JP2007333630A - Eddy current flaw detecting method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve inspection accuracy in a deep part of an inspection body by an eddy current flaw detecting device and an eddy current flaw detecting method of the inspection body having a probe with a simple structure. <P>SOLUTION: The eddy current flaw detecting device includes the probe having a pair of exciting coils arranged so that center axes are arranged on a same straight line and coil winding directions are same and the center axes and the inspection body surface are parallel, and an inspection coil arranged in the center of the pair of the exciting coils and arranged so that a center axis is vertical to the inspection body surface; a storage part storing a suitable AC frequency and a lift-off amount in accordance with the inspection target depth inside the inspection body; and a parameter value controlling means for making an AC frequency and a lift-off amount set by a parameter value setting mechanism to be the AC frequency and the lift-off amount. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  Forming a magnetic field that changes over time on an object to be inspected using a probe having an excitation coil for generating an eddy current in the object to be inspected and an inspection coil for measuring a change in the eddy current The present invention relates to an eddy current flaw detection apparatus for inspecting a body and an eddy current flaw detection method which is a flaw detection method used by the apparatus.

In structures such as nuclear power plants and aircraft, there is a demand for non-destructive inspection based on defect tolerance standards or damage tolerance design, and high defect detection capability and defect shape evaluation are required.
An eddy current flaw detection method and an eddy current flaw detection device, which is one of non-destructive inspections, generate a fluctuating magnetic field on the surface of an object to be inspected by bringing an excitation coil to which an AC voltage is applied closer to the object to be inspected. By detecting the eddy current generated in response to the inspection coil with an inspection coil, the apparatus inspects non-destructively for damage such as scratches and cracks near the surface of the object to be inspected.

The eddy current is characterized in that it decreases exponentially as the inspection object depth increases. Therefore, in Patent Document 1, four excitation coils are arranged in the probe so that the coil axis is parallel to the surface of the object to be inspected and the coil surfaces are opposed to each other, so that the eddy current is small on the surface of the object to be inspected. An eddy current flaw detector has been devised that creates an approximately maximum distribution inside and can inspect the inside of the inspection object.
The eddy current flaw detector is a rectangle whose side length D is 30 mm per side as shown in the detailed description of Patent Document 1 and FIG. 1 described in Patent Document 1 (corresponding to FIG. 10 of the present specification). The excitation coil 51 is provided with four, an interval L1 between the two inner excitation coils 51a and 51b forming a pair is 50 mm, an interval L2 between the two outer excitation coils 51c and 51d forming a pair is 70 mm, and a circular shape. The diameter d of the inspection coil 52 is 3 mm, and the AC frequency of the current flowing through the coil is 10 kHz. The lift-off amount of the probe 18 composed of the excitation coil 51 and the inspection coil 52 is 0 mm. This Patent Document 1 exemplifies a case where stainless steel (SUS316L) is inspected as an object to be inspected.

JP 2006-010665 A

In order to verify the technique disclosed in Patent Document 1, the inventors create an analytical numerical model of the eddy current flaw detector, and the eddy current intensity that can be generated at the inspection target depth (mm) and the depth. The relationship (A / m ² ) was examined. In this numerical analysis model, the lift-off amount and the AC frequency of the current flowing through the exciting coil can be variably set, and the material of the object to be inspected can be changed between stainless steel (SUS316L) and steel. The element division state of the numerical analysis model is shown in FIG. FIG. 9 shows a quadrant on the far right side of the analysis model.
The configuration of this analysis model follows the configuration of the probe described in Patent Document 1 described above, the central axis is arranged on the same straight line, the coil winding direction is the same, and the central axis and the surface of the object to be inspected. The inspection is provided with two sets of a pair of exciting coils arranged in parallel to each other in the axial direction, arranged in the center of the pair of exciting coils, and arranged so that the central axis is perpendicular to the surface of the object to be inspected. It becomes the structure provided with the coil.
Hereinafter, when viewed in the axial direction of the excitation coil, the inner excitation coil positioned on the inspection coil side is referred to as a coil A, and the outer excitation coil is referred to as a coil B.
Further, as shown below, the results obtained using this numerical analysis model are shown in FIG. 5, FIG. 6, FIG. 7, and FIG. 5 and 6 show the results according to the present invention, and FIGS. 7 and 8 show the results for explaining the problems of the prior art. In these figures, the horizontal axis indicates the inspection target depth (mm), and the vertical axis indicates the eddy current intensity (A / m ² ) that can be generated at that depth. Furthermore, the depth at which the intensity is 1/3 of the eddy current generated on the surface of the object to be inspected is shown below the horizontal axis as the detection limit. Furthermore, the material (either stainless steel or steel), AC frequency (either 10 Hz or 10 kHz), and lift-off amount (either 0 mm or 50 mm) of the object to be inspected are shown on the right side of each figure.
7 and 8 show the eddy current intensity caused by the magnetic field generated by using the coil A and the coil B separately, and the eddy current intensity caused by the combined magnetic field generated by using the coil A and the coil B simultaneously (see FIG. 7 shows-□-and FIG. 8 shows-●-), but in other drawings, only the result of the coil A is shown. Note that “(1.75)” in the description of the composite magnetic field graph in FIG. 7 is the amplitude adjustment value of the coil B, and “(1.44 + 0.226j)” in the description of the composite magnetic field graph in FIG. "Is a value obtained by displaying the amplitude adjustment value and the phase adjustment value of the coil B in complex numbers.

