JP2017096678A - Eddy current flaw detection probe for detecting thinned state of ground contact portion of object to be inspected and method for detecting reduction in thickness using eddy current flaw detection probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a thinned condition of a ground contact portion of the structure whose one part is embedded in a foundation part without performing troublesome work such as an excavation and the like of the ground.SOLUTION: An eddy current flaw detection probe 1 for detecting a thinned condition of a ground contact portion of an object to be inspected W detects the thinned condition of the ground contact portion adjacent to a surface of the ground in the ground for the object W to be inspected which is in a solid and/or a hallow columnar state and formed by a ferromagnetic substance metallic material with a base end part embedded in the ground and detecting a thinned state of the ground contact portion adjacent to the surface of the ground. A cross-section seen from a side is formed in a curved or bent shape, and one end side in a longitudinal direction is formed with an A surface 4 opposite to the surface of a healthy part 3 separated from the surface of the ground from among the objects W to be inspected, and the other end side in the longitudinal direction is formed with a magnetic core 2 formed with a B surface 5 opposite to the surface of the ground, and an excitation coil 6 windingly attached in the midst of the longitudinal direction of the magnetic core 2, and a detection coil 7 windingly attached to the peripheral edge of the end part for the other end part of the magnetic core 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an object to be inspected of a ferromagnetic material provided in a state in which a part of a foundation such as a ground is buried, such as a lighting column or a steel tower, and the part buried in the foundation Of these, the present invention relates to an eddy current flaw detection technique for detecting a thinning state of a ground portion of an inspection object.

  Among structures provided on roads and the like, there are many members such as steel columns made of steel pillars such as lighting columns, sign columns, signal columns, guard rail columns, or so-called angle members having an L-shaped cross section. Exists. In such a structure, a part of the structure is embedded in the foundation part such as the ground (hereinafter, such a structure is referred to as a partly embedded structure). Corrosion factors such as sea salt particles and condensed water are concentrated near the surface, or a macroscopic corrosion phenomenon progresses due to potential difference between the ground and the ground, resulting in significant thinning of the surface. Sometimes. Moreover, such a macro corrosion phenomenon occurs not only on the foundation ground but also in, for example, a steel pipe that is partially embedded in a concrete wall and the remaining portion projects horizontally.

The corrosion of the subsurface part accompanying such a thinning can be a factor of reducing the strength of the entire structure. On the other hand, this kind of corrosion at the ground part is particularly prominent within a range of about 50mm from the surface of the ground (hereinafter referred to as the ground including not only the ground but also the concrete foundation). It is not possible to detect the thinning state only by visually checking the appearance.
As a method for inspecting the thinning due to the corrosion of the ground portion, techniques as shown in the following (A) to (C) are conventionally known.
(A) The ground where the ground part is buried is removed by means of excavation or the like to expose the ground part, and the exposed ground part is observed visually, or the thickness is measured using calipers or the like. .
(B) An ultrasonic flaw detection method is used. Specifically, an ultrasonic flaw detector is attached to a portion of the structure exposed to the outside, an SH wave is transmitted from the flaw detector to the ground, and the presence or absence of a defect is determined from the reflected wave. (For example, refer to Patent Document 1).
(C) Apply the pulse current detection method. Specifically, a measuring probe including an excitation coil and a detection unit (for example, a receiving coil) on the surface of a portion where a defect such as thinning in the inspection object is assumed is applied to the inspection object at a predetermined inclination angle. Install so as to incline.

Specifically, the method (C) is performed as follows.
That is, the measurement probe is arranged so that the central axis of the exciting coil faces the intersection between the columnar object to be inspected and the surface of the ground, and a DC pulse current is passed through the exciting coil. In this way, when a direct current pulse current flows through the exciting coil, a magnetic field is generated in the exciting coil, and a sudden change in the magnetic field in the exciting coil causes an eddy current to be generated on the surface of the object to be inspected facing one end of the measurement probe. Cause it to occur. The magnetic flux lines generated by this exciting coil pass through the surface of the object under test, pass through the object from the ground, pass through the ground, and take a path that is sucked into the other end of the measurement probe.

On the other hand, the eddy current generated on the surface of the object to be inspected gradually penetrates the inside of the object to be inspected while attenuating. And is sucked into the other end of the measurement probe.
In other words, after the pulse current is cut off, a magnetic flux line is generated inside the inspection object due to a sudden change of the magnetic field in the exciting coil, but this magnetic flux line disappears inside the inspection object over time. Go. This disappearance process changes so that the path of the magnetic flux lines gradually spreads outward, so that the path of the magnetic flux lines penetrates the corroded portion of the ground part of the inspection object during the disappearance process. As a result, the eddy current decays rapidly. Therefore, the time change of the eddy current is detected by the detection unit, the time from when the eddy current is formed until the eddy current decays rapidly, that is, the remaining time of the eddy current is obtained, and the remaining eddy current is obtained. If the thickness of the object to be inspected is estimated from the time, it is possible to detect a thinning state at the corrosion location.

JP 2013-160683 A

The conventional methods (A) to (C) described above have the following problems.
The method (A) requires large-scale work for excavation of the ground and backfill after inspection. In the method (A), it is necessary to measure the thickness of a circular pipe or the like using a vernier caliper or the like after excavation, but such an operation is also troublesome.
The method (B) cannot be applied when the surface of the object to be inspected is covered with a coating film or the like. In other words, in order to apply the method (B), it is necessary to remove the coating film or the like in advance, and it is difficult to simply inspect while keeping the structure as it is.

The method (C) has various problems as shown below.
・ Low detection sensitivity for corrosion.
Since the corrosion location of the object to be inspected and the ground part is far away from the measurement probe, the magnetic resistance of the magnetic circuit passing through the object to be inspected and the corrosion location is large, resulting in fewer magnetic flux lines inducing the detection coil. End up. For this reason, the signal intensity is low, and the detection sensitivity of the thinned state is also low.
• If you attempt to investigate the corrosion distribution by turning the measurement probe around the object to be inspected, the measurement accuracy will be poor.

When examining the circumferential distribution of the degree of corrosion by rotating the measurement probe around the object to be detected, the distance between the probe core and the healthy surface of the object to be inspected is inconsistent due to the incomplete rotation mechanism. Change to rules. When such a change in distance occurs, the magnetic resistance also changes, and the strength of the magnetic flux lines penetrating through the corroded portion of the ground portion also changes, resulting in variations in the detection sensitivity of the thinned state. Therefore, if the distribution of corrosion is detected by turning the measurement probe around the object to be detected, the signal intensity varies depending on the location, so that the thinning state cannot be accurately detected.
・ The method of adjusting the sensitivity of the measurement probe according to the depth from the surface of the ground to the corroded area has not been established, and the thinning state could not be detected accurately depending on the depth of the corroded area. .
・ Distribution information of thinning along the depth direction from the surface of the ground cannot be obtained.
-In the conventional pulsed eddy current flaw detection method, the time at the point where the slope of the attenuation curve of the detection coil signal suddenly increases was measured, so that it was directly affected by signal noise, and the quantitativeness (reproducibility) was poor.

That is, even if any of the conventional methods (A) to (C) is adopted, it is difficult to reliably detect the thinning state of the ground portion of the inspection object.
The present invention has been made in view of the above-described problems, and detects the thinning state of the ground portion of the inspection object partially buried in the ground without performing troublesome work such as excavation of the ground. An object of the present invention is to provide an eddy current flaw detection probe and a corrosion evaluation method using the eddy current flaw detection probe.

