JPH11160285A - Magnetic flaw detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic flaw detector for effectively detecting presence or absence of a damage of a surface to be inspected by removing or reducing an influence of a structure existing in a surface direction crossing with a surface to be inspected at the time of detecting the presence or absence of the damage of the surface. SOLUTION: A detecting sensor 16 has an exciting coil 11, detecting coils 12, 13 disposed to perpendicularly cross the exciting coil at both ends of the exciting coil, and a shielding plate 15 for reducing an AC magnetic field of a depth side of this paper of the exciting coil. An AC signal generator 23 is connected to the coil 11. And, a detection signal processor 32 for detecting a phase difference and an output difference of the respective detecting coils and outputting signals indicating them is connected the detecting coils. The sensor 16 is disposed on a refractory coating so that the coil 11 becomes parallel to a steel frame. When an AC current is supplied to the coil 11, a diamagnetizing field is generated in the frame by the field, and induced voltages are generated in the respective detecting coils. When the detecting coils pass near a crack, an output difference and a phase difference of the induced voltages are generated, and hence the crack can be detected by the differences. And, an influence to the detecting coils from depth side is removed or reduced by the plate 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic inspection apparatus for inspecting a conductive test object for damage such as cracks and defects, and more particularly to a method for detecting damage to a steel frame covered with a fireproof coating inside a building. The present invention relates to a magnetic flaw detector capable of easily and highly accurately detecting a fire-resistant coating without removing it.

[0002]

2. Description of the Related Art Conventionally, various methods for non-destructively inspecting a damaged portion of a steel material have been proposed and implemented, but most of them are contact-type non-destructive inspection methods. For example, inspection of steel frame welds is generally performed by ultrasonic flaw detection.However, when ultrasonic waves are launched from a refractory coating, the distance from the steel frame is large and reflection from the steel frame surface cannot be ignored, so cracks In order to accurately detect the presence or absence, it is necessary to keep the probe that starts and receives the ultrasonic wave in contact with the test object. On the other hand, a non-destructive inspection method using an X-ray apparatus is a non-contact type, but has a problem that a large-sized apparatus must be used, which is not simple. Other non-contact inspection methods have limitations such that the distance from the inspection object can be only about 2 to 3 mm.

[0003] Generally, steel frames are required to have fire resistance performance assuming a fire. Therefore, a method of spraying a fire-resistant coating material (thickness of 65 mm: fire resistance for 3 hours) or a method of protecting with concrete is adopted. Inspection is extremely difficult with both conventional contact-type and non-contact-type inspection methods. For this reason, when performing a flaw detection inspection on a steel frame member, operations such as removal of the refractory coating material and restoration after the inspection are required before the flaw detection, which requires a great deal of labor and time. In addition, measures must be taken against dust and noise generated during work.

In view of such problems, the present applicant has previously filed an application for the following magnetic flaw detection apparatus and method in Japanese Patent Application No. 9-96196.

That is, a detection sensor used for magnetic flaw detection is provided with an exciting coil for generating an AC magnetic field, and near the both ends of the exciting coil in substantially the same direction as the axial direction substantially perpendicular to the axial direction of the exciting coil. And the detection sensor is separated from the test object by a predetermined distance, and the axial directions of the two detection coils are substantially perpendicular to the test object. And an AC magnetic field is generated from both ends of the exciting coil by applying an AC current to the exciting coil, and a concentric eddy current is generated in the test object by an electromagnetic induction action based on the AC magnetic field. An AC magnetic field caused by an eddy current is detected by the two detection coils, and damage to the object to be inspected is detected based on an output difference and a phase difference between detection signals from the two detection coils. .

In the magnetic flaw detector and method disclosed in Japanese Patent Application No. 9-96196, when inspecting a beam near a column-beam joint where a column and a beam are joined, if there is no damage, the beam portion is inspected. The AC magnetic field due to the eddy current leads the phase more than the AC magnetic field due to the eddy current at the column-beam joint. Utilizing the property that the phase lags behind the magnetic field, the presence or absence of damage is detected by the difference in the output pattern of the phase difference between the detection signals of the two detection coils.

[0007]

However, in the magnetic flaw detection apparatus and method disclosed in Japanese Patent Application No. 9-96196, as shown in the perspective view of FIG.
The upper flange 104A provided at the upper end of the web 106 so as to be orthogonal to the web 106, and the lower flange 104B provided at the lower end of the web 106 so as to be orthogonal to the web 106 have an H-shaped cross section. A beam 102 of this H steel is joined so as to be orthogonal to the column 100, and a gusset plate 110 is provided between the column 100 and the web 106 for the purpose of reinforcing the joint. Is mounted with a plurality of bolts 112, the column 100 and the beam 10 on the upper surface of the lower flange 104B
In the case of inspecting the damage near the joint with the second, the detection sensor reacts to the gusset plate 110 and the bolt 112,
There has been a problem that the difference in the output pattern of the phase difference becomes minute, making it difficult to detect damage. FIG.
In FIG. 2, a column 100 is used to clarify the structure of the column-beam joint.
And the fireproof coating sprayed on the surface of the beam 102 is omitted.

[0008] The above problems will be described more specifically.
In the magnetic flaw detection apparatus and method disclosed in Japanese Patent Application No. 9-96196, even if an object (the web 106 in FIG. 12) different from the inspection object is present in a direction intersecting the inspection surface of the detection sensor, the exciting coil If the distance from each of the two detection coils provided near both ends of the object to the object is equal, the effect of the object on each detection coil is substantially the same, and the difference between the detection signals from each detection coil indicates the damage. The influence of the object can be ignored because the presence or absence of the object is detected. However, when another object (the gusset plate 110 and the bolt 112 in FIG. 12) is attached to the object, The state becomes the same as when the surface of the (web 106) has irregularities, and the distance from each of the two detection coils to the object is different. The difference of the output pattern is considered to be fine.

In the column-beam joint having the above-described structure, a scallop 108 which is a substantially fan-shaped notch in a portion shown by a thick solid line in the enlarged view of FIG. It is a serious problem that it is particularly difficult to detect the damage of this part since the part in contact with the edge part of the part and the part at the end part of the welded part 120 are particularly easily damaged.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and when detecting the presence or absence of damage to a surface to be inspected, the effect of a structure existing in a plane direction intersecting with the surface to be inspected is detected. It is an object of the present invention to provide a magnetic flaw detector capable of reliably detecting the presence or absence of damage on a surface to be inspected by removing or reducing it.

