JP2002055083A - Eddy current flaw detection probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current flaw detection probe, capable of reducing generation of noise based on lift-off and capable of contributing to enhancement of detection accuracy. SOLUTION: The exciting coil 21 is constituted, so that the diameter thereof becomes 5 mm or larger, and the initial lift-off quantity thereof becomes 1.3 mm or more, to reduce an eddy current change ratio.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current inspection probe, and is particularly useful when applied to a nondestructive inspection of a conduit such as a heat transfer tube. 2. Description of the Related Art An eddy current flaw detection method is widely used for nondestructive inspection of a metal pipe made of a magnetic material such as a heat transfer tube, and various eddy current flaw detection probes for applying the method are used. Proposed. An example of the eddy current flaw detection probe is a self-induction system in which the excitation coil and the detection coil are the same, and a mutual induction system in which the excitation coil and the detection coil are configured by separate independent coils. Also, two types of detection methods, a self-comparison method and a standard comparison method, have been proposed. Here, the self-comparison method is a flaw detection method using a self-comparison type probe in which two coils having the same characteristics are integrally arranged side by side on the same plane. A current is generated, a detection signal, which is an output signal based on the eddy current, is obtained, and a predetermined flaw detection is performed by comparing the two detection signals. On the other hand, the standard comparison type eddy current flaw detection method is a flaw detection method using a standard comparison type probe in which two coils having the same characteristics are separated from each other. One coil and the other coil have different coatings. The only difference is that the measuring member is measured, and the flaw detection principle in the processing of the output signal of the coil and the like is exactly the same as that of the self-comparison method. Here, the member to be measured is a member to be subjected to the flaw detection, but the member to be measured is a standard member to be measured which is guaranteed not to have a flaw or the like, and the coil moves on the member to be measured. Without fixing, only the coil is moved on the member to be measured, and flaw detection of each part is performed. Accordingly, eddy current flaw detection probes are roughly classified into four types, that is, the number of combinations of the self-induction method or the mutual induction method and the self-comparison method or the standard comparison method. In any of the eddy current flaw detection probes described above, the detection signal is large when the lift-off, which is the distance between the eddy current flaw detection probe and the member to be measured, changes. Noise (noise) is included. In the eddy current inspection probe according to the related art, the deterioration of the S / N ratio due to the lift-off is dealt with by a trial and error approach, and there is no basic policy of designing and manufacturing the eddy current inspection probe. In view of the above prior art, an object of the present invention is to provide an eddy current flaw detection probe that can reduce the occurrence of noise due to lift-off and contribute to improvement in detection accuracy. [0006] The structure of the present invention to achieve the above object is based on the following findings. FIG. 1 shows the rate of change of the eddy current due to the lift-off variation obtained by calculation with various changes in the diameter (outer diameter) of the exciting coil. That is, assuming the positional relationship between the measured member 1 and the exciting coil 2 as shown in FIG.