In order to solve the above-mentioned problems, the eddy current flaw detection probe for detecting the thinning state of the ground portion of the inspection object according to the present invention employs the following technical means.
That is, the eddy current flaw detection probe for detecting the thinning state of the ground portion of the object to be inspected according to the present invention is a solid or hollow columnar shape, formed of a ferromagnetic metal material, and a base end portion on the ground. An eddy current flaw detection probe for detecting a thinning state of a buried portion in the ground and adjacent to the ground surface with respect to an embedded inspection object, and is formed in a curved or bent shape in a side view In addition, an A surface facing the surface of the healthy part of the object to be inspected away from the ground surface is formed on one end side in the longitudinal direction, and facing the surface of the ground on the other end side in the longitudinal direction. A magnetic core having a B surface formed thereon, an excitation coil attached in a winding shape in the longitudinal direction of the magnetic core, and a peripheral edge of the end relative to the other end of the magnetic core And a detection coil attached in a wound shape. .

Preferably, the eddy current flaw detection probe is used for intermittently or continuously measuring a plurality of portions of the healthy portion, and the eddy current flaw detection probe is formed on the magnetic core facing the sound surface of the inspection object. A magnetic measuring element or a correction coil wound around the peripheral edge of the A surface of the magnetic core may be provided on the center side of the A surface.
Preferably, the S / N ratio of the signal detected by the detection coil is increased with respect to the corroded portion that occurs in the inspection object having a thickness of T and is located at a depth D from the surface of the ground. Therefore, it is preferable to satisfy the relationship of the formula (1).

  Preferably, the surface T facing the healthy surface, the surface B facing the surface of the ground, and the surface C positioned above the surface A and parallel to the surface of the ground are substantially T A letter-shaped magnetic core, an excitation coil wound on the A-side of the magnetic core, a first detection coil wound on the B-side of the magnetic core, and the magnetic core It is good to have the 2nd detection coil wound by the C surface side.

Preferably, the magnetic core has a substantially L-shaped cross section, and the excitation coil is provided in a wound shape outside the detection coil provided on the B surface side.
Preferably, the magnetic core is formed with a notch having a parallelogram-shaped cross section from the intersection of the A surface and the B surface to the inside, and the excitation coil and the detection are provided in the notch. The coil and the correction coil are wound, and it is preferable that the following expression (2) is satisfied.

    On the other hand, in the thinning detection method using the eddy current flaw detection probe according to the present invention, when detecting the thinning state of the ground portion using the eddy current flaw detection probe described above, the A surface at each of the plurality of measurement positions. The magnetic flux density of the magnetic flux lines passing through or the maximum electromotive force generated in the correction coil is monitored, and the fourth root of the relative ratio of the fluctuation of the magnetic flux density or the maximum electromotive force is obtained. A sensitivity error due to variation in the gap between the eddy current flaw detection probe and the object to be inspected is corrected by dividing the signal output from the detection coil at the measurement position by the value of the root.

  Preferably, a plurality of eddy current flaw probes designed to increase the S / N ratio at different depths d are used, and each of the plurality of eddy current flaw probes is provided at a measurement location on the surface of the inspection object. The flaw detection signals are measured intermittently or continuously by facing each other, and the flaw detection signals at the same measurement position measured by each eddy current flaw detection probe are combined to determine the thinning state of the ground part of the inspection object. It is good to detect.

Preferably, a plurality of eddy current flaw detection probes each having a depth d [D ₁ , d ₂ , d ₃ ...] At which the S / N ratio increases are detected, and a plurality of flaw detection detections at the same measurement position are performed. Signal [ΔV ₁ , ΔV ₂ ,
ΔV ₃ ... Is measured, and the depths [d ₁ , d ₂ , d ₃ ... Are measured using the measured plurality of flaw detection signals [ΔV ₁ , ΔV ₂ , ΔV ₃ . The weight of the corrosion amount (thinning amount) [e ₁ , e ₂ , e ₃ ...] Of the multiple eddy current flaw detection probes [C] ⁻¹ of the response matrix [C] [Delta] V _1, [Delta] V _2, represented by formula linear combination of [Delta] V ₃ · · ·], using the equation of the linear combination, it is preferable to detect the thickness decrease states of Chisai portion of the object.

Preferably, for the flaw detection signal measured using the above-described eddy current flaw detection probe, the thinning state of the ground portion of the inspection object may be estimated using the attenuation constant λ obtained from the flaw detection signal. .
Preferably, the above-described eddy current flaw detection probe is used to compare the reference signal when measurement is performed on the healthy portion with the signal when measurement is performed on the ground portion, and the ground portion of the inspection object When detecting the thinning state, the reference signal may be obtained by lifting off the same eddy current flaw detection probe from the surface of the ground to the upper healthy portion.

  Preferably, two of the same eddy current flaw detection probes described above are prepared, and one eddy current flaw detection probe is placed away from the surface of the ground in order to obtain a reference signal for a healthy portion away from the surface of the ground, and the other eddy current flaw detection probe A flaw detection probe is installed adjacent to the surface of the ground in order to obtain a signal for the ground part, and the difference between the reference signal and the signal for the ground part is used to reduce the thickness of the ground part of the inspection object. It is good to detect the state.

  Preferably, in the above-described thinning detection method, an adaptive moving average method is used to obtain a value obtained by smoothing measurement noise from a measurement attenuation curve and a differential value at that time, which are necessary for obtaining an attenuation constant at an arbitrary time. Should be used.

  According to the eddy current flaw detection probe and the thinning detection method using the eddy current flaw detection probe for detecting the thinning state of the ground portion of the object to be inspected according to the present invention, the basic portion can be obtained without performing troublesome work such as excavation of the ground. It is possible to determine the thickness reduction situation of the ground part of the structure partially filled in.

It is sectional drawing which shows the basic composition of the eddy current test probe of this invention. It is the figure which showed the relationship between the magnetic flux line distribution which generate | occur | produces in the cross section of the eddy current test probe of 1st Embodiment and 2nd Embodiment, and the magnetic flux line which passes along the corroded part just under the ground. It is the figure which compared detection sensitivity with the eddy current test probe of 1st Embodiment and 2nd Embodiment, and the conventional eddy current test probe. It is the figure which showed the time behavior of the pulse excitation magnetic flux line distribution at the time of using the eddy current flaw detection probe of 2nd Embodiment in the cross-sectional state. It is the figure which showed typically the method of turning the eddy current flaw detection probe of 3rd Embodiment around the circular to-be-inspected object, and estimating the corrosion degree of a depth direction. It is the figure which showed typically the characteristic of the sensitivity with respect to the gap distance of an eddy current test probe, and a to-be-inspected object, and its correction method. It is the figure which showed each parameter which prescribes | regulates the geometrical shape of the eddy current test probe (magnetic body core) of this invention, and the relative position of a corrosion part. It is the figure which showed the approximate regression formula expressing each parameter dependence with respect to the sensitivity of a corrosion part thinning, and accuracy verification. It is the figure which showed the specific example (1) of the optimization design conditions. It is the figure which showed the specific example (2) of the optimization design conditions. It is the figure which showed the aspect of the geometric shape of the eddy current test probe suitable for corrosion depth. It is the figure which showed the method of test | inspecting three eddy current flaw detection probes which have a sensitivity in a different depth, turning around the to-be-inspected object simultaneously. It is the figure which showed the relationship between the magnetic flux line behavior of the three eddy current flaw detection probes which have a sensitivity in a different depth, and the condition of a sensitivity maximum depth. It is a figure which shows linearly the signal characteristic which measured the to-be-inspected object using the eddy current test probe of this invention. It is a figure which shows the signal characteristic which measured the to-be-inspected object using the eddy current flaw detection probe of this invention in logarithm. It is a figure which shows the change of the attenuation constant of the signal characteristic which measured the to-be-inspected object using the eddy current flaw detection probe of this invention. It is a figure which shows the correlation of the corrosion thinning amount which measured the to-be-inspected object using the eddy current flaw detection probe of this invention, and decay time. It is a figure which shows the time difference in the attenuation | damping curve which measured the to-be-inspected object using the eddy current flaw detection probe of this invention. It is a figure which shows the method comparison of the estimated corrosion amount which measured the to-be-inspected object using the eddy current test probe of this invention. It is a figure which shows the method of obtaining the reference signal measurement with respect to a healthy part by making it lift off above the ground surface. It is a figure which shows the Example of the eddy current test probe which made the reference part signal use and the buried part signal use integrated. FIG. 13B is a diagram that assumes a situation where the vicinity of the ground is protected by a covering material when the eddy current flaw detection probe of FIG. 13A is applied. It is a figure which shows a detection signal when there is no corrosion thinning part. It is a figure which shows a detection signal in case there exists corrosion thinning of depth 1mm in the underground part 25mm from the ground. It is a figure which shows a detection signal when there exists corrosion thinning of 1mm in depth in the underground part 25mm from the ground (when the space | interval of an eddy current test probe-to-be-inspected object: 0.2mm). It is a figure which shows the assembly | attachment method of the excitation, detection, and correction coil with respect to the magnetic body core which has a reverse L-shaped cross section. It is a figure which shows the method of a densely designed (high performance per volume) magnetic core shape and each coil mounting.

