JPS6064247A - Inspection processing method of iron pipe - Google Patents

Abstract

PURPOSE:To detect the coupling and the like of an iron pipe embedded in the ground, by performing frequency analysis of the data of magnetic-field distribution in the iron pipe, and removing the contribution of local magnetization, which is to become noises, by discrete Fourier transform and inverse discrete Fourier transform. CONSTITUTION:Cylindrical coordinates, in which the axis of a gas pipe P is (x) and an angle is theta, are set, and the distribution of a static magnetic field in the direction of the pipe axis is measured by a magnetism sensor. The frequency analysis of the data of the magnetic-field distribution with respect to the (x) axis is performed by discrete Fourier transformation. Based on the frequency distribution data obtained by the discrete Fourier transform, it is judged that the concentrated region of the constituent frequencies of the noise component is concentrated in, e.g., low frequency region. The low frequency component is removed from the data of the frequency distribution, and inverse discrete Fourier transform is performed. Thus the noise component is decreased to a large extent. By observing the place, where the change in magnetic field is large, the position of a coupling part and the position of a branch-pipe part can be readily detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a method for inspecting and processing iron pipes buried underground.

With iron pipes buried underground, such as gas pipes and water pipes, accidents often occur due to corrosion or poor welding at pipe joints and branch pipes. Therefore, the position of the joint of the iron pipe can be detected from inside the pipe, and even if an accident such as a gas leak occurs in this area, the position of the joint can be detected first.
It is necessary to inspect and repair this part. As described above, detecting the positions of joints, branch pipes, etc. is an important technique for maintenance management, but it has been found that conventional detection methods have problems.

BACKGROUND ART Conventionally, magnetic fields have been widely used as a measuring means in pipe inspection and processing methods. This method focuses on the fact that the magnetic field distribution changes in the vicinity of the joint, branch pipe, etc., and attempts to detect the joint, branch pipe, etc. based on the change. However, if the pipe to be inspected has been locally magnetized for a long period of time, changes in the magnetic field distribution will be detected in areas other than the joints and branch pipes, making it difficult to distinguish between the joints and the inner wall of the pipe. It turned out to be impossible. Possible causes of local magnetization include underground magnetism, especially in the case of pipes buried underground, or ground current.1For example, if the joint or branch pipe is located outside, In this case, this local magnetization is remarkable. Such tubes cannot be detected using conventional methods. Therefore, the present invention transforms the contribution of local magnetization, which causes detection noise, into a discrete Fourier transform (hereinafter referred to as F, T
.

) and inverse discrete Fourier transform (hereinafter I, D, F,
T.

This method solves the drawbacks of the conventional method by removing the following.

Hereinafter, details of the present invention will be described through detection of a static magnetic field within a gas pipe as a specific example.

FIG. 1 shows a gas pipe P having a joint part 1 and branch pipe parts 2 and 3. Pipe PFi diameter 180y+m, length 1505. , is. For convenience of measurement, as shown in the figure, cylindrical coordinates are set with the tube axis and the X angle as θ.

Figures 2 (a) to (c) show the results of measuring the static magnetic field distribution B in the axial direction of the gas pipe P using a fluxgate type magnetic sensor. 2,3
There is a large change in the magnetic field distribution at positions 4 and 5.6, which approximately correspond to the position , and in (b) and (c), a large change occurs at positions 7 and 8, which correspond to joint part 1. ing. However, as symbolized by the change when X≧700 in (C), large changes can be seen in areas other than the joint and branch pipes. This is noise due to local magnetization. Because of this noise, it is difficult to directly determine the positions of the joints and branch pipes from the measurement results shown in FIG.

Therefore, first, frequency analysis with respect to the X axis of the magnetic field distribution data of (a) = (b) - (c) in Fig. 2 is performed. For frequency analysis, F and T given by the following equation are used.

