APPARATUS FOR FORMING AN EXPLOSIVELY EXPANDED TUBE-TUBE SHEET JOINT INCLUDING A FIBRE REINFORCED INSERT HAVING A CLOSED END

Abstract: Apparatus for expanding a tube (12) into a bore formed in tube (10) sheet in which an explosive (22) is placed within the tube coextensive with that portion to be expanded. A tubular force-transmitting member (20), formed of a plastic, extends between the explosive (22) and the tube to transfer the force of the explosive (22) to the tube (12) to achieve a uniform expansion. A fiber material (40) is embedded in the plastic force-transmitting member (20) to increase the longi­ tudinal strength of the insert. One end of the force-­ transmitting member (20) extends proximate to the outside surface of the tube sheet and the other end (20a) is closed to contain the debris and gases from the explosion.

Description: APPARATUS FOR FORMING AN EXPLOSIVELY EXPANDED TUBE-TUBE SHEET JOINT INCLUDING A FIBER REINFORCED INSERT HAVING A CLOSED END This invention relates to an apparatus for explosively forming a tube-tube sheet joint and, more particularly, to such an apparatus utilizing an explosive which is placed within the tube to be expanded. Many current designs of heat exchangers feature the use of a plurality of heat exchange tubes disposed within a tube sheet and adapted to receive a primary fluid which is passed through the tubes in a heat exchange relationship with a secondary fluid passing over the tubes. Various techniques have evolved for securing the tubes within the tube sheet. For example, the tubes have been mechanically expanded into the tube sheets utilizing a mandrel or the like, or by rolling, i.e., by applying an outward radial force against the entire surface of the tubes. However, these techniques enjoy several disadvantages including local metal deformation, general lengthening of the tubes, and the application of axial stresses on the tube weld and compressive strains in the tube wall. In order to overcome the foregoing disadvantages, a technique of explosively forming the tubes within the tube sheet has evolved. According to this technique, an explosive charge is disposed within the area of overlap between the tubes and the tube sheet and is surrounded by a force transmitting member which, upon detonation of the explosive charge, expands the tube uniformly against the inner wall of the tube sheet. One problem associated with this type of explosive forming is the possibility of breakup due to longitudinal shock waves of the force-transmitting member. Also the gases and debris resulting from the explosion come out of the end of the force-transmitting member located adjacent the inner face of the tube sheet, which are unacceptable in many industrial applications, not the least of which is in connection with nuclear heat exchanger explosive expansion work. It is therefore an object of the present invention to provide an apparatus for securing a tube within a tube sheet in which the tube is explosively formed within the tube sheet without the problems set forth above. It is a more specific object of the present invention to provide an apparatus of the above type in which the strength of the force-transmitting member is increased in the longituainal direction to withstand any longitudinal shock wave. It is a further object of the present invention to provide an apparatus of the above type in which the debris and gases resulting from the explosion are contained within the forcetransmitting member Toward the fulfillment of these and other objects, an explosive is disposed within each tube coextensive with that portion of the tube to be expanded. A force-transmitting member is disposed between the explosive and each tube and contains a longitudinally extending fiber material to strengthen the latter member. The end portion of the force-transmitting member adjacent the inner surface of the tube sheet is closed so that it contains the debris and gases associated with the explosion of the explo sive. The above brief description, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the presently preferred but nonetheless illustrative embodiment in accordance with the present invention when taken in conjunction with the accompanying drawings in which: Fig. 1 is a longitudinal cross-sectional view of a tubetube sheet interface including the apparatus of the present invention; and Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1. Referring to Fig. 1 of the drawings, the reference numeral 10 refers in general to a tube sheet which can form a portion of a heat exchanger having a plurality of heat exchange tubes, one of which is shown by the reference numeral 12. Each tube 12-extends within a corresponding bore formed within the tube sheet 10, with one end of#each of the tubes extending flush with the outer surface of the tube sheet, and the other end extending through the inner surface of the tube sheet. The outer diameter of the tube 12 is slightly less than than the inner diameter of the tube sheet bore and the tube may be secured to the tube sheet 10 by an annular weldment 14 which welds the flush end of the tube to the outer surface of the tube sheet. Only a portion of the tube 12 is shown in the interest of clarity, it being understood that the heat exchanger would also include a vessel enclosing the tube sheet and having suitable inlets and outlets for a primary heat exchange fluid and a secondary heat exchange fluid. According to a typical arrangement of this type, the tubes 12 could be U-shaped with both ends of each tube extending through the tube sheet 10 and the heat exchanger would include a partition, or the like. The primary heat exchange fluid would enter the tubes 12 through one end from an area to the left of the tube sheet 10 as viewed in Fig. 1, pass through the tubes in a heat exchange relation with the secondary fluid passing through the vessel to the right of the tube sheet, and exit through the other ends of the tubes. The tube 12 is depicted in Fig. 1 prior to it being explosively formed in the tube sheet 10, along with the apparatus of the present invention for effecting the explosive forming. The latter apparatus includes an insert, shown in general by the reference numeral 18, which extends within the tube 12 and consists of a generally tubular force-transmitting member 20 and a rod-shaped explosive member 22 extending within the bore of the tubular member. The tubular member 20 has an outside diameter which is slightly less than the inner diameter of the tube 12, and a shoulder 23 is provided on the end of the tubular member which engages the weldment 14 to precisely locate the tubular member 20, and therefore the entire insert 18, within the tube 12. The length of the tubular member 20 is such that, when positioned within the tube as shown, it extends substantially coextensive with the area of overlap between the tube 12 and tube sheet 10. The end portion of the tubular member 20 extending adjacent the inner surface of the tube sheet 10 is closed, as shown by the reference numeral 20a. The explosive member 22 is disposed within the bore of the tubular member 20 intermediate the ends thereof and contains a predetermined number of grains of explosive distributed uniformly along its axis. The bore of the tubular member 20 extending between its closed end portion 20a and the corresponding end portion of the explosive member 22 is enlarged to form an inner cavity, or chamber, 23. A detonator cap 24 is provided externally of the tube sheet 10 and contains a very sensitive primary explosive which detonates readily when set off by a primer, an electrical blast cap, or the like, in a conventional manner. An energy transfer cord 26 connects the detonator cap 24 with the insert 18, and contains a relatively low number of grains of explosive, surrounded by a protective sheath preferably of a plastic material. The relative size of the sheath when compared to the explosive potential of the explosives of the cord 26 is such that the sheath will con¯tain the debris and gases resulting from the explosion as will be #eSc#rib#ed in detail later. Further details of the energy transfer¯cJord 26 are disclosed in copending patent application Serial No. (attor- ney's docket no. 16,429A - USD 1842A) filed November 15, 1982, and assigned to the same assignee as the present application. Referring again to Fig. 1, a counter-bore 32 is#f6rm#e'#'in the tubular member 20 for receiving a booster 34, with the buter surface of the booster 34 extending flush with the member 20 and connected to the other end of the energy transfer cord 26. Although not shown in the drawings, it is understood that the other end of the booster 34 is formed with a relatively small cavity. in which an explosive is disposed, with the booster being positioned so that the explosive does not fall outside of the axial location of the tube sheet 10. It is noted that the corresponding end of the explosive member 22 is slightly spaced from the latter end portion of the booster 34. A fiber material 40 is embedded in the force-transmitting member 20 and extends longitudinally for the length of the latter member. The fiber material 40 may be in the form of a continuous filament or may be in the form of a plurality of individual filaments. In either case, the sections or strands of the fiber material extends in a fairly closely spaced relationship as shown in Fig. 2. According to a preferred embodiment, the force-transmitting member 20 is formed of polyethylene and the fiber material 40 is in the form of fiberglass, graphite or boron. The booster 34 is detonated by the energy transfer cord 26 which, in turn, detonates the explosive member 22, with the resulting forces being transmitted, via the force-transmitting member, uniformly to the tube 12 to cause a uniform expansion of the tube against the wall portion -of the tube sheet 10 forming the corresponding tube-receiving bore. The booster 34 is necessary since, in order to properly contain the debris and gases resulting from the detonation of the energy transfer cord 26, the amount of explosives contained in the latter cord must be kept below that which is necessary to directly detonate the explosive member 22. This arrangement thus provides a distinct advantage over prior art arrangements. For example, the provision of the longitudinally extending fiber material greatly strengthens the forcetransmitting member in the longitudinal direction and minimizes the chance of breakup due to longitudinal shock waves. Further, the presence of the closed end portion 20a of the tubular member.20 contains the debris and gases resulting from the explosion within the cavity 23 and thus prevents their escape past the inner surface of the tube sheet 10. It is understood that several variations may be made in the foregoing without departing from the scope of the invention. For example, the exact materials used, including the number and type of explosives, in the various components can be varied within the scope of the invention. A latitude of modification, change and substitution is intended in the foregoing disclosure and, in some instances, same features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention therein.

