JPH11352109A - Device and method for inspecting eddy current - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current inspection device which has a simple structure and can eliminate an error in magnetic field measurement caused by temperature drift in a detection part. SOLUTION: A heater 32 is turned on beforehand to raise the temperature of a probe holder 3, and is set so as to keep the temperature, for example, at 50 deg.C. After the temperature of the probe holder 3 becomes constant, a current is supplied to a probe detection part 2 and a steel pipe T is carried to start the measurement of a decarbonized layer. The magnetic field measurement error of the probe detection part 2 can be eliminated, as the temperature drift in the probe detection part 2 is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current inspection apparatus and method for inspecting a surface layer of a magnetic material, such as a decarbonized area and a surface flaw, by an electromagnetic induction method. The present invention relates to an apparatus and an inspection method.

[0002]

2. Description of the Related Art A decarburized layer having a reduced carbon concentration may be formed on a surface layer of a steel material heat-treated at a high temperature. Since the decarburized layer locally has a small amount of carbon, the strength is lower than the surrounding structure, and a steel material formed up to a region where the decarburized layer is deep cannot be used as a member requiring strength. Therefore, it is important to detect the presence and depth of the decarburized layer on the surface layer of the steel material, and a means for such detection is strongly desired.

[0003] As a method of measuring the depth of the decarburized layer, generally, first, a part of a steel material is cut out, and a cross section of a surface layer portion of the cut part is taken with a micrograph. An inspector visually determines the depth of the decarburized layer based on this photograph. However, since this method is a destructive inspection, it is impossible to inspect the entire length of the steel material, and it takes several days to complete the determination.

As another method, there is a method of non-destructively detecting a decarburized layer using an eddy current inspection device. The eddy current inspection device detects a change in the impedance output of the coil by using an electromagnetic induction phenomenon, and inspects a state of a steel material surface layer based on a detection result. For example, when detecting a flaw on the surface of a steel material, a coil into which a probe is inserted as a detection unit,
That is, two probe coils are used, and when a change occurs in one of the impedance outputs, the difference between the two outputs is detected, and the presence or absence of a flaw is determined from the detection result. Further, in such an eddy current inspection apparatus, when current is supplied to the coil, the probe generates heat, and the temperature of the detection unit fluctuates (temperature drift). Although this temperature drift affects the impedance output, both coils are equally affected,
With respect to these output differences, the effects of temperature drift cancel each other out. If a decarburized layer is detected using this device, it can be inspected over the entire length of the steel material. However, the difference between the impedance outputs of the two coils does not produce a detection difference when the decarburized layer is present uniformly on the surface of the steel material, and there is a problem that the detection result cannot be obtained according to the depth of the decarburized layer. Was.

[0005]

SUMMARY OF THE INVENTION Accordingly, the applicant of the present application
An eddy current inspection device has been proposed which detects the depth of a decarburized layer by a self-comparison method using one coil (Japanese Patent Laid-Open No. 2-24).
No. 7556). With this method, the depth of the decarburized layer of the steel material can be detected. However, as mentioned above,
In the method using the impedance output difference between the two coils, the influence of the temperature drift of the detection unit is not affected. However, when the output of one coil is used, the temperature change of the detection unit greatly affects the impedance output. In particular, when a decarburized layer is detected using a high-sensitivity output, there is a problem that this effect cannot be ignored.

In order to correct the error of the detection result due to such a temperature drift, the present applicant has disclosed Japanese Patent Application Laid-Open No. 5-332810.
In Japanese Patent Laid-Open Publication No. H11-264, an eddy current inspection device capable of maintaining a constant temperature of an eddy current sensor used for a level gauge has been proposed. In this apparatus, the temperature of the sensor section is maintained at a predetermined temperature during casting before casting, and the temperature of the coil of the sensor section is measured while cooling the sensor section at the start of casting. The measured value of the level gauge is corrected according to the measured coil temperature. Thereby, the error of the detection result due to the temperature drift is corrected.

