JP5135193B2 - Cathodic protection system and cathodic protection method for buried pipelines using galvanic anode method - Google Patents

Description

  The present invention relates to a cathodic protection system for buried pipelines by an galvanic anode method, and a cathodic protection method using this system.

  Cathodic protection methods used for soil buried pipelines include the galvanic anode method and the external power supply method. In the galvanic anode method, a metal having a negative corrosion potential compared to the anticorrosion target is used as an anode (galvanic anode), which is connected to the anticorrosion target with an electric wire, and the galvanic current is generated by the action of a different metal cell between the galvanic anode and the anticorrosion target This is a method for preventing corrosion by causing the current generated from the anode to flow as an anticorrosive current into the anticorrosion target. In general, Mg (magnesium) anodes are often used as galvanic anodes for steel soil buried pipelines. In the external power supply system, a DC power supply is connected between the electrode (anode) installed in the soil and the anticorrosion target (cathode) to apply voltage, and direct current flows from the electrode through the soil to the anticorrosion target. This is a method for preventing corrosion.

  In the galvanic anode method, the backflow phenomenon in which the stray current flowing through the electrolyte in which the galvanic anode is installed flows from the galvanic anode into the anticorrosion object becomes a problem. For example, when a pipeline buried in soil is cathodic-protected by the galvanic anode method, the galvanic anode is electrically connected to the pipeline at a certain interval. If it is in the vicinity of the transportation path (rail), the leakage current generated when passing through the DC electric railway vehicle may flow into the flowing current anode because the flowing current anode is low-grounded.

  The current flowing into the pipeline through the galvanic anode will flow out of the coating defect to the electrolyte if the pipeline is coated with a high resistivity plastic, When the bituminous coating is applied to the line, it flows out to the electrolyte from a portion having a low ground resistance in the pipeline, and these current outflow portions are corroded.

  In particular, the current flowing through the rail and returning to the substation (referred to as return current) is as large as about 1000 A to 3000 A, and the rail leakage current is about 0.1% of the return current, but it is a large value for the corrosion phenomenon. Intense corrosion may be induced by the inflow of rail leakage current to the current-carrying anode, so that no backflow current from the current-carrying anode toward the anticorrosion target is generated against the DC stray current flowing into the current-carrying anode. Taking measures to prevent backflow is one of the important measures for cathodic protection management.

  Conventionally, as a backflow prevention measure for a current-carrying anode, providing a diode in a forward direction from the object to be corroded toward the current-carrying anode is performed between the wires connecting the object to be corroded and the current-carrying anode (for example, See Patent Document 1 below).

JP 2000-119883 A

  As shown in FIG. 1, when the galvanic anode M is installed near the selective drainage D, a large current caused by lightning strikes from the pipeline or the galvanic anode, If the diode M1 inserted between the pipelines P breaks down and becomes unable to exhibit the backflow prevention function of the diode M1, there arises a problem that the risk of corrosion of the buried pipeline P and the surrounding buried metal body P1 becomes extremely high. (In the drawing, the selective drainage D is connected to the rail R near the substation R2 in the DC electric railway R1, but the installation situation of the selective drainage D is not limited to this).

  If the dielectric breakdown occurs in the diode M1 installed between the current-carrying anode M and the pipeline P when the current-carrying anode M is installed near the position where the selective drainage D is installed, The current sucked up by the current collector D from the current flowing anode M into the pipeline P becomes extremely large, and the risk of corrosion at the outflow location of the current flowing into the pipeline P becomes extremely high. Further, since the current sucked into the pipeline P from the current flowing anode M by the current sucking action of the selective drain D becomes larger, the current from the peripheral electrolyte toward the current flowing anode M becomes a DC stray current, and the pipeline P If there is another buried metal body P1 (for example, another buried pipeline) in the vicinity of, a DC interference in which this DC stray current flows into the other buried metal body P1 occurs.

