JPH10288605A - Magnetic testing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect cracks smoothly and highly accurately without stripping or smoothing the coating. SOLUTION: A detecting sensor 14 is constituted of an exciting coil 11 and two detecting coils 12 and 13 arranged at locations of both end parts of the exciting coil 11 so as to be orthogonal with respect to the exciting coil 11. An a.c. signal generating part 23 to generate a.c. signals is connected to the exciting coil 11, and a phase detector 28 to detect the phase differences of output signals induced in each coil and a differential amplifier 29 to detect output differences are connected to the detecting coils 12 and 13 via amplifiers 24 and 25 and phase-shifters 26 and 27. The detecting sensor 14 is disposed on a fireproof coating so that the exciting coil 11 is in parallel with a steel frame, and an a.c. current is passed through the exciting coil 11. Then an eddy current is generated in the steel frame by the generated a.c. magnetic fields, and consequently demagnetizing fields are generated. Therefore, an induced voltage is generated at each of the detecting coils 12 and 13. As the output difference and phase difference of the induced voltages are generated when the detecting coils 12 and 13 pass the vicinity of a crack, it is possible to detect cracks smoothly and highly accurately by detecting those differences.

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 inspection object for cracks and defects, and a magnetic inspection method using the apparatus. In particular, the present invention relates to a method for covering a fireproof coating inside a building. The present invention relates to a magnetic flaw detection apparatus and a magnetic flaw detection method capable of easily and accurately detecting a damaged steel frame without peeling off a refractory coating.

[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, the inspection of steel frame welds is generally performed by ultrasonic flaw detection, but if ultrasonic waves are launched from the refractory coating, the distance from the steel frame is large and the reflection from the steel frame surface cannot be ignored, so there is no crack. In order to accurately detect the probe, the probe that starts and receives the ultrasonic wave must be 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. In addition, other non-contact inspection methods have limitations such that the distance from the inspection object can be only 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.

As an effective method for solving such a problem, there is an electromagnetic induction method capable of detecting a crack from above a coating material. For example, “Study on Non-Contact Damage Investigation Method for Damaged Steel Structures” (Summaries of Technical Papers of Annual Meeting of Architectural Institute of Japan; Sep. 1996)
According to the electromagnetic induction method shown in (Mon, Kuramochi Mitsugu, et al.), The coil for magnetic flaw detection is placed on the fireproof coating material or concrete slab of the surveyed part of the building so that its axial direction is The coils are arranged so as to be substantially vertical, and an alternating current is applied to the coil (hereinafter, referred to as an “exciting coil”), and the coil is scanned back and forth and right and left.

The AC magnetic field leaking from both ends of the exciting coil penetrates a refractory coating material, a slab, or the like, and generates a concentric eddy current in a steel frame by an electromagnetic induction action. If there is damage to the steel frame, this eddy current is interrupted by the flaw and the shape changes.This change is detected by the monitor of the measuring instrument, so that the damage state of the steel frame can be accurately determined without peeling the coating material. That can be detected.

[0006] A sensor for magnetic flaw detection (hereinafter referred to as a "detection sensor") used in the above-described conventional magnetic flaw detection method includes a coil (excitation coil) for generating an eddy current by flowing an alternating current, and the coil. It can be constituted by a measurement coil (detection coil) arranged in the same direction as or coaxially with the axial direction of the exciting coil. Among them, the detection coil is crossed by an AC magnetic field caused by an eddy current generated by the AC magnetic field of the excitation coil, and an induced electromotive force is generated. The change in the eddy current can be detected, and thus the presence or absence of damage can be determined.

[0007]

However, the above-mentioned conventional electromagnetic induction method has the following problems.

That is, in the flaw detection inspection operation, if the distance between the detection coil and the end face of the steel frame changes even if the height of the detection coil (the distance from the steel frame to be measured) is constant, the coil output changes. It becomes difficult to distinguish between an output change due to the change and an output change due to the flaw detection, thereby lowering the inspection accuracy. In order to accurately detect cracks with a single detection coil, use a crack-free steel frame in advance, measure the output change due to the end face, create a calibration curve, and compare the actual flaw detection results with the calibration curve to determine the crack. It is necessary to judge the presence / absence of this, and the above-described electromagnetic induction method requires a great deal of labor for inspection.

[0009] The steel frame is generally protected by spraying a refractory coating material. However, since the thickness of the steel frame varies greatly and the surface is uneven, the height of the detection coil from the steel frame is kept constant. And the inspection accuracy decreases. Conversely, if the inspection accuracy is to be maintained, it is necessary to smooth the surface of the refractory coating, which requires a great deal of labor and time. And
It is also necessary to take measures against dust and noise generated during the smoothing work (such as closing inspection target locations).