[0011]

In order to achieve the above object, a magnetic flaw detector according to claim 1 is provided with a magnetic field generating coil for generating a first alternating magnetic field and near the magnetic field generating coil. A detection coil for detecting a second AC magnetic field generated on the inspection surface of the conductive test object due to the first AC magnetic field generated from the magnetic field generating coil; and an inspection surface of the test object. A reducing member that reduces the intensity of the first AC magnetic field generated from the magnetic field generating coil in the intersecting plane direction, and wherein the magnetic field generating coil, the detection coil, and the reducing member are integrated. And a detection sensor unit configured to be movable.

Thus, in the magnetic flaw detector according to the first aspect, the intensity of the first AC magnetic field generated from the magnetic field generating coil is reduced in the direction intersecting the inspection surface of the object to be inspected. Since the member is provided in the detection sensor section,
Even if there is any structure in the detection sensor section in a plane direction intersecting the inspection surface of the object to be inspected, it is possible to remove or reduce the influence of the AC magnetic field on the detection sensor section from the structure. Also, since the reduction member is provided in the detection sensor unit so as to be movable integrally with the magnetic field generating coil and the detection coil, an AC magnetic field is applied to the reduction member due to the first AC magnetic field generated from the magnetic field generating coil. Even if it occurs, the effect of the alternating magnetic field from the reducing member on the detection coil is always constant, and this effect can be ignored.

According to a second aspect of the present invention, there is provided a magnetic flaw detection apparatus according to the first aspect, wherein the detection coil includes:
At each position near both ends of the magnetic field generating coil, two detection coils are arranged so that their axial directions are substantially orthogonal to the axial direction of the magnetic field generating coil and are respectively oriented in substantially the same direction. It is characterized by:

Thus, according to the magnetic flaw detector according to the second aspect, as the detection coil in the magnetic flaw detector according to the first aspect, a magnetic field is generated at each position near both ends of the magnetic field generating coil. Since two detection coils are used so as to be substantially orthogonal to the axial direction of the generating coil and to be oriented in substantially the same direction, the detection sensor unit is the same as the detection sensor of Japanese Patent Application No. 9-96196 described above. The self-calibration type sensor can reliably detect damage to the device under test based on the difference between the outputs of the two detection coils.

Here, the principle of inspecting the inspection object for damage using the detection sensor unit of the magnetic flaw detector according to claim 2 will be described.

In the case where a flaw detection operation is performed by the detection sensor of the magnetic flaw detector according to the second aspect of the present invention, the detection sensor is connected to an object to be inspected (for example, a steel plate or the like) whose two detection coils are conductive in the axial direction. ) Is arranged so as to be substantially perpendicular to the inspection surface. In this case, the magnetic field generating coil is substantially parallel to the test object. Then, in this state, an alternating current is applied to the magnetic field generating coil.

At this time, a part of the AC magnetic field leaking from both ends of the magnetic field generating coil flows through the object to be inspected.
An eddy current is induced on the surface of the test object. Then, an AC magnetic field crossing the two detection coils is generated by the eddy current, and an induced electromotive force is generated in the two detection coils.

Since the magnetic field generating coil is installed substantially parallel to the surface to be inspected of the object to be inspected, if there is no damage to the object to be inspected, the AC magnetic field leaks from both ends of the magnetic field generating coil. The generated eddy currents are also substantially equal, so that the voltages and phases of the output signals of the two detection coils are similar (see FIG. 7A).

However, if the test object has a crack,
When one of the detection coils passes over the crack, the flow of the eddy current generated on the surface of the test object is interrupted by the crack, and the magnetic field generated by the eddy current also changes. The balance between the output signals of the coils is lost (FIG. 7).
(B)). Therefore, by comparing the output signals of the two detection coils, it is possible to detect a crack in the test object with high accuracy even from over the fireproof coating that thickly covers the test object.

Further, in the above arrangement of the detection sensor section, the alternating magnetic field leaking from both ends of the magnetic field generating coil is
It spreads not only immediately below the detection sensor section but also in front and behind the detection sensor section. Accordingly, it is possible to detect flaws at the front or rear of the detection sensor unit, so that flaws at the corners of pillars can be detected.

Here, in an experiment using a column-column model in which columns are connected without providing a reduction member in the detection sensor section, a graph of an output difference detected when one column has a crack and The installation state of the detection sensor unit in this experiment is shown in FIG.
(A). In the figure, the horizontal axis represents the distance (X coordinate) of the tip of the detection sensor unit when the crack is taken as the origin, and the vertical axis represents the output difference between the two detection coils as the difference between the induced voltages of each coil. It is. As shown in the figure, the differential output voltage shows a large value near the position of the crack, and it can be seen that the crack position can be detected with high accuracy by using the output difference of the detection coil.

Further, in an experiment using a column-beam model in which a column and a beam are joined without providing a reduction member in the detection sensor section,
FIG. 11B shows a graph of the phase difference detected when there is a crack at the joint between the column and the beam, and the installation state of the detection sensor unit in this experiment. In the figure, the horizontal axis represents the distance (X coordinate) of the tip of the detection sensor when the crack at the joint is taken as the origin, and the vertical axis represents the phase difference between the output signals of the two detection coils to the same amplitude. This is expressed as an output voltage difference at the same point of the two adjusted output signals.

In such a column-beam model, the detection sensor cannot pass through the base of the column and an eddy current is also induced in the column when the column is inspected near the column. The signal of the coil changes and the output difference increases. In this case, it is difficult to determine the presence or absence of a crack in the joint due to the output difference.

Here, if there is no crack in the joint, the AC magnetic field due to the eddy current in the beam portion has a phase advanced from that of the AC magnetic field due to the eddy current in the column-beam joint portion, whereas the joint has a crack. In this case, the phase of the AC magnetic field due to the eddy current at the beam portion is delayed from the phase of the AC magnetic field due to the eddy current at the column-beam joint portion.
This change in phase appears as a difference in phase difference depending on the presence or absence of a crack in the joint, as shown in FIG. Therefore, it is possible to determine the presence or absence of a crack at the joint based on the phase difference between the individual detection coils.

FIGS. 11 (a) and 11 (b)
FIG. 11 shows a case where there is no structure on the side of the detection sensor unit on the back side or the front side of FIG. 11, but even when such a structure is present, each of the two detection coils and the above structure If the distances are substantially the same, the effect of the AC magnetic field exerted on each detection coil from the above structure is substantially the same, and the output difference and phase difference of each detection coil are respectively shown in FIG.
It behaves similarly to the graphs of FIG. 11A and FIG.

