Non-destructive testing methods

Abstract

To provide a nondestructive inspection method capable of estimating the presence or absence of reinforcement deterioration in a concrete structure.SOLUTION: Provided is a method for estimating the presence or absence of damage to an inspection object buried in a concrete structure, the method being conducted in the following manner: after moving a magnetizer in a first moving direction along a first direction of the inspection object to magnetize the inspection object, moving a magnetic flux density measuring device for measuring magnetic flux density in the first moving direction to measure a first magnetic flux density; after moving the magnetizer in a second moving direction which is an opposite direction of the first moving direction along the first direction of the inspection object to magnetize the inspection object, moving the magnetic flux density measuring device in the first moving direction to measure a second magnetic flux density; calculating an average value of a measurement value of the first magnetic flux density and a measurement value of the second magnetic flux density measured at the same position in the first direction of the inspection object; on the basis of the calculated average value, creating a fluctuation curve along the first direction of the inspection object; and on the basis of the fluctuation curve, estimating deterioration of the inspection object.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-destructive inspection method, and more particularly to a non-destructive inspection method for detecting damage to reinforcing bars, steel rods, steel wires, etc. installed in concrete structures using a magnetic flux leakage method. [Background technology]

[0002] Conventionally, magnetic leakage flux methods have been used as non-destructive testing methods for detecting damaged areas in reinforcing bars, steel rods, steel wires, etc. (hereinafter referred to as reinforcing bars, etc.) installed within concrete structures. In this magnetic leakage flux method, a magnet such as a permanent magnet is moved along the surface of the concrete to magnetize the reinforcing bars, etc., and then the magnetic flux density leaking from the surface of the concrete is measured. Then, the presence or absence of damage to the reinforcing bars, etc. is detected based on the results of the magnetic flux density measurement. Technologies for detecting damaged areas in reinforcing bars, etc. using this magnetic leakage flux method are disclosed in Patent Documents 1 to 6. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3734822 [Patent Document 2] Patent No. 5946638 [Patent Document 3] WO2020 / 027028 publication [Patent Document 4] WO2020 / 027043 publication [Patent Document 5] Patent No. 6305860 [Patent Document 6] Japanese Patent Publication No. 2020-148565 Summary of the Invention [Problem to be solved by the invention]

[0004] By using the techniques disclosed in Patent Documents 1 to 6, damaged areas where reinforcing bars or the like have broken can be detected, but it is difficult to detect thinning before it leads to breakage.

[0005] In view of the above circumstances, an object of the present invention is to provide a non-destructive inspection method that can estimate whether or not thinning has occurred in reinforcing bars or the like installed in a concrete structure. [Means for solving the problem]

[0006] A non-destructive testing method of a first invention is a method for measuring, outside the concrete structure, the magnetic flux density of an object to be tested that is embedded in the concrete structure and extends in a first direction, and estimating the presence or absence of damage to the object to be tested based on fluctuations in the measured magnetic flux density, the method comprising: moving a magnetizer in a first movement direction along the first direction of the object to magnetize the object to be tested, then moving a magnetic flux density measuring device that measures the magnetic flux density in the first movement direction to measure the first magnetic flux density; moving the magnetizer in a second movement direction that is opposite to the first movement direction along the first direction of the object to magnetize the object to be tested, then moving the magnetic flux density measuring device in the first movement direction to measure a second magnetic flux density; calculating an average value of the measured values ​​of the first magnetic flux density and the measured values ​​of the second magnetic flux density measured at the same position in the first direction of the object to be tested; and creating a fluctuation curve along the first direction of the object to be tested based on the calculated average value. A polynomial approximation curve is created based on a fifth-, sixth-, or seventh-order approximation equation of the fluctuation curve, and a corrected fluctuation curve is created by subtracting the polynomial approximation curve from the fluctuation curve. If two peaks of the same sign appear on the corrected fluctuation curve, it is determined that thinning of the inspection object has occurred between the two peaks. It is characterized by: The non-destructive inspection method of the second invention comprises: A method for measuring, outside the concrete structure, the magnetic flux density of an object to be inspected that is embedded in the concrete structure and extends in a first direction, and estimating the presence or absence of damage to the object to be inspected based on fluctuations in the measured magnetic flux density, comprising: moving a magnetizer in a first movement direction along the first direction of the object to magnetize the object to be inspected, then moving a magnetic flux density measuring device that measures the magnetic flux density in the first movement direction to measure the first magnetic flux density; moving the magnetizer in a second movement direction that is opposite to the first movement direction along the first direction of the object to magnetize the object to be inspected, then moving the magnetic flux density measuring device in the first movement direction to measure the second magnetic flux density; An average value of the measured values ​​of the first magnetic flux density and the second magnetic flux density measured at the same position in the first direction of the object to be inspected is calculated, a fluctuation curve along the first direction of the object to be inspected is created based on the calculated average value, a polynomial approximation curve formed based on a fifth-order, sixth-order, or seventh-order approximation equation of the fluctuation curve is created, a corrected fluctuation curve is created by subtracting the polynomial approximation curve from the fluctuation curve, and a subtraction fluctuation curve is created by removing values ​​greater than or smaller than a predetermined value from the corrected fluctuation curve, and if two peaks of the same sign appear in the subtraction fluctuation curve, it is determined that thinning of the object to be inspected has occurred between the two peaks. It is characterized by: Third Invention The non-destructive testing method is First or second invention In the case where multiple peaks of the same sign occur in the corrected fluctuation curve or the subtraction fluctuation curve, it is determined that thinning of the object to be inspected has occurred between the two peaks that are furthest apart in the first direction of the object to be inspected. Fourth Invention The non-destructive testing method is First or second invention The fluctuation curve is formed based on a first direction magnetic flux density, which is a magnetic flux density along a first direction of the object to be inspected. Fifth Invention The non-destructive testing method is First or second invention The fluctuation curve is a third direction differential curve obtained by first-order differentiation of a fluctuation curve formed based on a third direction magnetic flux density, which is a magnetic flux density in the normal direction of the surface of the concrete structure. [Effects of the Invention]

