JP3932282B2 - Corrosion protection coating damage detection device for buried piping - Google Patents

Description

[0001]
The present invention relates to an anticorrosion coating damage detection device for buried piping that detects damage of the anticorrosion coating in a metal pipe having an anticorrosion coating (painted film or the like) embedded in the ground from the ground surface by non-cutting. .
[0002]
[Prior art]
In general, metal pipes buried in the ground, such as gas pipes, are provided with anti-corrosion coatings such as paint films to prevent corrosion, but the anti-corrosion coatings are damaged due to secular changes and construction errors. May occur. In particular, if the corrosion protection coating that reaches the metal surface is left untouched, the metal surface may come into contact with electrolytes such as soil, which may lead to corrosion and lead to accidents such as gas leakage. There is a problem that it is extremely inefficient to excavate all installed ground and inspect for damage. Therefore, various methods for detecting such damage of the anticorrosion coating from the ground surface by non-cutting have been proposed.
[0003]
For example, as the method, an alternating current is supplied to a pipe from a fixed transmitter, and a potential difference on the ground surface caused by a current leaking from a damaged portion of the anticorrosion coating is detected by a wheel electrode attached to a receiver that moves on the ground surface. Thus, a technique for detecting the damage position of the anticorrosion coating is known (for example, see Patent Document 1).
[0004]
Here, since the potential difference that can be detected on the ground surface is extremely small, in order to suppress the noise and detect the potential difference with high accuracy, the detected potential difference signal is obtained using the alternating current signal that is energized in the embedded pipe as a reference signal. Synchronous detection (lock-in) is effective. However, it is practically applicable to transmit the AC current signal to the pipe to the receiving device by wire or wirelessly so that it can be used as a reference signal for synchronous detection from the viewpoint that the installation environment of the device is restricted. There is a problem that is difficult.
[0005]
Therefore, Patent Document 1 discloses that a reference signal transmitter having the same frequency as that of the alternating current signal is mounted on a receiving device as a method for obtaining the reference signal.
[0006]
However, in the technique disclosed in Patent Document 1, the transmitter for energizing the alternating current and the reference signal transmitter for obtaining the reference signal have independent and separate configurations. In practice, it is difficult to obtain a signal, and generally, there is a problem that the phase of the detected potential difference signal drifts with time due to a frequency shift, and the detection accuracy of the anticorrosion coating decreases.
[0007]
[Patent Document 1]
Japanese Examined Patent Publication No. 7-52166 [0008]
The present invention has been made to solve the problems of such prior art and provides an anticorrosive coating damage detection device buried pipe for detecting damage to accurately anticorrosion coating without restrictions such as installation environment This is the issue.
[0009]
In order to solve the above-mentioned problems, the inventors of the present invention have made extensive studies, and as a result, use an alternating magnetic field around the pipe that is naturally generated by supplying an alternating current to the pipe in order to detect a potential difference on the ground surface. The present invention has been completed. That is, according to the present invention, the counter electrode is provided between the counter electrode and the metal pipe having the counter electrode embedded in the ground and having the anticorrosion coating on the outer surface. A transmitting device for energizing a current; and a receiving device that includes a wheel electrode capable of moving on the ground surface directly above the pipe, detects a potential difference on the ground surface by the wheel electrode, and synchronously detects the detected potential difference signal; An apparatus for detecting damage to the anticorrosion coating, comprising: a coil for detecting a magnetic field generated by passing the alternating current through a pipe, and a magnetic field signal detected by the coil An object of the present invention is to provide an anticorrosion coating damage detection device for buried piping, which is used as a reference signal in the synchronous detection.
[0010]
According to the anticorrosion coating damage detection apparatus for buried pipes according to the present invention, the magnetic field generated by energizing the pipe with an alternating current is detected, and the detected magnetic field signal is used as a reference signal in synchronous detection. The frequency and the frequency of the reference signal can be made completely the same. Therefore, by synchronously detecting the detected potential difference signal with the reference signal, it is possible to accurately detect damage to the anticorrosion coating without causing a phase drift of the reference signal. Moreover, according to the anticorrosion coating damage detection apparatus for buried piping according to the present invention, the coil for detecting the magnetic field signal is provided in the receiving apparatus for performing synchronous detection. Therefore, anti-corrosion coating damage detection device buried pipe of this invention, since an alternating current signal to be supplied to the pipe from the transmitter in a wired or wireless for synchronous detection is not necessary to be transmitted to the receiving device, such as the installation environment It has the advantage of not being constrained.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0013]