  The eddy current intensity due to the combined magnetic field shown in FIGS. 7 and 8, which is the result of the prior art, is slightly relaxed because the slope of the graph is gentle. The absolute value of the eddy current intensity is weaker than when used individually. Here, the detection limit is an eddy current intensity that is 1/3 of the eddy current intensity on the surface of the object to be inspected.

  Further, as shown in FIG. 7, in the prior art, even if the object to be inspected is stainless steel (SUS316L), the surface of the object to be inspected can be obtained only by adjusting the magnitude of the reverse energization current in the coils A and B. The intensity of eddy current increased and the depth of 5 mm was the limit of detection of scratches. Moreover, as a method for solving such a problem, it is conceivable to adjust the energization currents of the coil A and the coil B in consideration of the phase. However, since it is easily affected by variations in materials and the like, there is almost no practicality. It was.

  When the above-described conventional technology is applied to a steel plate inspection object with more severe eddy current penetration, even if the energization currents of the inner coil and the outer coil are adjusted in consideration of the phase, as shown in FIG. The detection limit is less than 1 mm in depth, and there is a problem that sufficient inspection accuracy cannot be secured at a deep position from the surface of the object to be inspected.

  In addition, the technique disclosed in Patent Document 1 has a problem that the configuration is relatively complicated because a large number of coils are incorporated in the probe.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain an eddy current flaw detector capable of inspecting an object to be inspected using a probe having a simple structure. Even in a magnetic inspection object in which an eddy current flaw detection method used is relatively difficult to detect an eddy current, the inspection accuracy of defects at a relatively deep position from the surface of the inspection object is improved.

According to the present invention for achieving the above object, a magnetic field that changes with time is formed on an object to be inspected, and an excitation coil that generates an eddy current in the object to be inspected and a change in the eddy current are measured. A first characteristic configuration of an eddy current flaw detector for an inspection object provided with a probe including an inspection coil so as to be movable along the surface of the inspection object is arranged on the same straight line with the same coil winding direction. The pair of exciting coils arranged so that the central axis and the surface of the object to be inspected are parallel to each other, and arranged in the center of the pair of exciting coils, and the central axis is perpendicular to the surface of the object to be inspected. A probe having the inspection coil arranged, and a parameter value setting mechanism for setting an AC frequency in the energizing current of the exciting coil and a lift-off amount that is a distance from the surface of the object to be inspected. Along with the
A storage unit that stores the appropriate AC frequency and the lift-off amount according to the inspection target depth inside the object to be inspected,
Parameter value control means for causing the AC frequency and the lift-off amount set by the parameter value setting mechanism to be the appropriate AC frequency and the lift-off amount according to the inspection target depth inside the object to be inspected. It is in.

The first characteristic configuration is effective when a target inspection target depth is determined or when a detailed inspection is required at a specific location.
According to the first characteristic configuration, for example, using the inspection target depth as key information, the data table having a relationship between the inspection target depth held by the storage unit and the lift-off amount that can secure the eddy current intensity at the inspection target depth is searched. By doing so, it is possible to obtain a lift-off amount at which the eddy current intensity at the inspection target depth is appropriate. Similarly, the inspection target depth is searched by searching the data table representing the relationship between the inspection target depth held by the storage unit and the AC frequency at which the eddy current intensity can be secured at the inspection target depth, using the inspection depth as key information. An AC frequency at which the eddy current intensity at is appropriate can be obtained.