Claims: CLAIMS:- 1. Apparatus for expanding a tube into a bore formed in a tube sheet, comprising a tubular force-transmitting member extending within said tube coextensive with the portion of the tube to be expanded, explosive means disposed in the bore of said forcetransmitting member, so that the forces resulting from the explosion of said explosive means are uniformly transferred, by said force-transmitting member, to said tube to expand said tube into said bore, and a fibre material embedded within said forcetransmitting member and extending longitudinally along said member for increasing the longitudinal strength of said force-transmitting member. 2. - The apparatus of claim 1 wherein said explosive means is in the form of a rod-shaped member containing grains of explosive disposed uniformly along its axis. 3. The apparatus of claim 1 wherein said fibre material includes a plurality of spaced parallel segments, each extending longitudinally along said force-transmitting member. 4. The apparatus of claim 1 wherein said force-transmitting member has an open end adjacent the outer surface of said tube sheet for receiving said explosive means and a closed end for containing the debris and gases resulting from said explosion. 5. The apparatus of claim 4 wherein a portion of the bore of said force-transmitting member not containing said explosive means and extending between said explosive means and the closed end of said force-transmitting member is enlarged for receiving said debris and gases. 6. Apparatus for expanding a tube into a bore formed in a tube sheet comprising a tubular force-transmitting member extending within said tube coextensive with that portion of the tube to be expanded, and explosive means disposed in the bore of said forcetransmitting member so that the forces resulting from the explosion of said explosive means are uniformly transferred, by said forcetransmitting member, to said tube to expand said tube into said bore, said force-transmitting member having an open end adjacent the outer surface of said tube sheet for receiving said explosive means and a closed end for containing the debris and gases resulting from said explosion. 7. The apparatus of claim 6 wherein a portion of the bore of said force-transmitting member not containing said explosive means and extending between said explosive means and the closed end of said force-transmitting member is enlarged for receiving said debris and gases. 8. The apparatus of claim 6 wherein said explosive means is in the form of a rod-shaped member containing grains of explosive disposed uniformly along its axis.

Inventors: BERMAN, IRWIN
Applicants: FOSTER WHEELER ENERGY CORPORATION
Application year: 1984
Main classification: B23K20
IPC codes: B21D39, B23K20