JPS5834357A - Method and device for eddy current flaw detection - Google Patents

Abstract

PURPOSE:To detect flaws of a material to be detected in an axial and a circumferential direction, by arranging plural detecting probe coils zigzag in circumference, and rotating and scanning those probe coils electrically. CONSTITUTION:To a heat-resisting cylindrical fixture 101 having an enough diameter to be fitted around a steel tube T as a body to be detected, plural probe coils are fitted zigzag adjacently to the circumferential surface. Energizing coils are superposed upon this coil group. A flaw L of the steel tube T in an axial direction is detected by the combination of the plus output 1 and minus output 2 of, for example, adjacent probe coils, and the output difference between the both is used. Further, a flaw C or CCW in a circumferential direction is detected from the output difference between, for example, a minus output 2 and a plus output n'. Those probe coils are switched electrically and rotated and scanned. Consequently, flaws of a steel tube, conveyed at a high speed at high temperature, in an axial and a rolling direction and in a circumferential direction are detected efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an eddy current flaw detection method and apparatus, and more particularly to an eddy current flaw detection method and apparatus that are optimal for flaw detection of long strip materials on a hot production line.

BACKGROUND ART During the manufacturing process of seamless steel pipes, forge-welded steel pipes, etc. and the hot finishing process of electric resistance welded steel pipes, it is necessary to detect flaws in the rolling direction and in the local direction orthogonal to this. Steel pipes in this process are exposed to high temperatures of about 800° C. to 1100° C. and transported at high speeds, so it has been difficult to efficiently and accurately detect flaws during the process.

(3) An example of conventional flaw detection for steel pipes under hot conditions is eddy current flaw detection using a through coil. However, since this flaw detection method compares the test materials adjacent to each other in the tube axis/rolling direction, it has the drawback that it is difficult in principle to detect long linear or wrinkle-like flaws in the tube axis/rolling direction. Furthermore, if adjacent comparisons are not made, it is not possible to eliminate signals caused by changes in the material and dimensions of the test material and relative positional changes between the through coil and the test material, and it is only possible to detect extremely large flaws. This is due to the fact that it is known.

By the way, it is known that detection of linear or wrinkle-like flaws that are long in the tube axis rolling direction can be achieved in principle by a mechanical rotating probe using adjacent differential probe coils that scan across the flaws. However, when mechanically running the adjacent differential probe coils along the outer periphery of the steel pipe, the running speed is slow, so it could not be applied to the above-mentioned manufacturing line that performs high-speed production. In other words, the maximum rotational speed is limited by the diameter and rotational speed of the bearing, and the ability of the probe coil to follow the steel pipe surface (4) is due to the fact that the probe coil and scanning mechanism are two-mass rotating bodies. Restricted by centrifugal force, etc. In particular, it is known that the followability decreases as the rotational speed increases, and therefore an upper limit is placed on the mechanical rotational speed.

On the other hand, as a method of making the rotational scanning locus denser, there is a method of arranging a plurality of probe coils on the circumference for rotational scanning along the outer circumferential surface of the steel pipe. In this case, the probe coil should be 2 to 4
The two are arranged facing each other around the rotation axis. For example, if four probe coils are mechanically scanned at 500 to 1000 revolutions/min, if the effective detection area of one probe is 15-, then the area is 15X4X1000 or 60m/min.
It is possible to perform full-surface flaw detection scanning on minute steel pipes.

On the other hand, for example, the manufacturing speed of steel pipes immediately after drawing and rolling reaches 400 m1 min, and when using the above-mentioned flaw detection equipment, 60 ÷ 400 = 15 (ch), that is, 15 m1 for the total length of the material to be tested. can only scan an area of Therefore, flaws that can satisfy the full surface flaw detection conditions are limited to those with a predetermined length or more.

Scratches that occur on steel pipes are not limited to long scratches that occur in the tube axis/rolling direction, but also short scratches that occur in the tube axis/rolling direction.
Detection is required for this as well. In addition, flaws also occur in the circumferential direction of steel pipes, which have no length in the pipe axis direction, but for such flaws, the above-mentioned rotary scanning flaw detection using mechanical rotation requires the probe coil to scan across the flaws. It cannot be detected because it does not.

Flaws that occur in steel pipes are broadly classified into those that exist in the material before pipe making and those that occur during the rolling process.

If such flaws can be detected in real time immediately after rolling, they can be used not only for quality assurance, which has traditionally been the purpose of flaw detection, but also as a part of real-time corrective measures for previous processes, that is, as part of process control in a broad sense. Since it is possible to establish a non-destructive inspection system, there is a strong desire for a flaw detection system that satisfies such requirements.

