JPS61223550A - Electromagnetic induction flaw detection - Google Patents

Abstract

PURPOSE:To enable a flaw detection regardless of the shape in the a defect, by simultaneously detecting changes in the magnetic resistance of a magnetic circuit and changes in the impedance of a detection coil based on variations in eddy current. CONSTITUTION:As a high frequency current is supplied to detection coils 12 and 13 from a high frequency power source 15, an alternating magnetic flux is formed perpendicular to the direction of a defect 14. This alternating magnetic flux runs around a core 11 passing through a part of the surface of material S to be inspected to form a magnetic circuit containing a part of the material S being inspected. Therefore, as any defect 14 intercepting the magnetic circuit will increase the magnetic resistance of the magnetic circuit, an induction voltage is generated in the detection coils 12 and 13 to identify flaws. With the application of an alternating magnetic field to the materials S being inspected, an eddy current flowing over the surface of the material being inspected in the direction roughly perpendicular to the core 11. When a defect exists with the width extending along the orientation of the core 1 such as drill hole in the material S being inspected, the distribution of the eddy current is disturbed due to the defect and thus, the defect is detected as changes in the impedance of the detection coils 12 and 13.

Description

[Detailed description of the invention] This invention relates to an electromagnetic induction flaw detection method for detecting defects occurring on the surface of steel materials, etc.
This invention relates to an electromagnetic induction flaw detection method that can detect these flaws.

In general, as this type of electromagnetic induction flaw detection method, the eddy current flaw detection method and the magnetic flux leakage method are known.

The former method generates eddy currents on the surface of the inspected material by applying a high-frequency magnetic field, and detects the disturbance of the eddy currents due to defects as changes in the impedance of the detection coil.

The latter method generates magnetic flux on the surface of the material to be inspected, and detects leakage magnetic flux from defective parts using a magnetic sensor.

When the eddy current flaw detection method is classified according to the form of the probe coil, it is roughly divided into two types, as shown in FIG. In Fig. 3(a), two probe coils 1.2 are arranged in parallel to a typical defect 3 of a material S to be inspected, and these are differentially coupled.

On the other hand, in FIG. 4B, the core of each probe coil 4.5 is U-shaped to form a closed loop magnetic circuit via the material S to be inspected. And each probe coil 4.5
are disposed in a positional relationship perpendicular to the representative defect 3, and are differentially coupled.

On the other hand, the leakage magnetic flux testing method includes a probe rotation type in which the probe is rotated in the direction of the arrow without rotating the material S to be inspected, as shown in Figure 6 (al), and a probe rotation type in which the probe is rotated in the direction of the arrow as shown in Figure 6 (bl). The probe is roughly divided into a fixed type, in which the probe is fixed and rotates the inspected material S.In both types,
In order to detect magnetic flux leaked to the surface of the material S to be inspected due to the presence of the defect 9, a magnetic sensor 8 is separately provided close to the material S to be inspected.

<η°ゝ However, in the case of the eddy current flaw detection method shown in FIG. 5(a), each coil is in a closed loop, so there is a drawback that the efficiency of electric power usage is low. In addition, the eddy current flaw detection method shown in Figure (b) has the drawback that the shape is large due to the U-shaped cores being arranged side by side, and the minimum detectable flaw length is relatively large. .

On the other hand, in the case of the leakage magnetic flux method shown in FIG. 6, it is necessary to install a magnetic sensor, which has the disadvantage that the apparatus becomes bulky. In addition, although this method has a high detection ability for defects that exist in the direction perpendicular to the magnetic flux,
The drawback is that the detection ability is low for defects such as drill holes and dents that generate little leakage magnetic flux.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an electromagnetic induction flaw detection method that has a relatively simple configuration and is capable of flaw detection without being affected by the shape of the defect.

In order to achieve the above-mentioned object of 7'' reading, the present invention has the following features.

In the direction perpendicular to the typical defect direction of the inspected material,
An alternating magnetic field is applied to the material to be inspected to form a magnetic surface path that includes a portion of the material to be inspected. If there is a defect in the inspected material that interrupts the magnetic circuit, the magnetic resistance within the magnetic circuit changes. By detecting this change in magnetic resistance, the presence of the defect can be known. Furthermore, the alternating magnetic field generates eddy currents on the surface of the material to be inspected. However, if there are defects such as drill holes on the surface of the material to be inspected, the distribution of eddy currents will be disturbed. By detecting this disturbance in current distribution as a change in the impedance of the detection coil, defects such as drill holes that cannot be detected by detecting changes in the magnetic resistance are detected.

In this way, by simultaneously detecting changes in the magnetic resistance of the magnetic circuit and changes in the impedance of the detection coil based on changes in eddy current, it is possible to detect defects regardless of their shape.

Implementation ±1 Figure 1 is an explanatory diagram of a probe used in an embodiment of the present invention, in which (a) is a plan view, (b) is a side view, and (C) is a side view. It shows its electrical connection diagram.

Reference numeral 11 denotes a U-shaped core made of a high magnetic permeability material such as ferrite. Detection coils 12 and 13 are wound around the lower ends of both sides of the core 11 .

