JP5231899B2 - Cathodic protection method for pipelines - Google Patents

Description

  The present invention relates to a method for cathodic protection of a pipeline, and more particularly, to a method for cathodic protection of a pipeline that is embedded so as to cross under a railroad crossing portion of a DC electric railway and is laid through a sheath pipe disposed under the railroad crossing portion. .

  The railroad crossing portion of the DC electric railway has a portion of the rail buried in the ground so that vehicles and people crossing the railroad crossing can smoothly travel, and the rail is in a grounded state. Further, a groove is formed between the rail and the ground so that the wheel fits on the rail, and rainwater, dust, etc. accumulate in the groove and the grounding resistance tends to be low. Therefore, when a current flows through the rail during the operation of the DC electric railway vehicle, a current flowing out from the rail to the ground (referred to as a rail leakage current) is likely to be generated (in other words, the rail leakage resistance is low).

  In addition, since a recent DC electric railway uses a regenerative braking vehicle, the DC electric railway vehicle itself may have a function of sucking current from the ground to the rail like a substation. May be positive or negative (referred to as rail-to-ground potential). In such a level crossing section, when the rail ground potential is positive, as shown from point A to point B in FIG. 1A, the ground potential gradually increases toward the negative potential as the distance from the level crossing increases. When the rail-to-ground potential is negative, as shown in FIG. 1 (b) from point F to point G, the ground potential gradually increases toward the positive potential as the distance from the level crossing increases. This indicates a ground potential gradient.

  The pipeline buried so as to cross under the railroad crossing is in the above-described ground potential gradient as shown at point D in FIG. 1A or point I in FIG. At both ends of the pipeline, the ground potential changes from plus to minus, such as point C to point E in Fig. 1 (a), or from minus to plus, such as point H to point J in Fig. 1 (b). , Current flows in and out easily, that is, the corrosion risk is high. In particular, as shown in FIG. 4B, when the rail ground potential is negative, a large current outflow tends to occur at the center of the railroad crossing, so if a coating defect occurs at such a location. There is a risk of causing a major corrosion accident. Therefore, when the railroad crossing is in a state where the risk of corrosion is high, it is necessary to avoid the risk of corrosion by supplying a sufficient cathodic protection current to the pipeline.

  On the other hand, the rail-to-ground potential around the railroad crossing varies greatly and frequently depending on the operation status of the DC electric railway vehicle, and the supply of the cathodic protection current may be minimal when the DC electric railway vehicle is not operating. If the cathodic protection current is supplied to the pipeline without paying attention to such a situation where there is a high risk of corrosion without taking this situation into consideration, the pipeline becomes over-corrosion when the DC electric railway vehicle is not in operation, etc. There is a problem of over-corrosion risk such as cathodic stripping of the covering and hydrogen stress cracking, and in the situation where other buried pipelines cross under the railroad crossing, part of the cathodic protection current flows into the other buried pipelines. There is a problem in which a phenomenon in which electrolytic corrosion occurs at the outflow point (this phenomenon is called DC interference) occurs. Therefore, it is necessary to efficiently supply the cathodic protection current to the pipeline embedded so as to cross under the railroad crossing according to the state of occurrence of the corrosion risk.

  As a method for cathodic protection of a pipeline embedded so as to cross under a railroad crossing part of such a DC electric railway, for example, the following Non-Patent Document 1 describes a point where the pipe-to-ground potential is the most positive (the most cathodic protection situation). It is described that a reference electrode is installed at a bad point) and the cathodic protection current output from the anode of the external power supply system is adjusted by a constant potential automatic control rectifier.

In Patent Document 1 below, a local cathodic protection system is installed in the vicinity of the level crossing in addition to the main external power source cathodic protection system installed in one anticorrosion area. The minimum value of the probe inflow DC current density that flows into the probe installed under the railroad crossing is the minimum required probe inflow DC current density ( It is described that the setting is made to be 0.1 A / m ² ) or more. In this case, the direction in which the direct current flows from the electrolyte into the probe (cathodic protection direction) is positive. Further, the measurement condition of the probe inflow DC current density described above is assumed to be when it is raining and when the DC electric railway vehicle passes through the railroad crossing, and the measurement value measured at predetermined time intervals of the probe DC current density and the The constant potential control described above is performed when a positive correlation with the measured value of the rail-to-ground potential at the rail crossing measured at the same time as the measured value is confirmed and a statistically significant positive correlation is confirmed.
A. W. “Control of pipeline corrosion” by Peabody, NACE International, 1967, p. 145 JP 2007-291433 A

  Under the railroad crossing, a pipe protection sheath such as a fume pipe or steel sheath pipe is installed so that the wheel load of the vehicle crossing the railroad crossing does not act on the pipeline. Pipeline is laid. Under such circumstances, if the method described in Non-Patent Document 1 described above is to be adopted, there are the following problems.