However, in the column-beam model, the beam is H steel as shown in FIG. 12, and a gusset plate is attached to the connection between the beam web (corresponding to the above structure) and the column. In the case where the presence or absence of a crack on the upper surface of the lower flange or the lower surface of the upper flange near the column-beam joint was detected, the web where the gusset plate was attached was thicker by the thickness of the gusset plate. Since the distance is the same as the state, the distance from each detection coil to the wall surface on the web side is different, and the degree of the influence of the AC magnetic field on each detection coil from the side surface on the web side is different. The phase difference does not become the state shown in the graph of FIG. 11B, and it becomes difficult to determine the presence or absence of a crack at the joint based on the phase difference.

Therefore, the detection sensor unit is provided with a reducing member for reducing the intensity of the AC magnetic field generated from the magnetic field generating coil in a plane direction intersecting with the inspection surface of the inspection object. It has been experimentally confirmed that the phase difference between the detection coils can be substantially the same as that shown in FIG. 11B by removing or reducing the influence from the intersecting plane directions. Therefore, by providing the above-described reduction member in the detection sensor unit, it is possible to determine the presence or absence of a crack at the joint based on the phase difference between the individual detection coils.

Therefore, a magnetic flaw detector according to claim 3 is
3. The magnetic flaw detector according to claim 2, further comprising a detection unit configured to detect at least one of an output difference and a phase difference between output signals induced by the two detection coils.

As described above, according to the magnetic flaw detector according to the third aspect, at least one of an output difference and a phase difference between output signals induced by the two detection coils in the magnetic flaw detector according to the second aspect. Is detected, it is possible to easily inspect the inspection object for damage based on at least one of the detected output difference and phase difference.

According to a fourth aspect of the present invention, there is provided the magnetic flaw detection apparatus according to the third aspect, wherein the display means displays at least one of the output difference and the phase difference detected by the detection means; Determining means for determining a damage state of the inspection object based on at least one of the output difference and the phase difference detected by the means.

As described above, according to the magnetic flaw detector of claim 4, the display means for displaying at least one of the output difference and the phase difference detected by the detection means in the magnetic flaw detector of claim 3; Determining means for determining a damage state of the object to be inspected based on at least one of the output difference and the phase difference detected by the detecting means. The damage state of the test object can be easily determined based on the display content by the means, and when the determination means is provided, the damage state of the test object can be automatically determined.

The reduction member is installed on a side surface of the magnetic field generating coil that is orthogonal to an inspection surface of the device to be inspected, such that the center of the magnetic field generating coil in the axial direction and the center of the reduction member substantially match. Is preferred. In this way, by installing the reduction member on the side surface of the magnetic field generating coil that is orthogonal to the inspection surface of the device under test, the alternating magnetic field from the magnetic field generating coil in the surface direction that intersects the inspection surface of the device under test of the magnetic field generating coil The degree of reduction by the strength reduction member can be increased, and the detection coil is arranged so that the center of the magnetic field generation coil in the axial direction and the center of the reduction member substantially coincide with each other. The effect of the reducing member on the detection coil when the coil is arranged around the axial center of the coil can be made substantially uniform.

Preferably, the reduction member is a flat plate made of a non-magnetic and highly conductive metal material. As described above, by making the reducing member non-magnetic, it is possible to prevent magnetization of the reducing member due to an alternating magnetic field or the like generated from the magnetic field generating coil. An eddy current is easily generated by an AC magnetic field generated from the magnetic field generating coil, and the degree of reduction of the intensity of the AC magnetic field from the magnetic field generating coil in a plane direction intersecting the inspection surface of the device to be inspected can be increased. By using a flat plate as the reduction member, the reduction member can be easily installed on the detection sensor unit.

Preferably, the thickness of the reducing member is greater than a skin depth determined based on a frequency of an alternating current applied to generate the first alternating magnetic field in the magnetic field generating coil. . That is, the thickness of the reducing member is preferably larger than the skin depth δ determined by the following equation (1).

[0035]

(Equation 1)

Here, ω is the angular frequency of the AC magnetic field generated from the magnetic field generating coil, μ is the magnetic permeability of the reducing member, and σ is the conductivity of the reducing member.

By setting the thickness of the reducing member in this way, the degree of reduction of the intensity of the AC magnetic field from the magnetic field generating coil in the direction intersecting the inspection surface of the object to be inspected can be increased.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows constituent blocks of a magnetic flaw detector according to an embodiment of the present invention. As shown in the figure, the magnetic flaw detector according to the present embodiment includes a detection sensor unit 16 for detecting a magnetic change due to damage to a steel frame (steel plate) 35 covered with a refractory coating 34, A signal processor 33 that outputs the phase difference output signal 30 and the differential output signal 31 by processing the detected signal.

Here, the detection sensor section 16 is shown in FIG.
As shown in a side view of FIG. 2 and a front view of FIG. 2B (a view as seen from the direction of arrow S in FIG. 2A), an exciting coil 11 serving as a magnetic field generating coil disposed in the center portion, The detection coil 12 and the detection coil 13 arranged at respective positions near both ends of the coil, the handle 14 gripped when the detection sensor unit 16 is moved, and the rear side of each of the coils shown in FIG. (B) A shielding plate 15 as a reduction member attached to the side surface (right side). Exciting coil 11
The detection coils 12 and 13 can be realized by winding an insulated wire around a long cylindrical object. The cross-sectional shapes of the excitation coil 11 and the detection coils 12 and 13 can be arbitrarily and suitably changed, and may be, for example, circular or square. Further, as shown in FIGS. 2A and 2B, the dimensions of each part of the detection sensor unit 16 in the present embodiment are the lengths of the detection sensor unit 16 along the left-right direction of FIG. 2A. 2A, the height of the detection coils 12 and 13 along the vertical direction of FIG. 2A is 40 mm, and the shielding plate 15 is FIG.
The length of the shielding plate 15 along the left-right direction is 150 mm, the height of the shielding plate 15 along the up-down direction of FIG.
It is assumed that the thickness of No. 5 is 5 mm. The material of the shielding plate 15 in the present embodiment is aluminum.

FIG. 3 is a side view showing the positional relationship between the coils constituting the detection sensor section 16. Assuming that the axial directions (directions of lines passing through the center of the coil hollow portion and orthogonal to the opening) of the exciting coil 11, the detecting coil 12, and the detecting coil 13 in FIG. The Q and R directions are substantially orthogonal to each other, and the Q and R directions are set to be substantially the same. The distance d ₂ to the center axis of the distance d ₁ and the detection coil 13 from the other end from one end to the center axis of the detection coil 12 of the excitation coil 11 is set to be substantially equal to each other.

