JPS638424B2 - - Google Patents

Description

[Detailed description of the invention] In pressurized water reactors, fast breeder reactors, etc., the inner diameter is
A steam generator and a superheater are installed using thin tubes of about 10 to 30 mm as heat transfer tubes, and the heat generated in the cooling system and the reactor is exchanged through these.

It is highly desirable for the safe operation of the furnace to periodically inspect whether the thin tube is healthy or not, and to take measures to prevent damage from penetrating the tube wall.

Conventionally, methods such as X-ray inspection and eddy current inspection have been applied to inspect these thin tubes, but it is difficult to inspect them once they have been assembled as a structure.
It was accompanied by various difficulties.

In particular, when the total length of a helical coiled heat transfer tube is several tens of meters, such as in a fast breeder reactor steam generator, many welds and structures are installed on the outside of the tube to support it. Furthermore, due to the problem of radiation exposure, it is virtually impossible to inspect the tube from the outside, and it is necessary to insert a probe into the inner surface of the tube for inspection.

By the way, the tubes of steam generators are not necessarily straight, but may be helical or U-shaped, so flaw detection is carried out by inserting a probe that emits and receives ultrasonic waves into the tubes. It has been experimentally confirmed that the shape of the probe and the thickness of the cable connected to it greatly affect the ease of inserting the probe.

In other words, the minimum required components of an ultrasonic flaw detection probe are an exciter for emitting ultrasonic waves and a receiver for receiving ultrasonic waves and converting them into electrical signals, but the entire circumferential surface of the tube is In order to detect flaws, it is necessary to send and receive ultrasonic waves all over the circumference in some way. This is called scanning, and it is well known that conventional scanning methods include electrical methods and mechanical methods using motors, etc., and probes for thin tubes also perform this scanning. element is required.

The challenges when detecting flaws from the inner surface of a helical coiled tube with an inner diameter of approximately 20 mm and a total length of approximately 60 m are as follows.
The aim was to create a probe that could detect flaws at high speed and with high precision, and that could be inserted over the entire length of the pipe.

Therefore, in order to speed up flaw detection, the most effective method is to electrically scan the rotational scanning of an ultrasonic beam, but if the element for this scanning is installed outside the pipe, The structure is such that many signal lines from each exciter and receiver pass through the tube.

This situation will be explained using FIG. In Fig. 1, 1 is a cross section of the tube to be tested, and 2 is an ultrasonic probe with exciters or receivers 21, 22...
are arranged in a circumferential direction, and signal cables 21a, 22a, . . . are connected to each of them.

Numeral 3 is a multiplexer for excitation and reception by sequentially switching the vibrators for flaw detection in the circumferential direction of the tube. 100 is a flaw detection device.

The probe in Figure 1 shows an example in which the exciter and receiver are shared by a common transducer. Even in that case, if the circumferential direction is divided into about 16 sections, at least 16 cables will pass through the tube. It also becomes. In reality, the number of circumferential divisions needs to be even larger, and when the ultrasonic signal path is short, for example when the tube inner diameter is small or the tube wall thickness is thin, the exciter and receiver If we have this in common,
Since the next received wave returns before the excitation pulse and the reflected wave from the tube surface are sufficiently attenuated, it becomes impossible to detect flaws near the inner surface of the tube. In such a case, it is necessary to separate the two, but then the number of cables will be doubled.

Furthermore, since the amount of attenuation of high-frequency signals generally increases in inverse proportion to the cable diameter, it is not desirable to make the cable diameter too small in ultrasonic flaw detection that handles signals of several MHz.

In order to insert such a probe into a helical coiled thin tube, it is possible to connect a piano wire or the like to the probe and push it in, but experiments with thin tubes with an inner diameter of about 20 mm show that even with careful manipulation, If you insert about 10m at most,
It was experimentally confirmed that further insertion was impossible.

Therefore, it became clear that the probe needed to be inserted using water or air pressure, but even in this case, the diameter of the cable connected to the probe was several mm.
It has become clear that insertion becomes extremely difficult if the probe is inserted over the entire length of the steam generator heat exchanger tube, which is several tens of meters long and has an inner diameter of approximately 20 mm.The cable diameter must be thinned to about 2 to 4 mm. It was confirmed that it was necessary to do so.

As mentioned above, for probes that detect defects in helical coil-shaped heat transfer tubes, it is necessary to minimize the number of cables and reduce the finished outer diameter of the cables from the viewpoint of ease of insertion. By separating the exciter and the receiver, the number of cables increases, and in addition, it is necessary to use cables with as large a diameter as possible in order to improve the fidelity of the transmitted signal.

