JPH08233509A - Close-in distance-measuring method for double tubes - Google Patents

Abstract

PURPOSE: To provide a close-in distance-measuring method for double tubes, which obtains the separating distance at a plurality of places of the double tubes made of ferromagnetic metal. CONSTITUTION: A gas tube 10 made of steel tube and a sheath tube 11 are provided. An electromagnet 12, which is movably mounted on the inner wall of the gas tube 10, is provided. At first, points A-H of the inner wall of the gas tube 10 are sequentially magnetized. Then, the electromagnet 12 is moved and mounted again on the inner wall A of the gas tube 10. The inner wall A of the gas tube 10 and the sheath tube 11 in the vicinity of the inner wall A are magnetized. A part of the magnetic flux penetrates the vicinity of the inner wall A of the gas tube 10 and the tube wall of the sheath tube 11. Such a value of the magnetic flux leakage is measured by a probe and a Gauss meter. The magnetic flux leakage value is applied on the graph of the relationship of the (known distance)/(magnetic flux leakage value), and the separating distance between the gas tube 10 and the sheath tube 11 is obtained. The magnetic flux leakage value remains the same in repeated measurements conducted in many times. Therefore, the separating distance between the inner tube and the outer tube can be accurately obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the close distance of a double pipe, which is adapted to obtain the separation distances at a plurality of positions of a double pipe made of a ferromagnetic metal by utilizing the leakage flux method. is there.

[0002]

2. Description of the Related Art In recent years, in order to lay a gas pipe in the ground, not only an excavation method of excavating from the surface of the earth and burying it, but also a place where the surface of the earth cannot be excavated, such as an excavator, etc. The non-excavation method has been applied. In this construction method, there is a case where a double pipe structure is adopted in which the gas pipe 1 is built and laid inside a sheath pipe 2 having a diameter larger than the inner diameter of the gas pipe 1 (see FIG. 3). The gas pipe 1
Is not in a positional relationship in which the centers are aligned with the sheath tube 2 in cross section, but inside the sheath tube 2, a cable tube, a chemical solution, etc. Due to the arrangement of the injection pipe, the center of the gas pipe 1 is set to be eccentric below the center of the sheath pipe 2. Since the gas pipe 1 and the sheath pipe 2 are steel pipes in this arrangement, the electromagnet 3 is arranged on the inner wall of the gas pipe 1 so that the gas pipe 1
Is magnetized, the stray magnetic field is detected by the magnetic sensor 4, and the distance between the gas tube 1 and the sheath tube 2 is obtained based on the stray magnetic field, so that it can be grasped. It should be noted that such measurement was repeatedly performed, for example, at eight locations over the circumference of the inner wall of the gas pipe 1 (see FIG. 4).

[0003]

However, when it is necessary to re-measure immediately after the inner wall of the gas pipe 1 is magnetized once,
Due to the residual magnetism on the tube wall, the measured value in the re-measurement will be different from the original measured value. As a result,
An accurate value of the distance between the gas pipe 1 and the sheath pipe 2 could not be obtained. The present invention has been made in order to solve such a problem, and provides a method for measuring the close distance of a double pipe, which is configured to obtain the separation distances at a plurality of locations of a double pipe made of a ferromagnetic metal. The purpose is to do.

[0004]

In order to solve the above-mentioned problems, the present invention provides a double tube constituted by an outer tube made of a ferromagnetic metal and an inner tube contained in the outer tube, and an inner wall of the inner tube. Sequentially magnetizes in a predetermined direction over multiple locations around it,
After that, while magnetizing in the same direction over the inner pipe inner wall peripheral multiple places, while measuring the leakage magnetic flux value at each of a plurality of locations, based on these leakage magnetic flux values, the inner pipe and the outer pipe at the plurality of locations. The feature is that the separation distance is obtained.

[0005]

[Function] Initially, the inner wall made of a ferromagnetic metal is magnetized in the same direction over a plurality of locations around the inner wall of the inner tube. At this time, the residual magnetism exists at a plurality of locations, that is, at each location. In the state where the magnetic conditions in (3) are adjusted, they are sequentially magnetized again in the same direction. Then, when magnetizing, the leakage magnetic flux value is measured at each location, and the separation distance between the inner tube and the outer tube at the plurality of locations can be obtained based on these leakage magnetic flux values. in this way,
It was magnetized again in the presence of residual magnetism to measure the leakage flux value, and the separation distance between the inner tube and the outer tube was calculated based on this value, so the same location was repeatedly magnetized to determine the leakage flux value. It can be seen that the same value is obtained by measurement and the measurement data is stable.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an example of an apparatus for carrying out the method for measuring the close distance of a double pipe according to the present invention is shown in the drawings, and will be described in detail below. FIG. 1 shows a schematic cross-sectional view of the double pipe. This double pipe shows, for example, a gas pipe 10 laid in the ground, and a sheath pipe 11 having a diameter larger than the inner diameter of the gas pipe 10. On the inner wall of the gas pipe 10, there is provided an electromagnet 12 movably mounted. The gas pipe 10 and the sheath pipe 11
Is a steel pipe, and is magnetized by the electromagnet 12. The electromagnet 12 is configured such that it can be movably mounted at eight points A to H at regular intervals over the entire circumference of the inner wall of the gas pipe 10 by a movement support mechanism (not shown).
As shown in FIG. 2, the pair of magnetic poles 13a and 13b have inner walls A.
It is designed to be mounted in contact with points ~ H. A Gauss meter 14 is provided between the pair of magnetic poles 13a and 13b.
The probe 15 is arranged. By energizing the electromagnet 12, the points A to H on the inner wall of the gas pipe 10 are magnetized, and the sheath tube 1 outside the gas pipe 10 at the points A to H on the inner wall is magnetized.
1 is magnetized, and the leakage magnetic flux value corresponding to the sheath tube 11 is measured by the probe 15 and the Gauss meter 14.

