GB2102320A

GB2102320A - Explosive expansion of tubes into tube plates

Info

Publication number: GB2102320A
Application number: GB08217314A
Authority: GB
Inventors: Joseph W Schroeder; Irwin Berman
Original assignee: FOSTER WHEELER AUTOMATED WELDI
Current assignee: FOSTER WHEELER AUTOMATED WELDI
Priority date: 1981-06-15
Filing date: 1982-06-15
Publication date: 1983-02-02
Also published as: NL8202420A; GB2102320B; JPS5841625A; MX156807A; BE893530A

Abstract

In order to improve the quality of the joint the present invention proposes the use of an annular sealing member (16) which is disposed on the inner wall of the tube sheet (10) defining the opening, for example in a groove, prior to the tube (12) being expanded thereagainst. An insert (18) is provided for insertion into the tube (12) and includes a central portion containing an explosive and a force- transmitting portion extending between the central portion and the inner wall of the tube (12). The force- transmitting portion is adapted to transmit the force from the explosive to the wall of the tube (12) and force the latter against the sealing member (16) to seal the joint between the tube (12) and the tube sheet (10). <IMAGE>

Description

SPECIFICATION Explosive expansion of tubes into tube plates This invention relates to an apparatus for explosively forming a tube-tube sheet joint and, more particularly, to such an apparatus utilizing a sealing member between the tube and the tube sheet.

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, but this technique is limited to low pressure use. In high pressure work, it is customary to weld the tube ends to the tube sheet and then expand the tubes into the tube sheet. Also mechanical expansion of tubes within a tube sheet can be accomplished 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, the technique of explosively forming the tubes within the tube sheet has evolved. According to this technique, an insert is applied within the area of overlap between the tubes and the tube sheet and is exploded to expand the tube uniformly against the inner wall of the tube sheet. This technique has proven extremely advantageous but has some limitations.

For example, if the tubes and tube sheets are fabricated from materials that are incompatible from a modulus of elasticity and/or a thermal expansion standpoint an optimum expansion cannot be attained, which compromises the leak integrity of the interfaces between the tubes and the tube sheet. Also, the tube and the insert normally must be welded to a surface of the tube sheet to provide proper gauging, which is timeconsuming and costly from a production standpoint.

Further, if the operational temperatures of the particular heat exchanger are low, the tube sheets thin, and/or the environment corrosive, it is difficult to obtain adequate leak-tightness along the interface between the tubes and the tube sheet.

The present invention seeks to mitigate the above disadvantages and to this end provides a method of securing a tube in an opening in a tube sheet comprising locating an annular sealing member adjacent the inner wall of the opening and the outer wall of the tube; placing within the tube and in the opening an insert having an inner portion containing an explosive and an outer force-transmitting portion; and actuating the explosive to expand the force-transmitting portion of the insert against the tube and urge the tube against the inner wall of the opening confining the sealing member therebetween. The invention provides means by which tubes can be expanded into openings formed in the tube sheet ensuring high leak integrity, notwithstanding the fact that the tube and tube sheet may be of otherwise incompatible materials.Substantial leak tightness can be ensured, notwithstanding the fact that operational temperatures are low, the tube sheets thin and the environment corrosive.

Apparatus according to the invention for securing a tube within an opening formed in a tube sheet, comprises an annular sealing member disposed adjacent the inner wall of the tube sheet defining the opening; and an insert for insertion into said tube, which insert has a central portion containing explosive means, and forcetransmitting means extending between the central portion and the inner wall of said tube for transmitting force from the explosive means to the wall of said tube and against said sealing member to seal the interface between said tube and said tube sheet. The invention eliminates the need for welding the tube and/or the explosive insert relative to the tube sheet before the tubes are explosively formed into the tube sheet. The sealing ring is normally in the form of an O-ring.

The invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a partial, fragmentary, crosssectional view of a tube sheet of a typical heat exchange apparatus containing a plurality of heat exchange tubes; Figure 2 is an enlarged view showing a tubetube sheet interface including the apparatus of tie present invention; Figure 3 is a view similar to Figure 2, but showing the tube of Figure 2 after it has been explosively formed into the tube sheet; Figure 4 is a view similar to Figure 2, but showing an alternative embodiment of the apparatus of the present invention; Figure 5 is a view similar to Figure 3 but depicting the tube of Figure 4 after it has been explosively formed into the sheet.

Figure 6 is a view similar to Figures 2 and 4, but depicting another alternative embodiment of the present invention; and Figure 7 is a view similar to Figures 3 and 5, but depicting the tube of Figure 6 after it has been explosively formed into the tube sheet.

