JPH04158257A - Flaw detector for metallic material - Google Patents

Abstract

PURPOSE:To prevent abnormal flaw detection data from being created by removing drift noise via a filter from a received signal which is output from a receiving coil which receives remote field vortex flow of a metallic material to be inspected. CONSTITUTION:Respective receiving terminals RT4... of a plurality of received signal processing modules RQ1 to RQ9 of a received signal circuit RCC are connected to excitation terminals T1 to T9 of an excitation signal send-out circuit 1. Respective phase comparators 12... admit received signals f1 to f9 generated on receiving coils RC1 to RC9 of a vortex flow sensor PRB at one input, which are to be compared with reference signals F1 to F9 respectively which are input to the other input. Here the signals f1 to f9 at an output of a BPF 9 are at an illegal level ILL including drift noise due to vibrations, etc., but they are normal received signals NOF when dc components are removed by an HPF 10 and flaw detection data output from the comparator 12 is also normal flaw detection data NOD. If comparison 12 is made with the level ILL maintained, an abnormal received signal ILF and abnormal flow detection data ILD are created.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a metal material flaw detection device, and is particularly applicable to buried gas piping,
This invention relates to a metal material flaw detection device that performs maintenance and management of pipelines such as chemical plant piping and heat exchanger piping using the remote field eddy current method.

[Prior art and problems to be solved by the invention] In order to perform flaw detection on metal materials using the remote field eddy current method, the excitation coil and one or more receiving coils must be separated by at least twice the pipe diameter. An eddy current sensor arranged in the axial direction of the pipe is attached to a signal transmission cable, inserted into the pipe, and an excitation signal is applied to the excitation coil. The applied excitation signal has a relatively low frequency (several 10 Hz to several 100 Hz)
The voltage used is several volts to several tens of volts.

The electromagnetic waves generated by the excitation signal can be divided into those that pass through the wall thickness of the pipe under test and those that propagate within the pipe.The electromagnetic waves that propagate inside the pipe are divided into those that pass through the wall thickness of the pipe under test and those that propagate within the pipe. Since the frequency is much lower than the cutoff frequency, it is rapidly attenuated and hardly propagates. On the other hand, waves that pass through the wall thickness of the pipe are called indirect propagating waves, which propagate outside the pipe along the pipe and are slowly attenuated. and is detected by the receiving coil.

The signal detected by the receiving coil (hereinafter referred to as the received signal) is extremely weak (several μV to several tens of μV) because it passes through the pipe wall thickness twice, and the skin effect caused by passing through the pipe wall thickness is extremely weak. The phase changes due to the influence. In the remote field eddy current method, phase changes with good linearity with the pipe wall thickness are often used as information.

In the remote field eddy current method described above, when an eddy current sensor consisting of an excitation coil and a receiving coil is inserted into a test pipe and gradually advanced at a constant speed, the vibration of the eddy current sensor caused by the gradual advancement produces a normal reception signal output from the receiving coil. There are disadvantages such as noise being superimposed and the flaw detection data generated from the received signal changing to abnormal flaw detection data.

Furthermore, when using an eddy current sensor in which a plurality of receiving coils are arranged annularly on the inner wall of a pipe, there are drawbacks such as the inability to diagnose the pipe with high precision due to accumulated abnormal flaw detection data.

[Object of the Invention] The present invention has been made in view of the above-mentioned difficulties, and provides flaw detection for metal materials that can prevent the generation of abnormal flaw detection data by removing drift noise caused by vibrations included in the received signal output from the receiving coil. The purpose is to provide equipment.

In addition, by using a remote eddy current sensor equipped with multiple receiving coils, we can prevent the accumulation of abnormal flaw detection data.
The purpose of the present invention is to provide a metal material flaw detection device that can diagnose conduits with high precision.

[Means for Solving the Problems] A metal material flaw detection device according to the present invention includes a reference signal generating means for generating a reference signal, and an excitation signal having the same phase as the reference signal to generate a remote field eddy current in the metal material under test. an excitation coil, a reception coil that is separated from the excitation coil by a predetermined distance and receives remote field eddy currents and outputs a reception signal; a DC component removal means that removes a DC component from a reception signal output from the reception coil; The flaw detection data generation means compares the received signal from which the DC component has been removed by the component removal means with a reference signal and outputs flaw detection data.

Further, the metal material flaw detection apparatus according to the present invention is constituted by a plurality of receiving coils, a DC component removal means, and a flaw detection data generation means.

[Example] Hereinafter, an example of the metal material flaw detection apparatus according to the present invention will be described in detail with reference to FIGS. 1 and 2.

As shown in FIG. 1, the metal material flaw detection apparatus according to the present invention includes an excitation coil EC and a plurality of receiving coils RCn (n for explanation).
1 to 9), a reference signal generator 2, an excitation signal output amplifier 3, and a reference signal generation circuit 4.
It is composed of an excitation signal sending circuit 1 provided with an excitation signal sending circuit 1 and a receiving signal circuit RCC having receiving signal processing modules RQ, ~RQ4. RQs receiving side terminals RT, RT, ...... are cable CBL
The receiving coils RCt to RC9 are connected to each bare core wire P0.
The received signals f, ~f9 generated at the bare core wire P.

It is sent and received at ~P.

