JP4190078B2 - Pipeline cathodic protection method and anticorrosion external power device - Google Patents

Description

[0001]
【Technical field】
The present invention relates to a pipeline anticorrosion technique for transporting gas or oil.
[0002]
[Prior art]
For example, as a method for continuously transporting fluids such as gas and oil, a method is widely used in which a pipeline is buried in the ground and the fluid is allowed to flow inside. Normally, a coated steel pipe in which a steel pipe is insulated and coated with polyethylene or the like is used for the pipeline.
[0003]
This coated steel tube has the effect of preventing the occurrence of corrosion by insulating the steel from the outside, but in the unlikely event that a coating malfunctions, taking into account the increase in stray current in recent years, etc. It is necessary to take measures to ensure sufficient anticorrosion.
Therefore, conventionally, measures have been taken for pipelines by installing an Mg anode as a sacrificial electrode, or by installing an external power supply device (hereinafter referred to as an external power device) that supplies anticorrosion current.
[0004]
Although the installation of the Mg anode has an advantage of low cost, the anticorrosion effect is lower than that of an external electric device. For this reason, in an important pipeline for gas transportation or the like, a countermeasure using an external electric device or a combination of an external electric device and a Mg anode is often taken.
In addition, as a conventional external power device, a constant potential automatic is supplied to the pipeline so that the pipeline maintains a sufficient anticorrosion potential with respect to the ground. Controlled external power devices have been widely used.
[0005]
[Problems to be solved]
By the way, electrolytic corrosion in pipelines can be roughly divided into return-type electrolytic corrosion and extrusion-type electrolytic corrosion. These can be explained using an example in which rails of an electric railway that contributes to the generation of stray current crosses the 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.
[0006]
On the other hand, as shown in FIG. 4B, when the train 92 is in an accelerated state near the crossing portion, the potential of the rail 91 is relatively higher than the potential of the pipeline 7. In this case, current 99 flows in the pipeline 7 from the rail 91, then current flows into the ground 8 from the pipeline 7 in the far away from the rail 91, an extrusion-type electrolytic corrosion at distant S ₂ points Occurs.
[0007]
The conventional constant potential automatic control type external electric device is excellent in the effect of preventing “return-type electric corrosion” that occurs when current flows out from the pipeline into the ground at the place where the external electric device is installed. However, it is less effective for countermeasures against “extrusion-type electric corrosion” that occurs when stray currents that flow into the pipeline flow into the ground at a distance away from the location where the external power device is installed.
[0008]
On the other hand, measures can also be taken by installing an external electric device at the location where extrusion-type corrosion occurs, but the equipment cost increases greatly. Further, when the external power device and the Mg anode are used in combination, there are problems such as the occurrence of interference due to the inflow of current from the Mg anode.
Therefore, development of an anticorrosion method and an external electric device capable of taking measures against both the return type electric corrosion and the extrusion type electric corrosion by one unit has been desired.
[0009]
The present invention has been made in view of such conventional problems, and it is intended to provide a pipeline anticorrosion method and an anticorrosion external electric device capable of preventing both return-type electric corrosion and extrusion-type electric corrosion. It is what.
[0010]
[Means for solving problems]
The invention according to claim 2 is a method for preventing electrolytic corrosion of a pipeline due to stray current,
Using the anticorrosion external electric device according to the invention described in claim 1 to be described later, a constant potential current for setting a potential difference between the pipeline and the ground covering the pipeline to a predetermined value by a constant potential automatic control output. And supplying a compensation current for maintaining a current supply to the pipeline by constantly applying a constant voltage between the underground and the pipeline regardless of the potential difference. There is an anticorrosion method for the pipeline.
[0011]
What should be noted most in the present invention is that not only the constant potential current but also the compensation current is supplied to the pipeline, and the supply of current (anticorrosion current) to the pipeline is maintained.