[0007] First to third inventions According to the report, even if thinning that does not lead to fracture occurs in an inspection object embedded in a concrete structure, the occurrence of thinning can be detected. This increases the accuracy of detecting the occurrence of wall thinning. Fourth and fifth inventions According to this, the occurrence of wall thinning can be appropriately detected. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are schematic explanatory views of a nondestructive inspection device 1 used in the nondestructive inspection method of the present embodiment, in which (A) is a side view and (B) is a plan view. [Figure 2] 1A and 1B are schematic explanatory diagrams of a magnetizer 10 used in the nondestructive testing method of this embodiment, in which (A) is a side view of the magnetizer 10 moving in a first moving direction D1, and (B) is a side view of the magnetizer 10 moving in a second moving direction D2. [Figure 3] 1 is a schematic block diagram of a nondestructive inspection device 1 used in the nondestructive inspection method of the present embodiment. [Figure 4] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 100 mm, (B) is a schematic explanatory diagram of the corrected fluctuation curve in the X-axis direction when the thinning length of the inspection object P is 100 mm, and (C) is a schematic explanatory diagram of the subtraction fluctuation curve in the X-axis direction when the thinning length of the inspection object P is 100 mm. [Figure 5] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 200 mm, (B) is a schematic explanatory diagram of the corrected fluctuation curve in the X-axis direction when the thinning length of the inspection object P is 200 mm, and (C) is a schematic explanatory diagram of the subtraction fluctuation curve in the X-axis direction when the thinning length of the inspection object P is 200 mm. [Figure 6] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is short, (B) is a schematic explanatory diagram of the corrected fluctuation curve in the X-axis direction when the thinning length of the inspection object P is short, and (C) is a schematic explanatory diagram of the subtraction fluctuation curve in the X-axis direction when the thinning length of the inspection object P is short. [Figure 7] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 100 mm, (B) is a schematic explanatory diagram of the fluctuation curve in the X-axis direction when the thinning length of the inspection object P is 100 mm, and (C) to (E) are schematic explanatory diagrams of corrected fluctuation curves in the X-axis direction obtained by subtracting 5th, 6th, and 7th order polynomial approximation curves from the fluctuation curve when the thinning length of the inspection object P is 100 mm, respectively. [Figure 8] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 200 mm, (B) is a schematic explanatory diagram of the fluctuation curve in the X-axis direction when the thinning length of the inspection object P is 200 mm, and (C) to (E) are schematic explanatory diagrams of corrected fluctuation curves in the X-axis direction obtained by subtracting 5th, 6th, and 7th order polynomial approximation curves from the fluctuation curve when the thinning length of the inspection object P is 200 mm, respectively. [Figure 9] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is short, (B) is a schematic explanatory diagram of the fluctuation curve in the X-axis direction when the thinning length of the inspection object P is short, and (C) to (E) are schematic explanatory diagrams of corrected fluctuation curves in the X-axis direction obtained by subtracting 5th, 6th, and 7th order polynomial approximation curves from the fluctuation curve when the thinning length of the inspection object P is short. [Figure 10] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 100 mm, (B) is a schematic explanatory diagram of the corrected fluctuation curve of the first derivative in the Z-axis direction when the thinning length of the inspection object P is 100 mm, and (C) is a schematic explanatory diagram of the subtracted fluctuation curve of the first derivative in the Z-axis direction when the thinning length of the inspection object P is 100 mm. [Figure 11](A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 200 mm, (B) is a schematic explanatory diagram of the corrected fluctuation curve of the first-order derivative in the Z-axis direction when the thinning length of the inspection object P is 200 mm, and (C) is a schematic explanatory diagram of the subtracted fluctuation curve of the first-order derivative in the Z-axis direction when the thinning length of the inspection object P is 200 mm. [Figure 12] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is short, (B) is a schematic explanatory diagram of the corrected fluctuation curve of the first derivative in the Z-axis direction when the thinning length of the inspection object P is short, and (C) is a schematic explanatory diagram of the subtracted fluctuation curve of the first derivative in the Z-axis direction when the thinning length of the inspection object P is short. [Figure 13] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 100 mm, (B) is a schematic explanatory diagram of the fluctuation curve of the first-order derivative in the Z-axis direction when the thinning length of the inspection object P is 100 mm, and (C) to (E) are schematic explanatory diagrams of the corrected fluctuation curve of the first-order derivative in the Z-axis direction obtained by subtracting 5th, 6th, and 7th-order polynomial approximation curves, respectively, from the fluctuation curve when the thinning length of the inspection object P is 100 mm. [Figure 14] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is 200 mm, (B) is a schematic explanatory diagram of the fluctuation curve of the first-order derivative in the Z-axis direction when the thinning length of the inspection object P is 200 mm, and (C) to (E) are schematic explanatory diagrams of the corrected fluctuation curve of the first-order derivative in the Z-axis direction obtained by subtracting 5th, 6th, and 7th-order polynomial approximation curves, respectively, from the fluctuation curve when the thinning length of the inspection object P is 200 mm. [Figure 15] (A) is a diagram showing the state of thinning when the thinning length of the inspection object P is short, (B) is a schematic explanatory diagram of the fluctuation curve of the first-order derivative in the Z-axis direction when the thinning length of the inspection object P is short, and (C) to (E) are schematic explanatory diagrams of the corrected fluctuation curve of the first-order derivative in the Z-axis direction obtained by subtracting 5th, 6th, and 7th-order polynomial approximation curves, respectively, from the fluctuation curve when the thinning length of the inspection object P is short. DETAILED DESCRIPTION OF THE INVENTION

[0009] The non-destructive testing method of this embodiment is a method for estimating damage to an object to be tested that is buried inside a concrete structure using the leakage magnetic flux method, and is capable of detecting thinning that occurs in an object to be tested that extends in one direction, such as reinforcing bars, steel rods, steel wires, etc.

[0010] The concrete structure in which the inspection target to be inspected by the nondestructive inspection method of this embodiment is buried (hereinafter, sometimes simply referred to as the concrete structure to be inspected) is not particularly limited. For example, bridge girders, piers, deck slabs, etc. of roads and railways can be cited as concrete structures to be inspected by the nondestructive inspection method of this embodiment. In particular, the nondestructive inspection method of this embodiment is suitable as a method for inspecting thinning of rebars, etc., buried in concrete structures where no intersecting rebars exist between the inspection target and the surface of the concrete structure. For example, the nondestructive inspection method of this embodiment is suitable as a method for inspecting thinning of rebars, etc., buried in utility poles, etc.

[0011] The concrete structures inspected by the non-destructive inspection method of this embodiment are not limited to those with flat surfaces, but also include those with cylindrical surfaces. For example, pillar-shaped structures such as utility poles with cylindrical surfaces can also be listed as concrete structures inspected by the non-destructive inspection method of this embodiment.

[0012] The object to be inspected by the non-destructive inspection method of this embodiment is not particularly limited, and may be any object extending in one direction parallel to the surface of the concrete structure to be inspected, and which may be subject to damage such as thinning. For example, the object to be inspected may be a steel material such as prestressing steel rods (high-strength steel with a diameter of 10 mm or more), prestressing steel wires (high-strength steel wires with a diameter of 8 mm or less), prestressing steel strands (twisted prestressing steel wires), or a steel bar for reinforced concrete.

[0013] In the following, a case where the surface of a concrete structure to be inspected by the non-destructive inspection method of this embodiment is a flat surface will be described as a representative example.

[0014] In the following description, the surface of the concrete structure to be inspected includes the tangent plane of a cylindrical structure (curved concrete structure). In the case of a cylindrical curved concrete structure, the reinforcing bars to be inspected extend along the axial direction of the surface of the curved concrete structure (the central axis direction of the cylindrical surface). Therefore, the device used in the non-destructive inspection method of this embodiment measures the magnetic flux density while moving along the axial direction of the surface of the curved concrete structure. Furthermore, the magnetic sensor (described later) that measures the magnetic flux density measures the magnetic flux density while remaining parallel to the tangent plane of the surface of the curved concrete structure when the device moves along the axial direction of the surface of the curved concrete structure. Therefore, in the following description, when the surface of the concrete structure is used as a reference, it means that the tangent plane of the surface of the concrete structure is used as the reference for a curved concrete structure.

[0015] <Concrete Structure C> First, a concrete structure C to be inspected by the non-destructive inspection method of this embodiment will be briefly described.

[0016] The concrete structure C to be inspected is, for example, a structure such as a bridge girder, pier, or deck slab, and has an inspection object P, such as rebar, steel rod, or steel wire, buried inside the structure (see Figure 1). Specifically, the concrete structure C to be inspected has a planar surface CF, and the inspection object P is buried so as to extend parallel to this surface CF in one direction (the left-right direction in Figure 1). The direction in which this inspection object P extends, that is, the axial direction of the inspection object P (the left-right direction in Figure 1), will be referred to below as the first direction of the inspection object P.

[0017] In the following, the first direction of the inspection object P may be referred to as the X-axis direction, the direction parallel to the surface CF of the concrete structure C and perpendicular to the X-axis direction as the Y-axis direction, and the normal direction of the surface CF of the concrete structure C as the Z-axis direction (see Figure 1). The Z-axis direction referred to here is the third direction referred to in the claims.

[0018] In addition, the concept of the surface CF of the concrete structure C and the inspection object P being parallel not only refers to the case where the two are completely parallel throughout the entire inspection object P, but also includes the case where a part of the inspection object P has a slight inclination relative to the surface CF of the concrete structure C being inspected.

[0019] <Non-destructive inspection device 1 of this embodiment> Next, before describing the nondestructive inspection method of this embodiment, a nondestructive inspection device 1 used in the nondestructive inspection method of this embodiment will be described.

[0020] <Mobile object 2> As shown in FIG. 1, the non-destructive inspection device 1 has a moving body 2. This moving body 2 is structured so that it can move smoothly in one direction along the surface CF of the concrete structure C to be inspected. More specifically, the moving body 2 is structured so that it can move linearly along the direction of its central axis B (see FIG. 1(B)). Moreover, the moving body 2 has the function of being able to move while maintaining a constant distance H between the surface CF of the concrete structure C to be inspected and a magnetic flux measuring unit 5, which will be described later. Note that hereinafter, the direction of the central axis B of the moving body 2 (i.e., the direction of movement of the moving body 2) may be referred to as the x-axis direction (see FIG. 1).

