WO2008072508A1

WO2008072508A1 - Nondestructive test instrument and nondestructive test method

Info

Publication number: WO2008072508A1
Application number: PCT/JP2007/073441
Authority: WO
Inventors: Kiyoshi Hashimoto; Yasumitsu Tomita; Naoki Osawa
Original assignee: Osaka University
Priority date: 2006-12-14
Filing date: 2007-12-05
Publication date: 2008-06-19
Also published as: JP2010048552A

Abstract

A nondestructive test instrument having a small size and a light weight and used for stably evaluating a near-side crack, a far-side crack, and an internal crack at relatively low cost in a short time while avoiding the influence of lift-off by using a magnetic potentiometer method. A nondestructive test instrument comprises a pickup core (8) for measuring the magnetic potential between two points in the magnetic flux transmitted through the inside of the object under test from outside the object, a fourth coil (9), a second integrator (10), a second power amplifier (11), a third coil (12), a second coil (14) and a first integrator (15) both for correcting the intensity of the external magnetic field, and an A/D converter (13) and a microcomputer (1) for detecting a defect, if any, inside the object by detecting a variation of the measured magnetic potential difference when the pickup core is moved relatively to the object.

Description

Specification

Nondestructive inspection apparatus and nondestructive inspection method

Technical field

[0001] The present invention relates to a nondestructive inspection apparatus and a nondestructive inspection method using a magnetic potential difference.

Background art

[0002] In general, inspection of crack damage at a welded part of an object such as a hull structural member or a bridge structural member using welding technology often relies on visual inspection, and it cannot be said that the accuracy and efficiency of the inspection are high. On the other hand, some conventional non-destructive inspection apparatuses that inspect the state inside the subject without destroying the subject use ultrasonic waves, X-rays, and the electrical characteristics of the subject.

[0003] In a nondestructive inspection apparatus using ultrasonic waves, the surface of the inspection target part needs to be clean, so pretreatment such as paint removal is required. In non-destructive inspection equipment that uses X-rays, the X-rays themselves are harmful to the human body, and special expertise is required to handle them. In a non-destructive inspection apparatus that uses the electrical characteristics of a subject, it is necessary to pass a current through the target region of the subject to be examined, so the non-destructive inspection device needs to contact the target portion of the test.

[0004] Therefore, it is possible to inspect the subject in a non-contact manner, pretreatment such as paint removal is unnecessary, and the back side as well as the front side of the subject can be inspected, which is harmless to the human body. It is desirable to develop a simple, nondestructive inspection device for crack damage detection that has the characteristics of being such that it is independent of the skill of the inspector.

[0005] By the way, in contrast to a non-destructive testing apparatus that uses electrical characteristics that in principle requires an electric current to flow through a subject, a non-destructive testing apparatus that uses the magnetic characteristics of a subject uses a magnetic field. There is no need to bring the destructive inspection device into contact with the subject. There are many examples of the magnetic properties of this specimen, including measurement of residual stress due to magnetostriction, diagnosis of fatigue damage due to Barkhausen noise, and detection of flaws due to leakage magnetic flux.

[0006] As an example of such a conventional non-destructive inspection apparatus using the magnetic characteristics of a subject, a patent There is a magnetic flaw detector disclosed in Reference 1. This magnetic flaw detector uses two magnetic sensors provided at the center position of the magnetizer and at a position away from the center position to detect leakage magnetic flux under strong magnetization conditions, and from these two magnetic sensors. By calculating these two signals, the noise component that is included in both of them is canceled, enabling defect detection with a good S / N ratio.

[0007] Other examples of conventional nondestructive inspection apparatuses that use the magnetic properties of a subject include those disclosed in Non-Patent Documents 1 and 2.

[0008] However, the cracks of the specimen include a surface crack and an internal crack, and the surface crack is divided into a near side crack existing on the inspection surface and a far side crack existing on the back surface. There is a problem that the internal flaw and the far-side crack cannot be evaluated in the magnetic flaw inspection using the FEM.

[0009] In addition, as a method of non-destructive inspection using magnetism that does not adversely affect the human body and the environment, there is a method of using the magnetoresistance of the subject, but in this method of using magnetoresistance, internal cracks and far-side cracks are used. However, there is also a problem that stable evaluation is difficult because the effect of lift-off during measurement is large.

