JP2004286658A - Non-destructive inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-destructive inspection apparatus for solving the problem of safety and experience, without the risk of an inspector suffering suffocation or low-temperature burn by a coolant, and for detecting defects in the depths, even with respect to high-resistivity materials. <P>SOLUTION: The non-destructive inspection apparatus, using a SQUID device, comprises a coil for applying an AC magnetic field to a sample from the outside, a magnetic flux density multiplication means for multiplying magnetic flux density generated in the coil for applying it to the inside of the sample, and a refrigerator which operates electrically for cooling the SQUID device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nondestructive inspection device using a SQUID element.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, X-ray inspection, ultrasonic inspection, and SQUID nondestructive inspection are known as methods used as nondestructive inspection.
In the X-ray inspection, internal two-dimensional or three-dimensional visual information can be obtained. This method can be applied to a thick plate of several tens of mm when targeting a metal. However, a light element material such as carbon has a disadvantage that the contrast is lowered and cannot be used. In addition, there are problems that the inspector is exposed to the radiation and that a film must be attached to the back of the sample.
[0003]
Further, the ultrasonic inspection has an advantage that a deep defect can be detected, a non-contact inspection can be performed, and when a metal is targeted, it can be applied to a tens of mm thick plate. However, this method has a large internal attenuation and cannot be used for practical use due to the reflection of ultrasonic waves at the interface of the laminated structure. Non-contact inspection is not possible due to the need for media such as water to transmit ultrasonic waves There is a problem.
[0004]
The SQUID nondestructive inspection has an advantage that it can detect a defect in a deep part and can perform a noncontact inspection, and when it is applied to a metal, it can be applied to a thick plate of several tens of mm. However, this method cannot be applied to high-resistance materials such as carbon due to the difficulty of generating eddy currents, and there is a risk that the inspector may be suffocated by the coolant or burned at low temperatures. There is a problem that knowledge and proficiency are required to avoid it.
[0005]
The SQUID nondestructive inspection is a non-contact eddy current flaw detection method, and has an advantage that the inspection speed can be secured to scan a wide area in the nondestructive inspection of a large structure. In order for the induction coil used in this test to obtain sufficient sensitivity, a frequency magnetic field of 10 kHz to 100 kHz or more is usually used. For this reason, when applied to a metal material, there is a problem that only a defect having a depth of 1 mm or less near the surface can be inspected due to a skin effect.
[0006]
On the other hand, in various fields such as the construction and aerospace fields, the use of carbon fiber composite materials such as CFRP and C / C has been increasing in recent years. Laminated structures are often used in these composite materials, but such structures have been shown to be vulnerable to impact, and internal defects can occur even at low speed and low energy impact. There is a problem that it is easy. From this point, a non-contact inspection is strongly desired. However, these composite materials have an electrical resistivity about one to three orders of magnitude higher than that of a metal material. Therefore, it is more difficult to generate a sufficient amount of eddy current for detecting a defect in the eddy current flaw detection method using a normal induction coil than in a metal material. Since a material having a higher electrical resistivity has a smaller current attenuation in the depth direction due to the skin effect, it is possible to increase an eddy current by using a higher-frequency induced magnetic field. Assuming an electric resistivity of 10 ⁻⁵ [Ωm] as the conductivity, and when a 1 MHz induction magnetic field is applied to this material, the penetration depth of the current is about 6 mm. As described above, a defect detection method for a defect in a metal material and a composite material, particularly, a deep defect inspection method exceeding 10 mm has not been established.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of such problems of the related art, and there is no danger that an inspector suffers suffocation or low-temperature burn due to a coolant, and can solve the problems of safety and mastery. An object of the present invention is to provide a non-destructive inspection device capable of detecting a deep defect even in a high resistivity material.
[0008]
[Means for Solving the Problems]
According to the present invention, the above-mentioned problem is solved by the following technical means.
(1) In a nondestructive inspection device using a SQUID element, a coil for applying an alternating magnetic field to a sample from outside, a magnetic flux density multiplying means for multiplying a magnetic flux density generated by the coil and applying the same to the inside of the sample, A nondestructive inspection device comprising: a refrigerator that is electrically operated to cool the SQUID element.
(2) The nondestructive inspection apparatus according to (1), wherein the magnetic flux density multiplying means is made of a material having high magnetic permeability.
(3) The non-destructive inspection device according to (2), wherein a U-shaped ferrite is used as the high magnetic permeability material.
(4) The nondestructive inspection device according to any one of (1) to (3), wherein the refrigerator is a pulse tube refrigerator.
