Abstract:
The present invention relates to a length of pipe with a female end that is reinforced by a band of reinforcing material that extends around the female end. When the pipe and a similar adjacent pipe are threadably connected, the reinforcement material reinforces the female end against failure due to hoop stresses and/or lateral stresses. In this regard, the reinforcing material is any material with a higher resistance to hoop stresses and/or lateral stresses than the material from which the pipe is made. The present invention is also directed to manufacturing processes for manufacturing the pipe of the present invention.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to threaded, submersible pump drop pipe and casing assembly connection and method of manufacture for use in water well and related systems. 
         [0003]    2. Description of the Related Art 
         [0004]    Piping systems with threaded connections are well known in the art. Threaded connections connect lengths of pipe using internal threads on the female end of a pipe that interlock with external threads on the male end of a similar adjacent pipe. 
         [0005]    During manufacturing of the pipe, external threads are machined into the male end of the pipe and internal threads are machined into the female end of the pipe, typically through automated cutting processes. The shape of the threads, or “thread profile,” can vary greatly and often depends on the particular application of the pipe. For example, triangular threads, square threads, rounded threads, and even trapezoidal threads are well known in the art. 
         [0006]    Another thread characteristic that depends on the application of the pipe is whether the threads are machined on a pitch as the threads extend away from the leading edge of the pipe. Threads cut on a pitch, called “tapered threads,” create a pipe with a gradually changing circumference as the threads extend away from the leading edge of the pipe. As such, for example, the outer circumference of a male end of a pipe with tapered threads increases as the threads extend away from the male leading edge of the pipe, causing the male end of the pipe to be generally shaped as a truncated cone. 
         [0007]    Pipes with tapered threads are well known in the art and offer certain advantages over pipes with non-tapered threads (i.e., threads not cut on a pitch). For example, specific types of tapered threads such as NPTF threads (also known as Dryseal threads) are used in many piping applications to create watertight (or fluid tight) connections without requiring a sealing compound. The watertight connection is formed through a mechanical seal when the internal threads of the female end of a pipe deform into the external threads of the male end of an adjacent pipe (and vice versa) during tightening of the threaded connection. 
         [0008]    Tapered threads also have a disadvantage in that care must be taken not to apply too much torque so as to overtighten the connection. Threaded connections with tapered threads are considered “hand-tight” (also known as “finger-tight”) at the point when the male end of the pipe can no longer thread into the female end of an adjacent pipe by hand because the taper on the threads has caused the male end to become jammed within the female end. From hand-tight, a wrench is used to turn at least one of the connected pipes, making the connection “wrench-tight.” Wrench-tight is generally accepted as being a maximum of two turns past hand-tight. 
         [0009]    If one is not careful the threaded connection can be overtightened past wrench-tight and threaten the integrity of the connection. Overtightening the connection causes hoop stress on the female end of the pipe which, when large enough, will split the female end and cause a failed connection. Hoop stress is a problem with tapered threads that is well known in the art and often occurs near the last internal threads—i.e., the internal threads furthest away from the female leading edge of the pipe—although the failure can occur elsewhere on the female end. 
         [0010]    Another problem for threaded connections is lateral stress failure of the connection due to lateral forces on the pipe and/or the connection. Although pipes with tapered threads are susceptible to lateral stress failure, this type of failure most frequently occurs on pipes with non-tapered internal threads (i.e., threads that are not cut on a pitch) within the female end of the pipe. Lateral stress failure usually occurs because the manufacturing process for forming the internal threads weakens the pipe wall. Non-tapered internal threads, as well as tapered internal treads, are typically formed in the interior wall of the pipe at the female end by cutting out a portion of the pipe wall. Removing material from the pipe wall decreases the wall thickness and makes the female end of the pipe more prone to lateral stress failure. 
         [0011]    Lateral stress failure often occurs near the first internal threads—i.e., where the internal threads begin, near the female leading edge of the pipe—but can also occur elsewhere on the female end. In addition, the amount of threads cut into the female end of a pipe can increase its susceptibility to failure from lateral forces and pipes with more threads have a greater tendency to fail. As a result, a need also exists for strengthening pipes that use threaded connections to increase their resistance against lateral stress failure. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The present invention is directed to a pipe with a reinforced female end to protect against failure of a threaded connection due to hoop stress and/or lateral stress. 
