Abstract:
A plugging device for closing an opening defined by an end of a pipe with sealant comprises a cap, an extension, an inner seal, a guide, and at least one stop. The cap has an inner surface which defines a chamber adapted for retaining the sealant. The chamber is dimensioned slightly larger than the end so as to receive the end. The chamber and end define a gap therebetween. The extension has a distal end and is attached to the inner surface opposite the distal end. The inner seal is attached to the extension and sized larger than the opening. The guide is positioned forward of the inner seal and attached to the distal end. The guide is also dimensioned to be inserted into the opening. The stop is attached to the extender, and when the stop is disposed in the pipe, the stop is movable with respect to the conduit in one direction and also prevents misalignment of the cap with the pipe. A handle can also be included to allow the cap to be positioned robotically.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     This invention was made with government support under contract DE-AC05-960R22464, awarded by the United States Department of Energy to Lockheed Martin Energy Research Corporation, and the United States Government has certain rights in this invention. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATION 
     Not Applicable 
     FIELD OF THE INVENTION 
     This invention relates to plugs for pipes. More specifically, the invention relates to a robotically guidable pipe plug for sealing a pipe. 
     BACKGROUND OF THE INVENTION 
     Pipes are often required to be capped or plugged when the need for the pipe is no longer required. The goal of the capping or plugging is to prevent the contents of the pipe from exiting the pipe and/or to prevent material outside the pipe from entering the pipe. Occasionally, the cap or plug is required to be permanent. As such, the cap or plug should provide a perfect seal. One situation, for example, which may require a permanent cap or plug is when liquid and/or solid hazardous waste is cleaned from storage tanks. 
     As the tanks are being cleaned, it is desirable to isolate those pipes that may discharge material back into the tanks. Otherwise a portion of a tank that was cleaned may need to be recleaned if additional material is introduced into the tank. Additionally, because hazardous waste that combines with nonhazardous waste typically makes the non-hazardous waste hazardous, preventing the introduction of non-hazardous waste into the tank decreases the total amount of hazardous waste to be cleaned. As such, preventing the introduction of other material into the storage tank is particularly important when cleaning hazardous material from a storage tank. 
     Although plugging a pipe is a relatively simple operation when the pipe is accessible and is in a clean environment, plugging a pipe in a restricted access environment containing hazardous waste is more complicated. Hazardous waste, and in particular radioactive hazardous waste, can prevent a human being from directly performing the operation. In such a situation, a substitute for a human, for example a robotic arm, is preferably used to perform the operation. However, such a substitute, like a robotic arm, currently lack the dexterity of a human hand. Additionally, the substitute would likely be guided by video camera instead of human sight, and a video camera provides poor depth perception for an operator. As such, equipment to plug a pipe for use by a human will be difficult for an operation in which a human cannot directly perform the operation. 
     Another problem associated with plugging pipes is that the pipes to be plugged can have different angular orientations. For example, the pipe could be horizontal, vertical, or in a position in between. Thus, depending upon the orientation, different forces act upon the cap and these forces can change how the pipe is plugged and the method of plugging the pipe. For example, with a vertically oriented pipe, unless the cap is fixed upon attachment, the cap must be prevented from falling off the pipe from the force of gravity. Thus an additional piece of equipment may be needed to hold the cap in place until the cap is permanently fixed to the pipe. 
     Still another problem associated with the plugging of a pipe is that the pipe may not be round and/or clean. For example, depending upon the material flowing through the pipe and the age of the pipe, material may have accumulated within the pipe. The pipe could also be partially corroded. As such, both the exterior and interior of the pipe may not be perfectly clean. 
     Many reasons also exist for why the pipe may not be perfectly round. For example, wear and tear on the pipe may cause the pipe to go out of round. One particular example is when the pipe is cut to be capped. In such a situation, the cutting of the pipe may cause the pipe to go out of round or create burrs on the pipe. Additionally, the aforementioned accumulations and corrosion may also cause the pipe to go out of round. As such, a pipe that is out of round or a pipe that is not clean may not be efficiently capped using current methods. 
