Abstract:
An anti-rotational pipe coupling system is disclosed having pipe segments with end surfaces in which receptacles are arranged at spaced intervals circumferentially around each pipe. Interference bodies in the form of elongated pins are received within the receptacles of one pipe segment and extend outwardly from the end surface to engage complementary receptacles in another pipe segment arranged in facing engagement. The pins bear against the pipe segment sidewalls within the receptacles to prevent relative rotation of the pipe segments about a longitudinal axis coaxial with them. The pipe segments are received within a tube which uses flexible splines engaging concentrically aligned grooves in the tube and the pipe segments to prevent relative axial movement between the segments.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention concerns a pipe coupling system for joining pipe segments end-to-end, the coupling system preventing relative rotation of the pipes about their longitudinal axes.  
         BACKGROUND OF THE INVENTION  
         [0002]    Piping networks for the conveyance of liquids, such as water, as well as other fluids, such as compressed gases, are used across a wide spectrum of industrial, mining and agricultural activities. Such networks may conveniently be constructed from pipe segments of various lengths having prepared ends adapted to be joined and sealed together by a mechanical coupling system.  
           [0003]    In one such mechanical coupling system, shown in FIG. 1, pipe segments  20  are received within a tube  22 . O-ring seals  24  (only one being shown) are positioned symmetrically between tube  22  and each pipe segment  20  effecting a fluid-tight seal at the joint. The tube  22  has an inner surface  26  with an inwardly facing groove  28  arranged symmetrically and proximate to each end (only one groove  28  being shown). Pipe segments  20  have an outwardly facing groove  30  which is brought into concentric alignment with inwardly facing groove  28  upon insertion of pipe segment  20  into tube  22 . When the grooves  28  and  30  are concentrically aligned, a flexible spline  32  may be inserted through an aperture  34  in tube  22  in communication with inwardly facing groove  28 . The spline is received within grooves  28  and  30  and is positioned circumferentially around the pipe segments  20 . The spline engages both the tube and the pipe segments and prevents relative axial motion between them.  
           [0004]    While the coupling system described has many advantages, it makes no provision for preventing relative rotational motion of the pipe segments  20  about their longitudinal axes  36 . Certain applications, such as a coupling system for a well drop pipe described below, require that the pipes cannot rotate relative to each other.  
           [0005]    The well drop pipe  38 , shown in FIG. 2, extends within a well  40 . At the drop pipe&#39;s lower end  42 , a submersible pump  44  is mounted. Pump  44  is electrically powered and receives its power via an electrical cable  46  which extends into well  40  lengthwise along the drop pipe  38 . Drop pipe  38  may be constructed of several pipe segments  20  coupled axially by the tube and spline system depicted in FIG. 1. Submersible pumps such as  44  have an impeller (not shown) which rotates about the longitudinal axis  36  of pipe segments  20  to pump water  48  from the well  40 . Each time the pump starts, considerable torque is applied to spin the impeller. The torque may be as high as 1,500 ft-lbs for a 200 hp pump and results in an equal and opposite counter torque being applied to pipe segments  20 . Since there is no provision for reacting the counter torque at the tube  22 , the lower pipe segment  20   a  will rotate about its longitudinal axis  36  in response to the counter torque each time the pump starts. This unrestrained rotation of pipe segment  20   a  will cause the electrical cable  46  to wrap around the drop pipe  40  in a helix, eventually placing sufficient tension on the cable  46  to cause it to separate or pull out of the pump, causing a pump failure.  
           [0006]    There is clearly a need for an improved mechanical coupling system which prevents relative rotation of the pipe segments joined by the system.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0007]    The invention concerns an anti-rotational pipe coupling for preventing relative rotation between pipe segments joined together. In the coupling system, a pipe segment with a circumferential sidewall having a predetermined thickness defining an end surface positioned at an end of the pipe segment has a receptacle positioned in the sidewall at the end. The receptacle has an opening facing outwardly from the end surface. An interference body has a first portion sized to interfit within the receptacle and a second portion projecting outwardly from the receptacle beyond the end surface. The second portion of the interference body is engageable with another receptacle in an end surface of another pipe segment when the end surfaces are in facing engagement with one another. The interference body engages the receptacles in each pipe segment and prevents their relative rotation about a longitudinal axis coaxial with them.  
           [0008]    Preferably, there are a plurality of such receptacles arranged in spaced relation to each other radially around the end surface of the pipe segment, and a plurality of interference bodies, each engageable with a respective receptacle.  
           [0009]    In a preferred embodiment, the interference bodies comprise elongated cylindrical pins, the receptacles being cylindrical to receive the pins in mating engagement. One end of each pin interfits within a respective receptacle, the other end projects outwardly from the receptacle. Preferably, each pin has a longitudinal axis oriented substantially parallel to the longitudinal axis coaxial with the pipe segments to facilitate assembly and disassembly of the joint.  
           [0010]    It is advantageous that one of the pins has a diameter relatively larger than the diameter of the receptacle into which it is received thereby providing an interference fit between the one pin and its receptacle to retain the pin with the pipe segment.  