Hereinafter, an eddy current flaw detection probe 1 according to a first embodiment of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the eddy current flaw detection probe 1 according to the first embodiment is a probe used for an eddy current test for detecting defects existing in a material. This eddy current test is performed using the eddy current flaw detection probe 1 having a coil or the like, and the eddy current flaw detection probe 1 has a configuration capable of forming a magnetic field with the coil or the like. That is, when a current (pulse current) is passed through the coil of the eddy current flaw detection probe 1 to excite the magnetic field or to interrupt the current that has flowed, an eddy current is induced in the material due to a sudden change in the magnetic field. For example, when the case where the current flowing in the coil of the eddy current flaw detection probe 1 is interrupted is considered, the magnetic flux line excited by the coil gradually disappears and this eddy current also disappears. If there is a defect such as 11 thinning, the decay of the eddy current is accelerated as the magnetic flux lines pass through the defect. In the eddy current test, the degree of defect, in other words, the size of defect thinning, is measured by measuring the time from the formation of eddy current to the acceleration of decay using the property of time variation of eddy current. It is intended to inspect.

  Specifically, the inspection object W to be inspected by the eddy current flaw detection probe 1 of the present invention is a ferromagnetic metal material formed in a solid or hollow column shape, and a part thereof is embedded in the ground. It has become. In addition, as long as the to-be-tested object W made into the column shape of this invention is embedded partially, it may be deployed along an up-down direction, or may be deployed along a horizontal direction. In the following embodiments, the eddy current flaw detection probe 1 of the present invention will be described by taking an example in which the inspection object W is arranged along the vertical direction and a part of the lower end side is embedded in the ground. .

  In such an inspected object W, corrosion tends to occur in a portion embedded in the ground, particularly in a portion close to the ground surface among the embedded portions. Therefore, the eddy current flaw detection probe 1 according to the present invention is a portion embedded in the ground of the inspection object W, particularly a portion close to the ground surface (hereinafter referred to as a ground portion), which is a reduced thickness due to corrosion. It is mainly used to detect That is, the eddy current flaw detection probe 1 according to the first embodiment can accurately evaluate the corrosion generated at the ground portion of the inspection object W.

  The eddy current flaw detection probe 1 has a magnetic core 2 that is arcuate (fan-shaped) when viewed from above and whose middle in the longitudinal direction is curved or bent when viewed from the side. The magnetic core 2 is made of a material having a relative magnetic permeability of 1000 or more and generating very little eddy current. As such a magnetic core 2, a molded body of pure iron powder coated with ferrite or insulation is preferably used.

  One end of the magnetic core 2 is the surface of the inspection object W exposed to the surface (hereinafter referred to as the portion of the inspection object W embedded in the basement and possibly corroded, The part exposed to the ground and having a low possibility of corrosion is called “healthy part 3”, and the surface provided on the healthy part 3 is called “healthy surface 3a”). One end face is referred to as A-plane 4. The distance (gap) from the A surface 4 to the healthy surface 3a is sufficiently narrow (preferably, the opening width of 5) with respect to the length (opening width) along the vertical direction of the A surface 4 of the magnetic core 2. Less than%).

The other end of the magnetic core 2 is a B surface 5 that faces the surface of the ground. The B surface 5 faces the surface of the ground on which the inspection object W is laid. The distance from the B surface 5 to the surface of the ground can be employed with almost no restriction, from the one in contact with the surface of the ground to the one away from the surface of the ground to some extent.
An exciting coil 6 is provided in the middle of the magnetic core 2 in the longitudinal direction, in other words, on the body of the magnetic core 2 so as to wind around the body. Further, a detection coil 7 wound around the periphery of the end portion is provided at the end portion on the B surface side of the magnetic core 2.

In the eddy current flaw detection probe 1 according to the first embodiment described above, a thinned state of the ground portion is detected in the following procedure by causing a current to flow through the exciting coil 6 to generate a magnetic field.
As shown in FIG. 2, the A surface 4 of the magnetic core 2 can face the surface of the healthy part 3 exposed to the ground of the object W to be inspected. In this state, if a direct current pulse current is passed through the exciting coil 6 provided in the middle of the magnetic material core 2 in the longitudinal direction, or if the flowing pulse current is interrupted, a sudden change in the magnetic field is caused in the exciting coil 6. An eddy current is generated on the surface of the object W to be inspected (opposite the A surface 4 of the magnetic core 2) due to a sudden change in the magnetic field. At this time, the magnetic flux lines emitted from the magnetic core 2 pass under the surface of the inspection object W, pass through the vicinity of the ground portion below the ground surface, and penetrate into the ground, so that the B surface 5 of the magnetic core 2 It is formed along the path to be sucked in. That is, the magnetic flux lines generated by the exciting coil 6 take a path that is circular when the cross section is viewed.

For example, when the pulse current flowing through the exciting coil 6 is interrupted, the above-described magnetic flux lines and the eddy current formed on the surface of the inspection object W gradually disappear as time passes. The manner of disappearance of the magnetic flux lines is as shown in the lower side of FIG. 4 and disappears so that the annular magnetic flux lines spread from the center toward the outside.
At this time, the decay (disappearance) of the eddy current accelerates rapidly when taking a path through which the magnetic flux lines penetrate the corroded portion of the inspection object W below the ground surface. Therefore, the degree of thickness reduction (thickness) can be estimated by measuring the time from when the eddy current is formed to when the eddy current rapidly decreases.

In the eddy current flaw detection probe 1 of the first embodiment described above, the A surface 4 of the magnetic core 2 and the surface of the healthy portion 3 of the inspection object W are in a face-to-face state as described above, and a very close distance. The A surface 4 can be brought close to the inspection object W. Therefore, the magnetic flux lines excited by the exciting coil 6 can easily penetrate the inspection object W with a low magnetic resistance.
As a result, the eddy current flaw detection probe 1 and the object W to be inspected are more strongly magnetically coupled and pass through a corroded portion (a corroded portion of the subsurface portion) that exists at a deep position below the ground surface. The number of magnetic flux lines returning to the B surface 5 of the core 2 also increases, and a signal voltage is induced in the detection coil 7 with a strong intensity.

