JPH0338693Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a leakage magnetic flux detection device used for detecting defects such as thinning due to scratches or corrosion of steel pipes from the inside of the pipe.

[Conventional technology and problems]

As shown in FIG. 4, a conventional leakage magnetic flux detection device for use in a pipe includes a plurality of magnets 2 whose magnetization directions are aligned in the longitudinal direction of the pipe, which are fixed to a shaft 10 extending from a device (not shown) that moves in the longitudinal direction of the pipe. A brush 16 made of a material with high magnetic permeability, such as iron or nickel, is attached to the end of the magnet 2, and the brush 16 is brought into contact with the inner wall of the pipe by utilizing its elasticity. There is.

According to this method, the magnetic flux is transferred from the magnet 2 to the brush 1.
A plurality of magnetic sensors 3 arranged between the poles of the magnets 2 detect magnetic flux that is formed on the tube wall through the magnet 6 and leaks from the tube wall at a defective portion of the tube wall.

In this case, as the detection device moves, the lower brush 16 bends and wears due to misalignment, etc. as shown in FIG. may become unstable and good detection performance may not be obtained.

Further, at the bending part of the pipe 1, the brush 16 is separated from the pipe wall on the outside of the bending part, as shown in FIG.
Since the contact state changes, the magnetic flux formed on the tube wall changes, resulting in a problem that good detection performance cannot be obtained.

[Means for solving problems]

The purpose of the present invention is to provide an intra-pipe leakage magnetic flux detection device that advantageously solves the above-mentioned problems. A plurality of magnets 2 are arranged radially around the longitudinal axis of the tube with their magnetization directions aligned in the longitudinal direction of the tube, and each magnet 2 is guided by a guide 6 so as to move only in the radial direction of the tube, and is attached to the inner wall of the tube via a spacer. A leakage magnetic flux detection device for inside a pipe is characterized in that the magnetic flux comes into contact with the pipe wall and forms a magnetic flux on the pipe wall.

〔Example〕

Next, the present invention will be explained in detail using the embodiment shown in FIGS. 1 to 3.

In each of FIGS. 1 to 3, the upper half shows the state in which the detection unit is retracted, and the lower half shows the state in which it is pushed out.

In FIGS. 1 to 3, a guide 6 having a fan-shaped and U-shaped permanent magnet 2 when viewed from the tube axis direction has one end tapered on both sides of the permanent magnet 2.
A spacer 4a is abutted across the guide 6 and the magnet 2, and is fixed to the side surface of the guide 6 with a screw 12.

Furthermore, a plurality of magnetic sensors 3 for detecting leakage magnetic flux from the tube wall are arranged in the center space between the poles of the magnet 2, and are fixed with a filler 11 (for example, a synthetic resin such as epoxy) to form a detection unit 13. There is.

A plurality of detection units 13 are arranged between two flanges 5a and 5b of a frame 5 fixed to a shaft 10 extending from a device that moves longitudinally within a tube, so that the magnetization direction is aligned in the longitudinal direction of the tube.
The guides 6 are fitted into guide grooves 7 arranged radially and provided in the flange 14.

Each detection unit 13 is made to be able to slide radially along the guide groove 7, so that the outer diameter including the thickness of the spacer 4b is slightly smaller than the inner diameter of the tube 1 when it is most compressed toward the center of the tube. Make it.

Spacer 4b connects two adjacent detection units 13
It is fixed to the flange 14 with a screw 12 in a shape bent outward at the tip of the flange 14.

The spacers 4a and 4b are made of an elastic material that has a small coefficient of friction and is resistant to wear, such as tetrafluoroethylene resin.

A detection signal from each magnetic sensor 3 is passed through a hole 9 provided in the frame 5 and connected to an external measurement circuit through a signal line 8 passing through the shaft 10 to constitute a detection device.

[Effect]

Next, a method for detecting defects in pipes using this device will be explained.

Each detection unit 13 fitted radially into the guide groove 7 is inserted into the tube 1 from the tube end in a contracted state.

Since the magnetization directions of the detection units 13 are aligned in the longitudinal direction of the tube, a magnetic repulsion force is generated between adjacent magnets, and at the same time a magnetic attraction force is generated between the magnet 2 and the tube 1, so that each detection unit 13 is attached to the tube wall. It is pushed out in the direction and comes into contact with the tube wall via the spacers 4a and 4b.

In this state, leakage magnetic flux is continuously detected by moving this device within the pipe using a moving device (not shown).

When moving inside the pipe, even if the pipe is bent or the inner diameter of the pipe changes, the repulsive force of the magnet and the attraction force with the inner surface of the pipe always act. Pipe 1 means spacers 4a, 4b
A constant gap equal to the thickness of can be maintained.

As a result, magnetic flux is stably formed on the tube wall.
At the same time, since a constant gap can be maintained between the magnetic sensor 3 and the tube 1, good detection performance can be obtained without any change in detection sensitivity.

The detection signal is guided to a measurement circuit (not shown).

[Effect of idea]

In the device of the present invention, the plurality of detection units 13 arranged radially around the outer periphery of the frame 5 apply the magnetic repulsion force generated between adjacent magnets and the magnetic attraction force generated between the tube 1 and the magnet 2 to the guide groove 7. Since the detection unit 13 is always acting along the pipe wall, the detection unit 13 is pushed out toward the pipe wall without a complicated drive mechanism, and the spacer 4
It is brought into contact with the inner surface of the tube via a and 4b with a constant gap.

Therefore, the gap between the magnet 2 and the tube 1 is kept constant regardless of the bending, flatness, misalignment, etc. of the tube.
Since magnetic flux can be stably formed on the tube wall and at the same time the gap between the magnetic sensor 3 and the tube 1 is kept constant, there is no change in detection sensitivity and good detection performance can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the detection device of this embodiment (A-A cross-sectional view in Figure 2), and the upper part of Figure 2 is B-B in Figure 1.
The lower part of the cross section is a sectional view taken along the line DD in FIG. 1, and FIG. 3 is a sectional view taken along the line C-C in FIG. Stroke MIN), the lower half shows the pushed out state (stroke MAX). FIGS. 4a and 4b are longitudinal and transverse sectional views of a conventional device, and FIG. 5 is a longitudinal sectional view showing the state of the same device at a bend. 1...tube, 2...magnet, 3...sensor, 4...
...Spacer, 5...Frame, 5a, 5b...Flange portion, 6...Guide, 7...Guide groove, 8...
...Signal line, 9...Through hole, 10...Shaft, 1
1...Filling material, 12...Screw, 13...Detection unit.

Claims (1)

[Scope of utility model registration request] In an intra-pipe leakage magnetic flux detection device that detects flaws on the pipe wall from inside the pipe, a plurality of magnets 2 with magnetic sensors 3 arranged between poles are arranged radially around the longitudinal axis of the pipe, with their magnetization directions aligned in the longitudinal direction of the pipe. Each magnet 2 is attached to a guide 6 so that it moves only in the radial direction of the tube.
and comes into contact with the inner wall of the pipe via a spacer,
A leakage magnetic flux detection device for inside a pipe, which is characterized by forming magnetic flux on the pipe wall.