JP2005127963A - Nondestructive inspection method and its apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nondestructive inspection method and its apparatus for eliminating various constraints caused by the use of an external magnetic field and easily and accurately determining the existence of abnormity and abnormal regions in a ferromagnetic material under a nonmagnetic material. <P>SOLUTION: The strength of a naturally generated magnetic field is measured, which is independent of the artificial external magnetic field from the ferromagnetic material 12 under the nonmagnetic material 11. The existence of abnormity and its position 13 in the ferromagnetic material 12 are estimated from a distribution of the magnetic field strength found by the measurement. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a nondestructive inspection method and apparatus for estimating the presence / absence of an abnormality of a ferromagnetic material by measuring a magnetic field emitted from a ferromagnetic material under the non-magnetic material, and in particular, artificially. The present invention relates to a nondestructive inspection method and apparatus for estimating the presence / absence of an abnormality and its abnormality location by measuring the intensity of a magnetic field naturally generated from the ferromagnetic material without applying an external magnetic field to the ferromagnetic material.

  There is an X-ray transmission method using X-rays as a non-destructive inspection method for diagnosing whether or not an abnormality such as a fracture has occurred in a reinforcing bar embedded in concrete without destroying the reinforced concrete. However, the handling of radiation such as X-rays requires careful attention, and the X-ray transmission method cannot be used in a place where it cannot be accessed from both sides of the object to be measured.

  As a nondestructive inspection method when a ferromagnetic material such as a reinforcing bar is embedded in a nonmagnetic material such as concrete, there is a method using a magnetic field (for example, see Non-Patent Document 1).

According to this conventional non-destructive inspection method using a magnetic field, an external magnetic field is artificially applied to the ferromagnetic material to be inspected, and leakage from the ferromagnetic material at an abnormal location where a defect such as a fracture occurs. By detecting the magnetic flux, it is possible to determine the presence or absence of abnormality of the reinforcing bars in the concrete without being restricted as in the X-ray transmission method.
Electromagnetic Industry Co., Ltd., “Products”, second page, product name Micro Magnetic Flaw Detector, [online], [October 14, 2003 Search], Internet <URL: http://www.emic-jp.com/ pro / hihakai.html>

  However, in the conventional nondestructive inspection method using a magnetic field, it is necessary to artificially apply an external magnetic field to the inspection target, and therefore it is necessary to place the inspection target under the external magnetic field generator, and various restrictions are imposed on it. Receive.

  Accordingly, an object of the present invention is to eliminate various limitations caused by using an external magnetic field, and to relatively easily and accurately estimate the presence / absence of an abnormality in a ferromagnetic material under a non-magnetic material and the location of the abnormality. An object of the present invention is to provide a nondestructive inspection method and an apparatus therefor.

  Ferromagnetic materials such as iron have spontaneous magnetism due to the alignment of their electron spins at temperatures below the Curie point, and are naturally affected by geomagnetism in the manufacturing process. Yes.

  The present invention is basically characterized in that the presence or absence of an abnormality of a ferromagnetic material under a non-magnetic material and the location of the abnormality are estimated using a natural magnetic field that does not depend on an artificial external magnetic field.

  That is, the nondestructive inspection method according to the present invention measures the strength of a naturally occurring magnetic field that does not depend on an artificial external magnetic field from a long ferromagnetic material under the nonmagnetic material, and is obtained by the measurement. The presence or absence of abnormality of the ferromagnetic material and its location are estimated from the distribution of the magnetic field strength.

  In the nondestructive inspection method according to the present invention, the intensity of a relatively weak magnetic field that is naturally emitted from a magnetic substance, that is, a ferromagnetic substance, is measured. In a portion where an abnormality such as a fracture occurs in the ferromagnetic material, the magnetic resistance increases compared to the normal portion, and the magnetic field strength partially changes. Therefore, it is possible to estimate the presence / absence and location of abnormality of the ferromagnetic material under the non-magnetic material from the measured magnetic field intensity distribution.

  According to the non-destructive inspection method according to the present invention, without using an external magnetic field generator that tends to cause an increase in size, therefore, without being restricted by using this large external magnetic field generator, in the field, Nondestructive inspection can be performed easily and appropriately.