(5) The refrigerator performs a pulse tube refrigerator main body, a detachable cryostat that keeps a cooling unit at a vacuum, a valve switching motor separated from the refrigerator main body, and carries cooling gas and gas cooling. The nondestructive inspection device according to the above (4), comprising a compressor.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the nondestructive inspection device of the present invention will be described in detail.
A nondestructive inspection apparatus according to the present invention is a nondestructive inspection apparatus using a SQUID element, wherein a coil for applying an external AC magnetic field to a sample and a magnetic flux applied to the inside of the sample by multiplying the magnetic flux density generated by the coil It is characterized by comprising a density multiplying means and a refrigerator electrically operated for cooling the SQUID element.
[0010]
The nondestructive inspection device of the present invention utilizes an eddy current induction system using an electromagnet in which a ferrite core and an induction coil are combined. In a nondestructive inspection using a general SQUID element, an AC magnetic field is generated from an induction coil, and this magnetic flux is linked to a conductive sample to induce an eddy current inside the inspection object. The turbulence of the eddy current due to the defect is detected by a SQUID element as a defect signal due to magnetism. In the present invention, an induction coil is used in combination with a ferrite core. As a result, a strong magnetic field is externally applied to the object to be measured, and a deep defect in the object to be measured made of a high-resistance material can be detected.
[0011]
When using eddy currents in nondestructive inspection using SQUIDs, generally, the magnetic flux of the induced magnetic field is directly linked to the SQUID element, and the magnetic flux due to the eddy current generated in a defect-free part is linked to the SQUID. As a result, the wide dynamic range of the SQUID element cannot be utilized, and when the amount of magnetic flux exceeds the dynamic range, the FLL circuit does not operate normally and a problem may occur that measurement becomes impossible. On the other hand, in one embodiment of the present invention, a SQUID gradiometer that detects a difference between magnetic fluxes linked to the two pickup coils is used, and the total amount of magnetic flux linked to the two pickup coils is zero. , The output of the SQUID gradiometer becomes zero even when an electromagnet that generates a magnetic field exists near the SQUID gradiometer, and the induction magnetic field is made insensitive to the SQUID. Further, by employing the U-shaped ferrite core, the magnetic flux due to the eddy current generated in the portion having no defect is made insensitive to the SQUID gradiometer. Only when the eddy current distribution is disturbed by a defect, the symmetry of the current is broken, and a non-destructive inspection is performed by detecting a defect signal of the defect.
[0012]
In the present invention, the frequency of the AC magnetic field applied to the measurement object is 1 Hz to several kHz, and the magnetic flux density applied to the measurement object is several to several tens mT. When the magnetic field frequency and the magnetic flux density are in such ranges, it is possible to detect a deep defect of the measurement target.
[0013]
In addition, the SQUID element must be cooled for the SQUID nondestructive inspection system that can be used in the field. In the present invention, the cooling is performed using a small pulse tube refrigerator. The superconducting critical temperature Tc of the HTS-SQUID used for the sensor of the nondestructive inspection is about 90K even in the case of high quality, and it is necessary to cool the temperature to 80K or less in order to use it with sufficient characteristics. For this reason, conventionally, liquid nitrogen or the like has been used. However, handling refrigerants such as liquid nitrogen requires avoiding dangers such as suffocation and frostbite, and requires knowledge and proficiency in handling them. In addition, a small and easy-to-handle SQUID cooling means is required for detecting a defect in a large structure. Therefore, in the present invention, a small-sized pulse tube refrigerator having a structure in which the magnetic motor is separated from the cooling unit and having low vibration compared to other refrigerators is used.
[0014]
FIG. 1 shows a schematic configuration of a pulse tube refrigerator used in the present invention. This pulse tube refrigerator has a pulse tube refrigerator main body, a removable cryostat (low-temperature vacuum vessel) for keeping a cooling unit (cold head) at a vacuum, a valve switching motor separated from the main body, and a cooling gas. It consists of a compressor that transports gas helium and cools gas. Such a pulse tube refrigerator has high temperature stability by reducing magnetic noise derived from the refrigerator, vibration of the refrigerator, and magnetic noise from the compressor and the motor as much as possible. The temperature at which the refrigerator reaches the cooling section is 55K. In the present invention, a mechanism in which the cooling unit and the sample stage are separated and connected by a copper wire is used, thereby keeping the SQUID element away from the magnetic noise source, reducing the influence of vibration, and ensuring the temperature stability of the SQUID element. . In order to further reduce the influence of the vibration, a coaxial pulse tube refrigerator having a small vibration of the gas pipe is used.
[0015]
【Example】
Hereinafter, the present invention will be described in detail based on examples.
