JP3145561B2 - Eddy current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detector in an eddy current flaw detector for checking the soundness of a flat metal plate, a thin metal tube or the like.

[0002]

2. Description of the Related Art Generally, an eddy current flaw detector is used to determine the presence or absence of a defect in a metal object such as a metal flat plate and to confirm its soundness. As shown in FIG. 5, a conventional eddy current flaw detection apparatus includes an excitation coil 101, a detection coil 102,
3 and a flaw detector 120 having a display screen 51. The flaw detector 100 and the flaw detector 120
Are connected by a connection cable 130.

FIG. 6 shows an electromagnetically connected state of the eddy current flaw detector. 5 and 6, reference numeral 110 denotes a target metal to be inspected; 111, a surface defect in the metal to be inspected;
Numeral 31 denotes a magnetic field generated by the exciting coil 101, 132 denotes an eddy current generated by the magnetic field 131 generated by the exciting coil 101, and eddy currents 133 flowing through a metal as a subject.
141 is an AC oscillator built in the flaw detector 120.

[0004] An alternating current of a fixed size (amplitude) and a fixed frequency is passed from the oscillator 141 through the connection cable 130 to the exciting coil 101. When an alternating current flows through the coil 101, a magnetic field 131 is generated, and the magnetic field 131 is linked to the detection coil 102 and the test object metal 110, thereby generating an eddy current 132 in the test object metal 110. The eddy current 132 is generated concentrically with the exciting coil 101 when the test object metal 110 is healthy (when there is no defect). The eddy current 132 also generates a magnetic field 133, which affects the magnetic field 131 generated by the exciting coil 101.

In the detection coil 102, the magnetic field 131 generated by the subject metal 110 interlinks with the magnetic field 133 generated by the eddy current 132, and the detection coil 102
, An AC voltage is induced. Since the magnetic field 131 generated by the exciting coil 101 is always kept constant, it is possible to detect an abnormality (existence of a defect or the like) of the subject metal 110 by paying attention to a change in the voltage induced in the detection coil 102. Can be.

Various signal processing circuits exist inside the flaw detector 120. The signal processing circuit extracts only a change in the voltage induced in the detection coil 102, and the screen 5
1 is displayed as a waveform.

When the defect 111 exists in the metal 110 to be inspected, the flow of the eddy current 132 changes as compared with the case where there is no defect. At this time, the magnetic field 133 generated by the eddy current 132
Also changes as compared with the case where there is no defect.
The voltage induced at 02 also changes, and this change in voltage is observed on the screen 51 of the flaw detector 120 to determine the presence or absence of a defect.

In actual application, the waveform of the screen 51 of the flaw detector 120 at this time is observed while moving the flaw detector 100 along the test object metal 110. FIG. 7 shows an example of a signal waveform in each state. 7 in FIG.
7A shows a screen of the flaw detector 120 similar to FIG.
00 is a waveform example 121 when the object is stopped on the surface of the subject.
(B) shows a waveform example 122 due to a surface defect, and (c) shows a waveform example 123 caused by lifting of the flaw detector 100 generated when the flaw detector 100 is scanned.

[0009] As shown in FIG.
Is stationary on the object metal 110, the detection coil 10
No change occurs in the induced voltage of No. 2 and the flaw detector screen 51
Shows only spots. When the flaw detector 100 is scanned near the surface defect 111, the eddy current is disturbed by the defect, and the induced voltage of the detection coil 102 changes with a specific property. A waveform 122 as shown in FIG. 7 (b) appears. Flaw detector 100
The strength of the magnetic field 131 generated by the exciting coil 101 acting on the test metal 110 also changes due to the rise of the eddy current, and the intensity of the eddy current generated in the test metal changes.
Since the induced voltage of the detection coil 102 changes with a specific property, a waveform as shown in FIG. 7C appears on the screen 51 of the flaw detector 120.

As described above, in the eddy current inspection, the flaw detector 10
By observing the waveform that appears on the screen 51 of the flaw detector 120 at that time while moving 0 on the surface of the test object metal 110, it is possible to determine the presence or absence of a defect, etc., and to know the soundness of the test object metal 110. Can be.

[0011]

However, when the above-described conventional flaw detector 100 is used, as shown in FIG. 8, almost all the magnetic fields generated by the exciting coil 101 (the magnetic fields passing through the surface of the test object metal 110). 135 and the magnetic field 136 passing through the back surface of the test object metal 110) and all the eddy currents generated by these magnetic fields. As shown in FIG. 8, the magnetic field 135 passing through the surface portion of the test object metal 110 is generated by the difference between the paths coming out of the exciting coil 101 and returning to the exciting coil 101.
The strength is higher than the magnetic field 136 passing through the back surface of the subject metal 110. As a result, the abnormality existing near the surface of the test object metal 110 greatly affects the detection coil 102,
For abnormalities existing on the back surface of the test object metal 110,
The influence on the detection coil 102 is small.

