JP2693009B2 - Metal flaw detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a metal material flaw detector, and particularly to maintenance of pipelines such as buried gas pipes, chemical plant pipes, heat exchanger pipes, and the like.
The present invention relates to a metal material flaw detector for controlling by a remote field eddy current method.

[Prior Art and Problems to be Solved by the Invention] Conventionally, in order to detect a flaw in a metal material by using a remote field eddy current method, an exciting coil and one or more receiving coils are doubled in diameter. A probe configured by arranging it in the tube axis direction at a distance of about a certain distance or more is attached to a cable for signal transmission, inserted in a tube, and an exciting signal is applied to an exciting coil.

The applied excitation signal has a relatively low frequency (several 10 Hz to several
At 100 Hz), a voltage of several V to several tens of V is provided.

The electromagnetic waves generated by the excitation signal are divided into those that pass through the wall thickness of the test pipe and those that propagate inside the pipe. The electromagnetic waves that propagate inside the pipe are Since the frequency is much lower than the cutoff frequency, it is rapidly attenuated and hardly propagates.

On the other hand, what passes through the wall thickness of the pipeline is called indirect propagation wave, and propagates along the pipeline outside the pipe and is slowly attenuated, while at the same time, it partially passes through the wall thickness again and Permeates into and is detected by the receiving coil.

The signal detected by the receiving coil (hereinafter referred to as the received signal) is extremely weak (several μV to several tens of μV) because it passes through the pipe wall thickness twice, and the skin effect due to the passage of the pipe wall thickness It is affected by the phase change. In the remote field eddy current method, the phase change with good linearity with the pipe wall thickness is often used as information.

The amplitude and phase information of the received signal can be measured by a measuring device such as a so-called lock-in amplifier, or the measuring device can be configured by a known technique such as a differential amplifier, a band pass filter, a phase comparator. .

As described above, since the received signal in the remote field eddy current method is very weak, it is usually amplified in the probe section and then sent to the measuring instrument provided outside the conduit with the cable connecting the probe. By thus amplifying the weak signal, noise from outside the cable can be dealt with, and a high level excitation signal can be accommodated in the same cable.

However, when the amplifier is arranged in the probe section, the size of the probe becomes large and the rigidity increases, and it is not possible to deal with design conditions such as application to a small pipe diameter and an increase in the number of receiving coils. Further, the cost of the probe portion for satisfying this design condition is increased, the number of failure factors is increased, and the degree of freedom in designing the probe portion can be prevented. For this reason, it is desirable to send and receive the received signal without processing it with an amplifier, network, etc., but since the signal level is very small, the signal received from the outside of the cable and the excitation signal, that is, the disturbance, causes a disturbance signal in the original received signal. There is a problem that the signals are superimposed and the signal evaluation becomes difficult. Regarding disturbances from the outside of the cable, the above problems can be dealt with if the cable length is up to several tens of meters by a known technique such as using a so-called shielded transmission pair wire, but induction by an excitation signal, that is, against disturbance Can not deal with. In particular, when two or more receiving coils are provided and the receiving signal is transmitted and received by the multi-core cable, the level of the induction, that is, the disturbance, due to the excitation signal varies depending on the position of the multi-core cable, and even if the same defect is present, each receiving coil is different. Normal detection data cannot be obtained because the detection sensitivity differs depending on the type.

If the excitation signal line and the reception signal line are separate cables, induction by the excitation coil, that is, disturbance can be removed, but it is not desirable in terms of device configuration to insert two cables into the conduit. Also, there is a method of inducing an excitation signal, that is, a method of reducing disturbance by a cable structure, but there is a drawback that the cost of the cable increases if a special cable is used.

[Object of the Invention] The metallic material flaw detector according to the present invention has been made in view of the above-mentioned drawbacks, and uses an ordinary single multicore cable to induce an induction signal included in a received signal, that is, a disturbance signal. It is an object of the present invention to provide a metallic material flaw detector which can be removed to obtain a flaw detection signal with good resolution.

