JPS586141B2 - How to install an acoustic waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of attaching a waveguide rod for propagating acoustic information obtained at an acoustic vibration detection point to an acoustic-electric transducer.

For example, if a cooling water leak occurs during operation of a water-cooled nuclear reactor, a reactor coolant leak detection device that uses the phenomenon of leakage sound to quickly and accurately detect the leak, and an acoustic emission system. In a health monitoring device for various devices that utilizes the phenomenon (hereinafter abbreviated as "AE"), it is necessary to efficiently convert acoustic information obtained at a detection point into an electrical signal.

Taking the case of a water-cooled nuclear reactor as an example, primary cooling water normally circulates within the primary cooling system in a high temperature, high pressure, and highly activated state.

Therefore, in the operating state of the nuclear reactor, the temperature of the pipes, containers, etc. that constitute the pressure boundary of the primary cooling system is 200° C. or higher.

In addition, the locations where leakage and health of primary cooling water should be monitored are as follows:
They are extremely common, and in cases such as the riser pipe and inlet pipe of a pressure tube reactor, the number of pipes for the same purpose alone is several hundred or more.

Therefore, if a detector is attached to each pipe, a large number of detectors and a large number of electronic circuits attached thereto will be required, making the device complex and increasing equipment costs.

Therefore, a detector used in such an environment must satisfy the following conditions.

(1) Piezoelectric acoustic-electrical transducers (PZT) have a working temperature limit of approximately 60°C, so they must be installed in a location below this temperature. (2) Several hundred detection points can be detected using a small number of devices. (3) It must be detectable at a point as far away as possible from a high radiation environment.

In order to satisfy these conditions, metal waveguide rods with a diameter of 1 to 5 mm have conventionally been used.

That is, the tip of the metal waveguide rod is welded to the pipe wall or equipment wall, which is the acoustic vibration detection point, and the acoustic-electric conversion element is attached to the base end.

In addition, when using a small number of waveguide rods, as shown in FIG. 2a has a slightly larger diameter than the other waveguide rods 2b and 2c, and the waveguide rod 2b
, 2c are welded.

The tips of each waveguide rod 2a, 2b, 2c are welded to the wall surface of piping 3a, 3b, 3c, which is a detection point, respectively.

Acoustic vibrations from the AE source and the leakage sound source propagate through piping walls and equipment walls, and supply energy io to the waveguide rod.

Attenuation of waves in this type of waveguide rod is mainly caused by the welds 4 at the detection point, the welds 5 between the waveguide rods, and the master waveguide 2.
This occurs at the junction between a and the acoustic-electric transducer element 1.

The attenuation rate is 2 to 4 dB (
100-1000KHz), 6 at the welded part 5 of the waveguide rods
This results in a large value of ~8 dB.

Note that attenuation of waves can be prevented by using a silicon-based acoustic couplant at the coupling portion of the acoustic-electric transducer 1, so there is no problem.

Furthermore, if 10 to 20 detection points are monitored using one acoustic-electric transducer in the conventional method, it is impossible to weld all the other waveguide rods at one point of the master waveguide rod. Therefore, in terms of mechanical strength, each waveguide rod 9a, 9b, .
..., 9x must be installed at different welding positions, resulting in many branching points.

Therefore, the transmission of energy to the acoustic-electric conversion element 1 becomes poor, and the attenuation rate increases.

In addition, when the diameter of the waveguide rod becomes thicker than 10 mmφ, the frequency fraction formula fc∝c/d (where fo is the high-pass cutoff frequency (Hz), c is the velocity of the wave in the metal (cm/s), and d is the waveguide As you can see from the diameter of the wave rod (cm), the frequency is 100KHz.
More of the following frequency components (environmental noise components such as flow sound and pump rotation sound) will pass through, and the ratio of frequency components of 100 to 1000 KHz to frequency components of 100 KHz or less is smaller than in the case of a waveguide rod with a diameter of 5 mm or less. It is not appropriate because it will be small.

Furthermore, if the diameter of the waveguide rod is large, machining performance such as bending for attachment to a container, piping, etc. will deteriorate.

Therefore, in the conventional way of attaching waveguide rods, from the viewpoint of welding and attenuation rate, the number of waveguide rods that can be joined to one master waveguide rod is limited to about five.

An object of the present invention is to provide an acoustic waveguide which eliminates the drawbacks of the prior art as described above, has good wave propagation characteristics, and can connect a large number of waveguide rods to one acoustic-electric conversion element. The purpose is to provide an installation method.

The present invention will be explained in more detail below.

Insert the tip of a waveguide rod made of metal such as iron, copper, brass, stainless steel, aluminum, cadmium, etc. into a hole provided at the center of a solid waveguide cone in the shape of a pyramid or cone from the top, i.e. The ends are made into a thick shape, and silver solder or the like is poured into the gap between the two to join them.