[0012]
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 ground (hereinafter, appropriately referred to as tube-to-ground potential difference) is always maintained at a certain level or higher by the constant potential current and the compensation current. Specifically, a constant potential current is supplied in the vicinity of the anticorrosion site so that the ground potential is always maintained at a predetermined potential or higher than the potential of the pipeline. As a result, the pipeline in the vicinity of the constant potential current supply location can prevent the outflow of current from the pipeline and can prevent “return-type electric corrosion”.
[0013]
On the other hand, when the tube-to-ground potential difference is greater than or equal to a predetermined value, the constant potential current is not output due to its control characteristics. On the other hand, if the tube-to-ground potential difference is sufficiently secured at the place where the external power device is installed 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 electric corrosion occurs. It may be easy.
[0014]
On the other hand, in the present invention, a constant voltage is always applied between the ground and the pipeline so that the compensation current is output. For this reason, even when the constant potential current is not output, the compensation current is output and the anticorrosion current is continuously supplied to the pipeline.
[0015]
Therefore, if the tube ground potential in the vicinity of the installation site of the external power device is greater than or equal to a predetermined value, but the tube ground potential in the distance is about to decrease, the constant potential current is stopped, but the compensation current is supplied. As a result, the far-end tube-to-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 electric device of the present invention can prevent both the return type electric corrosion and the extrusion type electric corrosion by outputting the two types of anticorrosion currents, the constant potential current and the compensation current. Further, since these functions and effects can be exhibited by a single external power device as described above, the equipment cost can be reduced.
[0016]
Therefore, according to the present invention, it is possible to provide a pipeline anticorrosion method capable of preventing both return-type electric corrosion and extrusion-type electric corrosion.
[0017]
Next, the invention according to claim 1 is an anticorrosion external electric device for supplying an anticorrosive current for preventing the electrolytic corrosion of the pipeline due to stray current to the pipeline,
A constant potential control circuit for supplying a constant potential current for setting a potential difference between the pipeline and the ground covering the pipeline to a predetermined value;
By applying a constant fixed voltage between the ground and the pipeline regardless of the voltage difference, it has a a compensation current circuit for supplying a compensation current to maintain the current supply to the pipeline,
The constant potential control circuit is configured to output the constant potential current which is a direct current from a commercial power supply, and controls the value of the constant potential current according to a potential difference between the pipeline and the ground. An automatic control circuit for detecting the potential difference and sending a potential difference signal to the automatic control circuit, wherein the negative side of the constant potential control circuit is the pipeline and the positive side is the above Each is connected to a conducting electrode buried in the ground,
The compensation current circuit is connected in parallel with the constant potential control circuit between the commercial power source and the pipeline and the energizing electrode, and outputs the compensation current as a direct current from the commercial power source. It is comprised in the external electric apparatus for anticorrosion of the pipeline characterized by being comprised .
[0018]
What should be noted most in the present invention is not only the constant potential control circuit but also a compensation current circuit for outputting the compensation current.
In this case, the same effect as the conventional constant potential automatic control type external power supply device by the constant potential control circuit can be exhibited, and when the constant potential current is stopped, the compensation current circuit is used. Compensation current can be supplied to the pipeline. Therefore, the anticorrosion current can be constantly supplied to the pipeline, and as described above, both the return type electric corrosion and the extrusion type electric corrosion can be prevented.
[0019]
Therefore, according to the present invention, it is possible to provide a pipeline anticorrosion external electric device capable of preventing both return-type electric corrosion and extrusion-type electric corrosion.
[0020]
Next , the constant potential control circuit is configured to output the constant potential current which is a direct current from a commercial power supply, and the value of the constant potential current is determined according to a potential difference between the pipeline and the ground. An automatic control circuit for controlling the electric potential, and a potential detection unit that detects the potential difference and sends a potential difference signal to the automatic control circuit. The negative side of the constant potential control circuit is connected to the pipeline, Each side is connected to a current-carrying electrode buried in the ground,
The compensation current circuit is connected in parallel with the constant potential control circuit between the commercial power source and the pipeline and the energizing electrode, and outputs the compensation current as a direct current from the commercial power source. It is configured to.
