JPH05230677A - Corrosion preventive method for underground buried metallic pipe - Google Patents

Abstract

PURPOSE:To efficiently execute drainage when the stray current from electric train rails runs in an underground buried metallic pipe. CONSTITUTION:The stray current 111 from an electric train 14 flows into a pipe 12 which is the metallic pipe buried in soil 11. An inflow current 120 flows to a potential control type force drainer 20 from a drainage point 19. The amplifier AMP 2 of the potential control type force drainer 20 increases the internal resistance of a second transistor(TR) 22 to decrease a drainage current 122 and to prevent overprotection when the potential of the drainage point 19 changes to a base side with the potential of a reference electrode 18 as a reference. The internal resistance of the second TR 22 decreases to increase the drainage current 122 and the potential of the drainage point 19 is maintained at the base by utilizing the drainage current when the potential at the drainage point 19 changes to the noble side. A protective current 121 is supplied from a current rectifier 23 via a first transistor 21 to protect the pipe 12 when the drainage current does not flow and when the protective current cannot be maintained by the drainage current alone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion method for an underground metal pipe such as a gas transportation pipe, and more particularly to an anticorrosion method near a train track.

[0002]

2. Description of the Related Art Conventionally, underground metal pipes such as gas pipes are provided with a coating or the like on the surface to prevent corrosion. However, the coating cannot completely cover the underground metal pipe, and an electric current may flow between the soil and the underground metal pipe through a pinhole or the like. When a stray current is flowing in the soil, it flows in from one part of the underground metal pipe and flows out from the other part. Since an anodic reaction occurs at the place where the current flows, there is a risk of corroding the underground metal pipe.

FIG. 3 shows a method of preventing corrosion of a buried underground pipe in the vicinity of a railroad track, which is particularly susceptible to corrosion. A steel pipe 2 is buried in the soil 1. Rails 3 are laid on the surface of the soil 1. For the train 4 traveling on the rails 3, the supply current I0 is supplied from the substation 6 via the overhead line 5.
Is supplied. The supply current I0 returns to the substation 6 via the rail 3, but part of it flows into the pipe 2 as a stray current I1. The current flowing through the pipe 2 is the substation 6
Corrosion current I2 is generated in the vicinity of and flows out into the soil 1.

The diode 7 and the resistor 8 have a corrosion current I
It is provided to reduce 2. Substation 6 on pipe 2
By directly connecting the discharge point 9 in the vicinity and the ground side of the output from the substation 6 with the diode 7 and the resistor 8, a discharge current is caused to flow and the corrosion current I2 is reduced. Diode 7
The reason for using is to prevent the electric current from flowing into the discharge point 9 and flowing out from the other portion of the pipe 2 and corroding the flowing-out portion. The resistor 8 is inserted to limit the value of the drain current. When the value of the drain current increases,
This is because over-corrosion occurs and various problems occur.

[0005]

With the conventional anticorrosion method as shown in FIG. 3, the pipe 2 in the vicinity of the train track cannot be sufficiently anticorrosive. Train 4 on the train track
The location and amount of the stray current I1 change as the vehicle travels. Further, when the train 4 is equipped with a regenerative brake or the like, current may be supplied from the train 4 itself. Therefore, the ground potential of the rail 3 fluctuates sharply, the discharge current increases, and the fluctuation of the discharge pattern tends to increase.

For example, even if an attempt is made to limit the exhaust current on the basis of when the train 4 is in a constant running state,
The stray current I1 may increase or may not occur at all under the load condition of 1). Further, a constant current method or the like, in which the resistance value 8 is changed to keep the discharge current at a constant current value, has been put into practical use.
However, in terms of operating characteristics, when the change in the exhaust current is large due to the weather conditions and the like, the potential of the pipe 2 tends to be noble, and the pipe 2 is easily corroded.