Further, as shown in FIG.
Is composed of an AC signal generating unit 23 for supplying an AC current to the exciting coil 11 and a detection signal processing unit 32 as a detecting means for processing output signals of the detection coils 12 and 13.

Here, the AC signal generating section 23 includes an oscillating circuit 22 for generating an AC signal having a predetermined frequency,
And a constant current circuit 21 for amplifying the AC signal generated by the step 2 into a constant current AC current. Constant current circuit 21
Is connected to the exciting coil 11 and is connected to the constant current circuit 21.
Is supplied to the exciting coil 11 by the alternating current supplied from the
An alternating magnetic field is generated.

The detection signal processing section 32 is connected to the detection coil 12 and is capable of amplifying an output signal of the coil.
4. phase adjuster 26 capable of adjusting the phase of the output signal of detection coil 12 amplified by amplifier 24, detection coil 1
3, an amplifier 25 capable of amplifying an output signal of the coil, and a detection coil 13 amplified by the amplifier 25.
Is provided with a phase adjuster 27 that can adjust the phase of the output signal.

Further, the detection signal processing section 32 detects a phase difference between the two input AC signals, and outputs the detected phase difference information as a phase difference output signal 30 to the phase detector 28.
And a differential amplifier 29 that detects an output difference (voltage difference, power difference, and the like) between the two input AC signals, amplifies the detected output difference, and outputs the amplified output difference as a differential output signal 31. .

The phase detector 28 includes at least one of the oscillation circuit 22, the phase adjuster 26, and the phase adjuster 27.
Two devices are connected, and output signals of the two connected devices can be used as input signals. That is,
When the oscillation circuit 22 and any of the phase adjusters are connected to the phase detector 28, the phase detector 28 is connected to the reference AC signal output from the oscillation circuit 22. A phase difference from an output signal of one of the detection coils is detected. Then, the phase adjuster 2 is added to the phase detector 28.
6 and 27 are connected, the phase detector 28
Detects the phase difference between the output signal of the detection coil 12 and the output signal of the detection coil 13.

In order to improve the detection accuracy, the latter case in which the phase adjusters 26 and 27 are connected to the phase detector 28 is preferable. Further, the phase detector 28 may detect an output difference between two input signals at a certain phase (simultaneous point) as an amount indicating the phase difference.

The differential amplifier 29 includes a phase adjuster 2.
6 and the phase adjuster 27 are connected, and the differential amplifier 2
Reference numeral 9 detects an output difference between the output signals of the detection coil 12 and the detection coil 13 whose phases have been amplified and adjusted.

The above-described amplifiers 24 and 25, phase adjusters 26 and 27, phase detector 28, and differential amplifier 2
Reference numeral 9 indicates that an amplification factor and a phase can be adjusted by an adjustment knob (not shown) provided in the signal processor 33.

Next, FIG. 4 shows an example in which a magnetic flaw detection system is constructed by connecting a data display / analysis device to the output end of the signal processor 33. As shown in the figure, the signal processor 33 includes an XY recorder 50, an oscilloscope 52, and a computer 5 capable of displaying and recording at least one of the phase difference output signal 30 and the differential output signal 31.
4 is connected. Of course, other display devices,
For example, a digital display or the like can be used. By observing the signal waveform displayed and recorded by these devices, the operator can determine the damage state of the inspection object (steel frame 35).

The computer 54 not only displays the waveform of the phase difference output signal 30 and the waveform of the differential output signal 31 on a display and outputs the waveform to a printer (not shown), but also outputs the waveform of the phase difference output signal 30 and the differential output signal. It is possible to automatically determine the damage state of the test object based on the signal 31 and to perform processing for making each output signal and the damage state into a database. The XY recorder 50 and the oscilloscope 52 correspond to display means of the present invention, and the computer 54 corresponds to determination means of the present invention.

Next, using the magnetic flaw detector of the present embodiment, the damage situation near the column-beam joint where the beam is H steel and a gusset plate is attached to the joint between the column and the beam is shown. Fig. 5 (a) shows an example of sensor installation when performing an inspection.
5 to (c). 5 (a) is a side view, FIG. 5 (b) is a plan view of FIG. 5 (a) viewed from the direction of arrow U, and FIG. 5 (c) is a view of FIG. 5 (a) from the direction of arrow S. It is a front view. Also, as shown in FIG.
0 is a refractory coating 3 having a thickness of about 50 mm to 65 mm.
5A and 5B, the illustration of the refractory coating is omitted in FIG. 5A and FIG. 5B in order to clarify the structure of each part. In this sensor installation example, an installation example in the case of inspecting the upper surface of the lower flange 104B of the beam 102 for damage will be described.

As shown in FIG. 5 (c), first, a guide plate 114 (not shown in FIG. 5 (b)) is provided on the fireproof coating 34 covering the beam 102 of the object to be inspected so that its upper surface is substantially parallel to the surface to be inspected. And the detection sensor unit 16 is arranged on the guide plate 114. That is, the detection sensor unit 16
Is placed on the guide plate 114 in the inspection direction K (FIG. 5A).
Scan). Further, the guide plate 114 is provided with a shallow groove used for positioning the detection sensor unit 16, and a position scale is displayed along the groove (not shown).

The groove of the guide plate 114 is aligned with the inspection direction K, the detection sensor section 16 is scanned along this groove, and the position of the detection sensor section 16 is read by a position scale to reproduce an accurate position. Inspection accuracy can be further improved. The guide plate 114 is preferably made of a non-conductive plastic such as acrylic resin.

Next, the flow of the magnetic inspection operation when the damage state of the inspection object is inspected using the detection sensor unit 16 arranged as shown in FIG. 5 will be described with reference to the flowchart of FIG.

As shown in the flowchart of FIG. 6, first, before starting the inspection, the output adjustment and the phase adjustment of the detection coils 12 and 13 are performed (step 200). At the time of this adjustment, the detection sensor unit 16 is placed on a normal flat steel plate having no damage, and an alternating current is supplied to the excitation coil 11, thereby generating an induced voltage in the detection coils 12 and 13.

At this time, in the phase adjustment, the signal processor 33
The phase adjusters 26 and 27 are adjusted so that the phase difference output signal 30 output by the controller is equal to or substantially equal to zero, and the phases of the respective output signals are aligned. In the output adjustment, the differential output signal 31 is equal to zero. Alternatively, the output of each output signal is made uniform by adjusting the amplification factors of the amplifiers 24 and 25 so that they substantially match. These adjustments are simple operations just by turning an adjustment knob (not shown), and can be sufficiently performed by a beginner.

