JPS6310523Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a so-called rotating probe type ultrasonic flaw detector that detects flaws while rotating an ultrasonic probe along the outer periphery of a material to be tested. This is an idea regarding the configuration of a signal transmitting/receiving device.

In order to perform ultrasonic flaw detection on long rolled products with circular cross sections such as pipes or round bars,
This is a so-called detection method in which the probe is rotated at high speed along the outer circumference of the test material while the test material is conveyed in the axial direction, and the probe is scanned in a spiral around the outer circumference of the test material to detect flaws over the entire entire length of the test material. Rotating probe type flaw detectors are widely used in steel rolling mills. This flaw detector rotates a rotary probe holder equipped with a multi-channel probe around the outer circumference of the material to be tested at high speed, allowing for fast flaw detection and extremely high-efficiency inspection. It is used as an important non-destructive testing device in bar manufacturing factories.

Although this flaw detector is suitable for high-efficiency flaw detection, it is necessary to interpose a signal transmission device to send and receive flaw detection signals between the probe attached to the probe holder on the rotating part and the fixed part. It is no exaggeration to say that the overall performance of a rotating probe type flaw detector is influenced by the function and performance of this signal transmission device.

In conventional rotary probe flaw detectors, the most widely used signal transmission device from the early days of the flaw detector to the present day is the slip-ring brush. When considering the problem of transmission, this slip-ring brush signal transmission device is the most elementary and basic one, so in order to understand the present invention, we will briefly explain the slip-ring brush signal transmission device. I think it is necessary.

Figure 1 shows a slip ring as a signal transmission device.
An overview of the structure of a rotating probe type flaw detector using a brush is shown below. 1 is a steel pipe to be inspected and is guided by a guide 2 and transported in the direction of the arrow through a rotating probe type flaw detector. The rotor 3 of the probe rotation type flaw detector is supported by bearings 4a and 4b at both ends of the rotor, and is driven by a drive motor via a timing pulley 5 fitted to the end of the rotor shaft and a timing belt 6 meshing with the timing pulley 5. 7 and rotates at high speed. A probe holder 9 is attached to the face plate 8 on the end surface of the rotor 3 at the other end of the rotor 3, and the probe holder 9 has a plurality of probes 10a, 10b at key points.
...is installed. Coaxial cables 11a, 11b, . . . from this probe are connected to connectors 12a, 12b, .
Connected at On the other hand, the connectors 12a, 12b of the face plate 8 are connected to the connectors 12a, 12b of the face plate 8 by the coaxial cables 13a, 13b, .
... and _slip rings 14a ₁ , 14a 2 , 14b ₁ , 14b ₂ , 14 arranged on the outer periphery of the cylindrical portion of the rotor 3
c ₁ , 14c ₂ . . . are connected. Here, the slip ring 14a ₂ is attached to the shield of the coaxial cable.
a ₁ is connected to the center conductor, i.e. the probe 10a
Similarly, the contact 10b is attached to the slip rings 14b _{1 ,} 14b ₂ , and the probe 10c is attached to the slip rings 14c ₁ , _14a2 .
14c ₂ ... is connected.

FIG. 2 shows the structure of the brush part, in which the brush 15 is loosely fitted and held in the brush holder 16, and the coil spring 1
It is crimped onto the slip ring at step 7. cap 18
The coil spring 17 is compressed by. cap 1
The lead wire 19 from the brush 15 is drawn out through a hole provided in the center of the brush 8.

In the conventional signal transmission device using a slip ring and brush as explained above, since the transmission is essentially by sliding contact between the slip ring and the brush, contact noise and wear are unavoidable, and the maximum circumference depends on the brush material. There are limitations on speed, material selection is required depending on usage conditions, cross talk between channels due to electrostatic coupling between adjacent channels due to capacitance, and dirt on the slip ring may cause brush damage. There were problems such as the need for sophisticated maintenance of the slip rings and brushes due to unstable contact conditions.

An electromagnetic coupling signal transmission device that transmits signals in a non-contact manner as a method of solving the problems of the conventional signal transmission device using a slip ring brush as described above.
Alternatively, there are capacitively coupled signal transmission devices, which are in practical use.

