Abstract:
A pipe coupling assembly and method for protecting control lines is disclosed wherein a shoulder modification is made on the pipes to prevent breakage of a control line protector clamp. Particularly, the present invention relates to a coupling assembly for protecting a control line comprising a first pipe including a first stop surface, a second pipe longitudinally connected to the first pipe, a clamping device connected to the first pipe and the second pipe, the clamping device including a first clamping end connected to the first pipe and a control line receiving portion, and a control line extending along the length of the first pipe and the second pipe, the control line being positioned within the control line receiving portion of the clamping device. Additionally, the first stop surface is positioned at a predetermined angle relative to the first pipe to prevent breakage of the clamping device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     This invention relates generally to control line protector clamps, and more particularly to a modification made to a pipe coupling assembly including a control line protector clamp to prevent breakage of the control line protector clamp.  
         [0003]     2. Description of Related Art  
         [0004]     In well applications, sections of production tubing are linearly connected to form a production tubing string which is extended downwards into a well bore. The individual sections of production tubing are coupled together until a string of the desired length is formed.  
         [0005]     Traditional pipe couplings used in well applications may also be applied to other uses in the art, such as blast joints or underground applications. Examples of patented pipe coupling devices such as those used in well applications are disclosed in U.S. Pat. Nos. 4,613,165, Re. 34,017, 4,635,968, 4,299,413, and 6,123,363.  
         [0006]     U.S. Pat. Nos. 4,613,165 issued Sep. 23, 1986 and Re. 34,017 issued Aug. 4, 1992, each issued to Kuhne and entitled “Increased Tensile Strength Variable Diameter Protective Joint”, relate to a protective joint for tubulars, such as oil well production tubing, having a body portion with a first diameter and at least one coupling portion having an increased diameter portion. At least a part of both the first and increased diameter portions are included within a zone to be protected by the protective joint. The protective joint includes a plurality of first and second generally cylindrical annular protective rings, such as carbide rings. The first protective rings are coaxially located along the body portion of the tubular. The second protective rings are coaxially located along the increased diameter portion of an upset. The first and second protective rings have flat and parallel faces and are sized and configured to accommodate bending movements along the longitudinal axis of the tubular. For example, the first and second protective rings may have flattened parallel faces, sufficient inside diameters and be engagable with like protective rings along a plane intersecting and normal to the inside longitudinal axis of the tubular to accommodate bending movements along the longitudinal axis of the tubular.  
         [0007]     U.S. Pat. No. 4,635,968 issued to Kuhne on Jan. 13, 1987 entitled “Method and Apparatus for Protecting Consecutive Multiple Variable Diameter Couplings” relates to a method for installing multiple protective joints on tubulars. In particular, the tubulars have a body portion and an increased diameter portion for coupling to another tubular. At least a part of the body and increased diameter portions of each tubular are to be included in a zone to be protected. A plurality of first generally cylindrical annular protective rings are coaxially installed over the body portion of a first tubular. A plurality of second generally cylindrical annular protective rings are also placed coaxially locatable along the increased diameter portion of each tubular and are supported on the body portion with at least one sleeve coaxially located below along the body portion of the first tubular. During transport or storage the first and second protective rings are held in place by retainers. During installation a second tubular is coupled to the first tubular. The second protective rings are then placed over the increased diameter portion of the second tubular while using at least one sleeve to limit movement of the second protective rings in their radial direction and facilitate movement of those rings over the increased diameter portion of the second tubular while using at least one sleeve to limit movement of the second protective rings in the their radial direction and facilitate movement of those rings over the increased diameter and body portions of the coupled tubular. There can thus be provided a series of multiple protective joints for use on consecutive tubulars having increased diameter portions for coupling to another tubular.  
         [0008]     U.S. Pat. No. 4,299,413 issued to Neher on Nov. 10, 1981 entitled “Pipe Coupling” relates to a coupling assembly for connecting sections of pipe including a tubular sleeve adapted to receive the ends of the pipe section. The inside surface of the sleeve includes means for providing a pressure-tight seal between the pipe sections and the sleeve. A pair of generally arcuate clamp members is formed for connection to each other to form a clamp assembly. Each clamp member has an internal recess of such dimensions that when the clamp members are connected to each other about the sleeve, only the clamp members absorb the mechanical stresses exerted on the coupling. The clamp members about or surrounding the sleeve are spaced from and out of contact with the sleeve. Additionally, each clamp member can have flanged generally semi-cylindrical end sections, sized to fit about the pipe, and which form a split-ring clamp when the clamp members are fitted together in opposing relationship. The flanges are adapted for receiving fastening means for securing the clamp members together. The inner surface of the end sections includes means for securely gripping the outer surface of the pipe so that when the clamp members are fastened together about the sleeve, they hold the pipe sections together in a securely coupled relationship.  