FIG. 1 is a schematic configuration diagram showing an anticorrosion coating damage detection apparatus according to an embodiment of the present invention. As shown in FIG. 1, an anticorrosion coating damage detection device (hereinafter referred to as a detection device) 100 includes a transmission device 23 and a reception device 13, and is embedded in the ground and provided with an anticorrosion coating (paint film) 20 on the outer surface. The coating film damaged portion 21 in the steel pipe 19 is detected.
[0014]
The transmission device 23 includes a counter electrode 18 embedded in the ground 22 and is configured to pass an alternating current between the steel pipe 19 and the counter electrode 18. More specifically, the transmission device 23 includes a power amplifier 17, and a counter electrode 18 and a steel pipe 19 are connected to the power amplifier 17 (the power amplifier 17 and the steel pipe 19 are connected via a connection 15. The alternating current is energized. Here, the transmission device 23 according to the present embodiment includes a transmitter 14, and the oscillator 14 is about 200 Hz to 1 kHz suitable for detecting a magnetic field with a coil with high sensitivity as will be described later (this embodiment). In this case, a signal having a frequency of about 443 Hz is output and transmitted to the power amplifier 17. As a result, the power amplifier 17 energizes the steel pipe 19 with an alternating current having the above frequency. In addition, when the frequency is lower than the frequency range (200 Hz to 1 kHz), the sensitivity of magnetic field detection by the coil 2 to be described later is lowered. On the other hand, when the frequency is higher, the attenuation in the steel pipe 19 is increased. It is preferable to set the frequency within the range.
[0015]
On the other hand, the receiving device 13 includes two wheel electrodes 1 made of conductive rubber arranged at intervals along the longitudinal direction of the steel pipe 19 on the ground surface immediately above the steel pipe 19, thereby the ground surface. Can be moved. The receiving device 13 detects the ground surface potential difference by the wheel electrode 1 and detects the coating film damaged portion 21 by synchronously detecting the detected potential difference signal. Further, as described above, the receiver 13 is arranged in a direction in which a magnetic field generated by energizing the steel pipe 19 with an alternating current is effectively detected (the magnetic flux formed along the circumferential direction of the steel pipe 19 penetrates substantially orthogonally. And a magnetic field signal detected by the coil 2 is used as a reference signal in the synchronous detection.
[0016]
In order to detect the coating film damaged part 21 by synchronously detecting the detected potential difference signal on the ground surface, the receiving device 13 according to the present embodiment includes the band pass filter 3, the first in addition to the wheel electrode 1 and the coil 2 described above. AC amplifier 4, second AC amplifier 24, first synchronous detector 5, second synchronous detector 6, first low-pass filter 7, second low-pass filter 8, first DC amplifier 9, second DC amplifier 10, arithmetic circuit 11 and a display 12 are provided.
[0017]
Next, a method for detecting the coating film damaged portion 21 by the detection device 100 having the above-described configuration will be described. First, in order to reduce the contact resistance between the ground surface and the wheel electrode 1 with respect to the ground surface directly above the steel pipe 19, water is sprayed along the steel pipe 19 in advance, and then the steel pipe 19 is While passing the alternating current of the frequency mentioned above between the counter electrodes 18, the wheel electrode 1 is moved along the steel pipe 19, and the potential difference between two points on the ground surface (between each wheel electrode 1) is detected. The detected potential difference signal is input to the band-pass filter 3 of the receiver 13, and high-frequency and low-frequency noises are removed by the band-pass filter 3. That is, the noise component excluding the frequency component is removed. The output of the bandpass filter 3 is amplified by the first AC amplifier 4 and then input to the first synchronous detector 5 and the second synchronous detector 6, and a component synchronized with the phase of the reference signal described later is extracted. . Here, since each of the first synchronous detector 5 and the second synchronous detector 6 is a multiplier for two signals, the output signal of the first synchronous detector 5 and the second synchronous detector 6 includes the reference signal. A frequency component will be included. Therefore, the first low-pass filter 7 and the second low-pass filter 8 remove the frequency components of the reference signal from the output signals of the first synchronous detector 5 and the second synchronous detector 6, respectively, and convert them into quasi-DC components. The output signals of the first low-pass filter 7 and the second low-pass filter 8 converted into the quasi-DC component are respectively input to the first DC amplifier 9 and the second DC amplifier 10 and amplified, and then subjected to arithmetic processing by the arithmetic circuit 11. (For example, absolute value processing) is performed and input to the display 12.
