JPS58132657A - Electromagnetic ultrasonic flaw detector for slender pipe - Google Patents

Abstract

PURPOSE:To improve the sensitivity and resolution of the titled detector by a method wherein the coil of an electromagnetic sound transducer is divided into a plurality of coil groups, an exciting current is let to flow from a transmitter to them sequentially to generate an ultrasonic wave, and this wave is received, delayed and composed by a receiver. CONSTITUTION:An electromagnetic sound transducer 11 conducting ultrasonic flaw detection is formed by a method wherein ferrite cores 13 and permanent magnets 14 are arranged aternately between supporting bodies 12a and 12b, a coil 15 having coil groups 151-154 formed of a plurality of adjacent winding parts connected serially is wound on an outer periphery, and a unit thus formed is inserted into a slender pipe. An exciting current is let to flow from a transmitter 19 to each coil group sequentially to generate an ultrasonic wave. This wave is received by a receiver 20, delayed sequentially by a delaying circuit 24, and composed, and thereby a flaw is detected. Accordingly, a Lamb wave of high level is generated by composing Lamb waves, the Lamb wave detected is composed, and thereby the sensitivity and resolution can be improved sharply.

Description

[Detailed description of the invention] The present invention relates to an electromagnetic ultrasonic flaw detection device for thin tubes.

The present applicant has already proposed an electromagnetic acoustic transducer (hereinafter abbreviated as IMAT) that performs ultrasonic flaw detection by inserting a thin tube under pressure (No. 41, No. 56-149792). This EMAT
will be explained with reference to FIGS. 1 to 3.

11 in the figure is an electromagnetic acoustic transducer (Enu〒).
m, 11b and these supports j j a l j j
Nine ferrite cores 13 are alternately arranged and held between b.
. . , permanent magnet 14 . The permanent magnets 14... are arranged so that they have the same polarity with each other between the 7 elite cores IJ-, and the arrangement period (T , ) is equal to the wavelength λ of the line-generated ultrasound. As shown in FIGS. 1 and 2, coils 15 are arranged around the outer peripheries of the 7 elites; A1j... and the permanent magnets 14... Note that the distance t0 between the centers of adjacent coil windings is 1. /4 (-2/4), and each coil is connected in series.

Next, the operation when the ImTJJ having the nine structures described above is inserted into the thin tube 4 will be explained with reference to FIG.
When inserted into the thin tube 4, a magnetic flux BI in the direction perpendicular to the inside of the thin tube 4 is generated at the ferrite core IJ...
A magnetic flux B parallel to the axis of the thin tube 4 is generated in the central portion of the permanent magnets 14 . At this time, when the core 1s... and the permanent magnet 14 are wound around the outer periphery and a high frequency current of 9 coils 11iK is passed, an eddy current (2) parallel to the connection direction is generated in the thin tube 4 due to electromagnetic induction. However, a Lorentz force F is generated due to the interaction between this eddy current I and the magnetic flux BIIB distributed as described above. The direction of this Lorentz force F rotates with the same period as the period of the magnetic flux distribution, 3. As a result,
Ultrasonic waves (indicated by the dashed-dotted line in Fig. 4) that propagate transverse wave components perpendicular to i1 in the thin tube 4 and plate waves called five waves (indicated by the dashed-dotted line in Fig. 4) Generated on the network. This ultrasonic wave propagates through the thin tube 4, is reflected by defects in the thin tube 4, and returns.

However, it is necessary to convert this into an electrical signal in the reverse process to the above.Although the defective part of the thin tube 4 can be detected by 1°, the EMAT with the above structure has low sensitivity. It is necessary to connect many magnets 14 and increase the number of windings of the coil 7j to increase the excitation current and lengthen the excitation time. However, if the sensor section F:, MAT is lengthened, the inductance of the coil 15 increases, making it difficult to flow the excitation current.
The duration of the generated ultrasound (called the nosalus width) becomes longer. For this reason, if defects are densely present in the tubule,
There was a drawback that the reflected signals from each defect overlapped, resulting in a decrease in resolution.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and it is an object of the present invention to provide an electromagnetic ultrasonic flaw detection device for thin tubes that achieves improved sensitivity and improved resolution at the same time.