Referring to Figure 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 12. One end of each of the tubes 12 extends through an opening in the tube sheet in communication with the area extending to the other side of the tube sheet. Only a portion of the tube sheet 10 and the tubes 12 are 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.The heat exchanger would include a partition, or the like, so that the primary heat exchange fluid would enter the tubes 12 though one end from an area below the tube sheet 10 as viewed in Figure 1 , pass through the tubes in a heat exchange relation with the secondary fluid passing through the vessel above the tube sheet, and exit through the other ends of the tubes to the area below the tube sheet.

Figure 2 depicts a tube 12 inserted within the tube sheet 10 prior to it being explosively formed in the tube sheet, along with the apparatus of the present invention for explosively forming the tube within the sheet while ensuring leak tightness along the interface. The reference numeral 14 refers to a continuous groove formed in the inner wall of the tube sheet 10. The groove 14 has a rectangular cross section and receives a sealing ring 16 of an elastomer material which fits snugly within the groove and against the outer surface of the tube 12.

An insert shown in general by the reference numeral 18, is provided within the tube 12 and consists of a central axial member 20, a tubular member 22 and an annular member 24 extending between the axial member and the tubular member. The tubular member 22 has an outside diameter which is very slightly less than the inner diameter of the tube 12 and a shoulder 26 is provided on the end of the tubular member which engages the end of the tube 12 to precisely locate the tubular member 22, and therefore the entire insert 1 8, within the tube 12. The length of the members 20 and 22 are such that when positioned within the tube as shown, they are substantially coextensive with the area of overlap between the tube 12 and the tube sheet 10 while the length of the annular member 24 is less than that of the members 20 and 22 to define an air gap 28 adjacent the end of the tube 12.

A cap 29 is provided across the end of the tubular member 22 and serves to locate the end portion of the axial member 20 relative to the tube 12.

The central member 20 contains a predetermined number of grains of explosive, generally from twenty-five grains per foot to forty grains per foot, uniformly disposed along its axis.

'Primacord' is a known material which can be used, and is formed by embedding the grains of explosive in a fiber or plastic body.

The tubular member 22 and the annular member 24, which together function to transmit the the force from the explosive to the inner wall of the tube 12 can be extruded with the central member 20 and then cut to the desired lengths.

The air gap 28, which extends around the central member 20 in the area of the shoulders 26, functions to reduce the application of an excessive force through the free end of the tube 12. The force-transmitting members 22 and 24 may be fabricated of polyethylene or other thermoplastic hardenable resin having essentially the same properties as polyethylene.

Figure 3 depicts the tube 12 after the explosion and the attendant expansion of the tube, and therefore the sealing ring 16, against the inner walls of the tube sheet 10. It is seen that a portion of the tube 12, shown by the reference numeral 2a, expands relative to the other portion of the tube against the ring 16 and into the groove 14.

This encapsulates the ring 16 under considerable pressure and thus improves the leak integrity along the interface between the tube 12 and the tube sheet 10.

This superior sealing is achieved notwithstanding the fact that the tube 12 and the tube sheet 10 can be fabricated from materials that are incompatible from an expansion standpoint. For example, the tubes 12 may be fabricated from aluminium or titanium, while the tube sheet 10 can be fabricated from carbon steel.

It is understood that the sealing ring 16 can be fabricated from an elastomeric material such as rubber or plastic, or from metal rings or bands of a metal having a modulus of elasticity which is compatible with the tube and the tube sheet materials.

The embodiment of Figure 4 is similar to that of Figure 2 and identical structure is given the same reference numerals. In this arrangement, an elongated, counterbored groove 30 is provided in the tube sheet 10, and has a cross section that tapers radially inwardly from the lower end of the tube sheet, as viewed in the drawing, to a point intermediate the two ends of the tube sheet. The groove 30 can be formed in the tube sheet 10 by any conventional reaming procedure.

A sealing ring 32 is provided between the outer surface of the tube and the inner wall of the groove 30 and is located a small distance from the lower end of the tube sheet 10. The sealing ring 32 has a slightly smaller cross-section than the ring 16 of the previcus embodiment and can be fabricated from the same material.

The insert 18 of the embodiment of Figure 3 is identical to that of Figure 2 with the exception that the shoulder 26 is eliminated from the tubular force-transmitting member 22.

Figure 5 depicts the tube 12 of Figure 4 after it has been explosively expanded against the inner wall of the tube sheet 10. It is noted that the lower end portion of the tube is expanded outwardly to conform to the contour of the groove 30, and that a slightly bulging portion, shown by the reference 12b, is formed as a result of this portion acting against the sealing ring 32.

Figure 6 is an embodiment similar to Figure 4 and also features the use of an elongated groove 34 formed in the inner wall of the tube sheet 10 in a manner similar to that of the groove 30. The lower end portion of the groove 34 is of a substantially constant diameter while the remaining portion is tapered inwardly as shown.

An elongated, substantially cylindrical, sealing member 36 is provided which occupies a substantial portion of the groove 34. The outer surface of the member 36 conforms to the shape of the groove 34 while the inner surface has a length that is less than the length of the outer surface and engages a portion of the outer surface of the tube 12. The insert of the embodiment of Figure 6 is identical to that of Figure 4 and, therefore, will not be described in any further detail.