         [0013]    The pipe of the present invention has a female end for receiving a male end of a similar adjacent pipe. At least a portion of the pipe at the female end has a reinforcement band that extends circumferentially around the pipe. The reinforcement band is preferably in the form of a cylinder that extends completely around the circumference of the pipe, although other embodiments with the reinforcement band extending only partially around the circumference of the pipe are contemplated by the present invention. Regardless, the reinforcement band is made from a rigid material or materials that are stronger than the material or materials from which the pipe is made. More specifically, the reinforcement band should have material characteristics which withstand higher hoop stresses and/or lateral stresses than the pipe material. 
         [0014]    The present invention is also directed to a manufacturing processes to form the pipe of the present invention. The claimed manufacturing process is for extruded thermoplastic pipe, such as polyvinyl chloride (PVC) pipe or polyethylene pipe, which is belled with a mandrel after extrusion. Prior to belling, the reinforcement band is positioned around the female end of the pipe and when the pipe is enlarged through the belling process, the reinforcement band is embedded into the outer wall of the pipe or at least press fit against the outer wall of the pipe. In addition, a manufacturing process for implementing the reinforcing band into a thermosetting pipe, such as fiber reinforced plastic (FRP) pipe, is also disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of the preferred embodiment of the present invention. 
           [0016]      FIG. 2  is an exploded perspective view of the preferred embodiment of the present invention, as shown with the female end of one pipe and the male end of a similar adjacent pipe. 
           [0017]      FIG. 3  is a perspective view of the female end of the preferred embodiment of the pipe of the present invention. 
           [0018]      FIG. 3A  a cross sectional side view taken along the female end of the preferred embodiment of the pipe of the present invention shown in  FIG. 3 . 
           [0019]      FIG. 4  is a perspective view of the female end of an alternative embodiment of the pipe of the present invention. 
           [0020]      FIG. 4A  is a cross sectional view taken along the female end of the alternative embodiment of the present invention shown in  FIG. 4 . 
           [0021]      FIG. 5  is a perspective view of the female end of another alternative embodiment of the present invention. 
           [0022]      FIG. 5A  is a cross sectional view taken along the female end of the alternative embodiment of the present invention shown in  FIG. 5 . 
           [0023]      FIG. 6  is a cross sectional view of the pipe and a perspective view of a mandrel prior to insertion of the mandrel into the pipe, during the preferred manufacturing process for the preferred embodiment of the present invention. 
           [0024]      FIG. 6A  is a cross sectional view of the pipe and a perspective view of a mandrel after the mandrel has been initially inserted in the pipe, during the preferred manufacturing process for the preferred embodiment of the present invention. 
           [0025]      FIG. 6B  is a cross sectional view of the pipe and a perspective view of a mandrel after the mandrel has been further inserted into the pipe, during the preferred manufacturing process for the preferred embodiment of the present invention. 
           [0026]      FIG. 6C  is a cross sectional view of the pipe and a perspective view of a mandrel after the mandrel has been fully inserted into the pipe, during preferred manufacturing process for the preferred embodiment of the present invention. 
           [0027]      FIG. 7  is a cross sectional view of the pipe and a perspective view of a mandrel prior to insertion of the pipe onto the mandrel, during an alternative manufacturing process for an alternative embodiment of the present invention. 
           [0028]      FIG. 7A  is a cross sectional view of the pipe and a perspective view of a mandrel after the pipe has been partially inserted over the mandrel, during an alternative manufacturing process for an alternative embodiment of the present invention. 
           [0029]      FIG. 7B  is a cross sectional view of the pipe and a perspective view of a mandrel after the pipe has been fully inserted onto the mandrel, during an alternative manufacturing process for an alternative embodiment of the pipe present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Referring to  FIGS. 1 through 2A , the preferred embodiment of the present invention is shown with a pipe  10  and a similar adjacent pipe  12 . In practice, the pipe  10  has the same structure as the similar adjacent pipe  12  and therefore, a description of structure that is present for the similar adjacent pipe  12  applies equally to a description of the structure for the pipe  10 , and vice versa. 
