JP2548141Y2 - Eddy current flaw 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 used, for example, in the manufacture of steel pipes and for the inspection of heat exchangers and steam generators during their service life.

[0002]

2. Description of the Related Art Conventionally, an eddy current flaw detector for inspecting a (heat transfer) thin tube such as a steam generator comprises a detection coil and a flaw detector as shown in FIGS.

FIG. 5 shows an example of the overall configuration of an eddy current flaw detector. In FIG. 5, 1 is a probe, 2 and 3 are detection coils wound around the probe 1, 4 is a cable, 5
Is a flaw detector, 6 is a screen of the flaw detector 5, 7 is a signal waveform displayed on the screen 6, 8 is a subject thin tube, 9 is a defect such as a crack existing in the subject thin tube 8, and 10 is a probe 3 moving. FIG.

[0004] The two detection coils 2 and 3 wound around the probe 1 are connected to a flaw detector 5 by a cable 4, and an alternating current is applied to the detection coils 2 and 3. When an alternating current is applied to the detection coils 2 and 3,
A magnetic field is generated from the detection coils 2 and 3, and an eddy current flows through the test subject thin tube 8. The flow of the eddy current is constant at a portion where there is no defect in the subject thin tube 8, but when approaching the portion where the defect 9 exists, the flow of the eddy current is disturbed. The impedance of the detection coils 2 and 3 changes due to the eddy current flowing through the subject thin tube 8.

A state in which the impedance changes when the detection coils 2 and 3 approach the defect 9 of the subject thin tube 8 is detected by the flaw detector 5, subjected to signal processing and displayed on a screen 6 as a signal waveform 7. Therefore, by observing the signal waveform 7 on the screen 6 of the flaw detector 5 while moving the probe 1 in the direction of the arrow 10, it is possible to know whether or not there is a defect in the subject thin tube 8.

FIGS. 6A and 6B show the detection coils 2 and 3 and the directions 11 and 12 of the magnetic field generated in the conventional eddy current testing device. Conventionally, two detection coils 2 and 3 are formed in a coaxial circular shape, and a uniform magnetic field is generated all around the coils 2 and 3 in the direction of rotation. An eddy current is generated. Therefore, if a defect 9 having a length in the axial direction exists in the thin tube 8, the flow of the eddy current is disturbed, and the impedance of the detection coils 2 and 3 changes. Thus, the existence of the defect 9 can be known.

FIG. 7 is a functional connection diagram of a conventional flaw detector. As shown in the figure, the detection coils 2 and 3 and the variable impedances 21 and 22 form a bridge circuit, and an AC voltage is supplied from an oscillator 23. The output of the bridge circuit is input to the amplification / signal processing circuit 24,
The signal is amplified and signal-processed and transmitted to the display unit.

The bridge circuit composed of the detection coils 2 and 3 and the variable impedances 21 and 22 is adjusted so that the output thereof becomes zero when the detection coils 2 and 3 are placed in a place having no defect. Keep it. When the detection coils 2 and 3 come near the defect 9, an impedance change occurs in one of the detection coils 2 and 3, and some output is generated in this bridge circuit. The output generated by this bridge circuit is
The signal is input to the amplification / signal processing circuit 24, amplified and signal-processed, and transmitted to the display unit. Then, the defect is detected by observing the signal waveform displayed on the display unit.

[0009]

In the above-mentioned conventional eddy current flaw detection device, the eddy current of the thin tube fleshy portion caused by the magnetic field generated by the detection coils 2 and 3 flows only in the circumferential direction as described above. Therefore, for defects having no length in the axial direction, for example, cracks in the circumferential direction, the flow of the eddy current is not disturbed,
Since the impedance of the detection coils 2 and 3 does not change due to the defect, there is a problem that the detection sensitivity for such a defect is reduced.

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 flaw detector capable of reliably detecting a defect having no length in the axial direction and greatly improving flaw detection performance. And

[0011]

An eddy current testing apparatus according to the present invention comprises two ring-shaped magnetic cores having a plurality of radially outward projections arranged in parallel so that the projections face each other. A detection coil portion formed by providing a detection coil on each projection to form a magnetic pole, and selectively connected to the detection coil, the direction of the current flowing through the detection coil is forward rotation,
A high-speed switch for inverting and alternately switching the direction of a magnetic field generated from the magnetic pole in an axial direction and a circumferential direction; and a means for detecting a defect of a subject based on a detection signal of the detection coil unit. It is assumed that.

[0012]

The magnetic field generated by the detection coil switches in the axial direction or the circumferential direction each time the current is rotated forward or inverted by the high-speed switch. Therefore, the eddy current generated in the subject is switched in the circumferential direction or the axial direction every time the high-speed switch is operated.