Next, in the gas pipe 10 and the sheath pipe 11 as described above, the procedure for measuring the separation distance between the gas pipe 10 and the sheath pipe 11 at points A to H on the inner wall of the gas pipe 10 will be described. Initially, the electromagnet 12 is energized to sequentially magnetize the gas pipe 10 inner wall points A to H, which are steel pipes, and the electromagnet 12 is movably mounted on the gas pipe 10 inner wall points A to H by the movement support mechanism. Gas pipe 10 inner wall points A to H, and inner wall A to H
The sheath tube 11 close to the point is magnetized, which causes the inner wall A
It is possible to adjust the magnetic initial conditions of the sheath tube 11 near the points ~ H and the inner walls AH.

Then, again, the electromagnet 12 is moved and mounted on the inner wall A of the gas pipe 10, and electricity is supplied to the inner wall A of the gas pipe 10,
The sheath tube 11 near the inner wall A is magnetized. A part of the magnetic flux penetrates the inner wall A of the gas pipe 10 and the pipe wall of the sheath pipe 11, and the leakage magnetic flux value can be measured by the probe 15 and the Gauss meter 14. Since the leakage magnetic flux value is a value corresponding to the separation distance between the gas pipe 10 and the sheath pipe 11, the separation distance between the gas pipe 10 and the sheath pipe 11 can be calculated from the known distance-leakage magnetic flux value relationship graph. You can figure it out. Then, similarly, the electromagnet 12 is moved to the inner wall B of the gas pipe 10 to the inner wall H to be magnetized, and the respective leakage magnetic flux values can be measured,
The separation distance between the gas pipe 10 and the sheath pipe 11 near the inner wall B, ... Thus, prior to the measurement, by adjusting the initial magnetic condition, even if repeatedly magnetized and measured, the leakage magnetic flux value does not change. Therefore, based on these leakage magnetic flux values, The separation distance between the gas pipe 10 and the sheath pipe 11 at the points A to H on the inner wall of the gas pipe 10 can be accurately derived.

The embodiment for carrying out the method for measuring the close distance of the double pipe according to the present invention has been described above.
A plurality of, for example, three electromagnets 12 are attached to the inner wall of the gas pipe 10, and are sequentially moved to magnetize the wall of the gas pipe 10, and the leakage magnetic flux value is measured to separate the gas pipe 10 from the sheath pipe 11. It is also possible to adopt a configuration in which the distance is obtained.

[0010]

As described above, according to the present invention, the separation distance of the double tube is measured by measuring the leakage magnetic flux value, and is magnetized before the initial magnetic condition is adjusted before it is obtained. Since the leakage magnetic flux value is measured, the leakage magnetic flux value does not change no matter how many times the measurement is repeated, and therefore the separation distance between the inner pipe and the outer pipe can be accurately obtained.

[0011]

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional explanatory view of a double tube for carrying out a method for measuring a short distance of a double tube according to the present invention.

FIG. 2 is a schematic configuration explanatory diagram for obtaining a leakage magnetic flux value by an electromagnet in the double tube shown in FIG.

FIG. 3 is a schematic configuration explanatory diagram of a double tube for explaining the principle of the method for measuring the short distance of the double tube according to the present invention.

4 is a partially cutaway perspective explanatory view showing a mounting configuration of an electromagnet in the double pipe shown in FIG.

[Explanation of symbols]

 10 Gas Pipe 11 Sheath Pipe 12 Electromagnets 13a, 13b Magnetic Pole 14 Gauss Meter 15 Probe

Claims (1)

[Claims] 1. In a double tube constituted by an outer tube made of a ferromagnetic metal and an inner tube built into the outer tube, magnetization is sequentially performed in a predetermined direction over a plurality of locations around the inner wall of the inner tube, and thereafter, While magnetizing in the same direction over a plurality of locations around the inner wall of the inner pipe, measuring the leakage magnetic flux value at each of a plurality of locations,
A method for measuring a close distance of a double pipe, wherein the distances between the inner pipe and the outer pipe at the plurality of locations are obtained based on these leakage magnetic flux values.