Next, the detection sensor unit 16 is arranged to the start position X _s of the top of the refractory coating (step 202).
Here, as shown in FIG.
The origin is the joint of No. 2 and the distance from the origin to the tip of the detection sensor unit 16 along the longitudinal direction (inspection direction K) of the beam steel plate is X. That is, in step 202, X ←
And X _s. Note that the direction of the detection sensor unit 16 (the axial direction of the excitation coil 11) is made substantially coincident with the inspection direction K.

Then, an alternating current is supplied from the alternating signal generator 23 to the exciting coil 11 (step 204). As a result, an alternating magnetic field is generated in the exciting coil 11, and the excitation coil 11 shown in FIG.
(A) As shown in FIG.
A portion of 1, 42 flows through lower flange 104B, thereby generating eddy currents 43, 44 in lower flange 104B. The eddy currents 43 and 44 cause the demagnetizing field 4
5, 46 occur. The demagnetizing fields 45 and 46 intersect with the detection coils 12 and 13 having axes substantially perpendicular to the surface of the steel sheet. An induced voltage is generated and output as an output signal.

FIG. 7A shows a magnetic field when a position where there is no damage is inspected, and eddy currents 43 and 44 are shown.
Are substantially equal, the demagnetizing fields 45 and 46 are also equal, and it can be seen that the output signals of the respective detection coils exhibit the same phase and the same output amplitude. However, since the magnetic field shown in FIG. 7A is an alternating magnetic field, the directions of the arrows indicating the magnetic field directions are switched alternately (the same applies to FIG. 7B described later).

The magnetic fields 41 and 42 leaking from both ends of the exciting coil 11 reach the positions of the detection coils 12 and 13, however, at this position, the vertical components of the magnetic fields 41 and 42 are extremely small. Voltages induced by the magnetic fields 41 and 42 in the detection coils 12 and 13 oriented in the vertical direction of the excitation coil 11 can be ignored.

Further, the magnetic fields 41 and 42 leaking from both ends of the exciting coil 11 try to reach the position of the web 106 (see FIG. 5). Are magnetic fields 41 and 4 directed toward the web 106 because the shielding plate 15 (see FIG. 5) is attached.
The strength of 2 is reduced. In addition, a small demagnetizing field is generated from the web 106 by the influence of the eddy currents 43 and 44 generated in the lower flange 104B. The shielding plate 15 also reduces the influence of the demagnetizing field on the detection coils 12 and 13. Can be. Further, since the shield plate 15 is made of aluminum having high conductivity and is attached to the side of the detection sensor unit 16, the excitation coil 11
The demagnetizing field, which is much stronger than the demagnetizing field generated in the web 106 by the magnetic fields 41 and 42 generated from the web 106, is always generated, and the influence of the minute demagnetizing field from the web 106 can be relatively reduced. Therefore, the influence on the web 106 side can be neglected.

The output signals generated by the detection coils 12 and 13 are amplified by the amplifiers 24 and 25 shown in FIG. 1 and the phases are adjusted by the phase adjusters 26 and 27. Then, the differential amplifier 29 outputs a differential output signal 31 detected from each output signal, and the phase detector 28 outputs a phase difference output signal 30 detected from each output signal.

Therefore, as shown in the flowchart of FIG. 6, a display / recording device (see FIG. 4) connected downstream of the signal processor 33 moves the detection sensor section 16 to the position X.
Are detected (Step 206), and the phase difference output signal P (X) is detected (Step 208). At this time, using the XY recorder 50 of FIG. 4, the detected data is sequentially recorded on a recording paper, and the detected values displayed on the oscilloscope 52 and the digital display are plotted on the paper. Further, the detection value may be stored in a storage device of the computer 54.

Next, it is determined whether the arrangement position X of the current detection sensor unit 16 is matched to the inspection end position X _e (step 210). In the case of FIG. 5A, the inspection end position X _e is determined by setting the tip of the detection coil 12 to the column 100.
This corresponds to the position of the detection sensor unit 16 when the corner of the covering material covering the joint between the beam and the beam 102 is reached.

[0066] If the position X of the current time point is not the inspection end position X _e (step 210 negative decision), the detection sensor unit 16
Is moved in the inspection direction K by a predetermined distance ΔX. Thus, the position X of the detection sensor unit 16 is the X _s -ΔX.
Then, returning to steps 206 and 208, the differential output signal S (X) and the phase difference output signal P (X) are detected again for the updated position X, and the same processing is executed.

In this way, the start position X _s is sequentially determined.
Output signal S (X) from Δ to the end position X _{e in} ΔX steps
And a phase difference output signal P (X). here,
When inspecting the position where there is no crack, the detection coils 12 and 1
3 are almost in phase and the output amplitude levels are close, so that the differential output signal S (X) and the phase difference output signal P
(X) is a small value.

On the other hand, for example, as shown in FIG. 7B, when the detection sensor section 16 approaches the damaged section 80, the resistance value of the crack portion becomes large, so that the eddy current generated by the magnetic field 41 is reduced. In addition, the current value becomes smaller as compared with the case where there is no crack. Also, as the detection sensor unit 16 approaches,
The eddy current changes from 43a to 43b at the boundary of the damaged portion 80, and the demagnetizing fields 45 and 46 generated thereby also change. As a result, the magnetic flux crossing the detection coil 12 is different from the magnetic flux crossing the detection coil 13, so that the differential output signal increases.

[0069] Therefore, as shown in the flowchart of FIG. 6, when the position X of the current coincides with the completion of the inspection positions X _e (step 210 affirmative determination), the differential output signals from the position X _s to X _e S (X ) Is detected (step 214).

On the other hand, at a position where the detection sensor unit 16 is close to the joint between the column 100 and the beam 102, the magnetic field leaking from the end of the exciting coil 11 flows through the column perpendicular to the object to be inspected (the beam). However, the voltage induced in the detection coil near the column by the AC magnetic field due to the eddy current generated in the column changes, and the differential output signal changes regardless of the presence or absence of a crack in the joint. Further, since the absolute value of the output voltage changes depending on the height of the sensor, the size of the device under test, and the like, it is difficult to determine the presence or absence of a crack at the junction depending on the differential output signal. A gusset plate 110 is attached to the joint, and the distance from the detection coil 12 to the web 106 including the gusset plate 110 is determined by the gusset plate 110.
Is smaller than the distance from the detection coil 13 to the web 106 by the thickness of the detection coil 12 and the detection coil 1.
In the case of No. 3, the balance of the influence from the web 106 is lost, but the influence from the web 106 can be neglected by the action of the shielding plate 15 attached to the side surface of the detection sensor unit 16 as described above. As already described with reference to FIG. 11, even when the gusset plate 110 is attached to the joint, the influence of the gusset plate can be removed or reduced by the action of the shield plate 15, and the column 100 and the beam 102 can be reduced. An experimental result has been obtained in which the output pattern of the phase difference output signal is inverted depending on the presence or absence of a crack (damaged portion 82 in FIG. 5) at the junction with.

