JPS6044864A - Damage position detector for coating film of buried piping - Google Patents

Abstract

PURPOSE:To improve detecting accuracy through elimination of induced noises from stray current and transmission line, by inserting a detecting electrode inside its buried area, permitting it to displace in an axial direction of pipe and conducting damage detection of coating film by detecting magnetic field inside the pipe. CONSTITUTION:A DC power source 3 is connected by way of a switch 4 between a buried piping 1 provided with rust preventative coating film and supply electrode 2. Into this piping 1, a magnetic field detecting member 11A provided with sensors 21X, 21Y, 21Z detecting magnetic fields in directions XYZ mounted on a running bench 20 is fed with a thrusting force. A position of the member 11A is measured by a length of a wire 13, the position being indicated on a display unit 15. From this situation the wire 13 is wound around a drum 14 and the member 11A is drawn back and simultaneously, a switch 4 makes the switch on and off operations repeatedly to measure the magnetic field inside the pipe. In the neighborhood of a damage, a disturbance of an input current generates a magnetic field and thus, damage of coating is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried pipe coating damage location detection device for detecting damage locations in the anticorrosive coating of pipes buried underground.

In recent years, pipeline maintenance has become more important, especially from the viewpoint of corrosion prevention, underground burial A? There is a trend to investigate whether damage has occurred to the external anticorrosive coating of Eveline and to repair the damaged area.

In order to meet such demands, technology to accurately detect the location of damage to the coating is required.
Conventional exploration methods such as (2) needle electrode method, (3) tube current method, and (4) Pearson method have advantages and disadvantages.

These will be outlined below.

(1) Pipe-to-ground potential distribution method As shown in Figure 1, a series circuit of a DC power supply 3 and a switch 4 is connected between a pipe 1 buried underground and a current-carrying electrode 2 driven into the ground. This is a method in which the switch 4 is turned on and off, and the potential between the buried pipe 1 and the ground is sequentially measured using a voltmeter 5 while moving the detection electrode 6 along the pipe 1 to determine the potential distribution. The potential gradient in the vicinity is measured as the tube's ground potential. In the vicinity of the defective portion a, attenuation as shown in FIG. 2 is observed in the tube-to-ground potential when the switch 4 is turned on, so the position of the defect (damage to the anti-corrosion coating) can be detected from this distribution map.

However, the horizontal axis X shows the piping position, and the vertical axis V shows the voltage.

This method has the following problems.

(+) Accurate potential measurement is not possible when measuring on a paved road.

(11) Accurate measurement is difficult in areas with a lot of stray current, and accuracy is poor.

(iiD) There is a risk that the work will obstruct traffic, and there are restrictions on the implementation time.

(2) Needle electrode method As shown in Figure 3, with the DC power supply 3 connected between the buried pipe 1 and the current-carrying electrode 2, a pair of detection electrodes 6iA and 6B are placed at a distance of 1 to 2 m in the direction of the pipe. Grounded to the ground surface, −
The potential difference between the electrodes 61.6'B is measured by the voltmeter 5. When the positions of the detection electrodes 6iA and 6B are sequentially moved, it is possible to detect that there is a defect in the coating of the pipe 1, and the pipe metal in that part is exposed. When a defective part is in contact with surrounding soil or groundwater, current flows from the defective part according to the applied voltage and creates a potential gradient in the nearby soil, so the polarity of the potential changes as shown in Figure 4. The defective part a can be known as the position to be reversed.

Although this method is currently widely used, it has the following problems.

(1) Measurement is difficult on paved roads because the electrodes cannot be grounded.

(11) Accuracy is poor (approximately ±0.5 m) due to the influence of stray currents and other buried piping.

611) There is a risk that the work will obstruct traffic.

(3) In-pipe current method As shown in FIG. 5, a DC power supply 3 and a series and column circuit of a switch 4 are connected between the buried pipe 1 and the through-hole electrode 2, and the switch 4 is turned on and off. The direct current flows into the buried pipe 1 from the coating defect part a, flows through the pipe body, and returns to the power supply 3, so the voltage drop in the pipe body caused by this current is measured with a voltmeter 5 to detect the defect position. .