         [0031]    Pipe  10  has a female end  14 , an intermediate length  16 , and a male end  18 . The female end  14  has an enlarged exterior diameter  20  with preferably a distinct first cylinder section  22  and a distinct second cylinder section  24 . First cylinder section  22  terminates the female end  14  of the pipe  10  at a female leading edge  26 . In the preferred embodiment, second cylinder section  24  is between the first cylinder section  22  and the intermediate length  16 , and, transitions directly into the intermediate length  16 . In this regard, there is preferably an external shoulder  30  between the second cylinder section  24  and the intermediate length  16 . The male end  18  of the pipe  10  is opposite the female end  14  and is also adjacent the intermediate length  16 . The male end  18  has external threads  32  disposed thereon and terminates the pipe  10  at a male leading edge  34 . 
         [0032]    Internal threads  28  are formed on the interior surface of at least a portion of the female end  14  (see  FIGS. 1-5A ). In the preferred embodiment shown in  FIGS. 1-3A , the internal threads  28  are formed within the second cylinder section  24 . 
         [0033]    The form and number of internal and external threads  28 ,  32  depend on the application and size of the pipe  10 . For example, the preferred embodiment of the present invention for one inch diameter PVC drop pipe has internal and external threads  28 ,  32  that are tapered, have a triangular thread profile, and conform to ASTM Standard F-1498 for the amount of threads. Preferably, the external threads  32  start at a beveled male leading edge  34  of the male end  18  and the female end  14  has internal threads  28  within the second cylinder section  24  that begin approximately 0.93 inches from the female leading edge  26  and span over slightly more than one inch of pipe length within the second cylinder section  24 . One with skill in the art will recognize, however, that characteristics like the thread profile, the length of pipe  10  over which the threads span, whether the threads are tapered, and how far the threads start from their respective leading edges, will vary according to the application and size of the pipe  10 . 
         [0034]    Regardless of the thread characteristics and the pipe application, a reinforcement band  36  extends circumferentially around at least a portion of the female end  14  of the pipe  10 . The reinforcement band  36  is made from a material that has a greater resistance against hoop stress and/or lateral stress than the material from which the pipe  10  is made. As discussed in more detail infra, the material composition of the reinforcement band  36  and the dimensions of the reinforcement band  36  will largely depend on the manufacturing processes of the pipe  10 . Preferably, however, the reinforcement band  36  will be made from metal or some sort of metal alloy such as stainless steel. 
         [0035]    In its preferred embodiment, the reinforcement band  36  is a single, complete cylinder that extends around at least a portion of the enlarged exterior diameter  20  of the female end  14 . The edges of the reinforcement band  36  are also preferably embedded in the outer wall of the pipe  10  such that the material from which the pipe  10  is made at least partially covers the edges of the reinforcement band  36 . Embedding the reinforcement band  36  in this manner prevents the band  36  from becoming axially displaced from its original position around the pipe. However, in alternative embodiments the reinforcement band  36  may not be embedded in the outer wall of the pipe  10 . Instead, the outer wall of the enlarged diameter  20  may be formed to firmly press against the reinforcement band  36  with enough friction to hold the band  36  in place. 
         [0036]    Preferably, the reinforcement band  36  is positioned in the outer wall of the female end  14  opposite the internal threads  28  and extending along the length of at least a portion of the internal threads  28 . To provide the most protection against failure, at least a portion of the reinforcement band  36  should be placed opposite the last internal thread  29 , and preferably extend beyond the last internal thread  29  (see  FIG. 3A ). Likewise, at least a portion of the reinforcement band  36  may be positioned opposite and extend beyond the first internal thread. However, this positioning but may not be desirable, depending on the embodiment of the pipe  10 . For example, in the preferred embodiment of the pipe  10  the reinforcement band  36  is not positioned opposite the first internal thread because a shoulder  38  is present between the first cylinder section  22  and the second cylinder section  24 . In this regard, the preferred embodiment for the one inch PVC drop pipe mentioned above, has a reinforcement band  36  that is 1.53 inches wide and extends along the second cylinder section  24  from beyond the last internal thread  29  up to the shoulder  38 , making the reinforcement band  36  positioned opposite substantially all of the internal threads  28  (see  FIG. 3A ). 