     One current method of plugging a pipe is to fill the pipe with grout. Before filling, a second plug must be inserted into the pipe to block the flow of grout to all open sections of the pipe. A high pressure pump typically pumps the grout into the pipe. A pipe is then typically filled with approximately 20-30 feet of grout. Several problems are associated with the use of grout in a storage tank containing highly hazardous material in into which only a robot can enter. One such problem is that the grout cannot be easily placed within the pipe because of. limitations inherent with the use of a robotic arm. As previously stated, the robotic arm cannot be manipulated as dexterously as a human hand and this is exacerbated by use of the video camera to guide the movement of the robotic arm. Also, the hose system supplying the grout must be flushed immediately after use to prevent clogging the equipment. However, performing this operation inside the tank will increase the amount of hazardous waste to be cleaned. Additionally, tests have shown that grout does not provide a permanent seal over time when the grout is constantly subjected to water. Thus, not only is the introduction of the grout inside the pipe problematic, the grout will not necessarily provide a permanent seal. 
     Another tool that can be used to cap a pipe is to use a commercially available pipe plug. However, this tool requires that the pipe be perfectly round and clean before application. Otherwise, the tool will not necessarily plug the pipe. As such, this tool may not be appropriate for pipes that are out of round and/or not clean and cannot be placed into round and/or cleaned because of where the pipe is located. Additionally. this tool is only intended to be used temporarily, and thus would likely not provide a permanent seal. 
     This tool also requires that a nut be tightened as part of the installation process. Tightening of a nut is a process not easily accomplished by a robotic arm that is not specifically adapted for tightening of a nut. Also, even if the robotic arm is specifically adapted to tightening the nut, this adaptation would hamper the robotic arms ability to deliver the plug into the pipe. As such, two robotic arms would likely be necessary to apply this tool. Another problem associated with this tool is that it must be very precisely aligned within the pipe, and the required alignment is difficult to perform robotically. 
     Other methods of capping a pipe include welding a cap onto the pipe or applying a threaded cap onto a threaded pipe. Although relatively simple to perform when the pipe can be easily accessed, these methods are very difficult to perform robotically with a video camera. Additionally, if a threaded cap is to be used and the pipe does not have threads, for example after the pipe has been cut, creating the threads on the pipe robotically is also very difficult. 
     As such, the currently available tools are impracticable with use in a hazardous waste environment, particularly one in which a human being can not directly work. Also, the currently available tools do not permanently and adequately seal pipes that are not clean and are not perfectly round. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a device for sealing one opening in a pipe that only requires one robotic arm for installation. 
     It is another object of the invention to provide a device for sealing one opening in a pipe that is effective regardless of the orientation of the pipe. 
     It is yet another object of the invention to provide a device for sealing one opening in a pipe that is not perfectly round or clean. 
     It is a further object of the invention to provide a device that can be used to seal one opening in a pipe in a hazardous waste environment. 
     It is still another object of the invention is to provide advices that will permanently seal one opening in a pipe upon use. 
     These and other objects of the invention are achieved by the subject device which comprises a cap, an extension, an inner seal, a guide, and at least one stop. The cap has an inner surface which defines a chamber adapted for retaining sealant. The chamber is dimensioned slightly larger than the end of the pipe to be sealed so as to receive the end. The chamber and end define a gap therebetween. The extension has a distal end and is attached to the inner surface opposite the distal end. The inner seal is attached to the extension and sized larger than the opening. The guide is positioned forward of the inner seal and attached to the distal end. The guide is also dimensioned to be inserted into the opening. The stop is attached to the extender, and when the stop is disposed in the pipe, the stop is movable with respect to the conduit in one direction and also prevents misalignment of the cap with the pipe. A handle can also be included to allow the cap to be positioned robotically. 
     In a second embodiment of the invention, the extender and cap define a cap conduit extending from the cap and through the extender. The cap conduit can communicate material from inside the pipe to outside the pipe. The end of the cap conduit adjacent to the cap can also include a valve. This particular is particularly useful in placing a valve upon an end of a pipe that would not otherwise accept a valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There are shown in the drawings embodiments of the invention that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein: 
     FIG. 1 is a side elevation of a pipe plug including a handle. 