Therefore, as shown in the flowchart of FIG. 6, the presence or absence of a crack at the joint between the column 100 and the beam 102 is determined based on the phase difference output signal P (X) (step 21).
6) End the inspection. Steps 214 and 216
In detecting the damaged position, the operator looks at the waveform recorded by the XY recorder 50 or the like, and checks whether the change pattern of the waveform, the absolute value of the recording signal exceeds a predetermined reference value, or the signal output. The damage position is determined based on the pattern. Note that the determination criteria may be programmed so that the computer 54 automatically determines the damaged position.

In this embodiment, since two detection coils are used, a larger detection value can be obtained than in the case where only one detection coil is used, so that more accurate flaw detection can be performed. The reason why such a large output is obtained is that when the magnetic field on the damaged side of the two eddy currents generated in the steel sheet by the exciting coil changes, the other magnetic field changes in the opposite direction. Can be When estimated by the prototype device, an output improvement of about 7% is obtained as compared with one detection coil.

Here, an actual measurement example of the magnetic flaw detector according to the present embodiment is shown in FIGS.
5 shows that even if the gusset plate 110 is attached, the crack in the column-beam joint can be detected with high accuracy in the step 216 described above.
Note that the sensor height (height from the surface to be inspected to the detection sensor unit) when performing the actual measurement is 80 mm in all cases.

FIG. 8A shows the vicinity of the joint between the column and the beam when the shielding plate 15 is not provided on the detection sensor section 16 and the gusset plate 110 is not attached to the joint between the column and the beam. The change of the differential output voltage with respect to the sensor position when there is a crack and when there is no crack is shown. Regardless of the presence or absence of cracks, the differential output voltage increases when approaching the junction. Since the absolute value of the differential output voltage changes depending on the height of the sensor, the size of the device under test, and the like, it can be seen that it is difficult to determine the presence or absence of a crack at the junction based on the differential output voltage.

On the other hand, FIG. 8B shows the case where the shielding plate 15 is not provided on the detection sensor unit 16 and the gusset plate 110 is not attached to the joint between the column and the beam. It shows the change of the phase difference output voltage with respect to the sensor position when there is a crack near the joint and when there is no crack, and the change of the phase difference output is a small difference, but the output pattern depends on the presence or absence of a crack at the joint. Invert. Therefore, when the gusset plate 110 is not attached,
By detecting the output pattern of the phase difference output voltage without providing the shield plate 15 in the detection sensor section 16, it can be seen that the presence or absence of a crack in the joint can be detected with high accuracy. FIG. 8C shows that the shielding plate 15 is connected to the detection sensor unit 16.
Gusset plate 11 at the joint between column and beam
FIG. 7 shows a change in the differential output voltage with respect to the sensor position when there is a crack near the joint between the column and the beam when no 0 is attached. In this case, when the detection sensor unit 16 is brought closer to the joint,
The position where the differential output voltage starts to increase under the influence of the gusset plate 110 is the gusset plate 1 shown in FIG.
As compared with the case where there is no 10, the position becomes farther from the joint, and when the joint is further brought closer, the differential output voltage becomes larger as compared with the case where there is no crack. As described above, although there is a difference in the magnitude of the change of the differential output voltage as compared with the case where the gusset plate 110 is present, the absolute value of the differential output voltage is different from the sensor height or the test object. In this case as well, it is difficult to determine the presence or absence of a crack in the joint by the differential output voltage, as in the case where there is no gusset plate.

FIG. 8D shows the phase difference output voltage with respect to the sensor position when the shield plate 15 is not provided on the detection sensor unit 16 and the gusset plate 110 is attached to the joint between the column and the beam. In this case, the magnitude of the phase difference output voltage is considerably larger than the case without the gusset plate 110 shown in FIG.
This change in the output pattern is in the same direction regardless of the presence or absence of a crack, and the inversion of the output pattern as shown in FIG. 8B does not occur. Therefore, it is difficult to determine the presence or absence of a crack by the phase difference output voltage. .

FIG. 8E shows a case where the shield plate 15 is provided on the detection sensor unit 16 and the gusset plate 110 is attached to the joint between the column and the beam. It shows changes in the differential output voltage with respect to the sensor position when there is and when there is no. Regardless of the presence or absence of a crack, the differential output voltage increases when approaching the junction, but its value is smaller than when there is no shielding plate (in the case of FIG. 8C). Since the absolute value of the differential output voltage changes depending on the height of the sensor, the size of the device under test, and the like, it can be seen that it is difficult to determine the presence or absence of a crack at the junction based on the differential output voltage.

On the other hand, FIG. 8F shows the phase difference output voltage with respect to the sensor position when there is a crack near the joint between the column and the beam under the same conditions as in FIG. FIG. 8B shows the change in the phase difference output voltage due to the influence of the gusset plate 110.
As in the case where there is no shield plate shown in (1), the change in the phase difference output voltage is small but the output pattern is inverted according to the presence or absence of a crack in the joint. Therefore, it is understood that the presence or absence of a crack in the joint can be detected with high accuracy by detecting the output pattern of the phase difference output.

As described in detail above, in the magnetic inspection apparatus according to the present embodiment, the shielding plate 15 is
6 is provided on the side of the web 106 side so that the web 1
Since the influence of the AC magnetic field from the 06 side is removed or reduced, even when the gusset plate 110 is attached to the joint between the column and the beam, the damage at the joint between the column and the beam is surely ensured. Can be detected.

In the present embodiment, the case where the shield plate 15 is attached to the detection sensor section 16 having two detection coils has been described. However, the present invention is not limited to this. Even if there is only one detection sensor unit, the same effect as in the present embodiment, that is, the effect of removing or reducing the influence of the side of the detection sensor unit can be obtained by attaching the shielding plate. Can be.

In this embodiment, the case where aluminum is used as the material of the shield plate 15 has been described. However, the present invention is not limited to this, and
The material of No. 5 is preferably a non-magnetic and highly conductive metal, and for example, copper, stainless steel or the like can be applied.