  As described above, under the situation illustrated in FIG. 1, if the backflow prevention function of the diode M1 provided between the galvanic anode M and the pipeline P is broken, the risk of corrosion of the pipeline P is increased. Since this also causes direct current interference to the other buried metal body P1, it is necessary to quickly resolve such a situation. However, there is no effective means for determining whether or not the diode M1 is normal, and there is a problem that it cannot be dealt with immediately. Although monitoring the voltage between the terminals of the diode M1 or the current flowing through the shunt resistor is also conceivable, under the situation shown in FIG. Since the ground potential of the electric anode M is large and changes frequently, there is a problem that it is not possible to properly determine whether the diode M1 is normal or not only by monitoring the voltage between the terminals of the diode M1 or the current flowing through the shunt resistor. .

  When the pipeline P is a bitumen-coated pipeline, the rail leakage current flows into the pipeline P, and the flowing current is returned to the rail R by the selective drain D. In some cases, the pipe ground potential is more negative than the ground potential of the galvanic anode M near the location of the galvanic anode. In this case, if the backflow prevention function of the diode M1 is normal, the current generated by the galvanic anode is zero, and the anticorrosion situation of the pipeline P itself is good. When a large amount of current flows into the line P, direct current interference to the buried metal body close to the pipeline P occurs.

  And the pipeline P is a bituminous coating pipeline, and there are large coating defects in the bituminous coating and there are metal touches with other buried metal bodies, so When the generated current from the electric anode M is large, it means that the tube ground potential is positive compared to the ground potential of the galvanic anode, and in some cases, the tube ground potential may be more positive than the anticorrosion potential. Therefore, it is necessary to detect such a case and take appropriate measures.

  The present invention has been proposed to cope with such a situation, and in an embedded pipeline in which an galvanic anode is installed, an abnormality of a diode provided between the galvanic anode and the pipeline due to a lightning strike or the like. Can be quickly grasped and dealt with, and even when an galvanic anode is connected in the vicinity of the place where the selective drainage is installed, there is no need to increase the risk of corrosion of the pipeline. It is an object of the present invention to prevent direct current interference with the buried metal body.

In order to achieve such an object, the present invention has the following features.
One is a system for cathodic protection of buried pipelines by means of a galvanic anode, in order from the buried pipeline to the galvanic anode in the connection line that electrically connects the buried pipeline and the galvanic anode. A diode of a direction is inserted, and a constant current control circuit including a switching element for turning on and off the circuit is connected to the connection line in parallel with the diode, and a voltage between terminals of the diode and a main current of the connection line are monitored. Monitor control means for controlling on / off of the switching element, and the monitor control means is configured such that the voltage between the terminals is positive with respect to the forward direction of the diode and not more than a set voltage exceeding the operating voltage of the diode. Depending on whether or not the main current is a constant current value by the constant current control circuit, the embedded pipeline is turned on. And judging the corrosion situation.

  One is a method of cathodic protection of the buried pipeline by the galvanic anode method. The connection line electrically connecting the buried pipeline and the galvanic anode is directed from the buried pipeline to the galvanic anode. When a diode in the forward direction is inserted and the voltage between the terminals of the diode exceeds the value obtained by subtracting the ground potential of the galvanic anode from the anticorrosion potential, or becomes a negative value in the reverse direction with respect to the forward direction of the diode. When the voltage between the terminals of the diode is positive with respect to the forward direction of the diode and is equal to or less than the value obtained by subtracting the ground potential of the current anode from the anticorrosion potential. It is characterized by controlling to a constant current value.

  According to such a feature, the galvanic anode generation current is monitored by associating the condition that the constant current control circuit is turned on with the anticorrosion potential of the buried pipeline, and whether or not this is a constant current value, the buried pipe is monitored. It is possible to grasp the anticorrosion status of the line. In other words, as long as the constant current value is monitored, it can be said that the buried pipeline has no coating defects or metal touch and is sound in terms of cathodic protection management. The cathodic protection situation can be properly evaluated.