     FIG. 2 is a cross-section of a pipe plug viewed from the side. 
     FIG. 3 is a side elevation of an assembly of an extender, guide, seal, and two stops. 
     FIG. 4 is a side elevation of an extender, guide, seal, and one stop. 
     FIG. 5A is a plan view of a stop having six arms. 
     FIG. 5B is a side elevation of the stop in FIG.  5 A. 
     FIG. 6A is a plan view of a stop having three arms. 
     FIG. 6B is a side elevation of the stop in FIG.  6 A. 
     FIG. 7A is a plan view of a stop having two arms. 
     FIG. 7B is a side elevation of the stop in FIG.  7 A. 
     FIG. 8 is a cross-section of a second embodiment of a pipe plug having a cap conduit viewed from the side. 
     FIG. 9 is a cross-section of the pipe plug in FIG. 2 with a pipe partially inserted into the pipe plug. 
     FIG. 10 is a cross-section of the pipe plug in FIG. 2 with a pipe fully inserted into the pipe plug. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, a device for plugging an opening in the end of a pipe, according to the present invention, is illustrated. The pipe plug  10  comprises a cap  12 , a handle  14 , an extender  16 , a seal  20 , and a stop  22 . In use, the cap  12  is dimensioned to fit over the outside diameter of an end of a pipe (shown in FIGS.  9  and  10 ). Sealant (shown in FIGS. 9 and 10) inside the cap  12  is prevented from entering into the pipe by the seal  20 . Instead, the sealant enters a gap between the outside diameter of the pipe and the inside wall  26 . Once the sealant has set, the sealant and cap  12  act as a barrier to prevent any material inside the pipe from exiting the pipe or any material outside the pipe from entering the pipe. A more detailed discussion of the plugging of the pipe by the pipe plug  10  will follow later in the specification. 
     The cap  12  preferably serves two main functions. First, the cap  12  defines a cavity  28  for holding the sealant, and second, the cap  12  substantially surrounds the end of the pipe to prevent any material from entering or exiting the pipe. The inside diameter of the cap  12  should be slightly larger than the outside diameter of the pipe to be plugged. The difference in diameters provides a gap between the cap  12  and pipe into which the sealant can flow upon plugging of the pipe. Also, a larger cap diameter allows the cap  12  to be positioned over the end of the pipe without any interference. Interference is caused, for example, by the end of the pipe being out of round, the end of the pipe having being covered with foreign material, or the end of the pipe having burrs, for example caused by the pipe being cut at that location. For all of these reasons, and others, the inside diameter of the cap  12  is preferably larger than the outside diameter of the pipe. 
     However, providing a too large of difference between the two diameters can be detrimental to the ability of the pipe plug  10  to plug the pipe. As the difference in diameters increases, the potential also increases that the sealant will not fill the gap between the pipe and the cap  12 . In such a situation, the cap  12  and sealant may not provide a proper barrier, and thus, the pipe will not be completely plugged. Thus, the difference in diameters should be determined by balancing the ability of the cap  12  to easily fit over the end of the pipe and preventing too large of a gap between the pipe and cap  12  so as to conserve sealant. 
     The chamber  28  should have a depth so as to be capable of completely receiving the end of the pipe. Additionally, a longer length of the pipe is preferably inserted into the chamber  28 . Having the cavity  28  dimensioned to allow for insertion of a longer length of pipe allows for a longer gap between the inside surface  26  of the cap  12  and outside surface of the pipe and the cap  12  to cover a greater portion of the outside surface of the pipe. A longer gap allows the sealant to fill a greater space, and thus, a greater amount of sealant acts as a barrier between material inside the pipe and material outside the pipe. Also, by covering a greater portion of the outside surface of the pipe, the cap  12  may cover other openings formed in the pipe. These other openings may have been formed in the pipe for example, by corrosion or by physical damage to the pipe. 
     The cap  12  should be constructed from a material that is resistive to a corrosive environment and provide structural strength for the pipe plug  10 . Material outside the cap  12  and/or inside the pipe may be corrosive. Thus, to prevent this material from exiting and/or entering the pipe, the cap  12  should be capable of resisting a corrosive attack. Many materials are capable of such resistance and all are acceptable for this purpose. However, the presently preferred material for construction of the cap  12  is stainless steel. Stainless steel provides both good corrosion resistance and structural strength. 