This method has the following problems.

(1) In order to measure voltage, it is necessary to accept terminals on the piping, and installation is time-consuming.

61) The terminal spacing is long and the accuracy is poor (approximately ±10m).

(iii) There is a risk that the work will obstruct traffic.

(4) Pearson method As shown in Figure 6, a transmitter 7 is connected between the buried pipe 1 and the current-carrying electrode 2, and a current of about 750 Hz % IA is passed through a metal wire to measure the ground potential gradient. Two testers gA and 8B wearing Sufu 4 Iku are the receiver 9 and the connection line 1.
0 and walk along the pipe 1 at intervals of about 10 m, the potential between the two is converted into sound by the receiver 9. Detector 8
As A approaches the defective part, the potential difference gradually increases and the tone becomes louder. When the detector 8A comes directly above the defective part a, the beep becomes the highest, and when the detector 8A goes further and the defective part a is located in the center of both 8A and 8B, the beep becomes the lowest, and the p1 assistant 8B detects the defective part. When it comes directly above point a, the tone becomes the highest again.

This situation is illustrated in FIG. 7.

B indicates the volume of the outgoing tone.

This method has the following problems.

(1) Detection voltage is low on paved roads and accuracy is low.

0i) Subject to inductive disturbances from high-voltage power transmission lines, etc.

GiD work may cause traffic obstruction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a buried pipe coating damage location detection device that can detect corrosion-resistant coating damage locations with high accuracy without causing a hindrance to traffic.

The present invention connects a power source between a buried pipe having an anticorrosive coating and a current-carrying electrode, and also inserts a detection part of a magnetic field detection device into the buried pipe so that it can move freely in the pipe axis direction. In addition to detecting paint film damage by detecting the magnetic field, its position can be determined from the length of the wire that pulls the magnetic field detection unit.

FIGS. 8 and 9 are for explaining the operating principle of the present invention, and 1 shows a buried pipe having a coating film number as an anti-corrosion coating;
2 is a current-carrying electrode; 3 is a DC power supply connected between the buried pipe 1 and the current-carrying electrode 2;

When a DC voltage is applied between the pipe 1, the current-carrying electrode 2, and the ground in this manner, a DC current 5led1 flows from the paint damaged area areal. This current flows in the direction of the power source 3 with a current distribution as shown in FIG. At this time, a magnetic field H is generated within the tube due to the disturbance of the inflow current near the defective portion. If this magnetic field H is detected by running 11 detectors of a magnetic field detection device inside the pipe, damage to the paint film and its location can be detected.

In general, for the magnetic field H inside the tube through which current flows, since there is no current inside the tube, according to Ampere's law of circuit integration, in the region (inside the tube) C, the formula (
1) holds true.

f<c>1・di! = O...(1) If the current flows uniformly through the tube, this system will be point symmetric, so
Equation (2) holds true.

1(r, θ) = a(r) ...(2)(1)(2
), if we perform an arbitrary circumferential integral concentric with the pipe, we get 2πra
(r)=O(Vr),',a(r)=IH(r,θ)=O−(
3), and no magnetic field is generated inside the tube.

However, when the piping IK paint film is damaged and current flows through it, the current becomes uneven in the vicinity as shown in Figure 9.
Equations 2) and (3) do not hold, and a magnetic field is generated inside the tube. The directions of this magnetic field are the tube cross-sectional direction and the tube axis direction.

