JPH01167654A - Eddy current flaw detecting device for tube rod material - Google Patents

Abstract

PURPOSE:To accurately detect a defective signal by providing a variable cutoff frequency high-pass filter whose cutoff frequency is adjusted with the rotating speed signal of a detecting coil rotating mechanism behind a detecting circuit. CONSTITUTION:The detecting coil rotating mechanism 2 rotates and its rotating speed is converted into a voltage signal through a 1st pulse generator 8 and a 1st F/V converter 10 to set the cutoff frequency of the variable cutoff frequency high-pass filter 12. Then the tube rod material 1 begins to be conveyed by an axial conveying means 3 and flaw detection measurement is started. A phase shifter 6 is set to a phase for erasing a signal of distance variation between the tube rod material 1 and a detecting coil 5. After detection signals passed through the variable cutoff frequency high-pass filter 12, a detection signal 14 due to deformation of low equivalent frequency is suppressed and a detection signal 15 due to a flaw of high equivalent frequency has little variation, so the flaw signal 15 is relatively effective and the flaw detection accuracy is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an eddy current flaw detection device for metal tubes or bars.

[Prior Art] Eddy current flaw detection, which uses a detection coil to detect changes in eddy currents generated on a conductor by applying an alternating magnetic field to the conductor to determine the presence of flaws, has become widely used. If the object to be inspected is a flaw on the outer circumferential surface of a pipe or round bar, the material to be inspected is a pipe or a round bar.
A detection coil is provided that scans the surface of the tube and rod by rotating at a relatively high speed around the tube and rod while moving at a relatively low speed in the rod axis direction.

In eddy current flaw detection, not only in the case of tubes and bars, there is generally a phase difference between the excitation voltage applied to the detection coil and the induced voltage caused by the eddy current. When there is a change in the distance between
There may be differences due to changes in the material, etc., so phase detection of the detection coil induced voltage is performed to eliminate one specific phase component, such as a change in the distance between the detector and the pipe rod to be inspected, to determine the SN.
Efforts are being made to improve the signal-to-noise ratio.

[Problem to be solved] However, during the manufacture of tubes and bars, continuous deformation in the axial direction may occur in the tubes and bars, and this deformation causes signal changes after phase detection (hereinafter referred to as detection signals). Since the signal is usually considerably larger than the detection signal due to a flaw, the flaw detection sensitivity may be reduced.

The present invention aims to solve the above problems, and provides an eddy current flaw detection device that can detect defects such as flaws with high sensitivity even if there is deformation in the pipe rod to be inspected or changes in measurement conditions. The purpose is to obtain.

[Means for Solving the Problems] The eddy current flaw detection device for baton materials of the present invention includes
It is characterized by being provided with a variable cut-off frequency high-pass filter whose cut-off frequency is adjusted by the rotation speed signal of the detection coil rotation mechanism.

[Function] When observing the voltage waveforms of the detection signal due to material defects such as scratches and the detection signal due to baton deformation, as shown in Figure 2 (a) below, the former changes quickly and the latter changes slowly. It is recognized that Furthermore, it was also observed that the speed of these changes tended to increase as the rotation speed of the detection coil increased.

The present invention was made based on the above-mentioned phenomenon, and a high-pass filter is provided in order to separate the above-mentioned two signals having different rate of change, and the cut-off frequency of the high-pass filter is made variable to control the detection coil rotational speed. The presence or absence of a flaw is determined by determining the magnitude of the signal after changing it to follow the magnitude and suppressing a signal that changes slowly (as illustrated in FIG. 2(b), which will be described later).

[Example] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an eddy current flaw detection device for baton materials as an example, in which 1 is the baton material to be inspected, 2 is a detection coil rotation mechanism that rotates the detection coil 5 around the baton material 1, and 3 4 is an oscillator that supplies high-frequency excitation voltage to the detection coil 5; 5 is a detection coil that detects changes in eddy current on the surface of the baton material 1; 6 is a phase a phase shifter that manually adjusts the detection phase of the detector 7;
7 is a phase detector that detects the phase of the alternating voltage caused by the eddy current change detected by the detection coil 5 and generates a low frequency detection signal; 8
9 is a first pulse generator that detects the rotation speed of the detection coil rotation mechanism 2; 9 is a second pulse generator that detects the transfer speed of the axial transfer means 3; 10 is a pulse per hour of the first pulse generator 8; 11 is a second F/V converter that converts the number of pulses per time of the second pulse generator 9 into voltage; 12 is a first F/V converter that converts the number of pulses per time into voltage; A variable cut-off frequency high-pass filter 13 is a variable cut-off frequency high-pass filter mainly composed of a switched capacitor filter whose cut-off frequency is adjusted by voltage commands from the second F/V converters 10 and 11. This is a discrimination circuit that judges the magnitude of the output and, if it is large, determines and displays that there is a flaw.

The apparatus of this embodiment is configured as described above and operates as follows.

The detection coil rotation mechanism 2 rotates, and its rotation speed is determined by the first pulse generator 8. A voltage signal is generated by the first F/V converter 10 and a variable cut-off frequency high-pass filter 12
Set the cutoff frequency.

Thereafter, transport of the baton material 1 is started by the axial transport means 3, and flaw detection and measurement is then started.

The setting of the phase shifter 6 is adjusted to a phase that eliminates the distance change signal between the baton material 1 and the detection coil 5. An example of the output of the phase detector 7 is shown in FIG. 2(a).

In the figure, 14 is a detection signal when the baton material 1 is deformed, and 15 is a detection signal when the baton material 1 has a flaw.