     The extender  16  functions to at least support the seal  20  away from the bottom of the chamber  28 . The extender can also function to support the guide  18 , stops  22 , and the handle  14 . 
     The extender  16  is preferably positioned so as to not interfere with the insertion of the pipe into the chamber  28 . As such, the extender preferably extends outward from a substantially central position at the bottom of the chamber  28  towards the opening  30  of the chamber  28 . 
     The extender  16  is attached to the cap  12  in a manner so as to prevent any material from entering or exiting the pipe because of the means of attachment. An exception is an alternative embodiment of the invention which is discussed with regard to FIG.  8 . Many types of attachment are acceptable for the purpose of preventing any material from entering or exiting the pipe because of the means of attachment, and this invention is not limited as limited as to any of them. For example, the extender  16  and cap  12  can be formed integrally, such as in a casting. Alternatively, the extender  16  could be welded to the cap  12 . Still another illustrative example is the extender  16  being threaded into the cap  12 . 
     So long as the extender  16  is contained with the cap  12  and pipe, the extender  16  does not need to be constructed from a corrosion resistant material. However, in the situation where the extender  16  is attached to the cap  12  so as to pass completely through the cap  12 , the extender  16  should be constructed from a corrosion resistant material similar to that used for the cap  12 . The extender  16  is not otherwise limited as to the material from which the extender  16  can be constructed. 
     The seal  20  acts to prevent the sealant inside the chamber  28  from entering into the pipe. Many types of seals  20  are so capable and the invention is not limited as to any of them. In a presently preferred embodiment of the invention, the seal  20  is sized to be slightly larger than the inside dimensions of the pipe. The seal  20  is also preferably flexible at least around its periphery. Thus, insertion of the seal  20  into the inside of the pipe will deform the flexible periphery to conform with the inside dimensions of the pipe. The pressing of the periphery against the inside of the pipe will form a barrier that acts to prevent the sealant from entering the pipe. 
     The seal  20  is not limited as to the type of material from which it is constructed. Depending on the type of seal  20  used, different materials may be required. However, in the preferred embodiment, the outside periphery of the seal  20  is constructed from a flexible material which deforms to match the inside dimensions of the pipe and still provide a barrier that acts to prevent the sealant from entering the pipe. As the seal  20  will be contained within the cap  12 , the material of the seal  20  need only remain intact until the sealant has set. The seal  20  may be directly connected to the extender  16 . Alternatively, the seal  20  can be directly connected to either the guide  18  or the stop  22 . In either situation, any type of attachment is possible. For example, the seal  20  could be welded to the extender  16 , guide  18 , or stop  22 , or the seal  20  could be formed integrally with the extender  16 , guide  18 , or stop  22 . Alternatively, the seal  20  can be selectively removable. One example of which is the seal  20  having an opening through which the extender  16  can be positioned. The seal  20  could be prevented from movement in one direction by a stopper, for example a nut or a shoulder on the extender  16 . In a second direction, the seal  20  could be prevented from movement by a removable stopper, for example a nut. 
     In a preferred embodiment, the seal  20  is selectively removable from the extender  16 . The seal is prevented from movement in one direction by a nut  32 . The seal  20  is prevented from movement in a second direction by the guide  18 . The seal  20  is preferably selectively removable to allow seals  20  with different sizes to be placed onto a single cap  12 . This allows one size cap  12  to be used with pipes having the same outside dimensions but differing inside dimensions. 
     So long as the position of the seal  20  does not restrict the amount of sealant that can initially be placed within the chamber  28 , the seal  20  can be located anywhere within the chamber  28 . Preferably, the seal  20  is located adjacent the opening  30  to maximize the amount of sealant that can be introduced into the chamber  28 . 