  In the nondestructive inspection method according to the present invention, when the ferromagnetic material is embedded in the nonmagnetic material along the surface of the nonmagnetic material, the nonmagnetic material is formed on a surface along the surface of the nonmagnetic material. The magnetic field strength of the component perpendicular to the surface can be measured. By measuring the strength of the perpendicular component of the magnetic field along the surface of the non-magnetic material, the magnetic field strength can be properly measured while maintaining a substantially uniform distance from the ferromagnetic material to be measured. it can.

  In addition, the nondestructive inspection method according to the present invention can be applied to nondestructive inspection of reinforced concrete in which a nonmagnetic material is made of concrete and a ferromagnetic material is made of reinforcing steel embedded in the concrete. In this case, in the measurement of the magnetic field strength, the strength of the magnetic field along the thickness direction of the concrete is measured on a surface along the surface of the concrete. By measuring the magnetic field strength along the thickness direction of the concrete on the concrete surface, the strength of the magnetic field in the direction perpendicular to the reinforcing bars along the longitudinal direction of the reinforcing bars arranged along the concrete surface in the concrete. Can be measured on a surface having a substantially uniform distance from the reinforcing bar, so that an accurate strength distribution can be obtained, and whether or not an abnormality such as a fracture has occurred in the reinforcing bar or the location of the abnormality Can be determined relatively easily and accurately.

  When the rebar is a main rebar embedded in the concrete along the surface of the concrete along with an auxiliary rebar disposed at right angles to the rebar, prior to the measurement of the magnetic field strength for the inspection of the main rebar, A magnetic field strength of a component along the longitudinal direction of the main reinforcing bar is measured along a direction perpendicular to the longitudinal direction of the main reinforcing bar on the surface along the concrete surface, that is, along the longitudinal direction of the auxiliary reinforcing bar, and the main reinforcing bar is determined from the measurement result. And the magnetic field strength of the component along the thickness direction of the concrete can be measured for the inspection of the main reinforcing bars along the estimated embedded position.

  On the surface along the concrete surface, along the direction perpendicular to the longitudinal direction of the main reinforcing bar, measure the strength of the magnetic field of the component along the longitudinal direction of the main reinforcing bar, and from the intensity distribution obtained by the measurement, The depth position of the main reinforcing bar from the concrete surface can be obtained. Thereby, in addition to the presence / absence of abnormality of the main reinforcing bar and the determination of the abnormal position in the longitudinal direction of the main reinforcing bar, the depth of fog from the concrete surface at the abnormal part can be obtained.

  For determining the depth of cover, a pair of magnetic sensors arranged at a distance from each other in a direction perpendicular to the longitudinal direction of the main reinforcing bar on a surface along the concrete surface is integrally perpendicular to the longitudinal direction of the main reinforcing bar. The strength of the magnetic field component in the longitudinal direction of the main reinforcing bar is measured by the two magnetic sensors while being moved in the proper direction, and the depth position from the concrete surface can be obtained from the output difference between the two sensors. Since the distance between the peak point and the bottom point of the graph drawn by the output difference between the two sensors corresponds to the depth position, the depth position can be quickly and easily obtained from the graph.

  A nondestructive testing apparatus according to the present invention is a nondestructive inspection apparatus for estimating the presence / absence and location of a magnetic substance embedded in a nonmagnetic substance along the surface of the nonmagnetic substance. The intensity of the component in the direction perpendicular to the surface of the non-magnetic material of the naturally generated magnetic field that is moved along the longitudinal direction of the magnetic material on the surface along the surface of the magnetic material and does not depend on an artificial external magnetic field from the magnetic material And a display device for displaying a measurement value obtained by the sensor in relation to the measurement point.

  In the case of non-destructive inspection of reinforced concrete in which the non-magnetic material is made of concrete and the ferromagnetic material is a reinforcing bar embedded in the concrete, the magnetic sensor may use a magnetic flux density meter that measures the magnetic flux density by a magnetic field. A converter is provided between the magnetic flux density meter and the display device for converting the magnetic flux density measured by the magnetic flux density meter into an electrical signal corresponding to the magnetic flux density and outputting the electrical signal to the display device. .