  Here, the reason why it is preferable to hold the data table as described above is that the lift-off amount has a certain amount of lift-off amount as the depth becomes deeper when the inspection depth is a problem in the eddy current test. According to the new knowledge that it is better to perform the inspection. Further, the AC frequency is based on the result that the higher the frequency, the eddy current formed stays near the surface, and when it is desired to inspect a deep position as a depth, it is preferable to use the lower frequency side. Therefore, when the inspection target depth in the object to be inspected is specified, the AC frequency and the lift-off amount suitable for the depth are read from the data table, and the inspection can be performed satisfactorily by performing the inspection according to these parameters.

  Furthermore, since the lift-off amount and AC frequency are determined based on the data accumulated in advance in the data table, the time for determining the lift-off amount and AC frequency can be shortened, and the inspection is performed when the target inspection depth is determined. Can be made more efficient. In addition, since the inspection is performed with the setting that can secure the eddy current intensity at the inspection target depth by adjusting the lift-off amount and the AC frequency, the eddy current is detected with high sensitivity even at the inspection target depth that could not be inspected so far. And inspection accuracy can be increased.

This eddy current flaw detector includes an exciting coil that forms a magnetic field that changes over time on an object to be inspected, and generates an eddy current in the object to be inspected, and an inspection coil that measures changes in the eddy current. In moving the probe with respect to the object to be inspected and inspecting the object to be inspected,
A pair of exciting coils having a central axis arranged on the same straight line, the coil winding direction being the same, and the central axis being parallel to the surface of the object to be inspected;
Using the probe comprising the inspection coil disposed at the center of the pair of excitation coils and having a central axis perpendicular to the surface of the object to be inspected;
The AC frequency in the energization current of the exciting coil and the lift-off amount, which is the distance from the surface of the object to be inspected, are set according to the inspection object depth inside the object to be inspected. Will be inspected.

A probe according to the present invention, comprising: an excitation coil that forms a magnetic field that changes over time on an object to be inspected, and generates an eddy current in the object to be inspected; and an inspection coil that measures a change in the eddy current The second characteristic configuration of the eddy current flaw detector for an inspection object that is movable along the surface of the inspection object is such that the central axis is arranged on the same straight line, the coil winding direction is the same, and the central axis is inspected A pair of exciting coils arranged so as to be parallel to the body surface;
A probe having the inspection coil disposed at the center of the pair of excitation coils and disposed so that a central axis is perpendicular to the surface of the object to be inspected;
With a parameter value setting mechanism for setting an AC frequency in the energization current of the excitation coil and a lift-off amount that is a distance from the surface of the inspection object of the probe,
Inspection control means for setting two different at least one of the AC frequency and the lift-off amount set by the parameter value setting mechanism;
In two different parameter values, there is provided a flaw position determining means for determining whether a flaw exists on the front or back of the inspection object from the value of the inspection signal obtained from the inspection coil.

The second characteristic configuration is effective when the inspection depth is not determined or when it is determined on the front or back side of the scratch.
The probe used in this apparatus is a simple one having a pair of exciting coils identical to that used in the first characteristic configuration.
By the way, according to the second feature configuration, since the inspection is executed by setting at least one of the AC frequency and the lift-off amount so that the inspection target depth inside the inspection object is different, for example, the shallow inspection target depth is set. If the eddy current intensity measured by setting the corresponding lift-off amount is strong, it is determined that the scratch exists at a shallow position (surface side).

  On the other hand, the ratio of the eddy current intensity obtained in each setting can determine whether the flaw exists on the front or back of the object to be inspected. A specific determination method will be described in the second embodiment in the best mode for carrying out the invention.