     At a minimum, the pipe plug  10  consists of the cap  12 , the extender  16 , and the seal  20 . Upon installation, this combination will prevent material from exiting or entering the pipe via the opening in the end of the pipe. However, this combination is likely to be more difficult to install robotically than by human hand. For this reason, the presently preferred embodiment also includes a guide  18  for guiding the pipe plug  10  onto the pipe and/or includes a stop  22  for preventing removal of the pipe plug  10  and to help center the pipe plug  10  on the pipe. The most preferred embodiment includes both the guide  19  and stop  18 . Additionally, if the pipe plug  10  is to be positioned onto the pipe using robotics, a handle  14  which can be robotically gripped is also included as part of the most preferred embodiment. 
     The handle  14  functions to enable the pipe plug  10  to be more easily gripped. Many types of handles  14  can be used with this invention and the type preferably used depends upon the manner in which the pipe plug  10  is to be gripped. In the presently preferred embodiment, the pipe plug  10  will be handled robotically, and thus requires a handle  14  that can be gripped robotically. As many types of robotic grippers are known in the art of robotics, the type of handle  14  will depend upon the particular type of robotic gripper used for this application. In a presently preferred embodiment, as shown in FIG. 1, the extender  16  extends through the cap  12  and also acts as the handle  14 . 
     The guide  18  functions to guide the pipe plug  10  onto the pipe by first entering into the opening in the end of the pipe and then guiding the walls of the pipe towards the opening  30  of the chamber  28 . Many different shapes, for example spherical or pyramidal, have been used to guide an object into an opening, and all are acceptable as a shape for the guide  18 . However, the preferred shape for the guide is a conical shape that tapers to a spherical tip  34 . Cones otherwise taper to a point. However, a pointed tip is more likely to cause damage to an object than a spherical tip  34  if the tip is accidentally forced against the object. 
     By tapering outward from the tip  34 , the conical shape of the guide  18  acts to center the walls of the pipe within the opening  30  as the pipe is positioned closer to the opening  30 . Also, the seal  20  preferably continues the outward taper of the guide  18  so as to further center the pipe within the opening  30 . 
     The maximum outside transverse dimension of the guide  18  cannot be any larger than the inside dimensions of the pipe. Otherwise the guide  18  will not completely enter the pipe. Preferably, the maximum outside transverse dimension of the guide  18  is smaller by 75-80% than the inside dimension of the pipe to allow for possible irregularity in the inside dimension of the pipe. 
     The guide  18  is located so as to extend beyond the opening  30  of the chamber  28 . By locating the guide  18  beyond the opening  30 , the guide  18  can begin positioning the pipe towards the opening  30  before the pipe reaches the opening  30 . 
     The guide  18  may be directly connected to the extender  16 . Alternatively, the guide  18  can be directly connected to either the seal  20  or the stop  22 . In either situation, any type of attachment is possible. For example, the guide  18  could be welded to the extender  16 , seal  20 , or stop  22 , or the guide  18  could be formed integrally with the extender  16 , seal  20 , or stop  22 . Alternatively, the guide  18  can be selectively removable. In a presently preferred embodiment the extender  16  is threaded into the guide  18 . Thus, the guide  18  can be removed from the extender  16  by unthreading the guide  18 . 
     The stop  22  can serve many functions. One function of the stop  22  is to prevent the pipe plug  10  from being removed from the pipe after the pipe plug  10  is positioned onto the pipe. This is particularly important during the time when the sealant has not set and movement of the pipe plug  10  is still possible with any movement possibly disrupting the barrier being formed by the pipe plug  10 . Another function of the stop  22  is to align the pipe plug  10  with the pipe. Misalignment of the pipe plug  10  and pipe could lead to an incomplete barrier between the outside and the inside of the pipe. 
     The need for the stop  22  to prevent the pipe plug  10  from being removed from the pipe is typically most pronounced when the pipe is oriented vertically with respect to gravity. In such a situation, the weight of the pipe plug  10  will tend to pull the pipe plug  10  away from the pipe. With horizontally oriented pipes, a greater possibility of misalignment between the pipe and pipe plug  10  can occur because the weight of the pipe plug  10  is not typically balanced over the support points between the pipe and pipe plug  10 . This imbalance of weight causes a torque to be exerted on the pipe plug  10  with this torque possibly causing misalignment. 