Patent Document 1: Japanese Published Patent Publication “JP 2000-227419” (published on August 15, 2000)

Non-Patent Document 1: Hashimoto Seishi, Yasutaka Hamada, Naoki Osawa et al., “Study on non-destructive crack detection system using magnetic properties”, Proc. Of the Japan Shipbuilding Society, No. 4, pl31 — 132, November 25, 26, 2004

Non-Patent Document 2: Hashimoto Seishi, Yasuda Hamada, Naoki Osawa and others, “Study on crack damage detection system using non-destructive inspection using magnetic properties, Part 2 Application to welded joints”, Japan Marine Proceedings of Engineering Society Lecture, No. 1, November 24, 25, 2005

Disclosure of the invention

[0010] The present invention has been made in view of the above-described conventional problems. It is possible to detect a subject in a non-contact manner, remove the influence of lift-off, and remove a near side crack. An object is to provide a nondestructive inspection apparatus that can stably evaluate a far-side crack and an internal crack at a relatively low cost in a short time, and can be reduced in size and weight. A nondestructive inspection apparatus according to the present invention is a nondestructive inspection apparatus for inspecting a defect inside a subject to solve the above-described problem, and a transmission magnetic flux that passes through the inside of the subject. When the magnetic potential difference measuring means for measuring the magnetic potential difference between the two points from the outside of the subject and the subject and the magnetic potential difference measuring means are relatively moved, the magnetic field difference is measured. It is characterized by comprising defect detecting means for detecting the presence of a defect inside the subject by detecting a change in magnetic potential difference measured by the potential difference measuring means.

[0012] In addition, the nondestructive inspection method of the present invention is a nondestructive inspection method for inspecting a defect inside a subject using a nondestructive inspection apparatus in order to solve the above-mentioned problem. A magnetic potential difference measurement step of measuring a magnetic potential difference between two points of transmitted magnetic flux that passes through the inside of the subject by a magnetic potential difference measuring means provided in a destructive inspection apparatus; A defect detection means provided in a nondestructive inspection apparatus detects a change in magnetic potential difference measured by the magnetic potential difference measurement means when the subject and the magnetic potential difference measurement means are relatively moved. And a defect detecting step for detecting the presence of a defect inside the subject.

[0013] According to the configuration and the method, the magnetic potential difference measuring unit measures the magnetic potential difference between two points of the transmitted magnetic flux transmitted through the inside of the subject from the outside of the subject. Then, when the specimen and the magnetic potential difference measuring means are relatively moved, a change in the magnetic potential difference measured by the magnetic potential difference measuring means is detected, whereby a defect inside the specimen is detected. Detect the presence of.

[0014] Therefore, since the magnetic field is detected by using the magnetic potential difference between two points of the transmitted magnetic flux passing through the inside of the subject, it is necessary to bring the nondestructive inspection apparatus into contact with the subject. Absent . In addition, when inspecting using a magnetic potential difference, it is only necessary to consider the magnetic resistance between two points of the transmitted magnetic flux that passes through the inside of the subject, so that the distance between the nondestructive inspection device and the subject changes. The effect of lift-off due to can be removed. For this reason, it is possible to evaluate defects present in the specimen stably.

[0015] Furthermore, by transmitting the transmitted magnetic flux deep from the surface of the subject, it is possible to detect defects present at various positions inside the subject. Defects include various cracks such as surface cracks and internal cracks as well as various singularities of the specimen. Also, Surface cracks can be classified as so-called near-side cracks and far-side cracks. By using the non-destructive inspection device and non-destructive inspection method of the present invention, any of near-side cracks, far-side cracks and internal cracks can be used. It is possible to evaluate. Here, the “near side crack” is a surface crack on the measurement surface side of the subject, and the “far side crack” is a surface crack on the back side of the measurement surface of the subject. An “internal crack” is a crack inside the subject.

[0016] Further, when the subject and the magnetic potential difference measuring means are relatively moved, only the change in the magnetic potential difference measured by the magnetic potential difference measuring means is detected. Since the presence of internal defects can be detected, it can be evaluated in a short time. In addition, in order to detect changes in the magnetic potential difference, it is not necessary to magnetically saturate the measurement site of the subject, and the device can be reduced in size and weight. In addition, the simple method of using the magnetic potential difference makes the circuit configuration simple and enables the creation of a non-destructive inspection device at low cost.

[0017] From the above, it is possible to inspect the specimen in a non-contact manner, and the force S can be removed to remove the effects of lift-off, and near-side cracks, far-side cracks, and internal cracks are relatively low cost and in a short time. Providing a nondestructive inspection device that can be evaluated stably and can be reduced in size and weight.

[0018] Other objects, features, and advantages of the present invention will be fully understood from the following description. The advantages of the present invention will be apparent from the following description with reference to the accompanying drawings.

Brief Description of Drawings

FIG. 1 is a block diagram showing a configuration of a nondestructive inspection apparatus according to the present invention.

FIG. 2 is a diagram showing a plurality of embodiments of the nondestructive inspection device, (a) shows an embodiment of the nondestructive inspection device, and (b) is a diagram of the nondestructive inspection device. Another embodiment is shown, and (c) shows still another embodiment of the nondestructive inspection apparatus.

FIG. 3 is a schematic diagram showing the state of magnetic flux flowing through the nondestructive inspection apparatus, (a) showing the state of magnetic flux flowing through the nondestructive inspection apparatus when there is no defect in the subject, and (b) The state of the magnetic flux which flows into the said nondestructive inspection apparatus when a subject has a defect is shown.