FIG. 10 shows an embodiment of the present invention, in which 1 is a buried pipe, 2 is a current-carrying electrode, and 3 is a direct current connected between this electrode 2 and a corrosion protection terminal 1a of the pipe 1 via a switch 4. A power source 11 is a magnetic field detection device, and a detection unit (sensor) is inserted into the pipe 1 so as to be movable in the axial direction of the pipe.
It has 11 people and a measurement/display unit JIB connected to them via a signal cable 12. 13 is a wire for moving the magnetic field detection unit 11; 14 is a drum around which the wire 13 is wound; 15 is a position where the length of the wire is measured and its tip is displayed on the tab detection unit 11; The magnetic field detection unit JJA, which is an indicator, includes sensors 21X and 21Y that detect magnetic fields in the X direction, Y direction, and tube axis direction on the traveling platform 20, as shown in FIG.

21Z is placed thereon, and center risers 22 are attached to four locations on the side surface of the traveling base 20, to which the signal cable 12 and wire 13 are connected. A Hall element, a semiconductor sensor, or the like is used as the sensor.

Next, the operation will be described. The magnetic field detection unit JJA is fed into the piping 1 by pressure feeding. Its position is wire 13
The measured length is displayed on the display 15.

When the wire starts to be wound around the drum 14 from this state, the detection section 11k is pulled back. At the same time, switch 40 is turned on,
Repeat turning off and reading the display on the measurement/display section 11B, and calculate the difference. This eliminates the effects of earth's magnetism and residual magnetism at the pipe weld.

Measurement examples are shown in FIGS. 12(a) and 12(b). Figure 12 (,
) is the magnetic field in the X direction, and FIG. 12(b) is the magnetic field in the tube axis direction. In this example, a current of 5 A is passed through a 2-inch diameter gas pipe with a length of about 200 m through a current-carrying electrode.
The detection unit 11 had a size of about 10φ×40mm. As a result of the measurement, it was possible to accurately detect paint film damage of approximately 10 ctn2. In addition, the accuracy of the defect detection position is determined solely by the measurement accuracy of the length of the wire being fed, t, Q, 10 crn.
It falls within the following range.

Note that in the embodiment, a DC power source is used, but an AC power source may be used.

As described above, according to the present invention, the detection part (sensor) of the magnetic field detection device is inserted inside the buried pipe and moved in the pipe axis direction to detect the magnetic field inside the pipe and detect paint film damage. Since the position of the traction wire is known from the length of the traction wire, it is completely unaffected by road surface conditions such as pavement, and this also eliminates stray currents and noise induced by power lines. Exploration accuracy is significantly improved. Furthermore, since the working space on the road surface is small, there is no risk of interfering with traffic.

[Brief explanation of the drawing]

FIGS. 1 to 7 are explanatory diagrams of each conventional coating film damage detection method, and FIGS. 8 and 9 are diagrams explanatory of the operating principle and current distribution diagram of the buried pipe coating damage location detection device according to the present invention, FIG. 10 is a layout configuration diagram showing an embodiment of the present invention, FIG. 11 is a plan view showing a schematic configuration of a magnetic field detection section in the same embodiment, and FIG.
The figure is a graph showing a measurement example. 1... Buried piping, 2... Current-carrying electrode, 3... Power supply,
4...Switch, 11...Magnetic field detection device, 11 people.
...Magnetic field detection section, 11B...Measurement/display section, 12...
- Signal cable, 13... wire, 14... drum, 15... position indicator. To the applicant's representative Patent attorney Takeshi Suzue Onden Figure 1 Figure 2 - Subversion 1 x = 0 Figure 4 Figure 5 Figure 6 x = 0

Claims (1)

[Claims] A current-carrying electrode that is driven into the ground, a power source that is connected between a buried pipe having a coating film as an anticorrosion coating, and the current-carrying electrode, and a power source that is inserted into the buried pipe so that it can move freely in its axial direction. A magnetic field detection device having a magnetic field detection section and a measurement/display section connected to the magnetic field detection section via a signal cable, and a magnetic field detection section that moves the magnetic field detection section by winding a wire tied to the magnetic field detection section. A buried piping coating comprising a moving means, a position indicator for measuring the length of the wire and displaying the position of the magnetic field detecting section, and a pressure feeding means for feeding the magnetic field detecting section into the buried piping. Damage location detection device.