JPH08233511A - Proximate distance measuring method for double tubes - Google Patents

Abstract

PURPOSE: To estimate the most proximate distance of double tubes by applying a plurality of graphs for the relationship between an angle and the value of magnetic flux leakage prepared beforehand and to make it possible to suppress errors with less dispersion. CONSTITUTION: An electromagnet 12 is moved and mounted at points A-H of the inner wall of a conduit 10. The electromagnet 12 is energized for sequential magnetization. The values of the magnetic flux leakages at the respective points A-H of the inner wall are measured by a Gauss meter. Then, a graph of the curve connecting the values of the magnetic flux leakages is formed based on these magnetic flux leakage values. At the same time, the site of the maximum value of magnetic flux leakage is et at an angle 0. Then, the graph of the angle/(magnetic flux leakage value) based on the actual measurement is applied on the graph of the angle/(magnetic-flux leakage value) in the most proximate distance of a plurality of the different conduits 10 and sheath tubes 11, which are know beforehand so that the graphs are not intersected. Thus, the most proximate distance can be estimated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention provides a plurality of graphs of the relationship between an angle and a leakage magnetic flux value prepared in advance when the closest distance of a double tube made of a ferromagnetic metal is determined based on the leakage magnetic flux method. The present invention relates to a method for measuring the close distance of a double pipe, which is adapted to estimate the closest distance of the double pipe.

[0002]

2. Description of the Related Art In recent years, gas conduits laid underground are
Not only the excavation method of excavating from the surface of the earth and burying it, but also the places where the surface of the earth cannot be excavated, such as places where the installation environment is severe, the non-excavation method of using a machine is applied. In such a construction method, there is a case where a double pipe structure is adopted in which the conduit is built and laid inside a sheath pipe having a diameter larger than the inner diameter of the conduit. The conduit is not in a positional relationship in which the center is coincident with the sheath pipe in the cross section, but in the sheath pipe, a cable pipe or a pipe for injecting a drug solution or the like is provided in the space between the upper surface of the conduit outer wall and the sheath pipe. Due to the arrangement, the center of the conduit is set to be eccentric below the center of the sheath tube. Since the conduit 1 and the sheath pipe 2 are steel pipes as shown in FIG. 6, the electromagnets 3 are arranged at predetermined positions (points A to H) on the inner wall of the conduit to magnetize the conduit 1. Then, the leakage magnetic flux value on the spot was measured, and the proximity distance was derived from each leakage magnetic flux value data by using the graph of the relationship between the known proximity distance and the leakage magnetic flux (absolute value method).

[0003]

However, since the graph of the relationship between the close distance and the leakage magnetic flux as described above varies depending on the measurement conditions (the wall thickness of the tube, the usage state of the electromagnet 3, etc.), the different measurement conditions. Below, there is an error in that graph. Therefore, in order to obtain the closest distance d between the conduit 1 and the sheath tube 2, for example, a circle corresponding to the conduit 1 is illustrated, and from the point on the circumference of this circle corresponding to the magnetized position, Even if a plot is made according to the obtained proximity distance and a circle corresponding to the sheath tube 2 is drawn by connecting the plotted points, this circle has an error in the dimension, that is, the diameter, from the actual sheath tube 2. Therefore, the closest distance d must be inaccurate. The present invention has been made in order to solve such problems, when determining the closest distance of the double tube made of ferromagnetic metal based on the leakage flux method,
By fitting a plurality of graphs of the relationship between the angle and the leakage flux value prepared in advance, the closest distance of the double pipe was estimated, and the harmful effects resulting from the leakage flux value that fluctuates depending on the measurement conditions were eliminated. An object of the present invention is to provide a method for measuring a close distance of a heavy pipe.

[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. Magnetize the magnetic flux at each equal angle around the circumference, measure the leakage magnetic flux values, and create a curve graph connecting the leakage magnetic flux values based on these leakage magnetic flux values. The nearest distance is estimated by applying the angle-leakage magnetic flux value graph based on the actual measurement to the graph of the angle-leakage magnetic flux value at the time of the closest distance between the plurality of different inner and outer tubes. It is characterized by

[0005]

According to the present invention, the closest distance between the inner pipe and the outer pipe can be estimated even when the maximum leakage magnetic flux value cannot be measured or the leakage magnetic flux value varies, and the actual measurement can be performed. , It suffices to measure the leakage magnetic flux value at any position, that is, every equal angle.