FIG. 4 is a diagram showing the measurement results when there is no defect in the specimen, (a) is the pickup core (B) shows the measurement result with the excitation core.

FIG. 5 is a diagram showing measurement results when there is a defect in the specimen. (A) shows the measurement results with the pickup core, and (b) shows the measurement results with the excitation core.

FIG. 6 is a diagram showing a state when the magnetic flux of the exciting core is controlled to take a constant value.

FIG. 7 is a diagram showing the sensitivity of the nondestructive detection device when an alternating current is passed through the first coil and its frequency is changed.

Explanation of symbols

[0020] 1 microcomputer (frequency adjustment means, defect detection means)

2 Signal generator (External magnetic field applying means)

3 Preamplifier (External magnetic field applying means)

4 1st power amplifier (external magnetic field applying means)

5 First coil (external magnetic field applying means, coil)

6 Excitation core (external magnetic field application means)

7 Subject

8 Pickup core (magnetic path, magnetic potential difference measuring means)

9 4th coil (reverse magnetic field applying means, magnetic potential difference measuring means)

10 Second integrator (reverse magnetic field application means, magnetic potential difference measurement means)

11 Second power amplifier (reverse magnetic field applying means, magnetic potential difference measuring means)

12 3rd coil (reverse magnetic field applying means, magnetic potential difference measuring means)

13 A / D converter (defect detection means)

14 Second coil (External magnetic field correction means)

15 1st integrator (external magnetic field correction means)

20 Nondestructive inspection equipment

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] One embodiment of the present invention is described below with reference to Figs.

First, based on FIG. 1, the configuration of a nondestructive inspection apparatus 20 that is an embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of the nondestructive inspection apparatus 20. [0023] The nondestructive inspection apparatus 20 is an apparatus for inspecting a defect inside a subject. As shown in FIG. 1, a microcomputer (frequency adjusting means, defect detecting means) 1, a signal generator (external) Magnetic field application means) 2, Preamplifier (external magnetic field application means) 3, First power amplifier (external magnetic field application means) 4, First coil (external magnetic field application means, coil) 5, Excitation core (external magnetic field application means) 6 , Pickup core (magnetic path) 8, 4th coil (reverse magnetic field applying means, magnetic potential difference measuring means) 9, second integrator (reverse magnetic field applying means, magnetic potential difference measuring means) 10, second power amplifier (reverse) Magnetic field applying means, magnetic potential difference measuring means) 11, third coil (reverse magnetic field applying means, magnetic potential difference measuring means) 1 2, A / D converter (defect detecting means) 13, second coil (external magnetic field correcting means) 14 and a first integrator (external magnetic field correcting means) 15.

[0024] Note that the subject 7 is an object to be inspected by the nondestructive inspection apparatus 20, and is usually made of a magnetic material, but is not limited thereto, and is made of a material containing a magnetic material. If it is, it may be acceptable.

[0025] The microcomputer 1 controls the magnitude of the current or voltage generated by the signal generator 2 and the frequency in the case of AC in accordance with an instruction of an input unit (not shown), and is sent from the Α / D converter 13. Various processes are performed, such as processing the incoming digital data and displaying the processing results on a display unit (not shown).

[0026] The microcomputer 1 may be anything as long as it includes a control unit, a calculation unit, and a memory, and is provided either inside or outside the nondestructive inspection apparatus 20. It may be a thing.

[0027] The signal generator 2 determines the type of direct current or alternating current, the magnitude of the current or voltage, the amplitude, frequency, waveform, etc. in the case of alternating current according to the instructions of the microcomputer 1, and determines the preamplifier. A current is passed through 3 or a voltage is applied.

[0028] The preamplifier 3 adds the current or voltage sent from the signal generator 2 and the first integrator 15, and amplifies the added current or voltage and sends it to the first power amplifier 4. is there. The first power amplifier 4 amplifies the current or voltage sent from the preamplifier 3 and applies it to or flows through the first coil 5. The first power amplifier 4 sends analog data of a voltage value given to the first coil 5 or a flowing current value to the A / D converter 13. The first coil 5 generates a magnetic field inside the first coil 5 according to the current supplied from the first power amplifier 4 or flowing. The exciting core 6 is for increasing the magnetic permeability inside the first coil 5 and strengthening the magnetic field generated inside the first coil 5 so as to be applied to the subject 7 as an external magnetic field. As a material that increases the magnetic permeability inside the first coil 5, for example, a high magnetic permeability material such as amorphous ferrite or high magnetic permeability steel is preferable. By constructing the excitation core 6 using a high permeability material, the strength of the external magnetic field applied to the subject can be increased and concentrated on the measurement site of the subject.

[0030] The pickup core 8 is for forming a magnetic path provided outside the subject by connecting two points of the transmitted magnetic flux that passes through the subject. The fourth coil 9 gives an induced electromotive force to the second integrator 10 according to the change of the magnetic flux in the pick-up core 8.