Further, by arranging the excitation coil and the detection coil coaxially or in the same direction, the main focus is on flaw detection immediately below the excitation coil and the detection coil. It was difficult to do.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and makes it possible to easily and accurately inspect the damage state of members without peeling off or smoothing the current refractory coating, and at the same time, enabling the detection sensor. It is an object of the present invention to provide a magnetic flaw detection apparatus and method capable of detecting flaws in front or rear.

[0012]

[Means for Solving the Problems]

(Structure of the present invention) In order to achieve the above object, a first aspect is provided.
According to the invention, an exciting coil to which an alternating current can be applied and, at respective positions near both ends of the exciting coil, are arranged substantially in the same direction so as to be axial directions substantially orthogonal to the axial direction of the exciting coil. The magnetic flaw detector is configured to include a detection sensor composed of two detection coils.

According to a second aspect of the present invention, in the first aspect of the present invention, the detection sensor is arranged so that an axial direction of the two detection coils is substantially perpendicular to a conductive test object. And detecting means for detecting at least one of an output difference and a phase difference between output signals induced in the two detection coils when an alternating current is applied to the coils.

[0014] The invention of claim 3 is claim 1 or claim 2.
In the invention, the distance from the end of the excitation coil to the two detection coils can be arbitrarily changed.

According to a fourth aspect of the present invention, there is provided an exciting coil to which an alternating current can be applied, and a position near each end of the exciting coil which is substantially perpendicular to the axial direction of the exciting coil. In a magnetic flaw detection method for inspecting a damage state of a conductive object to be inspected by using a detection sensor composed of two detection coils fixed in the same direction, the detection sensor includes the two detection coils. An arranging step of arranging the exciting coil at an arbitrary position around the inspected object such that an axial direction thereof is substantially perpendicular to the inspected object; a supplying step of supplying an alternating current to the exciting coil; A detection step of detecting at least one of an output difference and a phase difference between the induced output signals, and an inspection for inspecting a damage state of the inspection object based on at least one of the detected output difference and the phase difference. Process and And wherein the Ranaru.

According to a fifth aspect of the present invention, in the inspection step of the fourth aspect, based on the output difference detected in the detection step, the vicinity of the position of the inspection object corresponding to the position where the detection sensor is disposed is determined. It is characterized by determining whether there is damage.

According to a sixth aspect of the present invention, in the inspection step of the fourth aspect, when another member running in a direction different from the direction of the object to be inspected is joined to the object to be inspected, the member to be inspected is connected to the member. It is characterized in that it is determined whether or not the joint is damaged based on the phase difference detected near the joint.

The invention of claim 7 is the invention of claims 4 to 6
In the arranging step of any one of the above, the height of the two detection coils of the two detection coils is adjusted at a constant position above the non-conductive guide plate fixed to the covering material by adjusting the height of the two detection coils from the inspection object. The detection sensor is arranged so that an axial direction is substantially perpendicular to the guide plate. (Principle of the invention) In the invention of claim 1, since two detection coils are used for the detection sensor, the sensor becomes a self-calibration type sensor, and the distance from the end face of the steel frame is determined by comparing the outputs of the two detection coils. The change in output due to the change can be calibrated by one measurement. Accordingly, it is possible to omit the trouble of preparing a calibration curve using a steel frame having no cracks in advance as in the related art, and it is possible to easily perform a flaw detection operation.

When two detection coils are used as described above, damage is detected using a magnetic field from two eddy currents generated in the steel frame by the excitation coil. When the magnetic field on the damage side changes, the other magnetic field is changed. Since it changes in the opposite direction, a larger output can be obtained than in the case of a single detection coil, and more accurate flaw detection can be performed. For example, when roughly estimated by a prototype device, an output improvement of 7% is obtained as compared with one detection coil.

Further, even if damage is present on either of the detection coils, an output change can be obtained, so that a single scan can detect a wider range of flaws, and the number of scans can be reduced by a factor of 1 / compared to the conventional one detection coil. It can be reduced to 2 or less.

When a flaw detection operation is performed by the detection sensor according to the first aspect of the present invention, the detection sensor is connected to the object to be inspected (where the two detection coils are electrically conductive in the axial direction). (For example, a steel plate or the like) (arrangement step). In this case, the excitation coil is substantially parallel to the test object. Then, in this state, an alternating current is supplied to the exciting coil (supply step).

