JPH0527802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electromagnetic ultrasonic measuring device that can measure the wall thickness of a steel pipe with high precision even if the shape is not a perfect circle.

[Background of the invention]

Until now, ultrasonic thickness gauges using piezoelectric elements, ultrasonic flaw detectors, and the like have been used to measure the thickness and flaw detection of metal materials. Such equipment uses a sound source (probe) to efficiently transmit ultrasonic waves into the specimen material.
A couplant (usually water) is required between the test material and the test material. For this reason, it is actually difficult to measure high-temperature materials, scales, or materials with significant surface irregularities.

Therefore, there is a strong demand for transmitting and receiving ultrasonic waves without being affected by the temperature or surface condition of the material to be tested.To meet this demand, magnetic fields and vortices are proposed as a method to eliminate the need for the medium. An electromagnetic ultrasonic flaw detection device that utilizes the Lorentz force caused by the interaction of electric currents has been proposed in Japanese Patent Publication No. 24867/1983.

Here, this type of device will be explained as follows, taking as an example the device disclosed in Japanese Patent Application Laid-open No. 179305/1983.

That is, FIGS. 3 and 4 show the main structure of each embodiment. According to this, the third
In the one shown in the figure, a DC excitation coil 12 is wound around a steel pipe 1, and a transmitting/receiving coil 11 is disposed at a position facing the steel pipe 1 at the center inside the DC excitation coil 12. It's getting old. The iron core 1 is also a DC excitation coil 1
2 from the outside.

In this configuration, most of the DC magnetic flux generated by the DC excitation coil 12 is parallel to the surface of the steel pipe 1. That is, the magnetic field By is parallel to the surface of the steel pipe, which is necessary for transmitting and receiving longitudinal electromagnetic and ultrasonic waves. By the way, the transmitting/receiving coil 11 is a DC excitation coil 12.
Although it is disposed at a position facing the surface of the steel pipe 1 at the center of the inside, in the past, one DC electromagnet was always required for one transmitting/receiving coil. However, in the case of the configuration shown in FIG. 3, the transmitter/receiver coil may be placed anywhere around the entire circumference of the steel pipe 1 as the test material as long as it is within the space between the DC excitation coil 12 and the surface of the steel pipe 1. This makes it possible to arrange not only one transmitting/receiving coil but also a plurality of transmitting/receiving coils facing the specimen.

In the case shown in Fig. 3, the DC excitation coil is wound as close to the surface of the steel pipe as possible in order to obtain a stronger magnetic field, but when wound in this way, the space in which the transmitter and receiver coils are placed becomes narrower. Installation of transmitting and receiving coils has become difficult.

On the other hand, in the case shown in FIG. 4, this point has been solved. As shown in the figure, the two DC excitation coils 14 and 15 are each independently connected to the steel pipe 1.
The DC magnetic fluxes (shown by dotted lines in the figure) generated from the two DC excitation coils 14 and 15 are excited so as to be added together. A transmitting/receiving coil 11 is disposed in a space between 15 and 15 facing the steel pipe 1.

Now, to explain how ultrasonic waves are transmitted and received with reference to FIG. When a pulse voltage is applied to the transmitting/receiving coil 11 from a pulse generator (not shown), a changing magnetic flux is generated, and this changing magnetic flux generates an eddy current i on the surface of the steel pipe 1. It turns out. As a result of the interaction between this eddy current i and the magnetic flux density By of the magnetic field component parallel to the surface of the steel pipe 1 of the DC magnetic field applied in advance, a changing strain Fz is generated in the direction perpendicular to the surface of the steel pipe 1 (Z direction). (Fleming's left-hand rule) occurs, and this changing strain Fz is in the direction perpendicular to the surface of the steel pipe 1 (Z direction).
This is where it spreads. That is, longitudinal waves are generated. The following relationship exists between this changing strain Fz, the magnetic flux density By, and the eddy current i.

Fz∝By·i...(1) That is, the changing strain Fz is proportional to the product of the magnetic flux density By and the eddy current i. The ultrasonic waves generated in this way propagate inside the test material 1 and are reflected by the inner surface of the test material 1, and the reflected ultrasound waves from the inner surface follow the process opposite to that described above (Fleming's right-hand rule). The electromotive force generated by the eddy current in the transmitter/receiver coil 11 is detected as an electromotive force. The detection signal level V _R is proportional to the square of By as shown in the following equation.