The second integrator 10 sends the result of integrating the induced electromotive force given by the fourth coil 9 to the second power amplifier 11 as a current value or a voltage value.

The second power amplifier 11 amplifies the current or voltage sent from the second integrator 10 and sends it to the third coil 12 and the A / D converter 13.

[0033] The third coin 12 is a magnetic field opposite to the external magnetic field applied to the subject according to the current or voltage sent from the second power amplifier 11 (hereinafter referred to as "reverse magnetic field"). Is applied to prevent a part of the transmitted magnetic field from passing through the pickup core 8.

[0034] The A / D converter 13 converts the analog current value or voltage value obtained from the first power amplifier 4 and the second power amplifier 11 into digital data, and outputs it to the microcomputer 1 as a measured value. To send. The second coil 14 provides the first integrator 15 with an induced conductive pressure corresponding to a change in the magnetic flux in the exciting core 6.

The first integrator 15 sends the result of integrating the induced electromotive force given by the second coil 14 to the preamplifier 3. Note that the amplification factors of the preamplifier 3, the first power amplifier 4, and the second partial amplifier 11 are the material, number of turns, and number of turns of the first coil 5, the second coinor 14, the third coinor 12, and the fourth coil 9, respectively. Depending on the magnetic permeability of the excitation core 6 and the pickup core 8, an appropriate value may be set in advance according to the purpose.

Here, an example of the configuration of the nondestructive inspection apparatus 20 will be described based on (a) to (c) of FIG. 2 (a) and 2 (b), the shape of the exciting core 6 is a donut shape. The figure shows the case where the shape is divided into 1/2 and 1/4. Note that the shape of one of the parts divided into the shape force m / n (m <n, where m and n are integers equal to or greater than 1) of the exciting core 6 is adopted, without being limited to such a case. Is possible.

[0037] Fig. 2 (a) is an example of a configuration of the nondestructive inspection apparatus 20 used when the measurement site of the subject is planar. In this embodiment, the exciting core 6 has a donut shape that is cut in half along the axis of symmetry (divided in half). Two parts of a substantially rectangular shape shown in the lower part of (a) of FIG. 2 are a part corresponding to a cut face of a doughnut-shaped shape. Since these two surfaces Α and Β are substantially on the same plane, when the subject 7 is planar, the excitation core 6 is easily brought into contact with the subject 7.

FIG. 2 (b) shows another example of the configuration of the nondestructive inspection apparatus 20 used for inspecting a defect when the subject has a shape bent at a right angle. In this embodiment, the excitation core 6 has a shape obtained by dividing a donut shape into quarters. Two plane C 'D forces corresponding to the donut-shaped cut shown in the lower part of Fig. 2 (b) Compared to Fig. 2 (a), the plane is inclined obliquely. In terms of inclination, the right side D is inclined 45 degrees upward as compared to the case of Fig. 2 (a). Left face C is tilted 45 degrees to the left. Then, the angle between the planes including the left side C and the right side D is approximately 90 degrees, so the shape of the subject 7 is 90 degrees with respect to the flat plate. In the case of a bent shape, the exciting core 6 can be easily brought into contact with the subject 7! /, And the structure becomes! /.

[0039] As can be seen from these examples, by appropriately adjusting the angle formed by the plane including each of the two end faces that are the measurement portions of the half-doughnut-shaped excitation core 6 with respect to the subject, Even if it is a shape that can be bent when it is bent at the same angle as the angle formed by the plane, it is possible to use a nondestructive inspection device.

[0040] Fig. 2 (c) shows still another example of the configuration of the nondestructive inspection apparatus 20, and the shape thereof is the measuring section E force S and the roundness on the subject 7 in the excitation core 6. It has the characteristic of being tinged. Therefore, the measurement part E for the subject 7 in the excitation core 6 is rounded! /, So that the measurement of the excitation core can be performed on the subject 7 having various shapes without changing the shape of the nondestructive inspection device 20. The site can be contacted. [0041] Next, FIG. 1, FIG. 3 (a), FIG. 3 (b), FIG. 4 (a), FIG. 4 (b), FIG. 5 (a), FIG. 5 (b) Based on FIGS. 6 and 7, the operation of the nondestructive inspection apparatus 20 will be described. First, based on (a) of FIG. 3 and (b) of FIG. 3, the principle by which the nondestructive inspection apparatus 20 detects defects inside the subject will be described. Fig. 3 (a) is a schematic diagram showing the state of magnetic flux flowing through the nondestructive inspection apparatus 20 when the subject 7 has no defect, and Fig. 3 (b) shows the case where the subject 7 has a defect. 6 is a schematic view showing a state of magnetic flux flowing through the non-destructive inspection device 20 of a combination.