           [0011]    While the anti-rotational coupling system may be used in conjunction with various other mechanical coupling systems, it is particularly suited for use with a coupling system comprising an elongated tube having an inner diameter sized to receive the pipe segments in mating engagement. The pipe segments have an outwardly facing circumferential groove formed proximate to their respective ends. The tube has an inner surface with inwardly facing circumferential grooves positioned proximate each end thereof. The outwardly facing grooves in the pipe segments are positionable in concentric alignment with the inwardly facing grooves in the tube upon mating engagement of the pipe segments and the tube. Apertures are formed through the tube at each end in communication with the inwardly facing grooves. Each aperture receives an elongated flexible spline insertable through the aperture and positionable circumferentially around the tube within both the inwardly facing and outwardly facing grooves when the grooves are positioned in coaxial alignment. The splines engage both the tube and the pipe segments to prevent axial motion thereof relatively to one another.  
           [0012]    It is an object of the invention to provide an anti-rotational coupling system that effectively prevents relative rotation of axially connected pipe segments about the longitudinal axes of the segments.  
           [0013]    It is another object of the invention to provide an anti-rotational coupling system which is simple to install.  
           [0014]    It is yet another object of the invention to provide an anti-rotational coupling system which is inexpensive to implement.  
           [0015]    It is again another object of the invention to provide an anti-rotational coupling system which is reliable.  
           [0016]    It is still another object of the invention to provide an anti-rotational coupling system which is compatible with currently available mechanical pipe coupling systems.  
           [0017]    These and other objects and advantages will be apparent upon examination of the following drawings and detailed description of preferred embodiments of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a partial sectional perspective view of a prior art pipe coupling system;  
         [0019]    [0019]FIG. 2 is a side view of a pipe coupling system of the prior art in operation;  
         [0020]    [0020]FIG. 3 is a perspective view of an anti-rotational pipe coupling system according to the invention;  
         [0021]    [0021]FIG. 4 is a cross-sectional view taken along lines  4 - 4  of FIG. 3;  
         [0022]    [0022]FIG. 5 is a longitudinal sectional view of the anti-rotational pipe coupling system shown in FIG. 3;  
         [0023]    [0023]FIG. 6 is a perspective view of the anti-rotational pipe coupling system shown in FIG. 3; and  
         [0024]    [0024]FIGS. 7 and 8 show detailed components used in the anti-rotational pipe coupling system according to the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    [0025]FIG. 3 shows a pipe segment  20  with the anti-rotational system  50  according to the invention. Pipe segment  20  has a circumferential side wall  52  with a predetermined thickness defining an end surface  54  positioned at an end  56  of the pipe segment. Anti-rotational system  50  comprises one or more receptacles  58  positioned in the sidewall  52  and facing outwardly from the end surface  54 .  
         [0026]    Receptacles  58  are sized and shaped to receive interference bodies  60 , which are preferably elongated cylindrical pins described in detail below. Each receptacle  58  and a respective interference body  60  cooperate such that one portion  62  of the body interfits within the receptacle while another portion  64  extends outwardly from the receptacle  58  beyond the end surface  54 . As shown in FIG. 5, the outwardly extending portion  64  of each body  60  is engageable with another receptacle  58   a  positioned in another end surface  54   a  of another pipe segment  20   a  when the end surfaces  54  and  54   a  are in facing engagement with one another. The interference body  60  bears on both pipe segments  20  and  20   a  and prevents relative rotation of the pipe segments about their longitudinal axes  36 .  
         [0027]    As noted above, interference bodies  60  are preferably elongated cylindrical pins, and the receptacles  58  are also cylindrical to receive the pins in mating engagement. Preferably, the pins have a longitudinal axis  66  which is oriented substantially parallel to longitudinal axis  36  of the pipe segments  20 . Keeping the various axes parallel facilitates the coupling of the pipe segments together, allowing the pins  60  to slip into and out of mating engagement as required.  
         [0028]    When the anti-rotational system is used in conjunction with an axial coupling means, such as the mechanical coupling system having tube  22  (see FIG. 5), the pins  60  are not visible once both pipe segments  20  and  20   a  are engaged with the tube  22 , and it may, therefore, be difficult to align the pins  60  with the receptacles  58   a  in pipe segment  20   a . However, the tube  22  cannot be secured to both of the pipe segments  20  and  20   a  by means of the flexible splines  32  unless the pins  60  are properly engaged within the receptacles because the outwardly facing groove  30  on at least one of the pipe segments will be prevented from properly aligning with the corresponding inwardly facing groove  28  on tube  22 , thereby preventing insertion of the spline  32  through aperture  34 . Only when the pins properly engage their respective receptacles do the outwardly facing grooves  30  align with the inwardly facing grooves  28  and permit insertion of the splines  32  to secure the pipe segments  20  and  20   a  to one another.  