Therefore, the screen 51 of the flaw detector 120 includes
The waveform 124 (see FIG. 9) due to the back surface defect 112 appears only small. FIG. 7C shows a waveform due to the lifting of the flaw detector 100, which is greatly affected by the magnetic field passing through the surface portion.
In this case, a large signal waveform appears. FIG. 9 shows a signal waveform due to a back surface defect caused by the flaw detector.
4 is a waveform 122 due to the surface defect in FIG.
00 becomes smaller than the waveform 123 due to the floating.
It is required that the soundness of the test metal 110 be sufficiently confirmed on any surface regardless of the front surface or the rear surface.

In actual flaw detection, during the scanning of the flaw detector 100, the lift of the flaw detector 100 often occurs, which often causes a signal waveform to be generated. It is necessary to detect the signal waveform separately from the signal waveform due to the lifting of the flaw detector. From this point, the above-mentioned conventional eddy current flaw detector has a problem that the detection sensitivity to the abnormality on the back surface of the subject is lower than that of the front surface of the subject.

The present invention has been made in view of the above circumstances. By providing a detection coil inside an excitation coil and arranging the position of the detection coil appropriately, only a magnetic field acting on the back surface of the subject metal can be used. It is an object of the present invention to provide an eddy current flaw detector capable of relatively improving the detection sensitivity to an abnormality such as a defect existing on the back surface while taking care that the detection coil is affected.

[0015]

An eddy current flaw detector according to the present invention is wound in a direction perpendicular to the surface of a test object metal.
Is, an exciting coil for generating a magnetic field to said subject a metal, is disposed inside portion of the exciting coil, the exciting coil
And wound in the same direction and a detection coil for detecting a change in magnetic field due to the subject metal, the detection coils, on
When the excitation coil is positioned on the surface of the test object metal,
Of the magnetic field generated by the excitation coil ,
It is characterized in that it is arranged at a position where a change in the magnetic field passing through the back surface can be detected more strongly than a change in the magnetic field passing through the front surface .

[0016]

Since the flaw detector according to the present invention is constructed as described above, of the magnetic field generated by the excitation coil, the detection coil is hardly affected by the magnetic field acting on the surface of the test object metal. The detection coil is affected only by a change in the magnetic field acting on the back surface of the sample metal, and a relatively large signal due to an abnormality such as a defect existing on the back surface of the sample metal appears. Accordingly, the signal waveform due to the lifting of the flaw detector during the scanning of the flaw detector becomes relatively small, and the detection sensitivity to the defect on the back surface of the subject can be improved.

[0017]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an eddy current flaw detector according to one embodiment of the present invention.
This will be described with reference to FIGS. FIG. 1 shows a coil shape of a flaw detector 10 according to one embodiment of the present invention.
For example, a square-shaped detection coil 02 is arranged near the center inside the excitation coil 01 formed in a square shape.
The position of the detection coil 02 is adjusted so that good defect detection can be obtained. The excitation coil 01 and the detection coil 02 are connected to a flaw detector via a connection cable 130 as in the case of FIG.

The basic operation of the excitation coil 01 and the detection coil 02 is the same as that of a conventional flaw detector. A magnetic field is generated by the excitation coil 01, and the eddy current in the test object metal 110 is generated by the detection coil 02. To detect the magnetic field affected by the above, and induce a voltage. Reference numeral 112 in the drawing denotes a back surface defect in the test object metal 110.

FIG. 2 shows a state of generation and use of a magnetic field by the flaw detector 10. In FIG. 2, reference numeral 11 denotes a magnetic field generated by the exciting coil 01 and passing through the front surface of the test metal 110, and reference numeral 12 denotes a magnetic field passing through the rear surface of the test metal 110.

The excitation coil 01 and the detection coil 0 shown in FIG.
2, the voltage induced by the detection coil 02 is generally affected only by a magnetic field passing through the detection coil 02 (linking with the detection coil 02).
It is not affected by the magnetic field passing outside. For this reason, the induced voltage of the detection coil 02 is not affected by the magnetic field 11 passing through the front surface of the subject metal 110, but is only affected by the magnetic field 12 passing through the back surface of the subject metal 110.