In other words, the electromagnetic ultrasonic flaw detection device for thin tubes of the present invention has the following advantages: ■ In the above-mentioned EMAT, all the coils are not directly connected to the coil 11, but are divided into multiple coil groups, so that the inductance can be reduced. It lowers the excitation current, making it easier to flow the excitation current, and together with the device described later, it is possible to improve sensitivity and resolution.

・2 As a device for flowing the above-mentioned EMATK excitation current, it is possible to control the timing of the current flowing through each coil group, thereby synthesizing the ultrasonic waves generated by each coil group, and as a receiver. By combining the signals detected by each coil group with a time delay, it can be used laterally with high sensitivity and low noise.

・Above] i: MAT, combining the transmitting/receiving device and other display devices, has higher sensitivity and resolution than K, and has a defect of 1 g.
The fact that you can read the issue directly.

This is a complete outline.

An embodiment of the present invention will be described below with reference to FIGS. 5 to 9.

11 in the figure is an EMAT, and this EMAT 11 is sandwiched between cylindrical supports 12* and 11b and these supports 12 and 1jb alternately as shown in Fig. 7. It includes a ferrite core 13... and a permanent magnet 14... The permanent magnets 14 are arranged with the ferrite cores 13 in between so as to have the same polarity. Further, the arrangement period (di) of the ferrite cores 13, 13 and the permanent magnets 14, 14 is equal to the wavelength λ of the generated ultrasonic wave. A coil 15 is wound around the outer periphery of the core 13 and the permanent magnet 14 as shown in FIGS. 5 and 6,
For example, four adjacent winding parts are connected in series = Ile group 1
5t, 15electrons, +J5g, , +J54 are formed, and the wire ends of these coil groups are extended to the outside.

Note that the distance t0 between the centers of the winding portions of adjacent coils is 1. /4 makes me feel good.

Further, as shown in FIG. 8, the transmitting/receiving device 11 is connected to the above-mentioned nine ERA device 11, to which a repeat/dulse signal is input from a pulse generator 16 to a transmitter. A display device II is connected to the receiver of this transmitting/receiving device.

The transmitting/receiving device rrFi as shown in FIG. It consists of the reception wi2°. Further, the signal transmitter 19 receives the signal input from the signal pulse generator 16, and a timing circuit 21 which generates the signal by delaying the signal by a preset time.
and a plurality of excitation current generating circuits 22 . . . which cause short-time high-frequency currents to flow through each of the coil groups 15 to 154 of the EMAT I J due to the noise of this circuit 21. Further, the receiver O has each coil group 151 of the EMAT 11.
A plurality of first amplifiers 23 that amplify the signals from ~15
..., a plurality of delay circuits 24 that delay the amplified signals from these amplifiers XS- by a predetermined time, and an adder 25 that adds the signals from these delay circuits 24...
The signal from the adder 2J is amplified and the signal from the display 1 is
11, and a second amplifier 2C that outputs an amplified signal.

Next, the operation of the electromagnetic ultrasonic flaw detection device for thin tubes of the present invention will be explained in the first place.
This will be explained with reference to FIGS. 0 and 11.

As shown in FIG. 10 (by inserting EMAT J 1 into the capillary tube 4 and repeatedly inputting pulses from the pulse generator IC to the timing circuit 21 of the transmitter 1#, the excitation current of the transmitter 1g is generated. Circuit z2 coil group IIs, 15
Snow, 15s K@11 As shown in the timing waveform diagrams in Figures (,) to (•), the excitation current is sequentially applied at different times.

That is, first, the coil group 15 consisting of the four endmost winding parts.
When an excitation current is applied to + at the timing shown in Fig. 11(a), the ultrasonic generation mechanism due to the combination of the coil 15, permanent magnet 14-, core 13, etc. explained using Fig. 4 above is generated. Ultrasonic waves (Lamb waves) are generated. This Lamb wave propagates within the wall of the thin tube 4 in the axial direction. Moreover, after 11 hours, this Lamb wave is generated in the coil group 16, which consists of four adjacent windings. reach. At this time, coil group 11. 1st to
When an excitation current is applied at the timing shown in FIG. 1(b) K, a Lamb wave is generated in the same way, and the phase coincides with that of the Lamb wave generated by the coil group 11+, so that the Lamb wave is amplified.