In this embodiment, the excitation coil 11
The case where an I-shaped coil is used has been described,
The present invention is not limited to this, and other types of coils such as U-shaped coils may be used.

In this embodiment, the case where the influence of the gusset plate 110 attached to the column-beam joint is removed or reduced by the shield plate 15 has been described. However, the present invention is not limited to this. Not web 1
Even when, for example, a reinforcing plate, a bolt, or the like is attached to a portion other than the joint portion 06, the influence of the reinforcing plate, the bolt, or the like can be removed or reduced by the shielding plate 15.

In this embodiment, the case where the test object is H steel having the surface to be inspected and the surface orthogonal to the surface to be inspected has been described, but the present invention is not limited to this. For example, it is needless to say that the influence from the oblique surface can be removed or reduced as in the present embodiment, for example, even for a steel material having a surface obliquely oblique at a predetermined angle on the surface to be inspected.

In the present embodiment, the detection coil 12
Although the case where the damage is detected based on the output difference between the output signals guided to the respective detection coils with the direction in which the insulation coating wire of the detection coil 13 is wound in the same direction has been described, the present invention is not limited to this. Instead, the direction in which the insulation coating wire of each detection coil is wound may be opposite to each other, and damage may be detected based on the output sum between output signals induced by each detection coil.

In the present embodiment, the dimensions of the shielding plate 15 are 150 mm in length, 75 mm in height and 75 mm in height, as shown in FIG.
Although the case where the plate thickness is 5 mm has been described, the present invention is not limited to this, and may have any suitable size.

As a result of a simulation performed by the applicant using shield plates of a plurality of sizes, the length of the shield plate is 1 to 3 times the axial length of the exciting coil, and the height of the shielding plate is It has been confirmed that it is effective to make the dimension 3 to 10 times the width in the direction orthogonal to the axial direction of the above.

In the present embodiment, the exciting coil 11
The case where the distance from one end to the center axis of the detection coil 12 and the distance from the other end to the center axis of the detection coil 13 are fixed has been described, but the present invention is not limited to this. Instead, a mode having an adjustment function that allows each distance to be changed may be adopted.

FIG. 9 shows an example of the detection sensor unit 16 provided with a means for realizing this adjustment function. The detection sensor unit 16 shown in FIG. 1 is configured to be able to slide each slide plate in a direction substantially coinciding with the axial direction of the excitation coil 11 and a slide plate to which the detection coils 12 and 13 are fixed. And a slide support having the exciting coil 11 fixed to the portion.

The slide support has a stopper for fixing each slide plate and a scale indicating the distance from the end of the exciting coil 11 to each detection coil. The operator loosens the stopper, moves the detection coils 12 and 13 while watching the scale, and tightens the stopper when a certain scale value is reached, so that the intervals d ₁ and d ₂ (see also FIG. 3) can be set freely. be able to. The distances d ₁ and d ₂ may be finely adjusted by using a screw or a helicoid.

Since the thickness of the fireproof coating varies depending on the fireproof standard, the distance between the detection sensor unit and the surface to be inspected changes according to the thickness of the fireproof coating. Here, the sensor height (2
FIG. 10 shows the result of a simulation of how the vertical component of the magnetic field generated from the exciting coil changes due to (between 0 and 100 mm). As shown in the drawing, it can be seen that the maximum component of the vertical component that generates an eddy current on the test object moves outward as the distance from the detection sensor unit increases. Therefore, as described above, the interval between the excitation coil and the detection coil is made variable, and the center of the detection coil is positioned above the maximum peak point of the vertical component, that is, the point where the eddy current becomes strongest, according to the sensor height. By enabling the arrangement, the detection sensitivity can be improved.

[0092]

According to the magnetic flaw detector according to the first aspect,
Since the detection sensor unit is provided with a reducing member for reducing the intensity of the first AC magnetic field generated from the magnetic field generating coil in a plane direction intersecting with the inspection surface of the inspection object, Even if any structure exists in the plane direction intersecting with the inspection surface of the body, the effect is obtained that the influence of the AC magnetic field on the detection sensor unit from the structure can be removed or reduced.

According to the magnetic flaw detector according to the second aspect, the detection coil in the magnetic flaw detector according to the first aspect is provided at each position near both ends of the magnetic field generating coil. Since the two detection coils are arranged so as to be substantially orthogonal to the axial direction and to be oriented in substantially the same direction, the detection sensor unit becomes a self-calibration type sensor and is based on the difference between the outputs of the two detection coils. Thus, it is possible to reliably detect damage to the test object.

According to the magnetic flaw detector of the third aspect, at least one of the output difference and the phase difference between the output signals induced by the two detection coils in the magnetic flaw detector of the second aspect is detected. Therefore, an effect is obtained that the inspection object can be easily inspected for damage based on at least one of the detected output difference and the phase difference.

According to the magnetic flaw detector of the fourth aspect, the display means for displaying at least one of the output difference and the phase difference detected by the detection means in the magnetic flaw detector of the third aspect, and the detection means Determining means for determining a damage state of the test object based on at least one of the detected output difference and the phase difference; therefore, when the display means is provided, the operator can display on the display means. It is possible to easily determine the state of damage to the object to be inspected based on the content, and it is possible to automatically determine the state of damage to the object to be inspected when the determination means is provided.

According to the magnetic flaw detector of the fifth aspect, since the reduction member is provided on the side surface orthogonal to the inspection surface of the inspection object of the magnetic field generating coil, the inspection surface of the inspection object of the magnetic field generating coil is provided. The magnitude of the reduction of the strength of the alternating magnetic field from the magnetic field generating coil in the plane direction intersecting with the direction of the magnetic field can be increased by the reducing member, and the axial center of the magnetic field generating coil and the center of the reducing member substantially coincide with each other. In this case, the effect of the reducing member on the detection coil when the detection coil is arranged around the axial center of the magnetic field generation coil can be made substantially uniform.

Further, according to the magnetic flaw detector of claim 6, since the reducing member is non-magnetic, magnetization of the reducing member due to an alternating magnetic field or the like generated from the magnetic field generating coil can be prevented. Is made of a highly conductive metal material, so that an eddy current is easily generated by the alternating magnetic field generated from the magnetic field generating coil on the reducing member, and the alternating current from the magnetic field generating coil in a plane direction intersecting the inspection surface of the device under test is The degree of reduction in the strength of the magnetic field can be increased, and the reduction member is a flat plate, so that the reduction member can be easily installed on the detection sensor unit.

