JPS60125560A - Method for inspecting metal surface - Google Patents

Abstract

PURPOSE:To output only a defect signal by removing a waveform caused by an external factor other than a defect on a metal surface from a detected signal. CONSTITUTION:An inspecting signal A of a detector outputs a signal X0 through an HPF15, an inspecting signal component Y0 for a direction phase shifted by 90 deg. against a phase of the signal X0 in a signal A is obtained. There is mixedly the waveform due to the external factor in addition to the waveform causes by an external factor in the signal X0. Thereupon, by taking a logical product by adding the signals X0, Y0 to a gate 19, the waveform due to the external factor is eliminated, and only the flaw signal X1 is obtained. The signal A forms a lift-off signal B through an LPF20, adds the signal B to a gate 21 to take a logical product with the signal Y0, and a lift-off correcting signal C is obtained. Next, by processing the signals C and X1 by a correcting circuit, an erroneous signal due to the external factor and the influence due to the lift-off variation are removed from the output signal, and only the flaw signal corresponding to the depth and length of the actual defect is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is designed to prevent cracks, corrosion, etc. on the surface or near the surface of cargo oil pipes installed in oil tankers, urban water and sewage pipes (large diameter pipes, and long metal plates). The present invention relates to an inspection method for detecting defects in.

Conventionally, defects in metal surfaces have been inspected by eddy current testing. The method involves bringing a detector equipped with a coil close to a metal surface, and applying the coil's high-frequency varying magnetic field to the metal surface. The eddy current generated on the metal surface affects the coil through self-induction or mutual induction and generates an induced electromotive force, so by detecting this, it is possible to know if there is an abnormality in the metal surface.

FIG. 3 shows the detection signal A and its phase due to the electromotive force induced in the coil when the detector is moved close to the metal surface. The detection signal A is output in the X-axis direction with its phase shifted by an angle θ with respect to the reference voltage input to the coil due to the impedance between the detector and the metal surface.

Movement of the detector or metal surface, vibrations received from the surrounding environment,
The vector value of the detection signal A fluctuates due to non-uniformity in the material of the metal surface, etc., but depending on these factors, the phase θ of the output signal (assumed to be the standard phase) may change, or the eddy current occurring on the metal surface may be disturbed. As a result, the vector direction of the detection signal A is influenced, and a pulse-like waveform is produced in a direction in which the phase of the detection signal A is shifted by a small angle Δθ. Although Δθ is a very small amount, signal A is normally used as a tube inspection signal. Therefore, as shown in Figure 7, due to some reasons during the relative movement between the detector and the metal surface,
When a waveform Q having the same shape as the defect display waveform P occurs in the inspection signal A, it is difficult to distinguish whether it is due to a defect in the metal surface or due to the influence of the outside world.

In addition, during inspection, the distance between the detector and the metal surface should be kept constant at 14 m (!j software), and the two should be moved relative to each other, but lift-off may occur due to waviness of the metal surface or imperfections in the moving device. It often fluctuates between

As the detector approaches the metal surface and the lift-off decreases,
The output signal due to a defect on the metal surface is output larger than the actual one, and conversely, if the detector is separated from the metal surface and the lift-off becomes large, the defect detection signal is output smaller than the one for the actual defect, and the metal surface based on the inspection data There is a risk of misjudgment when making an evaluation.

The present invention removes the waveform Q caused by external factors other than defects on the metal surface from the detection signal A, and
The purpose of this study is to clarify an inspection method that outputs only O.

A further object of the present invention is to clarify an inspection method that corrects the inspection signal to eliminate the influence of liftoff and output a inspection signal under the same conditions even if the detector liftoff varies during inspection.

The present invention outputs the flaw signal xO by passing the test signal A of the detector through a bypass filter, and outputs the test signal component yo in the direction shifted by 90' from the phase of the flaw signal XO in the test signal A. 'The component Yo in the phase shift direction and the flaw signal Xo are ANDed to generate a flaw signal X1 due to a defect on the metal surface.
It is characterized by detecting.

The present invention also passes the test signal A through a low-pass filter, outputs the low-frequency lift-off signal B in the test signal A, and separates the component Yo in the 90' phase shift direction and the lift-off signal B in the test signal A. AND lift-off correction signal C
The present invention is characterized in that the flaw signal x1 due to the metal surface defect is corrected by a lift-off correction signal C, and a flaw signal X due to the metal surface defect in which the influence of lift-off fluctuation is corrected is output.