  A measurement result is obtained by providing a geomagnetic measurement sensor in parallel with the magnetic sensor, and providing an arithmetic circuit for obtaining an output signal corresponding to an output difference between the two sensors, and supplying the output signal of the arithmetic circuit to the display device. Thus, the influence of geomagnetism can be eliminated, and thereby, the presence or absence of a reinforcing bar and its location can be determined with higher accuracy.

As the magnetic sensor, an MI sensor or a fluxgate type sensor capable of detecting a magnetic flux density of 10 ^{−4 to} 10 ⁻¹⁰ Tesla can be used. The MI sensor is a high-sensitivity magnetic sensor that uses the magneto-impedance effect of an amorphous magnetic wire, and the fluxgate sensor uses the non-linear high permeability characteristics of a soft magnetic material. By using these magnetic sensors, a magnetic field having a magnetic flux density of 10 ^{−4 to} 10 ⁻¹⁰ Tesla that is naturally emitted from a reinforcing bar in reinforced concrete can be relatively easily and easily detected. It can be measured reliably.

  According to the present invention, as described above, a nondestructive inspection can be easily performed in the field without using an external magnetic field generator, and thus without being subjected to various limitations caused by using this external magnetic field generator. It can be implemented properly.

  The features of the present invention will become more apparent from the following description along with the illustrated embodiments.

  FIG. 1 shows a nondestructive inspection apparatus 10 for carrying out a nondestructive inspection method according to the present invention as a whole. Reference numeral 10 shows a reinforcing bar 12 in which the nondestructive inspection method is embedded in a concrete body 11. Shows an example applied to the determination of whether or not an abnormality 13 has occurred.

  A nondestructive inspection apparatus 10 according to the present invention includes a magnetic detection unit 15 that is moved in a direction indicated by reference numeral 14 along a longitudinal direction of a reinforcing bar 12 on a plane along a surface 11 a of a concrete body 11. The movement of the magnetic detection unit 15 can be performed manually or mechanically using a drive mechanism. The magnetic detection unit 15 is fixedly provided with a magnetic sensor 16 made of, for example, an MI sensor, and a distance sensor 17 for obtaining a moving distance of the magnetic detection unit 15.

As described above, the ferromagnetic material such as the reinforcing bar 12 is naturally weakly magnetized due to the influence of the spontaneous magnetism due to the alignment of the electron spins or the geomagnetism in the manufacturing process. The MI sensor is a high-sensitivity magnetic sensor that utilizes the magneto-impedance effect of an amorphous magnetic wire, as is well known. The highly sensitive magnetic sensor 16 detects a minute magnetic flux density of 10 ^{−4 to} 10 ⁻¹⁰ Tesla due to a magnetic field naturally generated by the rebar 12.

In addition, a fluxgate type sensor can be used as the magnetic sensor 16 instead of the MI sensor. This flux gate type sensor magnetically modulates a minute DC magnetic field using the non-linear high permeability characteristic of a soft magnetic material, thereby separating the excitation frequency and the detection frequency to generate a DC magnetic field with a high S / N ratio. To detect. Therefore, even with this fluxgate type magnetic sensor, a minute magnetic flux density of 10 ^{−4 to} 10 ⁻¹⁰ Tesla by a magnetic field naturally generated by the reinforcing bar 12 can be detected well.

  As shown in FIG. 2, the magnetic sensor 16 is supported by the magnetic detection unit 15 to detect a magnetic flux density component Bz in a direction perpendicular to the surface 11a of the concrete body 11, for example, and a signal corresponding to the magnetic flux density component Bz. Is output to the converter 18. On the other hand, the distance sensor 17 outputs a signal corresponding to the moving distance from the origin position on the concrete body 11 to the counter 19.

  The converter 18 converts the magnetic flux density signal detected by the magnetic sensor 16 into a voltage signal, and outputs this electric signal to the magnetic flux density indicator 20 and the recorder 21. Further, the counter 19 outputs movement distance data corresponding to the signal from the distance sensor 17 to the recorder 21.

