Abstract:
A tool is provided for closing and sealing the open end of a pipe in connection with hydraulic pressure testing. The tool is inserted into the pipe lumen and can be operated from outside. It comprises inner and outer, opposed circumferential clamps; a front plate braced against the pipe end face; a movable back plate internal of the pipe lumen; and an O-ring, carried by the back plate, which can be squeezed by pressing the back plate against the inner clamp. Ports extend through the back plate to the upper and lower ends of its peripheral surface, for bottom filling and top venting of the pipe lumen.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under the Paris Convention to U.S. Application No. 61/536,625, filed Sep. 20, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method for sealing an open end of a pipe. More particularly, the invention relates to an apparatus and method for sealing an end of a pipe with gripping means provided interiorly and exteriorly on the pipe wall. Once sealed, the apparatus and method allows the pipe to be pressurized for testing purposes etc. 
     BACKGROUND OF THE INVENTION 
     In chemical or petrochemical plants etc., it is common for fluid materials (e.g. liquids, gases etc.) to be conveyed from one location to another using equipment such as conduits or pipes (collectively referred to herein as “pipes”). Such pipes are often manufactured from metal sections that are joined together by welds. For example, when joining adjacent ends of pipe together, it is common for each end to be provided with a flange that is welded to the respective pipe end. Once each flange is thus secured to the pipes, they are then bolted together to form a sealed joint. Typically, a gasket or other such sealing means is provided between the opposed faces of the flanges. Such flanges may also be provided on nozzles secured, by welding, to holding tanks and other such vessels so that pipes can be connected thereto. Alternatively, the connections between lengths of pipe or other equipment may be welded directly together (i.e. butt welded) to form the seal. In either case, it will be appreciated that each welded joint or section must have integrity and form a complete seal so as to prevent leakage of the materials being transported. This is particularly important when handling potentially hazardous materials such as flammable or toxic liquids where leakage of such fluids can lead to catastrophic consequences. Therefore, for reasons of safety, it is often necessary to periodically test the integrity of the welds used in joining the various pieces of equipment (such as pipes, vessels, flanges and the like) together. 
     The prior art provides various tools for conducting weld integrity tests on conduits. Many of such known tools are used in pressure tests wherein a highly pressurized zone is created at least at the region of a weld being tested and such pressure monitored. In such tests, a drop in pressure signifies a failed weld. For example, U.S. Pat. Nos. 6,131,441 and 5,844,127 (the entire disclosures of which are incorporated herein by reference) teach weld testing tools that isolate a particular section of a pipe (such section including a weld) and subject the section to a high pressure fluid within a constrained annular space defined by the tool and the inner surface of the pipe. The pressure of the fluid within the annular space is monitored whereby a drop in such pressure signifies a leak in the weld. 
     U.S. Pat. Nos. 6,463,791 and 7,874,217 (the entire disclosures of which are incorporated herein by reference) also teach apparatuses for testing welds. 
     In some cases, it is necessary to seal an end of a pipe to conduct the above mentioned pressure test. In this regard, PCT Application number PCT/CA2011/050121 (the entire disclosure of which is incorporated herein by reference) provides a tool for sealing an end of a pipe that incorporates a gripper or clamp for engaging the exterior surface of the pipe. Similarly, PCT Application number PCT/CA2011/050122 (the entire disclosure of which is incorporated herein by reference) also provides a sealing tool for sealing an end of a pipe, which comprises a device that includes a gripping device for engaging both the interior and exterior portions of the pipe. The end sealing devices taught in these references may be used to seal one or both ends of a given pipe (or another opening such as the case with a pipe having a “T” junction). Once the device of PCT/CA2011/050121 or PCT/CA2011/050122 is secured to the one or more ends of the pipe, the interior of the pipe is then pressurized and the pressure monitored as indicated above. While the device taught in PCT/CA2011/050122 provides an efficient and effective sealing device for the ends of pipes, it may be difficult to handle when scaled for large diameter pipes (i.e. pipes greater than 24 inches or 36 inches in diameter) in view of its increased weight. 
     There exists a need for a device for sealing an end of a pipe, particularly large diameter pipes, and for conducting the type of weld integrity stress tests mentioned above. In particular, there is a need for an apparatus that can be easily mounted on an open end of a pipe so as to effectively seal the pipe opening and maintain such seal during pressurization of the pipe interior. Such pressurization may be associated with pipe integrity testing methods. Preferably, such apparatus would not subject the pipe to any significant damage. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention generally provides an apparatus for sealing an open end of a pipe and for frictionally engaging or “gripping” the inner and outer surfaces of the pipe to prevent relative axial movement between the apparatus and the pipe. 
     In another aspect, the invention generally provides a method for sealing an open end of a pipe with a sealing apparatus and wherein the sealing apparatus frictionally engages or “grips” the inner and outer surfaces of the pipe to prevent relative axial movement between the sealing apparatus and the pipe. 
     In another aspect, the apparatus of the invention seals the open end of the pipe and pressurizes the pipe for conducting an integrity test thereof. 
     Thus, in one aspect, the invention provides an apparatus for sealing an open end of a pipe comprising:
         a front plate for positioning against the open end of the pipe;   a back plate adapted for insertion within the pipe, the back plate including a first face, a second face and a perimeter, wherein, when in use, the first face faces the open end of the pipe and the second face faces the lumen of the pipe;   a sealing member for forming a circumferential seal between the back plate and the inner surface of the pipe;   a first gripping means for frictionally engaging the inner surface of the pipe;   a second gripping means for frictionally engaging the outer surface of the pipe; and,   one or more connecting means for connecting together the front plate, the back   plate and the first and second gripping means and for urging the back plate towards the front plate;   wherein the first and second engagement means prevent relative axial movement between the apparatus and the pipe when the apparatus is in use;   and wherein the back plate includes two or more ports for providing a fluid connection into the pipe through the back plate, each of the ports having a first opening on the first face of the back plate and a second opening on the perimeter of the back plate, wherein, when the apparatus is in use, at least one of the ports is adapted to fill the pipe with a pressurizing fluid and another of the ports is adapted to vent the pipe.       