  Also, an abnormality occurred in the diode provided between the current-carrying anode and the pipeline due to lightning strikes, or the ground potential of the current-carrying anode became more positive than the tube-to-ground potential, or the tube-to-ground potential exceeded the anticorrosion potential When this happens, the constant current control circuit is turned off due to the voltage change between the current-carrying anode and the pipeline, making it impossible to monitor the constant current value. It is possible to quickly grasp and deal with the occurrence of direct current interference.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is an explanatory diagram for explaining a cathodic protection system for a buried pipeline by the galvanic anode method according to the embodiment of the present invention. The buried pipeline P has an outer surface covered with a bituminous coating, etc., and an galvanic anode M (for example, Mg anode) is electrically connected to the buried pipeline P via a connection line L. Yes.

  A forward diode 10 is inserted from the buried pipeline P toward the galvanic anode M in a connection line L that electrically connects the buried pipeline P and the galvanic anode M. The diode 10 has a high Zener voltage, and even if the voltage between the terminals of the diode 10 is negative (the potential on the galvanic anode side is more positive than the tube-to-ground potential) The current flowing through the connection line L is kept at zero, and a backflow prevention function is provided in which no current flows from the flowing current anode M to the buried pipeline P. A shunt resistor 11 is inserted in the connection line L in series with the diode 10. The shunt resistor 11 is used for monitoring a main current (a galvanic anode generated current) flowing through the connection line L.

  A constant current control circuit 20 including a switching element 21 for turning on and off the circuit is connected to the connection line L in parallel with the diode 10. The constant current control circuit 20 is configured by connecting a switching element 21, a battery power source (dry battery as an example) 22, and a variable resistor 23 in series. When the switching element 21 is turned on, the constant current control circuit 20 is connected to the connection line L, and a constant current from the buried pipeline P toward the galvanic anode M flows through the connection line L. The constant current value can be adjusted by the variable resistor 23. When the switching element 21 is turned off, the constant current control circuit 20 is disconnected from the connection line L. The connection line L has a pipe-to-ground potential of the buried pipeline P and a galvanic anode-to-ground potential of the flowing anode M. A current corresponding to the potential difference between them and the operating characteristics of the diode 10 flows.

  Monitor control means 30 is provided for monitoring the voltage between the terminals of the diode 10 and the main current of the connection line L to control the switching element 21 on and off. The monitor control means 30 is connected to the contact E1 on the side of the galvanic anode of the diode 10 and the contact E2 on the side of the buried pipeline P of the diode 10 and monitors the voltage between the contacts (voltage V between terminals). Further, a main current (a galvanic anode generation current) I flowing through the shunt resistor 11 connected to the contacts E3 and E4 on both sides of the shunt resistor 11 is monitored. Then, on / off control of the switching element 21 is performed based on the monitoring result of the inter-terminal voltage V, and the anticorrosion status of the buried pipeline P is determined based on the monitoring result of the main current I.

As the on / off control, the switching element 21 is turned on in a state where the voltage V between the terminals is positive with respect to the forward direction of the diode 10 and is not more than the set voltage V _F exceeding the operating voltage of the diode 10. That is, when the inter-terminal voltage V exceeds the set voltage V _F , the switching element 21 is turned off, and only the shunt resistor 11 and the diode 10 are connected between the buried pipeline P and the galvanic anode M. Even when the voltage V between the terminals becomes negative, the switching element 21 is turned off, and only the shunt resistor 11 and the diode 10 are provided between the buried pipeline P and the galvanic anode M. Connected.

When the voltage V between the terminals is positive with respect to the forward direction of the diode 10 and is not more than the set voltage V _F exceeding the operating voltage of the diode 10, the switching element 21 is turned on, and constant current control is performed on the connection line L. The circuit 20 is connected.

FIG. 3 is an explanatory diagram showing the relationship between the terminal voltage V and the galvanic anode generation current I when using the cathodic protection system of the buried pipeline by the galvanic anode method according to the embodiment of the present invention. As shown in the figure, when the inter-terminal voltage V is between 0 and the set voltage V _F , the galvanic anode generation current I is controlled to a constant current value I _C , and when the inter-terminal voltage V exceeds the set voltage V _F , The constant current control circuit 20 is disconnected from the connection line L, becomes a diode operating region, and generates a galvanic anode generation current I corresponding to the operating characteristics of the diode 10.

