JP2002156363A - Leakage flux flaw detecting method for conduit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of conventional leakage flux flaw detection method, in which when a leakage flux pig passes through an observation point 13, the final magnetization direction of a pipe becomes opposite to normal magnetization direction of the pig, which reduces the magnetization quantity of the pipe in the next measurement to reduce the flaw detection capacity. SOLUTION: When detecting flaws by running the leakage flux pig in the conduit, the NS poles of the magnet are laid reversely to the previous measurement, and the magnetization is enhanced by taking advantage of the residual magnetization of the previous measurement and the detecting capacity of the leakage flux is improved.

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 magnetic flux leakage from a conduit made of steel pipe.

[0002]

2. Description of the Related Art A DC magnetic field is formed on a tube wall by a magnet,
The mounting direction of the N and S poles of the magnet of the leakage magnetic flux pig (inspection pig) for detecting a defect or the like generated on the inner and outer surfaces of the wall by measuring the leakage magnetic flux on the inner surface of the tube is fixed. The tube wall of such a leakage magnetic flux pig is magnetized every time the inspection is repeated, and the defect detection performance is reduced by the influence of the magnetization. When the leakage flux pig passes through the observation point, the final tube magnetization direction is usually opposite to the magnetization direction of the leakage flux pig. For this reason, in the second and subsequent constructions, the amount of magnetization of the tube is reduced, and the ability to detect a defect of the leakage magnetic flux pig is reduced.

[0003]

SUMMARY OF THE INVENTION The present invention eliminates the effect that the tube is magnetized to reduce the accuracy due to repeated inspection by the leakage magnetic flux pig, and detects the defect of the leakage magnetic flux pig by reversing the influence of the magnetization. It is intended to provide a technology for improving functions.

[0004]

SUMMARY OF THE INVENTION According to the present invention, when a flaw is inspected by running a leakage magnetic flux pig inside a conduit, the measurement is performed by reversing the NS pole of the magnet from the previous measurement. This is a leakage magnetic flux inspection method. The tube wall is magnetized when flaw detection is performed by running the leakage magnetic flux pig, thereby causing residual magnetization.
When the flaw detection is performed by running the leakage magnetic flux pig in the conduit where the remanent magnetization is generated, if the flaw detection is performed by reversing the NS pole of the magnet from the previous measurement, it is emphasized by the remanent magnetization. As a result, the measurement sensitivity of the leakage magnetic flux pig can be improved. According to the present invention, not only the conventional problem that the defect detection capability of the flaw detection device is reduced due to the residual magnetization generated by the previous leakage magnetic flux flaw detection, but also the performance can be improved.

It is preferable to use a permanent magnet as the magnet, but it is also possible to use an electromagnet. If the direction of energization of the electromagnet is reversed and the NS pole of the magnet is reversed, forward and reverse poles can be realized very easily. It is preferable because it can be performed.

Next, as a second invention of the present invention, after the inside of the conduit is cleaned by a cleaning pig with a magnet, flaw detection is performed by running a magnet mounted on the cleaning pig and a leakage magnetic flux pig in which the NS pole is reversed. A method for detecting magnetic flux leakage from a conduit is provided. When laying a conduit, it is common to first clean the inside of the conduit with a cleaning pig, and even in the case of leakage magnetic flux flaw detection for maintenance performed after a certain period of use, use the cleaning pig before running the leakage magnetic flux pig. Cleaning is normally performed. In this case, a magnet is mounted on the cleaning pig to magnetize the pipe wall of the conduit, and the residual magnetism is used to perform leakage magnetic flux flaw detection.
The same effect can be obtained by the same principle as in the first invention. Also in this case, a permanent magnet or an electromagnet can be used as the magnet.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an explanatory diagram showing the principle of magnetic flux leakage inspection. When the NS magnet 1 having the leakage flux pig is brought into contact with the wall of the steel pipe 10 made of a magnetic conductive material, a magnetic flux 2 is generated in the wall of the steel pipe 10. The magnetic flux 2 formed so as to be saturated is uniformly distributed in the wall of the tube having no defect. However, as shown in FIG. 2, when there is a defect 11 in the tube wall, the magnetic flux leaks from the tube wall at this portion, and the leakage occurs. A magnetic flux 3 is generated. The presence of the defect 11 can be detected by detecting the leakage magnetic flux 3 with the magnetic sensor 4.

FIG. 3 shows the leakage magnetic flux flaw detection step, in which the observation point 13 is observed by moving the leakage magnetic flux pig having the magnet 1 in the direction of the arrow 20. FIG.
3A shows the traveling of the leakage magnetic flux pig, and FIG. 3B shows the magnetization direction of the tube wall at the observation point 13. As shown in FIG. 3C, when the pig passes through the observation point 13, the residual magnetism 1
2 is opposite to the magnetization direction of the magnet.

FIG. 1 is an explanatory view showing an embodiment of the present invention. FIG. 1A shows the previous measurement, in which a residual magnetization 12 occurs at an observation point 13. FIG. 1A shows a state similar to FIG. 3C. Next, in this measurement, as shown in FIG. 1 (b), the mounting direction of the magnet of the leakage magnetic flux pig is reversed from the previous time, and the NS pole is reversed. At the time of measurement, the magnetic field is emphasized at the observation point 13 in the same direction as the magnetization direction of the magnet and the residual magnetization direction, and the defect detection ability is improved.

In practicing the present invention, it is efficient to prepare a pair of pigs in which the direction of the NS pole of the magnet is reversed, and use these pigs alternately for measurement. Also, if a switching device for changing the direction of current supply is provided with the magnet as an electromagnet, it is possible to easily switch the forward and reverse of the NS pole with the same pig.

If the inside of the conduit is to be cleaned before the leakage magnetic flux is measured, a magnet is mounted on the cleaning pig and cleaning is performed, and the leakage magnetic flux measurement pig having the mounted magnet and the NS poles reversed is run. If this is the case, the defect detection capability of the leakage magnetic flux pig can be improved in the same manner as described above.

[0012]

According to the present invention, when performing a defect inspection of a pipe wall of a conduit with a leakage magnetic flux pig, the magnet is magnetized by the remanent magnetization of the previous measurement by reversing the NS of the magnet and the magnet at the previous measurement. It was emphasized that it was possible to improve the leakage magnetic detection ability.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment.

FIG. 2 is a principle diagram of leakage magnetic inspection.

FIG. 3 is an explanatory diagram of residual magnetization of a tube wall.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet 2 Magnetic flux 3 Leakage magnetic flux 4 Sensor 5 Brush 10 Tube wall 11 Defect 12 Remanent magnetization (magnetization direction) 13 Observation point 20 Pig traveling direction

Claims (4)

[Claims] 1. A method for detecting a magnetic flux leaking from a conduit, wherein the measurement is performed by inverting the NS pole of the magnet to a previous measurement when the leakage magnetic flux pig is caused to travel in the conduit to detect the defect. 2. A method for detecting flaws in a conduit, wherein the flaw detection is performed by cleaning the inside of the conduit with a cleaning pig with a magnet and then running a magnet mounted on the cleaning pig and a leakage magnetic flux pig in which an NS pole is reversed. Method. 3. The method according to claim 1, wherein the magnet is a permanent magnet. 4. The method according to claim 1, wherein the magnet is an electromagnet, and the direction of energization of the electromagnet is reversed so that the NS pole of the magnet is reversed.