However, these contactless signal transmission devices also
It has advantages and disadvantages due to its signal transmission characteristics and structural limitations, and it is difficult to say that it can be used in common in all cases.

This invention proposes a configuration that combines an electromagnetic coupling transmission device and an electrostatic coupling transmission device as a signal transmission device for a rotating probe type ultrasonic flaw detector, taking into account the flaw detection conditions and mechanical structure conditions. According to the present invention, it is possible to provide a rotating probe type ultrasonic flaw detector that is more suitable for the purpose of flaw detection than conventional methods in measuring the wall thickness of an ultrasonic flaw detection tube for steel pipes.

Hereinafter, embodiments of an electromagnetic coupling transmission device and then a capacitive coupling transmission device will be described, and the problems of each embodiment will be described.

Fig. 3 shows an embodiment of a rotating probe type flaw detector using electromagnetic coupling. In Fig. 3, the slip ring and brush parts in Fig. 1 are replaced with an electromagnetic coupling signal transmission device, so the explanation of the same contents as in Fig. 1 will be omitted.

On the outer periphery of the cylindrical portion of the rotor 3, disks 20 of electromagnetic coupling coils made of glass fiber epoxy substrates are arranged in a number corresponding to the number of channels. The disk 20 has an annular shape as shown in FIG.
A single conductive wire 21 is carved as a one-turn coil along the outer edge of the ring, and both ends of the one-turn coil are drawn out to the inner edge of the ring as shown at 22a and 22b. Conductive wire 21 on disk 20 and both end drawers 2
2a and 22b are fabricated by etching the above pattern from a glass fiber epoxy substrate with copper foil attached. A ferrite core 23 is arranged so as to surround a conductor 21 of a one-turn coil. A slit 24 is formed in one part of the ferrite core 23, and the disc 20 is inserted between the slits 24.
The ferrite core 23 is wound with a coil 25 having several turns. Furthermore, although not shown, an electromagnetic shielding plate is inserted between each disc to prevent crosstalk between adjacent channels.

If the pulser/receiver of the flaw detector 26 is connected to the coil 25 with the above configuration, a pulse is induced in the one-turn coil via the ferrite by the excitation pulse from the pulser during transmission, and this pulse is used for detection. Drive the feeler 10. In the case of reception, the reception signal is transmitted from the one-turn coil to the coil 25 via the ferrite, and then to the receiver of the flaw detector 26, contrary to the transmission.

The above-mentioned electromagnetic coupling type signal transmission device can effectively transmit and receive flaw detection signals between rotating parts and fixed parts without contact, and eliminates the problems of noise, wear, and maximum circumferential speed that were problems in signal transmission using slip rings and brushes. It is an excellent transmission device that has no limitations and solves the maintenance problem caused by dirty slip rings, and is effectively put into practical use in applications where the problems described below do not pose a problem.

This electromagnetic coupling type signal transmission device has one turn.
Because it is a coil coupling, the degree of coupling is low and the coupling loss is large.It depends on the design conditions, but for example, at 2MHz or 5MHz with a disk diameter of about 400mm,
This is because there is approximately 20 dB attenuation compared to when transmitting and receiving by connecting the probe directly to the flaw detector, and it is necessary to have a resonant coil on the probe side to compensate for this attenuation. The flaw detection waveform is broader than that of direct connection, and 2MHz,
At 5MHz, it is practical even though there are the above problems, but at even higher frequencies, for example 10MHz, the attenuation is large, reaching 40dB or more, so there is a problem that it is not practical in the high frequency range.

The above problem is that when performing ultrasonic flaw detection of steel pipes using a rotating probe type flaw detector, in normal ultrasonic flaw detection of steel pipes, flaws on the inner and outer surfaces in the axial direction of the pipe, and flaws on the inner and outer surfaces in the circumferential direction are detected using oblique angles. Since 2MHz or 5MHz is commonly used for flaw detection, there is no problem in using an electromagnetic coupling signal transmission device for flaw detection. In addition to oblique defect detection in the pipe circumferential direction, ultrasonic measurement of pipe wall thickness may be required. Pipe wall thickness measurement using ultrasonic waves is performed by making ultrasonic waves perpendicularly incident in the wall thickness direction and measuring the ultrasonic propagation time between multiple reflected echoes generated on the inner and outer surfaces of the pipe. For this reason, echo separation between multiple echoes becomes a problem, so it is absolutely necessary to use a high frequency region of at least 10MHz or more and to avoid broad waveforms in the signal transmission system. I'm getting old. For this reason, it can be seen that the above-mentioned electromagnetic coupling type signal transmission device cannot be used for measuring pipe wall thickness using ultrasonic waves.

