Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a method for mounting an
acoustic waveguide rod, or a rod-shaped metal member for
guiding acoustic wave, to effectively propagate acoustic
information obtained at any oE acoustic vibration detection
points to an electroacoustic transducer.
General:Ly, in a leak detection-system such as, for example,
a nuclear reactor coolant leak detector adapted to quickly and
accurately detect any coolant leakage by making use of a leak
sound resulted from the coolant leakage which accidentally
occurs during the reactor operation, or in a normalcy monitor-
ing system utilizing thephenomenon ofso-called acoustic emission
for various kinds of electrical and mechanical devices, it is
required to efficiently convert acoustic information obtained
at a detection point into an electric signal.
In the case of a water-cooled type nuclear reactor, for
example, the primary cooling water circulates in the primary
cooling system usually in a high temperature and high pressure
condition and in a highly radioactiva-ted state. Thus, pipes,
containers, etc. which constitute pressure boundaries of the
primary cooling system, are usually under a temperature above
200C when the reactor is in operation. In addition, there
are numerous spots which require constant monitoring for normal-
cy or leakage of the primary coollng water, and for instance
the number of risers or inlet pipes used in a pressure tube
type reactor totals more than several hundreds. Therefore,
if a detector is provided in each of these pipes or tubes,
there will be required a number of detectors as well as many
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appurtenant electronic circuits, resulting in a complicated
mechanism of the apparatus and the elevated equipment cost.
The detection system used under such circumstances needs
to meet the following requirements:
' (1) Since the threshold temperature for use of a piezo-
; electric type electroacoustic transducer (PZT) is around
1 60C, the system must be set at a place where the tem-
f perature will not rise above said level.
(2) The system must be able to monitor several hundreds
of detection points with a minimized number of means.
(3) It must be able to make detection at a location as
much away from the highly radioactive region as
possible.
In order to meet such requirements, there have been
heretofore employed an acoustic waveguide rod of metal having
a diameter of 1 to 5 mm. Such metallic waveguide rod is welded
at its distal end to a pipe wall or machine wall which is to
be an acoustic vibration detection point while the proximal
end is fixed to an electroacoustic transducer. In case only
a small number of waveguide rods are used, as shown in Fig. 1,
it is difficult to join an electroacoustic transducer 1 and
a plural number of waveguide rods, s~ that one master waveguide
, rod 2a is enlarged in diameter as compared with other waveguide
i rods 2b, 2c and the waveguide rods 2b, 2c are welded to a half-
way point of the length of the master waveguide rod 2a. The
distal ends of these waveguide rods 2a, 2b, 2c are welded to
the wall faces of the respective pipes 3a, 3b, 3c which are
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the detection points. The acoustic vibration from a source
of acoustic emission or leak sound propagates through the
pipe wall or machine wall to supply an energy ioto the wave-
guide rod. Attenua-tion of wave motion of this type of wave-
guide rod occurs principally at the welds 4 in the detection
areas, the welded portions S of the waveguide rod and the joint
of the master waveguide rod 2a and the electroacoustic transducer
1. The attenuation factor is 2 to 4 dB (100 to 1,000 KHz) at
the welds 4 in the detection areas and 5 to 8 dB at -the welded
portions 5 of the waveguide rod. The joint of the electro-
acoustic transducer 1 involves no serlous problem of attenua-
tion because it is possible to prevent wave attenuation by us-
ing an acoustic couplant of silicone type.
When 10 to 20 detection points are to be monitored by a
single electroacoustic transducer in a conventional system,
it becomes impossible to weld all of waveguide rods to a
master waveguide rod at one point. Thus, it is required from
the viewpoint of mechanical strength to weld the respective
waveguide rods 9a, 9b, .... 9x to a master waveguide rod 8 hav-
ing a diameter of about 10 mm at the different points along
its length as shown in Fig. 2, and hence many branching polnts
are provided. This obstructs propagation of energy to the
electroacoustic transducer 1 and increases the attenuation
factor; If the waveguide rod diameter is greater than 10 mm,
the frequency component of less than 100 KHz (environmental
noise component such as sound of flow or pump rotation) is
allowed to pass more than ~ther frequency components, that is,
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the ratio of the fre~uency component of 100 to 1,000 KH~ to
the frequency component of less -than 100 KHz becomes smaller
than that of the waveguide rod with a diameter of less than
5 mm. This is derived from the frequency fractional expres-
sion f ~ c/d, where f is high-pass cutoff frequency (Hz),
c is wave velocity (cm/sec) in me-tal, and d is waveguide rod
diameter ~cm). The large waveguide rod diameter also discommodes
machining such as bending work required for mounting of the
waveguide rod to a container or a pipe. Thus, according to
such conventional waveguide rod mounting method as described
above, the number of the waveguide rods that can be safely
joined to one master waveguide rod is about five at most, in
view of welding performance and attenuation factor.