In this eddy current flaw detector,
A probe including an excitation coil that forms a magnetic field that changes over time on an object to be inspected and generates an eddy current in the object to be inspected, and an inspection coil that measures a change in the eddy current. And inspecting the object to be inspected,
A pair of exciting coils having a central axis arranged on the same straight line, the coil winding direction being the same, and the central axis being parallel to the surface of the object to be inspected;
Using the probe comprising the inspection coil disposed at the center of the pair of excitation coils and having a central axis perpendicular to the surface of the object to be inspected;
An inspection obtained by performing inspection by setting two different AC frequencies in the energizing current of the exciting coil and at least one lift-off amount that is a distance from the surface of the object to be inspected, and obtaining from the inspection coil The inside of the inspection object is inspected based on the value of the signal by determining which of the front and back surfaces of the inspection object is flawed.

  According to a third characteristic configuration of the eddy current flaw detection apparatus for an object to be inspected according to the present invention, in addition to the first or second characteristic configuration, the lift-off amount is set within twice the coil diameter of the excitation coil. There is in point. In other words, the present invention has been completed by finding that it is preferable to perform flaw detection with the lift-off amount set within an appropriate range in relation to the coil diameter of the exciting coil.

The inventors have earnestly researched and found that a strong inspection signal can be obtained by keeping the lift-off amount within the above range.
According to the third characteristic configuration described above, in the apparatus having the first characteristic configuration described above, the appropriate lift-off amount stored in the storage unit is set to be within twice the coil diameter of the exciting coil, whereby the specific coil When conducting eddy current flaw detection using an excitation coil with a diameter, the depth that can be flawed with this probe is deeper than the range previously possible by generating a strong eddy current by appropriately setting the lift-off amount. It is possible to detect the scratch at the position with high sensitivity.
According to the third feature configuration, in the apparatus having the second feature configuration described above, the lift-off amount control means is 2 because the lift-off amount is limited to an appropriate range for detecting the eddy current. In determining the set lift-off amount, it is possible to eliminate the possibility of selecting a lift-off amount in which an invalid eddy current is detected, and to shorten the inspection time.

[First Embodiment]
A first embodiment having the first characteristic configuration of the present invention will be described with reference to FIGS. 1, 2, 5, and 6.
The eddy current flaw detector according to the present embodiment includes a pair of exciting coils 51 arranged such that the central axes are arranged on the same straight line, the coil winding direction is the same, and the central axis and the surface 10a to be inspected are parallel. A probe 18 having an inspection coil 52 disposed at the center of the pair of excitation coils 51 and having a central axis perpendicular to the surface 10a of the object to be inspected. By controlling the probe 18 in a direction perpendicular to the surface 10a to be inspected by a stage controller 17 and a Z fine movement stage 16, the distance between the inspected body 10 and the inspection coil 52 is an appropriate lift-off amount (illustrated as LO). It functions in the form. In this structure, the probe 18 is disposed and used so that the inspection coil 52 is closest to the surface 10a to be inspected. Furthermore, the multi-function synthesizer 11 appropriately measures the eddy current of the device under test 10 while passing the alternating current through the exciting coil 51 so that the current directions of the exciting coil 51a and the exciting coil 51b are the same. It functions as an AC frequency setting mechanism in the form of controlling to possible AC frequency.
In the present invention, the lift-off amount setting mechanism and the AC frequency setting mechanism function as a parameter value setting mechanism.

  Further, the control computer 14 has a storage unit 22 having a data table 26 for holding an appropriate AC frequency corresponding to the inspection target depth, as well as a data table 23 for holding an appropriate lift-off amount corresponding to the inspection target depth, and the storage unit 22. Parameter value control means 24 for determining an appropriate lift-off amount and an appropriate AC frequency. The parameter value control means 24 searches the data table 23 and the data table 26 using the inspection depth as a key, determines an appropriate lift-off amount and an appropriate AC frequency, and sends them to the parameter value setting mechanism.

  The control computer 14 also includes excitation coil control means 21 that controls the multi-function synthesizer 11 so that an appropriate AC current flows through the excitation coil 51, and a lock-in amplifier 12 that converts the AC voltage detected by the inspection coil 52 into a DC voltage. And an inspection signal acquisition means 25 for analyzing the direct current voltage.

  Next, the detailed flaw detection method in the first embodiment will be described based on the flow shown in FIG. First, the inspection target depth is input to the control computer 14 (step # 1). The parameter value control means 24 searches the data table 23 and the data table 26 as shown below, which the storage unit 22 has, using the inspection target depth as a key, and an appropriate lift-off amount and appropriate alternating current according to the inspection target depth. The frequency is determined (step # 2).