[0021] Specifically, the moving body 2 includes a main body 2a and a plurality of wheels 2r rotatably attached to the main body 2a (see FIG. 1(A)). The plurality of wheels 2r are arranged so that their rotation axes are perpendicular to the central axis B of the moving body 2. Furthermore, the plurality of wheels 2r are arranged so that their rotation axes are parallel to the surface CF of the concrete structure C to be inspected when the moving body 2 is placed on the surface CF of the concrete structure C to be inspected. Note that, hereinafter, the direction parallel to the rotation axes of the plurality of wheels 2r may be referred to as the y-axis direction, and the direction perpendicular to the x-axis and y-axis directions may be referred to as the z-axis direction (see FIG. 1). When the moving body 2 is placed on the surface CF of the concrete structure C, the z-axis direction is parallel to the normal direction of the surface CF of the concrete structure C (the Z-axis direction described above).

[0022] Furthermore, the multiple wheels 2r are provided so that they can move while maintaining a constant distance H (distance in the Z-axis direction) between the magnetic flux measuring unit 5 (more specifically, the magnetic sensor 6) and the surface CF of the concrete structure C to be inspected. In other words, by rolling the multiple wheels 2r while they are in contact with the surface CF of the concrete structure C to be inspected, the mobile body 2 can be moved along the X-axis direction on the surface CF of the concrete structure C to be inspected while maintaining a constant distance H in the Z-axis direction between the magnetic flux measuring unit 5 and the surface CF of the concrete structure C to be inspected. In the following, when the mobile body 2 is moved, the description will be given on the assumption that the direction of movement is along the X-axis direction.

[0023] There is no particular limitation on the number of wheels 2r provided on the moving body 2. As described above, as long as the moving body 2 can be moved in the X-axis direction while maintaining a constant distance in the Z-axis direction between the magnetic flux measuring unit 5 and the surface CF of the concrete structure C to be inspected, the number of wheels 2r may be one, or in the case of multiple wheels, may be three, four or more.

[0024] Furthermore, the structure of the mobile body 2 is not particularly limited as long as it can maintain a constant distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected and can move smoothly along the X-axis direction on the surface CF of the concrete structure C to be inspected. In the above example, the mobile body 2 has wheels 2r, but the above function can also be achieved by laying a guide rail or the like parallel to the surface CF of the concrete structure C to be inspected along the X-axis direction and moving the mobile body 2 along this guide rail. Note that maintaining a constant distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected also includes the case where the distance H between them varies by about 5 mm when the mobile body 2 moves along the surface CF of the concrete structure C.

[0025] <Magnetic flux measuring unit 5> The magnetic flux measuring unit 5 measures the magnetic flux density on the surface CF of the concrete structure C to be inspected, and is equipped with a magnetic sensor 6. The magnetic sensor 6 is capable of measuring the magnetic flux density in three axial directions, and is disposed on the base member 5a of the magnetic flux measuring unit 5. Specifically, the magnetic sensor 6 is disposed so that the magnetic flux density of the inspection object P in the X-axis, Y-axis, and Z-axis directions can be measured when the moving object 2 is placed on the surface CF of the concrete structure C to be inspected.

[0026] The magnetic sensor 6 may be any known magnetic sensor capable of measuring magnetic flux density in three axial directions. For example, a Hall element sensor, an MR sensor, an MI sensor, a TMR sensor, or the like may be used as the magnetic sensor 6. Furthermore, the magnetic sensor 6 may be configured to measure the magnetic flux density in three axial directions by using a plurality of magnetic sensors that can measure the magnetic flux density in one axial direction. For example, three magnetic sensors that measure the magnetic flux density in one axial direction may be arranged adjacent to each other to measure the magnetic flux density in three axial directions. Furthermore, the magnetic flux density may be measured in three axial directions by the magnetic sensor 6, but it may also be measured in only one axial direction or only two axial directions. When measuring the magnetic flux density in two axial directions, two magnetic sensors that measure the magnetic flux density in one axial direction may be arranged adjacent to each other to measure the magnetic flux density in the two axial directions.

[0027] <Control unit 4> 3, the control unit 4 has a position calculation function that calculates the position of the magnetic sensor 6 of the magnetic flux measurement unit 5, and an operation control function that controls the operation of the magnetic sensor 6 of the magnetic flux measurement unit 5. The control unit 4 also has a storage function that associates the data of the measurement value of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux measurement unit 5 with the position of the magnetic sensor 6 of the magnetic flux measurement unit 5 calculated by the position calculation function, and stores these data in a storage unit such as a memory.

[0028] Furthermore, the control unit 4 has an analysis function that uses the data stored in the storage unit to create graphs showing fluctuations in measured values ​​of magnetic flux density, etc.

[0029] Furthermore, if the control unit 4 is provided with a data communication function to send and receive measurement data, etc., between an external personal computer or cloud computer, it is possible to have the storage function, analysis function, etc. of the control unit 4 cooperate with an external personal computer, etc.

[0030] <Position calculation function> The control unit 4 has a position calculation function that calculates the amount of movement of the mobile object 2, in other words, the amount of movement of the magnetic sensor 6 of the magnetic flux measurement unit 5. This position calculation function calculates the distance that the magnetic sensor 6 of the magnetic flux measurement unit 5 has moved from the initial position (the position where the mobile object 2 is placed on the surface CF of the concrete structure C being inspected) to the current position, in other words, the current position of the magnetic sensor 6 of the magnetic flux measurement unit 5 with respect to the initial position. For example, if the position of the magnetic sensor 6 relative to a reference position of the mobile object 2 (e.g., the position of the wheel 2r) is stored in the storage unit, the position calculation function can calculate the distance that the magnetic sensor 6 has moved in the X-axis direction and the position of the magnetic sensor 6 after the movement (position in the X-axis direction) based on the amount of movement of the mobile object 2 from the initial position in the x-axis direction and the position of the magnetic sensor 6 relative to the reference position, using the reference position at the initial position as the basis.

[0031] The method for calculating the movement distance of the magnetic sensor 6 of the magnetic flux measurement unit 5 from the initial position in the X-axis direction to the current position is not particularly limited. As shown in FIG. 3, the mobile object 2 may be provided with a detector 4c that detects the movement distance from the initial position of the mobile object 2. For example, an encoder that can detect the amount of rotation (rotation angle) of the wheel 2r may be provided as the detector 4c. In this case, the position calculation function can calculate the movement distance of the magnetic sensor 6 of the magnetic flux measurement unit 5 in the X-axis direction from the initial position and the position of the magnetic sensor 6 of the magnetic flux measurement unit 5 relative to the initial position after the movement (position in the X-axis direction) based on the rotation angle of the wheel 2r detected by the detector 4c and the diameter of the wheel 2r.

[0032] Furthermore, the detector 4c that detects the movement distance from the initial position of the moving object 2 is not limited to the above-mentioned encoder that detects the movement distance in the X-axis direction based on the number of rotations of the wheel 2r. An optical mouse, an accelerometer, or the like may also be used as the detector 4c that detects the movement distance in the X-axis direction.

[0033] Furthermore, the method for determining the current position of the magnetic sensor 6 (in other words, the position where the magnetic sensor 6 is measuring the magnetic flux density) is not limited to the above-mentioned method. For example, a position marker may be provided on or near the concrete structure C, and the position of the magnetic flux measuring unit 5 relative to the position marker at the timing when the magnetic flux density is measured may be measured to determine the position where the magnetic flux measuring unit 5 measured the magnetic flux density (position in the X-axis direction).

