Patent Document

BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to improvements for a plug used to form a seal for tubes, pipes and similar conduits which transport steam, liquid or gases under pressure.  
         [0002]     An earlier version of this type of plug commercially exploited by the present Applicant is disclosed in U.S. Pat. Nos. 4,653,540, 5,289,851 and 5,560,394, the specifications of which are hereby incorporated by reference. The plug disclosed in U.S. Pat. No. 4,653,540 comprises a hollow housing member which has at one end a relatively large open bore surrounded by a thin wall, and a relatively smaller threaded bore which communicates with the larger bore. An insert member is provided which, in use, is threaded into the smaller bore thereby causing a tapered member, which may be formed on the insert member, to engage the open end of the large bore causing it to expand and bear against the wall of a heat exchanger tube into which the heat exchanger tube plug has been inserted.  
         [0003]     During use, the housing member is prevented from rotating relative to the heat exchanger tube by means of an eccentric assembly which is mounted on the end of the housing member. At the other end, the insert member has a cylindrical portion and a centrally disposed, integrally formed nut portion. The nut is proportioned and shaped to be grasped by a wrench for screwing the insert member into the housing member. The nut must be turned with a specific torque in order to assure a tight seal between the insert member and the tube. If excessive torque is applied, then the tube being sealed might be split, the threaded connection might strip or the drive surface could be damaged. The disclosure also suggests that instead of the projecting nut portion, a hexagonal recess may be formed in the end of the cylindrical portion for insertion of a hex wrench or similar tool.  
         [0004]     Early on during manufacture of the plug defined in U.S. Pat. No. 4,653,540, the plugs had a machined male hex that would accommodate a {fraction (11/32)} inch socket. This, however, proved unsatisfactory because the sockets split and could not be turned down to a diameter in order to fit in any tube smaller than {fraction (1/2)} inch. This would be necessary when the plug is recessed within the end of a tube to be sealed. The next design evolution entailed broaching a {fraction (1/4)} inch female square drive in plugs from 460 inches to 0.610 inches in diameter and a {fraction (3/8)} inch square drive in all plugs 0.620 inches and larger.  
         [0005]     U.S. Pat. No. 5,289,851 describes a tube plug that can be provided in dimensions down to 0.420 inches, yet which permits installation torque values of up to 700 inch pounds. In this improved plug, the insert member as disclosed in U.S. Pat. No. 4,653,540, has been replaced with a T45 Torx® socket head screw combined with a separately machined cone having an internal passage threaded to match the threads of the screw. A T45 Torx® drive can be torqued to 764 inch pounds before failure which permits a recommended installation value of up to 700 inch pounds to be utilized. It also allows over torquing to occur.  
         [0006]     In both U.S. Pat. Nos. 4,653,540 and 5,289,851 a tool is required to engage the insert member, and specifically, the recess portion or nut of the insert member, in order to screw the insert member into the housing member. Typically, the insert member includes a recess, such as a T45 Torx® socket head recess or a hexagon socket head recess, to engage the tool. However, such an arrangement creates a fair amount of slippage which can complicate the process of screwing the insert member into the housing member, especially in light of the high torsional forces that are being used. Thus, in order to reduce slippage between the tool and the recess of the insert member, an adhesive, such as a drive holding compound, may be applied to the recess or the end of the tool that engages the recess. Also, a specific amount of torque must be applied to the insert member which requires a special tool for measuring torque, which is sometimes difficult to use, particularly in situations where the portion of the tube to be sealed is in a somewhat inaccessible location, or where the lighting is poor.  
         [0007]     It would therefore be an improvement in this art if a tube plug having an insert member were provided with a drive system that did not require a separate tool for measuring or applying a desired torque.  
       SUMMARY OF THE INVENTION  
       [0008]     In one aspect of the invention, a tube plug kit is provided comprising a tube plug having a housing member and a locking member, the housing member having a longitudinal bore comprising a smooth portion communicating with a threaded portion, the locking member being mounted on the housing member. An insert member having a first threaded end portion is received within the threaded portion of the bore. An enlarged portion of the insert member is positioned to be drawn within the smooth portion of the longitudinal bore in response to rotation of the insert member in the longitudinal bore. A drive portion on the insert is configured to receive a torque applying tool in a rotationally driving manner. Also, a torque limiting region is located in the insert member to limit an amount of torque the drive portion can transmit to the first threaded end portion.  
