JP2002022695A - Method for detecting coating film damage position of embedded coated piping - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting a paint film damaged position of a buried pipe which can perform stable measurement and reliably detect a paint film damaged portion. A voltage is applied between a coated steel pipe (1) and a ground electrode (4) from an AC power supply (2) via a power amplifier (3) to pass a current. In this state, the inspection pig 6 is caused to run inside the coated steel pipe 1. The inspection pig 6 is provided with a pair of wheel electrodes 9 in the length direction of the inspection pig 6 via a copying mechanism 8.
A device for measuring and recording the voltage between the pair of wheel electrodes 9 is provided in the body of the inspection pig 6. There is almost no voltage between the two wheel electrodes 9 in places other than the paint film damaged part 5. However, when the damaged paint film 5 comes between the two wheel electrodes 9, a voltage is generated between the two wheel electrodes 9, so that the presence and size of the damaged paint film 5 can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a damaged position of a coating film of a buried coating pipe on the ground in a non-contact manner.

[0002]

2. Description of the Related Art In general, pipes buried underground are provided with a coating around the pipes to prevent corrosion.
However, if this coating film is damaged for some reason, corrosion proceeds from the damaged portion, and eventually a corrosion hole is formed in the pipe. For this reason, in the maintenance of buried piping,
It is important to detect the presence and location of coating damage at an early stage.

In order to respond to this, various coating film damage detection methods have been proposed. Among these, the potential difference method is known as being superior in terms of workability and measurement accuracy.

FIG. 2 shows this method. A voltage is applied between the buried steel pipe 11 and the ground electrode 14 from the AC power supply 12 via the power amplifier 13 to pass a current. In this state, the probe 16 is moved on the ground surface along the pipe axis direction of the buried steel pipe. The spacecraft 16 is provided with a pair of wheel electrodes 16a and 16b in the front-rear direction, and detects the potential of the ground with which each is in contact. The difference between these potentials is detected by the voltage detector 18 via the filter 17.

When the paint film of the buried steel pipe 11 has a paint film damaged portion 15, a current flows from the paint film damaged portion 15 according to the applied voltage, and a potential gradient is formed in the nearby soil. The direction of the potential gradient is reversed at a position immediately above the damaged portion 15 of the coating film. Therefore, the probe 16 is caused to travel along the tube axis direction of the buried steel pipe, and the traveling distance is represented on the horizontal axis, and the wheel electrodes 16a, 1
When a graph is created with the potential difference between 6b as the vertical axis, an S-shaped curve is drawn just above the coating film damaged portion 15. Therefore, by detecting the center position (zero cross point) of the S-shaped curve, the position of the coating film damaged portion 15 can be detected from the ground in a non-contact manner.

FIG. 3 is a view showing the result of detection of a damaged portion of the coating film by this method. In FIG. 3, the horizontal axis represents the moving distance of the probe, and the vertical axis represents the potential difference between the wheel electrodes of the probe. FIG.
In, the potential difference is positive in the left half and negative in the right half. This indicates that the direction of the potential gradient is reversed between the left half position and the right half position. Then, as described above, the center of the S-time curve in FIG. 3, that is, the position where the potential difference crosses zero can be determined to be right above the coating film damage position.

[0007]

However, the known potential difference method has the following problems. That is, since the actual detection of paint film damage is performed by running the probe on asphalt, the ground resistance is large, and the detection signal detected as the potential difference between the wheel electrodes must be weak. On the other hand, a stray current flows in the ground, so that the soil has a specific potential. This becomes noise when measuring the potential difference between the wheel electrodes. Further, the induced current due to the commercial frequency is superimposed on the potential difference detection value, which also becomes noise. Although these noises are removed to some extent by the filter processing, they cannot be completely removed because the S / N ratio of the original signal is small. For this reason, it is difficult to accurately and reliably detect the damaged portion of the coating film.

[0008] Of these methods, as a method of reducing the ground resistance, measurement is generally performed while water is sprinkled between the wheel electrodes 6a and 6b at a measurement location. But,
Even when watering is performed in this manner, the wheel electrodes 6a,
Since the output level of the signal changes depending on the installation condition of 6b, there is a problem in the reproducibility of the signal, and therefore, there is a problem that skill is required to determine the defective signal.

Further, when these methods are carried out, it is necessary to regulate the traffic on the pipeline, and the actual position of the pipeline cannot be accurately determined on the ground, and it is difficult to determine the measurement route. There is.

The present invention has been made in view of such circumstances, and provides a method for detecting a paint film damaged position of a buried pipe, which can perform stable measurement and reliably detect a paint film damaged portion. As an issue.

[0011]

According to a first aspect of the present invention, there is provided a method of detecting a damaged position of a coating film of a coating pipe buried underground, the method comprising: Applying a voltage between the steel pipe and the earth and detecting the coating film damage position by continuously measuring the voltage between two points in the length direction of the pipe inner surface using an inspection pig running inside the pipe Method for detecting damage position of paint film on buried paint-coated pipe (Claim 1)
It is.

