JP2000234188A - Electric protection method of pipe line, and external power supply device for electric protection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric protection method of a pipeline, and an external power supply device for electric protection which are capable of preventing both the return-type galvanic corrosion (caused by electric current flowing from a pipeline to the ground) and the push-out type galvanic corrosion (caused by stray current flowing into the pipeline). SOLUTION: In a method for preventing the galvanic corrosion of a pipeline 7 caused by the stray current, the current of the constant electric potential to keep the potential difference between the pipeline 7 and the ground 8 covering it to be not less than the specified value is supplied to the pipeline 7, and the constant voltage is constantly applied between the ground 8 and the pipeline 7 irrespective of the potential difference, and the compensating current to maintain the current supply to the pipeline 7 is supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for protecting a pipeline for transporting gas, oil, or the like from electricity.

[0002]

2. Description of the Related Art As a method of continuously transporting a fluid such as gas or oil, for example, a method in which a pipeline is buried underground and a fluid flows in the pipeline is widely used. For the pipeline, usually, a coated steel pipe in which a steel pipe is insulated and coated with polyethylene or the like is used.

[0003] This coated steel pipe has the effect of preventing the occurrence of corrosion by insulating the steel from the outside, but in consideration of the recent increase in stray current and the like, there is a problem in the coating by any chance. In such a case, it is necessary to take measures to ensure sufficient anticorrosion. Therefore, countermeasures have conventionally been taken for the pipeline by installing an Mg anode as a sacrificial electrode, or by installing an external power supply (hereinafter, referred to as an external power supply) for supplying an anticorrosion current.

[0004] The installation of the above-mentioned Mg anode has the advantage of low cost, but has a lower anticorrosion effect than that of the external power device. Therefore, in an important pipeline for gas transportation or the like, a countermeasure using an external power unit or a combination using an external power unit and a Mg anode is often taken. In addition, as a conventional external power device, a constant potential current is supplied to the pipeline to keep the potential difference above a certain level so that the pipeline maintains a sufficient anticorrosion potential against the ground.
The constant potential automatic control type external power device was widely used.

[0005]

Problems to be solved By the way, electrolytic erosion in pipelines can be roughly classified into return-type electrolytic erosion and extrusion-type electrolytic erosion. These can be explained using an example in which rails of an electric railway that contribute to the generation of stray currents cross a pipeline. That is, as shown in FIG. 4 (a), when the train 92 traveling on the rails 91 transverse to the pipeline 7 is using the regenerative brake in the case or near the cross section S ₁ in distant, relatively The rail potential becomes lower than the potential of the pipeline 7. In this case, current 99 flows out toward the rail 91 from the pipeline 7, return flow type electrolytic corrosion occurs in cross section S ₁ point.

On the other hand, as shown in FIG. 4B, when the train 92 is in an accelerating state near the crossing, etc.
The potential of the rail 91 is relatively higher than the potential of the pipeline 7. In this case, a current 99 flows into the pipeline 7 from the rail 91, and then flows out of the pipeline 7 to the underground 8 at a distance away from the rail 91, and the extruded electrolytic corrosion occurs at a distant point S _2. Occurs.

[0007] The above-mentioned conventional constant-potential automatic control type external power device is excellent in the effect of preventing "return-type electrolytic corrosion" which occurs when current flows out of the pipeline from the pipeline at the location of the external power device. However, there is little effect on countermeasures against "extrusion-type electrolytic corrosion" that occurs when stray current flowing into a pipeline flows out into the ground far away from the location of the external power equipment.

[0010] On the other hand, measures can be taken by installing an external electric device also at the location where the extrusion type corrosion occurs, but the equipment cost is greatly increased. Further, when the external power device and the Mg anode are used in combination, problems such as occurrence of interference due to inflow of a current from the Mg anode have occurred. Therefore, the development of an anticorrosion method and an external power device that can take measures against both the return-type electrolytic corrosion and the extrusion-type electrolytic corrosion with one unit has been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide a method for preventing corrosion of a pipeline and an external electric device for preventing corrosion, which can prevent both return-type and extrusion-type electrolytic corrosion. It is intended to provide.