The effects of the eddy current testing probe 1 of the first embodiment will be described in more detail in comparison with the prior art.
FIG. 3 is a diagram showing a magnetic flux diagram obtained by two-dimensional static magnetic field analysis in comparison with a case where the probe according to the prior art is used and a case where the eddy current flaw detection probe 1 of the first embodiment is used. The magnetic flux diagram shown on the left is a probe according to the prior art installed at an angle of 45 ° with respect to the surface of the ground, and the magnetic flux diagram shown on the right is the eddy current flaw detection probe 1 according to the first embodiment of the present invention. Is used. The inspection object W located below the surface of the foundation ground has a “corrosion spot 11” indicated by a square in the figure, and this “corrosion spot 11” is located at an average depth D from the surface of the foundation ground. ing. When the number of magnetic flux lines passing through the “corrosion spot 11” is n and the number of magnetic flux lines generated by the exciting coil 6 is N, the detection sensitivity of the degree of corrosion should be evaluated as “n / N”. Can do. Actually, when the relative permeability of the steel plate is 2000 and the permeability of the magnetic core 2 is 3800, which is sufficiently larger than that in the air (that is, they are ferromagnetic), the second is higher than the conventional example. It can be seen that the eddy current flaw detection probe 1 according to one embodiment has a detection sensitivity three times or more that of the prior art.

From this, it can be seen that the eddy current flaw detection probe 1 according to the first embodiment can detect the corroded portion 11 at the ground portion with high sensitivity.
[Second Embodiment]
Next, the eddy current flaw detection probe 1 according to the second embodiment will be described.
As shown in FIG. 2, the eddy current flaw detection probe 1 according to the second embodiment is used for intermittently or continuously measuring a plurality of locations of the healthy portion 3, and the healthy surface 3 a of the object W to be inspected. The magnetic measuring element 8 or the correction coil 9 wound around the peripheral portion of the A surface 4 of the magnetic core 2 is provided on the center side of the A surface 4 of the magnetic core 2 facing the surface.

  In other words, the eddy current flaw detection probe 1 according to the second embodiment sequentially approaches the eddy current flaw detection probe 1 to a plurality of locations of the healthy portion 3 and faces each other and intermittently measures the flaw detection detection signal of the healthy portion 3 by the detection coil 7. 5, the eddy current flaw detection probe 1 is swung around the axis of the inspection object W along the curved surface with respect to the inspection object W having a circular cross section as shown in FIG. The flaw detection signal is continuously measured by the detection coil 7.

  In this way, when the flaw detection signal is measured intermittently or continuously, the detection sensitivity of the flaw detection signal due to a change in the distance between the A surface 4 of the magnetic core 2 and the surface of the inspection object W (healthy surface 3a). It becomes important how to adjust. In particular, as shown in FIG. 5, when the eddy current flaw detection probe 1 is swung around the axis of the inspection object W and the circumferential distribution of the degree of corrosion is examined, the magnetic substance is taken into account because of the imperfection of the swiveling mechanism. The gap between the A surface 4 of the core 2 and the healthy surface 3a of the object W to be inspected is inevitably changed, and the accompanying change in magnetoresistance changes the strength of the penetrating magnetic flux lines. And pulling will affect the sensitivity. For this reason, since the intensity of the flaw detection signal varies depending on the location of the circumferential direction, it is difficult to accurately detect and compare the corrosion state.

Therefore, in the eddy current flaw detection probe 1 of the second embodiment, the magnetism measuring element 8 (magnetic field measuring element) is provided on the center side of the A surface 4 of the magnetic core 2 facing the sound surface 3a of the inspection object W, or A correction coil 9 is provided in a winding shape on the peripheral edge of the A surface 4 of the magnetic core 2.
If the signal of the detection coil 7 is corrected using a magnetic field (monitoring magnetic field) monitored by such a magnetic measuring element 8 or the correction coil 9, the amount of corrosion at a plurality of locations can be measured with high accuracy.

The correction of the detection sensitivity using the eddy current flaw detection probe 1 of the second embodiment will be described in detail in the next third embodiment.
[Third Embodiment]
Next, the eddy current flaw detection probe 1 according to the third embodiment will be described with reference to the drawings. The eddy current flaw detection probe 1 according to the third embodiment uses the eddy current flaw detection probe 1 according to the second embodiment to reduce the thickness of the ground portion. At the time of detection, the magnetic flux density of the magnetic flux lines penetrating the A surface 4 at each of the plurality of measurement positions is monitored by the magnetic measuring element or the maximum electromotive force generated in the correction coil 9 to monitor the magnetic flux density or the maximum The fourth root of the relative ratio of the electromotive force variation is obtained, and the signal output from the detection coil 7 at the measurement position is divided by the obtained fourth root value, whereby the eddy current testing probe 1 and the object W to be inspected. The sensitivity error due to the variation in the gap is corrected.

  That is, if the degree of penetration of the pulse magnetic field into the inspection object W is monitored by the magnetic measuring element 8 or the correction coil 9 at the portion where the magnetic flux lines penetrate (A curved surface of the magnetic core 2), the signal V of the detection coil 7 can be obtained. It can correct | amend with the following formula | equation (3).

ε represents a distance that brings the core A surface of the probe as close as possible to the object.
The model shown in FIG. 1 is obtained by using the two-dimensional static magnetic field analysis to obtain the detection sensitivity η _(x) of the subsurface portion shown in FIG. 2 while changing the gap distance x in the graph on the left side of FIG. In addition, the results of testing various correction methods using the monitoring magnetic field Bn _(x) or the correction coil 9 signal Vn _(x) are shown in the graph on the right side of FIG. Here, the (minimum) gap ε used as a standard for standardization was assumed to be ε = 0.2 mm, which assumed pipe wall coating that was actually assumed to be inevitable.

As shown in the graph on the left side of FIG. 6, when the gap distance x (standardized distance x / w) is changed, the relative detection sensitivity (detection sensitivity η _(x) of the ground portion is reduced to the minimum gap ε ₍ Which is divided by the detection sensitivity η _(0.2) in FIG. 4) also deviates from “1.0”, and it can be seen that the detection sensitivity varies greatly depending on the gap.
Therefore, as shown in the graph on the right side of FIG. 6, correction was attempted using various correction equations. When the flaw detection signal of the detection coil 7 was divided by the fourth root of the relative magnetic flux density, x / It was found that correction can be made with good accuracy within the correctable range of w ≦ 0.5 (w = 10, x ≦ 5mm or less).

Therefore, even if the eddy current flaw detection probe 1 is swung around the axis of the inspection object W as shown in FIG. 5, if the eddy current flaw detection probe 1 of the third embodiment described above is used, It is possible to accurately measure the amount of corrosion at a plurality of locations while suppressing variation in the intensity of the flaw detection signal associated with the change in the distance between the A surface 4 of the magnetic core 2 and the sound surface 3a.
[Fourth Embodiment]
Next, the eddy current flaw detection probe 1 according to the fourth embodiment will be described with reference to the drawings.

  The geometric shape of the eddy current flaw detection probe 1 according to the fourth embodiment is generated in the inspection object W formed with a thickness T, and the detection coil 7 is applied to a corroded portion located at a depth D from the surface of the ground. In order to increase the S / N ratio of the signal detected by, the relationship of Expression (1) is satisfied.

