U.S. patent number 3,590,877 [Application Number 04/761,273] was granted by the patent office on 1971-07-06 for explosive-activated plug.
This patent grant is currently assigned to The Babcock & Wilcox Company. Invention is credited to Phillip M. Leopold, Louis A. Sturiale.
United States Patent |
3,590,877 |
Leopold , et al. |
July 6, 1971 |
EXPLOSIVE-ACTIVATED PLUG
Abstract
A plug which can be inserted into a tube and containing a shaped
explosive charge which is detonated to expand the plug against the
surrounding tube surface with an impact that effects a
circumferential weld bond between the plug and tube surface to seal
the tube.
Inventors: |
Leopold; Phillip M. (Alliance,
OH), Sturiale; Louis A. (Irwin, PA) |
Assignee: |
The Babcock & Wilcox
Company (New York, NY)
|
Family
ID: |
25061730 |
Appl.
No.: |
04/761,273 |
Filed: |
September 20, 1968 |
Current U.S.
Class: |
138/89; 29/421.1;
138/97; 138/103; 165/76; 165/137; 228/2.5 |
Current CPC
Class: |
F42B
3/006 (20130101); B21D 39/042 (20130101); F42D
3/00 (20130101); F28F 11/02 (20130101); Y10T
29/49805 (20150115) |
Current International
Class: |
F42D
3/00 (20060101); F28F 11/00 (20060101); B21D
39/04 (20060101); F28F 11/02 (20060101); F16l
055/10 () |
Field of
Search: |
;138/114,89,97,103,108
;29/421 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ross; Herbert F.
Claims
What I claim is:
1. An explosive-activated plug which comprises a generally
cylindrical hollow metal body open at one end and closed at the
opposite end and disposed for insertion into the bore of a metal
tube to be sealed, a shaped explosive charge retained within said
hollow body, said explosive charge having an explosive material
distributed lengthwise within said body and including a cylindrical
block of explosive material, a cylindrical sheet of explosive
material positioned in contiguous adjoining relation to said
cylindrical block, and a conical sheet of explosive material
positioned in contiguous adjoining relation to said cylindrical
block, and means disposed within said body and operable from a
location outside thereof to detonate said explosive charge and
thereby expand said body radially outward against the surrounding
tube surface with an impact energy effecting a metallurgically
bonded contact between said body and surface to seal the bore, said
contact being over a zone extending completely around the
circumference of the body and along an axial length portion thereof
intermediate said ends.
2. An explosive-activated plug as defined in claim 1 wherein said
detonator means is positioned for contact with said cylindrical
block of explosive material.
3. An explosive-activated plug as defined in claim 1 wherein said
hollow body has a cylindrical bore extending axially inward from
said open end of the body, and a blind core communicating with said
cylindrical bore and tapering with decreasing cross-sectional area
toward said closed end of the body.
4. An explosive-activated plug as defined in claim 3 including
filler means disposed within said body to support said cylindrical
sheet of explosive material in contact with the surface of said
cylindrical bore, and to support said conical sheet of explosive
material in contact with the surface of said tapered blind bore.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates in general to the art of explosive welding,
and more particularly to an explosive-activated metal plug which
can be inserted into a tube or the like and then detonated into a
sealing configuration.
In the operation of heat exchangers wherein heat transfer occurs
between fluid passed through tubes and fluid in contact with the
outside of tubes it sometimes becomes necessary to seal one or more
tubes, in order to prevent mixing of the fluids, as in the case
where the tubes develop leaks. The sealing of tubes in the past has
generally been accomplished by means of mechanically expandable
plugs for tubes exposed to moderate fluid pressure differentials,
and by means of welded plugs for tubes exposed to high fluid
pressure differentials.
Ordinarily, where a high-pressure heat-exchanger tube is to be
sealed, a cylindrical plug is inserted at the tube sheet into the
bore of the tube, and a weld bead is deposited around the outside
and circumference of the joint between the tube and plug to form a
pressuretight seal. While in many cases such tube sealing technique
will be satisfactory, it has been found that fluid can sometimes
penetrate along the tube-plug interface and corrode through the
weld bead thereby causing leakage and necessitating extensive
repairs.