Further, when the voltage V between the terminals is negative (when the potential of the contact E1 is more positive than the potential of the contact E2), it becomes a diode operating region up to the Zener voltage V _Z , and the galvanic anode generation current I is 0. However, when the inter-terminal voltage V becomes negative with respect to the Zener voltage V _Z , current from the galvanic anode M to the buried pipeline P flows due to the reverse characteristics of the diode 10.

According to such a system, depending on whether or not the galvanic anode generation current (main current) I is a constant current value I _C by the constant current control circuit 20, the cathodic protection status of the buried pipeline and the direct current to other buried metal bodies are determined. It becomes possible to determine the risk of occurrence of interference. For this purpose, set to a value associated with the setting voltage V _F to the corrosion potential. Specifically, to a value obtained by subtracting the ground potential from corrosion potential galvanic anode M of buried pipeline P the set voltage V _F. In this way, by detecting that the galvanic anode generation current I is not a constant current value I _C by monitoring the galvanic anode generation current I, it is possible to determine the anticorrosion situation and the high risk of DC interference occurrence. It can be performed.

The galvanic anode M will be described more specifically as an Mg (magnesium) anode. Pipe potential to ground (P / S) (potential difference between buried pipeline P and surrounding ground) and ground potential of flowing anode M (Mg / S) (potential difference between flowing current anode M and surrounding ground) Since the relationship with the inter-terminal voltage V is V = {(P / S) − (Mg / S)}, if V _F = {(corrosion prevention potential) − (Mg / S)}, V ≧ V The state of _F becomes {(P / S) − (Mg / S)} ≧ {(anticorrosion potential) − (Mg / S)}, that is, (P / S) ≧ (anticorrosion potential). It shows that the potential (P / S) is on the plus side of the anticorrosion potential.

In the system according to the embodiment of the present invention, a state where the constant current value I _C is not continued in the monitoring of the galvanic anode generation current I in the state according to the embodiment of the present invention, where the corrosion risk that (P / S) ≧ (corrosion prevention potential) is satisfied. It can be grasped by detecting. (P / S) state of ≧ (corrosion potential), that is, a state of V ≧ V _F, the switching element 21 is a constant current control circuit 20 is switched off is disconnected from the connection line L, whereby a constant current A continuous output of value I _C cannot be obtained.

In addition, since the state of V = {(P / S)-(Mg / S)} <0 is the state of (P / S) <(Mg / S), the galvanic anode M to the buried pipeline P This is a state where the risk of inflow of DC stray current is high, and the state where the risk of occurrence of DC interference with other buried metal bodies is high, which is also an inappropriate state in terms of anticorrosion management. In the system according to the embodiment of the present invention, by detecting a state where the constant current value I _C does not continue by monitoring the galvanic anode generation current I, (P / S) <(Mg / S). It is also possible to grasp an inappropriate state.

Then, in the system according to the embodiment of the present invention, in the case of 0 ≦ V <V _F is the operation of the constant current control circuit 20, the protection current from the galvanic anode M constant current value I _C is generated become. The constant current value I _{C at} this time can be adjusted by the variable resistor 23 of the constant current control circuit 20. Since the state of 0 ≦ V <V _F is cathodic protection administrative pipeline P itself is in a state no problem, the constant current value I _C is preferably set to a low value which does not cause excessive corrosion and DC interference. In addition, since the constant current source is the battery power source 22, in order to replace the battery power source 22 at the time of periodic inspection once a year, it is preferable to set a value suitable for it.

  FIG. 4 is an explanatory view showing a more specific example of the cathodic protection system for buried pipelines by the galvanic anode method according to the embodiment of the present invention. Parts that are the same as those in FIG. 2 are assigned the same reference numerals and redundant description is omitted. In this example, the lightning protection elements 12 and 13 are inserted into the connection lines L on both the buried pipeline P side and the galvanic anode M side of the diode 10. The lightning protection means 12 and 13 are elements for protecting the diode 10 and the constant current control circuit 20 from a lightning surge, and can be constituted by a physical element (varistor) or a circuit having a lightning protection function. By providing the lightning protection means 12 and 13, it is possible to withstand lightning surges within the allowable range of the lightning protection means 12 and 13, and to protect the diode 10 and the constant current control circuit 20 from lightning surges. it can.