At this time, a part of the AC magnetic field leaking from both ends of the exciting coil flows through the device under test, whereby an eddy current is induced on the surface of the device under test. 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 exciting coil is installed substantially parallel to the surface of the device under test, if the device under test is not damaged,
The respective eddy currents generated by the alternating magnetic fields leaking from both ends of the exciting coil are also substantially equal.
The voltages and phases of the output signals of the detection coils are similar (see FIG. 11A).

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. 11).
(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 method of arranging the detection sensors in the above-described arranging step, the AC magnetic field leaking from both ends of the exciting coil spreads not only immediately below the detection sensor but also in front of and behind the detection sensor. Thus, it is possible to detect flaws in front of or behind the detection sensor, so that flaws in the corners of pillars and the like can be detected.

Here, in an experiment using a column-column model in which columns are connected, a graph of an output difference detected when one crack is present in the column and an installation state of a detection sensor in this experiment are shown. It is shown in FIG. In the figure, the horizontal axis is the distance (X coordinate) of the tip of the detection sensor when the crack is the origin,
The vertical axis shows the output difference between the two detection coils as the difference between the induced voltages of the coils. As shown in the figure, the differential output voltage shows a large value near the position of the crack.
It can be seen that the crack position can be detected with high accuracy by using the output difference of the detection coil as in the invention of (1).

Since the output difference reflects the position of the crack more sensitively than the absolute output of one detection coil, the inspection accuracy is higher than that of the conventional detection sensor. Further, since the presence or absence of a crack can be determined only by the output difference without comparing with a calibration curve, there is an advantage that a flaw detection operation can be performed without skill.

Further, in an experiment using a column-beam model in which a column and a beam are joined, a graph of a phase difference detected when a crack is present at a joint between a column and a beam and when there is no crack, and in this experiment, FIG. 2B shows the installation state of the detection sensor of FIG. 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 adjusts the phase difference between the output signals of the two detection coils to the same amplitude. It is expressed as an output voltage difference at the same point of the two output signals.

In such a column-beam model, the detection sensor cannot pass through the base of the column, and if the inspection is performed near the column, eddy currents are induced in the column. Signal 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, when there is no crack in the joint, the eddy current in the beam portion is advanced in phase with the eddy current in the column portion. On the other hand, when there is a crack in the joint portion, the eddy current in the beam portion is increased. Lags behind the eddy current of the column. 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 as in the invention of claim 6.

It is preferable that the output and the phase of the two detection coils be matched in advance using a normal test object without cracks.

Since the thickness of the refractory coating surrounding the test object varies depending on the fire resistance standard, the distance between the steel frame and the detection sensor (sensor height) may be large. Here, FIG. 3 shows the result of a simulation of how the vertical component of the magnetic field generated from the exciting coil changes depending on the sensor height (between 20 and 100 mm). As shown in the drawing, it can be seen that the vertical component that generates an eddy current on the test object moves the maximum peak point outward as the distance from the detection sensor increases. Therefore, in the invention of claim 3, the distance between the excitation coil and the detection coil is made variable, and the center of the detection coil is placed above the maximum peak point of the vertical component, that is, the point where the eddy current becomes strongest. It is possible to arrange according to the size. Thereby, the detection sensitivity can be improved.

Further, in the invention according to claim 7, the detection sensor is arranged at an arbitrary position on a guide plate of a non-conductive material fixed to the covering material by adjusting the height from the object to be inspected to be constant. Therefore, a constant sensor height can be obtained without smoothing the covering material. Therefore, high-precision inspection can be easily performed.

[0034]

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 of the present embodiment detects a magnetic change due to damage to a steel frame (steel plate) 35 covered with a refractory coating 34 and a detection sensor 14 for detecting the magnetic change. A signal processor 33 that outputs a phase difference output signal 30 and a differential output signal 31 by processing the signal.

Here, the detection sensor 14 includes an excitation coil 11 disposed at the center, a detection coil 12 and a detection coil 13 disposed at respective positions near both ends of the excitation coil.
Consists of These coils can be realized by winding an insulated wire around a long cylindrical object. The cross-sectional shape of the detection coil can be arbitrarily and suitably changed, and may be, for example, a square.

FIG. 5A is a side view showing the positional relationship between the coils constituting the detection sensor 14. As shown in FIG. 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 direction and the R direction are substantially orthogonal to the P direction and
The direction and the R direction are set to be substantially equal. The distance d ₁ from one end of the exciting coil 11 to the center axis of the detection coil 12 and the distance from the other end to the detection coil 1
The distance d ₂ to the center axis of No. ₃ is set to be substantially equal.