[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 is, for example, a gas conduit 10 laid in the ground,
A sheath tube 11 having a larger diameter than the inner diameter of the conduit 10 is shown. On the inner wall of the conduit 10, electromagnets 12 are movably mounted at eight points A to H at regular intervals by a movement support mechanism (not shown). That is, the conduit 10 and the sheath pipe 11 are steel pipes and are magnetized by the electromagnet 12.

In the conduit 10 and the sheath pipe 11 as described above, as shown in FIG. 2, the position of the closest distance d between the conduit 10 and the sheath pipe 11 is used as a base point for every 45 ° (points A to H, 8).
There is a graph prepared by obtaining the leakage magnetic flux value at each location) and connecting the leakage magnetic flux values at each location with a line. In this case, as shown in FIG. 3, the closest distance d
= 10 mm, 20 mm, 30 mm, 40 mm angle-flux magnetic flux value graphs are provided as known data.

Next, the conduit 10 and the sheath tube 1 as described above.
1, the procedure for estimating the closest distance will be described. The electromagnet 12 is movably mounted on the inner wall points A to H of the conduit 10 by the moving and supporting mechanism, and the electromagnet 12 is energized to sequentially magnetize. Then, the leakage magnetic flux values at the inner wall points A to H are measured by a Gauss meter (not shown). Next, based on these leakage magnetic flux values, as shown in FIG. 4, a curve graph connecting the leakage magnetic flux values is created, and the location of the maximum leakage magnetic flux value is set to an angle 0,
By fitting the graph of the angle-leakage magnetic flux value at the closest distance d between the plurality of different conduits 10 and the sheath pipe 11 known in advance so as not to intersect the graph of the angle-leakage magnetic flux value based on the actual measurement ( (See FIG. 5), the closest distance can be estimated. For example, in FIG. 5, the graph of the angle-leakage magnetic flux value based on the actual measurement shown by the dotted line can be fitted so as not to intersect between the graphs at the closest distance d = 10 mm and d = 20 mm. The closest distance between the conduit 10 and the sheath tube 11 is 1
It can be estimated to be between 0 mm and 20 mm.

[0009]

As described above, according to the present invention, when the closest distance of a double tube made of a ferromagnetic metal is determined based on the leakage flux method,
By fitting multiple graphs of the relationship between the angle and the leakage flux value prepared in advance, the closest distance of the double pipe can be estimated, and the actual measurement is that leakage occurs at any position, that is, at each equal angle. Only the magnetic flux value needs to be measured. Further, since a continuous graph formed by the leakage magnetic flux values for each equal angle is used, there is little variation and errors can be suppressed.

[0010]

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional explanatory view of a double pipe showing an actual measurement point and a closest position when a method of measuring a short distance of a double pipe according to the present invention is carried out.

FIG. 2 is a schematic illustration of a double tube when a graph of angle-leakage magnetic flux value is created in advance when the closest distance is calculated by applying the method for measuring the short distance of the double tube according to the present invention. It is a figure.

FIG. 3 is a graph of angle-flux magnetic flux values at different closest distances based on the double tube shown in FIG.

FIG. 4 is an angle for actual measurement, which is created based on the double pipe shown in FIG. 1 that shows the actual measurement point and the closest position.
It is a graph of a leakage magnetic flux value.

5 is an explanatory diagram showing a state in which the graph shown in FIG. 4 is superimposed on the graph shown in FIG.

FIG. 6 is a schematic cross-sectional explanatory view of a double pipe showing an actual leakage magnetic flux value measurement position and a closest position.

[Explanation of symbols]

 10 conduit 11 sheath tube 12 electromagnet

Claims (1)

[Claims] 1. In a double tube composed of an outer tube made of a ferromagnetic metal and an inner tube built into the outer tube, magnetization is performed at an equal angle around the inner wall of the inner tube, and the leakage magnetic flux value is measured. , Based on these leakage magnetic flux values, create a curve graph connecting the leakage magnetic flux values together, and use the maximum leakage magnetic flux value as the base point, and when the closest distance between a plurality of different inner and outer tubes known in advance. In the graph of angle-flux magnetic flux value at
A method for measuring the proximity distance of a double pipe, wherein the closest distance is estimated by applying a graph of angle-leakage magnetic flux value based on the actual measurement.