     In another aspect, the invention provides a method of sealing and pressurizing a generally horizontally oriented pipe having an open end, the method comprising:
         closing and sealing the pipe with a sealing apparatus positioned adjacent the open end of the pipe;   anchoring the sealing apparatus to the pipe with a first gripping means, for frictionally engaging the inner surface of the pipe, and with a second gripping means, for frictionally engaging the outer surface of the pipe;   forming a circumferential seal between the inner surface of the pipe and the sealing apparatus;   filling the pipe with a pressurizing fluid through a first port provided on the sealing apparatus and venting the pipe during the pressurizing process with a second port provided on the sealing apparatus, the first port being positioned vertically below the second port.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein: 
         FIG. 1  is a schematic cross sectional view of an apparatus according to an aspect of the invention, in use within a pipe. 
         FIG. 2  is a front perspective view of a back plate according to an aspect of the invention. 
         FIG. 3  is a front view of the back plate of  FIG. 2 . 
         FIG. 4  is a side cross sectional view of the back plate shown in  FIG. 3 , taken along the line A-A thereof. 
         FIG. 5  is a partial cross sectional view of the back plate shown in  FIG. 3 , taken along the line B-B thereof. 
         FIG. 6  is a magnified partial cross sectional view of the back plate shown in  FIG. 3 , taken along the line C-C thereof. 
         FIG. 7  is a perspective view of a first or inner compression ring according to an aspect of the invention. 
         FIG. 8  is a front view of the first compression ring shown in  FIG. 7 . 
         FIG. 9  is a side cross sectional view of the first compression ring shown in  FIG. 8 , taken along the line A-A thereof. 
         FIG. 10  is a perspective view of a first or inner gripper ring according to an aspect of the invention. 
         FIG. 11  is a side view of the first gripper ring shown in  FIG. 10 . 
         FIG. 12  is a front view of the first gripper ring shown in  FIG. 10 . 
         FIG. 13  is a side cross sectional view of a portion of the first gripper ring shown in  FIG. 12 , taken along the line A-A thereof. 
         FIG. 14  is a perspective view of a second or outer compression ring according to an aspect of the invention. 
         FIG. 15  is a front view of the second compression ring shown in  FIG. 14 . 
         FIG. 16  is a side cross sectional view of the second compression ring shown in  FIG. 15 , taken along the line A-A thereof. 
         FIG. 17  is a partial side cross sectional view of the second compression ring as shown in  FIG. 16 , in combination with a second gripper ring. 
         FIG. 18  is a perspective view of a second or outer gripper ring according to an aspect of the invention. 
         FIG. 19  is a front view of the second gripper ring shown in  FIG. 18 . 
         FIG. 20  is a side view of the second gripper ring shown in  FIG. 18 . 
         FIG. 21  is a side cross sectional view of a portion of the second gripper ring shown in  FIG. 19 , taken along the line A-A thereof. 
         FIG. 22  is a perspective view of a front plate according to an aspect of the invention. 
         FIG. 23  is a front view of the front plate shown in  FIG. 22 . 
         FIG. 24  is a side cross sectional view of the front plate shown in  FIG. 23 , taken along the line A-A thereof. 
         FIG. 25  is a schematic cross sectional view of an apparatus according to another aspect of the invention. 
         FIGS. 26 and 27  are front and rear perspective views, respectively, of the back plate ring as shown in  FIG. 25 . 
         FIG. 28  is a front view of the back plate ring as shown in  FIG. 26 . 
         FIG. 29  is a side cross sectional view of the back plate ring shown in  FIG. 28 . 
         FIG. 30  is a cross sectional perspective view of the apparatus shown in  FIG. 1  according to another embodiment. 
         FIG. 31  is a cross sectional perspective view of the apparatus shown in  FIG. 1 , according to another embodiment illustrating the bolts used to connect the apparatus. 
         FIG. 32  is a cross sectional perspective view of the apparatus shown in  FIG. 25  according to another embodiment. 
         FIG. 33  is a front view of the cap of  FIG. 25 or 32  in isolation. 
         FIG. 34  is a cross sectional perspective view of the apparatus shown in  FIG. 25  according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Throughout the description of the invention the following terms will be assumed to have the following associated meanings: 
     “Annular”—this term is used to describe a body having at least one outer diameter and at least one inner diameter. Thus, an “annular disc” will be assumed to be an object having an outer diameter and a central aperture thereby providing an inner diameter. 
     “Axial”—this term will be used to describe a direction taken along the longitudinal axis of a pipe or conduit. Thus, “axial force” or “axial stress” will be understood as being a force applied in a direction parallel to the longitudinal axis of the conduit. Similarly, the term “axially extending” will be understood to mean extending in a direction parallel to the longitudinal axis of the pipe. 
     “Radial”—this term will be used to describe a direction taken along the radius of the pipe or other object to which reference is made. 
     “Proximal” and “distal”—these terms will be used to describe the positions of various components of the invention once positioned over a pipe having an open end. The term “proximal” will be used to describe a position closer to the open end of the pipe. The term “distal” will be used to describe a position away from the open end of the pipe. 
     In general, the invention provides an apparatus that seals an end of a pipe. It will be understood that the pipe will have a generally circular cross section. The apparatus comprises at least one sealing member that engages the inner surface of the pipe wall and forms a seal between the pipe wall and the apparatus so as to prevent passage of fluids (i.e. liquids, gases, vapors etc.) from one side of the apparatus to the other. The apparatus also includes two gripping means to frictionally engage the inner and outer surfaces of the pipe wall, so as to prevent relative axial movement between the apparatus and the pipe. According to a method of the present invention, a pipe to be sealed is provided with an apparatus, such as that discussed above, which simultaneously grips the inner and outer surfaces of the pipe wall to prevent relative axial movement between the apparatus and the pipe. A seal is formed between the apparatus and the inner surface of the pipe to prevent passage of fluids from one side of the apparatus to the other. In a preferred embodiment, the apparatus of the invention is adapted for use with large diameter pipes (i.e. pipes having a diameter greater than 20 inches, including diameters of 36 inches or more). In particular, the apparatus of the preferred embodiment of the invention is designed to seal at least one end of a large diameter pipe and being designed to minimize weight so as to allow easy manipulation thereof. 
       FIG. 1  illustrates an apparatus  10  according to one aspect of the invention, provided on an end of a pipe  12 . As shown, the apparatus  10  comprises a back plate  14  that is adapted to be provided within the pipe  12 , proximal to the end of the pipe  12  to be sealed. An embodiment of the back plate is further illustrated in  FIGS. 2 to 6 . In the illustrated embodiment, the back plate  14  comprises a generally solid body, preferably in the shape of a disc, having a first, or proximal end face  13  and a second, or distal end face  15 . As will be understood, although the back plate  14  is illustrated in  FIGS. 2 to 6  in the form of a disc shaped body, various other shapes of the back plate  14  would be possible, and some of such other embodiments are discussed further below. As shown in  FIG. 1 , the back plate  14  comprises, according to a preferred embodiment, a generally circular disc having an outer diameter that is sized to be positioned within the pipe  12  and axially aligned therewith. It will be understood that the back plate  14  and other components of the invention, particularly those adapted for insertion within a pipe, will be designed to allow for some clearance so as to accommodate any imperfections in the pipe wall. In addition, as discussed further below, a given dimension of the apparatus of the invention may be used for a range of similar diameter pipes. 
     The back plate  14  includes a groove or recess  16  at the first or proximal end face  13  (i.e. the end facing, or proximal to the opening of the pipe when the apparatus is in use) for receiving a sealing member  18 , such as an O-ring and the like. As discussed further below, the sealing member  18  serves to form a fluid tight seal between the apparatus and the inner surface of the pipe when the apparatus is in use. 
     In a preferred embodiment, the second or distal end face  15  of the back plate  14  (i.e. the end facing away from, or distal to the opening of the pipe when the apparatus is in use) is provided with a radially inwardly directed bevel  20 , whereby the radius of the back plate  14  is reduced in an axial direction towards the second end face  15  thereof. As will be understood, the bevel  20  serves to facilitate installation of the back plate  14  within the pipe  12  being tested, particularly since the outer diameter of the back plate  14  would preferably be close to the inner diameter of the pipe  12  being sealed. It will also be understood that the back plate  14  would equally function without the bevel  20 . 
     As more clearly shown in  FIGS. 2 to 4 , the back plate  14  is provided with a plurality of circumferentially spaced bolt holes  22 . As illustrated in  FIG. 4 , the bolt holes  22  do not extend through the back plate  14 . The bolt holes  22  are preferably tapped so as to provide a threaded inner surface therein, into which first bolts are screwed. Such first bolts are illustrated at  90  in  FIG. 31  and discussed further below. In another embodiment, it will be understood that the first bolts may be permanently secured into the bolt holes  22  such as by welding and the like. As illustrated, the bolt holes  22  are preferably equidistantly spaced about the circumference of the back plate  14  at a specified radius thereof. The positioning of the bolt holes  22  corresponds to the positioning of bolt holes of other components of the apparatus, as discussed further below. 