[0021]
In this case, the automatic potential control circuit controls the constant potential control circuit according to the detection result while constantly detecting the tube-to-ground potential by the potential detection unit, so that the constant potential current can be accurately output. Can do. Also, by supplying the constant potential current by connecting the negative side of the constant potential control circuit to the pipeline and the positive side to the energizing electrode, it is possible to reliably prevent current from flowing from the pipeline to the ground side. 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.
[0022]
In this case, the power supply for the constant potential control circuit and the compensation current circuit can be shared, and the structure of the apparatus 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 INVENTION
Embodiment 1
A pipeline anticorrosion method and an anticorrosion external power device according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the external electric device 1 of this example is an anticorrosion external electric device (hereinafter referred to as an external electric device 1) for supplying the pipeline 7 with anticorrosive current for preventing electric corrosion of the pipeline 7 due to stray current. ).
[0024]
The external electric device 1 is a constant potential control circuit that supplies a constant potential current for setting the potential difference E ₁ (tube-to-ground potential difference) between the pipeline 7 and the underground 8 covering the pipeline 7 to a predetermined value E ₀ to the pipeline 7. 10 and a compensation current circuit 2 that constantly applies a constant voltage between the ground 8 and the pipeline 7 regardless of the potential difference and supplies a compensation current for maintaining the current supply to the pipeline 8. Have.
[0025]
The constant potential control circuit 10, together are configured to output the constant voltage current is a DC current from the commercial power source 19, an automatic to control in accordance with the value of the constant potential current to the tubes ground potential E ₁ a control circuit 14, and a potential detecting section 15 to send the difference signal by detecting a pipe ground potential E ₁ in the automatic control circuit 14. Further, the negative side of the constant potential control circuit 10 is connected to the pipeline 7, and the positive side is connected to the energizing electrode 18 embedded in the ground 8.
[0026]
Further, as shown in FIG. 1, the constant potential control circuit 10 includes a first transformer 11 connected to a commercial power source 19, a first rectifier circuit 12 connected thereto, and a first smoothing circuit 13 connected thereto. The first rectifier circuit 12 is connected to an automatic control circuit 14 having the potential detector 15. The potential detection unit is configured to detect a potential difference between the reference electrode 151 embedded in the ground and the pipeline 7.
[0027]
The 1st transformer 11 is for transforming the voltage of AC100V (or AC200V) of commercial power supply 19 to AC60V.
The first rectifier circuit 12 is configured to full-wave rectify the alternating current from the first transformer 11 and adjust the passing current according to an instruction from the automatic control circuit 14. The first rectifier circuit 12 is configured to prevent a reverse current flow.
The first smoothing circuit 13 is a circuit that converts the current that has been full-wave rectified by the first rectifier circuit 12 into a direct current.
[0028]
The compensation current circuit 2 is connected in parallel with the constant potential control circuit 10 between the commercial power supply 19 and the pipeline 7 and the energizing electrode 18, and outputs a compensation current that is a direct current from the commercial power supply 19. It is configured to
Specifically, the compensation current circuit 2 includes a second transformer 21, a second rectifier circuit 22, and a second smoothing circuit 23 as shown in FIG.
[0029]
The 2nd transformer 21 is for transforming the voltage of AC100V (or AC200V) of commercial power supply 19 to AC2-10V. The voltage value after transformation is configured to be arbitrarily set manually.
The second rectifier circuit 22 is configured to full-wave rectify the alternating current from the second transformer 21. The second rectifier circuit 22 is configured to prevent a backflow of current.
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 direct current.
