JP2651177B2 - Metal tube defect inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to corrosion of metal pipes such as steel pipes buried underground such as gas pipes and water pipes, or steel pipes of boilers and heat exchangers. The present invention relates to a metal tube defect inspection method for non-destructively detecting a defect such as the above.

[Conventional technology]

As shown in FIGS. 14 and 15, a conventional metal tube defect inspection method employs a transmission coil 2 in a metal tube 1 made of steel.
, And a plurality of receiving coils 3, 4, 5,... Are movably arranged at a constant interval (for example, about twice the pipe diameter), and the transmitting coil 2 and the receiving coils 3, 4, 5,. While being moved in the axial direction, an electromagnetic wave is generated from the transmission coil 2 as shown by an arrow A, and the electromagnetic wave is received by the reception coils 3, 4, 5,..., And the reception signal by the reception coils 3, 4, 5,. The defect inspection of the metal tube 1 is performed by a phase change caused by the defect 1a of the tube 1.

In this case, the plurality of receiving coils 3, 4, 5,... Are arranged close to the inner surface of the metal tube 1 and arranged in a line in the circumferential direction of the metal tube 1.

Now, as shown in FIG. 14, when a defect 1a is present in a part of the metal tube 1, the transmitting coil 2 and the receiving coils 3, 4, 5,. When the radio waves generated from the transmission coil 2 are received by the reception coils 3, 4, 5,... While being moved in the tube axis direction of the tube 1, the reception coils 3, 4 installed at positions away from the defect 1a
The phase of the received signal due to 5 is hardly affected by the defect 1a and hardly changes as shown in FIGS. 16 (a) and 16 (c). On the other hand, the phase of the signal received by the receiving coil 4 installed at a position close to the defect 1a is affected by the defect 1a, and depends on the position where the defect 1a exists as shown in FIG. 16 (b). Will change.

Thus, when the defect 1a exists in the metal tube 1, the defect 1a
Move the transmitting coil 2 and the receiving coils 3, 4, 5,... In the tube axis direction because the phase of the received signal due to the receiving coil, for example, 4, which is installed in the vicinity of, changes according to the position of the defect 1a. By monitoring the phases of the signals received by the receiving coils 3, 4, 5,..., The presence and position of the defect 1a of the metal tube 1 can be detected.

[Problems to be solved by the invention]

However, in this metal tube defect inspection method, a change in the tube material (permeability, etc.) (which becomes noise at the time of detecting a defect) occurs due to residual stress or the like due to rolling during the manufacture of the metal tube. In the case where a joint (which becomes a noise at the time of detecting a defect) is provided in the middle of a metal tube, a phase change occurs in a plurality of receiving coils 3, 4, 5,. However, there is a problem in that the phase change caused by the defect is buried, and the defect detection accuracy is low.

Hereinafter, this point will be described in detail with reference to FIGS. 17 and 18. Now, as shown in FIG. 17, a case where a changed portion 1b of the tube material is present all around the metal tube 1 and a defect 1c is present in a part of the changed portion 1b of the tube material. Think. In this case, the changed portion 1b of the pipe material is defective.
It exists over a much wider range than 1c, and the change in the material is not abrupt but changes gradually.

In the above case, while moving the transmission coil 2 and the reception coils 3, 4, 5,... In the tube axis direction of the metal tube 1 at a constant interval, the radio wave generated from the transmission coil 2 is received. , 4,5, ..., the phase of the signal received by the receiving coils 3,5 installed at a position distant from the defect 1c is hardly affected by the defect 1c, The phase changes only under the influence of 1b, and changes according to the position where the change portion 1b of the tube material exists as shown in FIGS. 18 (a) and 18 (c). On the other hand, the phase of the signal received by the receiving coil 4 installed at a position close to the defect 1c is affected by both the effect of the tube material change portion 1b and the effect of the defect 1c, as shown in FIG. 18 (b). As shown, the tube material changes according to the position where the change portion 1b and the defect 1c are present.

It should be noted that the same problem as described above also occurs when there is a defect near the pipe joint.