  One problem is that there is no appropriate verification electrode installed in the sheath tube as a verification electrode for constantly controlling the cathodic protection current. There is no guarantee that a saturated copper sulfate electrode will have a liquid junction over a long period of time in an electrolyte (usually mortar) environment in a sheath tube when trying to use a normally used saturated copper sulfate electrode (in the saturated copper sulfate electrode There is a risk that the saturated copper sulfate solution will flow into the electrolyte and no longer exhibit an electrode potential). Instead of using a saturated copper sulfate electrode, a permanent saturated copper sulfate electrode, or a metal electrode such as a zinc reference electrode or a magnesium reference electrode, the permanent saturated copper sulfate electrode installed in the sheath tube itself will be used for a long time. Cannot be confirmed to show a stable electrode potential. Further, in the metal electrode, the metal does not show a stable electrode potential in the ground potential gradient zone.

  In addition, the constant potential control using the reference electrode has a problem that the AC corrosion risk of the pipeline cannot be evaluated. In situations where there is a large risk of AC corrosion, constant potential control of the cathodic protection current should be performed on the assumption that the probe AC current density has passed the cathodic protection standard. If not, first, AC corrosion risk reduction measures are taken to confirm that the probe AC current density has passed the cathodic protection standard, and then the constant potential control of the cathodic protection current is performed. In the method described in Non-Patent Document 1, the probe current is not measured, and therefore there is a problem that the AC corrosion risk cannot be evaluated using the probe AC current density which is an AC component of the probe current density.

  On the other hand, since the conventional technique described in Patent Document 1 described above measures the probe current density, it is possible to evaluate the AC corrosion risk together. Although this conventional technology can achieve effective cathodic protection at railroad crossings, it directly measures the rail ground potential and correlates the probe DC current density with the rail ground potential to confirm the high corrosion risk. Therefore, there is a problem that it is difficult to carry out with a dangerous and difficult work of measuring the rail ground potential during operation of the DC electric railway vehicle.

  Also, if the cathode anti-corrosion current supplied to the pipeline by detecting the pipe ground potential state at the level crossing is controlled at a constant potential, if the pipe ground potential state changes frequently and greatly like the level crossing part, The DC power supply is turned off. Therefore, as in the example shown in Patent Document 1, there is no problem when local cathodic protection is applied to the railroad crossing and the entire anticorrosion area is subjected to overall cathodic protection by another main external power source. If you try to perform cathodic protection of the entire anticorrosion area including the railroad crossing with this DC power supply device, the pipeline in the anticorrosion area may become non-corrosive, and there is a risk of corrosion risk in areas other than the railroad crossing. .

  The present invention has been proposed to cope with such a situation, and reliably avoids the risk of corrosion of a pipeline embedded so as to cross under a railroad crossing portion of a DC electric railway. It is possible to efficiently supply the cathodic protection current without over-corrosion protection and direct current interference to other buried pipelines, and the pipeline laid through the sheath pipe placed under the rail crossing. Therefore, it is possible to control the cathodic protection current output while accurately grasping the cathodic protection situation under the railroad crossing, and to evaluate the AC corrosion risk. To provide a method that is easy to implement by avoiding the measurement of a pipeline, and a cathode cathodic protection system that is installed in the entire anticorrosion area including the railroad crossing. It like can be performed anticorrosion properly is an object of the present invention.