  The magnetic flux density indicator 20 operates to indicate the magnetic flux density Bz corresponding to the magnetic flux density signal from the magnetic sensor 16. The recorder 21 is composed of, for example, an XY recorder, and displays the distance information L from the distance sensor 17 and the magnetic flux density Bz from the magnetic sensor 16 at each distance in association with each other. Instead of the recorder 21, an information processing device such as a personal computer can be used, and the relationship between the distance information L and the magnetic flux density Bz can be displayed on the display.

  By moving the magnetic detection unit 15 along the longitudinal direction (Y-axis direction) of the reinforcing bar 12 indicated by reference numeral 14, the magnetic flux density Bz in the Z-axis direction is successively increased along the longitudinal direction of the reinforcing bar 12 by the magnetic sensor 16. Measured. By measuring the magnetic flux density Bz, a change characteristic of the magnetic flux density Bz along the longitudinal direction of the reinforcing bar 12 as indicated by the characteristic line 22 in the recorder 21 of FIG. 1 is obtained. When the rebar 12 is broken as indicated by reference numeral 13, the magnetic flux density Bz at this breakage point changes abruptly as indicated by reference numeral 23. And the abnormal position can be known from the distance information L corresponding to the abnormal location.

In the example shown in FIGS. 1 and 2, the example in which the vertical component Bz of the magnetic flux density B due to the magnetic field naturally generated from the reinforcing bar 12 is measured has been described. Instead, as shown in FIG. 3, the magnetic flux density component Bx in the direction perpendicular to the longitudinal direction of the reinforcing bar 12 on the surface 11a of the concrete body 11, the magnetic flux density component By in the direction along the longitudinal direction of the reinforcing bar 12, and The magnetic sensors 16 for detecting the magnetic flux density component Bz in the vertical direction described above are provided in the magnetic detection unit 15, and the magnetic sensor 16 detects the magnetic flux density components Bx, By, Bz, respectively, along the longitudinal direction of the reinforcing bar 12. The change of the absolute value | B | (| B | = (Bx ² + By ² + Bz ² ) ^1/2 ) of the magnetic flux density B can be obtained. By measuring the magnetic flux density B, it is possible to know the presence / absence and position of the reinforcing bar 12 more accurately regardless of the magnetization direction of the reinforcing bar 12.

  Since the magnetic flux density B from the rebar 12 is several hundred μT or less and that of the geomagnetism is several tens μT, the influence of this geomagnetism cannot be ignored. Therefore, it is possible to easily eliminate the influence of geomagnetism by measuring the geomagnetism intensity in advance and subtracting the pre-measured geomagnetic flux density from the magnetic flux density obtained by the magnetic sensor 16. Since the magnetic intensity can be measured, the presence / absence of abnormality can be determined with high accuracy, and the abnormal position can be specified.

  Instead of this simple correction method, a geomagnetic measurement sensor 24 similar to the magnetic sensor 16 can be provided in parallel with the magnetic sensor 16 as shown in FIG. The output of the geomagnetic measurement sensor 24 is input to the arithmetic circuit 26 through the converter 25 similar to the converter 18 connected to the magnetic sensor 16. When the arithmetic circuit 26 receives magnetic flux density signals from the magnetic sensor 16 and the geomagnetic measurement sensor 24 via the converters 18 and 25, the arithmetic circuit 26 outputs the output value of the geomagnetic measurement sensor 24 from the output value of the magnetic sensor 16. And the difference is output to each of the magnetic flux density indicator 20 and the recorder 21. The geomagnetic measurement sensor 24 can correct the measurement value of the magnetic sensor 16 with the correction value obtained simultaneously with the measurement value of the magnetic sensor 16, so that the influence of geomagnetism can be eliminated with higher accuracy. This makes it possible to measure the magnetic intensity more accurately, so that it is possible to determine the presence / absence of an abnormality and to specify the abnormal position with higher accuracy.

  An example in which the nondestructive diagnosis method according to the present invention is applied to diagnosis of a reinforcing bar in a concrete slab will be described with reference to FIGS.

