JPH07318536A - Method for detecting residual metal in metal pipe - Google Patents

Abstract

PURPOSE:To detect residual metal hingly accurately in a short time while discriminating from a flaw using a compact apparatus. CONSTITUTION:A flaw detection coil 1b, a coil 1c for detecting residual metal on the inner face, and a magnetic saturation coil 1a for imparting field to the periphery of the detection coils 1b, 1c are disposed oppositely to the outer periphery of a welded steel pipe 2. The residual metal detection coil 1c has coil width wider than that of the flaw detection coil 1b. The welded steel pipe 2 is magnetized by the magnetic saturation coil 1a within such range as both a flaw 3 and a bead chip 4 can be detected. The flaw 3 is discriminated from the bead 4 based on the detection signals from the detection coils 1b, 1c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a metal residue such as inner surface bead scrap (hereinafter simply referred to as "bead scrap") remaining in a metal pipe such as a welded steel pipe by discriminating it from a flaw. .

[0002]

2. Description of the Related Art In the production of welded steel pipe, for example, the inner bead existing inside the welded steel pipe is cut by an inner cutting tool. The bead scraps are removed by air purging after cutting the steel pipe to a specified size.
In some cases, it cannot be removed and remains in the steel pipe. Therefore, in order to detect the bead scraps remaining in the steel pipe, conventionally, a fluorescent lamp group is arranged at one pipe end, and a worker visually looks through the inside of the steel pipe from the other pipe end. There is.

However, it can be easily detected if the bead scraps are protruding from the pipe end or near the pipe end. For example, when the bead scraps remain in the center of the long steel pipe,
The long steel pipe is bent at its center due to its own weight, which makes it difficult to inspect and sometimes it cannot be detected. In addition, a large amount of removal residue may be produced due to a malfunction of the automatic removal device for bead cuttings. In this case, it is necessary to promptly detect the malfunction of the automatic removing device.

Therefore, the electromagnetic wave is radiated from one of the tube ends to propagate the electromagnetic wave by using the steel tube as a circular waveguide, and the propagated electromagnetic wave is received by the other tube end, and the electromagnetic wave is subjected to frequency modulation and / or power attenuation. Japanese Patent Laid-Open No. 4-215046 proposes a method of measuring internal pressure and detecting internal residues.

[0005]

However, the method proposed in Japanese Patent Application Laid-Open No. 4-215046 has a large installation, so that the installation space also increases, and the installation location is limited. Since electromagnetic waves are transmitted and received at both ends of the steel pipe, the detection accuracy fluctuates if the length of the steel pipe varies. The devices associated with the oscillator and the receiver must be placed close to both ends of the steel pipe, and thus cannot be processed at high speed. There is a problem such as.

The present invention has been made in view of the above-mentioned problems, and it is possible to detect a metal residue such as bead waste from a flaw with a compact device, and to detect the metal residue inside the metal pipe with high accuracy and in a short time. It is intended to provide a method for detecting a metal residue.

[0007]

In order to achieve the above-mentioned object, a method for detecting a metal residue in a metal pipe according to the present invention comprises an eddy current detection coil for detecting a flaw and an inner surface metal residue on the outer periphery of the metal pipe. An eddy current detection coil for object detection and a magnetic saturation coil that gives a magnetic field to the periphery of these eddy current detection coils are faced, and the coil width of the eddy current detection coil for detecting the inner surface metal residue is detected. The width of the eddy current detection coil is larger than that of the eddy current detection coil, and the magnetization of the metal tube by the magnetic saturation coil is performed within the range where both flaws and inner surface metal residues can be detected. Therefore, the flaw and the metal residue on the inner surface are discriminated from each other.

[0008]

As a method of inspecting a flaw generated in a welded portion of a welded steel pipe, there is an eddy current method using a through coil. In this eddy current method, the welded steel pipe is first sufficiently magnetized using a magnetic saturation device, and then a high-frequency alternating current is applied to the coil to generate a magnetic flux and induce an eddy current in the defective portion of the steel pipe. Is detected as a voltage change due to a change in coil impedance.