Moreover, in some heat exchangers, it is relatively difficult to
weld seal plugs using conventional equipment, because of space
limitations.
The invention avoids these disadvantages of prior art welded plugs
by employing an explosive activated plug in the form of a hollow
metal body that is inserted into the bore of a metal tube to be
sealed, and which contains a shaped explosive charge and a
detonator which can be set off from a remote location to detonate
the charge and thereby expand the plug body against the tube
surface with an impact of sufficient force that it creates a zone
of metallurgically bonded metal contact between the plug and
surrounding tube surface, which zone extends completely around the
circumference of the plug body and along an axial length portion
thereof intermediate its ends.
This metallurgically bonded, or weld, zone comprises a considerably
greater area of the plug surface than is possible when using the
conventional seal welding just around the exposed end of the
plug.
Consequently, through the use of the invention, a much more
extensive area of welding of the plug to the tube can be achieved,
and it will be appreciated that this explosive welding is
accomplished without the need for manipulating electrodes or any
other welding tools.
The various features of novelty which characterize the invention
are pointed out with particularity in the claims annexed to and
forming a part of this specification. For a better understanding of
the invention, its operating advantages and specific objects
attained by its use, reference should be had to the accompanying
drawing and descriptive matter in which there is illustrated and
described a preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is a longitudinal view, partly in section, of an
explosive-activated plug according to a preferred embodiment of the
invention shown as inserted into a tube to be sealed and prior to
detonation.
FIG. 2 is a transverse cross-sectional view of the plug and tube
shown in FIG. 1 as taken along line 2-2 therein.
FIG. 3 is a longitudinal sectional view of the plug and tube shown
in FIG. 1 as seen after detonation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In FIGS. 1 and 2 there is illustrated, by way of example, a typical
explosive-activated plug 10 constructed in accordance with the
invention. The plug 10 has an elongated hollow metal body 11, which
is generally cylindrical in form, closed at one end 12, and open at
its other end 13. In its contemplated use, the plug 10 is inserted
into the bore of a metal tube 14 that is to be sealed, the end
portion of tube 14 being received and retained by a tube sheet 15,
as in a typical heat exchanger (not shown).
Within the hollow interior of plug body 11 is a shaped explosive
charge 16 and a detonator 17. Detonator 17 is preferrably an
electrically operable type having lead wires 18 extending out
through the open rear end 13 of plug body 11 for connection to a
remote firing circuit (not shown).
The charge 16 is so distributed and arranged that when set off by
the detonator 17, the resultant explosion expands the plug body 11
against the surrounding tube surface 19 with an impact that drives
the exterior surface 20 of plug body 11 into metallurgically bonded
contact, i.e. cold-welding fusion, with tube surface 19 over a zone
22 extending completely around the circumference of body 11 and
along an axial length portion thereof intermediate the ends 12 and
13, as better seen in FIG. 3.
It has been found that such explosive welding of the plug 10 to the
tube 14 results in a perfect sealing of the tube 14 and can be
achieved by using an explosive charge 16 made up from a cylindrical
block 23 of explosive material which is positioned axially in
generally centered relation to the axial limits intended for zone
22, and in contact with detonator 17; a cylindrical sheet 24 of
explosive material positioned in contiguous adjoining relation to
the block 23; and a conical sheet 25 of explosive material
positioned in contiguous adjoining relation to block 23 and
cylindrical sheet 24.
To accommodate such charge 16 and to provide a plug 10 which will
deform radially within the zone 22 and without any significant
axial movement, the plug body 11 is made with a cylindrical bore
section 26 extending axially inward from the open end 13, and a
tapered blind bore section 27 that communicates with the
cylindrical bore section 26 and tapers with increasing
cross-sectional metal volume toward the closed end of plug body
11.
As can be readily noted from FIGS. 2 and 3, the plug body 11 is
most heavily reinforced at its forward end 12 whereas from its
center toward its rear end 13 the wall thickness of body 11 is
considerably lighter. This prevents blowout at the forward end
portion of plug 10, which, if it occurred, would destroy its
usefulness as a sealing means for tube 14.
