Abstract:
A plug for sealing the end of a tube including a cylindrical housing member having longitudinal bore that communicates with a threaded portion. An insert member having a threaded end portion is received within the threaded portion of the bore and supports a frustroconical member that deflects at least a portion of the wall of the housing member that is highly ductile. The frustroconical member has a correspondingly large angle of taper to deflect the wall of the housing member outwardly as much as possible without causing fracturing of the wall.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plug used to form a seal for tubes, pipes and similar conduits which transport steam, liquid or gases under pressure and, more particularly, to a plug having an increases degree of expansion to fit larger diameter tubes. 
     2. Description of the Related Art 
     In the construction of boilers and other heat exchange equipment, such as those used in the power generation and chemical industries, there is often a need to seal tubes, pipes and similar conduits which transport steam, liquid or gasses under pressure. This sealing is frequently accomplished by the insertion of a plug into the tube. For example, Applicant has disclosed several such plugs in U.S. Pat. Nos. 5,289,851, 6,883,547, and 6,981,524 that, upon insertion, will expand to sealingly engage the inner surface of a boiler or heat exchanger tube. These plugs are limited, however, in their degree of expansion and are thus unable to be used in circumstances where the plug needs to expand a large distance because the plug cannot expand sufficiently without degrading or fracturing, and thus will not properly maintains a seal against leakage of steam, water or other gasses or fluids, over an extended period of time and with a high degree of reliability. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention comprises a boiler tube plug having a hollow housing that cooperates with a threaded insert to deflect a portion of the hollow housing outwardly, thereby engaging the inside surface of a tube to be plugged. The deflected portion of the hollow housing is comprises of a highly ductile material and the threaded insert includes a frustroconical member that deflects the highly ductile wall of the hollow housing outward into engagement with the tube to be plugged as the insert is threaded into the hollow housing. Preferably, at least a portion of the wall of the housing has the mechanical property of high ductility and low hardness. To impart a large deflection, the frustroconical member should have more than four degrees of taper relative to the longitudinal axis of the housing. The resulting plug can expand up to about ten percent of its overall diameter in order to plug holes that are larger than possible with conventional plugs and can be used in high or low pressure applications, such as feedwater heaters, moisture separator reheaters, preheaters, condensers, coolers, fin-fan coolers or any other tubed heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of a heat exchanger tube plug made in accordance with the present invention; 
         FIG. 2  is a cross-sectional view of the housing member of a heat exchanger tube plug made in accordance with the present invention; 
         FIG. 3  is a cross-sectional view of an insert member of a heat exchanger tube plug made in accordance with the present invention; 
         FIG. 4  is a cross-sectional view of a heat exchanger tube plug made in accordance with the present invention after positioning into a heat exchanger tube and prior to activation; and 
         FIGS. 5A and 5B  are cross-sectionals view of the portion of the heat exchanger tube plug identified in  FIG. 1 . 
         FIG. 6  is a cross-sectional view of a portion of a housing member according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in  FIG. 1  a boiler tube plug  10  made in accordance with the present invention. Plug  10  comprises a hollow housing member  12  and an insert member  14 . Housing member  12  has a cylindrical body  16 , the rear portion of which is formed with a large open bore  18 . Bore  18  is surrounded by relatively thin wall  20 , the end portion  22  of which is deformable and will expand outwardly to provide a seal with a heat exchanger tube  24 , as is shown in  FIG. 4 , when insert member  14  is screwed into housing member  12 . Housing member  12  also includes a relatively smaller internally threaded cylindrical bore  28  which communicates with the large bore  18 . 
     As further seen in  FIG. 5B , end portion  22  of thin wall  20  has a predetermined thickness T that, as seen in  FIG. 5 , preferably includes a slight taper that extends from a thickness T 1  to a thickness T 2 . For plug  10  having an outer diameter of 0.60, thickness T 1  may be between 0.020 and 0.050 inches (or approximately 3.33 to 8.33 percent of the outer diameter) and extend to a T 2  of between 0.035 and 0.065 inches (or approximately 5.83 to 10.83 percent of the outer diameter). The increased thickness is accomplished by the use of a ductile material having an elasticity modulus between 10,000 ksi to 30,000 ksi and a low hardness (Brinell/Rockwell B) score. Thin wall  20  having thickness T and an elasticity of 10,000 ksi to 30,000 ksi is possible by using a material such as carbon or stainless steel, and processing the material to ensure the appropriate amount of ductility, such as by annealing to at least a temperature of 1,150° F. and cooling slowly. Alternatively, polymers, and metal alloys with sufficient mechanical ductility and elasticity may be used. As described below and seen in  FIG. 6 , the sealing region of thin wall  20  has been enhanced by machining sharp ascending deep grooves  60  to ensure a positive mechanical seal upon expansion. 
     At its front end  30 , housing member  12  is provided with an eccentric assembly  32  which serves to lock the housing member tightly within the boiler tube  24 , as is shown in  FIG. 4 , so that the insert member can be screwed into the housing member  12 . Eccentric assembly  32  comprises a cylindrical post  34  which projects axially from front end  30  of the housing member  12 , a ring member  36  which is mounted eccentrically on the post and is rotatable thereon, as shown in  FIG. 2 . As is shown in  FIGS. 1 and 2 , post  34  is disposed eccentrically relative to a longitudinal axis X-X of housing member  12 . 
     The outer cylindrical surface  39  of ring member  36  may be serrated or knurled in order to provide enhanced frictional gripping between ring  36  and tube  24 . Ring member  36  has a bore  40  which fits rotatably over post  34 . Post  34  has a groove  42  near a distal end  44  thereof for receiving a locking snap ring  46 . Snap ring  46  retains ring  36  on post  34 . 
     Housing member  12  has a series of axial grooves  48  at the end adjacent to ring member  36  for enhancing frictional gripping of housing member  12  to tube  24  to prevent continued rotation of housing member  12  within tube  24 . The outer surface of housing member  12  also 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. As seen in  FIG. 6 , although each groove  50  is defined by a common angle B, preferably 60 degrees, the depth of each groove  50  and thus the width of the upper opening of groove decreases toward the open end of housing  12 . In a preferred embodiment where plug  10  has an outer diameter of 0.60 inches, grooves  50  may be provided with the dimensions set forth in Table 1 below: 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 A1 
                 A2 
                 A3 
                 A4 
                 A5 
                 A6 
                 A7 
                 A8 
                 A9 
                 A10 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 X 
                 −.0020 
                 −.0079 
                 −.0177 
                 −.0314 
                 −.0485 
                 −.0693 
                 −.0945 
                 −.1237 
                 −.1566 
                 −.1935 
               