         [0009]     The torque limiting region could comprise a weakened portion such as by providing a portion of the insert with a reduced diameter or a frangible joint between the first threaded end portion and the drive portion.  
         [0010]     In another aspect of the invention, a drive system is provided for an insert member to be threadingly engaged with a tube plug, the drive system comprising an insert member having a first threaded end portion to be received within the tube plug and a drive portion configured to receive a torque applying tool in a rotationally driving manner. The system also includes a torque limiting region located in the insert member to limit an amount of torque the drive portion can transmit to the first threaded end portion.  
         [0011]     In a specific embodiment of the invention, a tube plug kit is provided comprising a tube plug having a housing member and a locking member. The housing member has a longitudinal bore comprising a smooth portion communicating with a threaded portion, and the locking member is mounted on the housing member. An insert member is provided having a first threaded end portion received within the threaded portion of the bore, an enlarged portion positioned to be drawn within the smooth portion of the longitudinal bore in response to rotation of the insert member in the longitudinal bore and a cylindrical, extending drive portion comprising an externally threaded region to receive a torque applying tool in a rotationally driving manner. A torque limiting region comprising a reduced diameter portion is located in the insert member to limit an amount of torque the drive portion can transmit to the first threaded end portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like or corresponding parts throughout the several views and wherein:  
         [0013]      FIG. 1  is a cross sectional view of a heat exchanger tube plug made in accordance with the present invention, in accordance with one embodiment;  
         [0014]      FIG. 2  is a cross sectional view of the apparatus of  FIG. 1 , being inserted into a recessed location;  
         [0015]      FIG. 3  is an isolated elevated side view of the insert of  FIG. 1 , in accordance with one embodiment;  
         [0016]      FIG. 4  is an isolated elevated side view of the insert of  FIG. 1 , in accordance with another embodiment, along with a driving tool;  
         [0017]      FIG. 5  is an isolated elevated side view of the insert of  FIG. 1 , in accordance with another embodiment;  
         [0018]      FIG. 6  is an isolated elevated side view of the insert of  FIG. 1 , in accordance with another embodiment;  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     In  FIG. 1 a  boiler tube plug  10  is shown which is made in accordance with the present invention. The plug  10  comprises a hollow housing member  12  and an insert member  14 . The housing member  12  has a cylindrical body  16 , the rear portion of which is formed with a large open bore  18 . The bore  18  is surrounded by relatively thin wall  20 , the end portion  22  of which will expand outwardly to provide a seal for a boiler tube  24  as is shown in  FIG. 2 , when the insert member  14  is screwed into the housing member  12 . The housing member  12  also includes a relatively smaller internally threaded cylindrical bore  28  which communicates with the large bore  18 .  
         [0020]     At its front end  30 , the housing member  12  is provided with a locking member  32  which serves to lock the housing member tightly within the boiler tube  24 , as is shown in  FIG. 2 , so that the insert member  14  can be screwed into the housing member  12 . In one embodiment, the locking member  32  includes an eccentric assembly that comprises a cylindrical post  34  which projects axially from the front end  30  of the housing member  12 , a ring member  36  which is mounted eccentrically on the post and is rotatable thereon. A description of such a tube plug can be found in U.S. Pat. Nos. 5,560,394; 5,289,851; and 4,653,540, the disclosures of which are incorporated herein by reference.  
         [0021]     The outer surface of the housing member  12  includes a plurality of annular grooves  50  adjacent to the open bore  18  of the housing member to enhance the sealing characteristics of the plug as described below.  
         [0022]     The insert member  14 , in the embodiment shown in  FIGS. 1-3  is comprised of a first threaded end  52  and an enlarged substantially cylindrical extension  56  having a second threaded end  54 . In this embodiment, the first threaded end  52  is inserted into the housing member and the second threaded end  54  receives an internally threaded tool (shown in  FIG. 4 ) which drivingly engages with the second end to turn the insert member  14  by applying a torque to the insert member.  
         [0023]     In the embodiment shown in  FIGS. 1-3 , the cylindrical extension  56  is provided with a torque limiting portion  58  in the form of a reduced diameter area which is designed to withstand only a prescribed torque before it shears off. The diameter and material of the reduced diameter portion is chosen to transmit up to the torque desired for insertion of the insert member  14  into the tube plug  10  by the correct amount. Excessive torque cannot be applied in that the reduced diameter portion, which comprises a torque limiting portion, will fail, and further transmission of torque will be terminated.  