The present invention was made to solve these conflicting demands, and its purpose is to insert a probe that electronically scans an ultrasonic beam from inside the tube over the entire length of the helical coiled tube. It is an object of the present invention to provide an ultrasonic flaw detection device for a helical coiled thin tube configured to perform flaw detection with high accuracy.

First, an outline of an ultrasonic flaw detection apparatus using the probe of the present invention will be explained.

FIG. 2 is a diagram showing an example of a flaw detection device to which the present invention is applied, in which there are i (i is an integer) probes 6 for excitation and reception, which are arranged in parallel in the circumferential direction of the tube 1. It consists of a transducer 2, a multiplexer 3 for sequentially switching the received signals of the i transducers, a preamplifier 4 for amplifying the received signal, and a channel selector 5 for switching the multiplexer. In other words, the first feature of the device of the present invention is that, in order to improve defect detection in short paths, the exciter and the receiver are separated and each has a plurality of transducers arranged side by side in the circumferential direction. is simultaneously excited to irradiate the entire circumference of the tube with an ultrasonic beam, and the receivers are sequentially switched to receive reflected waves.
A detailed embodiment of the probe 6, in which at least the exciter, the receiver, and the multiplexer are inserted into the pipe to greatly reduce the number of cables, is shown in FIG. By closing the electronic switches 31 to 3i in the multiplexer 3, the signals from any one of the receiving transducers 2 are sequentially taken out to the terminal 5a in the circumferential direction. controlled by. Further, the decoder 52
It outputs a signal that corresponds one-to-one to the output of the counter 51, and known types are used.

Furthermore, in order to make the probe smaller and lighter, the ultrasonic excitation transducer is designed to simultaneously excite with the same excitation pulse of several 100 V, and the relative positions of both the transmitting and receiving transducers are determined so that the received ultrasonic signal is Each pair is arranged at a suitable position so as to maximize the number of pairs.

When testing a thin tube using the flaw detection device configured as described above, first, channel switching circuit 1 shown in Fig. 2 is used.
A pulse (indicated by P _r in FIG. 3) for resetting the counter 51 in FIG. to be accomplished. Next, an excitation pulse shown as P _E in FIG. 3 is applied to the ultrasonic transmitting transducers 21' to 2i' shown in FIG. 4 via the cable 12a to output ultrasonic signals.

This ultrasonic wave returns from the boundary layer on the surface or bottom of the tube to be tested as surface reflection (S _S in Fig. 3) or bottom reflection (also B _r ).

Both reflected waves are converted into electric signals by the vibrator 21, passed through the electronic switch 31, inputted to the preamplifier 4 shown in FIG. 2, and amplified by the cable 13a.
is guided to the receiving circuit 13 by.

The receiving circuit 13 receives this signal and detects a reflected wave of a certain value or more between the surface wave and the bottom wave (for example, the third
It is determined whether there is a defect or not based on the presence or absence of D _r ) in the figure or the position of the surface wave. In this case, the probe has separate exciter and receiver,
Even when the ultrasonic beam path from the exciter to the tube inner surface is short or the tube inner thickness is thin, the excitation pulse surface retransmission waves, bottom surface reflection waves, etc. are resolved in time and can be clearly identified (in this case, (Although not shown, a sound insulating plate is usually provided between the exciter and receiver).

Next, when a channel switching pulse (Fig. 3 P _a ) is applied to the counter from the switching circuit 11 via the cable 11b, the count value of the counter changes by 1.
The fourth transducer receives the signal of the next transducer in the circumferential direction.
The switch 32 shown in the figure is closed to excite the excitation vibrator.

Thereafter, in the same manner, when all the transmissions and receptions of the i transducers are completed, a reset pulse is outputted again to repeatedly transmit and receive the i transducers, and the ultrasonic beam is electrically scanned and rotated at high speed. Resetting this counter is necessary to know the transmitting and receiving position of the ultrasonic beam in the circumferential direction. Note that 10 in Figure 2
is a control circuit that controls the overall timing.

In addition, there are three cables to supply power to each part of the probe 6 (for AC signal amplification,
Three wires are required: positive, negative, and ground wires, and the second
(shown as 14a and 14b in the figure), and even if the grounding wires of each part are made common, the minimum number of gable core wires required is six.

By the way, if the cable for vibrator excitation pulses and reception signals is about 1 mm or less, various adverse effects will appear electrically, and the mechanical tensile strength will be weak, which is problematic.

Therefore, in the device of the present invention, the counter reset signal cable and, for example, the positive power supply line are shared, and the channel switching pulse cable and the negative power supply line, for example, are shared, respectively, and the number of required cable core wires is reduced to four. This is the second feature.

A specific example to which this is applied is shown in FIG.