When a defect of a welded steel pipe is detected by this eddy current method, bead debris remaining on the inner surface of the welded steel pipe may be detected in addition to the flaw which is the original purpose, depending on the current value of the magnetic saturation device. Since the conventional eddy current method cannot judge whether it is a flaw or a bead scrap, they are treated as defective products.

The present inventor pays attention to this fact, and in the conventional eddy current method, a welded steel pipe having artificial flaws formed on the outer surface and bead scraps inserted on the inner surface was used, and the test frequency and phase angle were 4 KHz and 60 °, respectively. When the current value of the magnetic saturation device was variously changed and its detectability was confirmed, as shown in FIG. 2, when the current value is 10 A, the artificial flaw and the bead waste can be detected with the same signal. There was found. From this, it was found that both the flaw and the bead scrap can be detected with S / N ≧ 3 or more by setting the magnetic saturation current value to an appropriate value. However, this cannot distinguish between flaws and bead scraps.

Therefore, the present inventor has two eddy current detection coils (hereinafter, simply referred to as "detection coils") for detecting flaws and one for detecting inner surface metal residues, and further, the coil width of these detection coils. When the width of the inner surface metal residue detection coil was made larger than the width of the flaw detection coil, the inner surface metal residue detection coil could not detect flaws but only bead scraps could be detected. I found out.

An example thereof is shown in FIG. Fig. 3 shows a steel pipe with an artificial flaw of 1 mm in length on the outer surface and bead scraps of 50 mm in length inserted into the inner surface of the steel pipe. The test frequency and magnetic saturation current were set to 4 KHz and 10 A, respectively, and the coil width was varied. It is the result of detecting the S / N of the artificial flaw and the bead scraps in the case of making it. In the case of the embodiment shown in FIG. 3, it is understood that if the width of the inner surface metal residue detecting coil is 50 mm or more, only the bead waste can be detected without detecting the artificial flaw.

Further, FIG. 4 shows that the flaw detection coil has a width of 7 mm,
When the width of the inner surface metal residue detection coil is set to 50 mm and the size of the artificial flaw is variously changed under the same conditions as in FIG. 3, S / N of the artificial flaw is detected by each detection coil. is there. In the case of the embodiment shown in FIG. 4, it can be seen that the inner surface metal residue detection coil can detect a flaw of 17 mm or more, while the flaw detection coil cannot detect a flaw of 8 mm or more.

The present invention has been made on the basis of the findings obtained from the various test results described above. The flaw detection coil used conventionally and the inner surface metal residue detection having a width wider than that of the flaw detection coil are detected. By combining the coils and magnetizing the metal tube by the magnetic saturation coil within the range where both the flaw and the inner surface metal residue can be detected, it is possible to distinguish between the flaw and the inner surface metal residue depending on the form of the detection signal from these detection coils. Of.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The case of carrying out the method of the present invention using the apparatus having the construction shown in FIG. 1 will be described below. FIG. 1 shows an apparatus configuration for carrying out the method for detecting a metal residue in a metal tube according to the present invention.
It is drawing which shows an example.

In FIG. 1, reference numeral 1 denotes a detector for detecting a flaw 3 existing on the outer surface of the welded steel pipe 2 and a bead scrap 4 remaining in the welded steel pipe 2. When the welded steel pipe 2 passes through the detector 1, The flaw 3 and the bead scrap 4 are detected. This detection unit 1 is larger than the magnetic saturation coil 1a, a flaw detection coil 1b having a width of 7 mm, for example, which is disposed between the magnetic saturation coil 1a and the welded steel pipe 2 passing through the magnetic saturation coil 1a, and the flaw detection coil 1b. For example, a magnetic saturation coil 1a having a width of, for example, 50 mm, and a magnetic saturation coil 1a for magnetizing the welded steel pipe 2 within a range in which the flaw 3 and the bead scrap 4 can be detected by the magnetic saturation coil 1a are, for example, 10A.
And a DC power supply device 1d for supplying the DC current.