  The parameter value control means 24 sends the determined appropriate lift-off amount to the stage controller 17, and the stage controller 17 operates the Z fine movement stage 16, and the distance between the inspection coil 52 and the surface 10a to be inspected becomes the appropriate lift-off amount. The probe 18 is arranged (step # 3).

  Further, the parameter value control means 24 sends the determined appropriate AC frequency to the excitation coil control means 21, and the excitation coil control means 21 instructs the multi-function synthesizer 11 to generate an alternating current. The multi-function synthesizer 11 The AC current is sent to the exciting coil 51 and the lock-in amplifier 12 for signal detection while controlling the frequency of the current to be an appropriate AC frequency (step # 4).

  Next, the inspection coil 52 detects the magnetic field of the eddy current induced by the varying magnetic field at the inspection target depth in the inspection object 10 below the excitation coil 51, and the magnetic field of the eddy current that is an AC voltage is detected by the lock-in amplifier 12. The test signal acquisition means 25 analyzes the DC voltage and acquires the test result (step # 5).

  The data table 23 holds the relationship between the inspection target depth and the lift-off amount that can ensure the eddy current intensity at the inspection target depth. When the inspection depth is specified, the lift-off amount at which the eddy current intensity is appropriate can be derived by using the attached probe 18 by referring to the data table 23. It has become. As an example of the data table 23, when the inspection target depth is 0.0 to 2.5 mm, the lift-off amount is 0.0 mm, and when the inspection target depth is 2.5 to 22.0 mm, the lift-off amount is 50 mm. . Of course, when the inspection target depth is in the range of 0.0 to 22.0 mm, the lift-off amount increases monotonously as the inspection target depth increases so that the lift-off amount increases to 0.0 to 50.0 mm. It can also be set as the structure to make. This proper lift-off amount ensures the strength of the detection signal by keeping the lift-off amount within a range twice that of the excitation coil diameter.

  Hereinafter, the reason why the appropriate lift-off amount can be determined as described above will be described from the analysis result using the numerical analysis model performed by the inventor. Using the coil A described above, the inspected object 10 is a steel plate having a thickness of 30 mm, the frequency of the alternating current flowing through the exciting coil is 10 Hz, the lift-off amount is 0 mm (FIG. 5), and the case of 50 mm About each of (FIG. 6), it analyzed by controlling an electric current value so that an electric current osmose | permeates the inside of a steel plate.

  In the comparison between FIG. 5 and FIG. 6, in consideration of the detection limit, when the inspection depth is 0.0 mm or more and 2.5 mm or less, the eddy current intensity is measured by the lift-off amount of 0.0 mm, and the inspection depth is However, in the case of 2.5 mm or more and 22.0 mm or less, it can be seen that the eddy current strength can be secured by measuring the eddy current strength with a lift-off amount of 50 mm. Therefore, in the data table 23, the relationship between the inspection target depth and the lift-off amount as described above is used as an index. Further, the lift-off amount may be selected at a more detailed pitch, and the inspection target depth at which the eddy current intensity is appropriate for the lift-off amount and each lift-off amount may be held.

  Next, the data table 26 holds the relationship between the inspection depth and the AC frequency at which the eddy current intensity at the inspection depth can be secured. When the inspection target depth is designated, the AC frequency at which the eddy current intensity is appropriate can be derived at that depth by referring to the data table 26. Although it is desirable that the detected eddy current intensity is high, if one third of the eddy current intensity of the surface 10a to be inspected is the detection limit, the eddy current at a certain depth of inspection is below the detection limit. By lowering, the detection limit is widened so that the rate of decrease in eddy current intensity with respect to depth is relaxed. In this way, an appropriate AC frequency for each lift-off amount is determined, and the inspection table depth and the appropriate AC frequency for the inspection depth are held in the data table 26.

  Hereinafter, the reason why the appropriate AC frequency can be determined as described above will be described from the analysis results performed by the inventors. FIG. 8 shows the results when the AC frequency is 10 kHz, and FIG. 5 shows the results when the AC frequency is 10 Hz. Further, in consideration of the condition that one third of the eddy current intensity of the surface 10a to be inspected is the detection limit, the detection limit in the graph of FIG. 8 is 1.0 mm, and the detection limit in the graph of FIG. It turns out that it is 2.5 mm.