         [0009]     U.S. Pat. No. 6,123,363 issued to Burgard et al. on Sep. 26, 2000 entitled “Self-Centering Low Profile Connection with Trapped Gasket” relates to the assembly of a connection that uses cooperating grooved surfaces to provide an easily disassembled and assembled connection which is improved by the use of a centered lip and cooperating groove on the contact faces of the connection halves that engage the faces of complementary connection ends to prevent lateral misalignment while the pipe ends are brought together for axial alignment. The lip extends into the groove to trap a gasket retained within the groove and inhibit extrusion of the gasket between the contact faces under high pressure conditions. The centering device may be used with a clamping mechanism. The trapping cavity formed by the faces of the connection ends particularly enhances the pressure capacity of elastomeric gasket applications.  
         [0010]     After the production tubing string is formed, it is frequently necessary to install mechanically operated devices deep within the well bore. These devices can include such devices as safety valves, chemicals injection mandrels, and pumps. Control line are used to operate these mechanical devices, but the inaccessibility of the devices within the well bore makes the installation and operation of the control lines costly and time consuming. Therefore, the control lines are run down into the well bore along the length of the production tubing string.  
         [0011]     Thus, as the production tubing is pushed or pulled through the well bore, the control lines are pushed or pulled through the well bore as well. However, as the production line is longitudinally moved within the well bore, the pipe couplings between the sections of production tubing can collide with or become obstructed by the sides of the well bore as a result of the increased diameter of the production tubing coupling. This increased diameter is typically caused by either a pipe coupling device, such as those described in the references above, or, in the case of tubing, such as integral joint tubing, by a sloping external transition upset leading to the section of the tubing used for the coupling. When these wider sections of the production tubing string impact the sides of the well bore, the control lines may become trapped between the tubing and the sides of the well bore and become damaged or broken.  
         [0012]     In an attempt to prevent the breakage of the control lines, control line protector clamps are used. Control line protector clamps are clamps which are clamped around the production tubing at the couplings. Because the control lines may be damaged if crushed or broken, the control lines run through the clamps, for example, via holes or slots formed in the clamps which allow the control lines to move freely. The two ends of the clamps are clamped onto the production tubing on either sides of the pipe coupling, thereby extending over the section of the pipe with the increased diameter, as described above. Thus, when the pipe coupling section of the pipe with the increased diameter would have normally impacted the sides of the well bore, the clamp instead bears the brunt of the impact. Because the control line runs through the clamp, the control line is not impacted by the sides of the well bore and is not damaged or broken.  
         [0013]     However, as in the case of integral joint tubing, the pipe coupling may be integrated with the tubing. As described above, the sections of the tubing may include an upset sloping from the tubing body to an pipe coupling section which has an increased diameter. When a control line protector clamp is attached to tubing with a sloping upset, the clamp extends across this sloping upset. During operation, the tubing string will likely encounter a severe obstruction on the wall of the well bore while being moved within the well bore, the clamp may become caught on the obstruction. As the tubing string continues to move, the clamp will slide along the length of the tubing until it encounters the base of the upset. If the resistance caused by the obstruction is sever enough, the clamp may be forced to move along the upset, which thereby causes a wedgelike effect on the clamp. As the clamp travels further along this upset, the wedgelike forces acting on the clamp can break the clamp body, including the means of securing the clamp, such as clamp bolts, etc. If the clamp breaks, the clamp and its components can become disengaged from the pipe coupling. If this occurs, the clamp will fall away from the production tubing string, leaving the control line unprotected. The broken clamp can be very costly and time consuming to retrieve. If the broken clamp is impossible or impractical to replace, the entire clamp will need to be replaced. Also, when the clamp breaks, it is frequently necessary to stop the operation so the broken clamp can be retrieved, repaired, or replaced.  