When a voltage is applied between the coated steel pipe and the ground, as described above, if there is damage to the coating film, a current flows through the position and a potential gradient is generated in the ground. A potential gradient also occurs in the coated steel pipe. This potential gradient changes abruptly in a portion where coating damage occurs and current flows from there.

Therefore, the inspection pig is run in the pipe in a state where a voltage is applied between the coated steel pipe and the ground, and two points in the longitudinal direction of the inner surface of the pipe are detected by a voltage detecting device provided on the inspection pig. The voltage between them is measured continuously. Then, by detecting a position where the value of the voltage changes suddenly, it is possible to detect a coating film damaged position. Since the inspection pig is usually provided with a distance meter, the position of the coating film damage in the pipe can be specified by measuring the distance at the position where the coating film damage is detected.

A second means for solving the above-mentioned problem is a method of detecting a damaged position of a coating film of a coated pipe buried underground, wherein a voltage is applied between the coated steel pipe and the ground. And applying a test pig running inside the pipe to continuously measure the change in magnetic flux generated near the inner surface of the pipe, thereby detecting the damage position of the coating film. This is a method for detecting a coating film damage position (claim 2).

When a current flows through the pipe, a magnetic field in the circumferential direction is generated in the pipe. When the flow of the current changes due to a leakage current, the magnitude and direction of the magnetic field change. Therefore, the coating film damage position can be detected by continuously measuring the change in the magnetic flux generated near the inner surface of the tube.

A third means for solving the above-mentioned problem is as follows.
The first means or the second means, wherein a voltage between two points in the longitudinal direction of the tube inner surface or a change in a magnetic field generated near the tube inner surface is measured at a plurality of locations in the circumferential direction. This is a feature (claim 3).

In this means, the voltage between two points in the longitudinal direction of the tube inner surface or the change of the magnetic field generated near the tube inner surface is measured at a plurality of locations in the circumferential direction. By comparing the data, the position of the coating film damage in the circumferential direction can be detected.

A fourth means for solving the above problem is as follows.
In any one of the first means to the third means, wherein a voltage applied between the coated pipe and the ground is an alternating current having a frequency different from that of a commercial power supply, and among the measured voltages,
Only the component equal to the frequency of the applied voltage is treated as an effective detection signal (claim 4).

In this means, an AC voltage having a frequency different from the commercial frequency is applied between the painted pipe and the ground, and only the component equal to the frequency of the applied voltage is effective among the measured voltages. Because it is treated as a simple detection signal,
The influence of the commercial frequency and DC noise superimposed on the measurement signal can be removed, and accurate measurement can be performed.

A fifth means for solving the above problems is as follows.
The fourth means is characterized in that only a signal component synchronized with a voltage applied between the coated pipe and the ground is treated as an effective detection signal (claim 5).

This means can be used when a signal can be taken out from the inspection pig to the ground via a cable or the like. The signal component has the same phase as the applied signal as well as the same frequency as the applied signal. Since only the effective detection signal is treated, the noise component can be more effectively removed, and accurate measurement can be performed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a device for implementing the present invention. In FIG. 1, 1 is a coated steel pipe, 2 is an AC power supply, 3 is a power amplifier, 4 is a ground electrode,
Reference numeral 5 denotes a damaged coating film, 6 denotes an inspection pig, 7 denotes a scraper cup, 8 denotes a copying mechanism, and 9 denotes a wheel electrode.

The inspection pig is a device which travels in a pipe by being pushed by a fluid or pulled by a wire to inspect the pipe. In FIG. 1, a voltage is applied between the coated steel pipe 1 and the ground electrode 4 from an AC power supply 2 via a power amplifier 3 to pass a current. In this state, the inspection pig 6 is caused to run inside the coated steel pipe 1.

In the case of the example shown in FIG. 1, the inspection pig 6 is supported by the scraper cup 7 around the body thereof and is pushed by the fluid to travel through the coated steel pipe 1. The inspection pig 6 is provided with a pair of wheel electrodes 9 in the length direction of the inspection pig 6 via a copying mechanism 8. A device for measuring and recording the voltage between the pair of wheel electrodes 9 is provided in the body of the inspection pig 6. Although not shown, the inspection pig 6 is provided with an odometer for measuring the traveling distance, and the measured traveling distance of the inspection pig is recorded together with the measured voltage.

There is almost no voltage between the two wheel electrodes 9 in places other than the damaged portion 5 of the coating film. However, the coating film damaged part 5
Comes between the two wheel electrodes 9, a voltage is generated between them, so that the presence and the size of the coating film damaged portion 5 can be detected.