  As shown in FIG. 5 (a), the reinforcing bars 12 are arranged in parallel to each other at a predetermined interval in the X-axis direction, and the auxiliary reinforcing bars 12a each having a diameter of about 3 mm, and a Y perpendicular to the X-axis direction. The main reinforcing bars 12b are arranged in parallel to each other at a predetermined interval in the axial direction and each have a diameter of about 9 mm. As shown in FIG. 5 (b), they are perpendicular to the X-axis direction and the Y-axis direction. The reinforcing bars 12 were embedded in the concrete body 11 with the Z-axis direction as the thickness direction in parallel with the surface 11a of the concrete body 11. The cover depth D of the main rebar 12b was about 2 cm.

  In order to determine whether or not an abnormality has occurred in the main reinforcing bar 12b, the diagnostic method of the present invention is carried out. As a result, the main reinforcing bar 12b is broken at the position indicated by the symbol x indicated by reference numeral 13. In this example, it was proved that this occurred.

  On the surface 11a of the concrete body 11, the X-axis direction in which the auxiliary reinforcing bars 12a are arranged and the Y-axis direction in which the main reinforcing bars 12b are arranged are known, but it is unclear at which position the main reinforcing bars 12b are arranged. is there. Therefore, in order to detect a line along the main reinforcing bar 12b, that is, a buried position of the main reinforcing bar 12b, first, the magnetic detection unit 15 having the magnetic sensor 16 is moved along the X-axis direction. At this time, the magnetic sensor 16 of the magnetic detection unit 15 is installed in the magnetic detection unit 15 so as to detect the magnetic flux density component By in the longitudinal direction of the main reinforcing bar 12b, that is, the Y-axis direction. The magnetic flux density component By is measured while moving in the X-axis direction.

  A characteristic curve 27 of the magnetic flux density component By obtained by the recorder 21 similar to that shown in FIG. 1 is shown in the graph of FIG. The horizontal axis of the graph of FIG. 6 indicates the measured value (cm) from the origin in the X-axis direction, that is, the direction along the auxiliary reinforcing bar 12a, and the vertical axis indicates the magnetic flux density component By along the Y-axis direction, that is, along the main reinforcing bar 12b. (ΜT). Since the magnetic flux density component By reaches almost the peak point of each chevron at the location indicated by the arrow 27a on the characteristic line 27 in FIG. 6, each main reinforcing bar 12b is located at the X-axis position corresponding to each point indicated by this symbol 27a. It can be estimated that it is arranged. The bias component indicated by reference numeral 28 in FIG. 6 is a geomagnetic detection component.

  When measuring the position of each main reinforcing bar 12b, instead of measuring the magnetic flux density component By in the Y-axis direction, which is the longitudinal direction of the main reinforcing bar 12b, along the Z-axis direction that is the thickness direction component of the concrete body 11 The magnetic flux density component Bz can be measured. However, by measuring the magnetic flux density component By in the Y-axis direction along the longitudinal direction of the main reinforcing bar 12b, a clearer magnetic flux density change can be detected as compared with the case where the magnetic flux density component Bz is measured. .

  When the embedded position of each main reinforcing bar 12b is determined from the graph of FIG. 6 obtained by scanning the magnetic detection unit 15 in the X-axis direction, the main reinforcing bar 12b is then embedded at the determined embedded position of each main reinforcing bar 12b. While moving the magnetic detector 15 on the surface 11a along the longitudinal direction, that is, the Y-axis direction, the vertical direction along the Z-axis direction that is the thickness direction of the concrete body 11 is the same as described along FIG. A magnetic flux density component Bz is measured.

  The measurement result of the perpendicular magnetic flux density component Bz is shown by the characteristic line 29 in the graph of FIG. The horizontal axis of the graph of FIG. 7 shows the measured value (cm) from the origin along the Y-axis direction, that is, the longitudinal direction of the main reinforcing bar 12b, and the vertical axis is in the Z-axis direction, which is the thickness direction of the concrete body 11. A magnetic flux density component Bz (μT) perpendicular to the main reinforcing bar 12b is shown.

  In the graph of FIG. 7, the geomagnetic bias is indicated by reference numeral 30. Between the origin corresponding to the both side regions 31 of the characteristic line 29 of this graph and about 40 cm and about 180 cm to 220 cm, there is a large variation other than the periodic wavy shape due to the weak magnetic field from each auxiliary reinforcing bar 12a being observed. Is not found. From this, it can be estimated that the part corresponding to the both-sides area | region 31 of the main reinforcing bar 12b which is a measuring object is a healthy normal part.