         [0014]     Thus, there is a need for a device or method that prevents breakage of the control line protector clamps used to protect control lines that are positioned next to production tubing strings. This invention answers that need.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention provides a pipe coupling assembly for protecting control lines and a method of assembling a pipe coupling assembly for protecting control lines wherein a shoulder modification on the pipes is utilized to prevent axial movement of a clamp, thereby preventing clamp breakage.  
         [0016]     In particular, one embodiment of the present invention relates to a pipe coupling assembly for protecting control lines and a method of assembling a pipe coupling assembly for protecting control lines, the assembly and method comprising a first pipe including a first stop surface, a second pipe longitudinally connected to the first pipe, a clamping device connected to the first pipe and the second pipe, the clamping device including a first clamping end connected to the first pipe, the clamping device further including a control line receiving portion, and a control line extending along the length of the first pipe and the second pipe positioned adjacent to the first pipe and the second pipe, the control line being positioned within the control line receiving portion of the clamping device, wherein the first stop surface is positioned on the first pipe at a predetermined angle relative to a longitudinal axis of the first pipe to sufficiently minimize radial force acting against the first clamping end to prevent breakage of the clamping device when an axial force tending to move the clamping device towards the second pipe is applied. The second pipe may also comprise a second stop surface, and the clamping device may include a second clamping end connected to the second pipe, wherein the second stop surface is positioned on the second pipe at a predetermined angle relative to the longitudinal axis of the second pipe to sufficiently minimize radial force acting against the second clamping end to prevent breakage of the clamping device when an axial force tending to move the second clamping device towards the first pipe is applied.  
         [0017]     A second embodiment of the present invention relates to a pipe coupling assembly for protecting control lines and a method of assembling a pipe coupling assembly for protecting control lines, the assembly and method comprising a first pipe including a first stop surface, a second pipe longitudinally connected to the first pipe, and a clamping device connected to the first pipe and the second pipe, the clamping device including a first clamping end connected to the first pipe, the clamping device further including a control line receiving portion; and a control line extending along the length of the first pipe and the second pipe positioned adjacent to the first pipe and the second pipe, the control line being positioned within the control line receiving portion of the clamping device, wherein the first stop surface is positioned on the first pipe at a predetermined angle relative to the longitudinal axis of the first pipe to prevent the first clamping end from moving along the first stop surface in an overlapping manner when an axial force tending to move the clamping device towards the second pipe is applied. The second pipe may also comprise a second stop surface, and the clamping device may include a second clamping end connected to the second pipe, wherein the second stop surface is positioned on the second pipe at a predetermined angle relative to the longitudinal axis of the second pipe to prevent the second clamping end from moving along the second stop surface in an overlapping manner when an axial force tending to move the clamping device towards the first pipe is applied.  
         [0018]     A third embodiment of the present invention relates to a pipe coupling assembly for protecting control lines and a method of assembling a pipe coupling assembly for protecting control lines, the assembly and method comprising a first pipe including a first stop surface, a second pipe longitudinally connected to the first pipe, and a clamping device connected to the first pipe and the second pipe, the clamping device including a first clamping end connected to the first pipe, the clamping device further including a control line receiving portion; and a control line extending along the length of the first pipe and the second pipe positioned adjacent to the first pipe and the second pipe, the control line being positioned within the control line receiving portion of the clamping device, wherein the first stop surface is positioned on the first pipe at a predetermined angle relative to the longitudinal axis of the first pipe to prevent further movement of the first clamping end along the longitudinal axis toward the first stop surface after the first clamping end comes into contact with the first stop surface. The second pipe may also comprise a second stop surface, and the clamping device may include a second clamping end connected to the second pipe, wherein the second stop surface is positioned on the second pipe at a predetermined angle relative to the longitudinal axis of the second pipe to prevent further movement of the second clamping end along the longitudinal axis toward the second stop surface after the second clamping end comes into contact with the second stop surface.  
         [0019]     Each of the above and other embodiments of the present invention may include one or more variations wherein the angle of the first stop surface relative to a longitudinal axis of the first pipe is between 60 degrees and 90 degrees, the angle of the first stop surface relative to a longitudinal axis of the first pipe is 90 degrees, the angle of the first stop surface relative to a longitudinal axis of the first pipe is greater than 90 degrees, the first clamping end includes a substantially transverse clamp stop surface facing the first stop surface, the first stop surface extends circumferentially around the first pipe, and/or the first pipe and the second pipe are of the integral joint tubing type.  