     The first face  13  of the back plate  14  is also preferably provided with two or more first holes or ports  23 . As shown in  FIG. 4 , the holes  23  do not extend through the width of the back plate  14 . Therefore, the holes  23  do not protrude through the second face  15  thereof. In a preferred embodiment, two such holes  23  are provided on the back plate  14 . The back plate  14  is further provided with two or more radially extending second, or radial holes  30 , each of which extend radially through the outer perimeter of the back plate  14  and join with one of the first holes  23  described above so as to allow fluid communication between the first holes  23  and the second holes  30 . In the result, the combination of the first holes  23  and second, radial holes  30  result in ports or fluid passages on the back plate  14 . Such ports ( 23 ,  30 ) are used to provide fluid communication from the first face of the back plate  14  to the outer perimeter thereof, the purpose of which is described below. The first holes  23  may preferably be provided with couplings  24  that extend axially away from the first face  13  of back plate  14 . When the apparatus is in use, the couplings  24  preferably extend towards the opening of the pipe for ease of use. 
     The second holes  30  are preferably provided on opposite ends of the perimeter of the back plate  14 . That is, the second holes  30  are preferably provided approximately on opposite ends of a given diameter of the back plate  14 . With such arrangement, and when the apparatus is in use, the back plate  14  may be oriented so that the second holes  30  are positioned in opposite vertical directions, wherein one of the holes  30  is oriented downwards while the other is oriented upwards. In this way, a pressurizing fluid may be introduced through one of the holes  30  oriented generally vertically downwards when positioned in a pipe  12  and another of the holes  30  oriented generally vertically upwards may be used to vent the pipe during the filling procedure. As will be understood by persons skilled in the art, the pressurizing fluid, when introduced into the pipe  12 , will cause the contained air (or gases etc.) to rise vertically. Thus, having at least one of the holes  30  positioned at the upper end of the back plate  14  (when in use in a pipe) facilitates the venting procedure. The filling and venting process may be continued until the pressurizing fluid begins to exit from the upwardly oriented hole  30 , which would indicate that the pipe  12  is completely filled with the pressurizing fluid, and indicating that the pressurizing step may continue. In the above description, reference has been made to “vertically upwards” and “vertically downwards”. However, it will be understood that such orientation of the second holes  30  occurs when the back plate  14  is installed in a pipe when the apparatus of the invention is in use. It will also be understood that while having the second holes  30  being provided in opposite directions is preferred, the invention would function generally in the manner indicated above even where the second holes  30  are not exactly in the aforementioned orientations. In other words, various modifications can be made to the specific positioning of the second holes  30  while still achieving the desired result. Furthermore, while two second holes  30  and associated first holes  23  may be preferred (to provide two ports for filling and venting the pipe, accordingly), it will be understood that more than two of such holes may also be provided. 
     The ports or fluid passages formed by the first holes  23  and second, radial holes  30  (for convenience the combination of the first holes  23  and second holes  30  will be referred to as the ports or fluid passages  23 ) allow for fluid communication through the back plate  14  into the lumen of the pipe  12 , when the apparatus is in use. It will be understood that for such communication, and for the placement of the back plate  14  within the pipe  12 , the outer diameter of the back plate  14  would be preferably less than the inner diameter of the pipe  12 . Thus, the ports  23 , preferably including the couplings  24 , may be used to pressurize, vent and/or monitor the lumen of the pipe  12  during the use of the apparatus  10 . For this purpose, the ports  23  are preferably connected to any desired hoses, conduits, gauges and the like. It will be understood that the couplings  24 , where provided, may facilitate such connection. It will also be understood that, while the outer diameter of the back plate  14  is chosen to be less (or slightly less) than the inner diameter of the pipe  12  so as to allow the ports to function (i.e. to allow fluid to pass through the second holes  30 ), the back plate  14  will still have a sufficiently large outer diameter to allow the sealing member  18  to function. That is, as will be appreciated by persons skilled in the art, if the back plate  14  is of too small an outer diameter, the clearance between the back plate  14  and the inner surface of the pipe  12  would not be sufficient to allow the sealing member  18  to be deformed and would therefore not result in the required seal between the back plate and the inner surface of the pipe. The limitations of the outer diameter of the back plate would be known to persons skilled in the art. For example, such determination may be made by calculating the deformed outer diameter of the sealing member  18 . 
     The above mentioned holes  23  and  30  comprise one embodiment of the invention. It will be understood that in other embodiments, the radial second holes  30  may be omitted by providing first holes  23  that extend through the width of the back plate  14 . In such way, the aforementioned fluid communication through the back plate  14  is provided. In such case, the first holes  23  may be provided very close to the outer diameter of the back plate  14  so as to achieve the preferred filling/venting function discussed above with respect to the second holes  30 . 
     The back plate  14  may also be provided with a generally centrally located opening or thru-hole  26 , which is adapted to be connected to a hose, conduit or the like. The thru-hole  26  may be used to facilitate one or more of the pressurization, venting and/or monitoring functions relating to the interior of the pipe  12 , as will be described further below. In a preferred embodiment, the thru-hole  26  includes a coupling  28  that is secured thereto (such as be welding etc.), which serves to facilitate connection of the thru-hole  26  to the hose, conduit etc. mentioned above. 
     In one aspect, the back plate  14  may optionally be provided with a number of threaded, or tapped openings  32 , provided radially inwardly on the outer perimeter thereof. As shown in  FIG. 3 , the back plate  14  is, one embodiment, provided with two openings  32 , provided at one end thereof and circumferentially separated from each other. The openings  32  are adapted to receive bolts or screws or the like, such as, by way of example only, button head cap screws (BHCSs) that aid in positioning the back plate  14  when being installed within a pipe. Specifically, the BHCSs are used as legs to support the back plate  14  as it is inserted into the pipe. As will be understood, the use of screws, such as BHCSs, avoids direct contact between the outer edge, or perimeter of the back plate  14  and the inner surface of the pipe, thereby facilitating movement of the back plate  14  within the pipe. Further, the use of screws such as BHCSs, which have a rounded (or “button”-like) head, also facilitate the positioning of the back plate  14 . As will be understood, particularly where the apparatus of the invention is used with large diameter pipes, each component forming the apparatus, in particular the solid back plate  14 , would be fairly heavy. As such, the use of positioning aids such as BHCSs and the like facilitates the installation of the apparatus when used in a pipe. It will also be understood that such positioning aids or bolts are optional and that any similar type of device or devices may be used. 
     As shown in  FIG. 1 , the apparatus  10  also includes a first or inner compression ring  34  and an associated first or inner gripper ring  36 . As discussed below, and as illustrated in  FIG. 1 , the combination of the compression ring  34  and gripper ring  36  result in the gripper ring  36  frictionally engaging, or “gripping” the inner surface of the pipe  12 . The first compression ring  34  is shown in more detail in  FIGS. 7 to 9 . The first gripper ring  36  is shown in more detail in  FIGS. 10 to 13 . As shown in  FIG. 1 , the first compression ring  34  is initially positioned distally from the pipe  12  opening, when the apparatus is in use, as compared to the first gripper ring  36 . 
     Both the first compression ring  34  and the first gripper ring  36  are preferably generally annularly shaped bodies, each having an inner diameter and an outer diameter. As shown in  FIG. 1 , the outer diameters of both the first compression ring  34  and the first gripper ring  36  are sized to be inserted within the pipe  12  and axially aligned therewith. The outer diameter of the first compression ring  34  comprises a beveled edge  38 , whereby the compression ring  34  is provided with an outer diameter that tapers from one end of the compression ring  34  to the other. When positioned in a pipe  12 , the first compression ring  34  is arranged such that smaller outer diameter is positioned proximal to the pipe  12  opening, as shown in  FIG. 1 . As shown, for example, in  FIGS. 7 and 8 , the first compression ring  34  does not necessarily have an inner “diameter” per se but does have an inner opening of an irregular shape. It will therefore be understood that the term “inner diameter” as used in this context is for convenience and is not intended to limit the shape of the first compression ring  34  in any way. As will be understood from the present disclosure, the first compression ring  34  is preferably designed to have an inner opening of some nature. 
     The first gripper ring  36  has an inner diameter having a bevel or taper  40 , which is adapted to cooperate with the outer beveled edge  38  of the first compression ring  34  when the apparatus is in use. The bevel  40  of the first gripper ring  36  results in the gripper ring  36  having a gradually increasing inner diameter from one end of the ring  36  to the other. When in the installed position, the first gripper ring  36  is arranged so that the smaller inner diameter is positioned proximal to the opening of the pipe  12 . The outer diameter of the first gripper ring is generally constant and is sized to fit within the pipe  12 . 