[0010]

According to a first aspect of the present invention, there is provided a method for preventing electrolytic corrosion of a pipeline due to stray current, wherein the potential difference between the pipeline and the underground covering the pipeline is set to a predetermined value. A current is supplied to the pipeline by a constant potential automatic control output, and a constant voltage is constantly applied between the underground and the pipeline regardless of the potential difference to maintain the current supply to the pipeline. And a method for preventing corrosion of a pipeline.

The most remarkable point in the present invention is to supply not only the constant potential current but also the compensation current to the pipeline and to keep supplying the current (corrosion prevention current) to the pipeline. .

Next, the operation of the present invention will be described. In the cathodic protection method of the present invention, the potential difference between the pipeline and the underground (hereinafter, appropriately referred to as a pipe-to-ground potential difference) is always maintained at a certain level or more by the constant potential current and the compensation current. Specifically, a constant potential current is supplied such that the potential in the ground is always higher than the potential of the pipeline by a predetermined potential or more near the anticorrosion point. As a result, in the pipeline in the vicinity of the constant-potential current supply point, the outflow of current from the pipeline can be prevented, and "return-type electrolytic corrosion" can be prevented.

On the other hand, when the pipe-to-ground potential difference is equal to or greater than a predetermined value, the constant potential current is not output due to the characteristics of the control. On the other hand, when the tube-to-ground potential difference at the installation location of the external power device is sufficiently secured and the constant potential current is not supplied, the tube-to-ground potential difference at a distance away from the external power device becomes small, and extrusion-type electrolytic corrosion occurs. It may be in a state that is easy.

On the other hand, in the present invention, a constant voltage is always applied between the underground and the pipeline so that the compensation current is output. Therefore, even in a situation where the constant potential current is not output, the compensation current is output, and the anticorrosion current is always supplied to the pipeline.

Therefore, when the tube-to-ground potential in the vicinity of the external power device installation location is equal to or higher than a predetermined value, but the tube-to-ground potential in a distant place is about to decrease, the constant potential current is stopped. Is supplied, the far-ground potential is maintained at a predetermined value or more. Therefore, it is possible to prevent the occurrence of extrusion type electrolytic corrosion. That is, the external power device of the present invention can prevent both return-type electrolytic erosion and extrusion-type electrolytic erosion by outputting the two types of anticorrosion currents of the constant potential current and the compensation current. Further, since these functions and effects can be exhibited by one external power device as described above, it is also possible to reduce equipment costs.

Therefore, according to the present invention, it is possible to provide a method for preventing cathodic corrosion of a pipeline, which can prevent both return-type electrolytic corrosion and extrusion-type electrolytic corrosion.

Next, an invention according to a second aspect is an external corrosion protection device for supplying an anticorrosion current to the pipeline for preventing electrolytic corrosion of the pipeline due to stray current, wherein And a constant potential control circuit for supplying a constant potential current to the pipeline for setting a potential difference between the underground and the underground to a predetermined value, and a constant potential between the underground and the pipeline regardless of the potential difference. A compensating current circuit for applying a voltage to supply a compensating current for maintaining the current supply to the pipeline.

The most remarkable point in the present invention is to have not only the constant potential control circuit but also a compensation current circuit for outputting the compensation current. In this case, the same function and effect as the conventional constant potential automatic control type external power device by the constant potential control circuit can be exhibited, and when the constant potential current is stopped, the compensation current circuit is used. A compensation current can be provided to the pipeline. Therefore, the anticorrosion current can always be supplied to the pipeline without interruption, and as described above, both return-type electrolytic erosion and extrusion-type electrolytic erosion can be prevented.

Therefore, according to the present invention, it is possible to provide an external electric equipment for corrosion prevention of a pipeline, which can prevent both return-type electrolytic corrosion and extrusion-type electrolytic corrosion.

Next, as in the third aspect of the present invention, the constant potential control circuit is configured to output the constant potential current, which is a DC current, from a commercial power supply, and to output the constant potential current. An automatic control circuit for controlling a value according to a potential difference between the pipeline and the underground, and a potential detection unit for detecting the potential difference and sending a potential difference signal to the automatic control circuit. The negative side of the constant potential control circuit is connected to the pipeline, the positive side is connected to the current-carrying electrode buried in the ground, and the compensation current circuit is
It is connected between the commercial power supply, the pipeline and the energized electrode in parallel with the constant potential control circuit, and is configured to output the compensation current, which is a DC current, from the commercial power supply. preferable.