               
                 Z 
                 −.0034 
                 −.0068 
                 −.0102 
                 −.0136 
                 −.0160 
                 −.0200 
                 −.0236 
                 −.0270 
                 −.0300 
                 −.0339 
               
               
                   
               
             
          
         
       
     
     Insert member  14  is comprised of a headed cap screw  52  and a tapered ferrule  54 , which is preferably frustoconical. Preferably, cap screw  52  is a Hex socket head screw having a threaded shank  56  and an enlarged head  58  with a driving recess  60  formed in the head. While a Hex screw comprises a preferred embodiment, other types of recess drive apertures are known which permit high transmission of torque (e.g., above 450 inch pounds) while requiring minimal radial dimensioning for the recess. 
     Ferrule  54  has an internal passage  61  which is threaded to mate with the external thread of the shank  56  of screw  52 . Ferrule  54  may either extend up to and flushly abut an shoulder surface  57  of head  58  of screw  52 , particularly for smaller radius inserts  14 , or ferrule  54  may have an outer diameter greater than the diameter of the head  58  such that the ferrule  54  surrounds head  58  of screw  52 . Insert  14  could be made as an integral part, since socket head screws are readily available commercial items, with machining of the small cone  54  permits a substantial savings in machine time over integral formation of the insert  14 . As seen in  FIG. 5A , the outer surface of ferrule  54  decreases in radius from screw  52  toward first end  30 , thereby defining a taper angle A. Angle is greater than four degrees and, preferably, between 4 and 10 degrees. The use of an angle A that is greater than four degrees is another significant departure from conventional products as the use of such an angle would invariably result in fracturing of thin wall  22  due to the ductility of the composition used to make housing member  12 . As described above, the use of highly ductile material in combination with an increased angle allows for ten percent expansion of the outer diameter. For example, plug  10  having an outer diameter of 0.600 inches can expand up to 0.060 inches, whereas convention plugs are limited to a much lower expansion on the order of five percent, such as 0.030 inches for plug  10  having an outer diameter of 0.600 inches. 
     As seen in  FIG. 3 , threaded shank  56  of insert member  14  is sized to be received in the threaded smaller bore  28  of the housing member  12 . Thus, in use, insert member  14  is inserted into housing member  12  and threaded shank  56  is screwed into threaded bore  28  until outer surface  62 , preferably having a spiral groove therein, engages the mouth of large bore  18  and insert member  14  can no longer be turned by hand. Eccentric ring member  36  is then rotated relative to post  34 , by hand, until it is approximately concentric with body of housing member  12 . In this condition, plug  10  is sized so that it may be inserted into the end of heat exchanger tube  24  to the position shown in  FIG. 4 , although the clearances between the plug and the tube wall may be less exaggerated than shown in  FIG. 4 . 
     Driving recess  60  may then be engaged with an appropriate tool to cause ring member  36  to engage the sidewalls of the heat exchanger tube with its knurled surface and turn eccentrically on post  34 . Ring member  36  thus presses tightly against inner surface  80  of heat exchanger tube  24  so that ring member  36  can no longer turn on post  34  and housing member  12  is tightly locked against turning within heat exchanger tube  24 . When drive recess  60  is further turned by the tool, insert member  14  turns within housing member  12 , with threaded shank  56  screwing further into small bore  28 . At the same time, surface  62  of ferrule  54  engages thin wall  20  of large bore  18  and, as the increasing diameter of ferrule  54  enters into large bore  18 , ferrule  54  further deforms thin wall  20  of housing member  12  outwardly, increasing the diameter of bore  18 . As thin wall  20  is expanded outwardly, expanded end portion  22  engages inner surface  80  of heat exchanger tube  24  and makes an effective seal therewith. Annular grooves  50  increase the sealing potential of plug  10 . For example, if tube  24  has any corrosion on its inner surface  80 , the raised portions between the annular grooves  50  would cut through any scale and the scale would be retained in the grooves  50 , thereby enhancing the mechanical contact seal. By increasing the torque value permitted to be applied to insert member  14 , insert member  14  is driven further into housing  12 , thereby further increasing the deformation of tube  24  and further increasing the surface area of contact between thin wall  22  and tube  24 .