JPH052009A - Remote eddy current defectoscope - Google Patents

Abstract

PURPOSE:To securely inspect an abraded and thinned part of a metallic tube or the like by obtaining the difference of outputs of a pair of magnetic detecting elements arranged symmetrically at both sides in the axial direction of a transmission coil. CONSTITUTION:A transmission coil T is magnetized by a power source 30. The outputs of the same polarity from first transmission coils R1A. R2A are added to a differential output means 13, where the difference of the outputs of the coils R1A, R2A is obtained. A level distinguishing means 14 judges when the output of the differential output means 13 exceeds a preset value, making a display means 15 indicate the fact. Similarly, the differential outputs of receiver coils R1B and R2B, R1A and R1B, and R2A and R2B are respectively displayed by display means 18, 21, and 24. If a metallic tube 7 is abraded at a part 25, and the coil R1A is present at the part 25 while the coil R2A is at the other position than the part 25, the outputs of the receiver coils R1A, R2A become different and the differential output level from the differential output means 13 exceeds the distinguishing level set by the level distinguishing means 14. As a result, the display means 15 displays the abraded and thinned part 25. Thus, the inspection of an abraded and thinned part is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separated eddy current flaw detector used for inspecting a metal pipe such as an underground steel pipe for corrosion thinning.

[0002]

2. Description of the Related Art The remote eddy current flaw detection method is also called a remote field eddy current flaw detection method, in which a transmitter coil and a receiver coil are arranged in a metal tube with a gap in the axial direction of the tube. The spacing is usually such that the influence of the direct magnetic field from the transmitter coil does not affect the receiver coil.
It is necessary to dispose them at a distance of 2 to 4 times the pipe diameter (that is, the outer diameter of the pipe), and when an alternating current is applied to the transmitter coil, the magnetic flux from the transmitter coil penetrates the pipe to create an external space. As a result, the electromagnetic waves of this magnetic flux pass through the thick wall of the tube and pass through the air, which is the outer space, as it travels along the outer surface of the tube and penetrates the tube again and is received by the receiving coil. It is significantly smaller than the velocity at the time, and therefore its propagation time, that is, the phase difference between the transmitting signal of the transmitting coil and the receiving signal of the receiving coil changes in proportion to the wall thickness of the pipe. Corrosion thinning of the pipe corresponding to is detected.

In such a prior art, when inspecting the corrosion thinning of the outer surface of the pipe by the separated eddy current flaw detection method, even if the pipe is a sound pipe, the receiving coil of The output signal contains noise.

Another prior art solution to this problem is shown in FIG.
Is shown in. In order to inspect the corrosion-thinned portion 2 of the tube 1, the magnetic flux passing through the outside of the tube from the transmitting coil 3 excited by the AC power is detected by the pair of receiving coils 4 and 5, and these pair of receiving coils are detected. The outputs of 4, 5 are given to the differential output means 6 to obtain the differential outputs of these receiving coils 4, 5. In this way, the noise contained in the output signals of the receiving coils 4 and 5 can be eliminated. The receiving coils 4 and 5 are arranged at positions close to each other.

[0005]

In the prior art shown in FIG. 7 as described above, the interval between the receiving coils 4 and 5 is a small value as indicated by reference numeral L1 in FIG. 8 (1), Therefore, the length L2 in the pipe axis direction of the corrosion-reduced portion 2
Is larger than the distance L1 between the receiving coils 4 and 5, or when the portion 2 has a gentle surface shape with a small inclination, the difference between the receiving coils 4 and 5 obtained from the differential output means 6 is large. The dynamic output is as shown in FIG. 8 (2), and the corrosion-reduced portion 2 cannot be reliably detected.

In order to solve this problem, it is conceivable to increase the distance L1 between the receiving coils 4 and 5, but if this is done, the excitation flaw condition for the transmitting coil 3 of each receiving coil 4 and 5 will be 2. Different between the two receiving coils 4, 5 and thus their receiving coils 4, 5
A new problem arises that the flaw detection by the differential output of No. 5 becomes difficult.