However, since the steel material to be detected is not heated when the decarburized layer is detected, the detection result of the decarburized layer needs to be corrected only for the temperature drift of the detecting section caused by the current supplied to the coil. Therefore, the above-mentioned Japanese Patent Application Laid-Open No. 5-33
In the case of using the eddy current inspection device for a level gauge proposed in Japanese Patent Publication No. 2810, there is a problem that a portion of the steel material that is not necessary for detection of a surface layer portion is included and the configuration is large.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an eddy current inspection apparatus which can eliminate a detection signal error due to a temperature drift with a simple configuration.

[0009]

According to a first aspect of the present invention, there is provided an eddy current inspection apparatus, wherein a detector supported by a holder measures a magnetic field near a predetermined region of a magnetic material while magnetizing the predetermined region. In the eddy current inspection device for inspecting a surface portion of a magnetic material, the holder is provided with a heater, and includes a control unit that supplies power to the heater to control the temperature of the heater.

[0010] In the first aspect, since the detection section is heated by the heater provided in the holder, temperature drift of the detection section due to self-heating can be prevented.

According to a second aspect of the present invention, in the eddy current inspection apparatus according to the first aspect, the detection unit includes a probe coil for magnetizing the magnetic material, and the holder includes a through hole into which the detection unit is to be inserted. And the heater is embedded in a peripheral wall of the through hole.

According to the second aspect of the present invention, since the heater is disposed around the detecting section, it is easy to maintain the temperature of the detecting section constant.

An eddy current inspection apparatus according to a third invention is characterized in that, in the second invention, the heater is provided with a heating wire so that a current flows substantially parallel to an axial direction of the probe coil.

When a current flows through the probe coil,
Magnetic flux in the probe axis direction is generated near the coil. Therefore, when the heater is arranged concentrically with the probe coil, a magnetic flux in the same direction as the magnetic flux for magnetizing the magnetic material is generated near the heater, which may affect the magnetization of the magnetic material. According to the third aspect, a current flows through the heater substantially in parallel with the axial direction of the probe coil.
It does not affect the magnetic flux generated in the probe coil.

An eddy current inspection method according to a fourth aspect of the present invention is the eddy current inspection method for inspecting a surface portion of the magnetic material by measuring a magnetic field in the vicinity of the predetermined region while magnetizing a predetermined region of the magnetic material. The method further includes a step of heating the detection unit to a predetermined temperature by a heater in advance, and a step of performing measurement by the detection unit while maintaining the temperature of the detection unit constant.

According to the fourth aspect of the present invention, before the detection of the surface portion of the magnetic material, the heater is heated to maintain the temperature constant by the heater. Errors can be eliminated.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic configuration diagram showing a main configuration of an eddy current inspection device according to the present invention. As shown in the figure, a probe detection unit 2 is arranged in a position corresponding to the surface layer of a steel pipe T to be detected placed flat, in a non-contact or in contact manner. The probe detector 2 is supported in a probe holder 3 having a substantially rectangular parallelepiped shape. When the steel tube T is transported, the guide wheel 33 provided in the probe holder 3 rotates and moves parallel on the steel tube T at a predetermined distance. The probe detecting unit 2 is supplied with an alternating current by the decarburized layer detection control unit 4 to magnetize the steel pipe T, detects a leakage magnetic field near the probe detector 2 of the steel pipe T, and converts the detection signal to a decarbonized layer detection control unit. 4 is output. Further, the probe holder 3 has a heater as described later, and the temperature is controlled by the temperature control unit 5.

FIG. 2 is a schematic block diagram showing the configuration of the probe detection section 2 and the decarburized layer detection control section 4, in which the probe holder 3 is omitted. Probe detector 2
Is an iron core 21, an exciting coil 2 wound around the iron core 21.
2. It comprises a magnetic field detector 23 and a thermocouple 24 provided at the tip of the iron core 21. The coil 22 is a probe coil wound around the axis of the iron core 21. The magnetic field detector 23 includes a detection element (coil) that detects the strength of the magnetic field in a direction substantially parallel to the surface of the steel pipe T and a direction substantially perpendicular to the surface of the steel pipe T. A thermocouple is attached to the iron core 21, and measures the temperature of the probe detector 2.