The excitation signal f0 oscillated by the reference signal generation circuit 2 of the excitation signal transmission circuit 1 is amplified by the excitation signal output amplifier 3 and sent to the excitation side terminal T0, and the reference signals F, ~F, generated by the reference signal generation circuit 4 are transmitted. is the excitation signal f transmitted and received by the pair of core wires P0 to P of the cable CBL.

and the received signals f1 to f, corrected for the phase delay caused by mutual induction.When using a special cable CBL that shields the excitation signal fo, which has a higher voltage than the received signals f, to f, this reference signal F1 ~F may be in phase with the excitation signal f0.

Reception signal processing module RQ of reception signal circuit RCC, ~
RQ, respective receiving terminals RT, ~RT.

is connected to the input side of the differential amplifier 6 of the receiving signal interface 5, and the output side of the differential amplifier 6 is connected to the input side of the waveform shaper 10 via the low-pass filter 7, the receiving amplifier 8, and the band-pass filter 9. Ru. Noise of the same polarity generated in the pair of core wires P, -P9 is removed by a differential amplifier. Further, high frequency components of the received signals f1 to f outputted from the differential amplifier 6 are removed by a low pass filter 7. The received signals f, ~f, from which high frequency components have been removed by the low-pass filter 7 are sent to the input side of the bypass filter 10 via the band-pass filter 9, and the output side of the bypass filter 10 is connected to the input side of the waveform shaper 11. The output side of the waveform shaper 11 is connected to one input side of the phase comparator 12. The other input side of the phase comparator 12 is connected to the reception side terminal RT a, and the output side of the phase comparator 12 is connected to the reception side terminal RT via the flaw detection signal output device 13 .

Reception side terminals RT of each of the reception signal processing modules RQ 1 to RQ s, . . . are excitation signal transmission circuits 1
The phase comparators 12 are connected to excitation side terminals T, ~T9 of Signal F1~
Compare Fs.

Here, the received signal f1~ on the output side of the bandpass filter 9
f is an illegal level ILL that contains drift noise consisting of a DC component due to vibrations, etc., but when the DC component is removed by the bypass filter 10, it becomes a normal received signal NOF and the flaw detection data output from the phase comparator 12 is also normal. The flaw detection data is NOD. Further, when compared by the superior phase comparator 12 at the illegal level ILL, an abnormal reception signal ILF and abnormal flaw detection data ILD shown in parentheses are generated.

[Operation of the invention] For example, in the metal material flaw detection apparatus having the above configuration, the excitation signal output circuit 1
The reference signal F is sent from the excitation side terminal T1 of the receiving signal circuit RCC to the receiving side terminal RT4 of the receiving signal processing module RQ1 of the receiving signal circuit RCC.
1 is sent out and generated in the receiving coil RC of the eddy current sensor PRB, and is applied to the receiving side terminals RT, RT. When the signal f is at the normal level NOL, the phase is delayed to the 0 point, and when it is at the illegal level ILL, the phase is delayed to the 0 point.

When the received signal f1 is at the normal level NOL, Fig. 2 ■
A normally received signal NOF shown at the dot is generated at the output side of the bypass filter 10. Therefore, 0 on the output side of the phase comparator 12
Normal flaw detection data NOD is output at the point.

If the bypass filter 10 that removes the DC component is not provided, the received signal f1 is at the illegal level ILL shown in point ■ in Fig. 2, so a 0-point abnormal reception signal ILF and a 0-point abnormal flaw detection data ILD are generated. Therefore, generation of abnormal flaw detection data ILD cannot be prevented.

The bypass filter 10 in the above embodiment may be constructed of a transformer having a primary coil and a secondary coil.

[Effects of the Invention] The metal material flaw detection apparatus according to the present invention includes: a reference signal generating means for generating a reference signal; an excitation coil that applies an excitation signal in phase with the reference signal to generate a remote field eddy current in the metal material under test; A receiving coil that is provided at a predetermined distance from the excitation coil and receives remote field eddy currents and outputs a received signal; a DC component removing means that removes a DC component from the received signal output from the receiving coil; Since it is comprised of a flaw detection data generation means that compares the received signal from which the DC component has been removed with a reference signal and outputs flaw detection data, it is effective in preventing generation of abnormal flaw detection data.

Further, the metal material flaw detection device according to the present invention has the effect of preventing the accumulation of abnormal flaw detection data and making it possible to diagnose pipelines with high precision by providing a plurality of receiving coils, DC component removal means, and flaw detection data generation means. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the metal material flaw detection apparatus according to the present invention, and FIG. 2 is a characteristic diagram of the metal material flaw detection apparatus according to the present invention. 2...Reference signal generator (reference signal generation means) 1
0...Bypass filter (DC component removal means)
12... Phase comparator (flaw detection data generation means) E
C...Exciting coil RCz~RC,...Receiving coil agent Patent attorney Moritani -O

Claims (1)

[Scope of Claims] 1. A reference signal generating means for generating a reference signal, an excitation coil for applying an excitation signal in phase with the reference signal to generate a remote field eddy current in the metal material under test, and a predetermined source from the excitation coil. a receiving coil that receives the remote field eddy current and outputs a received signal; a DC component removing means that removes a DC component from the received signal output from the receiving coil; A metal material flaw detection apparatus comprising flaw detection data generating means for comparing a received signal from which components have been removed with the reference signal and outputting flaw detection data. 2. The metal material flaw detection apparatus according to claim 1, further comprising a plurality of said receiving coils, said DC component removal means, and said flaw detection data generation means.