Patent Application
20090211094
Heat exchangers are used in a variety of applications such as power plants, steam engines, and the like. These heat exchangers include a series of tubes that transfer heat exchange fluid. The individual tubes can begin to leak, and may need to be plugged in order to prevent further damage to the heat exchanger.
There are a wide variety of different methods used to plug leaking tubes. In certain applications, explosive devices are used to expand a plug in the tube to seal it off. But, this is very expensive. Mechanical devices can also be used. But, under repeated thermal cycling, these may fail due to different rates of thermal expansion.
Hall U.S. Pat. No. 5,189,789 discloses the use of a memory metal or Nitinol plug. Memory metals are alloys that undergo a reversible transformation from an austenitic state to a martensitic state with changes in temperatures. At colder temperatures, the alloy enters the martensitic state and reverts to the austenitic state at higher temperatures. A plug in the martensitic state can be bent or shaped. When the metal reverts to the austenitic state, it reverts to its original shape.
The plug disclosed in Hall U.S. Pat. No. 5,189,789 is formed from such a memory metal and includes a central post with a plurality of disks that extend perpendicular to the post. The disclosed plug is placed in a bath of methanol and dry ice to cause it to enter the martensitic state. It is then forced through a die, which bends or swages the disks, decreasing the exterior diameter of the plug. The plug can then be manually placed into a tube and heated, causing it to revert to the austenitic state at which point in time the disks will bend back to their original shape, increasing the diameter of the plug, thus plugging the tube.
An improved plug is disclosed in pending U.S. Application Ser. No. 11/396,739, entitled “Memory Metal Plug”, filed on Apr. 3, 2006, and published Jun. 7, 2007, the disclosure of which is hereby incorporated by reference. As with the plug disclosed in the Hall reference, this plug is deformed or swaged while in the martensitic sate. Thus, its diameter is decreased. The improved memory metal plug is installed by placing the swaged plug in a tube, preferably with a heat conducting holder, such as a stainless steel holder. The plug and holder are then heated, for example, with a blowtorch, which causes the plug to change from its swaged martensitic state and revert to the austenitic state increasing its diameter and sealing the tube.
When heat is applied from the one end, it will cause at least the disk or wing closest to the heating source to revert to the austenitic state. The disks farther from the heat source may not be heated and thus may remain in the martensitic state. Thus, they would not provide any sealing. Heat from the heat exchanger should eventually cause the remaining disks to revert to the austenitic state, which would insure that the tube remains sealed. However, with this method, there may be a short period of time in which the plug does not reach its strongest possible seal strength. This presents short term issues that must be addressed.
The present invention is premised on the realization that a memory metal or Nitinol plug can be inserted into a tube to seal the tube by positioning the plug in the tube with a holder which acts to heat the plug. The holder is connected to a current source once the plug is in position. The tubes are grounded so that the current flows through the holder and the plug to the tubes. Electrical resistance heats the Nitinol plug. The leading disk may have a slightly larger diameter than the trailing disks to ensure that current flows through the leading disk. This ensures that the entire memory metal plug is heated sufficiently to cause the entire plug to revert to the austenitic state and, thus, reach its maximum sealing capabilities immediately. Thus, if the heat exchanger is put back into operation and an extreme amount of pressure is initially incurred, the plug will remain in place.
Further, because the energy is supplied by a flexible cable, the plug can be inserted a relatively long distance into the tube and can even be inserted into a curved tube. Pulling back on the cable will release the expanded plug from the holder anywhere in the tube.
The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which:
The present invention utilizes a holder 10 designed to hold a memory metal plug 12 and insert the plug into a tube 14 of a heat exchanger 16.
The plug 12 includes a central shaft 18 and a plurality of disks 20 (20a, 20b, 20c, shown), as well as an outermost post 22. The peripheral edge 24 of each of the disks is intended to be slightly larger than the internal diameter of tube 14, as will be explained later in discussing the insertion of the plug into the tube.
Although the diameter of each disk may be the same diameter, the leading disk 20a may be slightly larger (i.e., about 0.003 in) than the trailing disks 20b and 20c, as discussed below.
The holder 10 includes a tube or case 30, having an internally threaded proximal end 32, and a distal end 34. The distal end 34 includes an inner portion 36, which is tapered as shown in
A collet 44 is located at the distal end 34 of the tube 30. The collet 44 includes a tapered outer surface 46, and includes a plurality of channels 47 which run partially along the collet 44. The channels 47 divide the collet 44 into a plurality of flared segments 48, which connect to a solid annular portion 50. The solid annular portion 50 has an internally threaded opening 52, which is adapted to receive the externally threaded end 56 of rod 54. Opposite end 56 of rod 54 is an enlarged head 58 which has a diameter slightly less than the diameter of the inner surface 60 of tube 30. A spring 62 is positioned between the annular ledge 38 and the head 58. Spring 62 applies pressure pulling the collet 44 in towards the annular ledge 38. A pin 64 extends through the oblong ports 43 and through rod 54.
The holder 10 is completed with a connector 70, which includes an externally threaded end 72, which is threaded into the internally threaded end 32 of tube 30. Connector 70 includes a hexagonal head portion 74. An insulated wire 76, which, as shown in
Once assembled, the tool acts to pull the collet 44 into the tube 30. More particularly, the rod 54 is urged toward the connector 70 by spring 62. This in turn pulls the collet 44 in the same direction. Because the collet 44 has a tapered outer surface 46, and the tube 30 has a tapered inner surface 36, the segments 48 are compressed, decreasing the size of opening 78 in collet 44.
The entire holder is preferably formed from an electrically-conductive metal, such as aluminum, steel, or the like. Stainless steel is preferred. The exterior of the holder 10 may be coated, or otherwise formed or surrounded, with an insulating material such as polyurethane, or the like.
The holder 10 is used to grasp the post 22 of plug 12 and insert plug 12 into a tube 14 of heat exchanger 16. More particularly, the plug 12 will be in a swaged martensitic state, represented by the plug 12 in
Holder 10 is attached to post 22, by moving collet 44 outwardly from tube 30 by grasping the ends of pin 64 and by moving pin 64 forwardly. This moves rod 54 forwardly, allowing the segments 48 of collet 44 to spring outwardly, expanding opening 78 to a size which will allow post 22 to be inserted.
Releasing the ends of pin 64 allows the spring 62 to pull the rod 54 and the collet 44 back into tube 30, applying pressure against post 22. This holds the plug 12 attached to holder 10.
The plug 12 and tool 10 are then inserted into a tube 14 as shown diagrammatically in
Once the plug is installed, the holder 10 is simply pulled from the tube 14. Initially, the force of the collet 44 against the post 22 will prevent the holder 10 from separating from the inserted plug 12. However, upon applying additional force, the tube 30 is pulled away from collet 44, allowing the segments 48 to expand outwardly, releasing the post 22, and allowing the holder 10 to be removed from the tube 14.
This device enables one to insert a Nitinol plug a relatively long distance within a tube and, further, can be used with a tube that is not linear.
This has been a description of the present invention along with the preferred method of practicing the present invention. However, the present invention should only be defined by the appended claims, WHEREIN WE CLAIM:
