JPH0457961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting corrosion position of a pipe body and an improvement in its detection method.

Conventionally, there are two types of devices for detecting the corrosion position of a test tube: one using an ultrasonic sampling method and the other using an eddy current sampling method. The former, which uses the ultrasonic sampling method, has a transmitter 2a that transmits ultrasonic waves into the inside of the test tube 1 and a receiver 2b that receives the ultrasonic waves, as shown in FIG. While inserting the equipped ultrasonic transceiver 2 and running it, pulsed ultrasonic waves are transmitted from the transmitter 2a, and as the ultrasonic waves propagate, the tube under test 1
The receiver 2b receives both the reflected waves reflected from the inner surface 1a and the outer surface 1b of the test tube 1, and measures the wall thickness of the test tube 1 from the arrival time difference between the two reflected waves. The position of a thin walled portion of the pipe 1 due to corrosion is detected.

By the way, in an apparatus using this ultrasonic sampling method, in order to efficiently propagate ultrasonic waves within the tube 1, the inside of the tube 1 is filled with water 3, and the transmitter 2a, the receiver 2b, and the tube 1 to be examined are connected. It is necessary to create an acoustic matching with the This increases the number of steps such as filling water before measurement and draining water after measurement, making the measurement work cumbersome. In addition, when inspecting the entire circumference of the tube 1 to be inspected, it is necessary to arrange a large number of transmitters 2a and receivers 2b radially, which makes the device large-scale. In the case of a small diameter tube of 2 inches, it is difficult to detect the corrosion position of the test tube 1 using this type of measurement method.

Next, in the method using the eddy current sampling method, a coil 4 is placed inside the test tube 1 as shown in FIG.
By applying an alternating current excitation current to this coil 4 from an alternating current power source 5, a magnetic field Hp is generated from the coil 4 to induce an eddy current 6 inside the tube 1 to be tested, and this eddy current 6 causes secondary magnetic field
In this case, the magnetic field Hs moves in the opposite direction to the magnetic field Hp and in a direction that decreases Hp, so it acts as a kind of resistance to the initial alternating current, and thereby As a result, the impedance of the coil 4 changes. Therefore, by measuring the impedance of the coil 4, changes and magnitude of the eddy current 6 can be known. Here, when the flesh of the test tube 1 becomes thinner due to corrosion, the electrical resistance of the test tube 1 increases and the eddy current 6 decreases.
If this is measured as a change in the impedance of the coil 4, the corrosion position of the test tube 1 can be detected.

However, when using the eddy current sampling method, the test tube 1
The eddy current 6 generated inside the test tube 1 tends to concentrate on the surface of the test tube 1 due to the skin effect of alternating current. The thickness of the area where the current is concentrated is called the skin depth, and in the case of steel, the skin depth is approximately 1 mm at 50Hz. Therefore, the present method in which the coil 4 is placed inside the tube to be inspected 1 has low sensitivity to corrosion on the outer surface of a tube with a wall thickness of 2 to 3 mm or more, making it difficult to detect the location of the corrosion. This is often the case. Further, if the frequency is lowered, although the skin depth increases, the eddy current itself decreases, which has the disadvantage of causing the same decrease in sensitivity as described above.

The present invention was made in view of the above-mentioned circumstances, and it is possible to easily detect the corrosion position on the outer surface of a small-diameter pipe, and to detect the corrosion position using a small detector and without the need for strict positioning. An object of the present invention is to provide a corrosion position detection device for a pair of tubes that can detect corrosion with high sensitivity.

Another object of the present invention is to provide a method for detecting a corroded position of a pipe body, which can easily detect a corroded position while effectively utilizing Ampere's law of circular integrals.