     As illustrated in FIGS. 3 and 4. One or more stops  22  can be used. Multiple stops  22  are preferably used when the extender  16  reaches a length in which the weight of the pipe plug  10  is not balanced in a horizontally oriented pipe. The use of two or more stops  22  prevents either end of the extender  16  from being displaced towards the inner walls of the pipe, and therefore prevents misalignment of the pipe plug  10  with the pipe. Also, multiple stops  22  can be used to provide additional gripping power to prevent the pipe plug  10  from being removed from the pipe. 
     If one stop  22  is to be used, the stop  22  is preferably located adjacent the seal  20 . As the stop  22  acts to prevent the extender  16  from being displaced towards the inner walls of the pipe, placing the stop  22  adjacent the seal  20  prevents the seal  20  from being positioned too close to the inner walls of the Otherwise, if the seal  20  is positioned too close to one wall, the seal  20  may not provide as an effective barrier for the other side of the wall. 
     As illustrated in FIGS.  5 (A &amp; B),  6 (A &amp; B), and  7 (A &amp; B), the stop  22  can have several different preferable shapes. However, each stop  22  preferably has at least two arms  24  are angled away from the direction in which the pipe plug  10  is to be inserted into the pipe. In a preferred embodiment, the arms are angled approximately 30 degrees from a transverse plane of the pipe. Each stop  22  is dimensioned so as to be slightly larger than the inside dimensions of the opening at the end of the pipe. 
     Upon insertion into opening of the pipe, these arms  24  act as flexible barbs. As such, movement of the pipe plug  10  into the pipe flexes the arms  24  inward to decrease the dimension of the stop  22 . This decrease in dimension lessens the amount of friction between the arms  24  and pipe and enables the stop  22  to be inserted into the opening of the pipe. However, movement of the pipe plug  20  out of the pipe flexes the arms  24  outward to increase the dimension of the stop  22 . This increase in dimension increases the amount of friction between the arms  24  and the pipe and prevents the stop  22  from being removed from the pipe. 
     The arms  24  of the stop  22  may be directly connected to the extender  16 . Alternatively, the arms  24  can be directly connected to either the seal  20  or the guide  18 . In either situation, any type of attachment is possible. For example, the arms  24  of the stop  22  could be welded to the extender  16 , seal  20 , or guide  18  or the arms  24  could be formed integrally with the extender  16 , seal  20 , or guide  18 . Alternatively, the stop  22  can be selectively removable. 
     In a presently preferred embodiment the arms  24  are connected to a center portion  34  of the stop  22  through which the extender  16  can pass. The stop  22  is held in position by stoppers on either side of the stop  22 . For example, these stoppers can be removable nuts  32  or the guide  18 . In a preferred embodiment, to remove the stop  22  from the extender  16 , a stopper on at least one side of the stop  22  must first be removed. The stop  22  can then be removed from the extender  16 . The stop  22  is preferably selectively removable to allow stops  22  with different sizes to be placed onto a single cap  12 . This allows one size pipe cap  12  to be used with pipes having the same outside dimensions but differing inside dimensions. 
     Although the stop  22  comprises at least two arms  24 , more arms  24  are presently preferable. The arms  24  are preferably positioned symmetrically with respect to one another. Otherwise, a stop  22  with unsymmetrically oriented arms  24  could cause the pipe plug  10  to be misaligned with the pipe. Arms  24  are preferable as an alternative to a single circumferential section because the arms  24  can be easily bent in both directions so as to allow entry in one direction and to prevent withdrawal in the other direction. A single circumferential section is less likely to be bent in either direction. 
     A two-armed stop  22  is illustrated in FIGS.  7 (A &amp; B). A stop  22  with two arms is best utilized when the pipe plug  10  is to be inserted into a vertically oriented pipe. In such a situation, the primary function of the stop  22  is to prevent the pipe plug  10  from being removed from the pipe. Although the two-armed stop  22  can be used in a horizontally oriented pipe to keep the pipe plug  10  from being misaligned with the pipe, misalignment is less likely with a stop  22  having more than two arms  24 . The presently preferred amount of arms  24  is six. This embodiment is illustrated in FIGS.  5 (A &amp; B). The six arms  24  of this stop  22  enable the stop  22  to effectively prevent the pipe plug  10  from being removed from the pipe and prevent misalignment of the pipe plug  10  and pipe. 