Accordingly, an object of the present invention is to provide a metal tube defect inspection method capable of accurately detecting the presence / absence and position of a defect in a metal tube.

[Means for solving the problem]

In the defect inspection method for a metal tube according to the present invention, the defect is considerably smaller than the changed portion and the joint of the tube material of the metal tube, and the receiving coil is sufficiently smaller than the changed portion and the joint of the tube material of the metal tube. It is made by paying attention to the fact that the size can be set to substantially the same size or more.

That is, this metal pipe defect inspection method includes disposing a transmission coil and a reception coil in a metal pipe so as to be movable in the pipe axis direction at a constant interval in the pipe axis direction, and placing the transmission coil and the reception coil in the pipe axis direction. The electromagnetic wave is generated from the transmitting coil while being moved to the receiving coil, the electromagnetic wave is received by the receiving coil, and the phase change of the signal received by the receiving coil due to the defect of the metal tube is monitored. In the metal tube defect inspection method for detecting the presence and location of a defect in a metal tube that is smaller than the The first and second coil portions are configured to be close to the inner surface of the metal tube and arranged in the circumferential direction of the metal tube. , A difference signal between the reception signals of the first and second coil units is used as a reception signal of the reception coil.

[Action]

According to the configuration of the present invention, the defect is considerably smaller than the changed portion and the joint of the tube material of the metal tube, the receiving coil is sufficiently smaller than the changed portion and the joint of the tube material of the metal tube, and is substantially equal to or more than the defect. Focusing on the fact that it is possible to set the size of the receiving coil, the first and second receiving coils are smaller than the changing portion and the joint of the tube material of the metal tube and have a size substantially equal to or greater than the defect of the metal tube. The first and second coil units are arranged in a state where the first and second coil units are arranged close to the inner surface of the metal tube and are arranged in the circumferential direction of the metal tube. The difference signal of the receiving coil is used as the receiving signal of the receiving coil, and the presence or absence and the position of the defect of the metal tube are detected by monitoring the phase change of the receiving signal of the receiving coil. Position due to the presence of the joint Change is to be canceled, the presence and position of a defect of the metal tube despite the presence of the change and the joint of the pipe material of the metal tube can be detected accurately.

In particular, the first and second coil portions are arranged close to the inner surface of the metal tube and arranged side by side in the circumferential direction of the metal tube, so that the first and second coil portions are not displaced in the tube axis direction. In the case where the tube material changes sharply in the axial direction of the metal tube, when the first and second coil portions cross the suddenly changing portion or when the joint portion between the metal tube and the joint is changed to the first and second portions, When the second coil section crosses the first and second coil sections,
Both the received signals of the coil section have the same waveform, and the difference signal between the received signals of the first and second coil sections does not show a phase change at the above-mentioned position, and the presence or absence and the position of the metal tube defect are extremely determined. Accurate detection is possible.

〔Example〕

One embodiment of the present invention will be described with reference to FIGS. In this metal tube defect inspection method, the defect is considerably smaller than the changed portion and the joint of the tube material of the metal tube, and the receiving coil is sufficiently smaller than the changed portion and the joint of the tube material of the metal tube and substantially equal to the defect. It is made by paying attention to the fact that the size can be set as described above.

That is, as shown in FIGS. 1 and 2, this defect inspection method for a metal tube includes a transmission coil 12 and a plurality of reception coils 13, 14, 15,... The transmission coil 12
, While moving the receiving coils 13, 14, 15,... In the tube axis direction, an electromagnetic wave is generated in the direction of arrow B from the transmitting coil 12, and the electromagnetic waves are received by the receiving coils 13, 14, 15,. , 14,15, ... received signal metal tube 11
By monitoring the phase change due to the defect 11a of the metal pipe, the metal pipe 11
The presence / absence and position of the eleven defects 11a are detected.

In this case, the plurality of receiving coils 13, 14, 15,... Are arranged close to the inner surface of the metal tube 1 and arranged in a line in the circumferential direction of the metal tube 11.