In order to achieve such an object, the present invention has the following features. One is a cathodic protection method for a pipeline that is buried so as to cross under a railroad crossing portion of a DC electric railway and is laid through a sheath pipe disposed under the railroad crossing portion, the railroad crossing in the sheath pipe The only probe that is installed in the center of the unit and that simulates the coating defect portion of the pipeline is connected to the pipeline, and the probe current in the probe and the probe on potential in the probe are measured within the set measurement time. It has a pre-measurement step to measure at the same time, so that the probe DC current density always passes the cathodic protection standard by utilizing the high correlation between the probe DC current density obtained from the measured probe current and the probe on potential. flop to be measured by the control reference electrode installed outside the ground potential gradient zone set reference value and in the crossing portion The constant current control for controlling the output current of the DC power supply device connected to the pipeline by comparing the turn-on potential, the average value of the probe DC current density is the output current of the DC power supply device connected to the pipeline. Control is performed by superimposing constant current control for controlling to a constant current value set so as to pass the cathodic protection standard .

Another one is a cathode anticorrosion method for a pipeline that is buried so as to cross under a railroad crossing portion of a DC electric railway, and is laid through a sheath pipe disposed under the railroad crossing portion. The only probe that is installed at the center of the railroad crossing and that simulates the coating defect portion of the pipeline is connected to the pipeline, and the probe current in the probe and the probe on in the probe within the set measurement time. A pre-measurement step of simultaneously measuring a potential, obtaining a probe DC current density from the measured probe current, obtaining a minimum value in the section of the probe DC current density for each basic section in the measurement time, The smallest value in the zone and the probe-on potential at the time of its appearance as one set of data, and the highest value in the interval from all the set data at the measurement time. When the correlation between the value and the probe-on potential is obtained and a significant correlation is found between the minimum value in the section and the probe-on potential, the set data having the probe-on potential on the minus side of the set threshold is A threshold having a minimum value in the section that is equal to or higher than the minimum required probe inflow DC current density is set, and when controlling the output current of the DC power supply device connected to the pipeline, the threshold is used as a reference value in the crossing section. Control in which constant current control that outputs a desired constant current is superimposed on constant potential control that controls the probe-on potential measured by the reference electrode for control installed outside the ground potential gradient zone to the reference value. It is characterized by performing .

  In the present invention having such a feature, when controlling the output current of the DC power supply device connected to the pipeline, a probe is installed in the sheath tube under the crossing, and the probe current and the probe-on potential are measured simultaneously. Using a high correlation between the probe DC current density obtained from the probe current and the probe ON potential, a constant based on the probe ON potential measured by the control reference electrode is used so that the probe DC current density always passes the cathodic protection standard. Potential control is performed. As a result, the cathodic protection current can be supplied while detecting the cathodic protection status under the level crossing with the probe on potential that is highly correlated with the probe DC current density. Thus, the risk of corrosion of the pipeline buried so as to be reliably avoided.

  Also, by measuring the probe-on potential with respect to the control reference electrode, the output control of the DC power supply device is performed while detecting the pipe-to-ground potential state under the railroad crossing, which changes depending on the operation status of the DC electric railway vehicle, etc. On the other hand, the cathodic protection current can be efficiently supplied without inconveniences such as over-corrosion and direct current interference with other buried pipelines.

  Only one probe is placed in the sheath pipe placed under the railroad crossing, and no reference electrode is placed in the sheath pipe or in the ground potential gradient zone, so the probe-on potential is stabilized via the reference electrode. Can be measured. Therefore, it is possible to control the output of the cathodic protection current while accurately grasping the cathodic protection status under the railroad crossing and the status of changes in the probe-on potential, even for pipelines laid through the sheath pipes installed under the railroad crossing. is there. The probe-on potential that is detected to control the output of the cathodic protection current is measured by installing a control reference electrode outside the ground potential gradient zone, so a metal electrode is used as the control reference electrode. Stable and continuous measurement can be performed.

  Since the probe is installed in the sheath tube under the railroad crossing and the probe current is measured, it is possible to evaluate the AC corrosion risk by the probe AC current density which is the AC component of the probe current. Therefore, when it is evaluated that the AC corrosion risk is high, it is possible to control the output of the cathodic protection current after taking AC corrosion risk reduction measures such as connection of AC induction reducing means.

  In addition, since the measurement of the rail ground potential having a direct contact with the rail can be omitted when the cathodic protection current is supplied, a method that is easy to implement can be provided.