[0034] <Operation control function> The control unit 4 has an operation control function that controls the operation of the magnetic sensor 6 of the magnetic flux measurement unit 5. This operation control function has the functions of determining the timing at which the magnetic sensor 6 of the magnetic flux measurement unit 5 measures the magnetic flux density and causing the magnetic sensor 6 of the magnetic flux measurement unit 5 to measure the magnetic flux density at that timing, and transmitting the measured value to the storage function. For example, when a measurement start signal is input using an operation button or the like, the operation control function then causes the magnetic sensor 6 to measure the magnetic flux density at predetermined time intervals (e.g., every 10 milliseconds) and transmit the measured value to the storage function (hereinafter, the act of causing the magnetic sensor 6 to measure the magnetic flux density and transmitting the measured value to the storage function may be referred to as measurement, etc.), or causes the magnetic sensor 6 to measure the magnetic flux density at predetermined distances based on the amount of movement of the mobile object 2 in the x-axis direction calculated by the position calculation function. Of course, the control unit 4 may also be configured to cause the magnetic sensor 6 to continuously measure the magnetic flux density and continuously transmit the measured value to the storage function when a measurement start signal is input using an operation button or the like.

[0035] If the position calculation function has the detector 4c as described above, the signal transmitted by the detector 4c may be directly supplied to the operation control function, and the operation control function may cause the magnetic sensor 6 to measure the magnetic flux density based on the signal transmitted by the detector 4c. For example, if the detector 4c is an encoder, the operation control function may cause the magnetic sensor 6 to measure the magnetic flux density in accordance with the rotation angle of the wheel 2r detected by the detector 4c (i.e., when the wheel 2r rotates by a predetermined angle). The timing at which the magnetic sensor 6 starts measuring the magnetic flux density may also be determined based on the signal transmitted by the detector 4c. For example, when the detector 4c detects that the wheel 2r has started to rotate from a non-rotating state and transmits a signal, the magnetic sensor 6 may start measuring the magnetic flux density based on the signal.

[0036] Furthermore, the magnetic sensor 6 of the magnetic flux measuring unit 5 may be in a state where it constantly measures the magnetic flux density regardless of a command from the operation control function. In this case, the operation control function only needs to have a function of transmitting a signal from the magnetic sensor 6 to the storage function at the above-mentioned time intervals or after a predetermined moving distance after a measurement start signal is input.

[0037] <Memory function> The storage function is a function that associates and stores the movement distance of the magnetic flux measurement unit 5 (i.e., the movement distance of the magnetic sensor 6) calculated by the position calculation function with the measurement value of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux measurement unit 5. Specifically, the storage function has a function that associates and stores in the storage unit the measurement value of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux measurement unit 5, the time when the magnetic sensor 6 measured the magnetic flux density, the position of the magnetic sensor 6 of the magnetic flux measurement unit 5 at that time (the movement amount in the x-axis direction of the mobile object 2, the signal of the detector 4c, etc.), and the movement direction of the magnetic sensor 6.

[0038] <Analysis function> The control unit 4 also has an analysis function for analyzing the data stored in the storage unit. This analysis function has a function for determining whether or not there is thinning of the inspection object P, using the data stored in the storage unit. The analysis function will be described in detail later.

[0039] The control unit 4 does not have to have the above-mentioned analysis function, and may have only the above-mentioned position calculation function, operation control function, and storage function. In this case, a function for supplying the data stored in the control unit 4 to an external device may be provided so that the data can be analyzed by an analysis device provided separately from the nondestructive testing device 1. In this case, the data may be supplied from the control unit to the analysis device via a wired or wireless connection, or the data may be stored in a storage device such as a USB and supplied from the control unit to the analysis device.

[0040] Furthermore, the analysis function may perform preprocessing such as smoothing or flattening of data as needed to improve the accuracy of the analysis. In other words, when forming a variation curve of magnetic flux density as described below, the analysis function may have a function for performing preprocessing such as smoothing or flattening of data to improve the accuracy of analysis based on the variation curve of magnetic flux density. The method for smoothing or flattening data is not particularly limited, and well-known methods (for example, moving average method, filtering, slope correction using an approximate straight line, etc.) can be used.

[0041] <Magnetizer 10> In the nondestructive inspection method of this embodiment, magnetization of the inspection object P is performed before measuring the magnetic flux density using the nondestructive inspection device 1. Specifically, as will be described later, in the nondestructive inspection method of this embodiment, the nondestructive inspection device 1 is moved in a first movement direction D1 (see FIG. 1(A)) to measure the magnetic flux density (hereinafter may be referred to as a first-stage measurement), and then the nondestructive inspection device 1 is moved again in the first movement direction D1 to measure the magnetic flux density a second time (hereinafter may be referred to as a second-stage measurement). At this time, magnetization of the inspection object P is performed before the first-stage measurement and before the second-stage measurement, respectively. This magnetization of the inspection object P is performed using a magnetizer, and therefore, hereinafter, an example of a magnetizer used for magnetization (hereinafter referred to as magnetizer 10) will be shown.

[0042] As shown in Fig. 2, the magnetizer 10 has a moving body 11. This moving body 11 has a structure that allows it to move smoothly in one direction along the surface CF of the concrete structure C to be inspected. Moreover, the moving body 11 has a function that allows it to move while maintaining a constant distance HM between the surface CF of the concrete structure C to be inspected and a magnetic force generator 12, which will be described later.

[0043] Specifically, the mobile body 11 includes a main body 11a and a plurality of wheels 11r rotatably attached to the main body 11a (see FIG. 2). The plurality of wheels 11r are arranged so that their rotation axes are parallel to the surface CF of the concrete structure C when the mobile body 11 is placed on the surface CF of the concrete structure C to be inspected. The plurality of wheels 11r are arranged so that the mobile body 11 can move while maintaining a constant distance HM (distance in the Z-axis direction) between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected. In other words, by rolling the plurality of wheels 11r while in contact with the surface CF of the concrete structure C to be inspected, the mobile body 11 can move along the X-axis direction on the surface CF of the concrete structure C to be inspected while maintaining a constant distance HM between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected. The following description is based on the assumption that the direction of movement of the mobile body 11 is along the X-axis direction.

[0044] There is no particular limitation on the number of wheels 11r provided on the moving body 11. As described above, as long as the moving body 11 can be moved in the X-axis direction while maintaining a constant distance in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected, the number of wheels 11r may be one, or in the case of multiple wheels, may be three, four or more.

[0045] Furthermore, the structure of the mobile body 11 is not particularly limited as long as it can maintain a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected and can smoothly move along the X-axis direction on the surface CF of the concrete structure C to be inspected. In the above example, the mobile body 11 has wheels 11r, but the above function can also be achieved by laying a guide rail or the like parallel to the surface CF of the concrete structure C to be inspected along the X-axis direction and moving the mobile body 11 along this guide rail or the like. Note that maintaining a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected also includes a case where the distance HM between them varies by about 5 mm when the mobile body 11 moves along the surface CF of the concrete structure C.

[0046] <Magnetic generator 12> The magnetic force generator 12 has a function of magnetizing the inspection object P buried in the concrete structure C. Specifically, the magnetic force generator 12 has a function of magnetizing the inspection object P to such an extent that the magnetic flux leaking from the magnetized inspection object P (i.e., the magnetic flux leaking from the surface CF of the concrete structure C) can be measured by the magnetic sensor 6 of the magnetic flux measuring unit 5 of the nondestructive inspection device 1 after a certain period of time (e.g., within 30 minutes) has elapsed since the inspection object P was magnetized by the magnetic force generator 12. In other words, the magnetic force generator 12 has a function of magnetizing the inspection object P so that the intensity of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux measuring unit 5 of the nondestructive inspection device 1 after a certain period of time has elapsed since the inspection object P was magnetized by the magnetic force generator 12 becomes an intensity sufficient to perform the analysis described below. For example, an electromagnet or a permanent magnet can be used as the magnetic force generator 12. In particular, if an electromagnet is used, the inspection object P etc. can be magnetized only when necessary, which makes it easier to prevent errors in analysis due to the measured magnetic flux density caused by the influence of unnecessary magnetization etc.

[0047] The magnetic force generator 12 is provided on the movable body 11 so that both magnetic poles (N pole and S pole) are aligned along the direction of movement of the movable body 11. Moreover, the magnetic force generator 12 is provided on the movable body 11 so that the distances from both magnetic poles to the surface CF of the concrete structure C to be inspected are both distances HM.

[0048] The magnetizer that magnetizes the inspection object P is not limited to the magnetizer 10 described above, and various magnetizers can be used. For example, a general permanent magnet may be moved manually in the first movement direction and the second movement direction. Furthermore, the inspection object P may be magnetized by an autonomous mobile robot or the like that has a permanent magnet or an electromagnet.