An object of this invention, therefore, is to provide an
improved acoustic waveguide rod mounting method which is free
of the problems of the prior art such as mentioned above and
which allows mounting of the waveguide rod with excellent wave
propagation characteristic.
Another object of this invention is to provide an acoustic
waveguide rod mounting method which allows propagation of wave
motion to an electroacoustic transducer without causing attenua-
tion of acoustic vibration at any detection polnt.
Still another object of this invention is to provide an
acoustic waveguide mounting method which allows connection of
a plurality of waveguide rods to a single electroacoustic
transducer.
These and other objects are accomplished in accordance
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with this invention which involves a method for connecting
a pipe wall or machine wall, whcih is an acoustic vibration
detection point, with an electroacoustic transducer through
the medium oF a me-tallic acoustic waveguide rod. The distal
end of the waveguide rod is secured to a metallic conical or
pyramidal solid waveguide member in a divergent form. The
bottom of the conical or pyramidal waveguide member is joined
to the acoustic vibration detection point. The proximal end
of the waveguide rod is fixed to the electroacoustic transducer.
The effective joint of the bottom of the conical or pyra-
midal waveguide member to the pipe wall can be obtained by
welding a cylinder of metal to the pipe wall, and joining
the bottom of the waveguide member to the surface of the
cylinder.
The acoustic waveguide rod mounting method of this inven-
tion is suitably applied to the case wherein a plurality of
waveguide rods are connected to a single electroacoustic trans-
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ducer. In this case~ each of the distal ends of the waveguide
~ rods is secured to the acoustic vibratlon detection point of
a the pipe wall by using the conical or~pyramidal wavegulde mem-
~ ber. The proximal ends of the waveguide rods are bunched and
arranged properly, and are united each other by solder. The
electroacoustic transducer is then joined to the solder sur~ace.
Thus the method of this invention is not necessitated to provide
a master waveguide rod to which the other waveguide rods are
joined, so that the increse of the attenuation factor due to
the welder points is prevented.
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Details of the invention, and of a preferred embodiment
thereof, will be further understood with reference to the
j drawings, in which:
Figures 1 and 2 are schematic drawings for illustrating
conventional waveguide rod mounting methods;
Figure 3 is a drawing showing a waveguide rod mounting
method according to this invention where only one waveguide rod
is mounted;
Figure 4 shows another waveguide rod mounting method
according to this invention where a plurality of waveguide
rods are mounted;
Figure 5 is an enlarged sectional view of the portion
where the waveguide rods are united in the method of Fig. 4;
Figure 6 is a graph showing comparatively the attenuation
factor of the present invention and that of the prior art;
and
` Figure 7 is a frequency spectrum of the output from a
waveguide rod mounted according to the method ofthis inven-
tion.
'~ Referring now to Fig. 3, there is described an embodi-
f rnent of the waveguide rod mount1ng method of th1s 1nvent1on
where only one waveguide rod is mounted.
A rod-shaped waveguide 12 made of a metaI such as iron,
copper, brass, stainless steel, aluminium,cadm1um, etc., has
ltS distal end inserted into a hole formed centrally in a
pyramidal or conical solid waveguide member 16 from the top
thereof. Then, the inseFted end of the waveguide rod 12
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and the conical solid member 16 are joined together by casting
silver solder or the like into the space therebetween to
thereby form a divergent distal end. The bottom of the con-
ical waveguide member 16 is joined to a wall surface 13 of a
pressurized container or a pipe which forms an acoustic detec-
tion point. This distal end arrangement can enlarge the joined
area between the conical waveguide member 16 and the wall 13
of the pressuri~ed container or pipe, making it possible to pre-
vent attenuation of the propagated wave at this joined portion.