An object of the present invention is to provide an eddy current flaw detection method and apparatus that can detect flaws in the rolling direction and circumferential direction of a long strip under hot conditions.

That is, the present invention detects flaws in the rolling direction by rotating and scanning the probe coil electrically without mechanically rotating the probe, and detects the state in which the material travels as the material to be inspected is manufactured. This method uses the method to detect flaws in the circumferential direction.

FIG. 1 is a block diagram showing an embodiment of the present invention. 1. The detection end 1 has a plurality of detection probe coils arranged circumferentially and in a zigzag pattern. A plurality of rows of probe coil groups are arranged on the (tube) axis, and the plurality of rows of the probe coil group are wrapped around one or more excitation coils to form a heat-resistant structure. The output of the detection end 1 is sent to a signal multiplexing processor 2 for detecting flaws in the tube axis/rolling (L) direction of the steel pipe (material to be tested). and signal multiplexing processing section 3 for detecting flaws in the circumferential (0) direction occurring along the circumference of the steel pipe. After performing high-frequency time-division multiplexing, the multiplexing processing section 2 sends the tube axis mid-rolling direction flaw information signal to the L-series time-division demodulator 4, which is provided separately from the detection end (7). Similarly, the circumferential flaw information signal of the multiplexing processing section 3 is also received by the 0-series time-division demodulator 5, which is provided separately from the detection end.
will be sent to. A clock pulse OP as a synchronization signal is applied to each demodulator and each multiplexing processing section. A time division pulse signal is required for signal multiplexing and demodulation of the multiplexed signal. Send as OP. The output signal of the drive circuit 7 is frequency-divided by a frequency divider circuit 8 and then passed through a bandpass filter 9 to a signal power amplifier 10 and a phase shifter 11.12.
1, the output signal of the drive circuit 7 is also sent to a frequency downscaling divider 13 having a plurality of frequency divider circuits, and the low frequency signal obtained by the frequency divider 13 is sent to the scanner drive circuit 14. be done.

The output of the time division demodulator 4 that demodulates the multiplexed tube axis/rolling direction flaw information signal is transmitted to a plurality of phase detectors 151 to 15? ,
(configuration including an amplifier). The output signal of the phase shifter 11 is applied to the phase detectors 151 to 15% as a reference voltage for phase detection. Phase detector 15. Each output signal of ~157L is output from the composite circuit 16. ~ Sent out to 16 Yu. This composite circuit 16.
~16 filters are constructed with a p filter that removes the high frequency range of the input signal, and a signal folding circuit that converts the sinusoidal signal into a single polarity signal. Composite circuit 161~
The signal waveform processed at 16% is sent to a scanner 17 that performs electronic rotational scanning approximation, and the scanner 17 receives the signal sent from the scanner drive circuit 14 (e.g. 3
Composite circuit based on 3Hz low frequency signal) 16ri ~ 16%
The outputs of are sequentially switched and outputted selectively. Composite circuit 161~
The 16% output is also sent to a second scanner, scanner 18. Scanning by the scanner 18 is performed based on the output of a shift register 19 connected to the scanner drive circuit 14. The shift register 19 has a scanning nose delay function for simulating a continuous rotation function while maintaining a 180 degree relationship with the rotation axis of the mechanical flaw detection device and maintaining a facing attitude. be. Therefore, scanner 1
The sampling operation by 8 is n corresponding to the number of signal sequences.
This is performed using a pulse whose origin is a point delayed by (TL/2) bits by the bit shift register 19. Each of the scanners 18 and 17 is provided with a bypass filter 20.21, which filters the low frequency signal generated when the scanner extracts the low-speed signal, that is, the fundamental signal of approximately 33 Hz in this embodiment, and the subharmonic, for example, the fifth harmonic. Low frequency interfering signals up to 165 Hz of waves are removed. The output signal of the bypass filter 20.21 is sent to each of the signal amplitude threshold detection circuits 22.23. An output signal from a threshold setter 24 for setting a screening level corresponding to the flaw depth is applied to these signal amplitude threshold detection circuits 22 and 23. The output signal of the signal amplitude threshold detection circuit 2223 is sent to the relay drive circuit 111r25, and each time the flaw signal exceeds the threshold, the relay 26 is driven to light the lamp 27 to notify that there is a flaw in the material to be detected.