Further, the bottom of the waveguide cone is coupled to a wall of a pressure vessel, piping, etc., which is an acoustic detection point.

In this way, the coupling area between the waveguide cone and the wall of the pressure vessel, piping, etc. becomes large, and it is possible to prevent the propagating waves from being attenuated at this coupling portion.

If only one waveguide rod is attached, the base end of the waveguide rod may be coupled to the acoustic-electric transducer through a disk.

Moreover, a conical shape may be used instead of a disk.

When a large number of waveguide rods are combined, the arrangement shown in FIGS. 3 and 4 may be used, for example.

The method of attaching the tip of each waveguide rod is almost the same as in the above case.

At the tip of each waveguide rod 12a, 12b, 12c, . . . , 12x, a waveguide cone 16a, 16b, 16c, .
Install 16x.

A desired pipe wall or equipment wall 13a, which is an acoustic vibration detection point. 13
b, 13c, . . . , 13x are provided with cylinders 17a. 1
7b, 17c, . . . , 17X are welded, and the waveguide cones 16a, 16b . 16c,...,
16x are joined by welding, silver soldering, or an appropriate jig.

Each waveguide bar 12a, 12b. The bases of the bundle fittings 12c, .
The tubes are tied together with a stepped circular tube 20 having a small diameter on the 9 side.

The upper end of the circular tube 20 is the waveguide bar 12a, 12b, 12c,...
・Set so that it protrudes outward by about 3 to 5 mm from the proximal end surface of , 12x.

Next, silver solder is poured into the top of the circular tube 20.

This silver solder fills the gaps 21 between each waveguide rod, and further forms a metal region 22 with a thickness of 3 to 5 mm up to the upper end of the circular tube 20.

The surface of the metal region 22 that is coupled to the acoustic-electric conversion element 11 is finished with a precision finish of about 6S and coated with an acoustic force plant.

This acoustic couplant may be made of conventional silicone grease.

In this way, the acoustic signal obtained at the acoustic vibration detection point is propagated to the acoustic-electric transducer element without being attenuated by the waveguide, and a master waveguide becomes unnecessary.

FIG. 5 shows a comparison example of the attenuation factors of the conventional master waveguide method and the waveguide rod bundling method of the present invention.

The symbol x in the figure a indicates an attenuation rate of approximately 8 dB when three waveguide rods each having a diameter of 4 mm are connected, a conical contact portion is used, and a signal is input to the mask waveguide rod.

In the case of the bundling method of the present invention using the same number of waveguide rods with the same wire diameter, b is approximately 2 dB, which coincides with c, the case of one waveguide rod represented by a black circle, within experimental error, and at the bundled part. It was confirmed that there was little attenuation.

Figure 6 shows a waveguide rod (diameter 4 mm, length 5 m) installed according to the method of the present invention when high-temperature, high-pressure water is released into the atmosphere.
) is the frequency spectrum of the output.

From this spectrum diagram, it can be seen that the signal propagates reliably up to a frequency of around 1000 KHz.

Since the present invention is a method for attaching a waveguide rod configured as described above, it is possible to efficiently transmit acoustic vibrations at a detection point to a waveguide rod, and also for one acoustic-electric conversion element. It is possible to couple a large number of thin waveguide rods without attenuating the acoustic signal, and therefore, it is possible to achieve an extremely excellent effect in that all of the above three conditions can be completely satisfied.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of the prior art, FIG. 3 is an explanatory diagram of an embodiment of the present invention, FIG. 4 is an explanatory diagram of the binding part, and FIG.
The figure shows the comparison results between the present invention and the prior art, and FIG. 6 shows the frequency spectrum of the output of the waveguide rod attached by the method of the present invention. 11...Acoustic-electric conversion element, 12a, 12b
, 12c,..., 12x... Waveguide rod, 13a
, 13b, 13c,..., 13x... detection point, 16a, 16b, 16c,..., 16X...
・Waveguide cone, 19... Bundling fittings, 20...
...Circular tube.

Claims (1)

[Claims] 1. A waveguide cone is connected in a tapered manner to the tip of a waveguide rod to which an acoustic-electric transducer is attached to the base, and the bottom of the waveguide cone is connected at an acoustic vibration detection point. A method of installing an acoustic waveguide that is fixed to a pipe wall or equipment wall. 2 A waveguide cone is connected to the tip of each of a large number of waveguide rods in a tapered shape, and the bottom of each waveguide cone is glued to the pipe wall or equipment wall that is the acoustic vibration detection point, and each waveguide is connected to the tip of each waveguide rod. A method of installing acoustic waveguide rods in which the bases of the wave rods are aligned, bundled, soldered together, and an acoustic-electric conversion element is attached.