Further, according to the magnetic flaw detector of the present invention, the thickness of the reducing member is determined based on the frequency of the alternating current applied to generate the first alternating magnetic field in the magnetic field generating coil. Since the thickness is made larger than the skin depth, an effect is obtained that the degree of reduction of the intensity of the AC magnetic field from the magnetic field generating coil in the plane direction intersecting the inspection surface of the inspection object can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing configuration blocks of a magnetic flaw detector according to an embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating a detailed configuration of a detection sensor unit according to the embodiment of the present invention, wherein FIG. 2A is a side view of the detection sensor unit, and FIG. It is a front view of a detection sensor part.

FIG. 3 is a diagram illustrating a positional relationship between an excitation coil and a detection coil in the detection sensor unit according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration example of a magnetic flaw detection system according to an embodiment of the present invention.

FIG. 5 is a schematic installation diagram of a detection sensor unit and a test object when an inspection of a test condition of the test object is performed by the magnetic flaw detection apparatus according to the embodiment of the present invention, (a) is a side view,
(B) is a plan view seen from the direction of arrow U in (a),
(C) is a front view seen from the arrow S direction in (a).

FIG. 6 is a flowchart showing a flow of a magnetic inspection operation according to the embodiment of the present invention.

FIG. 7 is a diagram showing distributions of a magnetic field generated when an alternating current is supplied to the exciting coil, an eddy current generated in the device under test, and a demagnetizing field generated by the eddy current according to the embodiment of the present invention. (A) is a diagram when the damaged portion is not near the position of the detection coil, and (b) is a diagram when the damaged portion is near the detection coil.

FIG. 8 is a graph showing a change in a differential output voltage or a phase difference output voltage at a column-beam joint with respect to a distance from a crack to a tip of a detection sensor unit. A differential output voltage when the column-beam joint is inspected by a detection sensor unit not provided with a shielding plate, and (b) shows a column-beam joint where a gusset plate is not attached and a shielding plate is not provided. Phase difference output voltage when inspected by the detection sensor unit,
(C) is a column to which a gusset plate is attached.-Differential output voltage when the beam joint is inspected by a detection sensor unit having no shielding plate. (D) is a column to which a gusset plate is attached. Phase difference output voltage when the beam joint is inspected by a detection sensor unit not provided with a shielding plate, and (e) is a detection sensor provided with a shielding plate at the column-beam junction where the gusset plate is attached. (F) is a phase difference output voltage when the column-beam joint to which the gusset plate is attached is inspected by the detection sensor unit provided with the shielding plate. 6 is a graph showing a change in the graph.

FIG. 9 is a configuration diagram in a case where a function of adjusting a distance between an excitation coil and a detection coil is provided.

FIG. 10 is a vertical magnetic field distribution at each sensor height of a magnetic field generated by an eddy current generated in a steel sheet when an alternating current is applied to an exciting coil.

FIG. 11 is a diagram for explaining the principle of the present invention,
(A) is a sensor part layout diagram and a graph of the differential output voltage with respect to the position of the sensor part tip when the inspection of the flaw detection state is performed by the column-column model, and (b) is a column-beam model in the column-beam model. 3A and 3B are a layout diagram of a sensor unit and a graph of a phase difference output with respect to a position of a tip of the sensor unit in the case of inspecting the presence or absence of a crack at a joint portion.

FIG. 12 is a diagram provided for describing a problem of the related art;
It is the perspective view which shows the column-beam joint part at the time of using a gusset plate, and the structure of its periphery, and the broken side view which expanded a part in this perspective view.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 excitation coil (magnetic field generating coil) 12 detection coil 13 detection coil 14 handle 15 shield plate (reducing member) 16 detection sensor unit 21 constant current circuit 22 oscillation circuit 23 AC signal generation unit 24, 25 amplifier 26, 27 phase adjuster 28 Phase detector 29 differential amplifier 30 phase difference output signal 31 differential output signal 32 detection signal processing unit (detection means) 33 signal processor 50 XY recorder (display means) 52 oscilloscope (display means) 54 computer (determination means) 100 pillar 102 beam (inspection object) 104 flange 106 web 108 scallops 110 gusset plate

Continued on the front page (72) Inventor Akira Umekuni 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside the Technical Research Institute, Takenaka Corporation (72) Inventor Masao Kibuchi 1-5-1, Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture No. 5 Kobe Steel, Ltd. Kobe Research Institute (72) Inventor Naoyuki Sato 6-1, Koriyama Koriyama, Taishiro-ku, Sendai City, Miyagi Prefecture Tokinnai Co., Ltd. (72) Inventor Norimitsu Hoshi, Taishiro-ku, Sendai City, Miyagi Prefecture 6-7-1, Koriyama, Tokin Co., Ltd.

Claims (7)

[Claims] A magnetic field generating coil for generating a first AC magnetic field; and a conductive member disposed near the magnetic field generating coil and electrically conductive due to the first AC magnetic field generated from the magnetic field generating coil. A detection coil for detecting a second AC magnetic field generated on the inspection surface of the inspection object; and a strength of the first AC magnetic field generated from the magnetic field generation coil in a plane direction intersecting the inspection surface of the inspection object. A magnetic flaw detector comprising: a reduction member configured to reduce the length of the magnetic field generating coil, the detection coil, and the reduction member that are integrally movable. 2. The detection coil is disposed at each position near both ends of the magnetic field generating coil such that the axial direction is substantially orthogonal to the axial direction of the magnetic field generating coil and is substantially in the same direction. 2. The magnetic flaw detector according to claim 1, wherein the magnetic flaw detector comprises two detection coils. 3. The magnetic flaw detection apparatus according to claim 2, further comprising a detection unit configured to detect at least one of an output difference and a phase difference between output signals induced by the two detection coils. 4. A display means for displaying at least one of the output difference and the phase difference detected by the detection means, and the inspection target based on at least one of the output difference and the phase difference detected by the detection means. The magnetic flaw detector according to claim 3, further comprising: a determination unit configured to determine a damage state of the body. 5. The reduction member is disposed on a side surface of the magnetic field generating coil that is orthogonal to an inspection surface of the device to be inspected, such that an axial center of the magnetic field generation coil and a center of the reduction member substantially coincide with each other. 5. The method according to claim 1, wherein:
The magnetic flaw detector according to any one of claims 1 to 4. 6. The magnetic flaw detector according to claim 1, wherein the reduction member is a flat plate made of a non-magnetic and highly conductive metal material. 7. The thickness of the reducing member is greater than a skin depth determined based on a frequency of an alternating current applied to generate the first alternating magnetic field in the magnetic field generating coil. The magnetic flaw detector according to any one of claims 1 to 6, wherein