On the other hand, the output of the 0-sequence demodulator 5 for the multiplexed circumferential flaw information signal is transmitted to a plurality of phase detectors 281 to 28. (
configuration including an amplifier). Phase detector 2
The output signal of the phase shifter 12 is applied to the phase detectors 281 to 28 as a reference voltage for phase detection.
~28. The n output signals are sent to each of the composite circuits 291-29rL. This composite circuit 29. ~29 units have the same circuit configuration and function as the composite circuits 161 to 167, and their output signal group is the same as the analog mixing circuit 30.
output and mixed in parallel. The analog mixing circuit 30 is
It has a function of detecting a flaw occurring along the circumferential direction of the steel pipe as a signal no matter where it faces the flaw detection probe coil, and the output signal is sent to the signal amplitude threshold detection circuit 31.

This signal amplitude threshold detection circuit 31 compares the selection level setting value corresponding to the SR output from the threshold value setter 32 with the output signal level of the analog mixing circuit 30, and converts the setting value into the output signal level of the analog mixing circuit 30. (11) Every time the number level is exceeded, an output signal is generated, and the output signal is sent to the relay drive circuit 33. The relay drive circuit 33 drives the relay 34 every time the signal amplitude threshold detection circuit 31j signal is output, and lights up the lamp 35 to notify that there is a flaw in the circumferential direction of the material to be detected. Note that the output of the signal power amplifier 10 is given to an exciter 36. The exciter 36
is used to induce an eddy current reaction in the material to be tested, and is used for electrical wires. @ It is the turned excitation coil.

Here, the structure of the detection end 1 and the principle of flaw detection will be explained with reference to figures. Figure M2 is a perspective view of the detection end 1 for flaw-detecting the steel pipe T to be tested. F is attached adjacent to the circumferential surface. An exciter/excitation coil 36 surrounding the coil group is superimposed on the coil group.

FIG. 3 is a developed view of the steel pipe T and the detection end 1 shown in FIG. 2, each developed in the circumferential direction. O, L shown in steel pipe T
, Ocw are -(12) examples of scratches scattered on the surface. Further, ω to ■ of the detection end 1 indicate the arrangement of the detection probe coils. The mutual connections of the plurality of detection probes are shown as follows.

Linear scratches such as the scratches on the steel pipe T shown in Figure 3 are from L1 to L
? Detection is performed in multiple detection areas divided into L, but one detection area is a combination of the positive and negative outputs of adjacent probe coils.

In other words, numbers are assigned to the output of each probe coil in order: OHI, OH2...YamaoH? If the output signal polarity is positive, OH1 is negative; if it is negative, OH. In order to obtain s III ~L, L, the following configuration may be used. For example, for oHl, it is a differential comparison with OH2, and for OH2, it is a differential comparison with OH3.
Hereafter, similar differential comparisons are made, and for the final Ql(t-, a differential comparison is made with the old one.The differential output Ll obtained in this way is , L2...L
(T)-1...L (9-1).

L? Each of the signals L is subjected to high frequency time division multiplexing by the multiplexing processing unit 2 shown in FIG. 1, and then transmitted to the time division demodulator 4.

Detection of linear flaws such as 0 or OCW shown in FIG. 3 is performed using the following probe coil connection configuration.

That is, the differential comparison output between the inverted output OH1 and the positive output OH- is O1, the differential comparison output between the inverted output OH2 and the normal output OHI is 02, and the same differential comparison is made thereafter and finally inverted. Detection information is output by setting the differential comparison output between the output 0HfL and the positive output OH (%-1)' as 0-.The differential comparison outputs obtained in this way are 01, 02, 03...0 %
are subjected to high-frequency time division multiplexing by the multiplexing processing section 3 and then transmitted to the O-sequence demodulator 5. FIG. 4 shows an example of the electrical combination of probe coils as described above.

(15) As shown in Figure 4, a row of probe coils from OH1 to OH- and a row of probe coils from CH11 to OH- are arranged in parallel on the circumferential surface as shown in Figure 2. It is located in The inverted output of the probe coils OHI to OH% is obtained by an inverter (INV). These inverted outputs and each channel (OH1~OH% and 0H11~0
A comparator (OOMP) performs a differential comparison with the output of H-) to obtain an L series output of output signals L1 to L% and a 0 series output of output signals 01 to 0%. The outputs L1 to L% are sent to the harmonic multi-solexer 21, and the outputs 01 to 09 are sent to the multiplexer 31, and one of them is output sequentially or arbitrarily. In addition to the multiplexer 21.31, the clock pulse OP applied to the demodulator 4.
Nx? L (where N is an integer value and n is the number of signal sequences) frequencies are used. Hikoo, the probe coils marked with * in Fig. 4 are for easy understanding when the probe coils in a circumferential annular arrangement are expanded.
) It means repeating once with the same sign prob coil.