[0049] <Non-destructive inspection method of this embodiment> A method for inspecting wall thinning of an inspection object P embedded in a concrete structure C to be inspected using the non-destructive inspection device 1 of this embodiment described above will be described. Note that the following description will be given on the assumption that the surface CF of the concrete structure C to be inspected is a horizontal plane. Of course, even if the surface CF of the concrete structure C to be inspected is a vertical plane or an inclined plane, wall thinning of the inspection object P can be inspected in a similar manner using the non-destructive inspection device 1 of this embodiment.

[0050] <First stage measurement> First, the magnetizer 10 magnetizes the inspection object P embedded in the concrete structure C to be inspected. This magnetization is performed by moving the magnetizer 10 along a first movement direction D1 (see FIG. 2(A)). Specifically, with multiple wheels 11r in contact with the surface CF of the concrete structure C, the magnetizer 10 is positioned so that the movement direction of the moving body 11 and the first direction of the inspection object P are parallel (in other words, so that the direction in which the north and south poles of the magnetic force generator 12 are aligned is parallel to the first direction of the inspection object P). Moreover, the magnetizer 10 is positioned so that the north pole of the magnetic force generator 12 is located forward in the movement direction of the first movement direction D1. In this state, by rolling the multiple wheels 11r of the magnetizer 10 and moving the magnetizer 10 in the first moving direction D1, the object P to be inspected can be magnetized by the magnetic force generator 12 while maintaining a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected.

[0051] After the inspection object P is magnetized by the magnetizer 10, the movable body 2 of the non-destructive inspection device 1 is placed on the surface CF of the concrete structure C to be inspected (see FIG. 1(A)). At this time, the movable body 2 is placed so that the moving direction of the movable body 2 and the first direction of the inspection object P are parallel to each other.

[0052] Once the moving body 2 is positioned, a measurement start signal is input using an operation button or the like, and the moving body 2 is moved in a first movement direction D1 (positive direction of the X-axis direction) along the first direction of the inspection object P. Then, the magnetic sensor 6 of the magnetic flux measurement unit 5 measures the magnetic flux density along the movement path of the magnetic sensor 6. In other words, the magnetic flux density along the first direction of the inspection object P at the position of the magnetic sensor 6 is measured. Then, the measurement value of the magnetic flux density measured by the magnetic sensor 6 is associated with the measurement position, measurement time, and movement direction of the moving body 2, and is stored in the memory function as the measurement result of the first-stage measurement.

[0053] When the movable body 2 is moved to the area where the inspection object P is to be inspected, that is, the distance where the inspection object P is to be inspected, the first stage measurement is completed.

[0054] <Second stage measurement> After the first-stage measurement is completed, the second-stage measurement is carried out. In the second-stage measurement, the magnetizer 10 is used to re-magnetize the inspection object P embedded in the concrete structure C to be inspected. Unlike the magnetization in the first-stage measurement, the magnetization in the second-stage measurement involves moving the magnetizer 10 along the second moving direction D2 (see FIG. 2(B)) to magnetize the inspection object P. Specifically, similar to the magnetization in the first-stage measurement, with multiple wheels 11r in contact with the surface CF of the concrete structure C, the magnetizer 10 is positioned so that the moving direction of the moving body 11 and the first direction of the inspection object P are parallel. Furthermore, the magnetizer 10 is positioned so that the N pole of the magnetic force generator 12 is located behind the moving direction of the second moving direction D2. In other words, the magnetizer 10 is positioned so that the N pole of the magnetic force generator 12 faces the same direction as in the magnetization in the first-stage measurement. In this state, by rolling the multiple wheels 11r of the magnetizer 10 and moving the magnetizer 10 in the second moving direction D2, the inspection object P can be magnetized by the magnetic force generator 12 while maintaining a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected.

[0055] In the second-stage measurement, magnetization is performed on the same region as in the first-stage measurement. Here, magnetization of the same region includes both the case where magnetization is performed on the same region as the region to which the magnetizer 10 was moved when magnetization of the first-stage measurement was performed, and the case where magnetization is performed on a region including the region where the first-stage measurement was performed. In other words, it includes both the case where there is a slight difference between the magnetization of the first-stage measurement and the magnetization of the second-stage measurement.

[0056] After the inspection object P is magnetized by the magnetizer 10, the movable body 2 of the non-destructive inspection device 1 is placed on the surface CF of the concrete structure C to be inspected, as in the first-stage measurement. At this time, the movable body 2 is placed in the first direction so that the magnetic sensor 6 of the magnetic flux measurement unit 5 is placed in the same position as the magnetic sensor 6 of the magnetic flux measurement unit 5 was placed at when the first-stage measurement started.

[0057] Once the moving body 2 is positioned, a measurement start signal is input using an operation button or the like, and the moving body 2 is moved in a first movement direction D1 (positive direction of the X-axis) along the first direction of the inspection object P, i.e., in the same direction as the first-stage measurement. Then, the magnetic sensor 6 of the magnetic flux measurement unit 5 measures the magnetic flux density along the movement path of the magnetic sensor 6. In other words, the magnetic flux density along the first direction of the inspection object P at the position of the magnetic sensor 6 is measured. Then, the measurement value of the magnetic flux density measured by the magnetic sensor 6 is associated with the measurement position, measurement time, and movement direction of the moving body 2, and is stored in the memory function as the measurement result of the second-stage measurement.

[0058] The second-stage measurement ends when the movable body 2 is moved to the region where the inspection object P is to be inspected, that is, to the same end position as in the first-stage measurement.

[0059] <Analysis> When the first and second stage measurements are completed, the analysis function of the control unit 4 determines whether the inspection object P is damaged, that is, whether there is any thinning.

[0060] <Alignment of first and second stage measurements> In the above example, the position of the magnetic sensor 6 of the magnetic flux measurement unit 5 at the start of the first-stage measurement (first-stage start position) is aligned with the position of the magnetic sensor 6 of the magnetic flux measurement unit 5 at the start of the second-stage measurement (second-stage start position) in the first direction. In this case, the first-stage start position and the second-stage start position may be slightly offset from each other in the first direction. For example, the positions of the two may be offset by approximately ±5 mm in the first direction.

[0061] Furthermore, as long as the position where the magnetic flux density was measured by the magnetic sensor 6 of the magnetic flux measurement unit 5 in the second-stage measurement can be correlated with the measurement position where the magnetic flux density was measured in the first-stage measurement, the first-stage start position and the second-stage start position in the first direction do not necessarily have to be aligned. For example, as long as the measurement results of the second-stage measurement are stored in the memory function by associating the distance in the first direction from the initial position of the first-stage measurement to the position of the magnetic sensor 6 of the magnetic flux measurement unit 5 where the second-stage measurement is being performed with the magnetic flux density measured at that position, the first-stage start position and the second-stage start position in the first direction do not necessarily have to be aligned. As long as the measurement results of the second-stage measurement are stored in the memory function by associating the coordinates of the magnetic sensor 6 of the magnetic flux measurement unit 5 where the second-stage measurement is being performed with the magnetic flux density measured at that position, with the initial position of the first-stage measurement as the origin, the first-stage start position and the second-stage start position in the first direction do not necessarily have to be aligned. Furthermore, if the coordinates of the position of the magnetic sensor 6 of the magnetic flux measuring unit 5 (or the reference position of the moving body 2) can be obtained using GPS or the like, it is not necessary to align the first stage start position and the second stage start position in the first direction.

[0062] <Installation position of magnetic sensor 6 of magnetic flux measuring unit 5> As described above, if the position of the magnetic sensor 6 of the magnetic flux measuring unit 5 in the second stage measurement can be made to correspond to the position of the magnetic sensor 6 of the magnetic flux measuring unit 5 in the first stage measurement, the mobile body 2 may be positioned and moved so that the magnetic sensor 6 of the magnetic flux measuring unit 5 is located behind the main body 2a of the mobile body 2 in the direction of movement (to the left of the main body 2a of the mobile body 2 in Figure 1) in the second stage measurement.