         [0020]     These and other features, objects and advantages of the present invention will be in part apparent to those skilled in art and in part pointed out hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a side view of a pipe coupling assembly for protecting control lines of the present invention.  
         [0022]      FIG. 2  is a side view of a prior art pipe connection.  
         [0023]      FIG. 3  is a cross-sectional view of a prior art pipe connection.  
         [0024]      FIG. 4  is a side view of a prior art pipe coupling assembly.  
         [0025]      FIG. 5  is a side view of a prior art pipe coupling assembly.  
         [0026]      FIG. 6  is a side view of a pipe coupling assembly for protecting control lines of the present invention.  
         [0027]      FIG. 7  is a side view of a pipe connection of the present invention.  
         [0028]      FIG. 8  is a cross-sectional view of a pipe connection of the present invention.  
         [0029]      FIG. 9  is a magnified side view of a portion of a pipe coupling assembly for protecting control lines according to one embodiment of the present invention.  
         [0030]      FIG. 10  is a magnified side view of a portion of a pipe coupling assembly for protecting control lines according to another embodiment of the present invention.  
         [0031]      FIG. 11  is a magnified side view of a portion of a pipe coupling assembly for protecting control lines according to a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]     As shown in  FIG. 1 , a pipe coupling assembly for protecting control lines of the present invention comprises a first pipe  100  longitudinally connected to a second pipe  200 , with a clamping device  300  connected to at least one of first pipe  100  and second pipe  200 . According to the preferred embodiment, first pipe  100  and second pipe  200  are integral joint tubing pipes. However, the present invention may be applied to any type of piping. First pipe  100  includes a first stop surface  140 , a sloping section  110 , and a connecting section  120 . Second pipe  200  includes a second stop surface  240 , a sloping section  210 , and a connecting section  220 . Any type of longitudinal connection may be utilized to facilitate the connection between first pipe  100  and second pipe  200 , such as the threaded connection between internal threaded portion  130  on the first fitting  100  and external threaded portion  230  on second fitting  200  in  FIG. 8 .  
         [0033]     Control line  400  extends along the length of first pipe  100  and second pipe  200  and is preferably positioned adjacent to first pipe  100  and second pipe  200 . Control line  400  may be any type of control line, for example, hydraulic lines, signal lines, such as coaxial cable, or electrical lines. As is shown in the figures, because control line  400  extends across the coupling of first pipe  100  and second pipe  200 , control line  400  is also adjacent to stop surfaces  140  and  240 , sloping sections  110  and  210 , and connecting sections  120  and  220 .  
         [0034]     Clamping device  300  extends across the connection between first pipe  100  and second pipe  200  in a generally overlapping manner and clamps to at least one of first pipe  100  via first clamping end  310  and second pipe  200  via second clamping end  320 . Clamping device  300  further includes a control line receiving portion  350  which is sized appropriately to be able to receive control line  400 . Control line receiving portion  350  may be of any type, such as a machined hole or slit, but is preferably a slit in which control line  400  is placed. Additionally, there may be a control line receiving portion  350  in either or both of first clamping end  310  and second clamping end  320 , or control line receiving portion  350  may extend the entire length of clamping device  300 , thus allowing control line  400  to pass through the main portion of the body of clamping device  300 . Note that clamping device  300  is not required to include both first clamping end  310  and second clamping end  320 . For some applications, clamping device  300  may be permanently affixed to second pipe  200  in a manner such that only one clamping end is used, such as first clamping end  310  on first pipe  100 . In this instance, after first pipe  100  and second pipe  200  are longitudinally connected, first clamping end  310  is clamped around first pipe  100  to protect control line  400 .  
         [0035]     Referring now to prior art  FIGS. 2-5 , which show a typical conventional pipe connection, connecting section  720  of first pipe  700  has a greater diameter than first pipe  700 . Also, connecting section  820  of second pipe  800  has a greater diameter than second pipe  800 . Sloping section  710  gradually slopes from the outer surface of first pipe  700  to the outer surface of connecting section  720 . Similarly, sloping section  810  gradually slopes from the outer surface of first pipe  800  to the outer surface of connecting section  820 . Note that neither first pipe  700  or second pipe  800  includes a stop surface such as first stop surface  140  on first pipe  100  or second stop surface  240  of second pipe  200  in  FIG. 1 . As shown in  FIG. 3 , first pipe  700  and second pipe  800  are typically threaded longitudinally together via internal threaded portion  730  of first pipe  700  and external threaded portion  830  of second pipe  800 .  