  In the comparison between FIG. 8 and FIG. 5, for example, when the inspection target depth is 0 mm or more and 1.0 mm or less, the eddy current is measured at an alternating frequency of 10 kHz where the eddy current intensity is strong. On the other hand, considering the condition that one third of the eddy current intensity of the surface 10a to be inspected is the detection limit, a depth of 1.0 mm or more cannot be measured at an AC frequency of 10 kHz from FIG. Therefore, it can be seen that when the inspection depth is 1.0 mm or more and 2.5 mm or less, the measurement result with higher accuracy can be obtained by measuring the eddy current intensity with an AC frequency of 10 Hz. Therefore, the data table 26 is used as a relation index between the inspection object depth and the AC frequency as described above. Further, the AC frequency may be selected at a more detailed pitch, and the inspection target depth at which the eddy current intensity is appropriate for the AC frequency and each AC frequency may be held.

[Second Embodiment]
A specific apparatus configuration of the second embodiment having the second characteristic configuration of the present invention will be described with reference to FIG.

  In the eddy current flaw detector according to this embodiment, a pair of central axes are arranged on the same straight line, the coil winding direction is the same, and the central axis and the surface to be inspected 10a are arranged in parallel. A probe 18 having an excitation coil 51 and an inspection coil 52 disposed in the center of the pair of excitation coils 51 and having a central axis perpendicular to the surface 10a to be inspected is provided.

  Further, the lift-off amount setting mechanism controls the Z fine movement stage 16 in the vertical direction with respect to the inspection object surface 10a so that the stage controller 17 sets the distance between the probe 18 and the inspection object surface 10a to an appropriate lift-off amount. It functions in a form in which a flaw detection inspection is executed at a target inspection position to inspect whether the flaw is on the front or back of the inspection object 10. Then, the AC frequency setting mechanism generates an AC current so that the multi-function synthesizer 11 has an appropriate AC frequency, and flows the AC current through the excitation coil 51 so that the directions of the currents of the excitation coil 51a and the excitation coil 51b are the same. Works in form.

  The control computer 14 that controls the probe 18, the lift-off amount setting mechanism, and the AC frequency setting mechanism determines the appropriate lift-off amount and the number of times of setting (set at least 2), and also determines the appropriate AC frequency and the number of times of setting. The value control means 24, the excitation coil control means 21 for controlling the determined appropriate AC frequency to flow through the excitation coil, the inspection signal acquisition means 25 for acquiring the inspection result, and the scratch position based on the acquired inspection result. A flaw position determining means 33 to be determined and an inspection control means 31 for controlling each means of the control computer 14 are provided.

The inspection control means 31 sends the lift-off amount determined by the parameter value control means 24 and the set number of lift-off amounts to the lift-off amount setting mechanism, and excites the AC frequency and the set frequency of the AC frequency determined by the parameter value control means 24. By sending it to the coil control means 21, it functions as an inspection control means.
Further, the inspection control means 31 operates in accordance with the flow shown in FIG. 4 later, sends the detection result of the magnetic field due to the eddy current to the flaw position determination means 33, and determines whether the flaw is on the front or back of the inspection object 10. Works in form.

  The inspection signal acquisition means 25 controls the lock-in amplifier 12 that converts the AC voltage detected by the inspection coil 52 into a DC voltage, analyzes and acquires the detected DC voltage, and sends it to the flaw position determination means 33.

  Next, a detailed flaw detection method in the second embodiment will be described based on the flow shown in FIG. First, the inspection control means 31 instructs the parameter value control means 24 to determine the AC frequency and its set number of times, the lift-off amount and the set number of times, and sets the set number of times in the variables F and I (step #). 1).

  Then, the inspection control unit 31 determines the setting order of the AC frequency and the lift-off amount. For example, when the number of times of setting the AC frequency is 1 and the number of times of setting the lift-off amount is 2, F = 1 and I = 2 are set, and after the AC frequency is set first, the lift-off amount is set. The Here, the number of times the AC frequency and lift-off amount are set is one time and the other is multiple times (step # 2).