The eddy current change rates when the lift-off amount changes by 0.1 mm and when the lift-off amount changes by 0.2 mm are analyzed by changing the diameter of the exciting coil 2. The frequency of the exciting current at this time was 400 kHz. Referring to FIG. 1, it can be seen that the larger the diameter of the exciting coil 2, the smaller the eddy current change rate, in other words, the less the effect of lift-off. FIG. 3 shows the change rate of the eddy current due to the lift-off variation obtained by calculation with various changes in the initial lift-off. That is, the measured member 1 and the exciting coil 2
2, the excitation coil 2 is moved by 0.1 mm for each initial lift-off to calculate the eddy current change rate. The diameter of the exciting coil at this time was 5 mm and 6 mm. Referring to FIG. 2, it can be seen that as the initial lift-off becomes larger, the eddy current change rate becomes smaller and the influence of the lift-off becomes less. From the eddy current change rate characteristics shown in FIGS. 1 and 3, it is understood that the diameter of the exciting coil and the initial lift-off are preferably as large as possible. The structure of the present invention based on such knowledge is as follows:
The features are as follows. 1) An eddy current is generated in a member to be measured by a coil supplying an exciting current, and the magnetic flux caused by the eddy current is changed by a flaw generated in the member to be measured. In the eddy current flaw detection probe for detecting a change, the coil diameter is 5 mm or more, and the initial lift-off amount is 1.3 mm or more. 2) In the eddy current flaw detection probe described in 1) above, the eddy current flaw detection probe is inserted into the inside of a tube to detect the inside of the tube, and has a coil diameter and an initial lift-off. The amount should be less than the diameter of the pipe. 3) An eddy current is generated in a member to be measured by an exciting coil for supplying an exciting current, and a magnetic flux caused by the eddy current is detected by a plurality of detection coils. In the eddy current flaw detection probe for detecting the change of the magnetic flux by utilizing the change due to the flaw generated in the member to be measured, the diameter of the coil is 5 m.
m or more and the initial lift-off amount is 1.3 mm or more. 4) In the eddy current flaw detection probe described in the above 3), the eddy current flaw detection probe is inserted into the inside of a tube to detect the inside of the tube, and has a coil diameter and an initial lift-off. The amount should be less than the diameter of the pipe. 5) In the eddy current inspection probe described in the above 3) or 4), the detection coil is constituted by four detection coils, and each of the detection coils has an axial direction with respect to the axial direction of the exciting coil. And are arranged around the excitation coil so as to be orthogonal to the excitation coil. 6) In the eddy current flaw detection probe described in 3) or 4) above, the detection coil is composed of two detection coils, and each of the detection coils has an axial direction with respect to the axial direction of the exciting coil. To be orthogonal to each other and penetrate the inside of the excitation coil. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 4 is an explanatory view conceptually showing the eddy current flaw detection probe according to the first embodiment. As shown in the figure, the eddy current flaw detection probe generates an eddy current in a member to be measured which is a magnetic material such as a metal by an excitation coil 11 for supplying an excitation current, and a magnetic flux caused by the eddy current is measured. The change of the magnetic flux is detected by utilizing the change due to the scratch generated on the member. The detection side is constituted by two detection coils 12, 13, and the detection coils 12, 1
3 is disposed such that each axis direction is orthogonal to the axial direction of the exciting coil 11 and penetrates through the inside of the exciting coil 11. In such an eddy current flaw detection probe, signal processing for obtaining a difference between output signals of the detection coils 12 and 13 is performed, thereby removing a signal (noise) caused by deformation of the measured member in a wide range. It is something to do. In the eddy current testing probe,
The exciting coil 11 has a diameter φ1 of 5 mm or more and an initial lift-off amount of 1.3 mm or more. The member to be inspected by such an eddy current inspection probe is not particularly limited as long as it is a magnetic substance. However, the member to be inspected is a conduit such as a heat transfer tube and the inner peripheral surface thereof is inspected for flaws. When performing, the diameter of the exciting coil 11 and the initial lift-off are restricted according to the diameter of the heat transfer tube. That is, the pipe diameter and the initial lift-off must be less than the pipe diameter. FIG. 5 is an explanatory view conceptually showing an eddy current flaw detection probe according to the second embodiment. As shown in the figure, the eddy current flaw detection probe has the detection coils 12 and 13 of the eddy current flaw detection probe shown in FIG. In this case, the detection coils 22 to 25 are arranged such that the respective axial directions are orthogonal to the axial direction of the exciting coil 21 and the exciting coils 2 to 25 are symmetrical with respect to the exciting coil 21.