  However, between the two side regions 31 of the characteristic line 29, the characteristic line 29 is observed to have a sudden vertical fluctuation including the valley-shaped bottom point indicated by reference numeral 29a. Therefore, it can be estimated that an abnormality such as corrosion has occurred between about 40 to 180 cm from the origin of the main reinforcing bar 12b to be measured, and in particular, there is a significant abnormality such as a fracture at each bottom point 29a. It can be estimated that it has occurred. The portion corresponding to the bottom point 29a is the location indicated by the symbol x shown in FIG. 5 (a) and FIG. 5 (b), and it was confirmed that the main reinforcing bar 12b was actually broken. .

  As described above, since the reinforcing bar 12 is embedded from the surface 11a of the concrete body 11 at a uniform depth D, the vertical component Bz of the magnetic field is measured along the longitudinal direction of the main reinforcing bar 12b. The magnetic detection unit 15 can be scanned in a state in which the distance between the reinforcing bar 12b and the magnetic sensor 16 is kept substantially constant, and thereby, it is relatively easy to accurately and reliably change the natural magnetic field generated by the main reinforcing bar 12b. By measuring the change in magnetic flux density, it is possible to determine whether or not an abnormality such as a fracture has occurred in the main reinforcing bar 12b, and to know the abnormal position.

  Further, according to the present invention, it is possible to measure the cover depth of the concrete at the location where the abnormality of the main reinforcing bar 12b as described above occurs.

  An outline of the principle will be described with reference to FIGS. As shown in FIG. 8, when a magnetic dipole having a component of vector m is at the origin, the magnetic flux density vector B generated at an arbitrary point (x, y, z) is

と表すことができる。

It can be expressed as.

  The magnetic flux density generated by the magnetic dipole has a symmetric distribution centered on the magnetic dipole when the component perpendicular to the xz plane is seen, and the first-order X-direction derivative (/ By / ∂x)

と表される。すなわち、磁気双極子のＹ成分が存在すれば、Ｘの位置とその深さが求められることになる。

It is expressed. That is, if the Y component of the magnetic dipole exists, the position of X and its depth are obtained.

(∂By / ∂x) when z = z ₀ (constant) in Equation 2 has a waveform as shown in the graph of FIG. 9, and the peak point of the peak of the waveform shown by (∂By / ∂x) Difference between (x1) and valley bottom point (x2)
z ₀ = X ₂ −X ₁
Represents the depth at the position of X.

  Therefore, the magnetic flux density change as shown in the graph of FIG. 9 is measured, and the difference between the peak point (x1) and the bottom point (x2) obtained from the characteristic line is calculated, so that the X position, that is, the abnormal position. The depth of is required.

  FIG. 10 shows a method of measuring the magnetic flux density component By along the longitudinal direction of the reinforcing bar 12 in order to obtain the depth of cover at the abnormal location of the reinforcing bar 12 (main reinforcing bar 12b). For the measurement of the magnetic flux density component By, although not shown, a magnetic detection unit 15 similar to that shown in FIG. 1 is used, and the magnetic sensor 16 is a magnetic flux density component in the Y-axis direction along the longitudinal direction of the main reinforcing bar 12b. It is installed in the magnetic detection unit 15 to detect By. This magnetic detector 15 moves the magnetic flux density in the Y-axis direction while moving the surface 11a of the concrete body 11 on the surface 11a of the concrete body 11 in the X-axis direction, which is the longitudinal direction of the auxiliary reinforcing bar 12a perpendicular to the main reinforcing bar 12b, at the abnormal location of the main reinforcing bar 12b. The component By is detected.

The measurement result is indicated by a characteristic line 32 in the graph of FIG. The horizontal axis of the graph indicates the moving distance in the x direction, and the vertical axis indicates the magnetic flux density component By in the Y axis direction. For example, by differentiating the magnetic flux density component By indicated by the characteristic line 32 by x using a differentiation operation by a differentiation circuit or a computer, a characteristic line of magnetic flux density change similar to that shown in FIG. 9 can be obtained. A graph obtained from the differentiation result is shown in FIG. As described with reference to FIG. 9, the difference (z ₀ = X ₂ −) between the peak point (x1) of the peak of the waveform indicated by the characteristic line 33 in the graph of FIG. 11B and the bottom point (x2) of the valley. By obtaining X ₁ ), it is possible to obtain the depth at the abnormal location, that is, the cover depth.