In the example shown in FIG. 1, only one pair of the wheel electrodes 9 is provided.
If it is on the opposite side in the circumferential direction, the detected signal becomes small, and the damaged coating film 5 becomes difficult to detect. Also,
Due to such circumstances, the size of the coating damaged portion 5 cannot be accurately detected. Therefore, in an actual inspection pig, it is preferable to provide a plurality of pairs of wheel electrodes 9 in the circumferential direction of the inspection pig 5. By doing so, the coating film damaged portion 5
Can be easily detected at any position in the circumferential direction, and the circumferential position of the defect can be detected by comparing the signal levels of the wheel electrode pairs.

The data recorded in the recording device is read out and analyzed after the inspection pig 5 is taken out of the pipe, and then the position, the size, the pipe circumference of the pipe damaged part 5 in the pipe length direction are determined. The direction position and the like are analyzed.

In order to increase the S / N ratio of the detection signal, an alternating current having a frequency different from the commercial frequency is used as the AC voltage to be applied, and the detected signal is filtered to make only the frequency component effective. It is preferable to take out as a signal. Further, when the traveling distance of the inspection pig 5 is short and the signal is not recorded inside the inspection pig 5 but can be sent to the ground through a wire and processed, the detected signal is applied to the painted pipe 1. Synchronous rectification by voltage can further improve the S / N ratio.

In FIG. 1, the wheel electrode 9 is used to detect the voltage between two points in the longitudinal direction of the pipe.
Any material such as a conductive rubber or a wire brush that reliably contacts the inner surface of the pipe can be used as an electrode.

Instead of measuring the potential difference between the two points using the wheel electrodes 9 shown in FIG. 1, a magnetic sensor is attached to the inspection pig 5 and the change in the magnetic field near the inner wall of the coated steel pipe 1 is measured. Is also good. When an electric current flows through a pipe, a magnetic field in a circumferential direction is generated according to Ampere's law. A part of the magnetic flux due to this magnetic field leaks out of the pipe, but if there is a leakage current due to coating film damage, the magnitude and direction of the magnetic field generated at that location change, so the inner wall of the coated steel pipe 1 By measuring a change in a nearby magnetic field, it is possible to detect a coating film damage position.

[0031]

As described above, according to the first and second aspects of the present invention, the damaged position of the coating film can be measured more accurately than the conventional method. According to the second aspect of the present invention, it is possible to detect the coating film damage position in the circumferential direction.

According to the third aspect of the invention, the influence of the commercial frequency superimposed on the measurement signal can be removed,
Accurate measurement can be performed. In the invention according to claim 4, the noise component can be more effectively removed, and accurate measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a device for implementing the present invention.

FIG. 2 is a diagram showing a conventional method for detecting a paint film damage position by a potential difference method.

FIG. 3 is a diagram showing a result of detection of a damaged portion of a coating film by a conventional potential difference method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Coated steel pipe 2 ... AC power supply 3 ... Power amplifier 4 ... Ground electrode 5 ... Damaged coating film 6 ... Inspection pig 7 ... Scraper cup 8 ... Copying mechanism 9 ... Wheel electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G053 AA11 AB22 BA02 BA12 BA19 BA26 BC02 CA02 CA18 DB27 2G060 AA10 AE05 AF09 AG07 AG11 EA03 HA02 KA13

Claims (5)

[Claims] 1. A method for detecting a damaged position of a coating film of a coated pipe buried underground, wherein a voltage is applied between the coated steel pipe and the ground and the inspection is performed in the pipe. A paint film damage position detecting method for a buried paint-coated pipe, wherein a paint film damage position is detected by continuously measuring a voltage between two points in the length direction of the pipe inner surface using a pig. 2. A method for detecting a damaged position of a coating film of a coated pipe buried underground, wherein a voltage is applied between the coated steel pipe and the ground and the inspection is performed in the pipe. A method for detecting a damage position of a paint film in a buried paint-coated pipe, wherein a damage position of a paint film is detected by continuously measuring a change in magnetic flux generated near an inner surface of the pipe using a pig. 3. A method for detecting a damaged position of a coating film on a buried coated pipe according to claim 1 or 2, wherein the voltage is generated between two points in the longitudinal direction of the inner surface of the tube or near the inner surface of the tube. A method for detecting a paint film damage position of a buried coating pipe, wherein a change in a magnetic field is measured at a plurality of locations in a circumferential direction. 4. One of claims 1 to 3
A method of detecting a paint film damage position of a buried coated pipe according to the paragraph, wherein the voltage applied between the coated pipe and the ground is an alternating current having a frequency different from that of a commercial power supply, and the measured voltage is A method for detecting a damage position of a coating film on a buried coating pipe, wherein only a component equal to the frequency of the applied voltage is treated as an effective detection signal. 5. The method according to claim 4, wherein only a signal component synchronized with a voltage applied between the coated pipe and the ground is effectively detected. A method for detecting a paint film damage position in a buried paint-coated pipe, which is treated as a signal.