Similarly, if an excitation current of 11sK is applied to the coil group 13 hours later at the timing shown in Fig. 11(e) K, m1(a)
A further amplified composite Lamb wave can be generated as shown in FIG. In this way, each coil group 11 is delayed from the transmitter 19 one after another.
1, 11 111 m...K to flow the excitation current K
Yes, the time to excite the coil group with high-level Lamb waves is jt.
can only occur.

On the other hand, when performing detection, nine signals detected by one set of coils are sent to the amplifier 2 of the receiver 20 in the reverse process to the above.
The signal level is set to 1 by shifting the time of the delay circuit 14 through the J and the adder 2j.
The white noise level of a double amplifier, etc. is reduced to IA, 1
The 1/N ratio is improved by n,4 times. If there is a defect in the thin tube 4, reflection occurs and is detected by the receiver 20, and the defect signal can be directly read from the display 1aK connected thereto.

As detailed above, according to the present invention, a high-level Lamb wave can be generated by combining Lamb waves, and when one detected Lamb wave is combined, it can be detected with a particularly high 8/N ratio, and it is highly sensitive and Has high resolution and PWR-? It is possible to provide a device useful for detecting flaws in thin tubes and the like incorporated in FBR steam generators or condensers.

Note that the electromagnetic ultrasonic flaw detection device for thin tubes according to the present invention is not limited to the configuration in which one llmT K transmitting/receiving device is connected, and the flaw detection device may be constructed by connecting the transmitter and receiver to separate EMATs.

[Brief explanation of drawings]

Figures 1 to 3 show the 91MA'r that the present application has already proposed. Figure 1 is a front view, Figure 2 is a right 11th view of Figure 1, and Figure 3 is a coil winding. FIG. 3 is a front view of the CMA'r before installation. FIG. 4 is an explanatory diagram showing the operating principle of the mT. Figures 5 to 7 show the components used in the electromagnetic ultrasonic flaw detection device for thin tubes of the present invention. Figure 5 is a front view, Figure 6 is a right side view of Figure S, and Figure 6 is a right side view of Figure S. Figure 7 is a front view of the m-piece before winding the coil. Fig. 8 is a schematic diagram showing the flaw detection device of the present invention, Fig. 9 is a schematic diagram showing the transmitting/receiving device in the flaw detection device of Fig. 8, and Fig. 10 is an explanatory diagram showing the operating principle of the flaw detection device of the present invention. , Figures 11(a) to (+) are waveform diagrams showing the timing when the excitation current is applied to each fill group in the coil group, and Figure 11(d) is a waveform diagram showing the timing when the excitation current is applied to each coil group with a delay. It is a waveform diagram showing a synthetic Lamb wave obtained from Totoku. 4... Fine IF, J 7-1311A?, Z J-
... Ferrite core, 14... Permanent magnet, 11...
Coil, No. 151 to 15...Coil group, xg...Δ
Le J generation 11, ty... Transmitting/receiving device, 1 #-.
・Display device, 1#...Transmitter, 20...Receiver, 22
...Excitation current generation circuit, 24...Delay circuit, 21.
...Adder.

Claims (1)

[Claims] A coil group consisting of a plurality of disc-shaped cores, cylindrical permanent magnets arranged in a Kli-order arrangement so that the polarities face each other between these cores, and coils wound several times around these cores and permanent magnets. , a transmitter that sequentially sends an excitation current to each of these coil groups, and a Δlus that is repeatedly input to this transmitter/4
an electromagnetic superstructure for thin tubes, comprising: a pulse generator; a receiver that sequentially delays and synthesizes good signals detected by each of the coil groups; and a display that displays the received signals from the receiver. Sonic flaw detection equipment.