Further, the receiving coil 13 is composed of first and second coil portions 13a and 13b which are smaller than the changed portion of the tube material of the metal tube 11 and the joint and which are substantially equal to or larger than the defect 11a of the metal tube 11. In addition, the first and second coil portions 13a and 13b are set in such a range that the change of the tube material of the metal tube 11 and the joint have substantially the same effect on the phases of the received signals of the first and second coil portions 13a and 13b. , That is, arranged side by side in the circumferential direction of the metal tube 11, and the difference signal between the reception signals of the first and second coil sections 13 a and 13 b is used as the reception signal of the reception coil 13. The receiving coils 14, 15 also have the same configuration as the receiving coil 13, and include first coil sections 14a, 15a and second coil sections 14b, 15b, respectively. In the above example, every other coil portion 13a, 13b; 14a, 14b; 15a, 15b is paired, but this combination can be set arbitrarily.

Thus, for example, the receiving coil 13 is constituted by the first and second coil units 13a and 13b, and the first and second coil units 1
When the phase of the difference signal between the reception signals 3a and 13b is monitored as the reception signal of the reception coil 13, the change in the tube material of the metal tube 11 is included in the reception signals of the first and second coil portions 13a and 13b. And the phase change due to the presence of the joint
11 is arranged within a range in which the change in the tube material and the joint have substantially the same effect on the phases of both the received signals of the first and second coil portions 13a and 13b, that is, the tube is brought close to the inner surface of the metal tube 11 and Since the difference signals are arranged in the circumferential direction, no change in phase due to a change in the tube material of the metal tube 11 or the presence of the joint appears in the difference signal.

Here, as shown in FIG. 1, a defect 11a exists in a part of the metal pipe 11 at a position where the pipe material does not change, and a pipe material change portion 11b exists in the middle of the metal pipe 11.
Will be described over the entire circumference, and a defect 11c is present in a part of the tube material change portion 11b. While moving the transmission coil 12 and the reception coils 13, 14, 15,... At a constant interval in the tube axis direction of the metal tube 11,
The radiated radio waves from the transmitting coil 12 are received by the receiving coils 13, 14, 15,.
When received in the phase of the received signal by the receiving coils 13 and 15 installed at a position away from the defects 11a and 11c, the change by the tube material changing portion 11b is canceled,
FIGS. 3 (a) and 3 (c) show no effect of defects 11a and 11c.
There is almost no change as shown in FIG.

On the other hand, the phase of the signal received by the receiving coil 14 installed at a position close to the defects 11a and 11c
Is canceled, and only the influence of the defects 11a and 11c remains. As shown in FIG. 3 (b), only the change corresponding to the defects 11a and 11c occurs.

Thus, when the defects 11a and 11c exist in the metal tube 11,
Since the phase of the received signal by the receiving coil installed near the defects 11a and 11c, for example, 14, changes according to the position of the defects 11a and 11c, the transmitting coil 12 and the receiving coil
While moving 13, 14, 15, ... in the tube axis direction, each receiving coil 1
By monitoring the phases of the received signals by 3, 14, 15,..., It is possible to detect the presence and location of the defects 11a, 11c of the metal tube 11.

Here, the configuration of the metal tube defect inspection apparatus used in the metal tube defect inspection method will be described with reference to FIGS. FIG. 4 shows an example of a metal tube defect inspection apparatus, and FIGS. 5 and 6 show another example.

First, in FIG. 4, the metal tube defect inspection apparatus
A resin-made coil bobbin 22 is covered with a flexible connecting rod 21 made of a non-magnetic material such as copper or plastic, and is screwed.
Fixed at 23. The coil bobbin 22 has a transmission coil 24
Is wound so that the winding axis is parallel to the tube axis of the metal tube, and an insulating resin 25 is applied to the outer periphery thereof. A centering cushion 26 made of sponge or the like is adhered to the entire periphery or a part of the outer periphery of both flanges 22a of the coil bobbin 22. 27 is a screw for fixing the end of the transmission coil 24.