On the other hand, as described above, there is a signal transmission method using capacitive coupling as a signal transmission device that can be used in the area of pipe wall thickness measurement where the signal transmission device using electromagnetic coupling cannot be used. A signal transmission device using this method will be explained below.

FIG. 5 shows terminals 26a and 26 of the ultrasonic flaw detector 26.
Fig. 2 is a connection diagram when conducting an experiment on the relationship between capacitance and flaw detection sensitivity in order to investigate the transmission characteristics by interposing capacitance as a transmission path between the probe 10 and the probe 10 instead of directly connecting them. . In other words, the test material steel pipe 1
Vertical flaw detection is performed using the probe 10 while immersed in water. Capacitors 27a and 27b are connected between the coaxial cable 28 of the probe 10 and the external connection coaxial cable 29. 27a is for the center conductor of the coaxial cable, 27b
is for shielding. Coaxial cable for external connection 2
9 are terminals 26a and 26 of the transmitter/receiver part of the flaw detector 26.
connected to b.

Figure 6 shows data obtained by measuring attenuation values for various capacitance values when connecting capacitances for direct connection in the above connection at 5 MHz and 10 MHz.

From the data in Figure 6, at 10MHz, the capacitance values of 27a and 27b in Figure 5 are each 2000P ^F.
If the above is the case, it can be seen that even if the capacitance value varies somewhat, the variation in flaw detection sensitivity is extremely small. According to this experiment, no change in the waveform of the flaw detection echo was observed at 2000 P ^F or higher compared to when the probes were directly coupled.

Generally, the relationship between the capacitance C(F) between parallel plane electrodes, the electrode area A (m ² ), and the inter-electrode distance d (m) is given by the following equation.

C=8.854×10 ^-12 ×A/d (1) The rotor diameter of a normal probe rotating type flaw detector varies depending on the maximum diameter of the applicable test material, but for example, 3" outer diameter 76.2
The ones that target mm are approximately 250 mm,
Considering a doughnut-shaped electrode as shown in FIG. 7, the inner diameter _D1 of the electrode disc is approximately 250 mm. If the electrode width is 50 mm and the effective diameter DE is 300 mm, the electrode area is 471 cm ² and the capacitance is 2000 P ^F.
Calculating the distance d between the electrodes from (1), d=0.2×10 ^-3 m
=0.2mm is required.

The distance between the electrode plates determined by the above calculation is 0.2 mm
It is impossible to maintain the gap between the rotating annular electrode and the stationary electrode at 0.2 mm by spatially fixing the stationary electrode, but it is impossible to maintain the gap between the rotating annular electrode and the fixed electrode at 0.2 mm by fixing the stationary electrode spatially. Create micro-gaps using air pressure,
It can be configured to be held in a non-contact state. An example of a capacitive signal transmission device using this method will be described below.

FIG. 8 is a diagram explaining the gist of the embodiment. The rotating annular electrode 31 is connected to the rotor 3 via the insulating plate 30.
It is attached to and rotates in the direction of the arrow in Figure 9. A fixed part side electrode 32 is disposed opposite to the rotating annular electrode 31, and the fixed part side electrode 32 is made of plate springs 33a equally distributed on the circumference of the fixed part side electrode 32 as shown in FIG. , 33b, 33c, 33d, . In addition, leaf springs 33a, 33b, 33c,
There are air hole nipples 34a, 34b, 34c, 34d... in the middle of each arrangement position of 33d..., and the air hole nipples are emptied by flexible vinyl pipes, rubber pipes, etc. (not shown). supply pressure.

