JPH03274455A - Method for diagnosing corrosion of pipe - Google Patents

Abstract

PURPOSE:To detect the pipe axial direction component of the leaked magnetic flux caused by corrosion and the depth of the diameter of a thin-wall part by magnetizing a pipe to be diagnosed and allowing magnetic detection elements to run through the pipe along with an exciting coil to detect leaked magnetic flux. CONSTITUTION:Magnetic flux is generated in the normal part of a pipe so as to magnetically saturate the same by the exciting coil 4 wound around the small diameter part at the center of the axial line direction of a core 3 composed of a high permeability material. A plurality of magnetic detection elements 5 are arranged on the small diameter part of the core 3 at equal intervals L in the peripheral direction thereof. When there is no thin-wall part due to the corrosion in the pipe 1, the magnetic flux due to the coil 4 entirely passes through the thin wall of the pipe 1 and, therefore, no leaked magnetic flux is generated from the pipe and leaked magnetic flux is not detected by the magnetic detection elements 5. When there is the thin-wall part 6 in the pipe 1, the magnetic flux due to the coil 4 is leaked from the pipe 1 and detected by the elements 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pipe corrosion diagnosis method for grasping and diagnosing the corrosion status of underground pipes such as steel pipes.

BACKGROUND OF THE INVENTION Conventionally, the so-called leakage flux method has been used to diagnose the state of corrosion and thinning of pipes. This leakage magnetic flux is also known as the pole-to-pole leakage flux method, in which the normal part of the tube is magnetized by an excitation coil so that it is magnetically saturated, and a magnetic detection element is provided within the range of this magnetically saturated part. When there is corrosion and thinning of the pipe, the magnetic flux leaking from the thick part of the pipe is
Detected by a magnetic detection element.

Problems to be Solved by the Invention In typical prior art, the peak value of the tube axis direction component of the leakage magnetic flux detected by a magnetic detection element is detected, and the diameter or depth of the thinned part corresponding to the magnitude of this peak value is determined. is estimated.

According to experiments conducted by the inventor of the present invention, it has been found that the correspondence between the wave height value of the horizontal component of the leakage magnetic flux and the diameter and depth of the thinned portion is not clear. The cause of this is that the magnetic sensing element is displaced from the thinned area in the circumferential direction, and some thinned areas are long and narrow, or have a gentle depression, and these various shapes It is not possible to accurately capture thinned areas that have

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for diagnosing corrosion of a metal pipe that can accurately detect the diameter and depth of a thinned portion caused by corrosion of a metal pipe.

Means for Solving the Problems The present invention magnetizes a tube to be diagnosed by an excitation coil, runs a magnetic detection element along with the excitation coil inside the tube, and detects the tube axis direction component of leakage magnetic flux detected by the magnetic detection element. This pipe corrosion diagnosis method is characterized in that the diameter and depth of the thinned portion are detected based on the radial component of the leakage magnetic flux.

Further, the present invention runs an exciting coil and a magnetic detection element, and uses the output of the magnetic detection element to detect the diameter of the thinned portion corresponding to the deviation ΔT between the maximum value and the minimum value of the radial component of the leakage magnetic flux. It is characterized by detecting.

Further, the present invention is characterized in that the diameter of the thinned portion corresponding to the half width of the component of the leakage magnetic flux in the tube axis direction is detected.

Further, the present invention is characterized in that the depth d of the thinned portion corresponding to the detected diameter and the peak value of the component of the leakage magnetic flux in the tube axis direction is detected.

Further, the present invention is characterized in that the depth d of the thinned portion corresponding to the detected radius and the amplitude of the radial component of the leakage magnetic flux is detected.

According to the present invention, a normal part of the tube to be diagnosed is magnetized by the excitation coil, for example, so as to be magnetically saturated, and a magnetic detection element, such as a detection coil, a hole, etc. element or magnetoresistive element is arranged, and this magnetic detection element measures the tube axial direction component of the leakage magnetic flux leaked by the thinned part and the radial direction component of the leaked magnetic flux, and detects the thinned part based on these components. It becomes possible to detect the radius and depth d with high accuracy.

In particular, according to the present invention, the excitation coil and the magnetic detection element are integrated and run at a predetermined constant speed, and the deviation amount ΔT between the maximum value and the minimum value of the radial component of the leakage magnetic flux is The diameter can be accurately corresponded to, and this was found through experiments by the inventor of the present invention.

The diameter of the thinned portion of the hole can also be determined by detecting the half width of the component of the leakage magnetic flux in the tube axis direction.

The diameter of the thinned part detected in this way, the peak value of the component in the tube axis direction of the leakage magnetic flux, and the depth d of the thinned part correspond accurately. The depth of the thinned portion can be detected based on the peak value of the component.

Furthermore, the depth d of the thinned portion is determined in accordance with the diameter of the thinned portion detected in this way and the amplitude of the radial component of the leakage magnetic flux.
It is also possible to detect.

Example FIG. 1 is a sectional view of one embodiment of the present invention.