Further, the receiving coil holder 28 is externally attached to the connecting rod 21 at an interval of about twice the diameter of the metal pipe, and is fixed with screws 29. The receiving coil holding body 28 has, for example, twelve receiving coil holding recesses 28a on the outer peripheral surface, and the receiving coil 31 wound around the coil bobbin 30 in the receiving coil holding recess 28a has a winding axis corresponding to the tube axis of the metal tube. They are fitted so as to be perpendicular to each other, and sealed and fixed with resin (not shown). Also, the receiving coil holder
A centering cushion 33 made of sponge or the like is entirely or partially adhered to the outer peripheral surface of the portion having the maximum diameter of 28.

34 and 35 are lead wires connected to the transmission coil 24 and the reception coil 31, respectively. In the above description, the transmission coil 24 and the reception coil 31 are of a coreless type, but may be of a type having a core.

Then, the metal pipe defect inspection apparatus shown in FIG. 4 is inserted into the metal pipe, and is moved in the pipe axis direction in the metal pipe.

5 and 6 (a) and 6 (b) are cross-sectional views of main parts of another example of the metal tube defect inspection apparatus. In this metal tube defect inspection apparatus, the receiving coil 37 wound around the U-shaped coil bobbin 36 in the receiving coil holding concave portion 28b provided on the outer peripheral surface of the receiving coil holding body 28 has a winding axis parallel to the tube axis of the metal tube. And sealed and fixed with resin (not shown). Numeral 38 is a lead wire drawn from the receiving coil 37, and the other components are the same as those in FIG.

Next, for the purpose of clarifying the operation of the configuration of the embodiment, a defect inspection experiment of the metal tube was performed between the embodiment and the conventional example.

First, as an embodiment, as shown in FIG.
Provided with a transmitting coil 42 and a receiving coil holding block 44 having a receiving coil 43 in which the first and second coil portions 43a and 43b are arranged close to each other in the circumferential direction. As shown in FIG. 9, a connecting rod 45 provided with a transmitting coil 46 and a receiving coil holding block 48 having a receiving coil 47 is used. As shown in FIG.
When there is a defect 53 in a rolling (residual stress during rolling) portion 52 of 1 m, tube diameter 80 mm) 51, the receiving coil 4 is moved while moving inside the metal tube 51 in the tube axis direction (direction of arrow C).
The phase change of 3,47 received signals was examined.

The measurement conditions include the distance between the transmission coil 42 and the reception coil 43 and the distance between the transmission coil 46 and the reception coil 47.
240 mm, the excitation frequency for the transmission coils 42 and 46 is 30 Hz, and the excitation voltage is also 15 V _PP . The metal tube defect inspection device was moved so that one of the receiving coils 43 and 47 passed right above the defect 53.

FIG. 10 (a) shows the phase change of the received signal in the case of the conventional example, and FIG. 10 (b) shows the phase change of the received signal in the case of the embodiment. As is clear from Figure 10 (a), in the case of the conventional example, with a phase change P ₁ by rolling portion 52 appears in the received signal, a phase change P ₂ due to a defect 53 is superimposed on the phase change P ₁ will be appear, will be a phase change P ₂ due to a defect 53 is buried in a phase change P ₁ by rolling portion 52, and it is difficult to detect the phase variation P ₂ due to a defect 53, a low detection accuracy of the defect 53.

On the other hand, as is clear from Figure 10 (b), in the case of embodiment, the phase change Q ₁ by the rolling portion 52 in the received signal becomes extremely small, the phase change is the phase change Q ₂ by rolling portion 52 due to the defect 53 will be appear clearly without being buried in Q _1, it is easy to detect the phase change Q ₂ due to a defect 53, a high detection accuracy of the presence and position of a defect 53.

In the waveform of FIG. 10 (a), both ends are high because a phase change due to the end of the tube appears, and in the case of the embodiment, this is also eliminated.