  For lightning surges exceeding the allowable range of the lightning protection means 12 and 13, an abnormality is detected by the function of the monitor control means 30, and this is remotely notified. That is, the monitor control unit 30 includes an abnormality detection signal output unit 31 and an abnormality detection signal transmission unit 32. Moreover, the monitor control means 30 is provided with the data storage means 33 as needed.

The abnormality detection signal output means 31 of the monitor control means 30 detects that the galvanic anode generation current I is continuously larger than the constant current value I _C and outputs an abnormality detection signal. Further, the abnormality detection signal output means 31 detects that the galvanic anode generation current I is continuously zero or in a negative state opposite to the forward direction of the diode 10 and outputs an abnormality detection signal. That is, the abnormality detection signal output means 31 compares the monitored galvanic anode generation current I with the constant current value I _C set by the constant current control circuit 20, and the state of I> I _C is set for a set time (for example, (24 hours) Anomaly detection signal is output when continuous. Further, the abnormality detection signal output means 31 outputs an abnormality detection signal when the state of I ≦ 0 continues for a set time (for example, 24 hours) in comparison with the monitored galvanic anode generation current I. The “abnormality” in the case where this abnormality detection signal is output is present in the vicinity of the buried pipeline P and the abnormality with respect to the soundness of the anticorrosion situation of the buried pipeline P including the failure of the backflow prevention function of the diode 10. If the abnormality is detected with respect to the DC interference risk of the other buried metal body P1, and the abnormality is detected, the countermeasure is examined on the assumption that the corrosion risk of the buried pipeline P and the DC interference risk of the other buried metal body P1 are increased.

  Moreover, the abnormality detection signal transmission means 32 transmits an abnormality detection signal to the management server in a remote place. According to this, the abnormality of the whole system including the soundness in the anticorrosion management of the buried pipeline P and the DC interference risk of the other buried metal body P1 can be grasped at a remote place.

  As shown in FIG. 1, the cathodic protection method using the cathodic protection system for the buried pipeline by the galvanic anode method is arranged near the buried pipeline P where the selective drainage D is installed. An example in which is connected will be described.

  In such an installation situation, when the selective drainage D is operated, the DC stray current in the vicinity of the buried pipeline P is sucked up, so that there is a risk of DC interference in the nearby buried metal body P1 (for example, buried metal pipeline). I will let you. Generally, the variable resistor of the selective drain D is adjusted to set the magnitude of the drain current so that no DC interference risk occurs. However, if the backflow prevention function for the flowing current anode M is impaired, the direct current stray current flows into the flowing current anode M having a low ground resistance due to the stray current sucking action of the selective drain D, and the direct current stray current toward the flowing current anode M is lost. As a result, a risk of direct current interference of the buried metal body P1 located in the vicinity of the buried pipeline P is generated. In the cathodic protection method according to the embodiment of the present invention, by preventing the DC stray current from flowing in and out between the current-carrying anode M and the surrounding electrolyte even when the selective drainage D is in operation, The risk of direct current interference of the buried metal body P1 located in the vicinity of the buried pipeline P is avoided, and further, whether the buried pipeline P is sound in terms of corrosion prevention management is monitored.

For this reason, in the cathodic protection method according to the embodiment of the present invention, the forward direction from the buried pipeline P to the galvanic anode M is connected to the connection line L that electrically connects the buried pipeline P and the galvanic anode M. The diode 10 is inserted, and when the inter-terminal voltage V of the diode 10 exceeds the value obtained by subtracting the ground potential (Mg / S) of the galvanic anode M from the anticorrosion potential, or in the reverse direction to the forward direction of the diode 10 The diode 10 is operated when the negative value becomes negative, and the voltage V between the terminals of the diode 10 is positive with respect to the forward direction of the diode 10 and the ground potential (Mg / S) of the galvanic anode M from the anticorrosive potential When the value is equal to or less than the subtracted value, the galvanic anode generation current I is controlled to a constant current value I _C.