It is an object of the present invention to provide a separated eddy current flaw detector which enables reliable inspection regardless of the size and shape of a corrosion-reduced portion such as a metal pipe.

[0008]

According to the present invention, there are provided a transmission coil, an AC power source for exciting the transmission coil, a pair of magnetic detection elements symmetrically arranged on both sides in the axial direction of the transmission coil, and a magnetic detection element. It is a separated eddy current flaw detection device characterized by including differential output means for obtaining a difference between respective outputs.

Further, according to the present invention, each of the transmitting coil, the AC power source for exciting the transmitting coil, the pair of first magnetic detecting elements symmetrically arranged on both sides of the transmitting coil in the axial direction, and the first magnetic detecting element. A first differential output means for obtaining a difference between outputs, and a pair of second magnetic detection elements symmetrically arranged on both sides in the axial direction of the transmission coil, each second magnetic detection element being the first magnetic detection element. Such a second, arranged in the vicinity of the element
An isolated eddy current flaw detection device comprising: a magnetic detection element; and a second differential output means for obtaining a difference between outputs of first and second magnetic detection elements arranged near each other.

[0010]

According to the present invention, the magnetic flux from the transmitter coil excited by the AC power source penetrates the tube, is transmitted to both sides in the axial direction of the transmitter coil, that is, both sides in the tube axis direction, and penetrates the tube again. Then, the pair of magnetic detection elements symmetrically arranged with respect to the transmission coil detects the difference, and the difference between the outputs of the pair of magnetic detection elements is obtained by the differential output means. The distance between each pair of magnetic detection elements is larger than that of the above-described prior art, and therefore, when there is a large corrosion-reduced portion extending in the tube axis direction, a differential output is obtained, and such a large corrosion-reduced thickness is obtained. It is possible to detect a portion or a portion with a small slope and gentle corrosion thinning.

According to the present invention, in addition to the pair of first magnetic detection elements, a pair of second magnetic detection elements is further provided.
The second magnetic detection elements are arranged symmetrically on both sides in the axial direction of the transmission coil, and the respective second magnetic detection elements are arranged in the vicinity of the first magnetic detection element, and thus one first magnetic detection element arranged in the vicinity of each other. And the difference between the outputs of one of the second magnetic detection elements
It is also possible to reliably detect a corrosion-reduced portion having a small corrosion-reduced portion or a steep corrosion-reduced portion with a large inclination in the pipe axis direction by detecting with a differential output means.

[0012]

1 is a simplified sectional view showing the structure of an embodiment of the present invention. The present invention is carried out in order to inspect the corrosion-thinning state of a metal pipe 7 such as a steel pipe buried in the ground. Symmetrically on both sides in the axial direction of the transmission coil T, the reception coil R1A, which is a pair of first magnetic detection elements,
R2A is placed. Another pair of receiving coils R1B and R2B, which are second magnetic detection elements, are arranged symmetrically on both sides of the transmitting coil T in the axial direction. The axes of these receiving coils R1A, R2A; R1B, R2B are aligned with the axis of the transmitting coil T. These four receiving coils R1A, R2A; R1B, R2B have the same size and shape. The axial distance L1A between the transmitting coil T and the receiving coil R1A is equal to the transmitting coil T and the receiving coil R2.
It is equal to the distance L2A from A (L1A = L2A). Further, the distances L1B and L2B between the transmitting coil T and the receiving coils R1B and R2B are equal (L1A = L2B). One of the first receiving coils R1A and one of the second receiving coils R1B are arranged very close to each other, and similarly, the other first receiving coil R2A and the other second receiving coil R2B are arranged very close to each other. Transmitting coil T and receiving coils R1A and R2
A; R1B and R2B are support members 8 made of a magnetic material.
Fixed by ~ 12.