[0063] <Detailed explanation of analysis functions> As described above, the non-destructive testing device 1 of this embodiment can determine whether or not there is thinning of the test object P by utilizing the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux measuring unit 5 in the first-stage measurement and the second-stage measurement. Hereinafter, a method for determining whether or not the inspection object P has thinned will be described.

[0064] <Method for Judging the Presence or Absence of Weight Loss of Inspection Object P> The analysis function has a function of estimating that weight loss has occurred in the inspection object P by analyzing the variation along the first direction (X-axis direction in FIG. 1) of the magnetic flux density measured by the magnetic sensor 6 in the first-stage measurement and the second-stage measurement. The weight loss of the inspection object P can be estimated based on the variation of the magnetic flux density in the X-axis direction along the first direction of the magnetic flux density and the variation of the magnetic flux density in the Z-axis direction (third direction) along the first direction of the magnetic flux density, respectively.

[0065] The data used in the following description is data obtained by measuring the magnetic flux density in the state shown in FIG. 1 in a concrete structure C where there is no magnetizing structure between the surface CF of the concrete structure C and the inspection object P.

[0066] In addition, the non-destructive inspection method of this embodiment may magnetize in a state where either the N pole or the S pole of the magnetic force generator 12 is arranged in front of the moving direction of the magnetizer 10, but it is necessary to reverse the magnetic pole located in front of the moving direction of the magnetizer 10 in the first moving direction D1 and the second moving direction D2. The following description is an analysis example using the measurement data when magnetizing in a state where the N pole of the magnetic force generator 12 is located in front of the moving direction of the magnetizer 10 in the first moving direction D1 and magnetizing in a state where the S pole of the magnetic force generator 12 is located in front of the moving direction of the magnetizer 10 in the second moving direction D2 as shown in FIG. 2. On the other hand, when using the data magnetized in a state where the S pole of the magnetic force generator 12 is located in front of the moving direction of the magnetizer 10 in the first moving direction D1 and magnetized in a state where the N pole of the magnetic force generator 12 is located in front of the moving direction of the magnetizer 10 in the second moving direction D2 (hereinafter sometimes referred to as reverse magnetization), the positive and negative of the magnetic flux density will be reversed with respect to the measurement data and analysis example used in the following description. Therefore, in the case of reverse magnetization, the negative peak will correspond to the positive peak of the measurement data and analysis example in the following description.

[0067] <X-axis direction> The weight loss of the inspection object P can be estimated by the following method based on the variation of the magnetic flux density in the X-axis direction along the first direction of the magnetic flux density.

[0068] <First method> First, the average magnetic flux density at the measurement position is calculated based on the magnetic flux densities obtained in the first and second measurement stages. Specifically, the average value of the magnetic flux densities measured in the first and second measurement stages, which are measured at the same position in the first direction of the inspection object P, is calculated.

[0069] Note that the measured values ​​of magnetic flux density obtained in the first and second measurement stages may contain disturbances such as noise, so processing may be performed to remove the effects of noise, etc., and to reduce fluctuations in magnetic flux density depending on the position. For example, before calculating the average magnetic flux density at the measurement positions, the magnetic flux density at each position obtained in the first and second measurement stages may be corrected using a method such as moving average or filtering.

[0070] Once the average value of the magnetic flux density at each position is calculated, a magnetic flux density fluctuation curve showing the relationship between the average value of the magnetic flux density at each position and the measurement position in the first direction is created based on this average value of the magnetic flux density (see Figures 7(B), 8(B), and 9(B)).

[0071] When creating a variation curve of the magnetic flux density, the average value of the magnetic flux density at each position may be corrected by a method such as moving average or filtering.

[0072] Once a magnetic flux density fluctuation curve (hereinafter sometimes simply referred to as a fluctuation curve) has been created, a sixth-order polynomial approximation curve of this fluctuation curve is created. Once the sixth-order polynomial approximation curve has been created, the values ​​of this sixth-order polynomial approximation curve (i.e., the values ​​at positions corresponding to the positions on the fluctuation curve) are subtracted from the fluctuation curve to create a corrected fluctuation curve (see Figures 4(B), 5(B), and 6(B)). Then, if thinning has occurred in the inspection object P, peaks corresponding to the position where the thinning has occurred, the thinning length (the length of the inspection object P in the first direction), and the thinning rate (thinning depth) are formed on the corrected fluctuation curve.

[0073] For example, as shown in FIG. 4(A), assume that the inspection object P, which is a steel material with a thickness of 9.0 mm, has a wall-thickness reduction of approximately 100 mm. In this case, as shown in FIG. 4(B), the corrected fluctuation curve has positive peaks of magnetic flux density near the positions corresponding to the ends of the wall-thickness reduction CR. In other words, the corrected fluctuation curve has two peaks on either side of the position where the wall-thickness reduction has occurred. Therefore, by checking the positions where the positive peaks occur on the corrected fluctuation curve, it can be estimated that the inspection object P has a wall-thickness reduction CR. Moreover, because the two peaks are located near both ends of the wall-thickness reduction CR, the length of the wall-thickness reduction CR can also be estimated.

[0074] Furthermore, when the depth of thinning varies as shown in Figure 4(A), the greater the depth of thinning, the larger the positive peak becomes, as shown in Figure 4(B). In other words, if the maximum value of the positive peak can be determined, it becomes possible to estimate whether the depth of thinning is deep or shallow, and how deep the thinning is.

[0075] Furthermore, as shown in FIG. 5(A), if the test object P, a 9.0 mm thick steel material, experiences a wall thinning of approximately 200 mm, the corrected variation curve exhibits positive peaks not only near the ends of the wall thinning CR but also at approximately its midpoint (the midpoint in the first direction). In other words, if the wall thinning is long, the corrected variation curve exhibits other positive peaks in addition to the two positive peaks near the ends of the wall thinning CR. However, no positive peaks appear on the corrected variation curve outside the wall thinning CR (to the right and left of the wall thinning CR in the first direction in FIG. 5(B)) from the two positive peaks near the ends of the wall thinning CR. Therefore, if the corrected variation curve exhibits multiple positive peaks, it can be inferred that the ends of the wall thinning CR are located near the positions of the two most distant peaks, and that the wall thinning CR of the test object P occurs between the two peaks. Therefore, by identifying the positions of the positive peaks on the corrected variation curve, it can be inferred that the wall thinning CR of the test object P occurs. Moreover, since the two most distant peaks are located almost at both ends of the metal-reduced area CR, the length of the metal-reduced area CR can also be estimated.

[0076] Furthermore, when the thickness reduction depth varies as shown in Fig. 5(A), the greater the thickness reduction depth, the larger the positive peak becomes, as shown in Fig. 5(B). In other words, if the maximum value of the positive peak can be determined, it becomes possible to estimate whether the thickness reduction depth is deep or shallow, and how deep the thickness reduction is.

[0077] Furthermore, as shown in Figure 6(A), when the test object P, which is a steel material with a thickness of 9.0 mm, has a very short thinning length (for example, a thinning length shorter than 10 mm), as shown in Figure 6(B), if the thinning depth is small, no clear peak can be seen near the position corresponding to the end of the thinning CR on the corrected fluctuation curve. On the other hand, when the thinning depth CR is large (for example, a thinning CR with a thinning depth of 6.3 mm or more), the corrected fluctuation curve has two positive peaks near the positions corresponding to both ends of the thinning CR, just as when the thinning length is long. Therefore, even if the thinning CR is very short, if the thinning CR has a certain depth, it can be estimated that the thinning CR of the test object P occurs between the two peaks.

[0078] When the wall-thinning depth is 6.3 mm or greater, it is difficult to determine whether a wall-thinning CR with a wall-thinning length of approximately 100 mm (see Figure 4) or a wall-thinning CR with a very short wall-thinning length (see Figure 6) has occurred. However, comparing Figures 4 and 6, negative peaks are formed in the valleys between positive peaks in both the case of a wall-thinning CR with a wall-thinning length of approximately 100 mm and the case of a wall-thinning CR with a wall-thinning length of less than 10 mm but a wall-thinning depth of 6.3 mm (a very short wall-thinning CR). However, the negative peaks formed in the valleys between positive peaks are smaller than the positive peaks in the case of a wall-thinning CR with a wall-thinning length of approximately 100 mm, but are equivalent in magnitude to the positive peaks in the case of a very short wall-thinning CR. Therefore, by comparing the height of the negative peaks formed in the valleys between positive peaks with the positive peaks, it is possible to determine whether a wall-thinning CR with a wall-thinning length of approximately 100 mm or a very short wall-thinning CR has occurred.