Further, the detection sensor 1 according to the present embodiment
Reference numeral 4 has an adjustment function that allows the distance d ₁ and the distance d ₂ to be arbitrarily changed within a predetermined range. FIG. 5 shows an example of the detection sensor 14 provided with a means for realizing this adjustment function.
(B). The detection sensor 14 shown in FIG. 1 is configured such that each of the slide plates can be slid in a direction substantially coincident with the axial direction of the exciting coil 11 and a slide plate to which the detection coils 12 and 13 are fixed, and a central portion thereof. And a slide support to which the exciting coil 11 is fixed.

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 sensors 12 and 13 while watching the scale, and tightens the stopper when a certain scale value is reached, so that the distances d ₁ and d ₂ can be set freely. The distances d ₁ and d ₂ may be finely adjusted by using a screw or a helicoid.

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

Here, the AC signal generating section 23 includes an oscillation circuit 22 for generating an AC signal of 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 as a 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 enhance the detection accuracy, the latter case where 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 inspection system is constructed by connecting a data display / analysis device to the output terminal 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.

Next, an example of sensor installation when an inspection of a damage situation is performed using the magnetic flaw detector of this embodiment is shown in FIG.
Shown in Here, as shown in FIG. 5C, a detection sensor 14 in which the exciting coil 11 is formed of an I-type coil is used. In FIG. 6, the numbers are in units of mm, and indicate the dimensions of the designated portions.
The cross-sectional shape of the I-shaped coil 11 may be either circular or square.

As shown in FIG. 6, first, a guide plate 17 is installed on a fire-resistant coating covering columns or beams of an object to be inspected, and a detection sensor 14 is arranged on the guide plate 17. That is, the detection sensor 14 scans the guide plate 17 along the detection direction 15. Further, the guide plate 17 is provided with a shallow groove used for positioning the detection sensor 14, and a position scale is also displayed along the groove (not shown).

The groove of the guide plate 17 is aligned with the inspection direction 15, the detection sensor 14 is scanned along this groove, and the position of the detection sensor 14 is read by the position scale to reproduce an accurate position. Can be further enhanced. The guide plate 17 is preferably made of a plastic product such as a non-conductive acrylic resin.

Next, the flow of the magnetic inspection method when the damage state of the inspection object is inspected using the detection sensor 14 arranged as shown in FIG. 6 will be described with reference to the flowchart of FIG.

As shown in the flowchart of FIG. 10, first, before starting the inspection, the output adjustment, the phase adjustment and the interval adjustment of the detection coils 12 and 13 are performed (step 20).
0). At the time of this adjustment, the detection sensor 14 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.

In the interval adjustment, the detection coil 12 is positioned at the peak position of the vertical magnetic field (see FIG. 3) determined according to the height of the detection sensor 14 from the steel plate to be inspected.
13 so that the center shaft portion of the thirteen is located at d ₁ and d ₂ (FIG.
(See (a) and (b)).

Next, the detection sensor 14 is arranged to the start position X _s of the top of the refractory coating (step 202). Here, as shown in FIG. 6, the joint between the column and the beam is defined as the origin, and the distance from the origin to the tip of the detection sensor 14 along the longitudinal direction (inspection direction 15) of the beam steel plate is defined as X. That is, in step 202, the X ← X _s. In addition,
Direction of detection sensor 14 (axial direction of excitation coil 11)
Are made to substantially coincide with the inspection direction 15.

Then, an alternating current is supplied from the alternating signal generator 23 to the exciting coil 11 (step 204). As a result, an AC magnetic field is generated in the exciting coil 11, and the excitation coil 11 shown in FIG.
As shown in FIG. 1 (a), the magnetic field 4
A part of 1 and 42 flows through the steel plate 35, thereby generating eddy currents 43 and 44 in the steel plate 35. The eddy currents 43 and 44 generate demagnetizing fields 45 and 46.
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. 11A shows a magnetic field when a position where there is no damage is inspected.
4, the demagnetizing fields 45 and 46 are also equal, indicating that the output signals of the respective detection coils have the same phase and the same output amplitude. However, since the magnetic field shown in FIG. 11A is an alternating magnetic field, the directions of the arrows indicating the magnetic field directions are alternately switched (the same applies to FIG. 11B described later).

The magnetic fields 41 and 42 leaking from both ends of the excitation 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.

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 flow chart of FIG. 10, a display / recording device (see FIG. 4) connected downstream of the signal processor 33 moves the detection sensor 14 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, the current position of the detection sensor 14
X is the inspection end position X_eJudge whether it matches
(Step 210). In addition, in the case of FIG.
X _eIndicates that the tip of the detection coil 12 is a joint between the column and the beam.
Of the detection sensor 14 when it reaches the corner of the covering material that covers
Corresponding to the position.