       FIG. 1 , illustrates the arrangement of the first compression ring  34  and the first gripper ring  36  when the apparatus is in use. As shown, the inner diameter bevel  40  of the first gripper ring is oppositely directed from the beveled outer edge  38  of the first compression ring when the apparatus is installed. In this arrangement, the oppositely oriented bevels serve to form a ramp to drive the first gripper ring  36  radially outwardly to frictionally engage the inner surface of the pipe  12 . That is, as will be understood by persons skilled in the art, as the first compression ring  34  and the first gripper ring  36  are axially moved towards each other, the oppositely directed bevels,  38  and  40 , result in the first gripper ring being subjected to a radially outward or expansive force, thereby forcing the outer diameter of the first gripper ring  36  against the inner surface of the pipe  12 . In one embodiment of the invention, as illustrated in the figures, the bevels  38  and  40  may be of the same slope. However, in other embodiments, the respective slopes of the bevels  38  and  40  may be different. The relative arrangement of the bevels will be apparent to persons skilled in the art with the aim of causing the first compression ring  34  to cause radially outward movement or deformation of the first gripper ring  36 . 
     To ensure that the first gripper ring  36  is radially outwardly deflected, as opposed to a radially inward deflection of the first compression ring  34 , the first compression ring  34  is preferably designed with a greater tensile strength. For example, in the embodiment illustrated in the figures (e.g.  FIGS. 1 and 7 ), the first compression ring  34  may be designed with greater mass as compared to the first gripper ring  36  to result in the required tensile strength. Alternatively, the first compression ring  34  may be made of a different, stronger material as compared to the first gripper ring  36  to achieve the same result. As a further alternative, or to further ensure that the first gripper ring  36  is radially outwardly deformed or expanded, the first gripper ring  36  is preferably provided with a series of cuts  42  that partially extend through the gripper ring  36 . As illustrated in  FIGS. 10 to 12 , and in accordance with a preferred embodiment of the invention, the first gripper ring  36  includes a plurality of cuts  42  that extend from one end and generally about half way through the width of the ring  36  body. As also shown, the cuts  42  preferably extend from both ends but in a staggered, or alternating manner. 
     In another embodiment, as illustrated in  FIGS. 10 and 11 , the first gripper ring  36  may be provided in two or more sections.  FIGS. 10 and 11  illustrate an embodiment of the invention wherein the first gripper ring  36  is provided in two sections comprising first and second sections  44   a  and  44   b , respectively. When the first gripper ring  36  is formed, the first and second sections  44   a ,  44   b  are preferably separated by two slots  46   a ,  46   b . In such manner, the separation offered by the slots  46   a ,  46   b  facilitates installation of the first gripper ring within the pipe  12 . It will also be understood that providing the first gripper ring  36  in two sections also facilitates removal of the apparatus  10 . That is, a one piece gripper ring  36  may be permanently deformed when expanded radially, in which case removal of same would be difficult. Thus, by having the gripper ring provided in two or more sections, each section may be easily removed from the pipe  12 . Various other means for causing radial expansion of the first gripper ring  36  may be used with the apparatus of the invention. 
     It will be understood that the first gripper ring  36  is not restricted in design to the above described two-part structure. Various other alternative structures, including a single body, may be used in the invention. 
     As shown in  FIG. 13 , the outer diameter of the first gripper ring  36  may preferably comprise a grooved  48  or other such textured or treated surface enhancement to further strengthen the frictional engagement between the gripper ring  36  and the inner surface of the pipe  12  when the apparatus is in use. It will be understood that such grooves  48  would be designed to not significantly damage the surface of the pipe  12 . 
     Referring again to  FIGS. 7 to 9 , the first compression ring  34  is shown to include a plurality of outer bolt holes  50  that are generally circumferentially equidistantly spaced. The bolt holes  50  are provided at a radius of the first compression ring  34  that corresponds to the positions of the threaded bolt holes  22  provided on the back plate  14 . As shown in  FIG. 9 , the bolt holes  50  extend through the width of the first compression ring  34 . As will be understood from the following description, the aforementioned first bolts (also discussed further below) for engaging the apparatus  10  will extend through the bolt holes  50  and engage the threaded bolt holes  22  of the back plate  14 . 
     As will be understood, due to the weight of the components of the apparatus of the invention, removal from within a pipe would be difficult without some means of grasping one or more components thereof. For this reason, one or more of components of the apparatus may optionally be provided with a means for extracting the apparatus of the invention from a pipe after the sealing operation has concluded. In one example as illustrated in  FIGS. 7 to 9 , such means of assisting the extraction comprises a number of further, inner bolt holes  52  that are provided generally circumferentially equidistantly on the first compression ring  34 , but at a radius that is less than that of the outer bolt holes  50 . In the example shown in  FIGS. 7 to 9 , it is noted that four inner bolt holes  52  are provided on the first compression ring  34 . However, it will be appreciated that the number of such bolt holes  52  can be varied based on the size and/or weight of the first compression ring  34 . The inner bolt holes  52  may be provided at a location close to the inner diameter of the first compression ring  34 . However, as an alternative, and as shown in  FIGS. 7 and 8 , the first compression ring  34  may be provided with a number of radially inwardly directed projections  54  to accommodate the inner bolt holes  52 . In the embodiment illustrated in  FIGS. 7 to 9 , the inner bolt holes  52  on the first compression ring  34  are threaded so as to accommodate bolts or the like therein, which also comprise the above noted means for extracting the apparatus. In particular, such bolts would preferably comprise eye bolts that can be screwed into the inner bolt holes  52  when the apparatus needs to be extracted from a pipe (or at any time), which allows a chain, rope or any other such device(s) to be connected to such bolts so as to allow the apparatus to be pulled towards the opening of the pipe. It will be understood that although the use of the above described means for extracting has been defined in terms of removing the apparatus from the pipe, it can similarly be used to assist in positioning the apparatus within the pipe. It will also be understood that the aforementioned bolts (e.g. eye bolts) may be permanently secured to the first compression ring  34 , if necessary, or provided, permanently or otherwise, on any other component of the apparatus. 
       FIG. 1  also illustrates the second or outer compression ring  56  and the second or outer gripper ring  58  of the apparatus  10 . As shown, the arrangement of the second compression ring  56  and second gripper ring  58  is the opposite of that described above with respect to the first compression ring  34  and first gripper ring  36 . This is primarily due to the fact that the second compression ring  56  and second gripper ring  58  are arranged to grip the outer surface of the pipe  12 . As discussed above, the first gripper ring  36  is adapted to be forced over the first compression ring  34 , whereby the first compression ring  34  forces the first gripper ring  36  radially outwardly within the pipe  12 , when the apparatus  10  is in use, to cause the first gripper ring  36  to frictionally engage the inner surface of the pipe  12 . In an opposite manner, the second compression ring  56  is designed to pass over the second gripper ring  58 , when the apparatus  10  is in use. As will be understood, this forces the second gripper ring  58  radially inwardly whereby the second gripper ring frictionally engages the outer surface of the pipe  12 . 
     The second or outer compression ring  56  is illustrated in more detail in  FIGS. 14 to 17 . As shown in  FIGS. 1 and 14 to 17 , the second compression ring  56  comprises a generally annular ring structure having an inner diameter that is beveled  60 . Such bevel  60  results in the second compression ring having a lower inner diameter at one end, which gradually increases when moving towards the opposite end. As shown in  FIG. 1 , when the apparatus  10  is in use, the second compression ring  56  is arranged so that the larger inner diameter thereof is positioned proximal to the opening of the pipe  12 . 
     The second or outer gripper ring  58  is illustrated in more detail in  FIGS. 18 to 21 . As shown, the second gripper ring  58  has an outer edge or diameter  62  that comprises a bevel, whereby, the outer diameter of the second gripper ring  58  tapers or gradually reduces from one end to the opposite end. When the apparatus  10  is installed on a pipe  12 , as shown in  FIG. 1 , the second gripper ring  58  is arranged so that the larger out diameter end is positioned proximal to the pipe  12  opening. 
     As illustrated in  FIG. 1 , when the apparatus is in use, the second compression ring  56  and second gripper ring  58  are arranged on a pipe, so that the second compression ring is distal to the opening of the pipe. In this arrangement it will be seen that as the second compression ring  56  and second gripper ring  58  are urged towards each other in the axial direction, the beveled inner diameter of the second compression ring  56  is driven over the beveled or tapered outer diameter of the second gripper ring  58 , thereby causing the second gripper ring  58  to be radially compressed against the outer surface of the pipe  12 . In other words, as with the first compressing ring  34  and first gripper ring  36  discussed above, the oppositely directed bevels of the second compression ring  56  and second gripper ring  58  form a ramp to drive the second gripper ring  58  radially inwardly to frictionally engage the outer surface of the pipe  12 . 