After the tube 12 of Figure 6 has been explosively formed against the inner wall of the opening in the tube sheet 10, it takes the shape as shown in Figure 7 with the lower end portion being tapered outwardly against the cylindrical sealing member 36, as shown.

As in the embodiment of Figure 2 the sealing members 32 and 36 of the embodiments of Figures 4 and 6, respectively, are encapsulated under pressure as a result of the expansion of the tubes 12 and thus effect a leak-tight interface between the tubes and the tube sheet.

It is thus seen that each embodiment of the present invention provides a superior leak-tight interface between the tube and the corresponding portion of the tube sheet, yet permits a tube and a tube sheet of incompatible materials to be utilized.

Also, the apparatus of the present invention eliminates any weldments, is easy and efficient in use and can be adapted to low operational temperature, thin tube sheets and/or corrosive environmental conditions.

A still further advantage of the apparatus of the present invention is that, due to the elastic nature of the sealing members of the foregoing embodiments, a pressure tight seal will be maintained with the apparatus of the present invention, notwithstanding the fact that the area of encapsulation of the sealing member changes due to differences in thermal expansion between the tube and the tube sheet.

Claims

1. Apparatus for securing a tube within an opening formed in a tube sheet, said apparatus comprising an annular sealing member disposed adjacent the inner wall of the tube sheet defining the opening; and an insert for insertion into said tube, which insert has a central portion containing explosive means, and force-transmitting means extending between the central portion and the inner wall of said tube for transmitting force from the explosive means to the wall of said tube and against said sealing member to seal the interface between said tube and said tube sheet.

2. Apparatus according to Claim 1 wherein the sealing member is disposed in a groove having a rectangular cross section.

3. Apparatus according to Claim 1 or Claim 2 wherein the sealing member is disposed in a counterbore formed in one surface of the tube sheet.

4. Apparatus according to Claim 3 wherein the counterbore has a tapered cross section.

5. Apparatus according to Claim 4 wherein the counterbore is tapered inwardly from said one tube sheet surface.

6. Apparatus according to any preceding Claim wherein the sealing member is in the form of an O-ring fabricated from an elastomeric material.

7. Apparatus according to any of Claims 1 to 5 wherein the wall of the sealing member varies in thickness in an axial direction.

8. Apparatus according to any preceding Claim wherein the force-transmitting means comprises a tubular member adapted to extend with the tube and make a relative close fit with the inner wall thereof, and an annular member extending between the central portion and the tubular member.

9. Apparatus according to any preceding Claim wherein the insert has a length dimension approximately equal to the thickness of the tube sheet.

10. Apparatus according to any preceding Claim wherein the insert comprises a central axial portion including a predetermined number of grains of explosive uniformly disposed therealong.

11. Apparatus according to any preceding Claim wherein the annular portion is a thermoplastic hardenable polyethylene resin.

12. Apparatus for securing a tube within an opening formed in a tube sheet substantially as described herein with reference to Figures 2 and 3; Figures 4 and 5; or Figures 6 and 7 of the accompanying drawing.

13. A tube sheet having a plurality of tubes secured in openings therethrough wherein an annular sealing member is confined between the inner wall of each opening and the respective tube secured therein, the portion of tube within each opening having been expanded against said inner wall to confine the sealing member therebetween by the explosion of an insert disposed within said tube portion.

14. A tube sheet according to Claim 13 wherein each sealing member is disposed in a groove formed in the inner wall of the respective opening.

15. A tube sheet according to Claim 14 wherein the groove has a rectangular crosssection.

16. A tube sheet according to Claim 13 wherein the sealing member is disposed on a counterbore formed in one surface of the tube sheet.

17. A tube sheet according to Claim 16 wherein the counterbore has a tapered crosssection.

1 8. A tube according to Claim 17 wherein the counterbore is tapered inwardly from said one tube sheet surface.

19. A tube sheet according to any of Claims 13 to 18 wherein the sealing member is in the form of an O-ring.

20. A tube sheet according to any of Claims 1 3 to 18 wherein the wall of the sealing member varies in thickness in an axial direction.

21. A tube sheet according to Claim 13 and substantially as herein described.

22. A method of securing a tube in an opening in a tube sheet comprising locating an annular sealing member adjacent the inner wall of the opening and the outer wall of the tube; placing within the tube and in the opening an insert having an inner portion containing an explosive and an outer force-transmitting portion; and actuating the explosive to expand the forcetransmitting portion of the insert against the tube and urge the tube against the inner wall of the opening confining the sealing member therebetween.

23. A method according to Claim 22 wherein the sealing member is located in an annular groove formed in the inner wall of the opening.

24. A method of securing a tube in an opening in a tube sheet substantially as described herein with reference to the accompanying drawing.