As described above, the magnetic field generated by the coil is such that the magnetic field passing through a short path is strong and the magnetic field passing through a long path is weak. In FIG. 2, the magnetic field 11 passing through the front surface of the subject metal 110 is the magnetic field 1 passing through the back surface of the subject metal 110.
Stronger than 2. By preventing the detection coil 02 from being affected by the strong magnetic field 11 passing through the surface of the test object metal 110, the influence (signal waveform) due to the surface defect and the effect due to the lifting of the flaw detector 10 (signal). Waveform) becomes smaller.

FIGS. 3 and 4 show examples of signal waveforms (the screen 51 of the flaw detector) due to these factors. FIG.
In (a), 21 is a signal waveform example when the flaw detector 10 is at rest, (b) 22 is a signal waveform example due to a surface defect, and (c) 23 is a signal waveform example when the flaw detector 10 rises. . As shown in FIG. 3, in the flaw detector 10 of the present invention, the voltage induced by the detection coil 02 is
0, which is not affected by the magnetic field 11 passing through the surface of the sample metal 110, the signal waveform of the factor due to the surface of the test object metal 110 is reduced (detection sensitivity is reduced), and the waveform 22 due to surface defects is reduced. , And the waveform 23 caused by the lifting of the flaw detector 10 appears smaller than the conventional flaw detector (example of waveform of the conventional flaw detector: see FIG. 7). On the other hand, FIG. 4 shows an example of a signal waveform due to a defect on the back surface of the test metal 110. In FIG. 4, reference numeral 24 denotes an example of a waveform due to a back surface defect of the test object metal 110, which appears on the flaw detector screen 51 with substantially the same size as a waveform example 124 due to a back surface defect by a conventional flaw detector.

When scanning a flaw detector in actual flaw detection, the flaw detector often rises. It is considered that the signal waveform due to the lifting of the flaw detector always occurs. It is often practically difficult to extract a signal due to a defect from a signal waveform caused by the lifting of the flaw detector, and in actual flaw detection, it is often difficult in this respect.

In the flaw detector 10 according to the present invention, a signal waveform (a signal waveform due to a surface defect, a signal waveform due to a lift of the flaw detector, etc.) caused by the surface portion of the subject metal 110 is reduced, and a signal waveform due to a back surface defect is reduced. Observation can be made more clearly, and detection sensitivity to a back surface defect can be improved. In the above-described embodiment, the case of detecting a defect in a metal flat plate has been described. However, a defect can be similarly detected in a thin metal tube.

[0025]

As described above in detail, according to the present invention, the detection coil is provided inside the excitation coil, and the position of the detection coil is appropriately considered so that the surface of the metal to be inspected (the side face on which the flaw detector is arranged) is provided. The amplitude of the signal waveform caused by the portion) can be suppressed, and the detection sensitivity to an abnormality such as a defect existing on the back surface of the test metal that is generally difficult to detect (opposite the flaw detector) can be greatly improved. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing a coil shape of a flaw detector according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a magnetic field by the flaw detector of the present invention.

FIG. 3 is a diagram showing an example of a signal waveform for each factor by the flaw detector of the present invention.

FIG. 4 is a diagram showing an example of a signal waveform due to a back surface defect by the flaw detector of the present invention.

FIG. 5 is a diagram showing a conventional eddy current flaw detector.

FIG. 6 is a view for explaining the principle of detection of a defect of a conventional flaw detector.

FIG. 7 is a diagram showing an example of a signal waveform for each factor by a conventional flaw detector.

FIG. 8 is an explanatory diagram of a magnetic field by a conventional flaw detector.

FIG. 9 is a diagram showing an example of a signal waveform due to a back surface defect by a conventional flaw detector.

[Explanation of symbols]

 REFERENCE SIGNS LIST 01 excitation coil 02 detection coil 10 flaw detector 11 magnetic field passing through surface of test metal 12 magnetic field passing through back face of test metal 21 signal waveform when flaw detector is stationary 22 signal waveform due to surface defect 23 flaw detector 24 Signal Waveform Due to Back Surface Defects 51 Screen of Flaw Detector 110 Subject Metal 112 Back Surface Defect in Test Metal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Showa 61-94760 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/72-27/90

Claims (1)

(57) [Claims] 1. A direction orthogonal to a surface of a test object metal.
Wound around the, an exciting coil for generating a magnetic field to said subject a metal, is disposed inside portion of the exciting coil, 該励
A detection coil wound in the same direction as the magnetic coil to detect a change in the magnetic field due to the test object metal, wherein the detection coil positions the excitation coil on the surface of the test object metal.
When the, through the back surface than the change in the magnetic field passing through the surface of the subject in the metal of the magnetic field that the exciting coil generates
An eddy current flaw detector arranged at a position capable of strongly detecting a change in a passing magnetic field.