     As with the first compression ring  34  and first gripper ring  36  discussed above, the second compression ring  56  and second gripper ring  58  are preferably designed so as to ensure that the second gripper ring  58  is compressed as opposed to causing radial expansion of the second compression ring  56 . For example, as discussed above, in a preferred embodiment, the second compression ring  56  will be designed to have greater mass or rigidity as compared to the second gripper ring  58 . Further, in a preferred embodiment as illustrated in  FIGS. 18 to 21 , the second gripper ring  58  may be provided with a plurality of cuts  64  extending axially from one or both ends towards the center of the ring  58 . As will be understood, such cuts  64  serve to reduce the rigidity of the gripper ring. In addition, the second gripper ring  58  is preferably provided with a slot  66  extending axially through the width of the gripper ring  58 . As will be understood, the slot  66  allows the second gripper ring  58  to be expanded and slid onto the outer surface of the pipe  12  when the apparatus is installed. When the apparatus is dismantled, the second gripper ring  58  may then be more easily removed off the pipe  12  by expanding same radially outwards. Various other means for causing radial compression of the second gripper ring  58  may be used with the apparatus of the invention. 
     The second gripper ring  58  may also be adapted to increase frictional engagement with the pipe  12 . For example, as discussed above, the inner diameter of the second gripper ring  58  may be provided with grooves  68 , as shown in  FIG. 21 , or some other textured or treated surface, which enhances the frictional engagement between the second gripper ring  58  and the outer surface of the pipe  12 . It will be understood that such grooves  68  would be designed to not significantly damage the surface of the pipe  12 . 
     Returning to  FIGS. 14 to 17 , it is noted that the second compression ring  56  is provided with a plurality of bolt holes  70  that extend axially through the width of the compression ring  56 . The bolt holes  70  are circumferentially equidistantly spaced and are adapted to receive second bolts (shown as  92  in  FIG. 31 ). The significance of the bolt holes  70  is discussed below. 
       FIGS. 1 and 22 to 24  illustrate a front, or sealing plate  72  of the apparatus  10 . The front plate  72  comprises the opposite end of the apparatus  10  from the back plate  14 . In a preferred embodiment, as illustrated in the figures, the front plate  72  comprises a generally annular disc having an outer diameter and an inner diameter. The outer diameter of the front plate  72  is designed to be greater than the outer diameter of the pipe  12  so as to allow a sufficient clearance there-between. Further, the inner diameter of the front plate  72  is designed to be smaller than the inner diameter of the pipe  12 . In this way, the annular front, or sealing plate  72  covers the edge of the pipe  12  at the open end thereof. The front plate  72  includes two series of bolt holes, each of such series comprising a plurality of circumferentially equidistantly spaced. A first series of bolt holes  74  is provided near the outer diameter of the front plate  72  and the second series of bolt holes  76  is provided near the inner diameter of the front plate  72 . The first series of bolt holes  74  are positioned to be aligned with the bolt holes  70  provided on the second compression ring  56 . The second series of bolt holes  76  are positioned to be aligned with bolt holes  50  of the first compression ring  34  and the bolt holes  22  of the back plate  14 . 
     Thus, as will be understood, the apparatus  10  of the invention may be divided into two sub-assemblies, namely, an inner sub-assembly, comprising the back plate  14  (including the sealing member  18 ), the first compression ring  34  and the first gripper ring  36 ; and an outer sub-assembly, comprising the second compression ring  56  and the second gripper ring  58 . 
     As shown in  FIG. 1 , the front plate  72  is adapted to be pressed against the open end of the pipe  12 . The front plate  72  may therefore optionally be provided with a groove or recess to accommodate the opening of the pipe  12  therein. Such groove or recess may optionally be provided with a sealing means to further seal the end of the pipe  12 . 
     As discussed above, while the back plate  14  is, in one embodiment, a generally solid disc that prevents direct fluid communication between the interior of the pipe  12  on both sides thereof (i.e. the back plate  14 , when in use, seals the portion of the pipe interior on the second side  15  thereof), all other components of the invention have inner diameters or openings. Thus, in such arrangement, the opening  26  and/or the ports  23  (i.e. inclusive of the first holes  23  and the second holes  30 ) provided on the back plate  14  are accessible through the front plate  72 . As mentioned above, the opening  26  and/or the holes  23 , preferably include respective couplings  28  and  24 . In one aspect, the pipe  12  being tested may be pressurized by introducing a pressurizing fluid through one or more of the opening  26  or holes  23 . Such elements would also be used to vent and/or monitor the interior volume of the pipe  12 . Pressurization of the pipe  12  allows for pressure testing to test the integrity of the pipe and/or one or more welds provided thereon. For example the pipe  12  may be formed of two or more segments or may include a valve, flange or other such equipment welded thereon. As discussed above, the testing of such welds is important. In use, the apparatus  10  of the invention allows the interior of the pipe  12  to be pressurized after the apparatus is installed. Preferably after venting any air within the pipe  12  (i.e. to remove any compressible gases), the pressure within the pipe  12  may then be monitored, wherein a drop in pressure signifies a weld or joint etc. that lacks the sufficient integrity. 
     In some situations, the pipe  12  may be open at more than one end. In such cases, more than one of the above discussed apparatuses may be used to seal both (or all of) the pipe openings. In such case, it will be understood that the pressurizing and venting procedures may be conducted through one or more of the apparatuses. 
     One of the advantages offered by the apparatus of the present invention over that of know pressure testing devices is that, in addition to sealing an end of a pipe, the apparatus also frictionally engages both the inner and outer surfaces of the pipe that is sealed. This feature results in the apparatus being effectively secured to the pipe and avoids the seal from being dislodged once the pipe is pressurized. As will be understood, the pressure testing of pipes is conducted at very high pressures and, as such, any dislodging of the sealing apparatus would result in a highly dangerous situation where the sealing apparatus may be explosively “shot out” from the pipe. 
     Another advantage of the apparatus of the invention can be seen in  FIG. 1 . Due to the installed arrangement of the back plate  14  and the first compression ring  34  and first gripper ring  36 , it will be seen that as the pressure distal (i.e. away from the opening of the pipe  12 ) builds within the pipe, the pressure serves to force the back plate  14  towards the pipe opening. In the result, the back plate  14  urges the first compressing ring  34  further against the first gripper ring  36 , which further increases the gripping or frictional force between the apparatus  10  and the inner surface of the pipe  12 . As will be appreciated, this results in the first compression ring  34  being maintained in position within the pipe  12 . In addition, due to the back plate  14  being forced against the immobilized first compression ring  34 , the sealing member  18  is further compressed between the back plate  14  and the first compression ring  34 . This therefore results in an increased seal being formed between the apparatus  10  and the inner surface of the pipe  12 . 
     The method of the invention will now be described with reference to the apparatus  10  discussed above. In general, the method of the invention comprises sealing or closing at least one end of a pipe  12  that is to be pressure tested. Such testing can, for example, be for the purposes of testing the integrity of one or more weld on the pipe  12 . The step of sealing comprises the formation of a circumferential seal with the inner surface of the pipe  12  to be tested and the closure of the lumen of the pipe  12  at a location close to the opening of the pipe. The apparatus also frictionally engages the inner and outer surfaces of pipe  12  so as to prevent relative axial movement between the apparatus  10  and the pipe  12 . The method also comprises, in one aspect, using one or more similar apparatuses  10  to seal an opposite end of the pipe  12  if needed (i.e. in situations where the pipe is open on both ends) or other openings in such pipe. The invention is not limited to the number of openings in the pipe. Once the seal or seals are formed at the one or more openings thereof the interior of the pipe is pressurized and the pressure monitored. If the pressure is maintained, the integrity of the pipe  12  and/or welds is verified. Any drop in the pressure within the pipe  12  signifies a failure in the pipe&#39;s integrity and/or that of at least one of the welds thereon. 
     As would be apparent from  FIG. 1 , in a first step, the inner and outer sub-assemblies of the apparatus  10  are positioned in and on the pipe  12 , respectively, at a location generally close to the opening of the pipe  12  that is to be sealed. In one aspect of the method, the inner sub-assembly is installed first followed by the outer sub-assembly. However, it will be understood that the order of installation can easily be reversed. Thus, in one aspect, the back plate  14 , with the sealing member  18 , may be first inserted into the pipe  12 , followed by the first compression ring  34  and then the first gripper ring  36 . As discussed above, the back plate  14  is preferably positioned and rotated (if necessary) within the pipe  12  so that the second holes  30  are oriented vertically away from each other. In situations where devices such as cap screws or the like are provided in the openings  32 , it will be understood that the second holes  30  would be pre-determined and, therefore, rotation of the back plate  14  for positioning the second holes  30  would not be necessary. 