As described above, it is difficult to adjust the exhaust current in order to prevent corrosion of the pipe 2 near the train track. For example, if a stable fluctuation pattern is shown, the control can be normally performed, but when the fluctuation pattern suddenly changes over a period of time, the potential level of the pipe 2 also suddenly changes, and the possibility of corrosion increases. .. As described above, it is difficult to keep the pipe 2 at a potential at which corrosion can be prevented, by the conventional method of adjusting the exhaust current.

An object of the present invention is to provide an anticorrosion method for an underground metal pipe which enables efficient drainage and is capable of reliable corrosion protection when drainage is not performed.

[0009]

SUMMARY OF THE INVENTION The present invention detects the potential difference between an underground metal pipe having a coating covering provided in the vicinity of a train track and a reference electrode provided on the soil to detect the metal pipe. When the tube-to-ground potential changes to the nobile side of the predetermined anticorrosion potential and changes to the noble direction, when the drain current is increased to limit the resistance of the drain current system and changes to the base direction , When the resistance is increased to reduce the exhaust current and the pipe ground potential of the metal pipe becomes more noble than the predetermined corrosion protection potential,
This is a method for preventing corrosion of a metal pipe buried in the ground, which is characterized in that a corrosion protection current is applied to the metal pipe.

[0010]

According to the present invention, the potential difference between the underground-embedded metal pipe having the coating covering provided in the vicinity of the train track and the reference electrode provided on the soil is detected. Therefore, it is possible to detect the tube-to-ground potential of the metal tube with reference to the potential of the reference electrode.
The resistance of the drain current system is limited to be small when the tube ground potential is lower than the predetermined anticorrosion potential and changes in the noble direction. When the pipe ground potential of the metal pipe is on the base side of the predetermined anticorrosion potential and further changes to the base direction,
Increase the resistance to reduce the drain current.

As a result, the value of the exhaust current can be limited in accordance with the tube-to-ground potential of the metal tube so as not to cause over-corrosion.

When the tube ground potential of the metal tube becomes nobler than the predetermined anticorrosion potential, an anticorrosion current is passed through the metal tube,
The metal pipe can be protected even when no discharge current flows.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a configuration for carrying out the present invention. The soils 11 and 12 are pipes 1 which are underground metal pipes.
2 is buried. Rails 13 are laid on the roadbed 13a on the surface of the soil 11. A train 14 runs on the rails 13, and electric power for running is supplied from an overhead wire 15.

A part of the current supplied from the overhead line 15 to the train 14 becomes a stray current I11 and flows into the pipe 12. The pipe 12 covers the steel pipe with a coating to prevent corrosion. However, a pinhole or the like is partially formed in the coating covering, and the current flowing between the pipe 12 and the soil 11 cannot be completely prevented. Therefore, when the stray current I11 flows into the pipe 12 in the vicinity of the train 14, the corrosion current I11 flows from other parts of the pipe 12.
12 flows into the soil 11.

In order to detect the tube-to-ground potential of the pipe 12 due to the stray current I11, a reference electrode 18 is provided near the discharge point 19 of the pipe 12. At the discharge point 19, a stray current I
Of the tube current I13 based on 11, the stray current I14 flowing from the soil 11 is excluded except for the portion that becomes the corrosion current I12.
A current including is extracted as an inflow current I20.

The potential of the reference electrode 18 and the inflow current I20 are applied to the potential control type forced drainer 20. Amplifiers AMP1 and AMP2 are provided in the potential control type forced drainage device 20, and the drainage point 19 is based on the potential of the reference electrode 18.
The potential of is detected. The output of the amplifier AMP1 controls the base of the first transistor 21. The output of the amplifier AMP2 controls the base of the second transistor 22. First
The collector of the transistor 21 has an AC current from the rectifier 23.
DC power obtained by rectifying C200V is applied. The emitter of the first transistor 21 is connected to the anode of the diode 24. The cathode of the diode 24 is commonly connected to the cathode of the diode 25. The anode of the diode 25 is connected to the emitter of the second transistor 22. The collector of the second transistor 22 has a drain point 19
Connected to. The commonly connected cathodes of the diodes 24 and 25 are connected to the rail 13 near the drain point 19 via the resistor 26. The first transistor 21 is controlled by the output of the amplifier AMP1 to determine the value of the anticorrosion current I21. The second transistor 22 has an amplifier AMP2.
Of the discharge current I22 is controlled by the output of. The adjustment of the amplifiers AMP1 and AMP2 is performed by the regulators VR1 and VR2 using variable resistors, respectively.