The bottom of the conical waveguide 16 may be directly
joined to the wall 13, but it is also possible to previously
weld a cylinder 17 to the wall 13 and then ~join the bottom of
the conical waveguide member 16 to the surface of the cylinder
17 by weld1ng, silver soldering or a suitable jig, as shown
in the drawing.
Joint of the proximal end of the waveguide rod 12 to an
electroacoustic transducer 11 can be effected with the inter-
mediate of a metal disc 18 when only one waveguide rod is
mounted; The disc may be substituted by a corical metal block.
In case a plural number of waveguide rods are used in
combination, an arrangement such as shown in Figs. 4 and5may
be employed. The distal end of each waveguide rod is joined
to the wall surface in the same way as the embodiment of Fig. 3.
That is, the distal ends of the respective wavegu1de rods~12a,
12b, 12c, ... 12x are secured to the corresponding conical wave-
guide members 16a, 16b, 16c, ... 16x. The cylinders 17a, 17b,
.
17c, ... 17x are previously welded to the desired pipe walls
or machine walls 13a, 13b, 13c, ... 13x which are the acoustic
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vibration detection points, and the conical waveguide members
16a, 16b, 16c, ... 16x are joined to the surfaces of the
respective cylinders.
The proximal ends of the respective waveguide rods 12a,
12b, 12c ... 12x are arranged properly and passed through
respective holes in a perforated bunching plate 19. The thus
bunched proximal end portions of the waveguide rods which have
been passed through the bunching plate are then united by a
round tube 20 which comprises a small diameter portion 20a
and a large diameter portion 20b, these portions 20a and 20b
being connected by a step portion 20c; The end of the small
diameter portion 20a abuts on the bunching plate 19 and fixed
thereto.
The round tube 20 is so designed that the top end of the
large diameter portion 20b is extended higher by a length of
about 3 to 5 mm than the proximal end eaces of the waveguide
rods 12a, 12b, 12c, ... 12x. Then silver solder is cast into
the round tube 20 from the top opening thereof. This silver
solder fills the spaces 21 between the respective waveguide
rods within the round tube to form a metal region 22 of 3-5 mm
thick reaching to the top end of the round tube 20. The face
of the metal region 22 to be joined to the electroacoustic
transducer 11 is subjected to fine fishining of approximately
6S and then coated with an acoustic couplant. This acoustic
couplant may be a conventional silicone grease. According to
this arrangement, th.e acoustic signal obtained at any acoustic
vibration detection point is propagated to the electroacoustic
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transudcer lt without decay by the waveguide rods, so that a
master waveguide rod is unnecessitated.
Fig. 6 is a graph showing comparatively the attenuation
factor given in a conventional master waveguide rod system and
that noted in the waveguide rod bunching system of this inven-
tion. In the graph, a mark X indicated by (a) is the attenua-
tion factor which is given when three waveguide rods having 4
mm diameter are combined conventionally by welding two of
these three rods to the remaining one master rod, and the
respective distal ends of the rods are contacted to a pipe
wall via a conical solid waveguide member, and a signal is
applied to the master rod. In this case, the attenuation fac-
tor (a) is about 8 dB. The point (b) shows the attenuation
factor of about 2 dB, which is observed in the bunching sys-
tem of this invention using the same number of waveguide rods
having the same diameter. This point (b) agrees, within the
experimental errors, with the attenuation factor curve (c)
obtained when a single waveguide rod is used. This ascertains
that substantially no attenuation takes place at the bunched
portion.
Fig. 7 is the frequency spec-trum of output from a wave-
guide rod (~ mm in diameter and 5 m in length) mounted accord-
ing to the method of this invention in a conditlon where high
tempera-ture and high pressure water was released into the
atmosphere. This spectral diagram indicates posltive pro-
pagation of acoustic vibration with frequency of up to about
1,000 KHz.
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Thus, when waveguide rods are mounted according to
the method of this invention, the acoustic vibration at any
detection point is efficiently propagated to an electroacoustic
transducer, and it becomes possible to Join a plurality of
fine waveguide rods to a single electroacoustic transducer
w:ithout causin~ attenuation of the acoustic signal. It will
be understood that the method of this invention can meet all
of the aforesaid three requirements which are necessary in
the acoustic vibration detection system under high temperature,
high pressllre, high radioactiv-ty and comp icated piplng state.
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