     As mentioned above, the first gripper ring  36  may be provided in one or more sections. Similarly, the second compression ring  56  is provided over the outer surface of the pipe  12 , followed by the second gripper ring  58 . Next the front plate  72  is positioned against the open end of the pipe  12 . A plurality of second bolts (discussed further below as element number  92  shown in  FIG. 31 )) is passed through the first series of bolt holes  74  of the front plate  72  and through the bolt holes  70  of the second compression ring  56 . First nuts are then provided and tightened so as to urge the second compression ring  56  axially towards the front plate  72 . In a preferred aspect, the front plate  72  is maintained pressed against the opening of the pipe  12  and, therefore, the tightening of the first nuts on the second bolts (element  92  as shown in  FIG. 31 ) results in the second compression ring  56  being moved towards the front plate  72 . 
     Similarly, first bolts (element  90  as shown in  FIG. 31 ) are passed through the second series of bolt holes  76  of the front plate  72 . The first bolts are also extended through the bolt holes  50  of the first compression ring  34  and into the threaded bolt holes  22  of the back plate  14 . Tightening of the first bolts into the back plate  14  results in the back plate  14  being urged axially towards the front plate  72  (primarily due to the front plate being pressed against the open end of the pipe  12  and, therefore being immobilized). In this process, the back plate  14  is moved axially towards the opening and, in the result, causes similar movement of the first compression ring  34  against the first gripper ring  36 . In the latter case, the lower outer diameter, proximal end of the first compression ring  34  is urged into the larger inner diameter, distal end of the first gripper ring  36 , thereby resulting in the first gripper ring  36  being expanded radially outwardly. Such radial expansion results in the formation of a frictional engagement (i.e. “gripping”) of the first gripper ring  36  with the inner surface of the pipe  12 . As shown in  FIG. 1 , the axial movement of the first gripper ring  36  is impeded once contact is made with the front plate  72 . Further tightening of the first bolts increases the frictional engagement between the first gripper ring  36  and the inner surface of the pipe  12 . Concurrently, the axial movement of the back plate  14  against the first compression ring  34  results in compression of the sealing member  18 . Due to the presence of the groove  16  on the back plate  14 , the compression of the sealing member  18  forces it to be radially outwardly expanded against the inner surface of the pipe  12 . In the result, the sealing member  18  forms a fluid tight circumferential seal with the inner surface of the pipe  12 . 
     In the above description, reference is made to the use of first and second bolts that are extended through respective bolt holes. It will be understood that in some embodiments, one or both of the sets of bolts may be permanently secured to at least one of the aforementioned components, such as by welding etc. For example, the second bolts may be permanently attached to either the front plate  72  or the second compression ring  56 , with nuts provided on the opposite ends thereof to cause the required axial advancement. Similarly, the first bolts may be permanently secured to the back plate  14  and allowed to extend through the bolt holes  76  provided on the front plate  72 . Nuts would then be provided on the ends of the first bolts and tightened to urge the back plate  14  towards the front plate  72 . 
     Although the use of bolts and associated nuts may be preferred, in other embodiments of the invention, other mechanical or hydraulic devices may also be used to achieve the desired result. For this reason, such bolts and the like may be generally referred to herein as means for urging. 
     As discussed above, once the two sub-assemblies of the apparatus  10  are positioned and installed, a pressurizing fluid is introduced into the lumen of the pipe  12  distal of the opening to pressurize the pipe  12 . In one aspect, the pressurizing fluid may be introduced through one of the ports  23 , and preferably via a coupling  24  associated therewith, where provided. The pressurizing fluid would be understood as being introduced through a hose or other such conduit (not shown) connected to one of the couplings  24 . The other of the couplings  24  would preferably be connected to a vent hose or conduit (also not shown) so as to facilitate venting of any air etc. within the pipe during the pressurization step. As mentioned above, the holes  23  are preferably connected to radial holes  30 , which extend through the outer diameter of the back plate  14 . The pressure within the pipe would then be increased to the desired testing value and the pressure monitored as described above. For this step, the hose of conduit associated with one or both of the couplings  24  may include a pressure gauge or the like. However, in one aspect, any venting of monitoring of the pipe  12  may be accomplished, at least partially, using the opening  26  and the associated coupling  28 , to which a separate vent hose or conduit and/or pressure monitoring means (i.e. pressure gauges and the like) may be attached. The hose or conduit may also be used to vent the interior of the pipe  12  either after the test is completed or during the pressurizing step. In one example, where two ends of a pipe are sealed according to the present invention, the pressurizing fluid comprising an inert gas or water etc. may be introduced at one end and any existing gases or vapors within the pipe may be vented through the other end. As discussed above, this filling/venting step is facilitated by positioning the back plate  14  within the pipe  12  being tested in such a manner so as to orient the second holes  30  vertically. 
     In the above description, the outer sub-assembly is described as being secured first onto the pipe  12 . However, it will be understood that the inner sub-assembly may be secured first before the outer sub-assembly. 
     It will be understood that the inner sub-assembly (i.e. the back plate  14 , first compression ring  34  and first gripper ring  36 ) and/or the outer sub-assembly (i.e. the second compression ring  56  and second gripper ring  58 ) may be loosely preassembled with the front plate prior to installation on the pipe  12 . Such pre-assembly is possible since the frictional engagement with the pipe  12  is achieved upon tightening the respective nuts and/or bolts. 
     The apparatus and method of the present invention may be used on a large variety of sizes and thicknesses of pipes. Two examples are provided below where the apparatus is designed for use with a 20″ schedule 120 pipe and a 36″ schedule 80 pipe. Persons skilled in the art would appreciate the required modifications required for using the apparatus of the invention with other diameters and schedules of pipes. 
     In cases where the pipe to be tested is of a large diameter, i.e. 36″ or more, various structural modification may also be made to facilitate the installation and/or use of the apparatus of the invention. By way of example, an apparatus according an aspect of the invention, for use in large diameter pipes (for example, pipes having a diameter of 36″ or more), is shown in  FIG. 25 , wherein elements that are similar to those described above are indicated with like reference numerals. As shown, the apparatus for use on larger sized pipes is very similar to that described above, with the exception of the previously described back plate  14  is replaced with a modified back plate shown at  14   a . Specifically, with the embodiment shown in  FIG. 25 , the modified back plate  14   a  is comprised of a back plate ring  78  that is secured, such as by welding or other such means, to an associated “bell” shaped cap  80 . As such, the singular term “back plate  14   a ” is used herein to refer to the combination of the back plate ring  78  and the cap  80 . The back plate ring  78  is illustrated in more detail in  FIGS. 26 to 29 . As will be understood, the back plate ring  78  and cap  80  function in the same manner as the back plate  14  described above. However, due to its larger size, the combination of the back plate ring  78  and cap  80  serves to facilitate the manipulation of the back plate  14   a  and the installation of the apparatus within a pipe  12 . 
     By replacing a solid disc back plate (such as illustrated by element  14  in previous figures) with a back plate  14   a  comprising a combination of a ring  78  and cap  80 , a further advantage is realized. Specifically, in the case of large diameter pipes, a suitably sized back plate  14  will be needed. It will be understood that while such a solid disc back plate  14  would function in the manner described above, such element would have considerable weight and, therefore, would be difficult to manipulate, use and transport. For example, with “small” diameter pipes (i.e. pipes of approximately 20 inches in diameter or less), the thickness of the back plate may only need to be 3 inches. However, for pipes having a diameter of 24 to 36 inches or more, a solid back plate such as shown at  14  in previous figures, would need to be roughly 6 inches thick in order to withstand the pressures that would accumulate in the pipe  12  during the pressure testing phase. Thus, such a back plate would be very heavy. 
     However, by replacing the solid disc  14  with the modified back plate  14   a , having the back plate ring  78  and cap  80  combination, a considerable weight reduction is realized. In such case, the ring  78  may only need to be 3 inches thick, with the cap  80  being even thinner. This is due to the orientation of the cap  80  and, specifically, the orientation of the convex side of the cap  80  facing within the pipe  12  (as shown in  FIG. 25 ). In this orientation, as pressure accumulates within the pipe  12 , force is applied to the cap  80  and, due to its “bell” shape, such force is distributed almost entirely to the outer edge thereof and against the ring  78 . The body of the cap  80  would therefore not be deformed, despite it relatively thin structure, since its shape would be able to withstand such deformation, which would not be possible with a flat plate-like structure. Thus, with the modified back plate  14   a  having such ring  78  and cap  80  combination, a high pressure may be created within the pipe  12  without risking collapse of the back plate. Although the embodiment illustrated in  FIG. 25  has been described in connection with “large” pipes, it will be understood that such embodiment may be used with any size of pipe. In any event, the combination of back plate ring  78  and cap  80  results in an apparatus that is easier to manipulate and transport due to its reduced weight. 