With respect to obtaining the cover depth at the abnormal location of the reinforcing bar, the magnetic flux density change characteristic as shown in FIG. 9 or FIG. 11B can be obtained without performing the differential operation as described above. In order to directly obtain the magnetic flux density change characteristic, in the example shown in FIG. 12, the magnetic sensors 16 similar to those described above are integrated in the X-axis direction on the surface 11a of the concrete body 11 while maintaining a minute distance Δx. The magnetic flux density component By (By ₁ , By ₂ ) at the abnormal location is measured by each of the one magnetic sensor 16. The magnetic flux density component By ₁ detected by one magnetic sensor 16 and the magnetic flux density component By ₂ detected by the other magnetic sensor 16 are subjected to arithmetic processing by an arithmetic circuit 34 that receives the respective output signals, and the difference ΔBy ( = By ₂ −By ₁ ) is output to the recorder 21. With this recorder 21, the distribution curve (∂By / ∂x) shown in FIG. 9 or FIG. 11 (b) according to the scanning in the X-axis direction of the magnetic detection unit 15 including the pair of magnetic sensors 16. A distribution curve of (ΔBy / Δx) approximated to (33) is obtained.

Therefore, according to the method shown in FIG. 12, a magnetic flux distribution curve as shown in FIG. 9 or FIG. 11 (b) can be obtained directly by magnetic measurement, and the depth at the abnormal point can be obtained from this magnetic flux distribution curve. The depth of fog (z ₀ = X ₂ −X ₁ ) can be obtained.

  Moreover, the measurement of the cover depth of a reinforcing bar can be applied to the depth measurement in the desired location of a reinforcing bar instead of the depth in the abnormal location mentioned above.

  In the above description, the example in which the main reinforcing bar 12b of the reinforcing bar 12 is the inspection target has been described. However, the auxiliary reinforcing bar 12a can be the inspection target. Further, the present invention can be applied to nondestructive inspection of ferromagnetic materials existing under various nonmagnetic materials other than concrete.

It is explanatory drawing which shows roughly the apparatus which implements the nondestructive inspection method which concerns on this invention. It is explanatory drawing which shows the perpendicular | vertical magnetic flux density vector from the test object shown in FIG. FIG. 3 is a view similar to FIG. 2 showing a three-dimensional magnetic flux density vector from the inspection object shown in FIG. 1. It is a block diagram which shows partially the modification of the nondestructive inspection apparatus shown in FIG. Fig.5 (a) is a top view which shows the reinforcement arrangement | positioning of the reinforced concrete which is a nondestructive inspection object based on this invention, FIG.5 (b) is a longitudinal cross-sectional view of a reinforced concrete. It is a graph which shows the change of the magnetic flux density obtained by measuring the magnetic flux density component of the longitudinal direction of a main reinforcement along the auxiliary reinforcement arranged at right angles to the main reinforcement. It is a graph which shows the change of the magnetic flux density obtained by measuring the magnetic flux density component of a perpendicular direction along the longitudinal direction of this main reinforcing bar along the embedding position of the main reinforcing bar obtained from the graph of FIG. It is explanatory drawing which shows the relationship between the magnetic dipole and magnetic flux density for demonstrating the measurement principle of the cover depth of a main reinforcement. It is a graph which shows the relationship between magnetic flux density change and fog depth. It is explanatory drawing for demonstrating the method of measuring the magnetic flux density component of the longitudinal direction along the direction orthogonal to the longitudinal direction of this reinforcing bar in the abnormal location of a reinforcing bar. FIG. 11A is a graph showing a change in magnetic flux density obtained by the measurement method shown in FIG. 10, and FIG. 11B is a graph similar to FIG. 9 obtained from the graph of FIG. It is. It is explanatory drawing which shows the other measuring method for obtaining the graph shown in FIG.11 (b).