[0018]
On the other hand, the magnetic field signal detected by the coil 2 is amplified by the second AC amplifier 24 and then input to the reference signal generator 25. The reference signal generator 25 has a reference having a phase of 0 degree and 90 degrees. A signal is created. The created reference signals are input to the first synchronous detector 5 and the second synchronous detector 6, respectively, and used for synchronous detection. Thus, since the magnetic field signal detected by the coil 2 is used as a reference signal in synchronous detection, the frequency of the reference signal and the frequency of the alternating current can be made completely the same.
[0019]
FIG. 2 shows an example of a signal waveform displayed on the display 12. 2A shows the waveform of the amplitude A (potential difference signal after being subjected to the absolute value processing by the arithmetic circuit 11), FIG. 2B shows the waveform of Acosφ, and FIG. 2C shows the waveform of Asinφ. , (D) show the waveforms of the phase φ. 2B and 2C are waveforms equivalent to those obtained when the output signal waveforms of the first low-pass filter 7 and the second low-pass filter 8 are directly observed, respectively. Moreover, the horizontal axis of FIG. 2 represents the distance from the coating film damaged part 21 (the intersection with the vertical axis corresponds to the position immediately above the coating film damaged part 21), and the vertical axes of FIGS. The vertical axis of FIG. 2D shows the potential difference, and the magnitude of the phase.
[0020]
On the display 12, the waveforms shown in FIGS. 2A to 2D are displayed. In FIG. 2A, the minimum position of the potential difference indicates the position of the coating film damaged portion 21, and FIG. ) And (d), the positive / negative reversal position of the potential difference indicates the position of the coating film damaged portion 21, and in FIG. 2 (d), the phase reversal position indicates the position of the coating film damage portion 21. Therefore, it is possible to easily detect the position of the coating film damaged portion 21 from each waveform (in addition to detecting by visually observing the waveform, automatically providing a means for detecting the minimum position and the reverse position) Can also be detected).
[0021]
As described above, according to the anticorrosion coating damage detection device for buried piping according to the present invention, a magnetic field generated by energizing the piping with an alternating current is detected, and the detected magnetic field signal is used as a reference signal in synchronous detection. Since it uses, the frequency of an alternating current signal and the frequency of a reference signal can be made completely the same. Therefore, by detecting synchronously the detected potential difference signal with the reference signal. It is possible to accurately detect damage to the anticorrosion coating without causing a phase drift of the potential difference signal. Moreover, according to the anticorrosion coating damage detection apparatus for buried piping according to the present invention, the coil for detecting the magnetic field signal is provided in the receiving apparatus for performing synchronous detection. Therefore, anti-corrosion coating damage detection device buried pipe of this invention, since an alternating current signal to be supplied to the pipe from the transmitter in a wired or wireless for synchronous detection is not necessary to be transmitted to the receiving device, such as the installation environment It has the advantage of not being constrained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an anticorrosion coating damage detection apparatus according to an embodiment of the present invention.
FIG. 2 shows an example of signal waveforms displayed on the display shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wheel electrode 2 ... Coil 13 ... Receiver 14 ... Reference | standard transmitter 15 ... Frequency divider 16 ... Mixer 18 ... Counter electrode 19 ... Steel pipe (piping)
DESCRIPTION OF SYMBOLS 20 ... Paint film (anticorrosion coating) 21 ... Paint film damaged part 23 ... Transmitter 100 ... Anticorrosion coating damage detection apparatus

Claims (1)

Transmitter device comprising a counter electrode embedded in the ground, energizing an alternating current between the counter electrode and a metal pipe embedded in the ground and coated with anticorrosion coating on the outer surface;
Damage to the anti-corrosion coating comprising a wheel electrode that can move on the ground surface directly above the pipe, and detecting a potential difference on the ground surface by the wheel electrode and synchronously detecting the detected potential difference signal. A device for detecting,
The receiving apparatus includes a coil for detecting a magnetic field generated by applying the alternating current to the pipe, and uses the magnetic field signal detected by the coil as a reference signal in the synchronous detection. Corrosion protection coating damage detection device.

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