In this case, while the tube-to-ground potential is constantly detected by the potential detecting section, the automatic control circuit controls the constant potential control circuit in accordance with the detection result, thereby accurately outputting the constant potential current. Can be output. In addition, the negative potential of the constant potential control circuit is connected to the pipeline, and the positive potential is connected to the current-carrying electrode to supply the constant potential current, thereby reliably preventing the flow of current from the pipeline to the underground. can do. The constant potential control circuit can be configured by combining, for example, a transformer, a rectifier circuit, a smoothing circuit, and the like.

In this case, the power source for the constant potential control circuit and the power source for the compensation current circuit can be shared, and the structure of the device can be simplified. The compensation current circuit can be configured by combining, for example, a transformer, a rectifier circuit, a smoothing circuit, and the like.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A method for protecting a pipeline from corrosion and an external device for preventing corrosion according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the external power device 1 of the present embodiment is an external power device for anticorrosion (hereinafter referred to as the external power device 1) for supplying an anticorrosion current to the pipeline 7 for preventing electrolytic corrosion of the pipeline 7 due to a stray current. ).

The external power unit 1 supplies a constant potential current to the pipeline 7 for setting a potential difference E ₁ (pipe-to-ground potential difference) between the pipeline 7 and the underground 8 covering the pipeline 7 to a predetermined value E _0. A potential control circuit 10 and a compensation current circuit that constantly applies a constant voltage between the underground 8 and the pipeline 7 regardless of the potential difference and supplies a compensation current for maintaining the current supply to the pipeline 8. And 2.

The constant potential control circuit 10 includes a commercial power supply 19
Together and is configured to output the constant electric potential current is a DC current from the automatic control circuit 14 for controlling the value of the constant potential current according to the pipe-ground electric potential difference E _1, a tube ground potential E ₁ A potential detector 15 for detecting and sending a potential difference signal to the automatic control circuit 14. The negative side of the constant potential control circuit 10 is connected to the pipeline 7, and the positive side is connected to a current-carrying electrode 18 buried in the underground 8.

The constant potential control circuit 10 includes a first transformer 11 connected to a commercial power supply 19 as shown in FIG.
And a first rectifier circuit 12 connected thereto and a first smoothing circuit 13 further connected thereto. The first rectifier circuit 12 is connected to an automatic control circuit 14 having the above-described potential detection unit 15. The potential detector is configured to detect a potential difference between the reference electrode 151 buried underground and the pipeline 7.

The first transformer 11 is connected to the AC1 of the commercial power supply 19.
This is for transforming a voltage of 00V (or 200V AC) to 60V AC. The first rectifier circuit 12
The configuration is such that the alternating current from the transformer 11 is full-wave rectified and the passing current is adjusted according to an instruction from the automatic control circuit 14. Further, the first rectifier circuit 12 is configured to prevent a backflow of current. First smoothing circuit 13
Is a circuit for converting the current that has been full-wave rectified by the first rectifier circuit 12 into a direct current.

The compensation current circuit 2 comprises a commercial power source 1
A constant-potential control circuit 10 is connected in parallel with the constant-potential control circuit 10 between the pipeline 9, the pipeline 7, and the energizing electrode 18, and is configured to output a compensation current, which is a DC current, from a commercial power supply 19. Specifically, as shown in FIG. 1, the compensation current circuit 2 includes a second transformer 21, a second rectifier circuit 22, and a second
And a smoothing circuit 23.

The second transformer 21 is connected to the AC1 of the commercial power supply 19.
00V (or AC200V) voltage of AC2-10
It is for transforming to V. The voltage value after the voltage transformation is configured so that it can be manually set arbitrarily. Second
The rectifier circuit 22 is configured to perform full-wave rectification on the alternating current from the second transformer 21. The second rectifier circuit 22
Are configured to prevent current backflow. The second smoothing circuit 23 is a circuit that converts the current that has been full-wave rectified by the second rectifier circuit 22 into a direct current.

The supply by using a telex apparatus 1 having such a configuration, the constant potential current for the electric potential difference E ₁ between the ground 8 pipeline 7 covering the predetermined value E ₀ in the pipeline 7 And underground 8 regardless of the above potential difference
A constant voltage is always applied between the pipeline 7 and the pipeline 7 to supply a compensation current for maintaining the current supply to the pipeline 7, so that the cathodic protection method can be easily implemented.

