JPH0244018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting damage to an underground metal pipe whose outer periphery is coated with an electrically insulating coating.

In order to ensure the healthy maintenance of pipe bodies, which are metal pipes that transport fluid, it is important to prevent external corrosion and damage caused by construction work. In order to prevent external corrosion, polyethylene lining has recently been generally adopted as a coating for surrounding steel pipes, and its insulation performance, that is, anticorrosion performance, has been dramatically improved. Furthermore, cathodic protection can be applied to prevent complete external corrosion. However, if the pipe body is damaged by waves due to construction on the road surface,
Fluid may leak out and cause an accident. In order to prevent such accidents, managers of buried objects should
Strict maintenance management must be carried out, such as patrolling the buried route and attending construction work near the buried object. Complementing such management work
In order to strengthen the system, if damage caused by any cause to the pipe body could be immediately detected, it would be extremely effective in preventing accidents.

An object of the present invention is to provide a method that can quickly detect damage to underground metal pipes.

Another object of the present invention is to provide a method for detecting damage locations in underground metal pipes.

FIG. 1 is a sectional view of one embodiment of the present invention.
A pipe body 2, which is an underground metal pipe for transporting fluid, is buried in the ground 1. A cross section perpendicular to the axis of this tube 2 is shown in FIG. A coating 4 made of an electrically insulating material such as polyethylene is coated on the outer periphery of the steel pipe 3, which is a metal pipe, over the entire circumference and length of the steel pipe 3. At the connection points 6a and 6b of the tube body 2, one terminal of the anticorrosion power sources 7a and 7b is connected, respectively. Corrosion prevention power supply 7
The other terminals of a and 7b are grounded.

In order to measure and compare the current values a and b of the anti-corrosion current flowing through the steel pipe 3 at a plurality of locations (two locations in this embodiment) between the connection points 6a and 6b at the same time, voltmeters 8 and 9 are installed, respectively. It will be done.

Referring to FIG. 3, both terminals 8a, 8 of voltmeter 8
b are connected to the steel pipe 3 of the tubular body 2 at intervals in the longitudinal direction of the steel pipe 3. When a current a ampere flows through the steel pipe 3 of the tube body 2, the voltage measured by the voltmeter 8 is defined as V volts, and the connection points 8a, 8
If the distance between b is 1 meter, and the electrical resistance per 1 meter length of the steel pipe 3 is r ohm, then the current a in the tube is expressed by the first equation.

a=V/l·r (1) A voltmeter 9 is also connected to the steel pipe 3 in the same way, and thereby the current value b flowing through the steel pipe 3 is measured.

When the coating 4 of the tube body 2 is not damaged, the current values a and b of the current flowing through the steel tube 3 obtained by the voltmeters 8 and 9 are equal and vary from moment to moment as shown in FIG. 4, for example. However, current is constantly flowing. If these currents Ia and Ib are expressed in rectangular coordinates,
This is shown by a straight line 10 in FIG. 5, and the slope of the straight line 10 is 45 degrees.

At the construction site 13 between the voltmeters 8 and 9, the excavator 14 is plunged into the ground 1, which causes the pipe body 2 to
Assume that the coating 4 is torn as shown in FIG. 6, and a metal excavator 14 comes into contact with the steel pipe 3. In this case, a large current flows into the steel pipe 3 via the excavator 14, and the first
The flow is divided into the steel pipe 3 at different ratios to the left and right in FIG. Therefore, the current values Ia and Ib obtained by the voltmeters 8 and 9 are different at the same time,
As shown by the straight line 11 in FIG. 5, a set of measurement current pairs (Ia, Ib) is distributed on a straight line parallel to the straight line 10 passing through the origin 0. This indicates that the tube body 2 was damaged between the connection points of the voltmeters 8 and 9. The distance between the voltmeters 8, 9 may range, for example, from 2 Km to 15 Km. Furthermore, straight line 11
Above, Ib is larger than Ia. Ib is large because the distance Lb between the damage occurrence point 20 and the connection point 6a shown in FIG. 1 is shorter than the distance La between the damage occurrence point 20 and the connection point 6b. This allows it to be determined that the damage occurred on the side closer to the connection point 6a.