The above-described equation (1) is the inspection object W formed with the thickness T, and the detection sensitivity is maximum for the corroded portion 11 at the subsurface portion located below the ground surface by the depth D. The geometrical shape of the magnetic core 2 of the eddy current flaw detection probe 1 is defined.
That is, the cross-sectional model of the two-dimensional static magnetic field analysis as shown in FIG. 7, that is, w ₁ (the length of the A surface 4 along the longitudinal direction of the columnar inspection object W), w ₂ (from the inspection object W). Length of the B surface 5 along the separating direction), h (distance from the ground to the lower end of the A surface 4 in a state where the B surface 5 is in contact with the ground), s (A surface 4 is the object to be inspected) B surface 5 from the surface of the object W to be inspected while being in contact with W
) (Distance from the end of the test object), D (depth from the ground surface to the corrosion spot 11), T (length of the test object W along the direction away from the test object W), etc. The detection sensitivity η of the depth D from the ground surface is obtained for the cross-sectional model. This detection sensitivity η can be expressed as the magnetic flux Φs (≈Bs · w ₂ ) penetrating the detection coil 7 divided by the magnetic flux line Φe (≈Be · D) penetrating the corroded portion of the depth D. .

Many of the above-described eddy current flaw detection probe 1 have various geometric dimensions (w ₁ , w ₂ , h, s), corrosion (representative) depth D, and inspection object W thickness T, which are dimensions of the inspection object W. When a two-dimensional static magnetic field analysis is performed on the model case and an approximate function 記述 す る describing the relationship of these dimensions with respect to the detection sensitivity η is obtained by regression analysis, the following equation (4) is obtained.

  FIG. 8A shows the correlation between the sensitivity obtained by the magnetic field analysis described above and the predicted value of the approximate function. Since the approximate function predicts the detection sensitivity well and the upper limit value is approximately in the vicinity of 1.5, the geometric shape of the eddy current flaw detection probe 1 can be defined by the equation (4 ') described later.

From the factors constituting the function of the equation (4 ′) (geometric dimensions of the eddy current flaw detection probe 1 and the inspection object W), the following qualitative design guidelines (1) to (5) can be listed for the optimum core shape. .
(1) “Depth D of corrosion spot 11 to be detected” and “Distance from the surface of the inspection object W to the end of the B surface 5 in a state where the A surface 4 is in contact with the inspection object W” ratio to "s"
D: s-1: 4.0
(2) “Distance s from the surface of the inspection object W to the end of the B surface 5 in a state where the A surface 4 is in contact with the inspection object W” and “the B surface 5 is in contact with the ground. With the distance from the ground to the lower end of the A surface 4 in the state "
s: h to 1: 5
(3) “Distance s from the surface of the inspection object W to the end of the B surface 5 in a state where the A surface 4 is in contact with the inspection object W” and “in a direction away from the inspection object W” The ratio with the length w ₂ of the B surface 5 along
_s: w 2 _~7: 7.3
(4) Ratio of “the length T of the inspection object W along the direction away from the inspection object W” and “the length w ₁ of the A surface 4 along the longitudinal direction of the columnar inspection object W”
T: w ₁ ˜1: 5.2
(5) Ratio of “cross-sectional area w ₁ ² of A surface 4” and “cross-sectional area w ₂ ² of B surface 5”
w ₁ ² : w ₂ ² to 10: 7
By defining the geometric shape of the eddy current flaw detection probe 1 in a shape that totally satisfies the design guidelines (1) to (5) described above, the corrosion that occurs in the inspection object W formed with a thickness T. The S / N ratio of the signal detected by the detection coil 7 can be increased with respect to a portion located at a depth D from the surface of the ground so that the sensitivity of the eddy current flaw detection probe 1 is best. Can be optimized design.

For example, FIG. 8B and FIG. 8C satisfy the relationship of the above-described formula (4 ′), and satisfy all the design indices of (1) to (5). That is, FIG. 8B corresponds to the level of the square mark in FIG. 8A, and FIG. 8C corresponds to the level of the circle mark in FIG. 8A.
In these eddy current flaw detection probes 1 of FIG. 8B and FIG. 8C, most of the magnetic flux lines that have entered the inside of the inspection object W from the A surface 4 pass through the corroded portion, and the corrosive state can be detected with high sensitivity. Recognize.

Next, a thinning detection method using the eddy current flaw detection probe 1 according to the fourth embodiment will be described with reference to the drawings.
The eddy current flaw detection probe 1 that satisfies the above-described equation (1) is designed so that the S / N ratio, that is, the detection sensitivity is increased at a position where the depth is D from the ground surface. A plurality of such eddy current flaw detection probes 1 are prepared by changing the depth D at which the detection sensitivity increases.

For example, in the eddy current flaw detection probe 1 shown on the left side of FIG. 9, w ₁ (length of the A surface 4 along the longitudinal direction of the columnar inspection object W) = 5.5 mm, w ₂ (separated from the inspection object W) Length of the B surface 5 along the direction to be) = 6.7 mm, h (distance from the ground to the lower end of the A surface 4 when the B surface 5 is in contact with the ground) = 5.1 mm, s ( The distance from the surface of the inspection object W to the end of the B surface 5 in the state where the A surface 4 is in contact with the inspection object W = 20.8 mm, D (depth from the ground surface to the corrosion point 11) ) = 35 mm, T (the length of the inspection object W along the direction away from the inspection object W) = 5 mm, which satisfies all the design indices (1) to (5) described above. .

9 and the eddy current flaw detection probe 1 shown on the right side of FIG. 9 are the same as those of the eddy current flaw detection probe 1 shown on the left side of FIG. Satisfies all 5) design indexes.
If a plurality of eddy current flaw detection probes 1 having different depths d at which the detection sensitivity is increased are used, distribution information in the depth direction of the corroded portion 11 is obtained, and whether further inspection such as ultrasonic diagnosis or confirmation of dug-up confirmation is necessary. Judgment (screening) becomes possible. However, it is unrealistic to accurately determine the corrosion depth distribution from only three to several signals, but it is necessary to determine whether or not to perform ultrasonic diagnosis and dug-up that require labor and cost ( The necessity of screening) is possible, so the benefits are great.

By the way, when the thinning detection method using the plurality of eddy current flaw detection probes 1 having different depths d described above is actually performed, the depth d becomes large (the detection sensitivity is maximized). A plurality of flaw detection signals [ΔV ₁ , ΔV ₂ , ΔV ₃ ] at the same measurement position are measured using a plurality of eddy current flaw detection probes 1 that are [d ₁ , d ₂ , d ₃ ].
Specifically, as shown in FIG. 10A, the above-described three eddy current flaw detection probes 1 are arranged at equal intervals in the circumferential direction with respect to the inspection object W having a circular cross section. Then, the three eddy current flaw detection probes 1 are simultaneously rotated, and flaw detection signals are continuously measured by the respective eddy current flaw detection probes 1. In this way, a plurality of flaw detection detection signals [ΔV ₁ , ΔV ₂ , ΔV ₃ ] can be detected continuously.

Further, a plurality of flaw detection detection signals [ΔV ₁ , ΔV ₂ , ΔV ₃ ] are obtained by alternately bringing the above-described three eddy current flaw detection probes 1 close to each other and facing the same measurement value with respect to the flat inspection object W. Is detected intermittently.
Using the plurality of flaw detection detection signals [ΔV ₁ , ΔV ₂ , ΔV ₃ ] measured in this manner, the amount of corrosion (thickness reduction) in the vicinity of the depth [d ₁ , d ₂ , d ₃ ] described above [ e ₁ , e ₂ , e ₃ ] is a determinant (2) of a linear combination of [ΔV ₁ , ΔV ₂ , ΔV ₃ ] with the inverse matrix [C] ⁻¹ of the response matrix [C] of each probe as a weight. And calculate the amount of thinning in the depth direction at the ground.