If these detection signals are approximated by a sine waveform of one cycle and the frequency of the sine wave is the iso-side frequency of the detection signal, then the iso-side frequency of the detection signal 14 due to deformation is fl, and the equality of the detection signal due to the flaw is It has been experimentally observed that there is a difference between the two frequencies, for example,
The isolateral frequency f1 of the detection signal due to deformation is 0.6 to 1.2
kHz, the equal side frequency f3 of the detection signal due to flaws is 1.8
~2.2 kHz. These iso-side frequencies change depending on the rotational speed of the detection coil rotation mechanism 2, and as the rotation speed increases, the iso-side frequency also tends to increase, but the ratio of the f and f2 remains unchanged. be.

The variable cut-off frequency high-pass filter 12 automatically selects the geometric mean equivalent value of ft5f2, which has been previously measured and input based on the rotational speed voltage output from the first F/V converter 10, and sets it as the cut-off frequency. It is made to be.

Variable cut-off frequency high-pass filter 12 adjusted in this way
The waveform of the detection signal after passing through is shown in Fig. 2(b).
14a is the waveform of the detection signal 14 due to deformation after passing through the same filter, and 15a is the waveform of the detection signal 15 due to a defect after passing through the same filter. Detection signal 1 by
5 hardly changes, the flaw signal 15 becomes relatively more powerful, and flaw detection accuracy improves.

The level of the signal after passing through the variable cut-off frequency high-pass filter 12 is determined by a discriminator 13, and if the level is greater than a predetermined level, a flaw alarm is output. In response to the warning, the driver takes predetermined measures such as marking the baton material.

Next, a specific example will be shown. Detects steel pipes with an outer diameter of 9.5 + awz made using a vertical pipe continuous winding and drawing machine. Coil rotation speed: 600
When testing with Orpm, by setting the cutoff frequency of the variable cutoff frequency high-pass filter 12 to 1.5 kHz,
The pipe material to be inspected 1 can be inspected without being affected by the deformation in which the outer diameter has changed by 0.1 rm at the extreme part of the pipe material to be inspected.
Micronodules 0.04 aa below the outer surface of the can be detected. The flaw detection ability without the variable cut-off frequency high-pass filter 12 was 0.07 am.

In this way, with the device of this embodiment, even if the baton material is deformed, the interference caused by it can be reduced.

Even if the rotational speed setting of the detection coil is changed due to a change in the outer diameter of the tube bar to be inspected, good flaw detection accuracy can be obtained without any operation.

In the above-described embodiment, the cutoff frequency of the variable cutoff frequency high-pass filter 12 was adjusted to follow the rotational speed of the detection coil rotation mechanism, but the rate of change of the detection signal depends on the baton material and the detection coil. In addition to the rotation speed signal of the detection coil rotation mechanism, the transfer speed signal of the axial transfer means (in FIG. 1, the second A second F/V converts the number of pulses per time of the pulse generator 9 into voltage.
By configuring the variable cut-off frequency high-pass filter 12 so that the cut-off frequency is adjusted and set according to the square root calculated value, A device with accurate interference signal suppression characteristics can be obtained.

[Effects of the Invention] The eddy current flaw detection device for baton materials of the present invention includes
A variable cut-off frequency high-pass filter whose cut-off frequency is adjusted by the rotation speed signal of the detection coil rotation mechanism is provided, so even if there is a change in the waveform of the detection signal due to a change in the circumferential rotation speed of the detection coil, it will not be caused by deformation of the baton material. Interfering signals are effectively suppressed, and defective signals such as flaws can be detected with high accuracy, resulting in significant economic effects such as improving the quality of product tubes and rods and early detection of process abnormalities.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an eddy current flaw detection device for baton materials as an example, Figure 2 (a) is a graph showing an example of the output of a phase detector, and Figure 2 (b) is a graph of a variable cut-off frequency high-pass filter. It is a graph showing an output example. 1... Nightstick material, 2... Detection coil rotation mechanism, 3... Axial direction transfer means, 4...
Oscillator, 5...detection coil, 6...phase shifter, 7...phase detector, 8゜9...
1st. Second pulse generator, 10°11...
...First. Second F/V converter, 12...
Variable cut-off frequency high-pass filter, 13...Discrimination circuit, 14...Detection signal due to tube shaft deformation, 14a
...Detection signal due to pipe deformation after passing through the filter, 15...Detection signal due to flaw, 15a...
...Detection signal due to flaws after passing through the filter. Patent applicant: Kobe Steel, Ltd. Representative: Patent attorney Fu Kobayashi @Figure 1

Claims (2)

[Claims] (1) A detection coil that applies an alternating magnetic field to the outer circumferential surface of a tube or bar (hereinafter referred to as a tube or bar) to detect changes in eddy currents induced on the outer circumferential surface, and eddy currents detected by the detection coil. a detection circuit that detects an alternating voltage due to a change in current; a detection coil rotation mechanism that rotates the detection coil around the outer periphery of the tube bar; and a detection coil rotation mechanism that determines the relative position of the detection coil rotation mechanism and the tube bar. In an eddy current flaw detection device for pipe and bar materials, which includes an axial direction transfer means for moving the bar material in the axial direction, a variable cutoff frequency whose cutoff frequency is adjusted by a rotation speed signal of the detection coil rotation mechanism is provided at a subsequent stage of the detection circuit. An eddy current flaw detection device for tube and bar materials, characterized by being equipped with a high-pass filter. (2) A variable cut-off frequency high-pass filter whose cut-off frequency is adjusted by the rotation speed signal of the detection coil rotation mechanism and the movement speed signal of the axial transfer means is provided at a subsequent stage of the detection circuit. An eddy current flaw detection device for pipe and bar materials according to claim 1.