The detection coils 12 and 13 are differentially coupled to each other,
As shown in FIG. 2(b), together with resistors R1 and R2, a bridge circuit is formed. Then, the midpoint potential of this bridge circuit is taken out as a detection signal. In the probe formed in this manner, the core 11 is disposed close to the surface of the material S to be inspected in a direction perpendicular to the defect 14 of the material S to be inspected. Next, the operation of the apparatus shown in FIG. 1 will be explained.

The above-mentioned flaw detection device is a so-called self-induction type flaw detection device, and as shown in FIG. An alternating magnetic flux in a direction perpendicular to the direction is formed. This alternating magnetic flux passes through a part of the surface of the material S to be inspected and circulates around the core 11.
form a magnetic circuit including part of the Therefore, detection coil 1
If a defect 14 that interrupts the magnetic circuit exists between the detection coils 12 and 13, an induced voltage is generated in the detection coils 12 and 13 because the magnetic resistance of the magnetic circuit increases. After this induced voltage is amplified by an amplifier 16 connected to the bridge circuit, a well-known synchronous detection (not shown) is performed.
Flaws are determined by applying the signal to a wave circuit or a level discriminator. Further, due to the alternating magnetic field applied to the material S to be inspected, an eddy current flows on the surface of the material to be inspected in a direction substantially perpendicular to the core 11. The eddy current flowing in this direction is the defect 14
The distribution is hardly disturbed by Therefore, this defect 14 does not cause a change in the impedance of the detection coil 12.13. However, the material to be inspected S
If there is a wide defect such as a drill hole in the direction in which the cores 11 are arranged, this defect disturbs the distribution of eddy currents and causes a change in the impedance of the detection coils 12,13. Changes in impedance of the detection coils 12 and 13 are taken out as a midpoint potential difference of the bridge circuit. After this midpoint potential difference is amplified in the same manner as described above, it is subjected to synchronous detection and level discrimination to determine the flaw signal to be detected. In this way, defects 14 along the axis of the inspected material S are detected as changes in magnetic resistance in the magnetic circuit described above, and defects such as drill holes, which are difficult to detect as changes in magnetic resistance, are detected by vortices. It is detected as a change in impedance of the detection coils 12 and 13 based on a change in current.

This invention is not limited to the self-induction type as in Embodiment 1, but can also be used in a mutual induction type magnetic flaw detection method. That is, as shown in FIG. 2, the U-shaped core 11
The excitation coil 17 may be wound around the central connecting portion. In this case differentially coupled detection coils 12 and 1
3 differential outputs are provided to amplifier 16. By arranging such a mutual guidance type probe so as to be orthogonal to the typical defect 14 of the inspected material S as in the first embodiment, the same effects as in the previous embodiment can be obtained.

Back Seed Box 1 As described in Embodiments 1 and 2, the present invention is not limited to one formed only by a single probe. For example, as shown in Fig. 3, there are detection coils (al, a2, ..., a5), (bl, b2, ...) on both sides.
・, b5) The plurality of wound cores 11 are inspected as the material S.
The probes may be formed by arranging them in a line along the direction of the defect. As shown in FIG. 2C, a bridge circuit is formed by differentially coupling a set of detection coils a1 to a5 on one side and a set of detection coils b1 to b5 on the other side. By forming the probe in this way, it is possible to detect flaws regardless of the shape of the defect, as in the embodiment described above, and it is possible to expand the flaw detection area while maintaining the sensitivity of the minimum detectable flaw length. can.

According to the third embodiment, the above-mentioned effects can be obtained, but the detection sensitivity changes depending on the length of the defect. Therefore, as shown in FIG. 4, a bridge circuit is configured for each pair of detection coils wound around each core, and after amplifying the midpoint potential difference of each circuit with amplifiers 161 to 165, the integrated circuit 2
The detection signal may be obtained by superimposing the detected signal.

With this configuration, constant detection sensitivity can be obtained regardless of the defect length.

As explained above, in the electromagnetic induction flaw detection method according to the present invention, an alternating magnetic field is applied to a material to be inspected to form a magnetic circuit including a part of the material to be inspected, and the magnetic field of this magnetic circuit is It detects flaws in the direction of interrupting the magnetic circuit by changes in resistance, and detects defects such as drill holes in the inspected material by changes in impedance of the detection coil based on changes in eddy current caused by the alternating magnetic field. There is. Therefore, according to the present invention, it is possible to detect defects regardless of their shape with a relatively simple configuration.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a self-induction type electromagnetic induction flaw detection method according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of a mutual induction type flaw detection method according to another embodiment of the invention, and FIG.
The figure is an explanatory diagram of a case where a plurality of detection coils according to another embodiment of the present invention are arranged in a row, FIG. 4 is an explanatory diagram of another embodiment of the present invention, and FIG. 5 is an explanatory diagram of a conventional An explanatory diagram of the eddy current flaw detection method, FIG. 6 is an explanatory diagram of the conventional leakage magnetic flux flaw detection method. 11...Core two 12.13...Detection coil, 14.
... Defect, S... Material to be inspected. Figure 1 (a) (b) (C) Figure 2 (a) Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) By applying an alternating magnetic field to the material to be inspected in a direction perpendicular to the defect direction, a magnetic circuit including a part of the material to be inspected is formed, and a change in magnetic resistance of this magnetic circuit is detected. Additionally, an electromagnetic induction flaw detection method characterized in that defects in the material to be inspected are detected by magnetically detecting changes in eddy currents generated on the surface of the material to be inspected by the alternating magnetic field.