In the capacitive coupling transmission device with the above configuration, the fixed side electrode 32 is spring-pressed to the rotating annular electrode 31, and the air hole nipples 34a, 34b, 3
Air pressure supplied from 4c, 34d... opens between the contact surfaces of the stationary side electrode 32 and the rotating annular electrode 31 and blows out, holding the stationary side electrode 32 in a floating state similar to a thrust air bearing. do. Note that both opposing surfaces of the stationary side electrode 32 and rotating annular electrode 31 must be finished to a flatness of approximately 0.05 mm, and at the same time, one of the opposing surfaces must be coated with a thin insulating resin, such as Teflon. By applying a fluororesin coating treatment, even if partial contact occurs, direct contact between the two electrodes is prevented, and a wear-resistant lubricant film prevents excessive friction from occurring due to contact between the two electrodes. is desirable. Further, the gap between the electrodes can be adjusted by adjusting the air pressure supplied.

Examples of capacitively coupled transmitters have been described above, and capacitively coupled transmitters have less transmission loss than electromagnetic coupled transmitters, are particularly suitable for high frequency transmission, and are characterized by less distortion of echo waveforms. . However, in electromagnetic coupling, one channel of transmission is possible with one electromagnetic coupling coil disk 20 as shown in Fig. 4, whereas in electrostatic coupling, as shown in the connection diagram in Fig. 5, the central conductor of the coaxial cable Coupling capacitor 27
2 of a and coaxial cable shield coupling capacitor 27b
A pair of capacitances is required. In an actual transmission device, this is achieved by not only the rotating annular electrode 31 shown in FIG. This means that one channel of transmission can only be achieved by two pairs of capacitive coupling. That is, compared to an electromagnetic coupling transmission device, the capacitive coupling transmission device doubles the number of donut-shaped disks mounted on the rotor 3 when transmitting the same number of channels.
In other words, it is necessary to prepare twice the number of transmission channels, thereby doubling the actual length of the rotor 3 in the axial direction, resulting in a problem that the mechanical section becomes larger. Particularly in steel pipe flaw detection, the steel pipe itself varies in size depending on the method of pipe making, but if the steel pipe itself has some bends and the rotor shaft length is long, it is necessary to hold the test material steel pipe 1 and the probe holder 9 concentrically. becomes difficult. It is desired that the rotor shaft length be short, both from the viewpoint of maintaining concentricity and from the viewpoint of equipment cost.

On the other hand, flaw detection using a rotating probe type ultrasonic flaw detector for steel pipes generally uses artificial defects in the axial and circumferential directions provided on the inner and outer surfaces of the standard test steel pipe as the reference flaw, and sets flaw detection conditions such as the detection sensitivity gate of the flaw detector. Set. In this case, as shown in FIGS. 10 and 11, the reference defect is subjected to oblique flaw detection with good detectability. Fig. 10A shows the inner reference defect 36 in the axial direction.
Similarly, Fig. 10B shows the situation of oblique sound field incidence from the probe 10 to a ₁ .
6b shows the oblique sound field incidence situation from the probe 10. In addition, FIG. 11 shows a reference defect 37 on the circumferential inner surface.
a, Probe 1 for circumferential outer surface reference defect 37b
This shows the oblique sound field incidence situation from 0. In other words, in these angle-angle flaw detection, the depth of the reference defect is 5 times the pipe wall thickness.
%, for example, if the wall thickness is 6 mm, the standard requires a defect of about 0.3 mm, and when this defect is used as a standard, a frequency of 5 MHz and a wavelength of 0.6 mm can be sufficient for detection. Therefore, it is advantageous to use an electromagnetic coupling transmission device for this angle flaw detection. On the other hand, in pipe wall thickness measurement, as shown in Fig. 12, ultrasonic waves are incident perpendicularly to the specimen from a probe, and the detected echo waveform, for example, the surface echo S ₁ in the echo waveform shown in Fig. 13, is detected.
The time difference between the rise of and the rise of bottom echo B ₁ , or the rise of bottom echo B ₁ and the rise of bottom echo B ₂
The wall thickness is measured by the time difference between the rising edges of
Frequency ranges above 10MHz are used. Therefore, it is essential to use a capacitively coupled transmission device for this wall thickness measurement.