That is, the external power device 1 of this embodiment has the above-described constant potential control circuit 10. The potentiostatic control circuit 10 coupled to automatic control circuit 15 compares the predetermined value E ₀ is the electric potential detecting section 15 a target value and the pipe-ground electric potential difference E ₁ was detected, the pipe ground potential E ₁ so it becomes a predetermined value E _0, to control the first rectifier circuit 12. More specifically controls the voltage V ₁ applied to between the pipeline 7 and the energizing electrode 18. Thereby, the constant potential control circuit 10
May the tubes ground potential E ₁ is constantly supplied to the constant potential current to a predetermined value E ₀ or more in the pipeline 7, it is possible to prevent a return flow type electrolytic corrosion.

On the other hand, the constant potential current, when the pipe-ground electric potential difference E ₁ is the predetermined value E ₀ or is not output on the characteristics of the control. Also, when the pipe-ground electric potential difference E ₁ of place where a telex device 1 is excessive, extrusion-type electrolytic corrosion in a state in which easily occurs it becomes smaller tube ground potential in the Far away from the telex apparatus 1 easy.

Here, the external power device 1 of the present embodiment has the compensation current
The circuit 2 is provided. The compensation current circuit 2 is provided with
In parallel with the control circuit 10, the pipeline 7 and the current-carrying electrode
18, a constant voltage V₂Is applied. That
Therefore, the above-mentioned tube-to-ground₁Becomes normal and constant potential current
The constant voltage V ₂
Compensation current continues to be supplied to pipeline 7
You. Therefore, it is possible to prevent the occurrence of extrusion type electrolytic corrosion.
it can.

This will be described with reference to FIG. FIG.
Is the time on the horizontal axis and the tube-to-ground potential difference on the vertical axis. Measured values of the code E ₁ a tube ground potential, E ₀ is the predetermined value. In FIG. 6B, the horizontal axis represents time, and the vertical axis represents a voltage applied from the external power device 1 between the pipeline 7 and the current-carrying electrode 18. The sign of V ₁ is applied from the constant-voltage control circuit 10, which V ₂ is applied from the compensation current circuit 2, in which the V ₃ together,. 3C, the horizontal axis represents time, and the vertical axis represents the current I ₃ supplied from the external power unit to the pipeline 7 through the underground 8.
Is taken.

The figure, in the point A previous and D after the point has a relatively high voltage V ₁ is applied from the constant voltage control circuit 10 to the pipe-ground electric potential difference E ₁ to maintain the E _0,
In between point A at the point D, the compensation voltage lower than the constant voltage V ₂ from the current circuit 2 indicates a state of being applied, also between the point B of the point C, the tubes ground potential E ₁ since is sufficiently maintained is the voltage V ₁ applied from the constant potential control circuit 10 in the state 0 (zero). On the other hand, from the compensation current circuit 2 is in a state constantly constant voltage V ₂ is applied.

In such a state, FIG.
As shown in FIG.
Voltage V applied₃Is the above V₁Is 0
However, the constant voltage V from the compensation current circuit 2₂, And
It is always kept above a certain level. That is, as shown in FIG.
In particular, the corrosion protection current I supplied to the pipeline 7₃Is fixed
When the potential control circuit 10₁(Before B)
And after C), the voltage V₁A match for
Potential current I₃₁Is supplied as an anticorrosion current. In addition,
When the voltage application from the potential control circuit 10 becomes 0,
When the flow is stopped (between BC)
The constant voltage V from the compensation current circuit 2 ₂Is applied
The compensation current I₃₂That the supply of
Become. Therefore, the tube-to-ground potential difference in the distance is maintained normally.
Can prevent extrusion-type electrolytic corrosion
You.

As described above, the external power device 1 of this embodiment can prevent both return-type electrolytic erosion and extrusion-type electrolytic erosion by outputting two types of anticorrosion currents, namely, a constant potential current and a compensation current. it can. In addition, as described above, these effects are
Since this can be exhibited by the external power unit, the equipment cost can also be reduced.