[0064] If the position X of the current time point is not the inspection end position X _e (step 210 negative decision), to move the detecting sensor 14 to the predetermined distance ΔX by checking direction 15. As a result, the position X of the detection sensor 14 becomes 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. 11B, when the detection sensor 14 approaches the damaged portion 80, the resistance value of the crack portion increases, so that the eddy current generated by the magnetic field 41 becomes: The current value is smaller than in the case where there is no crack. Also, with the approach of the detection sensor 14, the eddy current changes from 43a to 43b at the boundary of the damaged portion 80, and the demagnetizing fields 45 and 46 generated by the eddy current 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.

[0067] Therefore, as shown in the flow chart of FIG. 10, 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 the position where the detection sensor 14 is close to the joint between the column and the beam, 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), and As a result, the voltage induced in the detection coil close to the column due to the eddy current generated changes, and the differential output signal changes regardless of the presence or absence of a crack in the joint. However, 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 in the joint depending on the differential output signal. As already described with reference to FIG. 2, the crack at the joint between the column and the beam (the damaged portion 8 in FIG. 6).
An experimental result has been obtained that the output pattern of the phase difference output signal is inverted depending on the presence or absence of 2).

Therefore, as shown in the flowchart of FIG. 10, the presence or absence of a crack in the joint between the column and the beam is determined based on the phase difference output signal P (X) (step 216), and the inspection is terminated. In the detection of the damage position in steps 214 and 216, the operator looks at the waveform recorded by the XY recorder 50 or the like, and checks whether the change pattern of the waveform and the absolute value of the recording signal have exceeded the reference value. Alternatively, the damaged position is determined based on the signal output 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 conventional technique with one detection coil, and a 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, FIGS. 12 (a) to 12 (f) show actual measurement examples of the magnetic flaw detector according to the present embodiment, and show that cracks can be detected with high accuracy in the above steps 214 and 216.

FIG. 12 (a) shows the result of scanning the detection sensor at a height of 50 mm from above a partially cracked steel frame.
FIG. 12B is a graph showing the output fluctuation of each of the two detection coils, and FIG. 12B shows a differential output signal obtained by inputting the outputs of the two detection coils to the differential amplifier 29 under the same conditions. It is a graph of. In FIG. 12A, the vertical axis is enlarged, so that it can be seen that there is a slight change. However, it can be seen that the change is noticeably captured by performing the differential processing.

FIG. 12C shows a sensor height of 50 mm.
FIG. 12D shows a change in the differential output voltage with respect to the sensor position when scanning is performed on the steel frame completely broken at one position.
Is the change in the differential output voltage when the sensor height is 100 mm under the same conditions. The horizontal axis represents the distance from the crack position to the tip of the detection sensor 14 in mm.

In FIGS. 12C and 12D, there are two peaks in the differential output voltage because the differential output voltage peaks when the two detection coils pass through the cracks. The distance between the two peaks is equal to the distance between the shafts of the detection coils 12 and 13. FIG.
From FIG. 2C, it can be seen that at a sensor height of 50 mm, the position of the tip of one of the detection coils when the differential output voltage exceeds the reference value of 1.1 V can be determined as a crack position. Of course, this reference value is changed according to the sensor height. Even in the case of FIG. 12D in which the distance between the test object and the sensor is large, although the absolute value of the voltage is small, the voltage change pattern is the same as that of FIG. 12C. It can be seen that accurate detection is possible.

In the determination of the crack position, not only whether the reference value has been exceeded but also the change pattern of the differential output voltage is taken into account, so that a highly accurate determination can be made.

FIG. 12E shows a change in the differential output voltage with respect to the sensor position when there is a crack near the boundary between the column and the beam and when there is no crack. Regardless of the presence or absence of cracks,
As it approaches the junction, the differential output voltage increases. 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. 12 (f) shows the change in the phase difference output voltage with respect to the sensor position when there is a crack near the boundary between the column and the beam, and the change in the phase difference output. The output pattern is reversed depending on the presence or absence of a crack in the joint, though it is a small difference. 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 voltage.

As described above, in this embodiment, it is possible to detect the position of a crack and the like with high accuracy.
Comparing (c) with FIG. 12 (d), the differential output signal differs depending on the sensor height, so that in order to maintain accuracy, the sensor height must be kept constant during inspection. Recognize.

A method of attaching a guide plate for keeping the height of the sensor constant will be described with reference to FIGS.