         [0037]    In alternative embodiments, however, the reinforcement hand  36  may be positioned so that it extends beyond the first internal thread, or, the reinforcement band  36  may be positioned opposite only a smaller portion of the internal threads  28  such as in the embodiment shown in  FIG. 4A . In fact, the reinforcement band  36  may not be positioned opposite the internal threads  28  at all. For example, the reinforcement band  36  may extend around the first cylinder section  22  of the female end  14 . In another embodiment, the reinforcement band  36  may extend only partially around the circumference of the female end  14 . Furthermore, there may be more than one reinforcement band  36  present. Typically, the form of the reinforcement band  36  and whether more than one reinforcement band  36  is present will depend on factors like the application of the pipe  10  and strength of the material from which the reinforcement band  36  is made, as well as the thickness and width of the reinforcement band  36 . 
         [0038]    As mentioned, the preferred embodiment of the present invention has a distinct first cylinder section  22  and a distinct second cylinder section  24  at the female end  14  of the pipe  10  (see  FIGS. 1-3A ). The first cylinder section  22  and the second cylinder section  24  are separated from one another by the shoulder  38  between the two sections. The interior diameter of the first cylinder section  22  is larger than the interior diameter of the second cylinder section  24  with the interior diameter of the second cylinder section  24  being defined as the diameter at the crest of the last internal thread  29   
         [0039]    As the male end  18  of the similar adjacent pipe  12  is inserted into the first cylinder section  22  of the preferred embodiment of the pipe  10  it is funneled to the second cylinder section  24 . Preferably the male leading edge  34  of the similar adjacent pipe  12  is beveled to aid such funneling. Once at the second cylinder section  24 , the external threads  32  of the male end  18  encounter the internal threads  28  of the second cylinder section  24  and turning of the similar adjacent pipe  12  relative to the pipe  10  will cause the threads of the pipes to interlock in a manner well known in the art. 
         [0040]    The first cylinder section  22  of the preferred drop pipe embodiment is also preferably elongated so that it receives a substantial portion of the engaging external threads  32  from the similar adjacent pipe  12  before the external threads  32  begin to thread into the internal threads  28  of the pipe  10 . The engaging external threads  32  are only those threads which interlock with the internal threads  28  when tightened. The elongated first cylinder section  22  provides additional lateral strength to the threaded connection once the connection is formed and promotes increased watertightness of the connection. In this regard, pipes connected by threaded connections typically leak at the threads when lateral force is applied to the connected pipes and the elongated first cylinder section  22  protects against these lateral forces, as detailed in U.S. Pat. Nos. 6,666,480, 7,261,326, 7,470,383, and 7,425,024. 
         [0041]    Furthermore, the interior diameter of the first cylinder section  22  in the preferred PVC drop pipe embodiment of the present invention mentioned above is only slightly larger than the exterior diameter of the male end  18  of the pipe  10  at the crest of the external threads  32  and minimal clearance exists between the male end  18  of the similar adjacent pipe  12  and the female end  14  of the pipe  10  when the male end  18  is inserted into the first cylinder section  22  of the pipe  10 . 
         [0042]    Other embodiments of the present invention do not have a distinct first cylinder section  22  and a distinct second cylinder section  24 . In the alternative embodiment shown in  FIGS. 4 &amp; 4   a  the two different interior diameters are the interior diameter at the bevel and the interior diameter at the crest of the last internal thread  29 . This alternative embodiment of the pipe  10  has the reinforcement band  36  positioned opposite from the internal threads  28  of the female end  14  and the reinforcement band  36  extends along the length of only a portion of the internal threads  28 . In this regard, the reinforcement band  36  does not extend beyond the last internal thread  29  or the first internal thread. 