  Hereinafter, a case where F = 1 and I = 2 are set as an example. When the inspection control unit 31 determines that F = 1, the inspection control unit 31 sends the determined AC frequency to the excitation coil control unit 21, and the excitation coil control unit 21 supplies the AC synthesizer 11 with the AC current of the AC frequency. A command is issued to generate the current, and the AC current is controlled to be supplied to the exciting coil 51 in the probe 18 and the lock-in amplifier 12 for signal detection (step # 3).

  Next, when the inspection control unit 31 determines that I = 2, the parameter value control unit 24 returns the lift-off amount to the inspection control unit 31, and the inspection control unit 31 places the probe 18 at the lift-off amount. The lift-off amount is set in the controller 17 (step # 4). As described above, the lift-off amount is set to a range within twice the diameter of the exciting coil 51. Further, the designation method may be automatically generated in the apparatus, or may be separately input to the apparatus.

  The inspection control means 31 sends the lift-off amount to the stage controller 17, and the stage controller 17 activates the Z fine movement stage 16 so that the distance between the excitation coil 52 and the surface 10a to be inspected becomes an appropriate lift-off amount. Is arranged (step # 5).

  The inspection coil 52 in the probe 18 detects an eddy current magnetic field induced by a varying magnetic field generated at a depth to be inspected in the inspection object 10 below the excitation coil 51 as an AC voltage, and the lock-in amplifier 12 detects the AC. The voltage is converted into a DC voltage and sent to the inspection signal acquisition means 25 (step # 6).

  The processing from step # 4 to step # 6 is executed for each lift-off amount determined by the parameter value control means 24 in accordance with the number of times I is set (2 is set this time) (step # 7).

  The inspection signal acquisition unit 25 sends inspection data obtained by tabulating the DC voltage for each lift-off amount to the scratch position determination unit 33. The flaw position determination means 33 compares the respective inspection data, determines whether the DC voltage is on the front side or the back side in the depth direction, and obtains the inspection result (step # 8).

  The above describes the case where the AC frequency is set once and the lift-off amount is set multiple times. However, the lift-off amount may be set once and the AC frequency may be set multiple times. In that case, a series of inspections is performed by executing Step # 1, Step # 2, and Step # 3 of FIG. 4 and performing Step # 4 ′ to Step # 6 ′ a plurality of times and then performing Step # 8 ′. Inspected in order of execution. In other words, the AC frequency and the lift-off setting order are executed in a flow in which the order is changed as compared with the order of step # 1 to step # 8.

[Another embodiment]
In the second embodiment, only a part of the surface 10a to be inspected is measured. However, as shown in FIG. 3, the eddy current flaw detector includes an X automatic stage 19 and the probe 18 is inspected by the X automatic stage 19. The examination may be executed continuously by moving in parallel with the body surface 10a.

  In the second embodiment, the two set lift-off amounts are arbitrary, but one is a lift-off amount corresponding to the inspected object surface 10a (inspection depth = 0), and the other is the back side (inspection depth is inspected). By setting the lift-off amount corresponding to the depth corresponding to the plate thickness of the test object, it may be possible to determine whether the flaw is on the front or back side.

  In the second embodiment, the processing flow in which either one of the AC frequency and the lift-off amount is set, and the other is set to 2 and the inspection is executed is illustrated. However, the other is set two times or more and the inspection is performed. May be executed. Further, the inspection may be executed by setting a combination pattern in which each value of the AC frequency and the lift-off amount is changed two or more times.

  By providing an eddy current flaw detection apparatus and an eddy current flaw detection method for an object to be inspected to improve inspection accuracy in a deep part of the object to be inspected by an eddy current flaw detection apparatus for an object to be inspected having a probe having a simple structure according to the present invention. It can be effectively used for non-destructive inspection of nuclear power plants and aircraft.

Block diagram of the first embodiment of the eddy current flaw detector for an inspection object The flowchart which shows the work procedure of 1st Embodiment. Block diagram of a second embodiment of an eddy current flaw detector for an object to be inspected The flowchart which shows the work procedure of 2nd Embodiment. The graph which shows the eddy current intensity with respect to the depth of the steel plate in this invention The graph which shows the eddy current intensity with respect to the depth of the steel plate in this invention The graph which shows the eddy current intensity with respect to the depth of stainless steel (SUS316L) in a prior art The graph which shows the eddy current intensity with respect to the depth of the steel plate in the prior art Figure showing the element split state of the numerical analysis model The figure which shows the structure of the excitation coil and test | inspection coil in a prior art