When a circumferential magnetic field acts on the subject,
The eddy current in this part is in the axial direction, and short defects in the axial direction,
For example, the flow of the eddy current is disturbed by cracks in the circumferential direction,
The impedance of the detection coil changes. Therefore, it is possible to detect a defect that is short in the axial direction.

As described above, since the direction of the magnetic field generated by the detection coil is reversed with the operation of the high-speed switch, not only a defect having a length in the axial direction but also a defect having no length in the axial direction (the circumferential direction). Defect with a longer length).

[0015]

FIG. 1, FIG. 2, and FIG. 3 show an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 shows the probe inserted into the subject thin tube 8. The probe according to the present invention includes a first detection coil unit 30a and a second detection coil unit 30b, and each has a ring-shaped magnetic core 31,
A plurality of detection coils are wound around 32. The two ring-shaped magnetic cores 31 and 32 are arranged in parallel at a constant interval, and a plurality of, for example, four projections are respectively provided on the outer periphery thereof at equal intervals, in this case, at 90 ° intervals. , The detection coils a1 to a4, b1 to b
4 are wound around the magnetic poles 33a to 33d, 34a to 34
d. That is, the detection coils a1 to a4,
By energizing b1 to b4, each protrusion is
They act as a to 33d and 34a to 34d.

FIG. 2 is a functional connection diagram of the eddy current flaw detector according to the present invention. In the figure, L1 and L2 are oscillators 2
3, a signal line L0 is connected to detection coils a1 to a1.
4 is a common line to which the detection coils b1 to b4 are commonly connected. Variable impedances 21 and 22 constituting a bridge circuit are connected between the signal lines L1 and L2, and detection coils a1 to a4 are selectively connected through high-speed switches 41a1, 41a2, 42a1 and 42a2. The detection coils b1 to b4 are selectively connected via high-speed switches 41b1, 41b2, 42b1, and 42b2. The high-speed switches 41a and 41b are connected to the upper terminal in the figure when the driving current is normal rotation, and are connected to the lower terminal when the driving current is reversed. The high-speed switches 42a and 42b are connected to the lower terminal in the figure at the time of normal rotation, and are connected to the upper terminal at the time of inversion. These high-speed switches 41a, 42a, 41b, 4
2b all operate synchronously.

Among the detection coils a1 to a4, the coils a1 and a3 are directly connected between the signal line L1 and the common line L0, and the coils a2 and a4 have opposite polarities when the current is normal and when the current is reversed. Signal line L1 and common line L0
Connected to. That is, one end of each of the detection coils a2 and a4 is connected to the common terminal of the high-speed switches 41a1 and 41a2, and the other end is connected to the high-speed switches 42a1 and 42a2.
Are connected to a common terminal. High-speed switches 41a1, 41
In a2, the non-inverting terminal p is connected to the signal line L1, and the inverting terminal n is connected to the common line L0. In the high-speed switches 42a1 and 42a2, the non-rotating side terminal p is connected to the common line L.
0, and the inverting terminal n is connected to the signal line L1.

On the other hand, the detection coils b1 to b4
The coils b1 and b4 are directly connected between the signal line L2 and the common line L0, and the coils b1 and b3 are connected to the signal line L2 and the common line L0 with their polarities reversed when the current is normal and when the current is reversed. That is, one end of each of the detection coils b1 and b3 is connected to the common terminal of the high-speed switches 41b1 and 41b2, and the other end is connected to the common terminal of the high-speed switches 42b1 and 42b2. High-speed switches 41b1, 41b
2 has a non-inverting terminal p connected to the common line L0 and an inverting terminal n connected to the signal line L2. In the high-speed switches 42b1 and 42b2, the non-inverting terminal p is connected to the signal line L2.
, And the inverting terminal n is connected to the common line L0.

A signal extracted from the common connection point between the common line L0 and the variable impedances 21 and 22 is input to an amplification / signal processing circuit 24. in this case,
The common line L0 is used by grounding. The amplification / signal processing circuit 24 amplifies and processes the signal generated in the bridge circuit and transmits the signal to the display unit. Next, the operation of the above embodiment will be described.

As shown in FIG. 2, the detection coils constituting the bridge circuit are composed of coils a2 and a4 which are high-speed switches 41.
The polarities of the coils b1 and b3 are switched by the high speed switches 41b and 42b.

High-speed switches 41a, 42a, 41b, 4
When 2b is in forward rotation, the magnetic poles 33a to 33d of the first detection coil unit 30a are connected to the N pole, and the magnetic poles 34a to 34d of the second detection coil unit 30b are connected to the S pole. The direction of the magnetic field at this time is as shown in FIG. Since the lines of magnetic force are generated in the direction from the N pole to the S pole, the direction of the magnetic field also changes from the magnetic pole 33a to the magnetic pole 34a and from the magnetic pole 33b to the magnetic pole 34b as indicated by A1 to A4. That is,
The magnetic field is generated in the axial direction indicated by A1 to A4, and has the same direction as that of the conventional detection coils 2 and 3 shown in FIG. 6, so that the same detectability as the conventional one can be obtained.