[0042] As shown in Fig. 3 (a), when there is no defect in the subject 7, there are a total of eight magnetic fluxes generated inside the subject 7 by the exciting core 6, and two of these are the pickup cores 8. It is transparent. On the other hand, as shown in FIG. 3 (b), when the subject 7 has a defect, there are a total of eight magnetic fluxes generated in the subject 7 by the exciting core 6, and three of them are the pickup core 8. It is transparent. Compared to the case where there is no defect, the force that the excitation core 6 reduces the number of magnetic fluxes generated inside the object 7 by one and the number of magnetic fluxes that pass through the pickup core 8 increases by one. This shows that the magnetic resistance of the subject 7 has increased.

[0043] Then, the magnetic potential difference between the two points of the transmitted magnetic flux passing through the inside of the subject 7 is present when there is a defect in the measurement site of the subject 7! N / A, it can be seen that the situation is different. The nondestructive inspection apparatus 20 applies this principle.

Next, the operation of the nondestructive inspection apparatus 20 will be described with reference to FIG. The signal generator 2 supplies current or voltage to the preamplifier 3 according to the instruction from the micro computer 1. This current or voltage may be direct current or alternating current.

[0045] When alternating current is used, the frequency of alternating current or voltage can be changed to use the skin effect (adjusting the depth of transmitted magnetic flux from the surface of the subject). It is possible to measure the crack depth from the surface of the test object 7. For example, for the skin effect, the depth s from the surface on the measurement surface side of the subject 7 where the magnetic flux density is approximately 37% of the surface portion is a function of the frequency ω and is given by the following equation: ing.

[0046] [Equation 1]

Here, p is the resistivity of the subject, and is the magnetic permeability of the subject.

[0048] Therefore, the force S can be increased by increasing the frequency ω to reduce the depth s and decreasing the frequency ω to increase the depth s.

[0049] In addition, it is preferable that the amplitude of the alternating current or voltage is gradually increased after being gradually increased. Then, by applying a strong external magnetic field, the magnetization generated in the subject 7 can be removed, and the influence of the magnetization of the subject 7 can be reduced in the next measurement.

The current or voltage sent from the signal generator 2 is amplified by the preamplifier 3 and the first power amplifier 4 and sent to the first coil 5. A magnetic field is generated in the first coil 5 in response to this current or voltage. That is, the strength of the generated magnetic field can be changed according to the current or voltage of the first coil 5. The magnetic field generated in the first coil 5 is applied to the subject 7 as an external magnetic field because the magnetic permeability inside the first coil 5 is increased by the exciting core 6 and the strength thereof is increased. . The excitation core 6 is preferably configured using a material that increases the magnetic permeability inside the first coil 5, for example, a high permeability material such as amorphous ferrite or high permeability steel.

[0051] When an external magnetic field is applied to the subject 7 by the exciting core 6, a transmitted magnetic flux that passes through the inside of the subject 7 is generated. The magnetic potential difference due to the transmitted magnetic flux is referred to as the pickup core 8, the fourth coil 9, the second integrator 10, the second power amplifier 11, and the third coil 12 (hereinafter referred to as “magnetic potential difference measuring means” for simplicity). Force S).

Specifically, when the transmitted magnetic flux passes through the pickup core 8, the magnetic flux inside the fourth coil 9 changes, and therefore an induced electromotive force is generated in the fourth coil 9 by electromagnetic induction. The second integrator 10 integrates the induced electromotive force. The result of the integration is amplified by the second power amplifier 11 and fed back to the third coil 12. The third coil 12 generates a magnetic field (reverse magnetic field) opposite to the external magnetic field by this current or voltage.

Then, if the amplification factor of the second power amplifier 11 is set to an appropriate value, a reverse magnetic field can be applied so that part of the transmitted magnetic flux does not pass through the pickup core 8. At this time, the magnetic flux in the pickup core 8 becomes zero. The magnitude of the current flowing through the third coil 12 when the magnetic flux in the pickup core 8 is 0 is two points of the transmitted magnetic flux that passes through the inside of the subject. It corresponds to the magnitude of the magnetic potential difference between the two.

Therefore, when the current value or voltage amplified by the second power amplifier 11 is measured when the magnetic flux in the pickup core 8 is 0, the transmitted magnetic flux that passes through the inside of the subject is measured between two points. The result is equivalent to measuring the magnetic potential difference. The current value or voltage value of the analog data is converted into digital data by the A / D converter 13 and sent to the microcomputer 1 as a measured value.

[0055] Since the current value or voltage value is in accordance with the strength of the magnetic field of the reverse magnetic field, measuring the potential difference or voltage value between the two points of the transmitted magnetic flux passing through the inside of the subject. It is possible to measure the amount corresponding to the magnetic potential difference. Therefore, it is equivalent to detecting the magnetic potential difference between two points of the transmitted magnetic flux passing through the inside of the subject. Further, when the subject 7 and the magnetic potential difference measuring means are relatively moved, by detecting a change in the magnetic potential difference measured by the magnetic potential difference measuring means, defects inside the subject 7 can be detected. Can detect presence

[0056] In this way, in the nondestructive inspection apparatus 20, a part of the transmitted magnetic flux is prevented from passing through the pickup core 8, so that the influence of the magnetic resistance of the pickup core 8 and the nondestructive inspection apparatus 20 is greatly increased. Can be reduced. For this reason, the effect of lift-off due to the change in the distance between the nondestructive inspection apparatus 20 and the subject 7 can be eliminated. The “effect of lift-off” is the effect on the test result due to the change in the distance between the nondestructive inspection device 20 and the subject 7.