     As shown in  FIGS. 25 to 29 , the back plate ring  78  of the modified back plate  14   a  comprises a generally annular shaped disc having an outer diameter and an inner diameter. As with the back plate  14  previously described, the back plate ring  78  is provided with a plurality of threaded bolt holes  82  that are adapted to receive bolts, i.e. first bolts (discussed further below and shown as element  90  in  FIG. 32 ), extending from the front plate  72  in the manner described above. As also mentioned above, the first bolts (shown as  90  in  FIG. 32 ) may be permanently secured to the back plate ring  78 . 
     The back plate ring  78  is also provided with a groove  86  or similar structure that is adapted to receive a sealing member  18 , such as an O-ring or the like, in the same manner as described above. 
     The cap  80  is secured to the back plate ring  78  in any suitable manner, such as by welding or the like. It will be appreciated that the cap  80  is secured to the back plate ring  78  in a fluid tight manner so as to prevent passage of fluids, such as the aforementioned pressurizing fluid, through the joint between the cap  80  and the back plate ring  78 . 
     The cap  80  is provided with two or more ports  83  that provide fluid communication between opposite sides of the cap  80 . As shown in  FIG. 25 , the ports  83  extend through the cap  80  and, in a preferred embodiment, include couplings  84  that are adapted to connect to hoses or other such conduits in the same manner as described above with respect to couplings  24  of the back plate  14 . As discussed above with respect to the second holes  30 , in a preferred embodiment, the ports  83  are provided on opposite sides of the cap  80  so that, when the modified back plate  14   a  is positioned within a pipe, the ports  83  may be oriented vertically to facilitate the filling/venting step of the pipe as described above. 
       FIG. 32  illustrates the above mentioned arrangement of ports  83  on the cap  80  when the apparatus, including the modified back plate  14   a , is installed in a pipe  12 . As shown, the ports  83  are provided generally on opposite ends of the cap  80  so that, when positioned in the pipe  12 , the ports  83  are arranged vertically so that, as before, the lower oriented port  83  may be used to fill the pipe with a pressurizing fluid while the upwardly oriented port  83  can be used to vent the pipe  12  during the filling step. 
     In one embodiment, the cap  80  may be provided with a carriage apparatus such as that shown at  88 , which serves to facilitate installation of the cap  80  and back plate ring  78  assembly within a pipe. As will be understood, the weight of the back plate ring  78  itself, for use in a 36 inch pipe, may exceed 250 lbs and, as such, any carriage means etc. would assist the manipulation of the apparatus when being installed in the pipe  12 . 
     The operation or method of use of the apparatus shown in  FIG. 25  would generally be the same as that described above. 
       FIG. 32  illustrates the embodiment of  FIG. 25  with the first and second bolts included. As shown in  FIG. 32 , the first bolts  90  and second bolts  92  are provided through the front plate  72  in the same manner as described above. Thus, as shown, first bolts  90  extend through the bolt holes  76  of the front plate  72 , through bolt holes  50  of the inner or first compression ring  34  and into bolt holes  82  of the back plate ring  78 . As mentioned above, the first bolts  90  may be permanently secured to the back plate ring  78 . Nuts  94  are used on the first bolts  90  in order to urge the back plate ring  78  and the front plate  72  together. The second bolts  92  are provided through bolt holes  74  of the front plate  72  and through bolt holes  74  of the second or outer compression ring  56 . Nuts  96  and/or  98  are used on the second bolts  92  to urge the second compression ring  56  and the front plate  72  towards each other. 
       FIG. 32  also illustrates two other features of the subject embodiment of the invention. Specifically,  FIG. 32  illustrates a weld  100  that secures the cap  80  to the back plate ring  78 . In addition,  FIG. 32  illustrates some additional structure of the first or inner compression ring  34 . As shown, the first compression ring  34  may be provided with an inner diameter portion having a mesh-type structure that provides the first compression ring  34  with some rigidity and strength, while providing a reduced weight (as compared to a solid structure). In addition the members  102  forming the web structure may be used to remove the apparatus from the pipe  12 . 
       FIG. 33  illustrates the cap  80  in isolation and further illustrates the ports  83  provided thereon. As shown, the ports  83  include an internal stem  83   a  and an external stem  83   b . The internal stem  83   a  may be provided with couplings  84  to facilitate connection to a hose or the like. The external stem  83   b  protrudes into the lumen of the pipe (not shown). 
       FIG. 34  illustrates the apparatus of  FIG. 32  but without the aforementioned bolts so as to better illustrate the various elements of the apparatus.  FIG. 34  also illustrates a further embodiment of the invention wherein a plurality of couplings  104  that are provided on the back plate ring  78  of the back plate  14   a . The couplings  104  are used for assisting the placement of the back plate  14   a  within the pipe  12 . The couplings  104  are adapted to receive centering bolts or pins or the like, which serve to bias the back plate  14   a  against the inner surface of the pipe  12 . In one preferred aspect, the couplings  104  are threaded and are adapted to receive correspondingly threaded bolts (not shown). As would be apparent to persons skilled in the art, the bolts, when provided, would be turned so as to be inserted into the end of one of the couplings  104  that is closer to the center of the ring  78 . The bolt would then be turned so as to extend radially outwardly from the ring  78  and against the inner surface of the pipe. To balance the ring  78 , and therefore the back plate  14   a , a number of couplings  104  may be provided around the circumference of the ring  78 . In one embodiment, the couplings  104  may be provided in pairs. In another embodiment, six couplings  104  may be provided, with one coupling at each of the top and bottom and two pairs on the sides of the ring  78 . It will be understood that the terms “top”, “bottom” and “sides” refer to the ring  78  when positioned within a pipe. It will be understood that a variety of numbers and arrangements of the couplings  78  would be possible while providing the same positioning function. In use, the back plate  14   a  would be positioned within a pipe and the bolts provided in the respective couplings  104  turned so as to allow the back plate  14   a  to stand freely. The remaining elements of the apparatus may then be positioned and the entire apparatus tightened as described above. During the tightening process, the back plate  14   a  may be moved towards the front plate  72 . 
     In the above description, reference has been made to the use of bolts and the like for engaging the apparatus of the invention within a pipe. The use of such bolts is illustrated in  FIGS. 30 to 32 . 
       FIG. 30  illustrates a cross sectional perspective view of an apparatus according to an aspect of the invention. In particular,  FIG. 30  provides another view of the apparatus shown in  FIG. 1 , again without showing the aforementioned first and second bolts, for the purpose of convenience. However,  FIG. 31  illustrates the apparatus of  FIG. 30  as well as the aforementioned first and second bolts, shown at  90  and  92 , respectively. As shown in  FIGS. 31 and 30 , first bolts  90  extend through bolt holes  76  of the front plate  72 , through bolt holes  50  of the inner compression ring  34  (as shown more clearly in  FIGS. 7 to 9 ), and into bolt holes  22  of the back plate  14  (as shown more clearly in  FIGS. 2 to 4 ). As also mentioned above, in one embodiment, the first bolts  90  may be permanently secured to the back plate  14 . Once the components of the apparatus  10  as positioned, nuts  94  are then provided on the ends of the first bolts  90  and tightened so as to urge the components together. 
       FIG. 31  also illustrates the second bolts  92 , which extend through the bolt holes  74  of the front plate and through the bolt holes  70  of the second or outer compression ring  56 . Nuts  96  and  98  are provided on opposite ends of the second bolts  92 . As will be understood, and as described above, tightening of one or both sets of nuts  96 ,  98  urges the second compression ring  56  and the front plate  72  to together. As described above, and as will be understood, the second bolts  92  may be permanently secured to either of the front plate  72  or the second compression ring  56 , thereby avoiding the need for one set of the nuts  96  or  98 . It would be possible, in another embodiment, to have alternating second bolts  92  secured to either the front plate  72  or the second compression ring  56 , in which case, alternating ones of nuts  96  and  98  may be avoided. Although such an arrangement is possible according to the invention, it will be appreciated that it may not be ideal for ease of use. Nevertheless, various other combinations or embodiments will be possible to achieve the same purpose as described above, namely to urge the front plate  72  and second compression ring  56  together. 
     As discussed above, the apparatus of the invention is preferably used for sealing an end of a pipe so that the interior of the pipe can be pressurized such as for testing the integrity of the pipe. In one example, the integrity test is used for testing a weld that may be present on the pipe. Such a weld may serve to connect two pipe segments or to connect the pipe to another apparatus. It will also be understood that the apparatus of the invention may be used on both ends of the same pipe. In this way, two apparatuses of the invention may be used on opposite ends of a pipe segment and the above method conducted on such segment. 
     The above discussion has used geometric terms such as annular, disc, circumference, etc., for ease of reference. However, these terms should not be construed as limiting the invention to any specific shape of nozzle or pipe and various modifications of the apparatus will be apparent to persons skilled in the art to adapt same to any shape or design. 
     Examples 
     Specific embodiments of apparatuses according to the present invention will now be described for the purposes of illustration. It will be understood that the following examples are not intended to limit the invention in any way. 
     Two embodiments of the invention are described below with respect to the use of the apparatus of the invention on a 20″ schedule 120 pipe and a 36″ schedule 80 pipe. Suggested sizes of the respective components of the apparatus are provided in the Table 1 below. 
     