         [0043]    Further alternative embodiments with no distinct first and second cylinder sections  22 ,  24  and without distinct interior diameters that differ are also contemplated by the present invention. For example, the alternative embodiment shown in  FIGS. 4 &amp; 4A  could have a non-beveled female leading edge  26  with the internal threads  28  beginning at and extending from the female leading edge  26 . In addition, the alternative “flush mount” embodiment of the pipe  10  shown in  FIGS. 5 &amp; 5A  also do not have distinct first and second cylinder sections  22 ,  24  and do not have differing interior diameters at the female end  14 . 
         [0044]    The alternative flush mount embodiment of the present invention in  FIGS. 5 &amp; 5A  illustrates the pipe  10  and the similar adjacent pipe  12  without an enlarged exterior diameter  20  at the female end  14  and without an external; shoulder  30 . As such, the female end  14  is flush with the intermediate length  16 . Pipes without an enlarged exterior diameter  20  are well known in the art and when connected, the pipe  10  and the similar adjacent pipe  12  form a so-called “flush mount connection.” As shown in  FIG. 5A , the pipe  10  in this alternative embodiment does not have tapered internal and external threads  28 ,  32 , but rather, the internal and external threads  28 ,  32  are non-tapered threads with a trapezoidal thread profile. Depending on the application, however, the internal and external threads  28 ,  32  could be tapered and have a triangular or other-shaped thread profile. 
         [0045]    Additionally, the reinforcement band  36  in the flush mount embodiment shown in  FIGS. 5 &amp; 5A  is also not embedded in the pipe wall of the pipe  10 . Instead, the reinforcement band  36  is shrink fit on the outer wall of the female end  14  so that it tightly presses against the outer wall of the female end  14  of the pipe  10 , as explained infra. 
         [0046]    Turning to the manufacturing processes for the present invention,  FIGS. 6-6C  illustrate the preferred manufacturing method for the preferred embodiment for the pipe  10  when the pipe  10  is extruded and belled after such extrusion. As shown, a mandrel  40  is inserted into the pipe  10  after the pipe  10  has been extruded and cut into its desired length. 
         [0047]    Extruding the pipe and cutting it to the desired length are manufacturing processes that are well known in the art. After extrusion and cutting, the pipe  10  is typically moved to another location in the manufacturing assembly and one end of the pipe  10  is sufficiently heated to render it pliable. Once pliable, the pipe  10  is clamped into place and the mandrel  40  is forced into the heated end of the pipe  10  by a hydraulic cylinder (not shown) to form the contour of the female end  14  of the pipe  10 . The mandrel  40  is made of metal and when pressed against the inner circumference of the pliable end of the pipe  10 , the mandrel  40  will force the pliable end outward, thereby increasing both the inner and outer circumference of the pipe  10  where the mandrel  40  is inserted. The increase in both inner and outer circumference of the female end  14  creates the enlarged exterior diameter  20  and the external shoulder  30 . 
         [0048]    The reinforcement band  36  is sized so that when the mandrel  40  is inserted into the pliable end of the pipe  10 , the outer wall of the pipe  10  comes into contact with—and preferably deforms around—the edges of the reinforcement band  36 . The reinforcement band  36  is positioned over the pliable end of the pipe  10  prior to insertion of the mandrel  38 . Unlike the heated end of the pipe  10 , the reinforcement band  36  is not pliable and as the outer wall of the pipe  10  contacts the reinforcement band  36  the outer wall deforms around the edges of the reinforcement band  36  thereby embedding the reinforcement band  36 . 
         [0049]    The degree or amount of embedding of the reinforcement band  36  into the pliable end of the pipe  10  in the preferred embodiment will depend on the following factors: (1) the size of the reinforcement band  36  relative to the pipe  10  prior insertion of the mandrel  40 ; (2) the thickness of the reinforcement band  36 ; (3) the thickness of the outer wall of the pipe  10 ; and (4) the size of the circumference of the mandrel  40  relative to the pipe  10  prior to insertion of the mandrel  40 . With regard to the last factor, the size of the circumference of the mandrel  40  will dictate the amount by which the circumference of the pliable end of the pipe  10  is enlarged. With a one inch extruded PVC drop pipe, for example, the reinforcement band  36  is stainless steel, has an outer diameter of 1.522 inches, and is, at a minimum, 0.020 inches thick. 
