JPH07248314A - Probe for eddy-current flaw detection - Google Patents

Abstract

PURPOSE:To provide a probe that is available in a remote field eddy-current flaw detecting process capable of detecting any defect so sensitively in making flaw detecting signal be hard to receive any external effect. CONSTITUTION:An electric circuit such as a preamplifier 8 or the like is installed in space between a receiving coil 7 and a transmitting coil 3. This receiving coil 7 is set up in front of the transmitting coil 3 locking from the side of a signal source. Likewise, a magnetic shield 13 is installed in space between the transmitting coil 3, through which both transmitting and receiving probes are constituted so as to make them replaceable in terms of structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe used in a remote field eddy current flaw detection method used for maintenance inspection of pipes of heat exchangers, oil plants and the like.

[0002]

2. Description of the Related Art Remote field eddy current testing is a non-destructive testing handbook (Nondes
tuructive Testing Hnadbook) Vol. 4 Electromagnetic Testing (Electrnmagnetic Testing)
The example is described in. As shown in FIG. 7, a magnetic field 4 is generated from the transmission coil 3 by applying a voltage signal of several V to several 100 V to the transmission coil 3. Among the magnetic fields generated by the transmitting coil 3, the magnetic field 4 generated inside the tube has a magnetic permeability of the tube 6 when the flaw detection tube is a ferromagnetic material.
In each area, the magnetic field 4 is directly disturbed, which causes the S / N ratio to deteriorate. Transmitter coil 3 in remote field eddy current flaw testing
The influence of the direct magnetic field 4 is reduced by separating the distance between the receiving coil 7 and the receiving coil 7 by 2 to 3 times the outer diameter of the tube, and the indirect magnetic field 5 generated by the eddy current 19 generated in the tube 6 by the transmitting coil 3 is received. This is a method for flaw detection.

[0003]

However, in the above-mentioned remote field eddy current flaw detection method, the signal of the receiving coil 3 is as weak as a few μV, and is easily affected by external noise. Is likely to worsen. Further, the S / N ratio is deteriorated due to the influence of the signal applied by the transmitting coil 3 on the signal of the receiving coil 7. Therefore, an object of the present invention is to provide an eddy current flaw detection probe that can detect flaws with high sensitivity by making flaw detection signals less susceptible to external influences.

[0004]

In order to achieve the above object, the present invention provides an electric circuit such as a preamplifier between the receiving coil and the transmitting coil, and the receiving coil is placed in front of the transmitting coil when viewed from the signal source side. In addition, a magnetic shield is provided between the transmission coil and the reception coil, so that the transmission probe and the reception probe can be replaced.

[0005]

By providing a preamplifier between the receiving coil and the transmitting coil, the signal from the receiving coil at the tip can be amplified while reducing the influence of external noise. Further, by providing a preamplifier between the receiving coil and the transmitting coil, the signal received by the receiving coil can be amplified without the receiving coil receiving the interference of the transmitting signal. Further, since the reception signal amplified by the preamplifier can be amplified up to about several V, in this case, it is less likely to be affected by the transmission coil.

Further, by arranging the reception coil in front of the transmission coil as seen from the signal source side, the flaw detection signal is amplified by the preamplifier before passing through the transmission coil side, whereby the influence of the transmission signal on the transmission coil side is affected. It can be hard to receive.

Furthermore, by providing a shield between the transmission coil and the reception coil, the influence of noise due to the direct magnetic field can be eliminated by shielding the direct magnetic field generated from the transmission coil.

In the eddy current flaw detection test, the frequency at which flaw detection is performed is set according to the characteristics of the target test body, which determines the impedance of the coil. Since the flaw detection sensitivity and the S / N ratio change depending on the impedance characteristic of the coil, it is possible to adopt a configuration in which the probe can be replaced and to use another coil having the impedance characteristic suitable for the test body.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. A transmission voltage signal from the voltage source 1 causes the transmission signal cable 2 to conduct, and a current is passed through the transmission coil 3 in the probes 1 and 2 to generate a magnetic field. The magnetic field generated by the transmitter coil 3 is the direct magnetic field 4 directly generated by the transmitter coil 3,
An indirect magnetic field 5 is produced by the eddy currents produced in the tube 6 by the transmitter coil 3. Of this, the indirect magnetic field 5 propagates on the outer surface of the tube 6, and part of it returns to the inner surface of the tube again.

In the remote field eddy current flaw detection test, the influence of the magnetic field generated by the transmitting coil 3 is reduced by separating the distance between the transmitting coil 3 and the receiving coil 7 by several times the outer diameter of the tube, and the indirect magnetic field 5 is efficiently received. Is the way.
The indirect magnetic field 5 is received by the receiving coil 7 and a current signal is generated.

The voltage signal received by the receiving coil 7 is amplified by the preamplifier 8 between the receiving coil 7 and the transmitting coil 3 and input to the lock-in amplifier 10 through the receiving coil signal cable 9.