FIG. 2 is a block diagram showing the electrical construction of the embodiment shown in FIG. The transmission coil T is excited by the AC power supply 30. A pair of first receiving coils R1
The outputs of A and R2A having the same polarity are given to the differential output means 13 which is realized by an operational amplifier circuit or the like, whereby the difference between the outputs of the coils R1A and R2A is obtained.
The level discriminating means 14 judges that the output of the differential output means 13 exceeds a predetermined value, and causes the display means 15 to display this. Similarly, a pair of second
Outputs of the same polarity of the receiving coils R1B and R2B are given to the differential output means 16, and the differential output thereof is the level discrimination means 1.
Level discrimination is performed at a predetermined discrimination level by 7 and is displayed by the display unit 18.

Further, outputs of the same polarity of the one first receiving coil R1A and the one second receiving coil R1B are also given to the differential output means 19, and the differential output is discriminated by the level discriminating means 20 in advance. The levels are discriminated by level and displayed by the display means 21. Outputs of the same polarity of the other first receiving coil R2A and the other second receiving coil R2B are also given to the differential output means 22, and the differential output is level discriminated by the level discriminating means 23,
It is displayed by the display means 24.

Referring to FIG. 3, when the metal pipe 7 has a corrosion thinning portion 25 extending in the axial direction of the metal pipe 7, as shown in FIG. 3, one receiving coil R1A is corroded and reduced. Another receiving coil R2A located in the meat part 25
Is in a position outside the portion 25, the outputs of these receiving coils R1A and R2A are different from each other, so that the differential output level from the differential output means 13 is a predetermined discrimination level set by the level discrimination means 14. Over. Therefore, the display means 15 displays that such a large corrosion thinning portion 25 exists. The corrosion-reduced portion 25 is
Even a gentle defect having a smaller inclination can be detected in the same manner.

FIG. 4 is a diagram showing an experimental result of the present inventor. Transmitting coil T and each first receiving coil R1A, R2A
The distances L1A and L2A from the pipe 2 are set to twice the outer diameter D of the pipe 2, and this pipe 7 has a preliminary diameter 25A, that is, an outer diameter D34 mm
The length L3 of the defect 26 of the pipe 7 made of carbon steel of φ, inner diameter 27.6 mmφ, and wall thickness 3.2 mm artificially formed as shown in FIG. 4 (1) is 40 mm. ,
Defect depth is 2.7 mm and the width of the pipe 7 in the circumferential direction is 15 m.
When m, the defect 26 from the differential output means 13
It was confirmed that the differential output shown in FIG. 4 (2) was obtained corresponding to the above, and thereby the level discrimination circuit 14 exceeded the predetermined discrimination level 27, and thus the pipe 26 could be detected. In FIG. 4 (2), the vertical axis has one scale of 5
It is 00 mV. The detection operation by the receiving coils R1A and R2A is similarly achieved by the receiving coils R1B and R2B.

As shown in FIG. 5, when the pipe 7 has a small corrosion thinning portion 28 along the axial direction of the pipe 7, one first receiving coil R1A and the other second receiving coil R1B are provided.
The respective outputs of and are given to the differential output means 19 and their differential outputs are obtained, whereby the level discrimination means 2
0 and the display means 21 can similarly detect. The corrosion-reduced portion 28 can detect even a steep defect having a large inclination. The similar detection operation is similarly achieved by the receiving coils R2A and R2B.

Further, in the above-mentioned embodiment, since the receiving coils R1A and R1B are arranged on one side in the axial direction of the transmitting coil T, as shown in FIG. 6, the corrosion thinning up to the left end of the pipe 7 is performed. Partial flaw detection can be performed. Moreover, the receiving coils R2A and R2 are provided on the other side in the axial direction of the transmitting coil T.
Since B is provided, it is possible to perform flaw detection on the corrosion-reduced portion up to the vicinity of the right end portion 7b of the pipe 7 in FIG.