Reference numeral 5 denotes a flaw detector, which incorporates a flaw detection circuit 6, a bead waste detection circuit 7, an oscillator 8, a signal determination logic 9, and the like. Of these, the defect detection circuit 6 and the bead waste detection circuit 7 include an oscillator 8 for supplying an alternating current of 4 KHz to the respective detection coils 1b and 1c, and a bridge 6 for extracting impedance changes of these detection coils 1b and 1c.
a, 7a, amplifiers 6b, 7b for amplifying the output signals sent from the bridges 6a, 7a, and output signals from the amplifiers 6b, 7b for changing the voltage from the oscillator 8 by a certain phase Detector 6 that performs phase analysis by the control signals output from the detectors 6e and 7e
c and 7c, filters 6d and 7d for detecting signals from the flaws 3 and bead scraps 4 by removing noises of output signals from the detectors 6c and 7c, and these flaws 3 and bead scraps 4
And the amplitude discriminators 6f and 7f which output the signal from the outside as a defect signal.

The signals from the flaws 3 and the bead scraps 4 detected by the detection circuits 6 and 7 are sent to the signal determination logic 9 where there is a flaw 3 and whether there are bead scraps 4. It is determined whether or not there is either, and the result is output to the recorder 10, the alarm device 11, and the marker device 12. In addition, 13 is an oscilloscope.

Using the device having the above structure, the flaw 3
When the signal from the bead waste 4 is detected, the result is as follows. First, when the bead scraps 4 with a length of 50 mm are contained in the welded steel pipe 2, as shown in FIG.
The impedance of the flaw detection coil 1b of m and the inner surface metal residue detection coil 1c of width 50 mm both change at the same time. Next, when only the flaw 3 is on the outer surface of the welded steel pipe 2, as shown in FIG. 4, when the length of the flaw 3 is 8 mm or less, the impedance of only the flaw detection coil 1b changes and the flaw 3 When the length is 15 mm or more, the impedance of only the inner surface metal residue detection coil 1c changes. That is,
When only the flaw 3 is present on the outer surface of the welded steel pipe 2, generally only one of the impedances changes.

Therefore, in the method of the present invention, the signal determination logic 9 is used to detect the flaw detection coil 1b and the inner surface metal residue detection coil 1.
If the impedance of c changes at the same time, it is determined that the bead waste 4 is contained, and if the impedance of one of the flaw detection coil 1b and the inner surface metal residue detection coil 1c changes, there is a flaw 3. To judge. If neither impedance changes, it is determined that neither the flaw 3 nor the bead waste 4 is present.

[0021]

As described above, according to the method of the present invention, the bead scraps remaining in the welded steel pipe can be discriminated from the flaws in the welded steel pipe and detected at high speed without contact. Therefore, it is possible to detect a defect in the automatic bead cutting object removing device in real time. At the same time, the method of the present invention can detect flaws that have been overlooked by conventional visual inspection.

[Brief description of drawings]

FIG. 1 is a drawing showing an example of an apparatus configuration for carrying out the method for detecting a metal residue in a metal tube according to the present invention.

FIG. 2 is a diagram showing the relationship between defects and bead scraps and magnetic saturation current.

FIG. 3 is a drawing showing the relationship between the artificial flaw and the detectability of bead scraps according to the change in coil width.

FIG. 4 is a drawing showing a relationship between detectability by a flaw detection coil and an inner surface metal residue detection coil according to a change in flaw length.

[Explanation of symbols]

 1a Magnetic saturation coil 1b Defect detection coil 1c Inner surface metal residue detection coil 2 Welded steel pipe 3 Defect 4 Bead scrap 5 Flaw detector 6 Defect detection circuit 7 Bead scrap detection circuit 9 Signal judgment logic

Claims (1)

[Claims] 1. An eddy current detection coil for detecting flaws, an eddy current detection coil for detecting inner surface metal residues, and a magnetic saturation coil for applying a magnetic field to the periphery of these eddy current detection coils on the outer periphery of a metal tube. The width of the eddy current detection coil for detecting the metal residue on the inner surface of the coil is larger than the coil width of the eddy current detection coil for detecting flaws, and the magnetizing of the metal tube by the magnetic saturation coil is flawed. The method for detecting a metal residue in a metal pipe is characterized in that the flaw and the inner metal residue are discriminated from each other according to the form of the detection signal of each eddy current detection coil.