Specifically, as shown in FIG. 10B, based on the sensitivity center [d ₁ , d ₂ , d ₃ ] of each eddy current flaw detection probe 1, the depth direction is defined as depths d _{1/2 to} (d ₁ + d ₂ ) / 2 compartment, depth (d ₁ + d ₂ ) / 2 to (d ₂ + d ₃ ) / 2 compartment, depth (d ₂ + d ₃ ) / 2 to (d ₂ + d ₃ ) / 2 + d ₃ and divide into 3 sections, and the amount of corrosion (thickness reduction) of each section is [e ₁ , e ₂ , e ₃ ].
Assuming that changes in the flaw detection signals of the three eddy current flaw detection probes 1 with respect to the thickness reduction (difference of corrosion) are [ΔV ₁ , ΔV ₂ , ΔV ₃ ], [ΔV ₁ , ΔV ₂ , ΔV ₃ ] is It can be approximately expressed as a determinant of linear combination like the following formula (5).

The response coefficient [C _ij ] may be obtained by magnetic field analysis in the same manner as described above, or three tests in which three sections are recessed by grinding to simulate corrosion (thinning). The material may be obtained from the actual measurement under nine conditions for the three inspection objects W or measurement locations using the three eddy current flaw detection probes 1. If the inverse matrix [C] ⁻¹ of the 3 × 3 matrix [C _ij ] obtained in this way is obtained mathematically and used in the equation on the right side of the above equation (2), the same measurement position can be obtained. It is possible to estimate the thinning state of the three sections divided in the depth direction as [e ₁ , e ₂ , e ₃ ].

According to the thinning detection method using the eddy current flaw detection probe 1 described above, it becomes possible to detect the corrosion state of the ground portion of the inspection object W with high accuracy.
By the way, in the thinning detection method described above, by measuring the time from when the eddy current is formed to when the eddy current rapidly decreases, specifically, a sudden change portion of the slope of the attenuation curve of the detection coil 7 signal. Was measured to detect the amount of thinning of the ground part, that is, the state of thinning of the ground part. However, in this method of measuring the sudden change point of the slope of the attenuation curve, it is directly affected by the sensor distance change, etc., and the quantitative (reproducibility) is poor, and it is judged whether the eddy current is decreasing rapidly. Is often difficult in practice.

For example, in FIG. 11, when the magnetic flux lines that have penetrated (diffused) from the A surface 4 of the magnetic core 2 into the inspection object W begin to penetrate the corroded portion 11 at the ground, the detection coil 7 detects the magnetic flux line. The experimental results of the phenomenon that the magnetic field rapidly decays (dissipates) are shown.
11A shows the linear scale of the raw signal, FIG. 11B shows the logarithmic scale, and FIG. 11C shows the time transition of the attenuation constant λ (t) obtained thereby compared with the case without corrosion (broken line). Looking at the linear scale in FIG. 11A, all the results from “no thinning” to “2 mm thinning” overlap, and it is difficult to determine whether or not the eddy current is drastically reduced. In addition, even on the logarithmic scale shown in FIG. 11B, although it is better than FIG. 11A, it still remains difficult to determine whether the eddy current is rapidly decreasing.

  FIG. 11C shows the time transition of the eddy current attenuation constant λ (t) in comparison with the amount of thinning. The attenuation constant used in FIG. 11C is λ (t) ≡ (dI / dt) / I at an arbitrary time when the general attenuation curve is I (t) = Io · exp (−λt)). It is defined by (t). If the attenuation constant as shown in FIG. 11C is used, a clear difference can be seen in the attenuation constant according to the thinning amount, and it is possible to determine whether or not the eddy current is rapidly decreasing. Become.

That is, in the thinning detection method using the eddy current flaw detection probe 1 according to the present invention, the attenuation constant λ obtained from the flaw detection signal is used for the flaw detection signal measured using the eddy current flaw detection probe 1. You may make it estimate the thinning state of the ground part of the thing W. FIG.
Specifically, in an arbitrary time section of the attenuation curve obtained by measurement, the attenuation constant is calculated by polynomial regression, and the sudden change point can be obtained. Although the attenuation constant obtained in this way is slightly different from the actual corrosion thinning amount, it can be obtained by conducting a model test in advance and correlating with the actual corrosion thinning amount. By using the calibration curve, it is possible to accurately estimate the thinning amount of the sample.

  For example, as shown in FIG. 11D, at time (t = 0.8 msec), the difference between the decay constant with corrosion (the decay constant of the corrosion spot 11 to be inspected) and the decay constant without corrosion (reference signal) is FIG. 11D shows what kind of correlation the actual corrosion amount is. If the calibration curve as shown in FIG. 11D is acquired in advance, the actual thinning amount is accurately estimated by calibrating the value of the attenuation constant k calculated by polynomial regression using the calibration curve. be able to.

  Even if the same inspection object W is measured, the signal changes greatly as shown in FIG. 11E when the distance between the eddy current flaw detection probe 1 and the inspection object W changes. For example, flaw detection detection signal data is taken for a place where there is no thinning on the surface of the inspection object W, and the obtained flaw detection signal is used as a reference signal (reference). Then, the difference between the data of the flaw detection detection signal measured at the corrosion location 11 to be inspected and the reference signal is obtained.

In the case of a method that does not use the attenuation constant (rate) λ, this means obtaining the time difference at which the output is 3 V (Δt ₀ when the sensor distance is 0 in the figure). FIG. 11F shows a change in value depending on the sensor distance between the thinning amount obtained by this method and the thinning amount obtained by the method of obtaining the attenuation constant (rate) λ. Compared to this method, it can be seen that the method for obtaining the attenuation rate λ is less affected by changes in the sensor distance and can estimate the thinning amount with high accuracy.

As described above, by using the attenuation constant λ as the evaluation value instead of the time constant obtained from the threshold cross point of the absolute value of the attenuation curve, the influence due to the distance change between the inspection object W and the eddy current flaw detection probe 1 is reduced. Therefore, it is possible to quantify the degree of corrosion with high accuracy and reliability.
By the way, the reference signal described above is preferably obtained by the following two methods.

As shown in FIG. 12, the first method is to compare the reference signal when measurement is performed on the healthy part 3 with the flaw detection signal when measurement is performed on the ground part. When detecting the thinned state of the ground portion of W, the reference signal is obtained by lifting off the same eddy current flaw detection probe from the surface of the ground to the healthy portion 3 above.
In the second method, two identical eddy current flaw detection probes are prepared, and one eddy current flaw detection probe is installed away from the ground surface in order to obtain a reference signal for the healthy part 3 away from the ground surface. The other eddy current flaw detection probe is installed adjacent to the surface of the ground in order to obtain a signal for the ground part, and the ground signal of the object W to be inspected is obtained using a difference signal between the reference signal and the signal for the ground part. This is to detect a thinning state at the edge.

If these methods are used, the amount of thinning can be accurately estimated using the difference signal between the reference signal and the flaw detection signal.
In addition, in the above-described thinning detection method, the adaptive moving average method is used to obtain the value obtained by smoothing and removing the measurement noise from the measurement attenuation curve and the differential value at that time, which are necessary for obtaining the attenuation constant at an arbitrary time. It may be used.