Hereinafter, the principle structure of the present invention will be explained with reference to FIG. In the same figure, reference numeral 11 is a tube to be tested, and a power source 12 is connected to both ends of the tube 11 or at a predetermined length.
The cables 13, 13 are led out and connected directly or via anti-corrosion terminals 14, 14, etc., so that a current is passed in a predetermined direction into the flesh of the tube 11 to be inspected. On the other hand, there is a test tube 1 inside the test tube 11.
A magnetic field detector 15 for detecting a magnetic field generated by a current flowing in the meat part 1 is installed so as to be movable by traction, self-propelled, or pumping means. Furthermore, a magnetic field indicator 17 is connected to the magnetic field detector 15 via a signal cable 16.
After converting the detected magnetic field into an electric signal, it is displayed as a magnetic field on a magnetic field display 17. The magnetic field detector 15 also includes a wire drum 18.
A wire 19 led out from the wire 19 is connected, and a wire length meter 20 is connected in the middle of the wire 19. This wire length meter 20
For example, the distance traveled by the wire 19 and the position of the magnetic field detector 15 are measured and displayed by counting the marks attached to the wire 19 or by counting the number of revolutions of the wire 19 when it rotates in contact with the wire 19.

According to the above configuration, a current is passed in a predetermined direction across both ends or a predetermined length of the test tube 1, and while the magnetic field detector 15 is running within the test tube 1, the magnetic field detector 15 is The position and the magnetic field detected at that position can be measured and displayed by the wireless length meter 20 and the magnetic field display 17.

By the way, in general, since there is no current in the tube, the following equation holds true for the magnetic field inside the tube based on Ampere's law of circular integrals.

φHdl=0…(1) However, H is the strength of the magnetic field.

If there is no corrosion in the test tube 11, the current will be uniformly distributed in the flesh of the test tube 11 as shown in FIG. Therefore, since this system is point symmetric, equation (2) holds true.

H(r, θ)=a(r)…(2) However, a indicates a vector potential.

Therefore, from equations (1) and (2), if we perform circular integration on an arbitrary circumference concentric with the test tube 11, we get 2πra(r)=0(Δr) ∴ a(r)=H(r, θ)=0...(3) holds, and no magnetic field is generated inside the tube.

However, if there is a corroded part 11a in the test tube 11,
As shown in Figure 5a, the current distribution is non-uniform, so equation (2) and even equation (3) do not hold, so H≠0 and a magnetic field is generated inside the test tube 11. I will do it. In fact, the current distribution in Figure 5a is the same as the uniformly distributed current +i in Figure 5b and Figure 5c.
Considering that it is superimposed with the non-uniform current -i, the test tube 1
It can be understood that a magnetic field is generated inside 1. Therefore, if the magnetic field inside the test tube 11 in the tube cross-sectional direction is detected by the magnetic field detector 15, the test tube 11
Corrosion on the outside or inside of the product can be detected.

Regarding the magnetic field in the tube axis direction of the test tube 11, the sixth
As shown in the figure, the current distribution is disturbed in the corroded part 11a, so the position of the corroded part 11a in the tube 11 to be inspected is detected by measuring the magnetic field H in the tube axis direction formed by the current in the tube thickness direction. can do.

Next, as an embodiment of the present invention, a case where the present invention is applied to, for example, a buried gas pipe will be described with reference to FIG. In other words, it is approximately 200m long, buried underground.
A DC current of 40 A is applied to both ends of a 2-inch diameter gas pipe 11a from a power source 12 via a switch 21, a cable 13, and an anti-corrosion terminal 14. on the other hand,
As shown in FIG. 8, the magnetic field detector 15 includes a total of three sensors 15X in a cylindrical casing 15a made of plastic, for example, in order to measure magnetic fields in the X direction, Y direction, and axial direction of the tube cross section. ,15Y,1
5Z are arranged in a predetermined direction, and center risers 15b are arranged on the outer periphery of both ends of the casing 15a.
is installed.