In addition to the waveform P caused by defects on the metal surface, the inspection signal A includes waveforms caused by external factors. is mixed in. But two signals
By logically multiplying o and YO, if the pulse-like waveform in the inspection signal A is due to a defect on the metal surface, the waveforms P in the signals Xo and Yo are aligned, and the flaw signal X1 due to the metal surface defect is obtained. Go out. Furthermore, if the pulse-like waveform in test signal A is due to an external factor, even if pulse-like waveform Q exists in signal xO, there is no corresponding waveform in signal YO, and therefore two When the signals xO and yo are ANDed, pulses that do not produce an output and are caused by external factors are removed, and only the flaw signal xl due to defects on the metal surface can be output.

In addition, by applying a t-wave to the inspection signal A using a low-pass filter, the short-period pulsed waveforms P and Q caused by metal surface defects and external factors are removed, and only the long-period waveform B caused by lift-off fluctuations is output. .

Since the above lift-off signal B almost faithfully represents the lift-off at each instant during the inspection, it is multiplied by the lift-off correction signal C, which is the AND of the yo-fold signal, and an appropriate correction coefficient a, which is inversely proportional to the increase/decrease in lift-off. =aG is formed, and the correction circuit performs signal processing on the flaw signal X1 due to the metal surface defect, and when the lift-off correction signal C is large, as in Xi -aC or X1/aC, that is, when the detector is metal When the sensitivity increases as the detector approaches the metal surface, lower the value of the flaw signal
By increasing the value of 1 and correcting the influence of lift-off fluctuations, it is possible to output a flaw signal X that is as close to the same lift-off condition as possible.

FIG. 1 shows a situation in which the method of the invention is implemented to inspect the metal surface of a tube. This is a trolley equipped with M411 (11) running tracks, endless belts, wheels, etc.
The upper end of the detection arm (3) is swingably supported on the front part of the detection arm (3), and the lower end of the detection arm (3) is equipped with a detector (4). 5) Ni-yo! ItlI machine-
TS (6) is connected, and while the trolley (2) is traveling through the pipe at a low speed of 4 m/min, the detection arm (3) is moved perpendicularly to the traveling direction in the circumferential direction of the pipe 250 to 400 times per minute. The tube wall is inspected within the transition range of the detector (4) by reciprocating the tube at a speed of . The object to be inspected according to the present invention is not limited to pipe walls, but can also be applied to metal plates by swinging the detection arm back and forth with respect to a moving metal plate.

The detector (4) includes a large-diameter excitation coil (7) that generates a high-frequency alternating magnetic field, and a small-diameter detection coil ( 9), each of which is fixed in a holder (io). The lift-off of the detector (4) is set to 5 to 101111 in consideration of unevenness caused by corrosion on the metal surface, and the excitation coil (7) applies a high-frequency alternating magnetic field to the metal surface within the coil diameter to generate eddy currents. to occur. When the detector (4) and the metal surface are moved relative to each other while keeping the lift-off constant, the output of the detection coil (9) is constant if the metal surface has no defects and the eddy current is uniformly distributed. However, if a defect (11) occurs on the metal surface, disturbances occur in the eddy current in this portion, causing fluctuations in the phase and output value of the output of the detection coil (9).

FIG. 6 shows an example of a configuration for generating the test signal A. A high frequency voltage of approximately 5 Q KH2 is generated by an oscillator 112), amplified, and applied to the excitation coil (7). In the small-diameter detection coil (9) arranged coaxially with the excitation coil (7), induced electromotive force is generated due to mutual induction from eddy currents on the metal surface, so this is amplified and the test signal A is generated. can be obtained.

In addition, when implementing the present invention, the excitation coil (7) is omitted, and the detection coil (9) itself is excited by applying a high-frequency current, and the induced electromotive force generated in the coil itself due to self-induction is eliminated. The test signal A can also be obtained by detecting it using a bridge circuit and amplifying it.

For the test signal A, the phase of the reference signal DX from the phase shifter (13) is changed to the standard phase of the test signal for a normal metal surface (
Lift-off voltage phase) set to angle θ, '7' -)
(and by 141, bypass filter (18
By passing it through, it is possible to output the component XO of the test signal A in the direction of the standard phase angle θ.