Specifically, the Savitzky-Golay method, which is one of the adaptive moving average methods, is essentially a least-squares method of equally spaced discrete data, and the regression accuracy is equivalent to that, and weighted moving Compared to a simple moving average, a simple calculation algorithm called an average calculation has the advantage that a reduction in time resolution and distortion of the original signal can be suppressed and the processing time is short.
That is, if the Savitzky-Golay method is used, signal attenuation can be expressed as shown in Equation (6).

  When the coefficient of the column with the number of data “5” shown in Table 1 is used as the Savitzky-Golay coefficient, Expression (6) can be expressed as Expression (7).

Λ (t) ≡- (dI / dt) / I (t)
The attenuation constant can be obtained as a continuous function of time.

The coefficients in Table 1 can be obtained from the following formula.
In other words, for the weighting factor of the moving average (regression curve: 2-3 order polynomial), using the formula shown in Equation (8), and for the weight coefficient of the first derivative (regression curve: 3-4 order polynomial), The mathematical formula shown in Formula (9) is used.

Moreover, about Formula (8) and Formula (9), "A.Savitzky, MJEGolay" Smoothing and Differention of Data bye Simplified Least Squares Procedures, "Analytical Chemistry, vol.36, no.8, pp1627-1639,1964" And is known as official.
[Fifth Embodiment]
Next, the eddy current flaw detection probe 1 according to the fifth embodiment will be described with reference to the drawings.

  The eddy current flaw detection probe 1 according to the fifth embodiment detects a thinning state of a ground portion embedded in the ground foundation of the inspection object W with respect to the inspection object W of a tubular ferromagnetic metal material. An eddy current flaw detection probe that is close to the surface exposed to the ground of the inspection object W and parallel to the surface, and close to the surface of the ground foundation and on the surface of the ground foundation A T-shaped magnetic core 2 provided at three ends with a B surface 5 made parallel and a C surface 10 positioned above the A surface 4 and made parallel to the surface of the ground foundation; An excitation coil 6 wound around the A surface 4 of the magnetic core 2, a detection coil 71 wound around the B surface 5 of the magnetic core 2, and a winding near the C surface 10 of the magnetic core 2. The detection coil 72 is provided.

In the eddy current flaw detection probe 1 shown in FIG. 13A, the magnetic flux generated by the exciting coil 6 has a detection coil 71 (hereinafter referred to as the first detection coil 71) on the B surface 5 side and C if the inspection object W is in a uniform state. The magnetic flux changes generated in the two detection coils 71 and 72 even if the current (I) of the excitation coil 6 is changed because the detection coil 72 on the surface 10 side (hereinafter referred to as the second detection coil 72) is similarly affected. The voltage (inductive electromotive force) resulting from is the same (V1 = V2), and no voltage is generated between the coils.

  However, if there is corrosion thinning (the disappearance part of the ferromagnetic material) at the ground part, a difference occurs in the electromotive force between the first detection coil 71 and the second detection coil 72 (V1 ≠ V2). Using this difference, corrosion thinning can be detected with high sensitivity. In the metal material partially embedded, corrosion thinning occurs only at the ground part, and the corrosion thinning on the ground part is often slight, and the detection of corrosion thinning by the eddy current flaw detection probe 1 is effective.

  If the eddy current flaw detection probe 1 according to the fifth embodiment described above is used, the eddy current flaw detection probe 1 and the inspection object W are arranged by bringing the A surface 4 of the magnetic core 2 and the sound surface 3a of the inspection object W as close as possible. Are more strongly magnetically coupled, and the magnetic flux line excited by the exciting coil 6 current has a low magnetic resistance and easily penetrates the inspection object W. For this reason, the number of magnetic flux lines passing through the corroded portion 11 existing deep in the ground surface and returning to the B surface 5 of the magnetic core 2 increases, and the strength of the signal voltage induced in the detection coil 7 is also ensured. Is done. With this probe structure, the exciting coil 6, the first detection coil 7, and the second detection coil 7 are not close to each other, so that there is no structural interference and coils having suitable characteristics can be manufactured independently.

Moreover, since the differential (V2-V1) between the first detection coil 7 and the second detection coil 7 can be used as a detection signal, corrosion thinning can be quantitatively detected by a single measurement.
Further, as described above, the output when there is no corrosion thinning is V2-V1 = 0, and even when the thinning is small, the gain can be increased and the measurement can be performed with high sensitivity.
Using the reference signal for the upper healthy portion 3 of the eddy current flaw detection probe 1 installed close to the ground surface and the eddy current flaw detection probe 1 of the fifth embodiment described above, this signal for the lower buried corrosion portion is simultaneously measured. Thus, the degree of corrosion of the buried portion can be estimated with high sensitivity and efficiency from the difference. Further, even when the A surface 4 directed toward the inspection object of the eddy current flaw detection probe 1 cannot be brought close to by a corrosion-preventing coating or other coating material, the reference and this signal are differential under the same conditions. By performing the equation, the influence of the gap on the A surface 4 is canceled out, and highly reliable and accurate estimation is possible.

FIG. 13B is a modified example in the case where the vicinity of the ground of the inspection object W is protected by a covering material. Even in this case, since the eddy current flaw detection probe 1 of the present embodiment measures the sound part and the corrosion thinning part with the eddy current flaw detection probe 1 integrated, the eddy current flaw detection probe 1 and the object to be measured are detected depending on the presence or absence of a coating material for corrosion protection. Even if the distance varies, the distance from the object to be inspected W changes at the same time between the first detection coil 71 and the second detection coil 72. Therefore, as shown in FIGS. Non-uniformity (y1 ≠ y2) is not mistaken for corrosion. However, since the entire signal voltage is reduced when the A surface 4 is separated from the inspection object W, the quantitative value of the corrosion thinning amount is affected. In the case of quantitative evaluation, it is preferable to grasp the influence of the distance (y1) of the inspection object W from the A plane 4 in advance and apply an analysis method that is not affected.
[Modification 1 of Fifth Embodiment]
Next, modifications 1 and 2 of the eddy current flaw detection probe 1 according to the fifth embodiment will be described with reference to the drawings.

In the modification 1 of the eddy current flaw detection probe 1 of the fifth embodiment, a magnetic core 2 having a substantially L-shaped cross section is used, and an excitation coil is provided outside the detection coil 7 disposed on the B surface 5 side. 6 is arranged in a winding shape. Further, the correction coil 9 is provided in a winding shape at the peripheral portion of the end portion of the magnetic core 2 on the A surface 4 side.
The eddy current flaw detection probe 1 according to the first modification of the fifth embodiment is easy to manufacture, process, and assemble. That is, the magnetic core 2 formed of ceramic ferrite or the like needs to be processed by cutting and polishing, die pressing or cutting and polishing of an iron powder molded body, and a curved curved surface or the like cannot be processed freely. Generally difficult. However, if the eddy current flaw detection probe 1 is designed in an L shape surrounded by a right-angled plane as in the first modification, the magnetic core 2 can be easily processed, and the two detection coils 7 and the correction coil 9 are also internally arranged. Since a hollow and simple rectangular solenoid may be used, winding processing can be easily performed and assembly and disassembly can be easily performed.
[Modification 2 of Fifth Embodiment]
Next, an eddy current flaw detection probe 1 according to Modification 2 of the fifth embodiment will be described with reference to the drawings.

  In the eddy current flaw detection probe 1 of Modification 2 of the fifth embodiment, the magnetic core 2 has a notch portion having a parallelogram-shaped cross section from the intersection of the A surface 4 and the B surface 5 to the inside. The excitation coil 6, the detection coil 7, and the correction coil 9 are wound around the notch, and the following expression (2) is satisfied.

