JPH0752166B2 - Corrosion-proof coating damage detection method for buried metal pipes - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting, from the ground surface, a damaged position of an anticorrosion coating applied to the outer surface of a metal pipe buried in the ground.

[Prior art]

Generally, a metal pipe such as a steel pipe laid in the ground is coated with a bituminous material such as asphalt or a thermoplastic resin such as polyethylene on its outer surface to prevent corrosion.

When the anticorrosive coating is damaged by reaching the metal surface for some reason, and the metal surface directly contacts the electrolyte such as soil, that portion is corroded. In particular, if the damaged part is present in an environment with a difference in oxygen concentration or in an environment affected by the stray current of the electric railway, the metal tube may corrode at an abnormally fast rate and form a corrosion hole.

It is extremely important to maintain the corrosion protection coating of such underground pipes in a perfect state in order to prevent corrosion accidents, and often the damage of the corrosion protection coating is detected from the ground surface and excavated and repaired. Is treated.

As a conventional example of detecting the damage position of the anticorrosion coating, Japanese Patent Laid-Open No.
There is a method for detecting the position of corrosion protection coating damage of a buried metal pipe, which is proposed by Japanese Patent Laid-Open No. 61-210935.

The outline of this method will be described with reference to FIGS. 7 and 8. A metal pipe 2 which is laid in the ground by applying an anticorrosion coating 1 on the outer surface thereof.
Between the damaged coating part 3 of No. 3 and the counter electrode 5 embedded in the ground 4,
An electric potential difference between the ground surface is detected by the two wheel electrodes 8 in the receiving device 7 which moves on the ground surface directly above the metal tube 2 through an AC signal current from the measurement signal transmitter 6, and the detection signal and the transmitter 6 A reference signal transmitted by the electric wire 26 or the like or a wireless device (which is composed of a transmitter 28 having a transmitting antenna 27 and a receiver 30 having a receiving antenna 29) is input to the lock-in amplifier 9, and the lock The noise signal included in the detection signal is removed in the in-amplifier 9,
This is a method in which a signal having the same frequency as the reference signal is output as a direct current, which is then input to the display device 11, and the damaged position of the anticorrosion coating is detected from the change in the waveform of the direct current voltage displayed on the display device 11.

According to this method, there is an effect that it is possible to detect a minute ground surface potential generated by a very weak signal current.

[Problems to be solved by the invention]

However, in the conventional method, in order to input the reference signal to the lock-in amplifier 9, (1) the measurement signal transmitter 6 and the receiving device 7 are connected by the electric wire 26 or the like, or (2) the measurement signal transmission. Since it is necessary to connect the device 6 and the receiving device 7 by a wireless device, or (3) wirelessly connect the relay device and the receiving device that detect the reference signal from the buried metal pipe, and so on. , The following measurement problems occurred.

In the case of the connecting means of the above (1), since the electric wire 26 and the like are dragged when the receiver 7 is moved and measured, the measuring range is naturally limited, and it is applied on a road with heavy traffic or crossing a track. Has the drawback of being restricted. Further, in the case of the connecting means of the above (2) and (3), there is a drawback that radio waves are blocked by a structure such as a building and the wireless transmission of the reference signal is interrupted.

[Object and Structure of Invention]

SUMMARY OF THE INVENTION The present invention is intended to provide a method for detecting a corrosion position of an anticorrosion coating of a buried metal pipe, which is capable of solving the above-mentioned problems and accurately knowing a coating damage position. The point is to pass an AC signal current from the measurement signal transmitter 6 between the coating damage part 3 of the metal tube 2 laid in the ground by applying the anticorrosion coating 1 on the outer surface and the counter electrode 5 buried in the ground 4, The potential difference of the ground surface is detected by the wheel electrode 8 in the receiving device 7 moving on the ground surface directly above the metal pipe 2, and the reference signal transmitter 10 independent of the measurement signal transmitter 6 in the receiving device 7 outputs the signal. Measuring signal transmitter 6
At least 18 degrees relative to the output frequency of
A reference signal of the same frequency in a range smaller than 0 degree / hour,
The detection signal obtained by detecting the potential difference of the ground surface by the wheel electrode 8 in the receiving device 7 is input to the lock-in amplifier 9 to remove the noise signal of the signal which is not synchronized with the reference signal included in the detection signal and synchronized. A signal is displayed on the display device 11, and the damage position of the anticorrosion coating 1 is detected from the change of the waveform thereof.

〔Example〕

Next, a first embodiment in which the present invention is applied to a method of detecting a damage position of an anticorrosion coating of a buried metal pipe of a two-electrode moving type will be described in detail with reference to FIGS. 1 to 3.

1 and 2 show an anticorrosion coating damage position detecting device used in the first embodiment of the present invention, which is constructed by applying an anticorrosion coating 1 as described above to the outer surface of a metal pipe 2 made of a steel pipe. The anticorrosion-coated metal pipe 12 is buried in the ground, and the counter electrode 5 and the metal pipe 2 buried in the ground 4 are connected to the measurement signal transmitter 6, and the metal pipe of the metal pipe 2 is directly above the metal pipe 2. A receiving device 7 is provided which comprises two wheel electrodes 8 arranged at intervals in the longitudinal direction, the wheel electrodes 8 being constituted by conductive sponge rubber wheels.

The receiving device 7 includes an AC amplifier 14, a first phase detector 16, a first low-pass filter 18, a first DC amplifier 20, a first arithmetic circuit 22 and the AC amplifier 14 which are sequentially connected in series to a bandpass filter 13. Phase shift circuit 15, second phase detector 17, second low pass filter connected in series to the output section of the
A lock-in amplifier 9 including a second DC amplifier 21 and a second arithmetic circuit 23, a reference signal transmitter 10 and a display device 11 such as a balance recorder are provided. Bandpass filter 13 which is the detection signal input section
Of the phase shifter 15 which is connected to the input section of the reference signal oscillator 10 and the output section of the reference signal oscillator 10 is the reference signal input section of the lock-in amplifier 9.
And to the input of the first phase detector 16.

In the apparatus shown in FIGS. 1 and 2, an AC signal current is passed between the metal tube 2 and the counter electrode 5 by using a measurement signal transmitter 6, and the metal tube 2 is preliminarily provided on the ground surface directly above the metal tube 2. After sprinkling water along, move along the metal pipe 2
The potential difference between two points on the ground surface is detected by one wheel electrode 8, and the potential difference, that is, the detection signal detected by those wheel electrodes 8 is input to the detection signal input section of the lock-in amplifier 9.

On the other hand, the reference signal transmitted from the reference signal transmitter 10 is a signal of the same frequency in a range in which the relative position change with respect to the AC signal current output by the measurement signal generator 6 is at least less than 180 degrees / hour, The reference signal is input to the reference signal input section of the lock-in amplifier 9.

After the phase detector, the circuit that inputs the reference signal directly to the phase detector 16 and the phase detector 17 after the phase shift circuit shifts the phase by 90 degrees
There is a circuit to input to.

The detection signal input to the lock-in amplifier 9 is subjected to high-frequency and low-frequency noise removal by the band pass filter 13 and then amplified by the next AC amplifier 14 and subsequently amplified by the first phase detector 16 and the second phase detector. Entered in 17.

The first low-pass filter 18 and the second low-pass filter 19, which are serially connected to the first phase detector 16 and the second phase detector 17, which are multipliers of two signals, have the reference signal transmitter 10 in the detection signal. A noise signal having a frequency different from the output frequency is removed, and a signal having the same frequency is output as a DC voltage and input to the first DC amplifier 20 and the second DC amplifier 21.

The output signals of the first DC amplifier and the second DC amplifier 21 are
After being input to the display device 11 and processed by the first arithmetic circuit 22 and the second arithmetic circuit 23, the display device 11
In the display device 11, as shown in FIG. 3, the waveform 32 of amplitude A: (a) and the waveform 33 of Acosφ 33:
(B) Figure and Asinφ waveform 34: (c) Figure and phase φ waveform:
(D) Figure and are displayed.

In Fig. 3, the horizontal axis represents the distance from the damaged coating,
Further, the vertical axes in FIGS. (A), (b) and (c) show the potential difference, and the vertical axes in (d) show the magnitude of the phase.

In Fig. (A) showing the waveform 32 of the amplitude A among the respective waveforms, the minimum position of the electric potential is the position of the coating damage portion, and Acosφ
The waveform 33 of (b) and the waveform 34 of Asinφ shown in (c) of FIG. 3 are the positions of the coating damage portion where the potential is changed between positive and negative, and the waveform 35 of phase φ is shown in (d). In the above, since the phase inversion position is the position of the coating damaged portion, the position of the coating damaged portion can be easily confirmed from each waveform.

Since the method of the present invention is a system for detecting the position of the coating damaged portion by detecting the phase change, the output frequency of the measurement signal oscillator 6 and the output frequency of the reference signal oscillator 10 must be very close to each other. I won't. The practical allowable level of the relative phase change between the measurement signal transmitter 6 and the reference signal is (180 degrees /
Time)).

In the case of the first embodiment in which the present invention is applied to the two-electrode moving system, since four kinds of waveform changes of sine, cosine, amplitude and phase are displayed on the display device 11, it is possible to accurately detect the coating damage position. You can

Next, a second embodiment in which the present invention is applied to a method for detecting a corrosion position of an anticorrosion coating of a buried metal pipe of a one-electrode moving type will be described with reference to FIGS. 4 to 6.

4 and 5 show an anticorrosion coating damage position detecting device used in the second embodiment of the present invention, in which the insertion electrode 24 inserted into the ground near the receiving device 7 and one wheel electrode are provided. 8 is connected to a bandpass filter 13 which is a detection signal input section in the lock-in amplifier 9, but other configurations are the same as in the case of the anticorrosion coating damage position detecting device in the first embodiment. The plug-in electrode 24 is appropriately relocated as the receiving device 7 moves.

In the shape of the waveform 32 of the amplitude obtained by the method of the second embodiment, the peak point indicates the position of the coating damaged portion as shown in FIG. In FIG. 6, the horizontal axis represents the distance from the damaged coating portion and the vertical axis represents the potential.

In the case of the method of the second embodiment, since a large potential can be detected, the S / N ratio is excellent, and even smaller coating damage can be easily detected.

The method according to the present invention is not limited to the underground buried pipe, but can detect the damaged position of the underground buried cable and the corrosion protection coating of the cable protection pipe with high accuracy and high efficiency. Furthermore, by replacing the wheel electrode with a reference electrode such as a saturated calomel electrode or iron electrode, it is possible to detect the location of damage such as painting or polyethylene applied to structures such as steel pipe piles and steel sheet piles installed in rivers and harbors. can do. Moreover, by replacing the wheel electrodes with magnetic sensors, it can be used as a damage position detection by a magnetic field method and as a locator for a conduit.

〔The invention's effect〕

According to the present invention, the detection signal detected by the two wheel electrodes 8 in the receiving device 7 or the insertion electrode 24 inserted into the ground and inserted in the ground and the one wheel electrode 8, and the reference signal transmitter.
The reference signal from 10 is input to the lock-in amplifier 9, and the noise signal in the detection signal is converted into alternating current and removed,
Display device after converting the signal synchronized with the reference signal to direct current
Since it is displayed on 11, the coating damage position can be easily detected by amplifying even if the potential difference indicating the coating damage position is minute, and the reference signal independent of the measurement signal transmitter 6 in the receiving device 7 is provided. Since the oscillator 10 inputs the reference signal of the same frequency in the range in which the relative phase change with the AC signal current output by the measurement signal oscillator 6 is at least less than 180 degrees / hour to the lock-in amplifier 9, It is not necessary to connect an electric wire or the like from the transmitter 6 to the receiving device 7 to transmit a reference signal, so that even if the mutual distance between the measurement signal transmitter 6 and the receiving device 7 is relatively long, it is easy to prevent corrosion of the buried metal pipes. It is possible to obtain the effect that the coating damage position can be detected.

[Brief description of drawings]

1 to 3 show the present invention as a two-electrode moving method for detecting a damaged position of an anticorrosion coating of a buried metal pipe.
FIG. 1 shows an embodiment, and FIG. 1 is a schematic side view of an anticorrosion coating damage position detecting device used in the first embodiment,
FIG. 2 is a block diagram showing the flow of signals in the device, and FIG. 3 is a diagram showing waveforms displayed on the display device in FIG. FIGS. 4 to 6 show a second embodiment of the present invention as a method for detecting a corrosion position of a corrosion prevention coating of a buried metal pipe of a one-electrode moving type.
FIG. 4 shows an embodiment, and FIG. 4 is a schematic side view of an anticorrosion coating damage position detecting device used in the second embodiment,
FIG. 5 is a block diagram showing the flow of signals in the device, and FIG. 6 is a diagram showing waveforms displayed on the display device in FIG. FIGS. 7 and 8 show a conventionally proposed anticorrosion coating damage position detecting device, and FIG. 7 shows a case where a measurement signal generator and a receiving device are connected by an electric wire to transmit a reference signal. FIG. 8 is a block diagram showing a signal flow of FIG. 8, and FIG. 8 is a block diagram showing a signal flow when a reference signal is transmitted by connecting a measurement signal transmitter and a receiving device with a wireless device. In the figure, 1 is an anticorrosion coating, 2 is a metal tube, 3 is a damaged coating portion, 4 is ground, 5 is a counter electrode, 6 is a measurement signal transmitter, 7 is a receiving device, 8 is a wheel electrode, 9 is a lock-in amplifier, 10 is a reference signal transmitter, 11 is a display device, 12 is an anticorrosion coated metal tube, 24
Is a plug-in electrode.

Front Page Continuation (72) Inventor Miki Kuroda 5-9-1 Nishihashimoto, Sagamihara-shi, Kanagawa Inside the Sagamihara Technical Center, Nippon Steel Corporation (72) Inventor Kohei Saito 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas stock company (72) Inventor Kenichi Yamaguchi 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo gas stock company (56) Reference JP-A-61-210935 (JP, A)

Claims (1)

[Claims] 1. An AC signal current is passed from a measurement signal transmitter 6 between a coating damage portion 3 of a metal tube 2 laid in the ground with an anticorrosion coating 1 on the outer surface and a counter electrode 5 buried in the ground 4, The electric potential difference on the ground surface is detected by the wheel electrode 8 in the receiving device 7 moving on the ground surface directly above the metal pipe 2, and the receiving device 7
In the reference signal of the same frequency, the degree of relative phase change with respect to the output frequency of the measurement signal oscillator 6 output by the reference signal oscillator 10 independent of the measurement signal oscillator 6 is less than 180 degrees / hour. And a detection signal obtained by detecting the potential difference of the ground surface by the wheel electrode 8 in the receiving device 7 are input to the lock-in amplifier 9 to remove a noise signal of a signal that is not synchronized with the reference signal included in the detection signal, A method for detecting a damaged position of an anticorrosion coating of a buried metal pipe, which comprises displaying a synchronized signal on a display device 11 and detecting a damaged position of the anticorrosion coating 1 from a change in its waveform.