Next, as shown in FIG. 11, a metal pipe (length 1 m, pipe diameter) was measured using the metal pipe defect inspection apparatus shown in FIGS. 7 and 8.
80mm) When a joint 63 with a length of 10 cm is provided between 61 and 62, an artificial defect 64 is formed at a position near the joint 63 of the metal tube 62 (at a position 20 mm from the joint end) before and after the formation of the artificial defect 64. After the formation of, the phase change of the reception signals of the reception coils 43 and 47 was examined while moving the inside of the metal tubes 61 and 62 in the tube axis direction (the direction of arrow D).

The measurement conditions include the distance between the transmission coil 42 and the reception coil 43 and the distance between the transmission coil 46 and the reception coil 47.
It is 300 mm, the excitation frequency for the transmission coils 42 and 46 is 30 Hz, and the excitation voltage is also 15 V _PP . Further, the metal tube defect inspection device was moved so that one of the receiving coils 43 and 47 passed right above the defect 64.

FIG. 12 (a) shows the phase change of the received signal before the formation of the defect 64 in the conventional example, and FIG. 12 (b) shows the phase change of the received signal after the formation of the defect 64 in the conventional example. FIG. 13A shows the phase change of the received signal before the formation of the defect 64 in the embodiment, and FIG. 13B shows the phase of the received signal after the formation of the defect 64 in the embodiment. The change is shown.

Figure 12 (a), as is clear from (b), the case of the conventional example, before the formation of the defect 64, the phase change R ₁ appearing due to the joint 63 to the received signal, after the formation of defects 64, received Fittings 63 to signal
A phase change R ₁ due to the defect 64 appears, and a phase change R ₂ due to the defect 64 appears superimposed on the phase change R ₁ .
Will phase change R ₂ due to a defect 64 is buried in the phase change R ₁ by joint 63, and it is difficult to detect the phase change R ₂ due to a defect 64, a low detection accuracy of the defect 64.

On the other hand, FIG. 13 (a), as is clear from (b), in the case of embodiment, before the formation of defects 64, the phase change S ₁ by the joint 63 in the received signal becomes very small, the phase due to the defect 64 The change S ₂ clearly appears without being buried in the phase change S ₁ due to the joint 63, and the phase change S ₂ due to the defect 64
And the accuracy of detecting the presence or absence and position of the defect 64 is high.

Further, the first and second coil portions 13a, 13b, 14a, 14b, 15
a, 15b,... are arranged side by side in the circumferential direction of the metal tube 11 so that there is no displacement in the tube axial direction. When the second coil portions 13a, 13b, 14a, 14b, 15a, 15b,... Cross the suddenly changing portion or when the joint between the metal tube 11 and the joint is formed, the first and second coil portions 13a, 13b, 14a, 14b , 15a, 15b,... Cross the first and second coil portions 13a, 13b, 14a, 14b, 15
The received signals a, 15b,... have the same waveform, and the above-mentioned portions are the first and second coil portions 13a, 13b, 14a, 14b, 15a, 15b,.
In the difference signal between the received signals, the phase change does not appear at the above position, and the presence or absence and the position of the defect of the metal tube 11 can be detected with extremely high accuracy.

The metal tubes to be inspected for defects are not only iron,
Any material such as copper and aluminum may be used.

〔The invention's effect〕

According to the defect inspection method for a metal tube of the present invention, the defect is considerably smaller than the changed portion and the joint of the tube material of the metal tube, the receiving coil is sufficiently smaller than the changed portion and the joint of the tube material of the metal tube, and Focusing on the fact that it is possible to set the size of the receiving coil to be approximately equal to or larger than the defect, the receiving coil is smaller than the changed portion of the tube material of the metal tube and the joint, and has a size approximately equal to or larger than the defect of the metal tube. And the first and second coil portions are arranged close to the inner surface of the metal tube and arranged in the circumferential direction of the metal tube, and the first and second coil portions are arranged. The difference signal of the received signal of the coil unit is used as the received signal of the receiving coil, and by monitoring the phase change of the received signal of the receiving coil, the presence or absence and the position of the defect of the metal tube are detected. Changes in tube material and Will be a phase change due to the presence of the joint is canceled, the presence and position of a defect of the metal tube despite the presence of the change and the joint of the pipe material of the metal tube can be detected accurately.