It is arranged around 1. In the eddy current inspection probe according to the present embodiment, signal processing is performed so as to obtain a difference between the sum of the detection signals of the detection coils 22 and 24 and the sum of the detection signals of the detection coils 23 and 25. Thus, similarly to the eddy current flaw detection probe shown in FIG. 4, it is possible to remove a signal (noise) caused by deformation of the member to be measured in a wide range. In the eddy current testing probe,
The exciting coil 21 is also configured such that its diameter φ2 is 5 mm or more and the initial lift-off amount is 1.3 mm or more. The member to be inspected by the eddy current inspection probe is not particularly limited as long as it is a magnetic material. However, the member to be inspected is a conduit such as a heat transfer tube, and the inner surface of the member is inspected for flaws. When performing, the diameter of the exciting coil 11 and the initial lift-off are restricted according to the diameter of the heat transfer tube. That is, the pipe diameter and the initial lift-off must be less than the pipe diameter. The eddy current flaw detection probe according to the present invention need not be limited to the eddy current flaw detection probe shown in FIGS. Generally, the diameter of the exciting coil is 5 mm
As described above, if the initial lift-off amount is configured to be 1.3 mm or more, the eddy current change rate becomes sufficiently small, and the influence of the lift-off can be reduced as much as possible. In this case, when the member to be measured is a pipe, both the diameter of the coil and the initial lift-off amount must be smaller than the pipe diameter of the pipe. As described in detail with the above embodiments, the invention according to claim 1 generates an eddy current in a member to be measured by a coil for supplying an exciting current, and the eddy current In the eddy current flaw detection probe for detecting the change of the magnetic flux by utilizing the fact that the magnetic flux caused by the flaw changes due to the flaw generated on the member to be measured, the diameter of the coil is 5 mm or more, and the initial lift-off amount is Since it is configured to be 1.3 mm or more, the eddy current change rate becomes sufficiently small. As a result, according to the present invention, the effect of lift-off can be reduced as much as possible, and the S / N ratio can be improved accordingly. According to a second aspect of the present invention, in the eddy current flaw detection probe according to the first aspect, the eddy current flaw detection probe is inserted into the inside of the pipe to detect the inside of the pipe. In addition, since both the diameter of the coil and the initial lift-off amount are smaller than the diameter of the tube, the same flaw detection as in the invention described in [Claim 1] can be performed by inserting the coil into the tube. As a result, according to the present invention, the influence of lift-off can be reduced as much as possible in flaw detection of a pipeline, and the S / N ratio can be improved accordingly. According to a third aspect of the present invention, an eddy current is generated in a member to be measured by an exciting coil for supplying an exciting current, and a magnetic flux caused by the eddy current is detected by a plurality of detecting coils. In the eddy current flaw detection probe for detecting a change in magnetic flux caused by an eddy current due to a change in the magnetic flux caused by a flaw generated in the member to be measured, the diameter of the coil is 5 mm or more, and Since the initial lift-off amount is configured to be equal to or more than 1.3 mm, it is possible to sufficiently reduce the eddy current change rate in the eddy current flaw detection probe having a plurality of detection coils and reducing noise due to fluctuation of a member to be measured. it can. As a result, according to the present invention, the influence of the lift-off can be reduced as much as possible while having the plurality of detection coils to reduce the noise due to the fluctuation of the member to be measured. Can be improved. According to a fourth aspect of the present invention, in the eddy current flaw detection probe according to the third aspect, the eddy current flaw detection probe is inserted into the inside of the pipe to detect the inside of the pipe. In addition, since both the diameter of the coil and the initial lift-off amount are smaller than the diameter of the pipe, the same flaw detection as the invention described in claim 3 can be performed by inserting the coil into the pipe. As a result, according to the invention of the present application, the S / N ratio at the time of flaw detection can be improved also in the flaw detection of a pipeline, similarly to the invention described in [Claim 3]. According to a fifth aspect of the present invention, in the eddy current flaw detection probe according