The outputs of the multiplexers 21 and 31, that is, the outputs of the multiplexing processing units 2 and 3, are sent to the time division demodulator 4 and the 0-series demodulator 5. In the time division demodulator 4, the entire output of L1 to L- is taken out in synchronization with the multiplexer 21 according to the clock pulse OP, and in the 0 series demodulator 5, the total output of 01 to 0% is taken out in synchronization with the multiplexer 31 according to the clock pulse OP. Extract synchronously. The output of each demodulator is phase shifter 15+~15%
And the clock frequency (fN·n) is removed by the non-pass filters 281 to 281 are equipped with. Scanners 17 and 18 sequentially output nine inputs or selectively output any input, replacing conventional mechanical probe rotation with electronic rotational scanning. The scanning speed in this case is 33Hz when the output frequency of the branching unit 13 is 33Hz.
X60 x 2,000 is an approximation corresponding to mechanical rotation scanning of approximately 2,000 revolutions.

Figure 5 shows the composite circuit 161-16% and the scanner 17.1
8 is shown in an equivalent circuit. Each scanner is illustrated with a rotary switch. The scanner is a composite circuit16. The relationship for selecting ~169 is as shown in the table below, for example. That is, compared to mechanical rotational scanning, there is a 180 degree shift between the scanners 17 and 18 around the rotation axis, and a continuous rotation function is simulated while maintaining this relationship. As described above, the function of making this 180 degree difference is performed by the shift register 19.

FIG. 6 is a block diagram showing an example of application of the present invention to hot rolled steel pipe manufacturing equipment.

Materials such as round steel pieces, round bits or square steel pieces ψ square pits, etc. 40
is heated uniformly and sufficiently in a heating furnace 41, and then processed into a hollow steel tube shape by a punching machine 42. The perforated steel piece is processed using a plug mill (or mandrel mill) 43
The tube is processed into a rolled and drawn tube to produce a mother tube. Since the mother tube is cooled during the rolling tube processing process, it is reheated by the reheating furnace 44 as necessary. Thereafter, a steel pipe having a predetermined outer diameter and wall thickness is manufactured using a plurality of stands using a diameter-sizing machine or a drawing mill 45.

After this step, the electromagnetic induction flaw detection device 100 according to the present invention shown in FIG. 1 is installed to detect each (19) types of flaws that have occurred in the steel pipe. The steel pipe that has passed through the electromagnetic induction flaw detection device 100 is gradually cooled by a cooling bed 46. A defective steel pipe whose flaws have been detected by the electromagnetic induction flaw detection device 100 is cut by the cutting machine 47.
The defective steel pipes are removed from the line by the defective steel pipe sorting mechanism 48 without being sent to the factory. This defective steel pipe sorting mechanism 48 is a cutting machine 4
It may be provided after 7. A non-defective steel pipe is cut into an arbitrary predetermined length by a cutting machine 47, and the bent steel pipe is straightened by a straightening machine 49. The straightened steel pipe is sent to a cutting and chamfering machine 50, where it is cut to a specified length with high precision. The steel pipes that have undergone the above steps and have been made into products are then 100% inspected as part of product quality assurance using a conventional electromagnetic induction flaw detection device 51 and a conventional method. .

In such equipment, if defective products are screened only by the electromagnetic induction flaw detection device 51, the mill 43 or the drawing mill 44 may become cine-like due to various factors, and it may be possible to detect defective products. When steel pipes are manufactured continuously, defects are discovered only after the cutting process has been completed20), resulting in poor manufacturing efficiency and working against energy conservation. However, by applying the present invention, the conventional inconveniences can be solved, and even if defective steel pipes are manufactured, early detection and early corrective measures can be taken, and only good quality steel pipes can be processed through various refining processes. A production system that flows through the process becomes possible. The ability to establish such a line is due to the fact that, as described above, flaw detection can be performed at high temperatures by electrically rotating and scanning the probe coil instead of mechanically rotating and scanning it.

As is clear from the above, according to the present invention, by electrical probe coil rotation scanning, it is possible to efficiently and accurately remove flaws in the tube axis/rolling direction and circumferential direction of steel pipes being conveyed at high speed under high temperatures. can be detected.

The present invention is particularly effective when applied to hot finishing and processes, but it can also be applied not only to hot finishing but also to cold finishing, and can be applied not only to steel pipes but also to rod-shaped conductive materials such as pipes, wires, and rods. The present invention is also applicable to long strips of conductive material whose cross-sectional shape does not have a circular shape, such as shaped steel and rails.

