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Патент USA US3093748

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United States I Patent 0
1 ,.
Patented June. 11, 1963
A water conduit with a varying diameter of from 3
to 9 inches and passing underneath the concrete ?oor
John P. Danforth, Mount Clemens, and Robert E. Black,
Utica, Mich, assiguors to General Motors (Iorporation,
of an industrial plant at a depth of about two feet was
known to have a leak at some location beneath the con
crete ?oor. The conduit was blocked at a location down
stream of the estimated location of the leak {and the ra
Detroit, Mich, a corporation of Delaware
No Drawing. Filed Mar. it), 1958, Ser. No. 720,079
3 Claims. (El. Nil-lilo)
dioactive capsule was placed in the conduit upstream of
a conduit and has particular utility as a means for de
a suitable mark was made on the concrete floor directly
this location. The movement of the capsule was fol
lowed by means of a Geiger counter, carried by a work
This invention relates to a method for detecting the 1O man, until the source of the radioactivity signal became
?ow path or other ?ow characteristics of a ?uid through
stationary indicating that the capsule had stopped. After
tecting the location of leaks in a conduit.
over the stationary radioactive signal, the block in the
It has heretofore been proposed to trace the ?ow path
conduit was removed, the ‘capsule thence continuing its
through, or to detect the location of leaks in conduits 15 movement ‘downstream where it was captured for reuse.
by introducing a radioactive material into the ?uid which
‘On digging down to the conduit at the marked spot, the
is carried by the conduit such that the movement of the
location of the leak was found to be as indicated by
?uid can be detected by a Geiger counter. In practice, this
the marking. The capsule employed in this particular
method has various serious disadvantages. One of these
instance comprised a small quartz vial of sodium-24
disadvantages is that the radioactive material quickly
becomes diluted in the ?uid with the result that after a
short period, the radioactive signal is of reduced intensity
and is emitted from over a large area. Thus, the exact
flow path is diflicult to follow. An even more serious
(3O millicuries) sealed in a polyethylene vial and posi
tioned in the center of an ordinary sponge rubber ball
about 2 inches in diameter, small lead weights being in
serted in the ball such that its over-all density was the
same as that of water.
disadvantage of this previously proposed method is the 25 In the instance where there are multiple leaks, the lo
potential health hazard of the radioactive material which
cation of each of the leaks is indicated by changes in
is introduced into the conduit. This disadvantage is par
the rate of movement of the capsule. That is, the rate
ticularly acute Where the method is intended to be used
of ?ow, and therefore the movement of the capsule,
for the detection of leaks in mains for ?uids such as
is greatest up to the location of the ?rst leak, at which
water and fuel gas to which the public may be exposed. 30 location the rate of movement of the capsule diminishes.
It is ‘an object of the present invention to provide a
There is ‘a similar reduction in the rate of movement
safe and accurate method for detecting the ?ow path
at each Subsequent leak until, at the last leak, the cap
and other flow characteristics of a ?uid through a con
sule stops. To increase the speed of the capsule to
duit. Another object of the invention is to provide an
the leak location or locations, the ?uid may be admitted
improved method for determining the location of leaks
under increased pressure upstream in the conduit.
in a conduit. Still another object of the invention is the
In addition to expediting the location of leaks, the
provision of a method for determining the exact rate
method of this invention has numerous other important
and direction of ?uid ?ow through a conduit. A more
utilities. For example, it may be used to chart the pre
particular object of the invention is to provide a radio
cise path of an inaccessible conduit. It sometimes occurs
active tracer method of determining the ?ow path and
that the precise location of a branch line junction in a
rate of a ?uid through a conduit wherein the radioactive
conduit is not known. In accordance with the present
material is maintained separated from, and undiluted
invention, the main conduit line may be blocked down
by the ?uid.
stream of the estimated location of the junction ‘and the
These objects are accomplished in accordance with the 45 radioactive capsule placed in the conduit upstream of this
invention by incorporating a radioactive material in a
estimated location. The capsule is thereby forced to fol
capsule which is suitably weighted to have the same aver
low the ?ow through the branch line and the location
age density as that of the ?uid in the conduit, placing the
of the junction is thereby pinpointed. The invention
capsule in the ?uid, and then following the movement
may also be used to determine the nate of ?ow through
of the capsule by means of a radiation detector external 50 a conduit, the speed of the capsule, as it is followed by
of the conduit. Because the capsule has a density the
a radiation detector, being ‘an accurate indication of the
same as that of the liquid it has no inherent tendency to
speed of the ?uid.
either rise or sink in the ?uid and thus little tendency
Where the invention is used in a gas main the capsule
to frictionally engage the Walls of the conduit. The term
may take the form of a rubber balloon ?lled with a ra
“capsule” is intended to comprehend any supporting struc 55 dioactive gas or with ordinary gas together with a solid
ture for the radioactive material which maintains the
or liquid radioactive source, the weight of the ?lled bal
radioactive material separated from the ?uid and which
loon being adjusted such that its density is the same as
‘itself is su?iciently impervious to the ?uid such that its
that of the gas in the main. In the instance of an oil,
density is not materially altered during the period of
water or other ?uid main, the capsule may comprise a
immersion in the ?uid. For example, the capsule may 60 ?uid-tight metal, glass, quartz, or plastic member con
take the form of a hermetically sealed envelope or it may
taining the radioactive tracer.
take the form of a solid material having a satisfactory
While the invention has been described speci?cally
density. Where the method is used to detect the location
with reference to a particular embodiment thereof, it is
of leaks, the conduit is blocked against ?uid ?ow down
understood that changes and modi?cations may be made,
stream of the estimated location of the leak and the cap 65 all within the full and intended scope of the claims which
sule is inserted in the ?uid upstream of this estimated
location, the movement of the capsule then being fol~
We claim:
lowed by a radiation detector. The capsule moves with
1. A method for detecting the location of an opening
the ?uid until it arrives at the location of the leak at
in a ?uid conduit comprising the steps of blocking the
which point its movement downstream ceases.
70 conduit downstream of the estimated location of the open
The following speci?c embodiment of the invention
will serve to more fully illustrate:
ing, placing in the ?uid upstream of the estimated loca
tion of the opening a capsule having substantially the same
density as the fluid and containing a radioactive material,
detecting any change in the rate of movement of the
pressure is applied to the ?uid upstream in the conduit
to increase the rate of movement of the ?uid ‘and of the
capsule through the conduit by following said capsule
capsule through the conduit toward the opening.
with a radiation detector external of said conduit, and
then remove the capsule from the conduit.
References Cited in the ?le of this patent
" 2. A method for determining the location of a leak
in a ?uid conduit comprising the steps of blocking the
conduit downstream of the estimated location of the leak,
placing in the ?uid upstream of the estimated location
,Wolf ______________ __ Dec. 14,
Jahn ________________ __ Aug. 8,
Crisrnan ____________ __ Mar. 4,
Metcalf ____________ __ Mar. 10,
Chawner ____________ __ Apr. 5,
Morganstern ________ __ Feb. 11,
of the leak a capsule having substantially the same aver 10
age density as the ?uid and containing a vial of radio
active material, detecting with a radiation detector ex
ternal ‘of said conduit the position in said conduit at
which the capsule ceases to move downstream, and then
removing the block in the conduit thereby allowing the 15 “Application of Radioisotopes to Leakage and Hydrau
lic Problems,” by Pulman et al., Peaceful Uses of Atomic
capsule to commence its movement downstream for re
Energy, The United Nations ‘Press, 1955, vol. 15, pages
moval from the conduit.
147 to 151.
3. The method as set forth in claim 1 and wherein
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