     The stop  22  should be constructed from material that is stiff enough to support the weight of the pipe plug so as to prevent misalignment of the pipe plug  10  yet be flexible enough to decrease in size during entry. As the stop  22  will be completely enclosed by the pipe and pipe plug, the stop  22  is not required to be corrosion resistant. However, the stop should be constructed from a material that will not degrade before the sealant has set. The presently preferred stop  22  is constructed from thin spring steel. This material provides a combination of strength and flexibility presently preferred for this invention. It is noted that spring steel is only one example of many types of material that are acceptable for use with this invention. 
     An alternative embodiment of the invention is illustrated in FIG.  8 . The pipe plug  10   a  is similar to the previously mentioned pipe plug  10 , with the addition of one feature. This feature is a cap conduit  38  through the extender  16  and cap  12 . This cap conduit  38  allows material outside the pipe to enter the pipe and material inside the pipe to exit the pipe. This particular feature is useful for placing a valve (not shown) on the end of the pipe without the need to form threads on the pipe, which for example, are typically required to place a valve on the end of a pipe. For example, the valve could be positioned at the end of the channel  38  adjacent the cap  12 . 
     FIGS. 9 and 10 illustrate the plugging of a pipe  40  with the pipe plug  10 . Specifically, FIG. 9 illustrates the pipe  40  positioned within the chamber  28  and slightly above the sealant  42 . FIG. 10 illustrates the pipe  40  completely inserted within the chamber  28  and sealant  42 . As illustrated in FIG. 10, with the presently preferred stop  22 , the arms  24  are bent by the passage of the pipe  40  into the chamber  28 . The resiliency of the arms  24  presses against the pipe  40  and prevents the pipe  40  from being withdrawn from the chamber  28 . Also, when the pipe  40  is inserted into the chamber  28 , the pipe  40  displaces a volume of the sealant  42 . Because the seal  20  prevents the sealant  42  from passing past the seal  20 , the sealant flows into the gap between the inner wall of the cap  12  and the outer wall of the pipe  40 . This gap provides a hermetic seal between the cap  12  and pipe  40 . 
     Any sealant  42  capable of providing a hermetic seal between the cap  12  and pipe  40  can be used with this invention. However, in applications in which the cap  12  may be tilted during the application of the cap  12  onto the pipe  40 , the sealant  42  preferably has a sufficiently low viscosity to prevent the sealant  42  from flowing out of the cap  12 . 
     This feature is particularly important when the pipe plug  10  is to be maneuvered robotically inside a storage tank. In such a situation, a cap  12  containing the sealant  42  may be tilted or positioned upside down for a period of time. Also, because robotically maneuvering the cap  12  through the storage tank onto the pipe  40  takes time, the sealant  42  preferably has a long working time, most preferably approximately four hours. Otherwise, if the working time is shorter, the sealant  42  may have already begun to harden and thus be incapable of bonding the cap  12  to the pipe  40  by the time the pipe plug  10  is maneuvered into position 
     In a situation in which the pipe plug  10  is to be used in a highly radioactive environment, the sealant  42  should also be resistant to radiation. Also, because the sealant  42  is preferably placed in the cap  12  outside of the radioactive environment to reduce radiation exposure to the person preparing the pipe plug  10 , the sealant  42  preferably has a working time that allows for the cap  12  to be positioned onto the pipe  40  before setting. 
     Although any sealant  42  that includes the preferred characteristics is acceptable for use with this invention, the presently preferred sealant  42  is a two part (hardener and resin) epoxy adhesive produced by Devcon, an Illinois Tool Works Company located in Danvers, Maryland. This particular epoxy is resistant to radiation at doses up to approximately 5×10 8  Rad. With a contact radiation source producing 100 Rad/hour, the epoxy would have an expected life of approximately 570 years. This epoxy also includes a preferred characteristic of not being a hazardous material upon mixing. 
     It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. 
     The invention can take other specific forms without departing from the spirit or essential attributes thereof for an indication of the scope of the invention.