(Example 1)
FIG. 2 is a view schematically showing a schematic configuration of the nondestructive inspection apparatus according to the first embodiment of the present invention, in which a SQUID element, a refrigerator for cooling the SQUID element, and a U having an induction coil wound thereon. It consists of a letter-shaped ferrite core. In such a configuration, the non-destructive inspection apparatus is installed on a measurement object (sample), and an alternating current is applied to an induction coil wound around a ferrite core to generate an alternating-current induction magnetic field from an end surface of the ferrite core. This induction magnetic field is applied to the measurement object of the ferrite core to induce an eddy current in the measurement object. If the measurement object has no defects, the SQUID element is insensitive. If the measurement object has a defect, the defect disturbs the flow of the eddy current, and the defect is detected by the SQUID element cooled by the refrigerator.
According to such a configuration, it is possible to detect a deep defect of a high electrical resistance material such as carbon, and it is possible to perform a non-destructive inspection extremely safely without an inspector being exposed to a danger of suffocation or low-temperature burn due to a coolant. It can be carried out.
[0016]
(Example 2)
FIG. 3 is a view schematically showing a schematic configuration of a nondestructive inspection apparatus according to a second embodiment of the present invention, in which two U-shaped ferrite cores are used. An AC current is applied to an induction coil wound around a ferrite core disposed on both sides of the refrigerator to generate an AC induction magnetic field from an end surface of the ferrite core. This induction magnetic field is applied to the measurement object of the ferrite core to induce an eddy current in the measurement object. If the measurement object has no defects, the SQUID element is insensitive. If the measurement object has a defect, the defect disturbs the flow of the eddy current, which is detected by the SQUID element cooled by the refrigerator.
According to such a configuration, as in the first embodiment, it is possible to detect a deep defect of a high electrical resistance material such as carbon, and the inspector does not suffer from the danger of suffocation or low-temperature burn due to the coolant. In this way, nondestructive inspection can be performed extremely safely.
[0017]
(Example 3)
FIG. 4 is a diagram schematically illustrating a schematic configuration of a nondestructive inspection apparatus according to a third embodiment of the present invention, in which inspection is performed on a pipe-shaped measurement target such as a water pipe or a gas pipe. is there. This non-destructive inspection device is installed so that the object to be measured (sample) is sandwiched between both end surfaces of the ferrite core. An AC current is applied to the induction coil wound around the ferrite core, and an AC induction magnetic field is generated from the ferrite core end surface. Let it. This induction magnetic field is applied to the measurement object of the ferrite core to induce an eddy current in the measurement object. If the measurement object has no defects, the SQUID element is insensitive. If the measurement object has a defect, the defect disturbs the flow of the eddy current, which is detected by the SQUID element cooled by the refrigerator.
According to such a configuration, it is possible to detect a deep defect of the tubular high electric resistance material, and the inspector does not suffer from the risk of suffocation or low-temperature burn due to the coolant, and performs the nondestructive inspection extremely safely. be able to.
[0018]
【The invention's effect】
As described above in detail, according to the present invention, since the above configuration is employed, there is no danger that the inspector suffers suffocation or low-temperature burn due to the coolant, and safety and mastery problems can be solved. It is possible to provide a nondestructive inspection device capable of detecting a deep defect even with a high resistivity material.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a cooler used in a nondestructive inspection device of the present invention.
FIG. 2 is a view showing a schematic configuration of a nondestructive inspection apparatus according to a first embodiment of the present invention.
FIG. 3 is a diagram showing a schematic configuration of a nondestructive inspection apparatus according to a second embodiment of the present invention.
FIG. 4 is a diagram showing a schematic configuration of a nondestructive inspection apparatus according to a third embodiment of the present invention.

Claims (5)

In a nondestructive inspection apparatus using a SQUID element, a coil for applying an AC magnetic field to a sample from the outside, a magnetic flux density multiplying means for multiplying a magnetic flux density generated by the coil and applying the same to the inside of the sample, A non-destructive inspection device, comprising: a refrigerator that is electrically operated for cooling. The non-destructive inspection device according to claim 1, wherein the magnetic flux density multiplying means is made of a material having a high magnetic permeability. The non-destructive inspection apparatus according to claim 2, wherein a U-shaped ferrite is used as the high magnetic permeability material. The said refrigerator is a pulse tube refrigerator, The non-destructive inspection apparatus in any one of Claims 1-3 characterized by the above-mentioned. The refrigerator includes a pulse tube refrigerator main body, a detachable cryostat that keeps a cooling unit at a vacuum, a valve switching motor separated from the refrigerator main body, and a compressor that carries a cooling gas and performs gas cooling. The nondestructive inspection device according to claim 4, wherein:

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