         [0024]     The insert member  14 A, in the embodiment shown in  FIG. 4 , differs in the manner in which the torque limiting portion  58 A is constructed. In this embodiment, the torque limiting portion  58 A is formed by a reduced diameter portion which is achieved by a narrowing of the diameter in the cylindrical extension  56 A, but there is not an abrupt radial decrease in the diameter. Rather, the diameter decreases gradually to a smallest diameter. Again, the diameter and material of the reduced diameter portion  58 A is chosen to transmit up to the torque desired for insertion of the insert member  14  into the tube plug  10  by the correct amount. Excessive torque cannot be applied in that the reduced diameter portion, which comprises a torque limiting portion, will fail, and further transmission of torque will be terminated.  
         [0025]     A torque applying tool  70  is shown in  FIG. 4  which can be used with the insert members  14  shown in  FIGS. 1-5 . This tool  70  can comprise a rod  72  with a first end  74  that has a drive surface  76  in the form of a tapped bore sized to threadingly receive the second threaded end  54  of the insert member  14 A. The tool  70  can be threaded onto the second end  54  of the insert  14 A until the first end  74  of the rod  72  engages a shoulder  78  on the cylindrical extension  56 A. Alternatively, the tapped bore  76  might be shorter in length than the second threaded end  54 , so that the second threaded end will bottom out in the bore. In either event, once the tool  70  is fully threaded onto the insert  14 A, the rod  72  will transmit torque to the insert. The tool  70  is provided at its second end  80  with a drive surface  82  for engagement by a powered or manual tool  83  ( FIG. 2 ) as is well known for applying rotational torque. For example, the drive surface  82  could be a female square drive, other internal or recessed drive surfaces such as a hexagonal shape, a rectangular shape, a star shape, or other well known shapes used in driving tools. Other arrangements, such as a shaping of an outer surface of the second end  80  of the rod  72  could also be used to provide a drive surface for the rod.  
         [0026]     When a tool in the form of a rod  72  is used to drive the insert  14 , the use of the tube plug  10  is enabled, for example, in a heat exchanger tube bundle where the plug is to be inserted at a distal position, such as the far tube sheet, without removing the far head. Insertion of a tube plug  10  in such a relatively inaccessible location is shown in  FIG. 2 .  
         [0027]     The insert member  14 B, in the embodiment shown in  FIG. 5 , differs in the manner in which the torque limiting portion  58 B is constructed. In this embodiment, the torque limiting portion  58 B is formed by a joint in the cylindrical extension  56 B, but there is no decrease in the diameter. Rather, the joint  58 B is formed in such a way as to fail upon a predetermined level of torque being applied to it. The joint may be an adhesion such as welding, soldering, glue or similar adhering mechanisms. Excessive torque cannot be applied to the insert  14 B in that the joint  58 B, which comprises a torque limiting portion, will fail, and further transmission of torque will be terminated.  
         [0028]     The insert member  14 C, in the embodiment shown in  FIG. 6  is comprised of a first threaded end  52 , but no second threaded end. Instead of external threading formed on the exterior of a portion of the cylindrical extension  56 C, a tool receiving recess  60  is formed in an end of the extension disposed away from the first threaded end  52 . Such recess could be a square shape, a hexagonal shape, a rectangular shape, a star shape, or other well known shapes used in driving tools. Other arrangements, such as a shaping of an outer diameter of the cylindrical extension  56 C could also be used to provide a drive surface for the extension. Again, a torque limiting portion  58 C (of any of the types previously described) is provided in the extension  56 C to limit the amount of torque that is transmitted to the first threaded end  52  of the insert  14 .  
         [0029]     In each of the embodiments, the insert  14  with a torque limiting portion  58  will eliminate the use of a torque wrench during installation of the tube plug  10 . The described drive system with the torque limiting portion  58  will enable a mechanic to “torque to failure” thereby transmitting the correct amount of torque to the tube plug  10 . The use of a rod type tool  70  allows for installation of the tube plug  14  in inaccessible locations, saving enormous amounts of time and costs that would otherwise result from the downtime of a apparatus, such as a nuclear reactor which relies on the use of heat exchanger tubes that may need to be sealed with a tube plug.  
         [0030]     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

Technology Category: f