The decarburized layer detection control section 4 includes a first power supply section 41 for supplying an alternating current to the coil 22, a second power supply section 42 for supplying power to the magnetic field detector 23, and a detection signal from the magnetic field detector 23. A detection waveform display unit 42 and a decarburized layer depth detection unit 44 to be input are provided. Further, the temperature control unit 5 includes a temperature detection unit 51 to which a detection signal of the thermocouple 24 is input. When the coil 22 is energized by the first power supply unit 41, magnetic flux is generated in the axial direction of the iron core 21 by electromagnetic induction, and the steel pipe T is magnetized (see FIG. 2). A current is supplied from the second power supply unit 42 to the magnetic field detector 23, and the steel tube T is moved in the length direction, whereby the leakage magnetic field on the surface of the magnetized steel tube T is continuously detected. The detection signal is input to the detection waveform display section 42 and the decarburized layer depth detecting section 44, respectively, and the decarburized layer and its depth are detected. The detection of the decarburized layer and the detection of the depth are described in the above-mentioned Japanese Patent Application Laid-Open No. 2-247556, and the description thereof is omitted here.

FIG. 3 is a schematic perspective view showing the structure of a probe holder which is a feature of the present invention. Probe holder 3
Are made of synthetic resin and have a substantially rectangular parallelepiped shape, and four guide wheels 33, 33,. In FIG. 3, the guide wheels are omitted. The probe holder 3 is provided with a through hole 31 substantially at the center, and the probe detecting section 2 is inserted and held in the through hole 31. The probe holder 3 has a heater 32. FIG.
FIG. The heater 32 embeds a heating wire in the peripheral wall of the through hole 31, and the heating wire is
Are arranged in a direction that does not affect the magnetic flux generated by the coil 22. Specifically, as shown in FIG. 4, the heating wire is arranged in parallel to the axial direction of the through-hole 31, is folded in a hairpin curve shape near the opening, and is again arranged in parallel to the axial direction. Is repeated over the entire circumference of the peripheral wall. As described above, since the current flows through the heater 32 in a direction parallel to the axial direction of the coil 22, it does not affect the magnetic flux generated by the coil 22 of the probe detection unit 2 when the heater 32 is energized.

When the decarburized layer of the steel pipe T is detected by using the eddy current inspection device having the above-described configuration, first, the heater 32 is energized by the temperature control unit 5 to raise the temperature of the probe holder 3, and the probe detection unit 2, the temperature detector 51
Is set so as to keep the temperature indicated by, for example, 50 ° C. The temperature of the probe detector 2 is measured by the thermocouple 24, and after the temperature has become constant, the first power supply 41 and the second power supply 4
2, a current is supplied to the coil 22 and the magnetic field detector 23, and the steel pipe T is transported to start detection of the decarburized layer and measurement of its depth. Since the temperature of the probe detection unit 2 is set high in consideration of the temperature rise of the coil 22 and the magnetic field detector 23, the temperature is kept constant even when self-heating occurs due to the power supply.

As described above, by using the apparatus of the present embodiment, the temperature of the probe detector 2 during the detection of the decarburized layer can be kept constant.
It can be said that an error in the detection signal due to the temperature drift of the probe detector can be prevented.

In this embodiment, the case where the decarburized layer is detected while moving the steel pipe T with respect to the probe detecting section 2 is described as an example. However, the present invention is not limited to this. Is stopped, and the probe detector 2 is
The same effect can be obtained even if the decarburized layer is detected by bringing the distance closer.

Next, by using the above-described eddy current inspection device, the impedance output value of the arbitrary portion of the steel pipe T when the temperature of the probe detector 2 is kept constant and when it is changed is measured and compared. did. The results are shown in FIG. FIG. 5 is a graph showing the impedance output value,
The vertical axis shows the current value Y of the magnetic field detector when the current of the exciting coil 22 is zero, and the horizontal axis shows the current value X of the magnetic field detector when the current of the exciting coil 22 is the maximum. . The impedance value for each measurement time is plotted in the graph. Table 1 shows the impedance values (X, Y) and the temperature of the probe detector 2 with respect to the measurement time.