As is clear from FIG. 4, in the probe of the present invention, the cable core wires are 14a, 14b, 13a, 1
2a, and the counter reset terminal P _r
is connected to the negative pole line of the power supply through a differential circuit consisting of resistor R1 and capacitor C2,
Further, the channel switching pulse input terminal P _a is connected to the positive electrode line of the power supply.

In other words, as is clear from the operating waveform diagram in Figure 3, when a reset pulse or channel switching pulse is applied, the transmission and reception of the flaw detection pulse is interrupted, and if only the power supply voltage of the counter is maintained, the flaw detection itself has no effect.

The voltage of the counter (memory part) is diode D1
Since the pulse application is held for a short period of time by a holding circuit consisting of a capacitor C1 and a capacitor C1, the previous count value does not change.

In order to turn the power on and off, the output of the channel switching circuit 11 is connected to transistors T ₁ and T _{2 .}
signals P _r and P _a that are applied to switch elements consisting of
is given to the base.

As described above, the number of lines is reduced, for example, the vibration pulse cable 12a and the receiving signal cable 1.
For 3a, we used a commercially available coaxial cable with an outer diameter of about 1.5 mm to 2 mm, which does not have a large amount of attenuation, and used a 2-core shielded wire with the same diameter as the power supply wire. When three strands are used, the finished outer diameter can be set to about 3.2 to 4 mm.

Note that since the usage times of the excitation pulse cable 12a and the reception signal cable are different as shown in Figure 3, it is theoretically possible to use both cables in common, but in reality, both the transmission and reception ends and the cable characteristics are different. Since it is impossible to perfectly match the impedances, reflected signals appear within the cable.
It is easy to understand that if both are used in common, the influence of the ultrasonic transmission signal will be greatly affected by the received signal, degrading the flaw detection performance, so it is impossible to share them.

It is also possible to use a single power line to send an AC signal and rectify and smooth it within the probe to obtain positive and negative voltages, but this would require a cable for channel switching, so the number of cables would not be reduced.

In short, it is extremely difficult to reduce the number of cables to a level lower than that of the apparatus of the present invention without affecting the flaw detection performance.

As explained above, in the flaw detection device of the present invention, by arranging a plurality of exciters and receivers separated in the circumferential direction, surface reflected waves and bottom reflected waves are clearly detected even in small-diameter or thin-walled pipes. This improves the detectability of defects. In addition, it is configured to excite multiple exciters simultaneously and switch receivers sequentially, and these exciters, receivers, and multiplexers are inserted into the tube to connect the probe and flaw detection equipment installed outside the tube. By significantly reducing the number of transmission cables in between and improving insertion ease, it has the effect of being able to detect flaws over the entire length of the helical coiled tube.
By simultaneously exciting multiple exciters, the entire circumference of the tube is irradiated with an ultrasonic beam. In addition to requiring only one excitation cable, scanning requirements for multiplexers, etc. can be reduced, and the probe itself is small and lightweight. It is possible. Furthermore, according to the content of claim 2, there is an additional effect of facilitating the inspection of defects inside the helical coiled tube by further reducing the number of cables by superimposing the signal line on the power line. .

In the embodiment shown in FIG. 4, the same effect can be obtained even if the power supply lines for obtaining the reset pulse and the channel switching pulse are reversed.

[Brief explanation of the drawing]

Figure 1 is an example of a conventional ultrasonic flaw detection device, Figure 2
The figure is a diagram of a specific embodiment of the ultrasonic flaw detection device of the present invention.
3 is an operational waveform diagram of the embodiment shown in FIG. 2, and FIG. 4 is a partially detailed diagram of the embodiment shown in FIG. DESCRIPTION OF SYMBOLS 1... Thin tube, 2 ... Vibrator, 3... Multiplexer, 4... Preamplifier, 5... Channel selector, 6 ... Probe, 10... Control circuit, 11...
...Channel switching circuit, 12...Excitation circuit, 13...
...Receiving circuit, 14...Power supply.

Claims (1)

[Scope of Claims] 1. A probe equipped with a plurality of ultrasonic transducers arranged in a circumferential direction, a multiplexer that switches and connects the transducers to a flaw detection device, and a channel sector that indicates the switching destination of the multiplexer. In the ultrasonic flaw detection device for pipes, the ultrasonic transducer is divided into an exciter and a receiver and arranged in parallel, the multiplexer is connected only to the receiver, and the exciter, the receiver, the multiplexer, and the channel selector are connected. An ultrasonic flaw detection device for a helical coiled thin tube, characterized in that the probe is provided with: 2. The ultrasonic flaw detection device for a helical coiled thin tube according to claim 1, characterized in that a power supply line to a device in the probe is provided with means for superimposing a transmission signal to the channel selector.