V _R ∝B ² y・i ...(2) Here, the DC excitation coils 12, 14, 15
Regarding the magnetic flux density By, most of the DC magnetic flux generated by the DC excitation coils 12, 14, and 15 is a magnetic field By whose components are parallel to the surface of the steel pipe 1 necessary for transmitting and receiving longitudinal electromagnetic and ultrasonic waves. ,
If the amount of excitation for the DC excitation coils 12, 14, and 15 is increased, the magnetic field By will increase almost proportionally,
It has become easy to obtain values of 10,000 Gauss or more.

FIG. 5 shows an example of a typical manufacturing process for seamless steel pipes. According to this, the round billet material is heated to red heat and then passed through mill processes such as a piercer, mandrel, and reducer in order to be rolled. Further, FIGS. 6a and 6b show a configuration in which the reducer mill shown in FIG. 4 is applied to measure the wall thickness of a steel pipe. As shown in the figure, the steel pipe 1 is rolled through a plurality of reducer mills 30, and an electromagnetic ultrasonic measuring device 20 is arranged between the stands of a predetermined reducer mill 30. In this example, the 6th
As shown in Figure b, transmitting and receiving coils are arranged radially around the outer periphery of the six-channel steel pipe section 1, and the wall thickness is measured at six locations.

Here, to explain how the wall thickness measurement for one channel is performed, the transmitting/receiving coil 11 is connected to the pulser 3 while the DC excitation coils 14 and 15 are excited and the steel pipe 1 is penetrated.
1, the electromagnetic ultrasonic echo from the transmitter/receiver coil 11 is amplified by the amplifier 32 and displayed on the display 33, while the ultrasonic echo from the time of ultrasonic transmission to the first ultrasonic echo (first echo) is amplified by the amplifier 32 and displayed on the display 33. The time t is counted by a time counter 34. Therefore, once the time t is measured, the steel pipe wall thickness T is determined by the calculator 37 as follows.

T=C・t/2...(3) However, C is the ultrasonic sound speed in the steel pipe 1. The value of C is uniquely determined by the temperature of the steel pipe 1, but the thermometer 35 is used to measure the surface temperature of the steel pipe 1, and the sound speed correction circuit 36 measures the ultrasonic sound speed. It is designed to be corrected to correspond to temperature.

Figure 7 shows the diameter of the manufacturing process shown in Figure 6.
This figure shows the results of actually measuring the wall thickness of one channel using a low carbon steel pipe of 60.3 mm, wall thickness of 3.5 mm, and length of 60,000 mm. It can be seen from this that the measured values in hot and cold conditions are in relatively good agreement.

In this way, in the reducer process, the steel pipe is shaped into a relatively perfect circle, so the size of the gap g that exists between the iron core and the outer surface of the steel pipe is almost constant, as shown in Figure 6. , and it is clear that it can be made considerably smaller. however,
Since the piercer and mandrel mill processes involve rough rolling, the steel pipe is not perfectly round, and therefore the size of the gap g changes. In this case, it is necessary to make the inner diameter of the iron core large so that the outer surface of the steel pipe does not come into contact with the iron core, but if the inner diameter of the iron core is made large, the size of the gap g may become unnecessarily large, causing problems. It is said that it occurs. This is because if the size of the gap g becomes large, a sufficient magnetic flux density By cannot be secured, and therefore the detection signal level V _R
This is because it also becomes smaller. In order to solve this problem, it is conceivable to use a superconducting magnet instead of a normal electromagnet and to increase the magnetic flux density By even if the gap g is large.
However, in this case, the size of the device configuration cannot be avoided, and additional equipment is also required, so it cannot be said to be very practical.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic ultrasonic measuring device that can measure the wall thickness, thickness, etc. of a target object with high accuracy even when the cross-sectional shape deviates from the original shape.

[Summary of the invention]

For this purpose, the present invention has a donut-shaped good conductor disk, which is rotatably attached to a central core portion, so that a target object can pass through the center without contact. Various studies have been conducted to date on generating strong magnetic fields using static electricity methods, but the present invention proposes that when a metal plate with high conductivity is rotated at high speed in a magnetic field, a demagnetizing field due to an eddy current flowing in the disk is generated. This uses the principle that magnetic flux no longer passes through the inside of the disk, and the magnetic flux avoids the disk and converges.

[Embodiments of the invention]

The present invention will be explained below with reference to FIGS. 1 and 2.