And the situation where the galvanic anode generation current I does not maintain the constant current value I _C is detected, and the anticorrosion situation of the buried pipeline P is determined to be abnormal. When DC stray current such as rail leakage current flows into the buried pipeline P, the pipe ground potential (P / S) of the buried pipeline P is more positive and negative than the ground potential (Mg / S) of the galvanic anode M. In both cases, the corrosion of the buried pipeline P or the other buried metal body P1 and the operating state of the diode 10 can be determined by monitoring the galvanic anode generation current I in any of these cases. I can grasp it. A specific example for each case will be described below.

Case of (P / S)> (Mg / S);
For _{0 ≦ V <V F V F} = {( corrosion potential) - (Mg / S)} is set to, anticorrosion potential -1200mV _CSE (saturated copper sulfate electrode standard), (Mg / S) to -1500 mV _CSE Then, V _F = 300 mV. In the case of 0 ≦ V <V _F, as described above (P / S) has become a negative value than anticorrosion potential, the buried pipeline P in good cathodic protection conditions. Although (P / S) is a negative value from the anticorrosion potential, it is a positive value from (Mg / S), and therefore there is no risk of direct current interference of the buried metal body P1 in the vicinity of the pipeline. In this state, constant current control is performed, and a current having a constant current value I _C is caused to flow from the buried pipeline P to the galvanic anode M. By detecting the maintenance state of the constant current value I _C , it is possible to grasp what operating region the diode 10 is in.

The constant current value I _C is set to 1 mA, for example. In this case, the battery power source 22 of the constant current control circuit 22 is two alkaline dry cell types. Assuming that the electric capacity of the AA battery is 10000 mAh, the year of 8760 hours is within the battery life, and the battery power supply 22 can be maintained by replacing it once a year during regular inspections. . The remaining 1240 mAh of the electric capacity 8760 mAh consumed at a constant current value of 1 mA can be used for transmission of an abnormality detection signal or the like.

In the case of V _F ≦ V In this case, there is a defect in the coating of the buried pipeline P, or there is a metal touch (metallic contact) between the buried pipeline P and another buried metal body. As a result of this, (P / S) indicates a value greater than positive, indicating that the buried pipeline P is not in the proper cathodic protection state. In this case, since the constant current control circuit P is disconnected from the connection line L, the constant current value I _C cannot be maintained. As the inter-terminal voltage V increases, the main current I flowing through the diode 10 increases, thereby inducing the risk of direct current interference of the buried metal body P1 in the vicinity of the buried pipeline P. Therefore, such a state continues. For example, if it continues for 24 hours, the abnormality detection signal transmission means 32 is operated, and an abnormal state is transmitted to a remote management server.

Case of (P / S) ≦ (Mg / S);
In the case of V _Z <V <0, V _Z is a Zener voltage at which a reverse current starts to flow when a reverse voltage of the diode 10 is applied, as shown in FIG. When V _Z <V <0, the current is in the operating region of the diode 10, and the backflow prevention function of the diode 10 works to keep the galvanic anode generation current I at zero. Here, the diode 10 having a Zener voltage V _{Z that} is as large as possible on the negative side is used so that an appropriate backflow prevention function works even in the situation of (P / S) ≦ (Mg / S). In this case, the galvanic anode generation current I is zero, but if this state occurs continuously for 24 hours, the induction of the direct current interference risk of the buried metal body P1 in the vicinity of the buried pipeline P and the selective drain D If this state continues, the abnormality detection signal transmission means 32 is operated to transmit the abnormality state to the remote management server.

In the case of V ≦ V _{Z In} this case, since the voltage V between the terminals is on the negative side of the Zener voltage V _Z , the DC stray current flows into the galvanic anode M, and is selectively discharged from the buried pipeline P through the connection line L. It flows to the flow device D. At this time, since the galvanic anode M works to absorb the DC stray current, the DC interference risk of the embedded metal body P1 in the vicinity of the embedded pipeline P is induced. In addition, the fact that a large backflow current flows may indicate a failure of the diode or the variable resistor of the selective drain D. If such a state continues continuously for 24 hours, the abnormality detection signal transmission means 32 is also operated, and the abnormality state is transmitted to a remote management server.