[0030]
By using the external power device 1 having such a configuration, a constant potential current for setting the potential difference E ₁ between the pipeline 7 and the underground 8 covering the pipeline 7 to a predetermined value E ₀ is supplied to the pipeline 7. Easily implement an anticorrosion method in which a constant voltage is always applied between the underground 8 and the pipeline 7 regardless of the potential difference, and a compensation current is supplied to maintain the current supply to the pipeline 7. be able to.
[0031]
That is, the external power device 1 of this example includes the constant potential control circuit 10. The automatic control circuit 15 connected to the constant potential control circuit 10 compares the tube-to-ground potential difference E ₁ detected by the potential detecting unit 15 with a predetermined value E ₀ that is a target value, thereby comparing the tube-to-ground potential difference E _1. so it becomes a predetermined value E _0, to control the first rectifier circuit 12. Specifically, the voltage V ₁ applied between the pipeline 7 and the energizing electrode 18 is controlled. As a result, the constant potential control circuit 10 can supply a constant potential current to the pipeline 7 so that the tube-to-ground potential difference E ₁ is always greater than or equal to the predetermined value E ₀ , thereby preventing return-type electric corrosion. Can do.
[0032]
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 becomes smaller tube ground potential in the Far away from the telex apparatus 1 easy.
[0033]
Here, the external power device 1 of this example has the compensation current circuit 2. The compensation current circuit 2 always applies a constant voltage V ₂ to the pipeline 7 and the conducting electrode 18 in parallel with the constant potential control circuit 10. Therefore, even when the pipe-ground electric potential difference E ₁ becomes a normal supply of the constant potential current is stopped, the compensation current by the constant voltage V ₂ is continuously supplied to the pipeline 7. Therefore, it is possible to prevent the occurrence of extrusion-type electric corrosion.
[0034]
This will be described with reference to FIG.
FIG. 4A shows time on the horizontal axis and the pipe-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. 5B, the horizontal axis represents time, and the vertical axis represents the voltage applied from the external power device 1 between the pipeline 7 and the conducting electrode 18. Reference numeral V ₁ is applied from the constant potential control circuit 10, V ₂ is applied from the compensation current circuit 2, and V ₃ is a combination thereof.
In FIG. 5C, the horizontal axis represents time, and the vertical axis represents the current I ₃ supplied to the pipeline 7 from the external power supply through the ground 8.
[0035]
The figure shows that before the point A and after the point D, a relatively high voltage V ₁ is applied from the constant potential control circuit 10 in order to maintain the tube-to-ground potential difference E ₁ at E _0. in between, 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 is sufficiently maintained Therefore, the voltage V ₁ applied from the constant potential control circuit 10 is in a state of 0 (zero).
On the other hand, from the compensation current circuit 2 is in a state constantly constant voltage V ₂ is applied.
[0036]
In such a state, as shown in FIG. 5B, the voltage V ₃ actually applied between the pipeline 7 and the conducting electrode 18 is the compensation current even when V ₁ becomes zero. is the value of the constant voltage V ₂ from the circuit 2 are always kept constant or more. That is, as shown in FIG. (C), protective current I ₃ is supplied to the pipeline 7, between the constant voltage control circuit 10 applies a voltage V ₁ (B previous and C later), the potentiostatic current I ₃₁ commensurate with the voltage V ₁ is supplied becomes protective current. When the voltage application from the constant potential control circuit 10 is 0 and the constant potential current is stopped (between B and C), the constant voltage V ₂ is applied from the compensation current circuit 2. _Therefore , the supply of the compensation current I ₃₂ is always ensured. Therefore, the pipe-to-ground potential difference at a distance can be maintained normally, and extrusion-type electric corrosion can be prevented.
[0037]
Thus, the external electric device 1 of this example can prevent both the return type electric corrosion and the extrusion type electric corrosion by outputting two types of anticorrosion currents, that is, a constant potential current and a compensation current. Further, since these functions and effects can be exhibited by a single external power device as described above, the equipment cost can be reduced.