       
         
               
               
             
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Size of component (in inches) 
               
             
          
           
               
                   
                 Apparatus 
                 Apparatus 
               
               
                 Component 
                 for 20″ pipe 
                 for 36″ pipe 
               
               
                   
               
             
          
           
               
                 Back plate (14) (14a, 78, 80) o.d. 
                 16.75 
                 34.75 
               
               
                 Radius of bolt holes (22) on back plate 
                 14.25 
                 30.75 
               
               
                 (14) 
               
               
                 Inner compression ring (34) max. o.d. 
                 16.67 
                 34.75 
               
               
                 Radius of outer bolt holes (50) on inner 
                 14.25 
                 30.75 
               
               
                 compression ring (34) 
               
               
                 Radius of inner bolt holes (52) on inner 
                 9.25 
                 27.5 
               
               
                 compression ring (34) 
               
               
                 Inner gripper ring (36) o.d. 
                 17.0 
                 35.0 
               
               
                 Inner gripper ring (36) min. i.d. 
                 15.5 
                 33.5 
               
               
                 Outer compression ring (56) o.d. 
                 28.25 
                 44.25 
               
               
                 Outer compression ring (56) min. i.d. 
                 20.5 
                 36.5 
               
               
                 Radius of bolt holes (70) on outer com- 
                 23.75 
                 39.5 
               
               
                 pression ring (56) 
               
               
                 Outer gripper ring (58) i.d. 
                 20.0 
                 36.0 
               
               
                 Outer gripper ring (58) max. o.d. 
                 21.75 
                 37.75 
               
               
                 Front plate (72) o.d. 
                 27.25 
                 44.25 
               
               
                 Front plate (72) i.d. 
                 10.417 
               
               
                 Radius of outer bolt holes (74) on front 
                 23.75 
                 39.5 
               
               
                 plate (72) 
               
               
                 Radius of inner bolt holes (76) on front 
                 14.25 
                 30.75 
               
               
                 plate (72) 
               
               
                   
               
             
          
         
       
     
     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the purpose and scope of the invention as outlined in the claims appended hereto. Any examples provided herein are included solely for the purpose of illustrating the invention and are not intended to limit the invention in any way. Any drawings provided herein are solely for the purpose of illustrating various aspects of the invention and are not intended to be drawn to scale or to limit the invention in any way. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.