Explanation of symbols

14: Control computer 16: Z fine movement stage 18: Probe 21: Excitation coil control means 22: Storage unit 24: Parameter value control means 25: Inspection signal acquisition means 31: Inspection control means 33: Scratch position determination means 51: Excitation coil 52 : Inspection coil

Claims (6)

A probe having an excitation coil for generating an eddy current in the inspection object and an inspection coil for measuring a change in the eddy current is formed on the inspection object surface by forming a magnetic field that changes over time on the inspection object. An eddy current flaw detector for an object to be inspected that is movable along
A pair of exciting coils, the central axes being arranged on the same straight line, the coil winding direction being the same, and the central axis and the surface of the object to be inspected being parallel;
The probe having the inspection coil disposed at the center of the pair of excitation coils and disposed so that the central axis is perpendicular to the surface of the inspection object,
With a parameter value setting mechanism for setting an AC frequency in the energization current of the excitation coil and a lift-off amount that is a distance from the surface of the inspection object of the probe,
A storage unit that stores the appropriate AC frequency and the lift-off amount according to the inspection target depth inside the object to be inspected,
Inspected with a parameter value control means for causing the AC frequency and the lift-off amount set by the parameter value setting mechanism to be the appropriate AC frequency and the lift-off amount according to the depth to be inspected inside the object to be inspected. Body eddy current flaw detector. A probe having an excitation coil for generating an eddy current in the inspection object and an inspection coil for measuring a change in the eddy current is formed on the inspection object surface by forming a magnetic field that changes over time on the inspection object. An eddy current flaw detector for an object to be inspected that is movable along
A pair of exciting coils, the central axes being arranged on the same straight line, the coil winding direction being the same, and the central axis and the surface of the object to be inspected being parallel;
The probe having the inspection coil disposed at the center of the pair of excitation coils and disposed so that the central axis is perpendicular to the surface of the inspection object,
With a parameter value setting mechanism for setting an AC frequency in the energization current of the excitation coil and a lift-off amount that is a distance from the surface of the inspection object of the probe,
Inspection control means for setting two different at least one of the AC frequency and the lift-off amount set by the parameter value setting mechanism;
The eddy current of the object to be inspected is provided with a flaw position determining means for determining whether a flaw exists on the front or back of the inspected object from the value of the inspection signal obtained from the inspection coil at two different parameter values. Flaw detection equipment.   The eddy current flaw detector for an object to be inspected according to claim 1 or 2, wherein the lift-off amount is set within twice the coil diameter of the exciting coil. A probe including an excitation coil that forms a magnetic field that changes over time on an object to be inspected and generates an eddy current in the object to be inspected, and an inspection coil that measures a change in the eddy current. An eddy current testing method for inspecting the object to be inspected,
A pair of exciting coils having a central axis arranged on the same straight line, the coil winding direction being the same, and the central axis being parallel to the surface of the object to be inspected;
Using the probe comprising the inspection coil disposed at the center of the pair of excitation coils and disposed so that the central axis is perpendicular to the surface of the object to be inspected;
The AC frequency in the energization current of the exciting coil and the lift-off amount, which is the distance from the surface of the object to be inspected, are set according to the inspection object depth inside the object to be inspected. Eddy current inspection method to be inspected. A probe including an excitation coil that forms a magnetic field that changes over time on an object to be inspected and generates an eddy current in the object to be inspected, and an inspection coil that measures a change in the eddy current. An eddy current testing method for inspecting the object to be inspected,
A pair of exciting coils having a central axis arranged on the same straight line, the coil winding direction being the same, and the central axis being parallel to the surface of the object to be inspected;
Using the probe comprising the inspection coil disposed at the center of the pair of excitation coils and disposed so that the central axis is perpendicular to the surface of the object to be inspected;
An inspection obtained by performing inspection by setting two different AC frequencies in the energizing current of the exciting coil and at least one lift-off amount that is a distance from the surface of the object to be inspected, and obtaining from the inspection coil An eddy current flaw detection method for inspecting the inside of an object to be inspected, wherein it is determined from the signal value whether a flaw exists on the front or back of the object to be inspected.   The eddy current flaw detection method according to claim 5 or 6, wherein the lift-off amount is set within twice the coil diameter of the exciting coil.

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