The magnetic field detector 15 employs a method in which, for example, the magnetic field detector 15 is forced to a predetermined position and then pulled back using a wire 19 . The length of the wire 19 fed into the test tube 11 can be determined by counting and displaying the mark displayed on the wire 19 or the number of revolutions of the rotating body using the wire length meter 20, and the position of the magnetic field detector 15. Measure. On the other hand, the magnetic field detector 15
The detected magnetic field is sent to a magnetic field indicator 17 via a signal cable 16, where changes in the magnetic field are read. Note that the influence of earth's magnetism and residual magnetism of the pipe welded portion can be eliminated by turning on and off the current output from the power source 12 with the switch 21 and reading the difference.

Next, FIG. 9 shows an example of measurement when a corroded portion 11a exists in the tube 11 to be tested. That is, power supply 1
2, a direct current of 20A was applied to the test tube 11 and the strength of the magnetic field was observed on the magnetic field indicator 17, as shown in Figure 9a.
For a corroded part 11a of 300 mm ³ , the magnetic field in the X direction of the tube cross section appears as shown in Fig. 9b, and the magnetic field in the tube axis direction appears as shown in Fig. 9c, which sufficiently covers the corroded part 11a on the outer surface. I was able to detect it.

The magnetic field detector 15 is small, about 10 mm x 40 mm, and a 1-inch tube can also be used. Magnetic field sensor 15X, 15Y, 15
As Z, for example, a small sensor such as a Hall element or a semiconductor sensor can be used. In addition, the power source 12 uses both direct current and alternating current, and the skin effect that distinguishes between internal and external corrosion causes the current to concentrate on the outer surface of the tube, reducing sensitivity to internal corrosion. It is best to compare and distinguish between DC current and AC current. Further, in the embodiment, the underground pipe 11a is shown, but the present invention can be similarly applied to general piping such as piping inside a building or a boiler tube.

As detailed above, according to the present invention, a magnetic field detector is inserted into the test tube while a current is flowing through the test tube, and the magnetic field generated from the disturbance in the current distribution due to corrosion is detected while the test tube is running. This eliminates the need to fill the test tube with water for measurement, and the magnetic field detector itself can be made compact using semiconductor elements, so strict positioning is required even for small-diameter tubes. The location of corrosion can be detected without having to do so. Furthermore, since it is not an eddy current sampling method, there are no problems caused by the skin effect, and the problem of decreased sensitivity can be solved.

Furthermore, by effectively utilizing Ampere's law of circular integrals, it is possible to easily detect the corroded position of the tube from the presence or absence of magnetic flux.

[Brief explanation of drawings]

Figures 1 and 2 are schematic configuration diagrams for explaining the conventional device, Figure 3 is a diagram of the principle configuration of the device of the present invention, and Figures 4 to 6 show the state of current distribution in the flesh part of the tube to be inspected. FIG. 7 is a diagram showing the application to a buried gas pipe, FIG. 8 is a configuration diagram of a magnetic field detector, and FIG. 9 is a diagram showing measurement results when a corroded part hits a pipe to be inspected. 11... Test tube, 11a... Corroded part, 12...
Power supply, 15... Magnetic field detector, 17... Magnetic field indicator, 18... Wire drum, 19... Wire, 2
0...Wire length meter.

Claims (1)

[Scope of Claims] 1. A current supply means for passing a current in the axial direction of the test tube, and a magnetic field caused by the current distribution in the test tube wall portion formed by the current from the current supply means. Corrosion position of a pipe body, characterized by comprising a magnetic detector that detects the presence or absence of corrosion by detecting the presence or absence of corrosion, and a running position detection means that detects the running position while running the magnetic detector in the pipe to be inspected. Detection device. 2 A current is applied in the direction of the tube axis of the tube, and based on Ampere's law of circular integrals, when there is no corrosion in the tube, a magnetic field is not generated approximately on the central axis within the tube. A corrosion position detection method for a pipe body, characterized by detecting the presence or absence of corrosion in a pipe body.