Here, the operation of the second coil 14 and the first integrator 15 will be described. The external magnetic field applied to the subject 7 by the excitation core 6 decreases as the distance between the excitation core 6 and the subject 7 increases. In other words, if more accurate measurements are to be made, it is necessary to remove the effects of lift-off as much as possible.

[0058] The second coil 14 and the first integrator 15 are provided to eliminate the influence of the lift-off as much as possible. As the distance between the excitation core 6 and the subject 7 increases, the magnetic flux of the excitation core 6 changes accordingly. Then, an induced electromotive force is generated in the second coil 14 due to the change of the magnetic flux. This induced electromotive force is integrated by the first integrator 15 and sent to the preamplifier 3. According to the law of electromagnetic induction, the second coil 14 is induced according to the change of magnetic flux in the exciting core 6. An electromotive force is generated.

Therefore, if the current or voltage output from the first integrator 15 is appropriately amplified and fed back to the current or voltage flowing through the first coil 5, the magnetic flux in the exciting core 6 can be kept constant. That is, the external magnetic field that generates the transmitted magnetic flux from the outside of the subject 7 can be kept constant. Therefore, in the nondestructive inspection apparatus 20, the influence of lift-off due to the change in the distance between the nondestructive inspection apparatus 20 and the subject 7 can be removed.

[0060] As described above, the nondestructive inspection apparatus 20 uses the magnetic field property to inspect using the magnetic field difference between two points of the transmitted magnetic flux that passes through the inside of the subject 7, and thus is nondestructive. There is no need to bring the inspection device 20 into contact with the subject 7. Also, when inspecting using a magnetic potential difference, it is only necessary to consider the magnetic resistance between two points of the transmitted magnetic flux that passes through the inside of the subject 7, so that the distance between the nondestructive inspection device 20 and the subject 7 is small. It is possible to remove the effects of lift-off caused by changes. For this reason, it is possible to stably evaluate defects existing in the specimen 7.

Furthermore, near-side cracks, far-side cracks and internal cracks can be evaluated by transmitting the transmitted magnetic flux deep from the surface of the subject 7. Here, the “near-side crack” is a surface crack on the measurement surface side of the subject 7, and the “far-side crack” is a surface crack on the back side of the measurement surface of the subject 7. The “internal crack” is a crack inside the subject 7.

[0062] Further, when the subject 7 and the magnetic potential difference measuring means are relatively moved, the inside of the subject 7 is detected only by detecting a change in the magnetic potential difference measured by the magnetic potential difference measuring means. Because the presence of defects can be detected, the specimen can be evaluated in a short time. Then, in order to detect a change in magnetic potential difference, it is not necessary to magnetically saturate the measurement site of the subject 7, and the nondestructive inspection apparatus 20 can be reduced in size and weight. Furthermore, since the simple method of using the magnetic potential difference is used, the circuit configuration is simple, and the nondestructive inspection apparatus 20 can be created at low cost.

[0063] From the above, it is possible to inspect the specimen in a non-contact manner, and to remove the influence of lift-off. In addition, near-side cracks, far-side cracks, and internal cracks can be relatively low-cost and in a short time. Providing a nondestructive inspection device 20 that can be evaluated stably and can be reduced in size and weight. Here, based on the comparison between FIG. 4 (a) and FIG. 4 (b) and FIG. 5 (a) and FIG. The results of measuring the change in magnetic potential difference will be explained.

[0065] Fig. 4 (a) is a diagram showing the measurement result of the pickup core 8 when the subject 7 has no defect, and Fig. 4 (b) shows the excitation when the subject 7 has no defect. FIG. 6 is a diagram showing the measurement results of core 6. On the other hand, (a) in FIG. 5 is a diagram showing the measurement results of the pickup core when there is a defect in the object, and (b) in FIG. 5 is the excitation core when there is a defect in the object. It is a figure which shows a measurement result. However, these figures are graphed as changes in magnetic flux in the excitation core 6 and the pickup core 8 rather than changes in the magnetic potential difference. Time on the horizontal axis indicates time, and Flax on the vertical axis indicates magnetic flux.

[0066] When FIG. 4 (a) and FIG. 5 (a) are compared, there is a marked difference in the measurement results of the pickup core 8. FIG. As shown in FIG. 4 (a), the absolute value of the change in magnetic flux in the pickup core 8 when there is no defect (Crack) is on the order of two digits. On the other hand, as shown in Fig. 5 (a), the change in magnetic flux when there is a defect is on the order of three digits. This indicates that it is possible to detect a defect in the subject 7 by detecting a change in magnetic flux in the pickup core 8, that is, a corresponding change in magnetic potential difference.