[Means for Solving the Problems] A metallic material flaw detector according to the present invention includes a reference signal generator that generates a reference signal, a power amplifier that amplifies the reference signal to a predetermined power and supplies AC power, and AC power. An exciting coil that applies an exciting signal to generate a remote field eddy current in the metal under test, and a plurality of receiving coils that are provided separately from the exciting coil for a predetermined period and that receive the remote field eddy current and output a plurality of received signals, In a multi-core cable composed of an excitation signal transmission pair line for applying an excitation signal to an excitation coil and a plurality of reception signal transmission pair lines for outputting a plurality of reception signals from a plurality of reception coils, and in a multi-core cable For a plurality of received signals respectively induced by the excitation signal, a phase shift is performed at a predetermined phase angle from the excitation signal applied to the excitation coil, and a predetermined vibration is applied. A plurality of circuits that output a reception signal obtained by subtracting the guidance correction signal from each reception signal that has received the guidance by subtracting the guidance correction signal adjusted to the width, and the reception signal from which the guidance correction signal is subtracted and the reference signal. A plurality of phase comparators that compare phases and output a plurality of flaw detection data are provided.

[Embodiment] A preferred embodiment of the metallic material flaw detector according to the present invention will be described in detail below with reference to FIG.

In FIG. 1, EQn (for the sake of explanation, n is 1 ... 9) is a received signal processing device. Received signal processor EQ ₁
Is a received signal processing unit 2, a disturbance signal forming unit 8, a signal output unit 11
It consists of.

The reception signal processing unit 2 includes a differential amplifier 3, a low pass filter 4, a reception amplifier 5, and a band pass filter 6,
A reception signal f ₁ described later is input to the differential amplifier 3 via the terminals T ₁ and T ₂ to which the reception signal transmission pair line P _{1 of the} cable CBL shown in FIG. 2 is connected. The received signal f ₁ input to the differential amplifier 3 has its high-frequency component removed by the low-pass filter 4, amplified by the receiving amplifier 5, and sent to the band-pass filter 6. The received signal output from the band pass filter 6 includes an excitation signal transmission pair line P described later according to the position of the reception signal transmission pair line Pn of the multi-core cable CBL shown in FIG.
Induction by an excitation signal of ₀ , that is, a disturbance signal is included.

The disturbance signal forming unit 8 includes an attenuator 9 and a phase shifter 10,
The reference signal input via the terminal T ₃ is appropriately attenuated by the attenuator 9, and the received signal transmission pair line Pn shown in FIG.
The phase shifter 10 shifts the phase angle corresponding to the phase shift corresponding to the position of, to generate a phase shift signal.

The signal output unit 11 includes an arithmetic circuit 12, a waveform shaper 13, a phase comparator 14, and a low-pass filter 15. The signal output unit 11 outputs the phase shift signal output from the phase shifter 10 of the disturbance signal forming unit 8 and the reception signal processing unit 2. The reception signal output from the band pass filter 6 is calculated by the calculation circuit 12, the phase shift signal forming the disturbance signal is removed from the reception signal, and the phase comparator 14 via the waveform shaper 13
Send to The phase comparator 14 compares the phase of the reference signal input from the terminal T _{4 with} the phase of the received signal from which the disturbance signal output from the waveform shaper 13 has been removed, and the terminal compares with the low-pass fill 15 according to the comparison. A flaw detection signal is output from T ₅ .

A reference signal generator 20 that outputs a reference signal sends an excitation signal in phase with the reference signal to the excitation coil PC of the probe PRB as AC power via the power amplifier 21. Excitation coil PC
Sends the remote field vortex generated in the pipe to the receiving coils SC ₁ to SC ₉ .

Receiver coil SC ₁ to SC ₉ outputs the respective received signal to the terminal T _1, T ₂ via the received signal transmission wire pair P ₁ to P ₉ reception signal processing circuit EQ ₁ ~EQ _9.

The multi-core cable CBL shown in FIG. ₂ is an ordinary 20-core cable having transmission pair wires P _{0 to} P ₉ and composed of a central cord CB ₁ and an outer cover CB ₂ .

[Operation of the Invention] In the metal flaw detector having the above-described configuration, the received signals f _{1 to} f ₉ are received signal transmission pair line P ₁ of the cable CBL.
An induction signal, that is, a disturbance signal, is generated by the unique excitation signal based on the excitation signal transmission pair line P ₀ corresponding to the positions of P ₉ to P ₉ , as shown in FIG. Phase θn can be pre-measured,
Moreover, the phase difference of each disturbance signal is about 15 ° at the maximum, and the phase of each disturbance signal hardly changes depending on the voltage of the excitation signal.
Further, since only the amplitude of the disturbance signal changes in proportion to the voltage of the excitation signal, it is possible to reliably calculate the received signal due to the original remote field eddy current and to perform flaw detection with high accuracy.