         [0036]     Now referring to  FIG. 4 , clamping device  900  is connected to a prior art pipe coupling between first pipe  700  and second pipe  800  with control line  600  passing through control line receiving portion  950 . During operation, axial and/or longitudinal force F may be applied to clamping device  900  in a longitudinal manner, thus forcing clamping device  900  to move along both first pipe  700  and second pipe  800  towards second pipe  800 . If force F is of a sufficient magnitude, clamping device  900  slides along first pipe  700  towards sloping section  710 . Thus, if force F is maintained for a sufficient duration of time, first clamping end  910  of clamping device  900  will eventually come into contact with the base of sloping section  710 , as shown in  FIG. 5 . When this occurs, first clamp stop surface  930  on first clamping end  910  comes into contact with the base of sloping section  710 . If force F continues to force clamping device  900  along first pipe  700  and second pipe  800 , first clamping end  910  will move up sloping surface  710 , thereby allowing sloping surface  710  to have a wedge-like effect on first clamping end  910 . This wedge-like effect of sloping surface  710  on first clamping end  910  exerts a force F T  against first clamping end  910  which includes a radially outward force component F R .  
         [0037]     If F T , and specifically F R , increases to an excessive level, such force may cause first clamping end  910  to structurally weaken, fracture, or even completely break. If first clamping end  910  breaks, clamping device  900  may disengage from first pipe  700 , thereby possibly exposing control line  600  to damage or breakage. This problem can also occur in the opposite direction if a force F′ is applied, thereby forcing second clamp stop surface  940  to contact sloping section  810  and eventually causing second clamping end  920  to structurally weaken, fracture, or break.  
         [0038]     As shown in  FIGS. 1 and 6 - 8 , the present invention minimizes the chance of either first clamping end  310  or second clamping end  320  weakening, fracturing, or breaking as a result of longitudinal forces F or F′, specifically, as a result of the radial components of those forces acting against clamping device  300  and forcing either first clamping end  310  onto sloping section  110  or second clamping end  320  onto sloping section  220 .  
         [0039]     According to the present invention, first pipe  100  further includes first stop surface  140 . First stop surface  140  is formed into the base section of sloping surface  110  to minimize the chance that first clamping end  310  will break during operation. The specific characteristics of first stop surface  140  will be described in more detail below.  
         [0040]     Thus, according to the preferred embodiment as shown in  FIG. 1 , clamping device  300  is attached to both first pipe  100  and second pipe  200  via first clamping end  310  and second clamping end  320 . When a force F is applied to clamping device  300  and is of a sufficient magnitude to cause clamping device  300  to move relative to first pipe  100 , clamping device  300  slides along first pipe  100  and second pipe  200 . As shown in  FIG. 6 , if force F is maintained, first clamping end  310  of clamping device  300  will slide along first pipe  100  until it comes into contact with first stop surface  140 . When first clamp stop surface  330  of first clamping end  310  comes into contact with first stop surface  140 , first clamping end  310  of clamping device  300  is largely prevented from moving any further along the surface of first pipe  100 . This effect is possible by forming first stop surface  140  at any angle sufficient to sufficiently minimize or eliminate the above-described wedge-like effect capable of structurally damaging, fracturing, or breaking first clamping end  310  and causing clamping device  300  to possibly disengage from first pipe  100 . Also, first stop surface  140  preferably extends circumferentially around first pipe  100 . However, first stop surface  140  may be formed in a different manner, such as a plurality of radial portions, or any other design sufficient to achieve the above-described functionality.  
         [0041]     As illustrated by  FIGS. 9-11 , first stop surface  140  may be formed at a variety of angles. Specifically, first stop surface  140  may be formed at a 90 degree (90°) angle relative to the longitudinal axis of first pipe  100 . Thus, angle X may be formed to be 90 degrees. Thus, when first clamping end  310  of clamping device  300  comes into contact with first stop surface  140 , first clamp stop surface  330  axially abuts first stop surface  140 . This axial abutment eliminates all radial forces and any possible wedge-like effect of sloping surface  110  on first clamping end  310 . Thus, sloping surface  110  will not cause first clamping end  310  to break and will likewise prevent clamping device  300  from breaking and disengaging from first pipe  100 . An angle X of 90 degrees is preferred because it is easily formed by machining or any other method.  
         [0042]     Thus, when angle X is 90 degrees, first stop surface  140  sufficiently minimizes any radial, wedge-like forces acting against first clamping end  310  and prevents breakage of first clamping end  310  and disengagement of clamping device  300  when force F tending to move clamping device  300  towards second pipe  200  is applied. Also, first stop surface  140  prevents first clamping end  310  from moving along first stop surface  140  in an overlapping manner when an axial force F tending to move clamping device  300  towards second pipe  200  is applied. Moreover, first stop surface  140  prevents further movement of first clamping end  310  along the longitudinal axis of first pipe  100  toward first stop surface  140  after first clamping end  310  comes into contact with first stop surface  140 .  
         [0043]     According to a second embodiment of the present invention and as shown in  FIG. 10 , first stop surface  140  may be formed at an angle less than 90 degrees relative to the longitudinal axis of first pipe  100 . While any angle sufficient to prevent breakage of first clamping end  310  may be used, it is preferred, according to this embodiment, that angle X be between approximately 60 degrees (60°) and ninety degrees (90°). However, any angle less than 60 degrees may be used for first stop surface  140  if the angle is sufficient to prevent first clamping end  310  from structurally weakening, fracturing, or breaking under operational conditions. Thus, when first clamping end  310  of clamping device  300  comes into contact with first stop surface  140 , first clamp stop surface  330  comes into contact with first stop surface  140 . This abutment minimizes radial forces acting against first clamping end  310  and sufficiently minimizes the possibility of a wedge-like effect of sloping surface  110  on first clamping end  310 . Thus, sloping surface  110  will not cause first clamping end  310  to break and will likewise prevent clamping device  300  from breaking and possibly disengaging from first pipe  100 .  
         [0044]     Thus, according to the second embodiment described above, first stop surface  140  sufficiently minimizes any radial, wedge-like forces acting against first clamping end  310  and reduces the chance of breakage of first clamping end  310  and disengagement of clamping device  300  when force F tending to move clamping device  300  towards second pipe  200  is applied. Also, first stop surface  140  minimizes the possibility of first clamping end  310  from moving along first stop surface  140  in an overlapping manner when an axial force F tending to move clamping device  300  towards second pipe  200  is applied. Moreover, first stop surface  140  minimizes the possibility of first clamping end  310  moving further along the longitudinal axis of first pipe  100  toward first stop surface  140  after first clamping end  310  comes into contact with first stop surface  140 .  
         [0045]     According to a third embodiment of the present invention and as shown in  FIG. 11 , first stop surface  140  may be formed at an angle greater than 90 degrees relative to the longitudinal axis of first pipe  100 . Angle X may be any angle greater than 90 degrees (90°). Thus, when first clamping end  310  of clamping device  300  comes into contact with first stop surface  140 , first clamp stop surface  330  axially abuts the upper corner of first stop surface  140  created by angle X exceeding 90 degrees. This abutment eliminates all radial forces and any possible wedge-like effect of sloping surface  710  on first clamping end  310 . Thus, sloping surface  710  will minimize the possibility of first clamping end  310  breaking and will likewise prevent clamping device  300  from breaking and disengaging from first pipe  100  due to the wedge-like effect of sloping section  110 .  
         [0046]     According to another embodiment of the present invention, clamping device  300  may include both first clamping end  310  and second clamping end  320 . Additionally, first stop surface  140  and second stop surface  240  can be formed on both first pipe  100  and second pipe  200 , respectively. Thus, when a force F is applied to clamping device  300  causing clamping device  300  to slide along first pipe  100 , first clamping end  310  comes into contact with first stop surface  140  as described above. Similarly, when a force F′ is applied to clamping device  300  causing clamping device  300  to slide in the opposite direction along second pipe  200 , second clamping end  320  and second clamp stop surface  340  comes into contact with second stop surface  240 . Second stop surface  240  may be of any design described above for first stop surface  140 . Thus, the present invention minimizes the possibility of clamping device  300  becoming structurally weakened, fractured, or broken in response to longitudinal forces in either direction.  
         [0047]     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made, in carrying out the above processes, in a described instrument, and in the construction set forth, without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.  
         [0048]     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between.