Inside the metal, for example, steel pipe 1 buried underground,
A diagnostic device 2 is arranged so as to be movable in the tube axis direction.

FIG. 2 is a perspective view of this diagnostic device 2. Referring to FIGS. 1 and 2, an excitation coil 4 is wound around a small diameter portion in the axial center of a core 3 made of a high magnetic permeability material. Generate magnetic flux so that it can be saturated. Magnetic detection elements 5 are arranged in the small diameter portion of the core 3 at equal intervals in the circumferential direction. As shown in FIG. 1 (1), when there is no thinning part due to corrosion in the tube 1, all the magnetic flux from the excitation coil 4 passes through the wall thickness of the tube 1, and therefore leaks from the tube 1. No magnetic flux is generated, and no leakage magnetic flux is detected by the magnetic detection element 5.

When the tube 1 has a thinned portion 6 as shown in FIG. Magnetic detection element 5
may be a detection coil, a Hall element, a magnetoresistive element, or the like.

Referring to FIG. 3, the thinned portion 6 of the tube 1 has a diameter and a depth d, and the thickness of the tube 1 is t in the description below. When such a thinned portion 6 exists, the magnetic flux 7 leaks inward in the radial direction of the tube 1. Although this magnetic flux also leaks outward in the radial direction of the tube 1, it is not shown in FIG. 3 for the sake of simplification of explanation. The leakage magnetic flux 7 is represented by a vector φ1, which can be divided into a component φH in the tube axis direction and a component φT in the radial direction of the tube 1.

FIG. 4 is a perspective view of the magnetic detection element 5. Specifically, this magnetic detection element 5 includes two magnetic detection elements 5a and 5b.
are formed in pairs, and are arranged in the small diameter portion of the core 3 at equal intervals L (see FIG. 2) in the circumferential direction as described above. One magnetic detection element 5a detects the tube axis direction component φH of the leakage magnetic flux, and the other magnetic detection element 5b detects the radial direction component φT of the leakage magnetic flux. Reference marks 5a, 5b
are collectively indicated by reference numeral 5. - within the shell a magnetic sensing element 5;
has a directionality with high sensitivity to the magnetic flux to be detected, selectively detects each magnetic flux φH2φT in the tube axis direction and the radial direction, and derives an output proportional to the magnitude of these magnetic fluxes.

FIG. 5 shows an output waveform obtained when the thinned portion 6 travels when detecting the component φH of the leakage magnetic flux in the tube axis direction detected by the magnetic detection element 5a.

The output waveform due to the component φH of the leakage magnetic flux in the tube axis direction has a peak value VH, and a width at half the value VH/2 of the peak value VH, that is, a half width ΔVH can be obtained.

FIG. 6 shows the output waveform of the magnetic sensing element 5b due to the vertical component φT of the leakage magnetic flux. This output waveform has a maximum value 8 and a minimum value 9 when the magnetic sensing element 5b travels through the thinned part 6. is obtained, and the amplitude V between these maximum values 8 and minimum values 9
T can be measured. Furthermore, the deviation amount ΔT between the local maximum value 8 and the local minimum value 9 can be obtained.

FIG. 7 is a graph showing the experimental results of the inventor of the present invention.

As described above, the waveform shown in FIG. 6 can be obtained by the magnetic detection element 5b that detects the vertical component φT of the leakage magnetic flux.
The deviation amount ΔT between the maximum value 8 and the minimum value 9 corresponds to the diameter of the thinned portion 6.

In the experimental results shown in Figure 7, the Japanese Industrial Standard 200 ASGP
A steel pipe is used, its outer diameter is 216.3 mmφ, and the pipe 1
The wall thickness t is 5.8 nm. The depth d of the thinned part 6 is 4
．． 3 mm, the magnetic detection element 5b
Characteristic 10 is obtained when the area is directly below the
Characteristic 11 is obtained at a position shifted by an interval L/2 from the center in the circumferential direction. Similarly, characteristics 12 to 15 are the first
Obtained as shown in the table.

Table 1 From the above, it can be seen that the deviation amount ΔT between the maximum value 8 and the minimum value 9 corresponds to the diameter of the thinned portion 6.

FIG. 8 is a graph showing the relationship between the half-value width ΔV H of the output waveform obtained by the tube axis direction component φH of the leakage magnetic flux detected by the magnetic detection element 5a and the diameter of the thinned portion 6. Characteristic 16 is obtained when the magnetic detection element 5a is directly under the thinned portion 6, and the distance from the thinned portion 6 to the circumferential direction of the tube 1 is L/2.
Characteristic 17 is obtained when the magnetic detection element 5a is located at a position shifted by 1. Similarly, the characteristics 16', 16'',
17'17'' is obtained as shown in Table 2.

Table 2 From this, it is understood that the leakage magnetic flux component φH in the tube axis direction corresponds to the diameter of the thinned portion 6.