         [0029]    While it is possible to prevent relative rotation of the pipes about the longitudinal axis  26  with a single pin  60 , it is preferred to use a plurality of pins as shown in FIG. 3. The number of pins and their diameter are selected so as to keep the bearing stresses in the circumferential sidewall  52  below a threshold value proportional to the bearing failure allowables for the particular material comprising the pipe segments  20 . While the anti-rotational system is not limited to any particular material, it is particularly suitable for use with pipe segments  20  and tubes  22  made of engineering thermoplastics, PVC being preferred, but other materials including CPVC, polyethylene and fiberglass also being feasible. Pins  60  are preferably stainless steel due to this material&#39;s strength and resistance to corrosion. However, other non-corroding materials, including aluminum, coated steel (galvanized or plated), as well as high-strength engineering thermoplastics, are also feasible. Splines  32  are preferably also engineering thermoplastics, such as PDT for flexibility and strength.  
         [0030]    In assembling the anti-rotational pipe coupling system according to the invention, it is preferred to first engage the portion  62  of pins  60  in receptacles  58  on one pipe segment  20  as shown in FIG. 3, and then interfit pipe segment  20  into one end of tube  22  as shown in FIG. 6. To secure the pipe segment  20  to tube  22 , flexible spline  32  is inserted into the concentrically aligned grooves  28  and  30  near the end of the tube receiving the pipe segment. Next, the other pipe segment  20   a  is interfitted into the other end of tube  22 , the pins  60  are aligned with receptacles  58   a  in pipe segment  20   a  and the pipe segment  20   a  is pushed toward pipe segment  20 , engaging the extending portion  64  of pins  60  with receptacles  58   a  as shown in FIG. 5. Once the pipe segments are properly engaged the other flexible spline  32  may be inserted into the concentrically aligned grooves  28  and  30  at the other end of the tube  22  to secure pipe segment  20   a  to it.  
         [0031]    To facilitate assembly and disassembly of the joint and prevent loss of the pins, it is convenient to have the pins  60  interfit within receptacles  58  with some degree of interference. At the same time, it is desired to have the same pins slide relatively easily into and out of receptacles  58   a  in the adjoining pipe segment  20   a . Both receptacles  58  and  58   a  should be the same size, however, so that all pipe segments are identical, thus, allowing any pipe segment to couple to any other segment.  
         [0032]    These constraints are met by disrupting the surface of one of the aforementioned pin portions, for example, portion  62 , to enlarge the pin portion by giving it a greater effective diameter. Thus, when enlarged pin portion  62  engages receptacle  58 , as shown in FIG. 4, the larger effective diameter results in an interference fit between the pin and the receptacle, effectively retaining the pin in pipe segment  20 . However, the remaining portion of the pin  64  is substantially unaffected and is sized relative to receptacle  58   a  to easily slide in and out with no significant interference. These properties of the pins facilitate engagement of the pins with the receptacles during assembly of the joint and prevent the pins from being lost during handling, assembly and disassembly of the pipe segments.  
         [0033]    [0033]FIGS. 3, 4,  7  and  8  show several methods for disrupting the pin surface and obtaining a larger effective diameter over a portion of the pin. In the pin  60  shown in FIGS. 3 and 4, longitudinal grooves  68  are swaged into the surface of portion  62  at 120° intervals circumferentially around the pin. The swaging operation outwardly displaces metal on each side of the grooves, thus forming raised areas  70  between them. The raised areas  70  effectively expand the diameter of the pin over the portion  62  where the grooves  68  are located.  
         [0034]    [0034]FIG. 7 shows another pin  60   a , which has barbs  72  extending radially outwardly from a portion  62   a  of the pin and effectively increasing its diameter over that portion. Barbs  72  have a pointed end  74  which faces toward the other pin portion  64   a . In operation, the barbed portion  62   a  is first inserted into the receptacle  58  of one of the pipe segments  20 , the barb ends  74  engaging the pipe segment sidewall within the receptacle to retain the pin therein.  
         [0035]    [0035]FIG. 8 shows yet another pin  60   b  wherein a portion of the pin  62   b  is knurled. The knurling operation disrupts the surface over portion  62   b  and produces a textured surface  76  comprising a plurality of projections  78  extending radially outwardly from the pin to create a larger effective diameter over portion  62   b . When portion  62   b  of pin  60  is inserted into a receptacle  58 , the projections effectively engage the pipe segment sidewall within the receptacle, again with the object of retaining the pin within the receptacle during handling, assembly and disassembly of the joint.  
         [0036]    Other details which facilitate assembly of the pipe joint include countersinking the receptacles  58  and  58   a . Countersunk receptacles provide a larger target and a funneling effect which guides the pin into the receptacle, making engagement between receptacle and pin easier to attain. Further refinements include chamfered pin ends  80 , shown in FIG. 7, and crowned pin ends  82 , shown in FIGS. 3 and 8. These details and refinements provide significant advantages to joint assembly, especially when constructing the joint in the field as is often the case.  
         [0037]    The anti-rotational pipe coupling system according to the invention promises to provide a simple, cost effective and practical solution to the problem of preventing relative rotation between pipe segments joined by means of a mechanical coupling which does not otherwise prevent such relative motion.