to the third or fourth aspect, the detection coil comprises four detection coils. Since each of the axial directions is orthogonal to the axial direction of the exciting coil and is disposed around the exciting coil so as to be symmetric with respect to the exciting coil, the member to be measured having four detection coils In the eddy current flaw detection probe in which the noise due to the fluctuation of the eddy current is reduced, the eddy current change rate can be made sufficiently small. As a result, according to the present invention, the influence of the lift-off can be reduced as much as possible while having the four detection coils to reduce the noise due to the fluctuation of the member to be measured. The ratio can be improved. According to a sixth aspect of the present invention, in the eddy current flaw detection probe according to the third or fourth aspect, the detection coil comprises two detection coils. Since each axis direction is arranged so as to be orthogonal to the axis direction of the excitation coil and penetrate the inside of the excitation coil, it has two detection coils to reduce noise due to fluctuation of the member to be measured. In the eddy current flaw detection probe described above, the eddy current change rate can be made sufficiently small. As a result, according to the present invention, the influence of the lift-off can be reduced as much as possible after having the two detection coils to reduce the noise due to the fluctuation of the member to be measured, and the S / N is accordingly reduced. The ratio can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a characteristic diagram in which a change rate of an eddy current due to a lift-off variation is calculated by variously changing the diameter (outer diameter) of an exciting coil. FIG. 2 is an explanatory diagram conceptually showing a positional relationship between a member to be measured and an exciting coil assumed for obtaining the characteristic diagrams shown in FIGS. 1 and 3. FIG. 3 is a characteristic diagram in which a change rate of an eddy current due to a lift-off variation is calculated by variously changing an initial lift-off. FIG. 4 is an explanatory view conceptually showing an eddy current inspection probe according to the first embodiment of the present invention. FIG. 5 is an explanatory view conceptually showing an eddy current flaw detection probe according to a second embodiment of the present invention. [Explanation of Signs] 11 Excitation coils 12, 13 Detection coil 21 Excitation coils 22, 23, 24, 25 Detection coil

Claims (1)

Claims 1. An eddy current is generated in a member to be measured by a coil supplying an exciting current, and a magnetic flux caused by the eddy current is changed by a flaw generated in the member to be measured. An eddy current flaw detection probe for detecting a change in magnetic flux by utilizing the eddy current flaw detection probe, wherein a coil diameter is 5 mm or more and an initial lift-off amount is 1.3 mm or more. . 2. The eddy current flaw detection probe according to claim 1, wherein the eddy current flaw detection probe is inserted into the inside of a tube to detect the inside of the tube, and has a coil diameter and a diameter. An eddy current flaw detection probe, wherein the initial lift-off amount is less than the diameter of the tube. 3. An eddy current is generated in a member to be measured by an exciting coil for supplying an exciting current, and a magnetic flux caused by the eddy current is detected by a plurality of detection coils. In an eddy current flaw detection probe for detecting a change in magnetic flux by utilizing a change caused by a flaw generated in a member to be measured, a coil diameter is 5 mm or more, and an initial lift-off amount is 1.3 mm or more. An eddy current flaw detection probe characterized in that it is configured so as to be formed as follows. 4. The eddy current flaw detection probe according to claim 3, wherein the eddy current flaw detection probe is inserted into the inside of a tube to detect the inside of the tube, and has a coil diameter and An eddy current flaw detection probe, wherein the initial lift-off amount is less than the diameter of the tube. 5. The eddy current inspection probe according to claim 3 or 4, wherein the detection coil comprises four detection coils, and each of the detection coils has an excitation coil in each of the axial directions. An eddy current flaw detection probe characterized by being disposed around an exciting coil so as to be orthogonal to the axial direction of the exciting coil and to be symmetric with respect to the exciting coil. 6. The eddy current flaw detection probe according to claim 3 or 4, wherein the detection coil comprises two detection coils, and each of the detection coils has an excitation coil in each axial direction. An eddy current flaw detection probe, which is disposed so as to be orthogonal to the axial direction of the probe and penetrate the inside of the exciting coil.