Here, Jctl is the X coordinate of the discretely measured position n=
0 # 1 + 2 +”・e N-”B (for) is at position: t! Magnetic field B(g) at l k = 0.1, 2. ..., N-1 is the frequency intensity t=, /TTN is the total number of data, and FIG. 3 shows the results of performing F and T. Next, in order to investigate the constituent frequencies of the noise part,
Perform only the second half (c≧780) of Figures (b) and (c), F, and T. The results are shown in FIG. As can be seen by comparing FIG. 3 and FIG. 4, the constituent frequency components of the noise component are concentrated in the low frequency region. Here, the low frequency component refers to a component with a long wavelength of change in magnetic field distribution with respect to the X axis. The opposite is true for high frequency components.

Therefore, in order to remove the noise component from the magnetic field distribution in FIG. 2, remove the low frequency component from the frequency distribution data in FIG. 3 (make it zero).1. It turns out that all you have to do is D, F, T. This is equivalent to passing it through a kind of filter. 1. D, F, and T are given by the following equations.

The symbols are the same as those in equation (1). FIG. 5 is a diagram of the magnetic field distribution obtained in this way. In FIG. 5, it can be seen that the noise component is significantly reduced compared to FIG. 2.

This tendency is particularly noticeable in (b) and (c). In this way, from FIG. 5, the position of the joint (
9, 12, 13) and the position of the branch pipe (1o, ii) can be detected.

In the example described above, the low frequency component of the magnetic field distribution of the gas pipe was removed, but the magnetic field distribution and the noise may vary depending on the type of pipe, the age of burial, the usage environment, and various other conditions. . The gist of the present invention is to remove noise by the difference in the constituent frequencies of magnetic field changes caused by noise and magnetic field changes caused by joints, branch pipes, etc. Therefore, if the constituent frequency of the noise is high frequency, , high frequency components may be removed.

In other words, by first measuring a sample of the target to be detected, examining the frequency components that make up the noise, and then removing the frequency components corresponding to the noise from the measurement data, the range of detectable targets can be greatly expanded. . Further, in the above example, the usefulness of the present invention was described through detection using a magnetic field inside a pipe, but it can also be applied, for example, to the case where a pipe buried underground is measured from the ground surface.

By using the present invention, it is possible to detect objects with high precision that were undetectable or cause many false detections due to noise with conventional methods, and also facilitate the maintenance and management of objects buried underground. It has the effect that it can do.

[Brief explanation of drawings]

Fig. 1 shows a gas pipe used as a measurement sample to explain the present invention, (a) is a front view, (b) is a side view, and Figs. 2 (a) to (C) are gas pipes. The axial magnetic field distribution diagram in the gas pipe shown in Figure 1, Figures 3 (a) to (c) are frequency distribution diagrams with F, T, and F, T, respectively, based on the magnetic field distribution shown in Figure 2.
Figures (b) and (((re) are frequency distribution diagrams of F, T, t, and Figures 5 (a) to (e), excluding only the noise components that occur in the latter half of Figures 2 (b) and (e). ) is a magnetic field distribution diagram after noise has been removed. 1... Joint part, 2, 3-... Branch pipe part Patent applicant Figure 4 (Import of Amended Document for Spectrum Procedures) Director General of the Patent Office 1, Indication of Case 1982 Patent Application No. 172546
No. 2, Title of the invention Inspection and processing method for iron pipes 3, Relationship with the case of the person making the amendment Applicant No. 33-1 (423) Shiba Go-cho 1, Minato-ku, Tokyo NEC Corporation Representative Tadahiro Sekimoto 4; Agent 〒108 Tokyo GL! Resident Mita Building 5, 37-8 Shiba 5-chome, Minato-ku, Drawing subject to amendment 6, Contents of amendment 1) Figure 5 of the drawings attached to this application will be amended as shown in the attached drawing.

Claims (1)

[Claims] (1) Measure the static magnetic field distribution of the iron pipe, perform frequency analysis on the magnetic field distribution data using discrete Fourier transform,
Determine the concentration region of the constituent frequencies of the noise component based on the frequency distribution data obtained by discrete Fourier transform,
A method for inspecting iron pipes, comprising removing frequency components in areas where noise components are concentrated and performing inverse discrete Fourier transform on the frequency distribution data.