assembly  10 . These bending loads, coupled with high tensile loads, can severely stress the shaft  24 , particularly at its base where it joins the mid-section  23  of the head piece  11 . The fillet  27  at the base of the shaft  24  avoids stress riser phenomena in this area and greatly improves the resistance of the shaft to mechanical failure at this point. Unavoidable bending deflections of the shaft  24  do not normally result in excessive stress in the bearing assemblies  18  because of their inherent ability to self-align to the local deflections in the shaft. The seal assembly  16 , because it seals on a radial plane, can readily tolerate a limited eccentricity of the shell body  12  relative to the head piece  11  at this location due to bending of the shaft  24 . The pressure relief valve  81  allows limited release of lubricant from the bearing cavity if excessive heat build-up occurs in the swivel assembly  10  so as to protect the seal assembly  16  from excessive pressure.  
         [0021]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.