[0025]

[Table 1]

As shown in Table 1, from the detection time 16:54 to 1
During the period until 7:25, the heater 32 of the probe holder 3 was not energized. As shown in the graph, in the impedance value during this period, the X value is almost constant, and the Y value increases with time. At time 17:25, the power of the heater 32 was turned on. As the temperature of the probe detector 2 increases, the impedance value changes irregularly. Then, after time 18:05 when the temperature of the probe detection unit 2 became constant at approximately 50 ° C. by the temperature control unit 5, the impedance value became approximately constant and showed a substantially constant value until the detection was completed at time 20:30.

From these results, the eddy current inspection apparatus according to the present embodiment can maintain the temperature of the probe detector 2 constant with a simple configuration, eliminate errors in magnetic field measurement, remove the decarburized layer of the steel pipe T and its depth. It can be seen that the height can be detected with high accuracy.

In the present embodiment, the steel pipe T
It describes the case of detecting the decarburized layer of the surface layer of the above.However, the present invention is not limited to this, and it can be applied to the case where the inner surface side of the steel pipe is detected. Get.

The eddy current inspection apparatus and method of the present invention can be applied to not only the case of detecting a decarburized layer but also the case of detecting a surface defect such as a flaw, and obtain the same effect.

[0030]

As described above, in the present invention, since the detector for inspecting the surface state of the magnetic material is held by the holder and the holder is provided with the heater, the temperature drift of the detector due to self-heating is reduced. Without the occurrence, it is possible to detect a defect in the surface layer portion of the magnetic material with high accuracy. Further, when the probe detection section is held in the through hole of the holder, the heater is embedded in the peripheral wall of the through hole, so that the present invention has an excellent effect such that the detection section can be easily maintained at a predetermined temperature.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a main configuration of an eddy current inspection device according to the present invention.

FIG. 2 is a schematic block diagram illustrating a configuration of a probe type detection unit and a decarburized layer detection control unit.

FIG. 3 is a schematic perspective view showing the structure of a probe holder according to the present invention.

FIG. 4 is a development view of a peripheral wall of a through hole of the probe holder of FIG. 3;

FIG. 5 is a graph showing an impedance output value of the eddy current inspection device of the present invention together with a comparison result.

[Explanation of symbols]

 2 Probe Detector 3 Probe Holder 22 Coil 23 Magnetic Field Detector 31 Through Hole 32 Heater T Steel Pipe

Continued on the front page (72) Inventor Toshifumi Fukuda 1850 Minato, Wakayama-shi, Wakayama Sumikin Control Engineering Co., Ltd. Inside the corporation

Claims (4)

[Claims] 1. An eddy current inspection device for inspecting a surface layer portion of a magnetic material by measuring a magnetic field in the vicinity of the predetermined region of a magnetic material while a detection unit supported by a holder magnetizes the predetermined region of the magnetic material. An eddy current inspection device, comprising: a holder provided with a heater; and a controller for supplying power to the heater to control the temperature of the heater. 2. The apparatus according to claim 1, wherein the detection unit includes a probe coil for magnetizing the magnetic material, the holder includes a through hole into which the detection unit is to be inserted, and the heater is embedded in a peripheral wall of the through hole. The eddy current inspection device according to claim 1, wherein 3. The eddy current inspection device according to claim 2, wherein the heater is provided with a heating wire so that a current flows substantially parallel to an axial direction of the probe coil. 4. An eddy current inspection method for inspecting a surface layer of a magnetic material by measuring a magnetic field in the vicinity of the predetermined region while magnetizing a predetermined region of the magnetic material. A step of heating to a predetermined temperature, and a step of subsequently performing measurement by the detection unit while maintaining the temperature of the detection unit constant.