GB2100386A

GB2100386A - Plugging tubes

Info

Publication number: GB2100386A
Application number: GB8205731A
Authority: GB
Original assignee: Foster Wheeler (London) Ltd
Current assignee: Foster Wheeler (London) Ltd
Priority date: 1981-04-27
Filing date: 1982-02-26
Publication date: 1982-12-22
Also published as: JPS57179594A; ES8405914A1; ES511580A0; BE892992A; GB2100386B; NL8201719A

Abstract

The invention relates to a plugging assembly for tubes, particularly for closing heat exchanger tubes in the event of leaks developing which could result in separate fluids becoming unintentionally mixed. According to the invention, such plugging apparatus comprises a plug member (14) for insertion into the end of a tube (12), a force-transmitting sleeve (20) within the member (14), and an explosive element (22) within the sleeve (20). A plurality of projections (24) extend from the outer surface of the member (14) to an extent such that in use they will be proximate the inner surface of a tube (12) in which the plug member is inserted. Upon detonation of the explosive element (22), the plug member (14) is expanded radially outwardly to drive the projections (24) against the tube (12). <IMAGE>

Description

SPECIFICATION Plugging assembly for heat exchanger tubes This invention relates to a plugging assembly for sealing a heat exchange tube and, more particularly, to such an assembly utilizing an explosive activated plug member.

Many current designs of heat exchangers feature the use of a large plurality of heat exchange tubes through which a primary fluid is passed in a heat exchange relationship with a secondary fluid passing over the tubes. During the lifetime of such a heat exchanger, a number of heat exchange tubes often develop cracks and leaks which potentially could allow the normally separated fluids to come into direct contact with each other and thus diminish the efficiency of the unit.

The most simple manner of dealing with these types of leakage is to simply disable the particular heat exchange tube in question, i.e., to close it off at both ends in the vicinity of the tube sheet or sheets. This has been done in the past by welding heat plugs in the respective ends of the tubes.

However, this requires relatively good access to the tubes and results in a weld bead that could become corroded and fail. Mechanically driven plugs have been suggested, but these are also not without problems since they, for example, are difficult to install with any consistency and have a relatively low pullout strength.

It is, therefore, an object of the present invention to provide an explosive activated plugging assembly for sealing a tube which can easily be installed with a miniinum of effort and expense.

It is a further object of the present invention to provide a plugging assembly of the above type in which possible leak paths are disrupted and leak resistance and pullout strength of the expanded seal are relatively high.

Toward the fulfillment of these and other objects, the assembly of the present invention features the use of a plug member having a plurality of circular projections extending from the outer surface thereof and adapted to extend in close proximity to the inner surface of the tube to be sealed. An explosive charge is disposed in a force transmitting sleeve within a bore formed in the plug member and, upon detonation of the explosive, the plug is expanded radially outwardly to drive the projections against the tube. An interference fit is formed between the outer surface of the projections and the inner wall of the tube which disrupts possible leak paths and develops a relatively high leak resistance and pullout strength.

The invention will now be described by way of example and with reference to the accompanying drawing wherein:~ Fig. 1 is a partial fragmentary front elevational view of a tube sheet of a typical heat exchange apparatus containing a plurality of heat exchange tubes; Fig. 2 is an enlarged longitudinal sectional view taken along a tube of Fig. 1 and showing the plugging assembly of the present invention inserted therein; and Figs. 3 and 4 are views similar to Fig. 2 but depicting alternate embodiments of the plugging assembly of the present invention.

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 12. The ends of the tubes 12 shown in the drawings are mounted to one side of the tube sheet 10 and extend through openings 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 would 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 through one end from an area below the tube sheet as viewed in Fig. 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.

In order to plug, or seal, an end of one or more of the tubes 12 for the reasons indicated above, a plug member 14 is inserted into the end of a tube 12, as shown in Fig. 2. The plug member has an open end 1 4a extending flush with the lower surface of the tube sheet 1 O, as viewed in Fig. 2, a closed end 1 4b extending proximate to the upper surface of the tube sheet and a central bore 1 6 extending between these ends.

The outer diameter of the plug member 14 is slightly less than the inner diameter of the tube 1 2 and a plurality of spaced circular rings, or projections, 18 are formed on the outer surface of the plug member. The circular projections 18 extend to the inner surface of the tube 1 2 with just enough clearance to permit insertion of the plug member 14 into the tube. According to the embodiment of Fig. 2, the projections 18 are conical shaped in longitudinal cross section, with the angle of the cone being approximately 600.