[0079] <Second method> The first method described above also makes it possible to estimate the location where the wall-thinning CR has occurred, the wall-thinning length (the length of the inspection object P in the first direction), and the wall-thinning rate (wall-thinning depth). On the other hand, if a subtraction fluctuation curve is created by excluding values ​​smaller than a predetermined value from the corrected fluctuation curve, the two peaks of the corrected fluctuation curve, i.e., the positions of both ends of the wall-thinning CR, can be more appropriately estimated.

[0080] When the above-described reverse magnetization is performed, negative peaks occur near both ends of the wall-reduced CR. Therefore, if a subtraction fluctuation curve is created in which values ​​greater than a predetermined value are excluded, the two peaks of the corrected fluctuation curve, i.e., the positions of both ends of the wall-reduced CR, can be more appropriately estimated.

[0081] For example, Figures 4(C), 5(C), and 6(C) show subtraction fluctuation curves obtained by subtracting a threshold value of +1 μT (tesla) from the corrected fluctuation curve. As shown in Figures 4(C), 5(C), and 6(C), the subtraction fluctuation curves are curves that have only mountain-shaped peaks near the positions of both ends of the metal-reduced area CR, so the position and size of the peaks can be clearly grasped. Therefore, the positions of both ends of the metal-reduced area CR, the metal-reduced length, and the metal-reduced depth can be more appropriately estimated. The threshold value can be a value determined from a fluctuation range without thinning.

[0082] <About polynomial approximation curves> In the above example, a case was described in which a corrected fluctuation curve was created by subtracting the values ​​of a 6th-order polynomial approximation curve from a fluctuation curve, but the polynomial approximation curve subtracted from a fluctuation curve is not necessarily limited to a 6th-order polynomial approximation curve. For example, as shown in Figures 7 to 9, even when the values ​​of a 5th-order or 7th-order polynomial approximation curve are subtracted from a fluctuation curve, peaks are formed in the corrected fluctuation curve near the positions of both ends of the metal loss CR. Therefore, it is also possible to estimate the metal loss CR using a corrected fluctuation curve obtained by subtracting the values ​​of a 5th-order or 7th-order polynomial approximation curve from a fluctuation curve.

[0083] <Estimation of wall thinning CR based on fluctuation curve> As in the above example, when a corrected variation curve or a subtraction variation curve is created, it becomes a curve with a peak, making it easier to estimate the weight loss CR. However, it is also possible to estimate the weight loss CR based on the variation curve.

[0084] For example, as shown in FIGS. 7(B), 8(B), and 9(B), when there is no weight loss CR, the variation curve becomes a gentle mountain-shaped curve with a peak. However, when weight loss CR occurs, regardless of the weight loss length, a region including the position where weight loss CR occurs is formed where the magnetic flux density becomes almost a constant value (that is, a portion that becomes a curve close to flat). Therefore, it is possible to estimate the occurrence of weight loss CR based on the variation curve.

[0085] <Z-axis direction> Based on the variation of the magnetic flux density in the Z-axis direction along the first direction of the magnetic flux density, the weight loss of the inspection target P can also be estimated by the following method.

[0086] <First method> First, based on the measurement position in the X-axis direction along the first direction and the magnetic flux density in the Z-axis direction measured at the measurement position in the first-stage measurement, a first-stage measurement value curve is created. Similarly, based on the measurement position in the X-axis direction along the first direction and the magnetic flux density in the Z-axis direction measured at the measurement position in the second-stage measurement, a second-stage measurement value curve is created. Then, the first-stage measurement value curve and the second-stage measurement value curve are differentiated once to create a first-stage differential curve and a second-stage differential curve. When the first-stage differential curve and the second-stage differential curve are created, the average value of the magnetic flux density of the first-stage differential curve and the magnetic flux density of the second-stage differential curve is calculated at each position in the X-axis direction along the first direction. And when the average value of the magnetic flux density at each position is calculated, based on this average value of the magnetic flux density, a variation curve of the magnetic flux density showing the relationship between the average value of the magnetic flux density at each position and the measurement position in the first direction is created (see FIGS. 13(B), 14(B), and 15(B)).

[0087] Note that the measured values ​​of magnetic flux density obtained in the first-stage measurement and the second-stage measurement are affected by noise, etc., and therefore may be processed to remove the effects of noise, etc., and to reduce fluctuations in magnetic flux density depending on position. For example, before differentiating the first-stage measurement value curve and the second-stage measurement value curve once, the magnetic flux density at each position on the first-stage measurement value curve and the second-stage measurement value curve may be corrected using a method such as moving average or filtering.

[0088] Once the magnetic flux density fluctuation curve (hereinafter sometimes simply referred to as the fluctuation curve) has been created, a sixth-order polynomial approximation curve of the fluctuation curve is created, similar to the analysis in the X-axis direction. Once the sixth-order polynomial approximation curve has been created, the values ​​of this sixth-order polynomial approximation curve (i.e., the values ​​at positions corresponding to the positions on the fluctuation curve) are subtracted from the fluctuation curve to create a corrected fluctuation curve (see Figures 10(B), 11(B), and 12(B)). Then, if thinning has occurred in the inspection object P, peaks corresponding to the position where the thinning has occurred, the thinning length (the length of the inspection object P in the first direction), and the thinning rate (thinning depth) are formed on the corrected fluctuation curve.

[0089] For example, as shown in FIG. 10(A), assume that the inspection object P, which is a steel material with a thickness of 9.0 mm, has a thinning length of approximately 100 mm. In this case, as shown in FIG. 10(B), the corrected fluctuation curve has positive peaks of magnetic flux density near positions corresponding to the ends of the thinning CR. In other words, the corrected fluctuation curve has two peaks on either side of the position where the thinning CR occurs. Therefore, by checking the positions where the positive peaks occur on the corrected fluctuation curve, it can be estimated that the thinning CR has occurred in the inspection object P. Moreover, since the two peaks are located approximately at both ends of the thinning CR, the length of the thinning CR can also be estimated.

[0090] Furthermore, when the thickness reduction depth varies as shown in Fig. 10(A), the larger the thickness reduction depth, the larger the positive peak becomes, as shown in Fig. 10(B). In other words, if the maximum value of the positive peak can be determined, it becomes possible to estimate whether the thickness reduction depth is deep or shallow, and what the thickness reduction CR is.

[0091] Furthermore, as shown in FIG. 11(A), if the test object P, a 9.0 mm thick steel material, experiences a wall thinning of approximately 200 mm, the corrected variation curve exhibits positive peaks not only near the ends of the wall thinning CR but also at approximately its midpoint (the midpoint in the first direction). In other words, if the wall thinning is long, the corrected variation curve exhibits positive peaks in addition to the two positive peaks at the ends of the wall thinning CR. However, no positive peaks of the corrected variation curve appear outside the wall thinning CR (to the right and left of the wall thinning CR in the first direction in FIG. 11(B)) from the two positive peaks at the ends of the wall thinning CR. Therefore, if the corrected variation curve exhibits multiple positive peaks, it can be inferred that the ends of the wall thinning CR are located near the positions of the two most distant peaks, and that the wall thinning CR of the test object P occurs between the two peaks. Therefore, by identifying the positions where positive peaks occur on the corrected variation curve, it can be inferred that the wall thinning CR of the test object P occurs. Moreover, since the two most distant peaks are located almost at both ends of the metal-reduced area CR, the length of the metal-reduced area CR can also be estimated.

[0092] Furthermore, when the thickness reduction depth varies as shown in Fig. 11(A), the larger the thickness reduction depth, the larger the positive peak becomes, as shown in Fig. 11(B). In other words, if the maximum value of the positive peak can be determined, it becomes possible to estimate whether the thickness reduction depth is deep or shallow, and the extent of the thickness reduction CR.