         [0050]    It should be noted that the mandrel  40  shown in  FIGS. 6-6C  is designed to form the preferred embodiment of the present invention. As a result, the reinforcement band  36  is positioned over the pliable end of the pipe  10  at a distance that is far enough from the female leading edge  26  so the reinforcement band  36  will embed into the outer wall of the pipe  10  at the second cylinder section  24 , opposite where the internal threads  28  will be formed—a step that occurs later in the manufacturing process. As mentioned above, the reinforcement band  36  could be positioned over the pliable end of the pipe  10  so that it embeds in other positions on the outer wall of the pipe  10 . It should further be noted that the reinforcement band  36  could be positioned over the end of the pipe  10  prior to heating the end of the pipe  10 . 
         [0051]      FIGS. 7-7B  show an alternative manufacturing process of the present invention, which in this case, is directed to manufacturing the alternative embodiment of the invention shown in  FIGS. 4-4A . In this alternative manufacturing process, the mandrel  40  stays static and the pliable end of the pipe  10  is urged over the mandrel  40 . Again, the reinforcement band  36  is positioned over the pliable end of the pipe  10  and is sized to have the outer wall of the pipe  10  contact it during the enlarging process, but in this instance, the reinforcement band  36  moves at the same rate with the pliable end of the pipe  10  as the pipe  10  is urged onto the mandrel  40 . 
         [0052]    Once the mandrel  40  is inserted into the one of the pipe  10 , or the one end of the pipe  10  is urged onto the mandrel  40 , a cooling agent such as water is applied to the now-enlarged end of the pipe  10 . The cooling agent cools the pipe  10  and conforms the enlarged end of the pipe  10  to the shape of the mandrel  40 . From this point, the mandrel  40  is removed from the pipe  10 , or vice versa, and the pipe  10  has acquired the contour of the mandrel  40  and the reinforcement band  36  is positioned thereon. 
         [0053]    Once the mandrel  40  is removed from the pipe  10 , the internal threads  28  and external threads  32  are formed. In the preferred embodiment, the internal threads  28  are machined into at least a portion of the interior surface of the second cylinder section  24 , or alternatively, throughout the entire interior surface of the second cylinder section  24 , using processes that are well known in the art. Similar processes form the external threads  32  on the male end  18 . 
         [0054]    When the female end  14  of the pipe  10  does not have an enlarged exterior diameter  20  like the alternative embodiment shown in  FIGS. 5 &amp; 5A , the process to install the reinforcement band  36  on the female end  14  may be altered. On way to manufacture this embodiment of the present is to shrink fit the reinforcement band  36  on the female end  14 . Shrink-fitting is a well-known manufacturing process. The reinforcement band  26  is initially sized such that its interior dimensions are almost identical to the dimensions of the outer wall of the pipe  10  at the female end  14 . The reinforcement band  36  is also made from a material that has a coefficient of thermal expansion which allows the reinforcement band  36  to expand when heated and contract back to its original shape when cooled. In this regard, the reinforcement band  36  is preferably made from a material that has a high coefficient of thermal expansion, such as aluminum or brass. The reinforcement band  36  is heated and expands, and then, is positioned around the female end  14  of the pipe  10 . After it is moved to its desired position, the reinforcement band  36  is cooled and contracts back to its original shape, causing it to press against the outer wall of the pipe  10 . 
         [0055]    It should be finally noted that the pipe  10  of the present invention is not limited to extruded pipe  10 . The apparatus of the present invention can be implemented into thermosetting pipe and pipes made from other composite materials. In this regard, adding a step for installation of the reinforcement band  36  can be implemented into manufacturing processes that are well known for these other types of pipe. For example, and not by way of limitation, positioning the reinforcement band  36  over the mandrel  40  during the filament winding processes for FRP pipe is within the scope of the apparatus contemplated by the present invention. 
         [0056]    Although the present invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon the reference to the above-description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.