To maintain the conical explosive sheet 25 supported in contact
with the surface of tapered bore section 27, and the cylindrical
explosive sheet 24 in contact with the surface of the cylindrical
bore section 26, there are respectively provided a frustoconical
filler piece 28 and a cylindrical filler piece 29, both expediently
made of a material such as styrofoam.
Externally, the plug body 11 is provided with a pair of radially
projecting flange parts 30 that engage the tube surface 19 and
serve to support the plug body 11 in a coaxial spaced relation to
the tube 14 such that prior to detonation of the charge 16, a
predetermined radial standoff distance is established between tube
surface 19 and the cylindrical exterior surface portion 31 of body
11. The provision of such standoff distance allows the development
of sufficient impact velocity along the plug surface 31 upon
detonation of the explosive charge to achieve good bonding to tube
surface 19.
In the course of developing the invention a prototype heat
exchanger was constructed using Inconel tubes five-eighths inch
O.D. by 0.035 inch wall thickness received in a 231/2 inches thick
AISI 1020 steel tube sheet having 0.635-inch diameter tube holes
spaced 0.875 inch center-to-center. The tubes were roll expanded
into the holes over a depth of three-quarters inch and then seal
welded to the tube sheet.
Several explosive-activated plugs constructed substantially the
same as plug 10 were tested in the prototype to determine whether
the basic configuration of the plug 10 and its charge 16 would be
capable of effecting a fluid pressuretight seal of a typical
Inconel tube against a 3200 p.s.i. differential across the
plug.
The plugs were machined from Inconel bar stock of the same alloy as
that used for the tubes.
In terms of the reference numbers used in describing the plug 10,
the typical test plug had the following dimensions: ##SPC1##
In the test plugs, the explosive charge 16 was made up from
Detasheet C which is a PETN-base explosive manufactured by Du Pont.
The cylindrical block 23 was approximately three-eights inch
diameter by three-sixteenths inch thick and weighed 4.6 grains. The
cylindrical sheet 24 and conical sheet 25 portions of charge 16
were made by wrapping Detasheet around styrofoam filler pieces such
as those exemplified by 29 and 28 and taping the outside of the
assembled charge 16 and filler pieces 28, 29 to retain the several
components in their desired relative positions. The cylindrical and
conical sheets 24 and 25 were both approximately one-sixteenth inch
thick and weighed 28.9 grains and 14.0 grains respectively. The
detonator 17 used for each test plug was a X-549-D Minidet type
manufactured by Du Pont.
To determine the effect of tube surface oxidation upon the sealing
capabilities of the plugs, the Inconel tubes were first oxidized in
a steam atmosphere of 900.degree. F. for 20 days. The resultant
oxide coating on the inside of the tubes is believed to be
representative of the worst that would be encountered in actual
heat exchanger service.
The tubes were then explosively plugged using the apparatus and
method here disclosed without any further surface preparation.
Hydrostatic tests were performed on all tubes that were plugged and
it was found that in each case the plugs were able to withstand
3,200 p.s.i. water pressure without encountering any leakage.
In addition, the plugged tubes were given a helium leak check using
2,000 p.s.i. helium pressure behind each plug, and again no leakage
was detected.
Several of the plugged tube specimens were split longitudinally and
analyzed metallographically to determine the extent of welding. The
oxide layers on the tubes apparently had little or no effect on the
bond. The weld bond zone was found to extend completely around the
plug circumference and over an axial length portion approximately
one-half inch long located /1/4 inches from the rear end of the
plug.
In the metallographic examination, it was noted that some slight
evidence of the oxide appeared at the edges of the bond zone, as
would be expected, because of the jetting action occurring during
the explosive welding, which results in displacement and dispersion
of surface layers along the metal interface.
While in accordance with the provisions of the statutes there is
illustrated and described herein a specific embodiment of the
invention, those skilled in the art will understand that changes
may be made in the form of the invention covered by the claims, and
that certain features of the invention may sometimes be used to
advantage without a corresponding use of the other features.
* * * * *