[0038]
Embodiment 2
In this example, the effect of the external power device 1 of Embodiment 1 was quantitatively evaluated. As shown in FIG. 3, the case where the rail 91 of the electric railway crosses the pipeline 7 is taken as an example. In the vicinity of the rail crossing portion S ₁ of the pipeline 7, the external electric device 1 is installed, and the conducting electrode 18 is embedded in the underground 8. 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, the pipe-to-ground potential differences E ₁ and E ₄ at the points S ₁ and S ₂ were measured while the external electric device 1 was operated.
As a result, in the _{S 1} site of telex apparatus 1 near the tube ground potential _{E 1} is the highest value 6300 (-mv), and the tubes ground potential _{E 4} of _{S 2} points in that time, 1800 (-mv) It became.
[0040]
In contrast, when the same test when installing a conventional potentiostatic automatically controlled telex apparatus in place of the telex apparatus 1, tube ground potential E ₁ in the S ₁ point is 6300 (-mv) in the case of, it fell _{S 2} point of the tube ground potential difference _{E 4} up to about 800 (-mV).
[0041]
From these results, it can be seen that the external electric device 1 has a higher effect of maintaining the anticorrosion potential at a distance than the conventional one, and can exert an excellent effect on the extrusion-type electric corrosion.
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a pipeline anticorrosion method and an anticorrosion external electric device capable of preventing both return-type electric corrosion and extrusion-type electric corrosion.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing the configuration of an anticorrosion external power device in Embodiment 1;
FIG. 2 is an explanatory diagram showing (a) tube-to-ground potential difference, (b) output voltage, and (c) output current in Embodiment 1.
FIG. 3 is an explanatory diagram showing an installation state of an external electric device for corrosion prevention in Embodiment 2;
FIG. 4 is an explanatory diagram showing the generation principle of (a) return-type electrolytic corrosion and (b) extrusion-type electrolytic corrosion in a conventional example.
[Explanation of symbols]
1. . . Anti-corrosion external electrical equipment,
10. . . Constant potential control circuit,
11. . . First transformer,
12 . . A first rectifier circuit,
13. . . First smoothing circuit,
14 . . Automatic control circuit,
15. . . Potential detector,
151. . . Reference electrode,
18. . . Conducting electrode,
19. . . Commercial power supply,
2. . . Compensation current circuit,
21. . . Second transformer,
22. . . A second rectifier circuit,
23. . . Second smoothing circuit,
7). . . pipeline,
8). . . Underground,

Claims (2)

  An anti-corrosion external electric device for supplying anti-corrosion current to the pipeline to prevent electric corrosion of the pipeline due to stray current,
  A constant potential control circuit for supplying a constant potential current for setting a potential difference between the pipeline and the ground covering the pipeline to a predetermined value;
  A compensation current circuit for supplying a compensation current for constantly applying a constant voltage between the ground and the pipeline regardless of the potential difference and maintaining a current supply to the pipeline;
  The constant potential control circuit is configured to output the constant potential current which is a direct current from a commercial power supply, and controls the value of the constant potential current according to a potential difference between the pipeline and the ground. An automatic control circuit for detecting the potential difference and sending a potential difference signal to the automatic control circuit, wherein the negative side of the constant potential control circuit is the pipeline and the positive side is the above Each is connected to a current-carrying electrode buried in the ground,
  The compensation current circuit is connected in parallel with the constant potential control circuit between the commercial power source and the pipeline and the energizing electrode, and outputs the compensation current as a direct current from the commercial power source. An external electric device for anticorrosion of a pipeline, characterized in that it is configured to do so.   In the method of preventing the electrolytic corrosion of the pipeline due to the 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 supplied to the pipeline by a constant potential automatic control output. Regardless of the potential difference, a constant voltage is constantly applied between the ground and the pipeline to supply a compensation current for maintaining a current supply to the pipeline. Anticorrosion method.

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