In the flaw detection, if a discontinuous portion such as a defect is present in the steel pipe 6, a difference in amplitude and phase difference between the transmission voltage signal and the voltage signal received by the receiving coil occurs. The transmission voltage signal is partially input to the lock-in amplifier 10 as the reference signal 11,
The signal from the receiving coil signal 9 is a lock-in amplifier.
Input into 10 and measure the amplitude and phase difference.

FIG. 2 shows the connecting portion of the probe. The probe is divided into a receiving coil 7, a preamplifier 8, a portion for performing signal processing such as a magnetic shield 13 and a transmitting coil 3, and each portion is connected by a connector 14. For the transmitting coil 3 and the receiving coil 7, it is possible to select a probe that has the best conditions for flaw detection sensitivity and S / N ratio, depending on the test body on which flaw detection is performed.

As another embodiment, as shown in FIG. 3, by adding a filter circuit 15, a flaw detection frequency component other than the signal of the defective portion received by the receiving coil 7 can be removed. Further, as shown in FIG. 4, various signal processing circuits such as the analog / digital converter 16 can be provided.

Further, as shown in FIG.
And the receiving coil 7 can be connected by a flexible means,
It is also applicable to curved pipes such as U-shaped pipes. However, for a bent pipe such as a U-shaped pipe, the size of the transmitting / receiving coil is limited, and the size of the coil is limited so that the coil can pass through the curved pipe portion. On the other hand, if the circuit of the signal processing portion is made sufficiently small with respect to the inner diameter of the pipe, the probe of the present invention can perform the same signal processing on the bent pipe as on the straight pipe portion.

As shown in FIGS. 6 (a), 6 (b), 6 (c), and 6 (d), various signal processing circuits, magnetic shields, and the like can be replaced even when the bent pipe is inspected. It is also possible to use a combination of processing circuits. Further, for the transmitting coil 3 and the receiving coil 7, it is possible to use a probe having the best conditions for flaw detection in accordance with the characteristics of the test body.

[0017]

According to the present invention, by arranging the receiving coil on the tip side, it is possible to reduce the influence of interference by the transmitting coil. Further, by disposing the preamplifier between the receiving coil and the transmitting coil, it is possible to amplify a signal of several μV to a signal of several V before the receiving coil receives the interference of the transmitting coil. Further, at this time, since the preamplifier is arranged between the receiving coil and the transmitting coil, the shield wire from the receiving coil can be shortened and the signal can be amplified before being affected by the external signal source. , S / N ratio is improved. Furthermore, since the amplified received signal is amplified up to several V when passing through the transmitting coil portion, it is not affected by the transmitting coil. By blocking the direct magnetic field from the transmitting coil with a magnetic shield between the transmitting coil and the receiving coil, the influence of the direct magnetic field can be reduced. As described above, according to the present invention, since the sensitivity can be improved without damaging the information of the defect signal to be detected, it is possible to perform flaw detection with high sensitivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an eddy current flaw detection probe according to the present invention.

FIG. 2 is a detailed view showing the structure and connection mechanism of the probe.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a configuration diagram showing another embodiment of the present invention.

FIG. 5 is a configuration diagram showing another embodiment of the present invention.

FIG. 6 is a configuration diagram showing another embodiment of the present invention.

FIG. 7 is a view for explaining the action of a conventional remote field eddy current flaw detection.

[Explanation of symbols]

1 ... Voltage source, 2 ... Transmission signal cable, 3 ... Transmission coil,
4 ... Direct magnetic field, 5 ... Indirect magnetic field, 6 ... Tube, 7 ... Receiving coil, 8 ... Preamplifier, 9 ... Received signal cable, 10 ... Lock-in amplifier, 11 ... Reference signal, 12 ... Probe, 13 ... Magnetic shield, 14 … Probe connection pin, 15… Filter circuit, 16… Analog / digital converter, 17… Electrical circuit, 18
… U-shaped tube, 19… Eddy current

Claims (6)

[Claims] 1. A pair of a transmission coil and a reception coil, which are coaxially wound, and a preamplifier, which is arranged between the transmission coil and the reception coil and to which the reception coil is connected, are provided. An eddy current flaw detection probe characterized in that an output signal extraction direction is arranged on the transmission coil side. 2. The eddy current flaw detection probe according to claim 1, further comprising a magnetic shield provided between the transmitting coil and the receiving coil to reduce an influence of a direct magnetic field generated by the transmitting coil. 3. The eddy current flaw detection probe according to claim 1, wherein a filter circuit is provided between the transmission coil and the reception coil to remove signals other than a frequency component for flaw detection. 4. The eddy current flaw detection probe according to claim 1, wherein a signal processing circuit, a magnetic shield, or another mechanism is replaceable between the transmitting coil and the receiving coil. 5. The eddy current flaw detection probe according to claim 1, wherein the coil can be replaced with another coil so as to match the characteristics of the probe according to the characteristics of the test body. 6. The structure according to claim 1, wherein the transmitting coil and the receiving coil are connected to each other by means having flexibility so that the transmitting coil and the receiving coil can be applied to a bent pipe portion. Probe.