In the above-mentioned embodiment, the anticorrosive flow flowing through the steel pipe 3 of the pipe body 2 is influenced by the provision of a plurality of power supplies 7a and 7b, and also changes greatly due to the influence of underground stray current. The above-mentioned 4th
The state is shown in the figure. In such a case, if the current values Ia and Ib are individually differentiated in level when the coating layer 4 is damaged, it is difficult to detect whether or not damage has occurred. In the above embodiment, the current value
Since Ia and Ib are compared at the same time, the current value
Even if Ia and Ib change significantly over time, it is possible to accurately detect damage to the coating 4.

As another embodiment of the present invention, in order to supply the steel pipe 3 of the tube body 2 with a corrosion protection current larger than that of the corrosion protection power supplies 7a and 7b for damage detection and to facilitate measurement with the voltmeters 8 and 9, Detection power supply and anti-corrosion power supply 7
Corrosion prevention power sources 7a, 7b and detection power sources may be periodically switched and used by preparing corresponding power sources 7a and 7b individually.

As described above, according to the present invention, a power source is connected at a plurality of different connection points along the longitudinal direction of an underground metal pipe, and the current flowing through the metal pipe is transmitted at the same time at a plurality of points between the connection points. Since the measured values are compared with each other, it is possible to detect damage to underground metal pipes when the current values differ from each other, and rapid damage detection is possible. It becomes possible. Furthermore, since the damaged point of the underground metal pipe exists on the side where the current value is large, it is therefore possible to confirm the damaged location.

Further, according to the present invention, both terminals of the voltmeter are connected at intervals in the longitudinal direction of the metal tube, and the current value based on the measured voltage value is compared to determine whether there is damage to the coating. This makes it possible to accurately detect and detect damage without being affected by changes in resistivity on the ground surface or stray currents underground, and it is also possible to detect and detect damage accurately, even when buried metal pipes are not used for their original purpose, such as transporting fluids. It is possible to detect and detect damage while still in use.

Furthermore, the present invention compares the simultaneous values of the anti-corrosion current constantly flowing through the metal pipe between two connection points provided at intervals in the longitudinal direction of the underground metal pipe, and detects that the current value is different. Since it is determined that the coating may sometimes be damaged, detection of damage to the coating of long underground metal pipes can be carried out at the same time as corrosion protection, compared to when the corrosion protection current is supplied from only one connection point. It is possible.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an embodiment of the present invention;
The figure is a cross-sectional view perpendicular to the axis of the steel pipe 2, Figure 3 is a diagram showing the connection state of the voltmeter 8, Figure 4 is a waveform diagram of currents Ia and Ib, and Figure 5 is a current value Ia and Ib at the same time. FIG. 6 is an enlarged cross-sectional view of the pipe damaged at construction site 3. 1...Ground, 2...Pipe body, 3...Steel pipe, 4...
Painting, 6a, 6b...Connection points, 7a, 7b...
...Anti-corrosion power supply, 8, 9...Voltmeter, 13...Construction area.

Claims (1)

[Claims] 1 Two connection points 6a, 6b provided at intervals in the longitudinal direction of the metal pipe 3 of the underground metal pipe 2 configured by coating the outer periphery of the metal pipe 3 with an electrically insulating coating 4 One terminal of the anti-corrosion power supplies 7a, 7b is connected to the other, and the other terminal of the anti-corrosion power supplies 7a, 7b is grounded, and an anti-corrosion current is constantly passed from the connection points 6a, 6b between the two connection points 6a, 6b. Then, connect both terminals of the voltmeters 8 and 9 at intervals in the longitudinal direction of the underground metal pipe 2, and
The currents a and b flowing through the underground metal pipe 2 are measured based on the voltage measurement values in step 9, respectively, and the currents a,
A damage detection method for underground metal pipes in which simultaneous values of b are compared and it is determined that coating 4 is damaged on the side where the values of each current a and b are larger.