Explanation of symbols

10 Nondestructive inspection equipment 11 Concrete (Non-magnetic material)
11a Surface 12 (12a, 12b) Reinforcing bar (ferromagnetic material)
12a Auxiliary rebar 12b Main rebar 13 Abnormal location 15 Magnetic detection part 16 Magnetic sensor 18 Converter 20 Magnetic flux density indicator (display device)
21 Recorder (display device)

Claims (10)

  Measure the intensity of a naturally occurring magnetic field that does not depend on an artificial external magnetic field from a long ferromagnetic material under a non-magnetic material, and determine the ferromagnetic material from the distribution of the magnetic field strength obtained by the measurement. A nondestructive inspection method characterized by estimating the presence or absence of an abnormality and the location of the abnormality.   The ferromagnetic material is embedded in the nonmagnetic material along the surface of the nonmagnetic material, and has a component perpendicular to the surface of the nonmagnetic material in the magnetic field on the surface along the surface of the nonmagnetic material. The inspection method according to claim 1, wherein the strength is measured.   The non-magnetic material is concrete, and the ferromagnetic material is a reinforcing bar embedded in the concrete, and the magnetic field strength of the component along the thickness direction of the concrete is measured on the surface along the surface of the concrete. The inspection method according to claim 2, wherein:   The rebar is a main rebar embedded in the concrete along the concrete surface perpendicular to the auxiliary rebar embedded in the concrete along the surface of the concrete, prior to the measurement of the magnetic field strength, Measure the strength of the component along the longitudinal direction of the main rebar along the longitudinal direction of the auxiliary reinforcing bar on the surface along the concrete surface, and estimate the embedded position of the main reinforcing bar from the measurement result, The inspection method according to claim 3, wherein the magnetic field strength of the component along the thickness direction of the concrete is measured along the estimated embedding position.   Measure the strength of the component along the longitudinal direction of the main reinforcement of the magnetic field along the direction perpendicular to the longitudinal direction of the main reinforcement on the surface along the concrete surface, and from the intensity distribution obtained by the measurement The inspection method according to claim 4, wherein a depth position of the abnormal portion from the concrete surface is obtained.   While integrally moving a pair of magnetic sensors arranged on the surface along the concrete surface in a direction perpendicular to the longitudinal direction of the main reinforcing bar in a direction perpendicular to the longitudinal direction of the main reinforcing bar The intensity of the component along the longitudinal direction of the main reinforcing bar of the magnetic field is measured by the two magnetic sensors, and the depth of the abnormal portion from the concrete surface is obtained from the output difference between the two sensors. Item 5. The inspection method according to Item 4.   A non-destructive inspection apparatus for estimating the presence or absence of an abnormality of a ferromagnetic material embedded along a surface of the non-magnetic material in a non-magnetic material, and on the surface along the surface of the non-magnetic material. A magnetic sensor for measuring the intensity of a component perpendicular to the surface of the non-magnetic material of a naturally generated magnetic field that is moved along the longitudinal direction of the ferromagnetic material and does not depend on an artificial external magnetic field from the ferromagnetic material; A nondestructive inspection apparatus comprising: a display device that displays a measurement value obtained by the sensor in relation to the measurement point.   The non-magnetic material is concrete, the ferromagnetic material is a reinforcing bar embedded in the concrete, and the magnetic sensor is a magnetic flux density meter that measures the magnetic flux density due to the magnetic field. The converter according to claim 7, wherein a converter that converts the magnetic flux density measured by the magnetic flux density meter into an electric signal corresponding to the magnetic flux density and outputs the electrical signal to the display device is provided between the display device and the display device. Nondestructive inspection equipment.   Further, the present invention includes a geomagnetic measurement sensor provided in parallel to the magnetic sensor, and an arithmetic circuit that outputs an output signal corresponding to an output difference between the two sensors to the display device so as to eliminate the influence of geomagnetism. The nondestructive inspection device described. The nondestructive inspection apparatus according to claim 7, wherein the magnetic sensor includes an MI sensor or a fluxgate type sensor capable of detecting a magnetic flux density of 10 ^{−4 to} 10 ⁻¹⁰ Tesla.

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