As another embodiment of the present invention, only the first receiving coils R1A and R2A or the second receiving coils R1B and R1B,
Only R2B may be provided and configured.

As still another embodiment of the present invention, instead of using the differential output means 13, 16, 19, 22, the receiving coils R1A, R2A; R1 for which the difference between the outputs should be obtained.
It is possible to connect the outputs of B and R2B so as to have opposite polarities, thus omitting the differential output means 13, 16, 19, and 22.

The present invention can be widely applied to inspect not only the metal pipe 7 such as the underground steel pipe but also other metal inspected objects. The object to be inspected may be, for example, a flat plate.

As the magnetic detection element, not only the receiving coil but also a Hall element or other structure may be used. In the present invention, it is also possible to detect a thin portion such as a recess other than the corrosion thin portion.

[0023]

As described above, according to the present invention, the transmission coil is excited by the AC power source, and the magnetic flux from the transmission coil passes through the external space, for example, the metal pipe to be inspected, and is transmitted through the external space. Since the magnetic flux is detected by penetrating the tube again into a pair of magnetic detection elements symmetrically arranged on both sides in the axial direction of the coil, the differential output of the pair of magnetic detection elements is obtained. Can be set to be large, and therefore a relatively large corrosion thinning portion can be detected, and even if such a portion is a gentle defect having a small inclination, it can be detected.

Further, according to the present invention, when the pair of magnetic detection elements is referred to as a first magnetic detection element, another pair of second magnetic detection elements is provided on both sides in the axial direction of the transmission coil. The second magnetic detection elements are arranged symmetrically, each second magnetic detection element is arranged in the vicinity of the first magnetic detection element, and differential output between one first magnetic detection element and one second magnetic detection element arranged in the vicinity thereof. It is also possible to detect a small corrosion-thinning portion or a steep corrosion-thinning portion having a large slope.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the embodiment shown in FIG.

FIG. 3 is a cross-sectional view for explaining the operation when detecting a smooth corrosion-thinning portion 25 that is large in the pipe axis direction and has a small inclination.

FIG. 4 is a diagram showing an experimental result of the present inventor.

FIG. 5 is a cross-sectional view for explaining an operation when detecting a steep corrosion-thinning portion having a small inclination and a large inclination in the pipe axis direction.

FIG. 6 is a cross-sectional view showing a state when inspecting a corrosion-reduced portion of both ends 7a and 7b of the pipe 7.

FIG. 7 is a cross-sectional view showing the configuration of the prior art.

8 is a diagram showing experimental results of the prior art shown in FIG.

[Explanation of symbols]

7 Metal tube 13, 16, 19, 22 Differential output means 14, 17, 20, 23 Level discrimination means 15, 18, 21, 24 Display means 25, 26, 28 Corrosion thinning part R1A, R2A first receiving coil R1B, R2B second receiving coil

Continued front page    (72) Inventor Souichi Kishino             4-1-2 Hirano-cho, Chuo-ku, Osaka City, Osaka             Gas Co., Ltd.

Claims (2)

[Claims] 1. A transmission coil, an AC power supply for exciting the transmission coil, a pair of magnetic detection elements symmetrically arranged on both sides in the axial direction of the transmission coil, and a differential for obtaining a difference between respective outputs of the magnetic detection element. An isolated eddy current flaw detector comprising: an output unit. 2. A transmission coil, an AC power supply for exciting the transmission coil, a pair of first magnetic detection elements symmetrically arranged on both sides in the axial direction of the transmission coil, and a difference between respective outputs of the first magnetic detection element. And a pair of second magnetic detection elements symmetrically arranged on both sides in the axial direction of the transmission coil, wherein each second magnetic detection element is in the vicinity of the first magnetic detection element. And a second differential output means for determining a difference between respective outputs of the first and second magnetic detection elements arranged close to each other. Remote eddy current flaw detector.