FIG. 7 shows an example in which a guide plate is attached to a so-called box column having a rectangular cross section. In the figure, 62 is a guide plate, 60 is a guide plate 6
2 is a mounting plate for mounting the mounting plate 2 on the box pillar, 64 is a hexagonal bolt for joining the guide plate 62 and the mounting plate 60,
66 is a round bar for height adjustment.

The procedure for mounting the guide plate on the box column is as follows. First, the position of the guide plate is determined, and then the steel frame of the box column (the center of the box column or the nearest Adjust the height from the steel surface to the guide plate accurately. At this time, the height of the guide plate is adjusted to be exactly the same from the start end to the end.

Next, as a procedure, the position of the mounting plate 60 is determined according to the height-adjusted guide plate 62, and the mounting plate 60 is connected to the guide plate using a height adjusting round bar.
Is adjusted, and the mounting plate and the guide plate are fixed with the hexagon bolts 64. By firmly fixing the guide plate whose height has been accurately adjusted in this way to the box column, the guide plate does not move even during the execution of the magnetic flaw detection method. Height is kept constant, and high-precision inspection becomes possible.

FIG. 8 shows an example in which two guide plates are attached to a so-called H-shaped beam having an H-shaped cross section. In this case, by scanning the detection sensor 14 over the two guide plates, the flaw detection state of the two inspection surfaces of the H class can be inspected.

In the figure, 70 is a first guide plate, 7
2 is an acrylic plate as a second guide plate, 61 is a mounting plate for mounting the first guide plate 70 and the second guide plate 72, 68 is a hexagon bolt for positioning the mounting plate 61, and the other is It is the same as FIG.

The method of attaching the first and second guide plates to the beam of the H rope is as follows. First, the position of the second guide plate 72 is determined, and then the round bar 66 for height adjustment is used. The height from the steel frame of the H class to the second guide plate 72 is accurately adjusted. At this time, the height of the guide plate is adjusted to be exactly the same from the start end to the end.

Next, as a procedure, the position of the mounting plate 61 is determined according to the height-adjusted guide plate 72, and the mounting plate 60 is connected to the guide plate using a height adjusting round bar.
Is adjusted, the mounting plate and the guide plate are fixed with a hexagonal bolt 64, and fixed to the H class with a hexagonal bolt 68 for positioning.

Next, as a procedure, after the position of the first guide plate 70 is determined in accordance with the mounting plate 61, the first guide plate 70 is removed from the steel frame of the H class using the round bar 66 for height adjustment.
Adjust the height precisely. And hexagon bolt 64
Thus, the first guide plate 70 is fixed to the mounting plate 61.

By firmly fixing the first and second guide plates, the heights of which have been accurately adjusted, to the H class, each guide plate can be moved even during the execution of the magnetic flaw detection method. Therefore, the height of the detection sensor 14 from the object to be inspected from the class H is kept constant, and high-precision inspection can be easily performed.

Further, FIG. 9 shows a state in which a scanning jig (guide plate and its support) is attached to the upper surface of the lower flange (numbers are in units of mm). In the figure, 90 is a web surface plate which functions as a support for the guide plate, 91
Is a scanning plane plate that functions as a guide plate.

The procedure for mounting the scanning jig is as follows. First, the web surface plate 90 is mounted so as to be substantially parallel to the web surface while sliding on the refractory coating of the flange. Attached so as to be substantially parallel to the flange along with 90. Magnetic flaw detection is performed by scanning the detection sensor 14 on the scanning surface plate 91 with the scanning jig attached in this manner.

It can be seen that the use of such a scanning jig can easily cope with a change in the flange width. However, the web surface plate is for creating a surface (referred to as a reference surface) parallel to the web surface, and need not necessarily be parallel to the axial direction of the web. 7 to 9 use a non-conductive material that does not affect the AC magnetic field, for example, a plastic material such as an acrylic resin. Further, the scanning jigs of FIGS. 7 to 9 can cope with a slight improvement even if the attached member has a special shape.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above example. For example, as the exciting coil 11, in the above embodiment, FIG.
Although an I-shaped coil as shown in (1) is used, other types of coils such as a U-shaped coil may be used.

Further, in the above-described embodiment, the case where the inspection direction 15 in FIG. 6 substantially coincides with the longitudinal direction of the steel frame has been described as an example. However, the present invention is not limited to this. The direction, for example, the width direction of the steel frame, may be selected as the inspection direction.