Embodiment 2 In this embodiment, the effect of the external power device 1 of Embodiment 1 was quantitatively evaluated. FIG.
As shown in the figure, the rail 91 of the electric railway is
Let's take the case of crossing as an example. The rail cross section S ₁ near the pipeline 7, has established a telex apparatus 1, the ground 8 is embedded energizing electrode 18. In addition, the S ₂ a point distant 2km from S ₁ point of the rail cross section, and placed potential detector 85 for measuring the tube ground potential E _4.

[0039] Then, in a state of being operated the telex apparatus 1 was measured _{S 1} point and _{S 2} point of the tube ground potential _E 1, _{E 4.} As a result, in the _{S 1} site of telex apparatus 1 near the highest value tube ground potential _{E 1} is 6300 (-m
V) next to, at that time the _{S 2} point of the tube ground potential difference E
₄ became 1800 (-mV).

On the other hand, when a similar test was performed in the case where a conventional constant-potential automatic control type external power unit was installed in place of the external power unit _1, the tube-to-ground potential difference E at the point S1 was determined.
₁ in the case of 6300 (-mV) it is, fell _{S 2} point of the tube ground potential difference _{E 4} up to about 800 (-mV).

From these results, it can be seen that the external power device 1 has a higher effect of maintaining the anticorrosion potential at a distant place than the conventional device, and can exert an excellent effect on the extrusion type electrolytic corrosion.

[0042]

As described above, according to the present invention, it is possible to provide a method for preventing cathodic corrosion of a pipeline and an external anticorrosion device capable of preventing both return-type electrolytic corrosion and extrusion-type electrolytic corrosion. it can.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an external power device for anticorrosion according to a first embodiment.

FIG. 2 shows (a) a tube-to-ground potential difference in Embodiment 1;
(B) Explanatory drawing which shows an output voltage and (c) output current.

FIG. 3 is an explanatory diagram showing an installation state of an anticorrosion external power device according to a second embodiment.

FIG. 4 is an explanatory view showing the principle of generation of (a) return-type electrolytic corrosion and (b) extrusion-type electrolytic corrosion in a conventional example.

[Explanation of symbols]

 1. . . 9. external power device for anticorrosion, . . 10. constant potential control circuit, . . 11. first transformer, . . 12. first rectifier circuit; . . 13. first smoothing circuit; . . Automatic control circuit, 15. . . Potential detection section, 151. . . Reference electrode, 18. . . Current-carrying electrode, 19. . . Commercial power, 2. . . Compensation current circuit, 21. . . Second transformer, 22. . . Second rectifier circuit, 23. . . 6. second smoothing circuit; . . 7. pipeline . . Underground,

Claims (3)

[Claims] In a method for preventing electrolytic corrosion of a pipeline due to stray current, a constant potential current for setting a potential difference between the pipeline and the ground covering the pipeline to a predetermined value is output by a constant potential automatic control output. Supply a constant voltage between the underground and the pipeline regardless of the potential difference, and supply a compensation current for maintaining a current supply to the pipeline. The method of cathodic protection for pipelines. 2. An anticorrosion external power device for supplying an anticorrosion current to a pipeline for preventing electrolytic corrosion of the pipeline due to a stray current, wherein a potential difference between the pipeline and the underground covering the pipeline is determined. A constant potential control circuit for supplying a constant potential current for setting a predetermined value to the pipeline; and a constant voltage applied between the underground and the pipeline regardless of the potential difference, to the pipeline. And a compensation current circuit for supplying a compensation current for maintaining the current supply of the pipeline. 3. The constant-potential control circuit according to claim 2, wherein the constant-potential control circuit is configured to output the constant-potential current, which is a DC current, from a commercial power supply, and outputs the constant-potential current to the pipeline and the pipeline. An automatic control circuit for controlling according to a potential difference from the underground, and a potential detecting unit for detecting the potential difference and sending a potential difference signal to the automatic control circuit, and having a negative side of the constant potential control circuit. Is in the above pipeline,
The + side is connected to each of the current-carrying electrodes buried in the ground, and the compensation current circuit is provided between the commercial power supply, the pipeline, and the current-carrying electrode.
An external power device for protecting a pipeline from corrosion, wherein the external power device is connected in parallel with the constant potential control circuit and configured to output the compensation current, which is a DC current, from the commercial power supply.