[Effect of the Invention] According to the metallic material flaw detector of the present invention, a reference signal generator that generates a reference signal, and amplifies the reference signal to a predetermined power,
A power amplifier that supplies AC power, an excitation coil that applies an excitation signal by AC power to generate a remote field eddy current in the metal under test, and a remote field eddy current that is separated from the excitation coil for a predetermined period and receives multiple remote field eddy currents. One composed of a plurality of reception coils that output reception signals, an excitation signal transmission pair line that applies an excitation signal to the excitation coil, and a plurality of reception signal transmission pair lines that output a plurality of reception signals from the plurality of reception coils The multi-core cable and the multiple reception signals respectively induced by the excitation signal in the multi-core cable are phase-shifted and predetermined by the phase angle predetermined from the excitation signal applied to the excitation coil. A plurality of circuits for subtracting the induction correction signal adjusted to the amplitude and outputting the reception signal obtained by subtracting the induction correction signal from each reception signal that has been induced, By including a plurality of phase comparators that compare the phases of the received signal from which the derivation correction signal is subtracted and the reference signal and output a plurality of flaw detection data, the normal received signal is included in the received signal using a single multicore cable. The flaw detection signal with high resolution can be obtained by removing the disturbance signal induced by the excitation signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a metallic material flaw detector according to the present invention, FIG. 2 is a configuration diagram of a cable used in the embodiment of FIG. 1, and FIG. 3 is a disturbance signal of the cable of FIG. It is a characteristic view which shows a measured value. PC: Excitation coil SC _{1 to} SC ₉ …… Reception coil f _{1 to} f ₉ …… Multiple reception signals CBL …… One multi-core cable P ₀ …… Excitation signal transmission pair line P _{1 to} P ₉ …… Multiple reception signal transmission pair lines 9, 10, 12 ... Multiple circuits that output reception signals (9 ... attenuators) (10 ... multiple phase shifters) (12 ... multiple arithmetic circuits) 14 ... … Multiple phase comparators 20 …… Reference signal generator 21 …… Power amplifier

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Takao Yamagishi 4-1-2 Hirano-cho, Chuo-ku, Osaka-shi, Osaka Within Osaka Gas Co., Ltd. (72) Inventor Katsumi Morihara 4-chome, Hirano-cho, Chuo-ku, Osaka-shi, Osaka 1-2 No. 2 in Osaka Gas Co., Ltd. (72) Inventor Shigeru Fujiwara 2-12-12 Nishi-chuo, Kure-shi, Hiroshima Prefecture China X-ray Co., Ltd. Development Division (72) Inventor Toshihide Kawabe 2 Nishi-chuo, Kure-shi, Hiroshima Prefecture No. 1-12, China X-ray Co., Ltd. (56) Reference JP-A-63-221240 (JP, A) JP-A-63-298052 (JP, A) JP-A-62-172259 (JP, A)

Claims (1)

(57) [Claims] 1. A reference signal generator (20) for generating a reference signal.
And a power amplifier (21) that amplifies the reference signal to a predetermined power and supplies AC power, and an excitation coil (PC) that applies an excitation signal by the AC power to generate a remote field eddy current in the metal under test. When a plurality of receiving coils for outputting provided apart a predetermined distance from the exciting coil to receive the remote field eddy current plurality of received signals _{(f 1 ~f 9) (SC} 1 ~SC 9), the excitation coil ₁ composed of an excitation signal transmission pair line (P ₀ ) for applying the excitation signal and a plurality of reception signal transmission pair lines (P _{1 to} P ₉ ) for outputting the plurality of reception signals from the plurality of reception coils. A multi-core cable (CBL), and a predetermined phase from the excitation signal applied to the excitation coil, with respect to the plurality of reception signals respectively induced by the excitation signal in the multi-core cable A plurality of circuits (9, 10) for phase-shifting the received signal and subtracting the induction correction signal adjusted to a predetermined amplitude and subtracting the induction correction signal from each of the reception signals that have been induced. , 12 ...), and a plurality of phase comparators (14 ...) Comparing the phases of the received signal from which the induction correction signal is subtracted and the reference signal and outputting a plurality of flaw detection data.
A metal material flaw detection device characterized by comprising: