JPS63191049A - Detection of anticorrosion cover damage position for buried metal pipes - Google Patents

Abstract

PURPOSE:To detect a cover damage position accurately, by using a reference signal with the frequency the same as that of an AC signal for measurement when a ground surface potential difference is measured employing a wheel electrode. CONSTITUTION:A receiver 7 with a wheel electrode 8 is placed on the surface of ground where a metal pipe 2 provided with an anti-corrosion cover 1. An AC signal current runs is supplied by a measuring signal transmitter 6 between the metal pipe 2 and an opposed pole 5, and a potential difference is measured between two points on the ground surface with the wheel electrode 8 moving along the metal pipe 2 to be inputted into a detection signal input section of a lock-in amplifier 9. A signal with the frequency the same as that of an AC signal current is supplied from a reference signal oscillator 10 to a reference signal input section of the lock-in amplifier 9. After a noise signal with the frequency different from that of the reference signal is removed from a detection signal and changes in the phase are detected to learn the position of a cover damage part. This enables elimination of a wire for reference signal transmission thereby facilitating the detection of a damage position regardless of a longer distance between the transmitter 6 and the receiver 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting, from the ground surface, the position of damage to an anticorrosive coating applied to the outer surface of a metal pipe buried underground.

[Prior art]

Generally, metal pipes such as steel pipes laid underground are coated with bituminous material such as asphalt or thermoplastic resin such as polyethylene on the outer surface to prevent corrosion.

If the above-mentioned anti-corrosion coating is damaged for some reason and reaches the metal surface, and that metal surface comes into direct contact with an electrolyte such as soil, that portion will corrode. In particular, if the damaged part exists in an environment with differences in oxygen concentration or in an environment affected by stray currents from electric railways, there is a risk that the metal pipe will corrode at an abnormally high rate and form corrosion holes.

Maintaining the anti-corrosion coating of underground pipes in a pristine condition is extremely important in order to prevent all corrosion accidents, and damage to the anti-corrosion coating is often detected from the ground surface and repaired by excavation. Such measures will be taken.

As a conventional example of detecting the position of damage to the anticorrosive coating, there is a method for detecting the position of damage to the anticorrosion coating of buried metal pipes proposed in Japanese Patent Application No. 60-50520.

The outline of this method will be explained with reference to FIGS. 7 and 8. There is a gap between the damaged coating part 6 of the metal pipe 2, which is laid underground with anti-corrosion coating fi1 on the outer surface, and the counter electrode 5, which is buried in the ground 4. , a potential difference on the ground surface is detected by two wheel electrodes 8 in a receiving device 7 that moves on the ground surface directly above the metal tube 2 through an alternating signal current from a measurement signal transmitter 6, and the detection signal and the transmitter 6 are transmitted. from the electric wire 26 etc. or the unimaginable device (the transmitter 28 and the receiving antenna 2 which make the transmitting antenna 27 7)
The reference signal transmitted by the receiver filter 0 (consisting of a receiver filter 0 with A frequency signal is output as a direct current, then inputted to the display device 11, and the display device 11
This is a method for detecting the location of damage to the anti-corrosion coating from changes in the waveform of the DC voltage displayed on the screen.

This method has the effect of detecting minute ground potentials caused by very weak signal currents.

[Problem that the invention seeks to solve]

However, in the conventional method, in order to input the reference signal to the lock-in amplifier 9, it is necessary to (1) connect the measurement signal transmitter 6 and the receiver 7 with an electric wire 26 or the like, or (2) transmit the measurement signal. It is necessary to transmit by a method such as connecting the receiver 6 and the receiving device 7 with a wireless device, or (3) wirelessly connecting a relay device that detects a reference signal from a buried metal pipe and the receiving device. There were measurement problems as shown below.

In the case of the connection means (1) above, since the electric wire 26 etc. are drawn when the receiving device 7 is moved and measured, the measurement range is naturally limited, and moreover, it cannot be used on roads with heavy traffic or when cutting off tracks. has the disadvantage that its application is restricted. Further, in the case of the connection means (21(3)), there is a drawback that the radio waves are blocked by a structure such as a pill, and the wireless transmission of the reference signal is quickly interrupted.

[Purpose and structure of the invention]

The object of the present invention is to provide a method for detecting the position of damage to the corrosion-resistant coating of buried metal pipes, which can solve the above-mentioned problems and accurately determine the position of damage to the coating. In this case, an AC signal current is passed from a measurement signal transmitter 6 between the damaged part of the metal pipe 2, which is laid underground with an anti-corrosion coating 1 on the outer surface, and a counter electrode 5 buried in the ground 4. The potential difference on the lichen surface is detected by the @ ring electrode 8 in the receiving device 7 moving on the ground surface directly above the metal tube 2, and the reference signal transmitter 10 in the receiving device 7 outputs the output of the front measurement signal transmitter B. A reference signal of the same frequency as the detection signal and the detection signal are input to the total lock-in amplifier 9, noise signals of the reference signal and asynchronous signal included in the detection signal are removed, and the synchronized signal is displayed on the display device 11. death,
The present invention provides a method for detecting a damaged position of an anticorrosive coating on a buried metal pipe, which is characterized by detecting a damaged position of the anticorrosive coating 1 from a change in the waveform.

[Implementation]

Next, a first embodiment of the present invention applied to a two-electrode movable blade type method for detecting the position of damage to the anticorrosive coating of buried metal pipes will be described in detail with reference to FIGS. 1 to 6.

1 and 2 show a corrosion protection coating damage position detecting device used in the first implementation &lI of the present invention, which is constructed by applying the above-mentioned corrosion protection coating 1 on the outer surface of a metal tube 2 made of a steel pipe. The anti-corrosion coated metal pipe 12 is buried underground, and the counter electrode 5 and the metal pipe 2 buried in the ground 4 are connected to the measurement signal transmitter 6B. A receiving device 7 is provided, comprising two wheel electrodes 8 spaced apart in the longitudinal direction of the tube;
The car @ polarization 8 is composed of conductive sponge rubber wheels.

The receiving device 7 includes an AC amplifier 14 . First phase detector 16
．． No. 10 - Zosu Filter 18. First DC amplifier 20
．． A phase shift circuit 15 connected in series to the first arithmetic circuit 22 and the output section of the AC amplifier 14. Second phase detector 17. 20th-, 6th filter 19. Second DC amplifier 21. A lock-in amplifier 9 consisting of a second arithmetic circuit 2, a reference signal transmitter 10, and a display device 1 such as an equilibrium recorder.
1, each wheel electrode 8 is connected to the input part of a band filter 15 which is the detection signal input part of the lock-in amplifier 9, and the output part of the reference signal transmitter 10 is connected to the input part of the band filter 15 which is the detection signal input part of the lock-in amplifier 9. Phase shift circuit 15 which is a reference signal input section
and is connected to the input section 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 using the measurement signal transmitter 6, and the metal tube 2 After sprinkling water along the metal surface 2, the potential difference between two points on the ground surface is detected by the two wheel electrodes 8 moving along the metal surface 2, and the potential difference detected by these wheel electrodes 8, that is, the detection signal is locked. It is input to the detection signal input section of the in-amplifier 9.

- 10,000, the reference signal transmitted from the reference signal transmitter 10 is a signal with the same frequency as the AC signal current outputted by the measurement signal transmitter 6, and the reference signal is input to the reference signal input section of the lock-in amplifier 9. Ru.

After the phase detector, there are a circuit that inputs the reference signal directly to the phase detector 16, and a circuit that shifts the reference signal by 90 degrees in a phase shift circuit and then inputs it to the phase detector 17.

The detection signal input to the lock-in amplifier 9 is
After high-frequency and low-frequency noises are removed by the filter 16, the signal is amplified by the next AC amplifier 14, and then input to the first phase detector 16 and the second phase detector 17.

A first phase detector 16, which is a two-signal multiplier. A tenth filter turf 8 connected in series to the second phase detector 17. 21st: The filter filter 9 removes the noise signal of a frequency different from the frequency output by the reference signal transmitter 10 from the detection signal, outputs the signal of the same frequency as a DC voltage, and generates a first DC voltage. Amplifier 20. 2nd @flow amplifier 21
Enter.

The output signals of the first @ current amplifier and the second DC amplifier 21 are input to the display device 11, and are also input to the first arithmetic circuit 22.
After being subjected to arithmetic processing by the second arithmetic circuit 23, it is input to the display device 11, and in this display device 11,
As shown in Fig. 5, waveform 2 of amplitude A: (a) figure and A waveform of cosφ 55: (b) figure and As1nφ
The waveform 54 of (c) and the waveform of phase φ = (d) are displayed.

In the figure, the horizontal axis indicates the distance from the damaged coating,
Further, the vertical axes in FIGS. (a), (b), and (c) indicate the potential difference, and the vertical axis in FIG. (d) indicates the magnitude of the phase.

Among the waveforms, in the diagram (a) showing the waveform 32 of wave il@A, the minimum position of the potential is the position of the coating damage part,
(b) diagram showing waveform 53 of Acosφ and As1nφ
In the diagram (C) showing the waveform filter 4, the position where the potential changes between positive and negative is the position of the coating damage part, and in the diagram (d) showing the waveform filter 5 of the phase φ, the position where the potential changes between positive and negative is the position where the phase is reversed. Since is the position of the damaged coating, the position of the damaged coating can be easily confirmed from each waveform.

Since the method of this invention detects phase changes to determine the position of the damaged coating, the output frequency of the measurement signal transmitter 6 and the output frequency of the reference signal transmitter 10 must be very close to each other. No.

The practical allowable degree of phase change is desirably smaller than (180 degrees/hour), taking into consideration the moving speed of the receiving device 7 and the time required to check the damaged part of the coating.

In the case of the first embodiment in which this invention is implemented in a two-electrode movement method, four types of waveform changes, sine, cosine, amplitude, and phase, are displayed on the display device 11, so it is possible to accurately detect the coating damage position. Can be done.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 to 6, in which the present invention is applied to a method for detecting the position of damage to the anticorrosive coating of buried metal maple pipes using a one-electrode movement method.

FIGS. 4 and 5 show a corrosion protection coating damage position detecting device used in a second embodiment of the present invention, which includes an insertion electrode 24 inserted into the ground near the receiving device 7 and a grounded wheel electrode. 8 is connected to a band filter 15 which is a detection signal input section in a lock-in amplifier 9, but the other configuration is the same as that of the anti-corrosion coating damage position detecting device in the first embodiment. Note that the insertion polarization 24 is moved as appropriate as the receiving device 7 moves.

In the shape of the amplitude waveform filter 2 obtained by the method of the second embodiment, the peak point indicates the position of the damaged coating, as shown in FIG. In FIG. 6, the horizontal axis represents the distance from the damaged part of the coating, 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 damage to the coating can be easily detected.

The method according to the present invention is capable of detecting damaged positions of anticorrosion coatings not only for underground pipes but also for underground cables and cable protection pipes with high precision and high efficiency. Furthermore, by replacing wheel electrodes with reference electrodes such as saturated calomel electrodes or iron electrodes, we can detect damaged locations of paint, polyethylene, etc. on structures such as steel pipe piles and sheet piles installed in rivers, ports, etc. can do. Also for wheel electrodes! By replacing it with an air sensor, it can be used to detect damage locations using a magnetic field method or as a dedicated locator.

〔Effect of the invention〕

According to the present invention, the detection signals detected by the two wheel electrodes 8 in the receiving device 7 or the insertion electrode 24 inserted into the ground and grounded and one wheel electrode 8 and the reference signal from the reference signal transmitter 10, The noise signal in the detection signal is converted to AC and removed by the lock-in 9, and the signal synchronized with the reference signal is converted to DC and then displayed on the display 11, indicating the location of damage to the coating. Even if the potential difference is minute, the coating damage position can be easily detected by amplifying it. Furthermore, the reference signal transmitter 10 in the receiving device 7 uses the AC signal '
Since the reference signal with the same frequency as the current is input to the lock-in angle 9', there is no need to connect an electric wire or the like from the measurement signal transmitter 6 to the receiver 7 to transmit the reference signal. Effects such as being able to easily detect the position of damage to the anticorrosive coating of buried metal pipes can be obtained even if the mutual distance between the receiving device 7 and the receiving device 7 is relatively long.

[Brief explanation of the drawing]

FIGS. 1 to 5 show a first method of implementing the present invention in a two-electrode moving method for detecting the position of damage to the corrosion-resistant coating of buried metal pipes.
Embodiments are shown, and FIG. 1 is a schematic side view of a corrosion protection coating damage position detection device used in the first embodiment;
FIG. 2 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. 2. 4 to 6 show a second method of implementing the present invention in a method for detecting the position of damage to the corrosion protection coating of buried metal pipes using a one-electrode moving method.
Embodiment FIG. 4 is a schematic side view of a corrosion protection coating damage position detection 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. 7 and 8 show a conventionally proposed anti-corrosion coating damage position locating device, in which FIG. 7 connects a measuring signal generator and a receiving device with an electric wire to transmit a reference signal. FIG. 8 is a block diagram showing the signal flow when the measurement signal transmitter and the receiving device are connected by a wireless device to transmit the reference signal. In the figure, 1 is an anti-corrosion coating, 2 is a metal tube, the filter is a damaged part of the coating, 4 is the ground, 5 is a counter electrode, 6 is a measurement signal transmitter, 7 is a receiver, 8 is a wheel electrode, 9 is a mouth, a twist-in-ang, 10
1 is a reference signal transmitter, 11 is a display device, 12 is a metal tube with anti-corrosion coating, and 24 is an insertion electrode.

Claims (1)

[Claims] An alternating current signal current is passed from a measurement signal transmitter 6 between a damaged coating part 3 of a metal pipe 2 which has been laid underground with an anti-corrosion coating on its outer surface, and a counter electrode 5 which is buried in the ground 4. The wheel electrodes 8 of the receiving device 7 moving on the ground surface detect the potential difference on the ground surface, and the reference signal transmitter 10 of the receiving device 7 outputs a reference signal having the same frequency as the output frequency of the measurement signal transmitter 6. , the detection signal is input to the lock-in amplifier 9, the reference signal and the noise signal of the asynchronous signal included in the detection signal are removed, the synchronized signal is displayed on the display device 11, and the anti-corrosion coating is determined based on the change in the waveform. A method for detecting a damaged position of a corrosion-resistant coating of a buried metal pipe, the method comprising: detecting a damaged position of a buried metal pipe.