In particular, the first and second coil portions are arranged close to the inner surface of the metal tube and arranged side by side in the circumferential direction of the metal tube, so that the first and second coil portions are not displaced in the tube axis direction. When the first and second coil portions cross the suddenly changing portion in a case where the tube material in the axial direction of the metal tube changes suddenly, the first and second joint portions between the metal tube and the joint are formed.
When the first coil section crosses, both received signals of the first and second coil sections have the same waveform, and the difference signal between the received signals of the first and second coil sections includes a phase change at the above position. Does not appear, and the presence / absence and position of a defect in the metal tube can be detected very accurately.

[Brief description of the drawings]

1 and 2 are schematic sectional views of a metal tube defect inspection apparatus used in a metal tube defect inspection method according to one embodiment of the present invention, FIG. 3 is a waveform diagram of a signal received by a receiving coil, and FIG. The figure is a cross-sectional view showing one specific example of a metal pipe defect inspection apparatus, FIG. 5 is a cross-sectional view of a main part showing another specific example of the metal pipe defect inspection apparatus, and FIGS. 6 (a) and 6 (b). Is a front view and a side view showing the configuration of a receiving coil, respectively.
FIGS. 8, 8 and 9 are schematic diagrams for explaining the experimental conditions, respectively. FIGS. 10 (a) and 10 (b) show reception in the conventional example and the embodiment when there is a material change in the metal tube, respectively. FIG. 11 is a schematic diagram for explaining experimental conditions, and FIGS. 12 (a) and 12 (b) are conventional diagrams before and after formation of a defect near a joint of a metal tube, respectively. 13 (a) and 13 (b) are waveform diagrams showing the phase change of the received signal in the embodiment before and after the formation of the defect near the joint of the metal tube, respectively. , FIG. 14 and FIG. 15 are schematic sectional views of a metal tube defect inspection apparatus used in a conventional metal tube defect inspection method, FIG. 16 is a waveform diagram of a signal received by a receiving coil, and FIG. Sectional view for explaining the disadvantages,
FIG. 18 is a waveform diagram of a received signal for explaining a defect. 11 ... metal tube, 12 ... transmission coil, 13, 14, 15 ... reception coil, 13a, 14a, 15a ... first coil part, 13b, 14b, 15b ...
... Second coil section

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takao Yamagishi 5-1, 1-1 Hirano-cho, Higashi-ku, Osaka-shi, Osaka Inside Osaka Gas Co., Ltd. (72) Yasuji Hosohara 1-5-20, Kaigan, Minato-ku, Tokyo (72) Inventor Koichi Yasui 19-18 Sakuradacho, Atsuta-ku, Nagoya-shi, Aichi Prefecture Toho Gas Co., Ltd. (56) References JP-A-61-223549 (JP, A) JP-A-62- 255863 (JP, A)

Claims (1)

(57) [Claims] 1. A transmitting coil and a receiving coil are disposed in a metal tube so as to be movable in the tube axis direction at a constant interval in the tube axis direction, and the transmission coil and the receiving coil are moved in the tube axis direction while being moved in the tube axis direction. By generating an electromagnetic wave from a transmission coil and receiving the electromagnetic wave by the reception coil, and monitoring a phase change of a signal received by the reception coil due to a defect in the metal tube, a change portion and a joint of the tube material of the metal tube In the metal tube defect inspection method for detecting the presence or absence and position of the defect of the metal tube smaller than the, the receiving coil is smaller than the change portion and the joint of the tube material of the metal tube and the defect of the metal tube The first and second coil portions are configured to be substantially equal in size or larger, and the first and second coil portions are brought close to the inner surface of the metal tube and Place them in a line in the circumferential direction,
A defect inspection method for a metal tube, wherein a difference signal between the reception signals of the first and second coil units is used as a reception signal of the reception coil.