Also, a phase shifter (shifts the phase of the reference signal Dx from 131 by 90° using a phase shift circuit +1B to create another reference signal Dy, which is then gated) +1? ) and passing it through the bypass filter (181), the test signal A
, component Y in the direction of 90° phase shift with respect to the direction of standard phase θ
It is possible to output O.

The xO times signal is a mixture of the /N6tless waveform P due to defects on the metal surface and the waveform Q due to external factors, so the 4th
In the device of the first embodiment shown in the figure, this is a game) (1
91 and the signal YO in the direction of 90° phase shift with respect to the standard phase θ
By performing the AND operation, it is possible to output the flaw signal X1 from which the waveform Q caused by external factors has been eliminated.

Furthermore, as shown in the inspection apparatus of the second embodiment shown in FIG. Create a signal C and receive the flaw signal x
By processing the signal in the correction circuit (22) together with the flaw signal X1, the influence of lift-off variation is corrected in the flaw signal X1, and a flaw signal X close to the actual size of the defect can be output.

The flaw signal , the value of the flaw signal X is sufficiently reliable, which has the advantage of improving the accuracy of judgment.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the implementation status of the present invention, FIG. 2 is an enlarged sectional view of the tester, FIG. 3 is a phase analysis diagram of the test signal, and FIG.
The figure is a block diagram of the first embodiment of the inspection device, FIG. 5 is a block diagram of the second embodiment of the inspection device, FIG. 6 is a block diagram showing signal processing of the inspection device, and FIG. 7 is a block diagram of the signal processing of the inspection device. It is a waveform diagram in a process. A...Test signal B...Lift-off signal C...Lift-off correction signal DX, Dy...Reference signal P...
Defect waveform Q: False waveform xl...Flaw signal due to metal surface defect X...Flaw signal corrected for the influence of lift-off (4)...
・Detector (7)... Excitation coil (9)... Detection coil (13)... Phase shifter (15) (181.
... Bypass filter (20) ... Low pass filter (22) ... Correction circuit Applicant Kubota Iron Works Co., Ltd.

Claims (1)

[Claims] ■ A high frequency varying magnetic field is applied to the metal surface, and the inspection signal A due to the induced electromotive force generated in the coil is passed through a bypass filter to output a flaw signal XO, and the phase of the flaw signal xO in the inspection signal A is A component YO in a direction phase-shifted by 90° is detected, and the component YO in the 90° phase-shifted direction and the flaw signal
A method for inspecting a metal surface, characterized in that a flaw signal x1 due to a defect on the metal surface is detected by ANDing the following. ■ Claims in which the coil is installed on a self-propelled vehicle running in the pipe, and is simultaneously moved in the direction of travel of the self-propelled vehicle and swung back and forth in a direction perpendicular to the traveling direction to inspect the metal surface of the pipe. Inspection method in Section 1. ■ A high-frequency varying magnetic field is applied to the metal surface, and the inspection signal A due to the induced electromotive force generated in the coil is passed through a bypass filter to output the flaw signal XO, and the phase of the inspection signal A is shifted by 90 degrees with respect to the phase of the flaw signal XO. The component YO in the direction of the phase shift is detected, and the component YO in the 9o0 phase shift direction and the flaw signal Xo are detected.
and outputs a flaw signal X1 due to a defect on the metal surface, and at the same time, the inspection signal A passes through a low-pass filter and outputs a lift-off signal B, and the 9'0° phase shift direction component YO and the lift-off signal B and outputs a lift-off correction signal C, corrects the flaw signal X1 due to the metal surface defect with the lift-off correction signal C, and outputs a flaw signal X due to the metal surface defect in which the influence of the lift-off signal has been eliminated. Characteristic metal surface inspection method. ■ The coil is placed on a self-propelled vehicle running in a pipe, and at the same time as it moves in the direction of travel of the self-propelled vehicle, it is swung back and forth in a direction perpendicular to the traveling direction to inspect the metal surface of the pipe. Inspection method in scope 1. ■ The flaw signal X1 due to a metal surface defect is X = X1 - aC where C is the lift-off correction signal a is a correction coefficient (constant). The inspection method according to claim 3, which outputs the following.