[0067] When comparing (b) in FIG. 4 and (b) in FIG. 5, there is almost no change in the magnetic flux in the exciting core 6, and the difference in the measurement result of the pickup core 8 is it force ^s Wakakaru is due to the presence or absence of cracks (defects).

Next, based on FIG. 6, the non-destructive inspection apparatus 20 includes the second coil 14 and the first integrator 15 (hereinafter, sometimes referred to as “external magnetic field correction unit” for simplicity). We will explain the results of comparing the cases!

[0069] The horizontal axis is the distance (gap) between the exciting core 6 and the subject 7, and the vertical axis is the ratio of the core magnetic flux to the change in the gap of the exciting core 6. A solid line indicates a case where it is controlled by the external magnetic field correction unit, and a broken line indicates a case where it is not controlled by the external magnetic field correction unit. As shown in FIG. 6, by providing an external magnetic field correction unit in the nondestructive inspection apparatus 20, it can be said that the magnetic flux in the exciting core 6 is kept almost constant.

Next, based on FIG. 7, when alternating current is used as the current that the signal generator 2 of FIG. The measurement results of the sensitivity of the detection signal by the pickup core 8 when the frequency is changed will be described. In FIG. 7, the measurement results are shown when the specimen 7 has a defect force or far-side crack!

[0071] The horizontal axis is the frequency of the alternating current applied to the exciting core 6, and the vertical axis is the magnetic flux density when the frequency is changed! /, NA! /, And the magnetic flux when the frequency is changed. Ratio to density (Bm / B

0), indicating the sensitivity of the detection signal by the pickup core 8.

As shown in FIG. 7, it can be seen that the sensitivity increases as the frequency decreases.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and technical means disclosed in different embodiments are appropriately used. Embodiments obtained in combination are also included in the technical scope of the present invention.

[0074] Further, in addition to the above-described configuration, the nondestructive inspection apparatus of the present invention prevents a part of the transmitted magnetic flux from passing through a magnetic path provided between the two points and provided outside the subject. Preferably, a reverse magnetic field applying means for applying a reverse magnetic field is provided, and the magnetic potential difference measuring means measures the magnetic potential difference between the two points from the strength of the magnetic field of the reverse magnetic field.

[0075] According to the configuration, the reverse magnetic field applying means applies a reverse magnetic field so that a part of the transmitted magnetic flux does not pass through a magnetic path provided outside the subject by connecting the two points. To do. The magnetic potential difference measuring means measures a magnetic potential difference between the two points from the strength of the reverse magnetic field.

Therefore, since a part of the transmitted magnetic flux is not transmitted through the magnetic path, the influence of the magnetic resistance of the magnetic path and the nondestructive inspection apparatus can be greatly reduced. For this reason, the effect of lift-off due to the change in the distance between the non-destructive inspection device and the object can be eliminated.

In addition to the above-described configuration, the nondestructive inspection apparatus of the present invention includes an external magnetic field applying unit that applies an external magnetic field that generates the transmitted magnetic flux from the outside of the subject, and the transmitted magnetic flux is constant. It is preferable to provide an external magnetic field correcting means for correcting the strength of the external magnetic field.

According to the above configuration, the transmitted magnetic flux inside the subject is constant even when the distance between the external magnetic field applying means and the subject is increased. Therefore, in the nondestructive inspection apparatus, a nondestructive inspection device is provided. The effect of lift-off due to the change in the distance between the device and the subject can be removed. Further, the nondestructive inspection apparatus of the present invention, in addition to the above configuration, the external magnetic field applying means increases the magnetic permeability inside the coil, the coil generating a magnetic field according to the flowing current, and the external magnetic field It is preferable to include an excitation core for applying to the subject.

[0080] According to the configuration, it is possible to change the strength S of the magnetic field generated in the coil according to the current flowing in the coil. The excitation core is made of a material that increases the magnetic permeability inside the coil, for example, a high permeability material such as amorphous ferrite or high permeability steel, so that the strength of the external magnetic field applied to the subject is increased. The force S is used to concentrate on the measurement site of the subject.

[0081] Further, in the nondestructive inspection device of the present invention, in addition to the above configuration, the current is preferably an alternating current.

[0082] According to the above configuration, the characteristics of the transmitted magnetic field can be changed by changing the AC characteristics. For example, by changing the amplitude, frequency, or waveform of the alternating current or voltage, the transmitted magnetic field can be changed according to each change.

In addition to the above configuration, the nondestructive inspection apparatus of the present invention preferably includes frequency adjusting means for adjusting the frequency of the alternating current.