It is explanatory drawing which showed the state which installed the electromotive anode near the selective exhaust device. It is explanatory drawing explaining the cathodic protection system of the buried pipeline by the galvanic anode system which concerns on embodiment of this invention. It is explanatory drawing which showed the relationship between the voltage V between terminals at the time of using the cathodic protection system of the buried pipeline by the flowing current anode system which concerns on embodiment of this invention, and the flowing current anode generation | occurrence | production current I. It is explanatory drawing which showed the more specific example of the cathodic protection system of the buried pipeline by the galvanic anode system which concerns on embodiment of this invention.

Explanation of symbols

P: buried pipeline, P1: buried metal body, M: galvanic anode, L: connecting wire,
10: Diode, 11: Shunt resistance, 12, 13: Lightning protection means,
20: constant current control circuit, 21: switching element, 22: battery power supply, 23: variable resistor, 30: monitor control means, 31: abnormality detection signal output means, 32: abnormality detection signal transmission means, E1, E2, E3 E4: Contact

Claims (10)

A system for cathodic protection of buried pipelines using a galvanic anode method,
Insert a forward diode from the buried pipeline toward the galvanic anode into the connecting line that electrically connects the buried pipeline and the galvanic anode,
A constant current control circuit including a switching element for turning on and off the circuit is connected to the connection line in parallel with the diode,
Monitor control means for monitoring the voltage between the terminals of the diode and the main current of the connection line to control the on / off of the switching element,
The monitor control means turns on the switching element in a state in which the voltage between the terminals is positive with respect to the forward direction of the diode and not more than a set voltage exceeding the operating voltage of the diode, and the main current is controlled by the constant current control. A cathodic protection system for buried pipelines using an galvanic anode method, wherein the corrosion prevention status of the buried pipeline is determined based on whether or not a constant current value is generated by a circuit.   2. The cathodic protection system for buried pipelines by the galvanic anode method according to claim 1, wherein the set voltage is a value obtained by subtracting the ground potential of the galvanic anode from the anticorrosion potential.   3. The cathodic protection system for buried pipelines by the galvanic anode method according to claim 1 or 2, wherein the constant current value is 1 mA.   The galvanic anode method according to any one of claims 1 to 3, wherein the monitor control means detects that the main current is continuously larger than the constant current value and outputs an abnormality detection signal. Cathodic protection system for buried pipelines.   2. The monitor control means outputs an abnormality detection signal by detecting that the main current is continuously zero or a negative state in the reverse direction with respect to the forward direction of the diode. Cathodic protection system for buried pipelines using the galvanic anode method according to any one of -4.   The buried pipeline according to any one of claims 1 to 5, wherein lightning protection means is inserted into both the connecting line on the buried pipeline side of the diode and the connecting line on the current-carrying anode side. Cathodic protection system.   6. The cathodic protection system for buried pipelines according to the galvanic anode method according to claim 4, wherein the abnormality detection signal is transmitted to a remote management server via communication means. A method for cathodic protection of a buried pipeline by a galvanic anode method,
Insert a forward diode from the buried pipeline toward the galvanic anode into the connecting line that electrically connects the buried pipeline and the galvanic anode,
The diode is operated when the voltage between the terminals of the diode exceeds a value obtained by subtracting the ground potential of the current-carrying anode from the anticorrosive potential or when the value becomes a negative value in the reverse direction with respect to the forward direction of the diode. ,
When the voltage between the terminals of the diode is positive with respect to the forward direction of the diode and is equal to or less than the value obtained by subtracting the ground potential of the galvanic anode from the anticorrosive potential, the galvanic anode generation current is controlled to a constant current value. Cathodic protection method for buried pipelines using the galvanic anode method.   The buried pipeline cathodic protection method according to claim 8, wherein a situation in which the current flowing from the galvanic anode is not maintained at the constant current value is detected to determine that the corrosion protection status of the buried pipeline is abnormal.   10. The method of cathodic protection for buried pipelines according to claim 8, wherein the galvanic anode is connected in the vicinity of a place where the selective drainage is installed.

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