Next, the high-speed switches 41a, 42a, 41
When b and 42b are inverted, the coils a2, a4, b1,
The direction of the current flowing to b4 is reversed, and as shown in FIG. 4, the first detection coil unit 30a has the magnetic poles 33a and 33c of the N station,
The magnetic poles 33b and 33d are S stations. The second detection coil unit 30b has the magnetic poles 34a and 34c at the N station and the magnetic poles 34a and 34c.
b and 34d become S poles. Since magnetic lines of force are generated only in the direction from the N pole to the S pole, the magnetic field in this case is, as shown in FIG. 4, in the direction from the magnetic poles 33a, 33c to the magnetic poles 33b, 33d, and from the magnetic poles 34a, 34c to the magnetic poles 34b, 34d.
, That is, in the circumferential direction indicated by B1 to B4.

When a circumferential magnetic field acts on the fleshy portion of the subject thin tube 8, the eddy current in this portion becomes axial, and the eddy current flows due to a short defect in the axial direction, for example, a crack in the circumferential direction. Is disturbed and the impedance of the coil changes, so that it is possible to detect such a defect that is short in the axial direction.

As described above, in the flaw detector according to the present invention,
The direction of the magnetic field generated by the detection coil
Since it is reversed with the operations of a, 42a, 41b and 42b, not only defects having a length in the axial direction but also defects having a length in the axial direction (length in the circumferential direction) can be detected. Become. In the above embodiment, the number of magnetic poles in one row in the circumferential direction is four, but the number is not limited to four and may be smaller or larger.

Further, in the above-described embodiment, the detection coil from the inner surface of the thin tube has been exemplified. However, the present invention is not limited to this, and can be applied not only to flaw detection from outside the thin tube or round bar, but also to The present invention can also be applied to a flat plate.

[0026]

According to the present invention, as described in detail above, the direction of the current flowing through the detection coil is rotated forward and reverse by the high-speed switch, and the direction of the magnetic field generated from the magnetic pole is alternately arranged in the axial direction and the circumferential direction. Because it is switched, not only defects with a length in the axial direction, but also defects without a length in the axial direction, which were difficult to detect with conventional flaw detection equipment, can be detected, greatly improving the performance of flaw detection equipment. Can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a detection coil portion of an eddy current inspection device according to an embodiment of the present invention.

FIG. 2 is a functional connection diagram in the embodiment.

FIG. 3 is a view showing a magnetic field of a detection coil in the embodiment.

FIG. 4 is a view showing a magnetic field of a detection coil in the embodiment.

FIG. 5 is a configuration diagram showing a conventional eddy current inspection device.

FIG. 6 is a diagram showing a conventional detection coil and a direction of a magnetic field thereof.

FIG. 7 is a functional connection diagram of a conventional eddy current testing device.

[Description of Symbols] 5 ... flaw detector, 6 ... screen, 7 ... signal waveform, 8 ... subject thin tube, 9 ... defect, 22, 22 ... variable impedance, 23
... Oscillator, 24 ... Amplification / signal processing circuit, 30a ... First detection coil unit, 30b ... Second detection coil unit, 31, 32 ...
Magnetic core, 33a to 33d, 34a to 34d ... magnetic pole, 41a
1, 41a2, 41b1, 41b2, 42a1, 42a
2, 42b1, 42b2 ... high-speed switches, a1 to a4,
b1 to b4: detection coil, L1, L2: signal line, L0
... a common line.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoya Shimizu 1-1-1, Wadazakicho, Hyogo-ku, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Hirosaku Takami Niihama, Araimachi, Takasago-shi, Hyogo 2-8-8 Takahashi Engineering Co., Ltd. (72) Inventor Yoshihiro Kojima 2-8-25 Aramachi Shinhama, Takasago City, Hyogo Prefecture Takahashi Engineering Co., Ltd. (56) References Real Opening Sho 55-97448 (JP) , U)

Claims (1)

(57) [Scope of request for utility model registration] 1. A two-pole magnetic core having a plurality of radially outward projections is arranged in parallel so that the projections face each other, and a magnetic pole is formed by providing a detection coil on each of the projections. And a high-speed switching device selectively connected to the detection coil and rotating and reversing the direction of a current flowing through the detection coil to alternately change the direction of a magnetic field generated from the magnetic pole in an axial direction and a circumferential direction. An eddy current flaw detection device comprising: a switch; and means for detecting a defect of the subject based on a detection signal of the detection coil unit.