To summarize, as explained in connection with FIG. 7, the magnetic sensing element 5 obtained by the radial component φT of the leakage magnetic flux
By detecting the maximum value 8 and minimum value 9 of the output of b and the deviation amount ΔT, the diameter of the thinned part 6 can be determined, and as described in connection with FIG. 8, the leakage magnetic flux can be determined. Half width ΔV of the output of the magnetic detection element 5a that detects the component φH in the tube axis direction
The diameter of the thinned portion 6 can also be determined by H.

FIG. 9 shows the wave height ■H corresponding to the tube axis direction component φH of the leakage magnetic flux obtained by the magnetic detection element 5a and the thinned portion 6.
Characteristics 18 to 23, which are graphs showing the relationship between the radius and the depth d, are shown.

From this, after determining the diameter of the thinned portion 6 as described above, the depth d of the thinned portion 6 can be determined by detecting the peak value VH of the magnetic detection element 5a due to the component φH in the tube axis direction. You can know.

Table 3 and FIG. 10 are graphs showing the correspondence between the amplitude VT of the radial component φT of the leakage magnetic flux detected by the magnetic detection element 5b, the diameter of the thinned portion 6, and the depth d thereof.

Therefore, as described above, after determining the diameter of the thinned portion 6, the depth d of the thinned portion 6 can be determined by determining the amplitude VT from the waveform of the magnetic detection element 5b.

In the above embodiment, the circumferential spacing between the magnetic sensing elements 5 is, for example, 12 mm.

According to the experiments of the present inventor, preferably, as shown in the above-mentioned FIG.
Next, as described in relation to FIG. 9, the magnetic detection element 5a determines the peak value VH due to the tube axis direction component φH of the leakage magnetic flux, and as described above. It has been confirmed that by determining the depth d of the thinned portion 6 using the diameter determined by the method, thinned portions 6 having various shapes can be measured with small measurement errors and high accuracy. It was done.

It is not necessary to cause magnetic saturation in the normal portion of the tube 1 by the excitation coil 4, and it is sufficient as long as the leakage magnetic flux 7 in the thinned portion 6 can be detected by the magnetic detection element.

Effects of the Invention As described above, according to the present invention, the magnetic detection element allows
It becomes possible to accurately detect the diameter and depth of the thinned portion based on the tube axis direction component and the radial direction component of the magnetic flux leaked by the thinned portion due to corrosion.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a diagnostic device 2 according to an embodiment of the present invention and its vicinity, FIG. 2 is a perspective view of the diagnostic device 2, and FIG. , FIG. 4 is a perspective view of the magnetic detection elements 5a and 5b, FIG. 5 is a diagram showing the output waveform when the horizontal component φH of the leakage magnetic flux 7 is detected by the magnetic detection element 5a, and FIG. 6 is a perspective view of the magnetic detection element 5b. Fig. 7 shows the output waveform obtained when the radial component φT of the leakage magnetic flux is detected by the magnetic detection element 5b. Graph showing the diameter of the thinned portion 6 corresponding to the amount ΔT, No. 8
The figure is a graph showing the relationship between the half-width ΔVH of the tube axis direction component φH of the leakage magnetic flux and the diameter of the thinned part 6 depending on the output of the magnetic detection element 5a. FIG. 10 is a graph showing the relationship between the wave height VH due to the axial component φH and the diameter and depth d of the thinned portion 6. The graph in FIG. It is a graph showing the relationship between the radius and depth d of the flesh portion 6. 1...Tube, 2...Diagnostic device, 3...Core, 4...
・Exciting coil, 5, 5a, 5b... Magnetic detection element, 6
... Thin thinning part, 7... Magnetic flux, 8... Maximum value, 9...
・Minimum value, φH... tube axis direction component of leakage magnetic flux, φT・
... Radial component of leakage magnetic flux, VH ... Peak value, ΔV
H...Half width, VT...Amplitude, ΔT...Difference amount

Claims (5)

[Claims] (1) The tube to be diagnosed is magnetized by an excitation coil, a magnetic detection element is run inside the tube together with the excitation coil, and the tube axis direction component of the leakage magnetic flux detected by the magnetic detection element and the leakage magnetic flux are detected by the magnetic detection element. A method for diagnosing corrosion of a pipe, characterized in that the diameter and depth of a thinned part are detected based on the radial component of the pipe. (2) The excitation coil and the magnetic detection element are run, and the diameter D of the thinned part corresponding to the deviation ΔT between the maximum value and the minimum value of the radial component of the leakage magnetic flux is determined by the output of the magnetic detection element. A method for diagnosing corrosion of a pipe according to claim 1, which comprises detecting corrosion of a pipe. (3) The method for diagnosing corrosion of a pipe according to claim 1, characterized in that the diameter D of the thinned portion corresponding to the half width of the component of the leakage magnetic flux in the pipe axis direction is detected. (4) The tube according to claim 1, wherein the depth d of the thinned portion corresponding to the detected diameter D and the peak value of the tube axis direction component of the leakage magnetic flux is detected. Corrosion diagnosis method. (5) Corrosion diagnosis of a pipe according to claim 1, characterized in that the depth d of the thinned portion corresponding to the detected diameter D and the amplitude of the radial component of the leakage magnetic flux is detected. Method.