[0093] Furthermore, as shown in Figure 12(A), when the thickness of the test object P, which is a steel material with a diameter of 9.0 mm, is very short (for example, thickness less than 10 mm), if the thickness reduction depth is small, as shown in Figure 12(B), no clear peak can be confirmed near the position corresponding to the end of the thickness reduction CR on the corrected variation curve. On the other hand, when the thickness reduction depth is large (for example, thickness reduction of 6.3 mm or more), two positive peaks appear on the corrected variation curve near the positions corresponding to both ends of the thickness reduction CR, just as in the case of a long thickness reduction. Therefore, even if the thickness reduction CR is very short, if the thickness reduction CR has a certain depth, it can be estimated that the thickness reduction CR of the test object P occurs between the two peaks.

[0094] Furthermore, when the wall-thinning depth is 6.3 mm or greater, it is difficult to determine whether a wall-thinning CR with a wall-thinning length of approximately 100 mm (see Figure 10) or a wall-thinning CR with a very short wall-thinning length (see Figure 12) has occurred. In this case, if there is a negative peak of the same height in the valley between the peaks, it can be determined that the wall-thinning is very short, making it possible to estimate whether a wall-thinning CR with a wall-thinning length of approximately 100 mm or a very short wall-thinning CR has occurred.

[0095] <Second method> The first method described above also makes it possible to estimate the location where the metal thinning CR has occurred, the length of the metal thinning (the length of the inspection object P in the first direction), and the rate of metal thinning (depth of metal thinning). On the other hand, similar to the analysis in the X-axis direction, if a subtraction fluctuation curve is created in the Z-axis direction by excluding values ​​smaller than a predetermined value from the corrected fluctuation curve, the two peaks of the corrected fluctuation curve, i.e., the positions of both ends of the metal thinning CR, can be more appropriately estimated.

[0096] When the above-described reverse magnetization is performed, negative peaks occur near both ends of the wall-reduced CR. Therefore, if a subtraction fluctuation curve is created in which values ​​smaller than a predetermined value are excluded, the two peaks of the corrected fluctuation curve, i.e., the positions of both ends of the wall-reduced CR, can be more appropriately estimated.

[0097] For example, Figures 10(C), 11(C), and 12(C) show subtraction fluctuation curves obtained by subtracting a threshold value of +1 μT (tesla) from the corrected fluctuation curve. As shown in Figures 10(C), 11(C), and 12(C), the subtraction fluctuation curves are curves that have only mountain-shaped peaks near the positions of both ends of the metal-reduced area CR, so the position and size of the peaks can be clearly grasped. Therefore, the positions of both ends of the metal-reduced area CR, the metal-reduced length, and the metal-reduced depth can be more appropriately estimated. The threshold value can be a value determined from a fluctuation range without thinning.

[0098] <About polynomial approximation curves> In the above example, a case was described in which a corrected fluctuation curve was created by subtracting the values ​​of a sixth-order polynomial approximation curve from a fluctuation curve, but the polynomial approximation curve subtracted from a fluctuation curve is not necessarily limited to a sixth-order polynomial approximation curve. For example, as shown in Figures 13 to 15, even when the values ​​of a fifth-order or seventh-order polynomial approximation curve are subtracted from a fluctuation curve, peaks are formed in the corrected fluctuation curve near the positions of both ends of the metal loss CR. Therefore, it is also possible to estimate the metal loss CR using a corrected fluctuation curve obtained by subtracting the values ​​of a fifth-order or seventh-order polynomial approximation curve from a fluctuation curve.

[0099] <Estimation of wall thinning CR based on fluctuation curve> As in the above example, when a corrected fluctuation curve or a subtraction fluctuation curve is created, the curve has a peak, making it easy to estimate the metal loss CR. However, just like the analysis in the X-axis direction, it is also possible to estimate the metal loss CR based on the fluctuation curve in the Z-axis direction.

[0100] For example, as shown in Figures 13(B), 14(B), and 15(B), when there is no metal-reduced area CR, the fluctuation curve is a gentle mountain-shaped curve with a peak, but when there is metal-reduced area CR, a portion where the magnetic flux density is a nearly constant value (i.e., a portion where the curve is nearly flat) is formed in the region including the position where there is metal-reduced area CR, regardless of the metal-reduced area length. Therefore, it is possible to estimate the occurrence of metal-reduced area CR based on the fluctuation curve. [Industrial Applicability]

[0101] The non-destructive inspection method of the present invention is suitable as a method for detecting thinning of reinforcing bars, steel rods, steel wires, etc. installed in concrete structures. [Explanation of symbols]

[0102] 1. Non-destructive testing equipment 2. Mobile 5 Magnetic flux measurement section 6 Magnetic Sensors 10 Magnetizer 11 Mobile 12 Magnetic generator B Central axis of moving body 2 SA reference plane C. Concrete structures CF Surface of concrete structure C P Inspection subject CR thinning

Claims

1. A method for estimating the presence or absence of damage to an inspection object embedded in a concrete structure, the method comprising: measuring, outside the concrete structure, a magnetic flux density of the inspection object extending in a first direction; and estimating the presence or absence of damage to the inspection object based on fluctuations in the measured magnetic flux density, the method comprising: a magnetizer is moved in a first movement direction along a first direction of the object to be inspected to magnetize the object to be inspected, and then a magnetic flux density measuring device that measures magnetic flux density is moved in the first movement direction to measure a first magnetic flux density; moving the magnetizer in a second movement direction that is opposite to the first movement direction along a first direction of the object to be inspected to magnetize the object to be inspected, and then moving the magnetic flux density measuring device in the first movement direction to measure a second magnetic flux density; calculating an average value of the first magnetic flux density measurement value and the second magnetic flux density measurement value measured at the same position in the first direction of the test object; creating a variation curve along the first direction of the test object based on the calculated average value; A polynomial approximation curve is created based on a fifth-order, sixth-order, or seventh-order approximation formula of the fluctuation curve; A corrected fluctuation curve is created by subtracting the polynomial approximation curve from the fluctuation curve; If two peaks of the same sign appear in the corrected variation curve, it is determined that thinning of the inspection object occurs between the two peaks. A non-destructive inspection method characterized by:

2. A method for estimating the presence or absence of damage to an object to be inspected, the object being embedded in a concrete structure and extending in a first direction, by measuring the magnetic flux density outside the concrete structure and estimating the presence or absence of damage to the object to be inspected based on fluctuations in the measured magnetic flux density, comprising: a magnetizer is moved in a first movement direction along a first direction of the object to be inspected to magnetize the object to be inspected, and then a magnetic flux density measuring device that measures magnetic flux density is moved in the first movement direction to measure a first magnetic flux density; moving the magnetizer in a second movement direction that is opposite to the first movement direction along a first direction of the object to be inspected to magnetize the object to be inspected, and then moving the magnetic flux density measuring device in the first movement direction to measure a second magnetic flux density; calculating an average value of the first magnetic flux density measurement value and the second magnetic flux density measurement value measured at the same position in the first direction of the test object; creating a variation curve along the first direction of the test object based on the calculated average value; A polynomial approximation curve is created based on a fifth-order, sixth-order, or seventh-order approximation formula of the fluctuation curve; A corrected fluctuation curve is created by subtracting the polynomial approximation curve from the fluctuation curve; creating a subtraction fluctuation curve by removing values ​​greater than or less than a predetermined value from the corrected fluctuation curve; If two peaks of the same sign appear in the subtraction variation curve, it is determined that thinning of the inspection object occurs between the two peaks. A non-destructive inspection method characterized by:

3. When a plurality of peaks of the same sign appear on the corrected fluctuation curve or the subtractive fluctuation curve, it is determined that thinning of the inspection object occurs between the two most distant peaks in the first direction of the inspection object.

3. The non-destructive inspection method according to claim 1 or 2.

4. The variation curve is a variation curve formed based on a first direction magnetic flux density, which is a magnetic flux density along a first direction of the test object; 3. The non-destructive inspection method according to claim 1 or 2.

5. The variation curve is This is a third-direction differential curve obtained by first-order differentiation of a fluctuation curve formed based on the third-direction magnetic flux density, which is the magnetic flux density in the normal direction of the surface of a concrete structure.

3. The non-destructive inspection method according to claim 1 or 2.

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