  That is, the eddy current flaw detection probe 1 according to the modified example 2 has the exciting coil 6, the detection coil 7, and the correction coil 9 wound in an oblique direction from the edge of the inspection object W toward the body portion of the magnetic core 2. By forming the notch for turning so that the cross-section has a parallelogram shape, the contact cross-sectional width w1 with the object W is made larger than the height h of the magnetic core 2 from the ground foundation, The cross-sectional width w2 facing the ground foundation is made larger than the distance from the surface of the inspection object W to the end near the B plane.

  If the eddy current flaw detection probe 1 according to the second modification is used, of the magnetic core 2 shape, the cross-sectional width with respect to the object W to be inspected: w1 and the cross-sectional width with respect to the ground foundation: w2 are effective as much as possible. The density can be increased, and a dense structure with the maximum cross-sectional area of three coils (excitation, detection, correction) can be obtained, and the specific sensitivity per unit volume of the eddy current flaw detection probe 1 can be maximized.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. In particular, in the embodiment disclosed this time, matters that are not explicitly disclosed, for example, operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that a person skilled in the art normally performs. Instead, values that can be easily assumed by those skilled in the art are employed.

DESCRIPTION OF SYMBOLS 1 Eddy current flaw detection probe 2 Magnetic body core 3 Healthy part 3a Healthy surface 4 A surface 5 B surface 6 Excitation coil 7 Detection coil 71 1st detection coil 72 2nd detection coil 8 Magnetic measuring element 9 Correction coil 10 C surface W Inspected object

Claims (13)

Compared to an object to be inspected that is solid or hollow and is made of a ferromagnetic metal material and whose base end is embedded in the ground, the reduction of the ground portion in the ground and adjacent to the surface of the ground An eddy current flaw detection probe for detecting a flesh condition,
Formed in a curved or bent shape when viewed from the side, an A surface facing the surface of a healthy portion of the object to be inspected away from the ground surface is formed on one end side in the longitudinal direction. On the end side, a magnetic core having a B surface facing the surface of the ground,
An exciting coil attached in a winding shape in the middle of the longitudinal direction of the magnetic core;
For the other end of the magnetic core, a detection coil attached to the periphery of the end in a winding shape,
An eddy current flaw detection probe for detecting a thinning state of a ground portion of an object to be inspected. An eddy current testing probe used to intermittently or continuously measure a plurality of locations of the healthy part,
The eddy current flaw detection probe is a magnetic measuring element on the center side of the A surface of the magnetic core facing the sound surface of the object to be inspected, or a correction coil wound around the peripheral portion of the A surface of the magnetic core, The eddy current flaw detection probe for detecting the thinning state of the ground portion of the inspection object according to claim 1, comprising: Thickness has occurred in the object to be formed, and for the corroded portion located at a depth from the surface of the ground,
The reduced thickness state of the ground portion of the object to be inspected according to claim 1 or 2, wherein the relationship of the expression (1) is satisfied in order to increase the S / N ratio of the signal detected by the detection coil. Eddy current flaw detection probe for detecting
A substantially T-shaped surface having an A surface facing the sound surface, a B surface facing the surface of the ground, and a C surface positioned above the A surface and parallel to the surface of the ground. A magnetic core;
An exciting coil wound around the A surface of the magnetic core;
A first detection coil wound around the B-side of the magnetic core;
A second detection coil wound on the C surface side of the magnetic core;
The eddy current flaw detection probe for detecting the thinning state of the ground portion of the inspection object according to any one of claims 1 to 3. As the magnetic core, one having a substantially L-shaped cross section is used.
The ground portion of the inspection object according to any one of claims 1 to 3, wherein the excitation coil is disposed in a wound shape outside the detection coil disposed on the B surface side. Eddy current flaw detection probe for detecting thinning conditions. In the magnetic core, a notch portion having a parallelogram-shaped cross section is formed from the intersection of the A surface and the B surface toward the inside,
The to-be-inspected according to any one of claims 1 to 3, wherein the excitation coil, the detection coil, and the correction coil are wound around the notch, and the following equation (2) is satisfied. An eddy current flaw detection probe for detecting the thinning state of the ground part of an object.
In detecting the thinning state of the ground part using the eddy current flaw detection probe according to any one of claims 1 to 6,
Monitoring the magnetic flux density of the magnetic flux lines penetrating the A-plane at each of the plurality of measurement positions, or the maximum electromotive force generated in the correction coil;
Find the fourth root of the relative ratio of the fluctuation of the magnetic flux density or the maximum electromotive force,
The sensitivity error due to the variation in the gap between the eddy current flaw detection probe and the object to be inspected is corrected by dividing the signal output from the detection coil at the measurement position by the calculated fourth root value. A thinning detection method using an eddy current flaw detection probe. Using a plurality of eddy current flaw detection probes designed to increase the S / N ratio at different depths d,
Measuring the flaw detection signal intermittently or continuously by facing each of the plurality of eddy current flaw detection probes to the measurement location on the surface of the inspection object,
The eddy current flaw detection probe according to claim 7, wherein a thinning state of the ground portion of the inspection object is detected by combining flaw detection detection signals at the same measurement position measured by each eddy current flaw detection probe. Thinning detection method using Using a plurality of eddy current flaw detection probes whose depths d at which the S / N ratio increases become [d ₁ , d ₂ , d ₃ ...], A plurality of flaw detection detection signals [ΔV at the same measurement position are used. ₁ , ΔV ₂ , ΔV ₃ ...]
Using the measured flaw detection signals [ΔV ₁ , ΔV ₂ , ΔV ₃ ...], The amount of corrosion (thickness reduction) at the depth [d ₁ , d ₂ , d ₃ . [E ₁ , e ₂ , e ₃ ...] Are weighted by the inverse matrix [C] ⁻¹ of the response matrix [C] of the plurality of eddy current flaw detection probes [ΔV ₁ , ΔV ₂ , ΔV _3. The eddy current flaw detection probe according to claim 7, wherein the thinning state of the ground portion of the inspection object W is detected using the linear combination formula. The thinning detection method used. For the flaw detection signal measured using the eddy current flaw detection probe according to claim 1,
A thinning detection method using an eddy current flaw detection probe, characterized in that a thinning state of a ground portion of an inspection object is estimated using an attenuation constant λ obtained from the flaw detection detection signal. Using the eddy current flaw detection probe according to any one of claims 1 to 6,
When detecting the thinning state of the ground part of the inspection object by comparing the reference signal when measuring the healthy part and the signal when measuring the ground part,
A thinning detection method using an eddy current flaw detection probe, wherein the reference signal is obtained by lifting off the same eddy current flaw detection probe from a ground surface to an upper healthy portion. Preparing two identical eddy current flaw detection probes according to any one of claims 1 to 6;
One eddy current flaw detection probe is placed away from the ground surface in order to obtain a reference signal for a healthy part away from the ground surface,
Install the other eddy current flaw detection probe adjacent to the surface of the ground in order to take a signal to the ground part,
A thinning detection method using an eddy current flaw detection probe, wherein a thinning state of a ground portion of an inspection object is detected using a difference signal between the reference signal and a signal for the ground portion. In the thinning detection method in any one of Claims 8-10,
An eddy current flaw detection probe characterized by using an adaptive moving average method to obtain a value obtained by smoothing measurement noise from a measurement attenuation curve and a differential value at that time, which are necessary for obtaining an attenuation constant at an arbitrary time. The thinning detection method used.