[0094]

As described above, according to the first aspect of the present invention, the detection sensor used for magnetic flaw detection is constituted by the excitation coil and the two detection coils substantially orthogonal to the axial direction of the coil. This eliminates the need for preparing a calibration curve using a crack-free test object in advance as in the related art, thereby providing an effect that a flaw detection operation can be easily performed. Also, by using two detection coils, a larger output can be obtained than in the case of one detection coil, which enables more accurate flaw detection, and the output changes even if there is damage on either of the detection coils. Is obtained, a wider range can be detected by one scan, and the number of scans can be reduced to half or less as compared with the conventional case of one detection coil.

Further, according to the invention of claim 2, since at least one of the output difference and the phase difference between the output signals induced in the two detection coils is detected, the coating material can be easily removed without peeling. In addition, the effect that the damage state can be inspected accurately can be obtained.

Further, according to the third aspect of the present invention, since the interval between the exciting coil and the detecting coil can be changed, the detection is performed at the maximum peak point of the vertical component, that is, at the point where the eddy current becomes strongest. The center of the coil can be arranged according to the sensor height, and the effect of improving the detection sensitivity can be obtained.

According to the fourth aspect of the present invention, at least one of the output difference and the phase difference between the output signals induced in the two detection coils is detected, and based on the detected value, the object to be inspected is detected. Since the damage status is inspected, an effect is obtained that the damage status can be easily and accurately inspected without peeling the covering material.

Further, according to the fourth aspect of the present invention, a detection sensor having two detection coils that are substantially perpendicular to the axial direction of the exciting coil can be used. The AC magnetic field leaking from both ends of the exciting coil spreads not only directly below the detection sensor but also in front of and behind the detection sensor because it is arranged so as to be substantially vertical, and thus damage located in front of or behind the detection sensor. Flaw detection becomes possible.

Further, according to the fifth aspect of the present invention, based on the output difference between the output signals of the two detection coils, damage is caused in the vicinity of the position of the inspection object corresponding to the position where the detection sensor is disposed. Since it is determined whether or not there is, the effect of being able to detect the damaged position with high accuracy is obtained.

Further, according to the invention of claim 6, when another member running in a direction different from the object to be inspected is joined to the object to be inspected, based on the phase difference detected in the vicinity of the joint. Since it is determined whether the joint is damaged or not, even if the detection sensor cannot be arranged over the joint, it is relatively easy to determine whether the joint has a crack. Is obtained.

According to the seventh aspect of the present invention, the detection sensor is arranged at an arbitrary position on the non-conductive guide plate fixed to the covering material with the height from the object to be inspected being fixed. As a result, the height of the sensor is kept constant without smoothing the covering material, so that an effect of easily performing high-precision inspection can be obtained.

[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.

FIG. 2 is a diagram for explaining the principle of the present invention,
(A) is a sensor arrangement diagram and a graph of a differential output voltage with respect to a position of a sensor tip when a flaw detection state is inspected by a column-column model, and (b) is a joint between a column and a beam in a column-beam model. 3A and 3B are a sensor arrangement diagram in the case of inspecting for the presence or absence of a crack in a portion, and a graph for each presence or absence of a crack in the phase difference output with respect to the position of the sensor tip.

FIG. 3 is a vertical magnetic field distribution for each sensor height of a magnetic field generated by an eddy current generated in a steel plate when an alternating current is applied to an exciting coil.

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

5A and 5B are schematic diagrams of a detection sensor according to an embodiment of the present invention, in which FIG. 5A shows a positional relationship between an excitation coil and a detection coil, and FIG. 5B shows a distance between the excitation coil and the detection coil. (C) is an external view when an I-shaped coil is used as an exciting coil.

FIG. 6 is a schematic installation diagram of a detection sensor and an inspection object when inspecting the inspection state of the inspection object by the magnetic inspection method according to the embodiment of the present invention.

FIG. 7 is a diagram showing a state diagram when an acrylic plate functioning as a guide plate of a detection sensor is attached to a box column during an inspection of a flaw detection state, and a diagram showing a procedure for attaching the acrylic plate.

FIG. 8 is a diagram showing a state diagram when an acrylic plate functioning as a guide plate of a detection sensor is attached to a beam of an H-line at the time of inspection of a flaw detection state, and a diagram showing a procedure for attaching the acrylic plate.

FIG. 9 is a diagram showing a state in which a scanning jig is attached to a lower flange upper surface.

FIG. 10 is a flowchart showing a flow of a magnetic flaw detection method according to the embodiment of the present invention.