First, the main structure of an embodiment of the apparatus according to the present invention will be described. FIG. 1 shows its configuration. As shown in the figure, ring-shaped bearings 47 and 48 are attached to the magnetic pole portion of the iron core 13, and these are further fitted with a gear 4 made of a donut-shaped good conductor.
5 and 46 are rotatably mounted. The transmitting/receiving coil 11 is suspended from the iron core 13 between these gears 45 and 46, and is disposed as radially as possible with respect to the steel pipe 1. Therefore, if the gears 45, 46 are rotated at high speed while the DC excitation coils 14, 15 are excited to generate magnetic flux, eddy currents will flow on the surfaces of the gears 45, 46, resulting in secondary Due to the action of the magnetic field, the main magnetic flux between the magnetic poles N and S is driven to the vicinity of the surface of the steel pipe 1, and as a result of the magnetic flux convergence effect, the magnetic poles N,
This makes it possible to create a high magnetic field on the surface of the steel pipe 1 between S.

In this example, the gears 45 and 46 are rotated by a drive motor 42 attached to the side surface of the DC excitation coil 15. Drive motor 4
2, the other end of the shaft 43 is the DC excitation coil 1
Gears 41 and 42 are rotatably housed on four sides via bearings 44, and are attached to a shaft 43.
The gears 45 and 46 are rotated through the gears 45 and 46. Also, although it is sufficient to have only one gear 45, 46, the transmitter/receiver coil 1
Generally, two or more such gears are required because the magnetic flux distribution directly below the gear is disturbed.
It is appropriate to arrange a transmitting and receiving coil between the gears. FIG. 2 shows the results of magnetic field simulation using the actual scale dimensions of the devices shown in FIGS. 4 and 1, respectively. Second
Figure a corresponds to Figure 4, and Figure 2 b corresponds to Figure 1, but in Figure 2 a, a considerable amount of fringing flux ΦF occurs between the magnetic poles, which is really necessary.
There is a limit to the magnetic flux Φg on the surface of the steel pipe corresponding to the magnetic poles N and S, and the magnetic flux density is also limited to 14,000 to 15,000 Gauss. On the other hand, in Fig. 2b, there is almost no fringing flux ΦF due to the presence of the rotating bodies (gears 45, 46) as good conductors, and the magnetic flux Φg' on the surface of the steel pipe is extremely large, and the result of magnetic field analysis is 30,000~ depending on the rotation speed of the body
It is now possible to generate a strong magnetic field of 50,000 Gauss. Therefore, from equation (2) it is clear that (30~
50) ² / (14 to 15) ² = 4 to 10 times higher sensitivity,
Even if the size of the gap g shown in Figure 6 is large, the wall thickness of steel pipes can be measured with great accuracy on rolling lines such as mandrel mills and piercers.

Although the present invention has been described above, it is clear that the present invention can be applied not only to hollow steel pipes but also to solid pipes.

〔Effect of the invention〕

As explained above, the present invention has the advantage that the wall thickness and thickness of a tubular object can be measured with high precision even if the cross-sectional shape is not a perfect circle.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the main part configuration of an embodiment of the device according to the present invention, FIGS. 2a and b are diagrams for considering the extent of the effects of the present invention, and FIGS. 3 and 4. 5 is a diagram for explaining the typical manufacturing process of jointless steel pipes, and FIGS. FIG. 7 is a diagram showing the configuration when measuring the wall thickness of a steel pipe by applying the method shown in FIG. 11... Transmitting/receiving coil, 13... Iron core, 14,
15...DC excitation coil, 45, 46... (rotating) gear, 47, 48... bearing.

Claims (1)

[Claims] 1. Two cored DC excitation coils that are excited by a DC power supply and wound around a steel pipe, and a space in which the DC excitation coils are excited by a pulse generator output and surround the steel pipe. and a transmitting/receiving coil arranged in the steel pipe, and generating ultrasonic waves in the steel pipe through interaction between the magnetic field generated by the DC excitation coil and the eddy current generated on the surface of the steel pipe by exciting the transmitting/receiving coil, In an electromagnetic ultrasonic measuring device that measures the thickness of a steel pipe by measuring reflected or transmitted ultrasonic waves, a donut-shaped good conductor disk is rotatably arranged between opposing magnetic poles of an iron core so as to surround the steel pipe. An electromagnetic ultrasonic measuring device characterized by a configuration. 2. The electromagnetic ultrasonic measuring device according to claim 1, wherein a plurality of good conductor disks are arranged on the same axis so as to surround a steel pipe, and a transmitting and receiving coil is arranged in the space between the good conductor disks.