FIG. 2 shows the potential at drain point 19 controlled in the embodiment shown in FIG. The value of the electric potential is copper sulfate (C
uSO ₄ ) standard electrode is shown as a reference.

In this embodiment, the amplifier AMP1 is connected to Vz (-
1100 mV) and the amplifier AMP2 to Vm
(-1500 mV). When the discharge current is not flowing and the tube-to-ground potential at the discharge point 19 changes to a nobler side than the set potential, the amplifier AMP1 activates the first transistor 21 so that the anticorrosion current I21 flows. The pipe ground potential of the pipe 12 can be maintained in the anticorrosion potential setting region. When the discharge current flows, the discharge point 19
Since the tube-to-ground potential of the above-mentioned changes to the base side from the set potential, the internal resistance of the second transistor 22 of the amplifier AMP2 is controlled to be large, and the value of the drain current I22 is reduced to reduce the tube-ground potential of the drain point 19. Keep the potential in the anticorrosion potential setting range.
An electrode made of zinc (Zn) or magnesium (Mg) can be used as the reference electrode 18. This is because the zinc and magnesium electrodes are cheaper and easier to use. The electrode potential of zinc is Vz (-1100 mV), and the electrode potential of magnesium is Vm (-1500 mV).

According to this embodiment, the anticorrosion current I21 and the drain current I22 are ORed by the diodes 24 and 25 (O
Since the R) circuit is connected, the anticorrosion diode 24 is biased in the reverse direction and the anticorrosion current I21 does not flow when the drain current I22 is large.

As described above, the potential change to the noble side when the discharge current does not flow and the potential change to the base side when the discharge current flows are automatically suppressed, and the pipe 12 is set to an appropriate corrosion protection potential range. Can be maintained.

[0021]

As described above, according to the present invention, the tube-to-ground potential of the metal tube can be accurately measured with the reference electrode as a reference. Since the discharge current value can be controlled based on the measured pipe-to-ground potential, the discharge current of the underground buried metal pipe is efficiently controlled by controlling the discharge current value to an appropriate value, and no corrosive environment is formed. .. Further, even if the drain current does not flow, the anticorrosion current is made to flow through the metal pipe on the nobler side of the predetermined anticorrosion potential, so that stable corrosion protection of the underground buried metal pipe can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration for explaining an embodiment of the present invention.

FIG. 2 is a graph showing a tube-to-ground potential in the embodiment shown in FIG.

FIG. 3 is a schematic cross-sectional view showing a conventional corrosion prevention method for a pipe 2.

[Explanation of symbols]

 11 Soil 12 Pipe 13 Rail 14 Train 15 Overhead Wire 18 Reference Electrode 19 Discharge Point 20 Potential Controlled Forced Discharger 21,22 Transistor 23 Rectifier 24,25 Diode 26 Resistance AMP1, AMP2 Amplifier VR1, VR2 Regulator

Claims (1)

[Claims] 1. An anticorrosion method in which the potential of a metal pipe having a coating covering provided in the vicinity of a train track and a reference electrode provided in soil is detected to determine a potential of the metal pipe to ground is predetermined. When it changes to the nobile side of the potential, it increases by restricting the resistance of the drain current system to increase the drain current, and when it changes to the base direction, it increases the resistance and drains the current. An anticorrosion method for an underground metal pipe, characterized in that an anticorrosion current is passed through the metal pipe when the current is reduced and the earth potential of the metal pipe becomes more noble than a predetermined anticorrosion potential.