[0084] According to the above configuration, if the skin effect is used by changing the frequency of the alternating current (adjusting the depth of the transmitted magnetic flux from the subject surface), the crack depth from the subject surface on the measurement side, etc. Can be measured. For example, for the skin effect, the depth s from the surface on the measurement surface side of the subject where the magnetic flux density is approximately 37% of the surface portion is a function of the frequency ω of the alternating current and is given by the following equation: I understand! /

[0085] [Equation 2]

Here, ρ is the resistivity of the subject, and 11 is the magnetic permeability of the subject. Therefore, the depth S is reduced by increasing the AC frequency ω, and the depth S is increased by reducing the frequency ω by the force S.

[0088] In addition to the above-described configuration, the nondestructive inspection device of the present invention preferably increases the amplitude of the alternating current gradually and then decreases it gradually.

[0089] According to the above configuration, by applying the strong external magnetic field, the magnetization generated in the subject can be removed, and the influence of the magnetization of the subject can be reduced in the next measurement.

[0090] Further, in the nondestructive inspection apparatus of the present invention, in addition to the above configuration, the shape of the exciting core is a donut-shaped shape m / n (m <n, where m and n are integers of 1 or more It is preferable that it is a shape of one piece of those divided.

[0091] According to the above configuration, the excitation core adopts the shape of one of the donut-shaped shapes divided into m / n (m <n, where m and n are integers greater than or equal to 1) is doing. Therefore, it is possible to appropriately adjust the angle formed by the plane including each of the one end face and the other end face that are the measurement parts for the subject of the excitation core. For this reason, even when the object has a shape that can be obtained when the flat plate is bent at an angle that is the same as the angle formed by the flat surface, the nondestructive inspection apparatus can be used.

[0092] Further, in the nondestructive inspection apparatus of the present invention, in addition to the above configuration, it is preferable that the measurement unit for the subject in the excitation core is rounded.

[0093] According to the above configuration, since the measurement unit for the subject in the excitation core is rounded, the measurement portion of the excitation core can be applied to the subject having various shapes without changing the shape of the nondestructive inspection apparatus. Can be contacted.

Industrial applicability

[0094] The present invention detects crack damage in welded steel structures such as ships and bridges, and detection of crack damage in pipes made of steel and martensitic stainless steel in power plants and chemical plants. For example, the present invention can be widely applied to an inspection apparatus that detects crack damage or the like of an object made of a magnetic material.

Claims

The scope of the claims

[1] A nondestructive inspection device for inspecting a defect inside a subject,

A magnetic potential difference measuring means for measuring a magnetic potential difference between two points of transmitted magnetic flux passing through the inside of the subject from the outside of the subject;

By detecting a change in the magnetic potential difference measured by the magnetic potential difference measuring means when the subject and the magnetic potential difference measuring means are relatively moved, a defect inside the subject is detected. A nondestructive inspection apparatus comprising defect detection means for detecting existence.

[2] A reverse magnetic field applying means for applying a reverse magnetic field so that a part of the transmitted magnetic flux does not pass through a magnetic path provided between the two points and provided outside the subject,

The magnetic potential difference measuring means includes

2. The nondestructive inspection apparatus according to claim 1, wherein a magnetic potential difference between the two points is measured from a magnetic field strength of the reverse magnetic field.

[3] An external magnetic field applying unit that applies an external magnetic field that generates the transmitted magnetic flux from the outside of the subject;

The nondestructive inspection apparatus according to claim 1, further comprising an external magnetic field correction unit that corrects the strength of the external magnetic field so that the transmitted magnetic flux is constant.

[4] The external magnetic field applying means includes a coil that generates a magnetic field according to a flowing current;

4. The nondestructive inspection apparatus according to claim 3, further comprising an excitation core for increasing the magnetic permeability inside the coil and applying the external magnetic field to the subject.

5. The nondestructive inspection apparatus according to claim 4, wherein the current is an alternating current.

6. The nondestructive inspection apparatus according to claim 4, further comprising frequency adjusting means for adjusting the frequency of the alternating current.

[7] The nondestructive inspection device according to claim 5 or 6, wherein the amplitude of the alternating current is gradually increased after being gradually increased.

[8] The shape of the exciting core is a shape of one of the donut-shaped shapes divided into m / n (m <n, where m and n are integers of 1 or more). Characteristic claims

4. Non-destructive inspection device according to 4.

[9] The measuring part for the subject in the excitation core is rounded. The nondestructive inspection device according to claim 4.

A nondestructive inspection method for inspecting a defect inside a subject using a nondestructive inspection device,

A magnetic potential difference measuring step of measuring a magnetic potential difference between two points of a transmitted magnetic flux transmitted through the inside of the subject from the outside of the subject by a magnetic potential difference measuring means provided in the nondestructive inspection apparatus; ,

A change in magnetic potential difference measured by the magnetic potential difference measuring means when the subject and the magnetic potential difference measuring means are relatively moved by the defect detecting means provided in the nondestructive inspection apparatus. A nondestructive inspection method comprising: a defect detection step for detecting the presence of a defect inside the subject by detection.