Particularly in ultrasonic flaw detection of seamless steel pipes, uneven thickness of the pipe is likely to occur due to the normal process, and uneven thickness is also a quality control factor. Therefore, in addition to the above-mentioned ultrasonic flaw detection of the inner and outer surfaces of the tube in the axial direction and the circumferential direction, it is necessary to perform ultrasonic measurement of the tube wall thickness, and there are examples of this being carried out using a rotating probe type flaw detector. All of these embodiments used slip-ring brushes due to signal transmission frequency constraints. In other words, this embodiment uses 8 channels for axial defect detection, 8 channels for circumferential defect detection, and 1 channel for pipe wall thickness measurement, all of which are configured to transmit signals using slip-ring brushes. The essential drawbacks of the slip-ring brush described above were unavoidable.

In this invention, as shown in Fig. 14, as signal transmission devices, an electromagnetic coupling transmission device for the oblique flaw detection channel and an electrostatic coupling transmission device for the pipe wall thickness measurement channel are assembled into one probe rotating type flaw detector. By incorporating them together, we were able to significantly improve the performance and maintainability of the conventional rotating probe type flaw detector.

An embodiment of the invention described above is shown in FIG.
Rotating annular electrodes 31-1 and 31-2 are attached to the capacitive coupling transmission device and the rotor 3 via insulating plates 30-1 and 30-2, respectively. Fixed part side electrodes 32-1 and 32-2 are provided opposite to electrode 31-2, respectively. Furthermore, disks 20-1, 20-2, 20-3, etc. of electromagnetic coupling coils corresponding to the required number of channels are attached to the rotor 3 as an electromagnetic coupling transmission device, and these are ferrite cores 23-1, 23-3.
2, 23-3... are arranged so as to wrap around the coil carved on the disk. Ferrite core 23-
1, 23-2... has several turns of coil 25-
1, 25-2, 25-3... are wound.

With the configuration described above, multi-channel oblique flaw detection signal transmission and single-channel tube wall measurement signal transmission can be performed using a single rotary probe by taking advantage of the advantages of the electromagnetic coupling type and capacitive coupling type, respectively. This can be achieved with a flaw detector.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of a conventional rotating probe flaw detector using a slip-ring brush, Figure 2 is a structural diagram of the brush section shown in the previous figure, and Figure 3 is the slip-ring brush shown in Figure 1. Fig. 4 is a diagram showing the circuit configuration of the electromagnetic coupling in Fig. 3, Fig. 5 is a diagram showing the circuit configuration using capacitive coupling, and Fig. 6 is the measured data of the attenuation value of the ultrasonic transmission waveform with respect to the connection capacitance when the circuit is connected as shown in Fig. 5, Fig. 7 is a diagram showing a disk-shaped annular electrode for capacitive coupling, and Fig. 8 is FIG. 9 is a configuration diagram showing a signal transmission device using the circular electrode shown in FIG.
The figure is a configuration diagram of the rotating annular electrode and fixed part side electrode in Figure 8, Figures 10A and B are diagrams showing the incidence of ultrasonic waves on the inner and outer reference defects in the axial direction, and Figure 1
Figure 1 shows the incident situation of ultrasonic waves on inner and outer reference defects in the circumferential direction, Figure 12 shows the situation where ultrasonic waves are incident perpendicularly to the test material, and Figure 13 shows the situation detected in the previous figure. FIG. 14 is a block diagram showing the signal transmission device according to the present invention. 10... Probe, 28, 29... Coaxial cable, 31... Rotating annular electrode, 32... Fixed part side electrode, 33a, 33b, 33c, 33d... Leaf spring, 34a, 34b, 34c, 34d ...Air hole nipple, 20-1, 20-2, 20-3, 20
-4...Disc of electromagnetic coupling coil, 31-1, 3
1-1', 31-2, 31-2'...Rotating annular electrodes.

Claims (1)

[Scope of utility model registration request] In a signal transmission device that sends and receives signals between the rotary part probe of a multi-channel contact rotating type flaw detector and the fixed part flaw detector, the oblique flaw detection channel consisting of multiple channels uses electromagnetic coupling. A signal transmission device for a multi-channel probe rotary probe that is equipped with a combination of a signal transmission section and a signal transmission section using capacitance coupling in the pipe meat measurement channel.