FIG. 11 is a diagram showing distributions of a magnetic field generated when an alternating current is applied to the exciting coil, an eddy current generated in the steel sheet, 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. 12 is a graph showing a change in a signal output from the signal processor according to the embodiment of the present invention with respect to a distance from a crack to a tip of a detection sensor, where (a) shows a partially fractured specimen. (B) is a differential output voltage when a partially fractured specimen is used, and (c) is a differential output voltage at a sensor height of 50 mm when a fully fractured specimen is used. , (D) is the differential output voltage at a sensor height of 100 mm when using a fully fractured specimen, (e) is the differential output voltage when the column-beam joint has a crack, and (f) is the column. -Shows a graph of the change in phase difference output voltage when there is a crack in the beam joint.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Excitation coil 12 Detection coil 13 Detection coil 14 Detection sensor 21 Constant current circuit 22 Oscillation circuit 23 AC signal generation part 24 Amplifier 25 Amplifier 26 Phase adjuster 27 Phase adjuster 28 Phase detector 29 Differential amplifier 30 Phase difference output signal 31 Differential output signal 32 Detection signal processing unit 33 Signal processor 50 XY recorder 52 Oscilloscope 54 Computer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Sato 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside the Technical Research Institute, Takenaka Corporation (72) Inventor Akira Umekuni 1-5-5 Otsuka, Inzai City, Chiba Prefecture 1 Inside Takenaka Corporation Technical Research Institute (72) Inventor Keita Yamazaki 1-5-5 Otsuka, Inzai City, Chiba Prefecture 1 Inside Takenaka Corporation Technical Research Institute (72) Inventor Masao Kibuchi Takatsuka, Nishi-ku, Kobe City, Hyogo Prefecture 1-5-5 Inside Kobe Steel, Ltd. (72) Inventor Naoyuki Sato 6-7-1, Koriyama, Taishiro-ku, Sendai City, Miyagi Prefecture Inside (72) Inventor, Sadaaki Abe 6, Koriyama 6, Taishiro-ku, Sendai City, Miyagi Prefecture -7-1 Tokin Co., Ltd. (72) Norimitsu Hoshi Inventor 6-7-1 Koriyama, Taishiro-ku, Sendai, Miyagi Prefecture Tokin Co., Ltd. (72) Susumu Kanazawa 6-7-1, Koriyama, Taihaku-ku, Sendai-shi, Miyagi Pref.

Claims (7)

[Claims] An excitation coil to which an alternating current can be applied, and an excitation coil disposed in each of positions near both ends of the excitation coil so as to be substantially in the same direction as an axial direction substantially orthogonal to an axial direction of the excitation coil. A magnetic flaw detector including a detection sensor comprising: two detection coils; 2. The method according to claim 1, wherein the detecting sensors are arranged such that an axial direction of the two detecting coils is substantially perpendicular to a conductive test object. The magnetic flaw detector according to claim 1, further comprising: a detection unit configured to detect at least one of an output difference and a phase difference between output signals induced in the detection coils. 3. The magnetic flaw detector according to claim 1, wherein the distance from the end of the excitation coil to the two detection coils can be arbitrarily changed. 4. An exciting coil to which an alternating current can be applied, and fixed to each position near both ends of the exciting coil in substantially equal directions so as to be axial directions substantially orthogonal to the axial direction of the exciting coil. A magnetic flaw detection method for inspecting the damage state of a conductive test object using a detection sensor composed of two detection coils, wherein the detection sensor is disposed in an axial direction of the two detection coils. An arranging step of arranging the excitation coil at an arbitrary position around the inspection object so as to be substantially perpendicular to the inspection object; a supplying step of supplying an alternating current to the excitation coil; and an output induced by the two detection coils. A detection step of detecting at least one of an output difference and a phase difference between signals; and an inspection step of inspecting a damage state of the inspection object based on at least one of the detected output difference and the phase difference. Consisting of Magnetic flaw detection method characterized. 5. In the inspection step, it is determined based on an output difference detected in the detection step whether or not there is damage near a position of the inspection object corresponding to a position where the detection sensor is disposed. The magnetic flaw detection method according to claim 4, wherein: 6. In the inspection step, when another member running in a direction different from the object to be inspected is joined to the object to be inspected, a position detected in the vicinity of a joint between the object to be inspected and the member. 5. The magnetic flaw detection method according to claim 4, wherein it is determined whether or not the joint is damaged based on the phase difference. 7. In the arranging step, the heights of the two detection coils are set at an arbitrary position on a non-conductive guide plate fixed to a covering material by adjusting a height from an object to be inspected to be constant. 7. The magnetic flaw detection method according to claim 4, wherein the detection sensor is arranged so that a direction is substantially perpendicular to the guide plate.