The projections 18 are shown axially spaced at equal intervals and spanning a distance from the open end 1 4a of the plug member 14 to approximately midway between the ends 1 4a and 1 4b, it being understood that each projection extends continuously around the outer surface of the plug member. The plug member 14 and the projections 18 can be fabricated from a suitable metal.

A force transmitting member, in the form of a plastic sleeve 20, extends within the bore 16 of the plug member 14. The sleeve 20 extends from the end 1 4a of the plug member 14 to a location beyond the location of the endmost row of projections 18, i.e., approximately midway between the ends 1 4a and 14b of the plug member. The sleeve 20 can be fabricated from a thermoplastic hardenable resin of a conventional composition.

A cord-like explosive member 22 extends within the sleeve 20 for the entire length of the sleeve 20 and projects outwardly from the ends of the sleeve and the plug member 14. The explosive member 22 contains a predetermined number of grains of explosive uniformly disposed along the axis of the member and embedded within a fiber or plastic body. The projecting portion of the explosive member 22 can be connected to a detonator cap (not shown) which can be connected, in a conventional manner, to a remotely located electric detonator or the like.

Upon detonation of the explosive member 22 in the manner suggested above, the shock wave of the detonation is transmitted in a radial direction via the plastic sleeve 20, to the plug 14, forcing the plug and therefore the circular projections 18 against the inner wall of the tube 12. Due to the very high pressures which act for a very short time, the plug is expanded to a diameter greater than the tube hole 10. As a result, the projections 1 8 coin, or emboss, into the inner tube surface and function to disrupt possible leak paths and develop a relatively high leak resistance and pullout strength. As a result a highly effective mechanical leak-proof seal is formed.

The embodiments of Figs. 3 and 4 are similar to that of Fig. 2, and include identical components which are given the same reference numerals.

According to the embodiment of Fig. 3, a plurality of axially spaced, circumferentially extending projections 24 are provided on the outer surface of the plug member 14. Each projection 24 has a rectangular cross section with a portion of the outer surface being removed (by suitable machining) to form a concave counterbore. As a result, each projection 24 has two pointed portions 24a and 24b which extend continuously around the outer surface of the plug member 14 immediately adjacent the inner surface of the tube 1 2. Upon detonation of the explosive member 22 in the manner described in connection with the previous embodiment, the projections 24a and 24b coin, or emboss, into the inner tube surface in the same manner, and with the same result, as the projections 1 8 of the previous embodiment.

According to the embodiment of Fig. 4, a plurality of axially spaced, circumferentially- extending projections 26 are provided on the outer surface of the plug member 14. The projections 26 have a substantially square cross section, extend continuously around the outer surface of the plug member 14, and function in a manner identical to the projections 18 and the projections 24 of the embodiment of Figs. 1 and 2, respectively.

It is understood that reference has been made throughout the specification to the term "projections", notwithstanding the fact that the projections can actually be formed as a result of a plurality of continuous, axially-spaced grooves being machined into the outer surface of the plug members.

As a non-limitative example of the dimensions and spacing of the projections formed on the plug member according to the present invention, the projections 26 of the embodiment of Fig. 4 can have a height (measured in a direction parallel to the axis of the plug) of approximately .06 inches, and a depth (corresponding to the depth of the corresponding groove) of .02 inches. The spacing between the projections is equal to their height (.06 inches) and, after the explosion, the projections emboss into the inner tube surface for a distance of approximately .002 inches.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some 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

1. An explosive-activated plugging apparatus for sealing a tube, said apparatus comprising a plug member having an internal bore and an outer diameter slightly less than the inner diameter of the tube to be sealed, a force transmitting sleeve extending within said bore of said plug member, explosive means extending within said sleeve, and a plurality of projections extending from the outer surface of said plug member and adapted to extend in close proximity to the inner surface of said tube, said projections extending around said explosive means so that, upon detonation of said explosive means, said plug is expanded radially outwardly to drive said projections against said tube.

2. The apparatus of claim 1 wherein said plug member has a closed end and an open end for receiving said sleeve and said explosive means.

3. The apparatus of claim 1 wherein said projections have a conical cross section.

4. The apparatus of claim 3 wherein the angle of said cone is approximately 600.

5. The apparatus of claim 1 wherein said projections have a rectangular cross section.

6. The apparatus of claim 5 wherein a concave counterbore is formed in said projections.

7. The apparatus of claim 1,2,3,4,5 or 6 wherein each of said projections extends continuously around the outer surface of said plug member.

8. The apparatus of claim 1,2, or 6 wherein, after said expansion, said projections emboss into the inner surface of said tube.

9. An explosive-activated plugging apparatus for sealing a tube substantially as described herein with reference to Figure 2, Figure 3, or Figure 4 of the accompanying drawings.