Furthermore, for materials with a high rolling ratio, most of the flaws are elongated in the rolling direction, so of the flaw detection methods described above, this can only be applied to the detection of flaws in the rolling direction. In addition, to detect flaws other than those in the rolling direction, eddy current flaw detection using a through-coil method, which is conventionally used, is applied, and when used in combination with the device of the present invention, various flaws can be detected. It goes without saying that this is also possible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a perspective view showing the detection end 1 and the material to be tested according to the invention, and Fig. 3 is the detection end 1 and the material to be tested in Fig. 2. FIG. 4 shows a detailed circuit diagram of the detection end l and multiplexing processing units 2 and 3 according to the present invention, and FIG. 5 shows the relationship between the composite circuit and the scanner according to the present invention. The equivalent circuit diagram, FIG. 6, is a block diagram showing an example of application of the present invention. 1... Detection end, 2, 3... Multiplexing processing section, 4...
Time division demodulator, 5... 0 series demodulator, 6... Main oscillator, 7... Drive circuit, 8... Branch circuit, 9... Bandpass filter, 10... Signal power amplifier, 11.12
... Phase shifter, 13... Frequency reduction divider, 14...
・Scanner drive circuit, 151~15n 1281~
28? L...Phase detector, 161 to 167L, 291
~297L...Composite circuit, 17.18...Scanner, 19...Shift register, l', 20.21...High nose filter, 22.23...Signal amplitude threshold detection circuit, 21. 31...Multiplexer, 24...
Threshold value setter, 25.33...Relay drive circuit, 26.
34...Relay, 27.35...Lamp, 30...
- Analog mixing circuit, 31... Signal amplitude threshold detection circuit, 32... Threshold setter, 36... Exciter, 200,
300...Multiplexer, INV...Inno-
OOMP... comparator. Agent Tatsuyuki Unuma (and 2 others) 2nd 3rd UwA Vice) Kanae

Claims (2)

[Claims] (1) Excite the rolled elongated strip to generate an eddy current,
In an eddy current flaw detection method in which flaw detection is performed by detecting changes in the eddy current due to flaws in the strip material using a probe coil,
Output signals of the first plurality of probe coils arranged at a predetermined interval on the entire circumferential surface on a required diameter through which the rolled elongated strip can pass are taken out with the polarity reversed for every other probe coil, and By differential comparison of the output signals of one set of probe coils, flaws in the rolling direction are detected over the entire circumference of the rolled elongated strip, and flaws are detected near the spacing area of the adjacent one set of coils. A flaw in the circumferential direction perpendicular to the rolling direction is detected by differential comparison between the output signal of the second probe coil and the output signal of the probe coil that outputs the polarity inversion signal of the first probe coil. Eddy current flaw detection method. (2) In an eddy current flaw detection device that excites a rolled elongated strip material to generate an eddy current, and detects a change in the eddy current due to a flaw in the rolled elongated material using a probe coil, flaw detection is performed on the rolled elongated strip material. a first plurality of probe coils disposed at predetermined intervals over the entire circumferential surface on a required diameter through which the probe coils can pass; and a first plurality of probe coils disposed parallel to the probe coils and positioned between adjacent coils. The output signals of the second plurality of probe coils provided and the first plurality of probe coils are
A first multiplexing processing section that takes out flaw signals in the rolling direction by inverting and taking out every other probe coil and differentially comparing them with the adjacent probe coil on one side, multiplexes and outputs the flaw signals; a first detection section that demodulates and shapes the waveforms of a plurality of flaw detection signals; a first scanner that sequentially electrically scans the plurality of outputs of the first detection section; and a plurality of outputs of the first detection section. a second scanner that sequentially electrically scans the first scanner with a predetermined delay time;
a first driving section that compares the second scanner output with a set value and controls an output circuit based on the comparison result;
a second multiplexing processing unit that extracts flaw signals in nine circumferential directions by differential comparison between the output signals of the plurality of probe coils and the output signal of the probe coil that outputs the inverted output signal, multiplexes the signals, and outputs the multiplexed signals; , a second detection unit that demodulates the output of the second multiplexing processing unit into a plurality of flaw detection signals and shapes the waveform;
A mixing circuit that mixes a plurality of outputs of the detection section in an analog manner, and a second driving section that controls the output circuit based on a comparison result between the output signal of the mixing circuit and a set value. Eddy current flaw detection equipment.