  Even when the probe-on potential under the railroad crossing is frequently and greatly changed, the cathodic protection current is set so that the probe direct current density passes the cathodic protection standard (above the minimum required probe inflow direct current density) in all states. In addition, it controls the potential and outputs a constant cathodic protection current at all times so that the probe DC current density passes the cathodic protection standard on average regardless of the probe on potential below the level crossing. In addition, it is possible to always maintain a good cathodic protection state even under a railroad crossing that greatly changes, and it does not create an anticorrosion state in which the DC power supply is turned off. As a result, a predetermined anticorrosion area including under the railroad crossing, while properly performing local cathodic protection under the railroad crossing, using a single DC power supply device for the pipeline embedded so as to cross under the railroad crossing. Cathodic protection current can always be supplied to the whole.

  Hereinafter, embodiments of the present invention will be described. FIG. 2 is an explanatory diagram showing a system configuration for carrying out the pipeline cathodic protection method according to the embodiment of the present invention. The railroad crossing Lc is provided at a location that crosses a road or the like of a rail (DC electric railway rail) L, and a sheath tube C such as a fume tube is disposed below the rail crossing Lc. And the pipeline P is laid so that it may pass through the inside of the sheath pipe C under the level crossing part Lc, and cross the level crossing part Lc. The pipeline P has a coating Pc on its surface. More specifically, the pipeline P can be a steel pipeline with a high resistivity coating such as plastic. Further, the pipeline P is insulated in a predetermined anticorrosion region, and an anticorrosion region in the range of several tens to several hundreds of meters is formed between insulating joints (not shown).

  In such a crossing portion Lc, a DC current of 1000 to 3000 A flows through the rail L during operation of the DC electric railway vehicle, and a rail leakage current is generated under the crossing portion Lc. As a result, as shown in FIG. 1, a ground potential gradient zone is formed immediately below and around the railroad crossing Lc.

  The probe 10 is installed in the sheath tube C with respect to such a level crossing Lc. More specifically, the probe 10 is installed in the sheath tube C near the center of the rail crossing Lc. Normally, when the pipeline P is embedded, the probe 10 is tied and fixed to the pipeline P with an insulating band such as polypropylene, and embedded in the ground together with the sheath tube C, so that the electric wire connected to the probe 10 can be drawn out to the ground. Keep it. The probe 10 is a test piece that simulates a coating defect portion of the pipeline P, and is a conductive member formed of the same material as the constituent material of the pipeline P. Here, only one probe 10 installed in the sheath tube C is connected to the pipeline P, and current flow between the probes due to the connection of the plurality of probes 10 to the pipeline is eliminated. .

Prior measurement process;
Prior to performing the cathodic protection of the pipeline P, as shown in FIG. 2A, the probe 10 described above is connected to the pipeline P, and the probe current and the probe in the probe 10 are set within the set measurement time. 10 simultaneously measures the probe-on potential. The measurement time is 2 to 3 hours, and the probe current I and the probe on potential E are measured every predetermined sampling time (for example, 0.1 ms). The probe current I is measured by a probe ammeter 11 connected between wires connecting the probe 10 and the pipeline P. The probe-on potential E is a tube-to-ground potential when the connection between the probe 10 and the pipeline P is on, and the electric wire connecting the probe 10 and the pipeline P and the reference electrode (for example, saturated copper sulfate electrode) 12 Measured by a probe-on electrometer 13 connected between the wires connecting. Here, the collation electrode 12 is installed in the terminal box TB formed outside from the ground potential gradient zone formed by the railroad crossing Lc.

This pre-measurement step is preferably performed under conditions that are severe for cathodic protection, and in particular during rainy weather when rail leakage resistance is low and during operation of a DC electric railway vehicle in which rail leakage current is significantly generated. In addition, when verifying the correlation between the probe DC current and the probe-on potential, it is necessary to verify that the correlation between the two (negative correlation) increases due to the operation of the DC electric railway vehicle. The rail ground potential ER _{/ S} is measured at the same time as the probe current I and the probe on potential E only once.

Calculation process of probe direct current density I _DC , probe on potential E _ON, etc .;
For example, the probe direct current density _IDC is obtained by averaging the probe current measurement values measured every 0.1 ms every unit time (for example, 20 ms) and dividing by the probe cross-sectional area A. Furthermore, the probe AC current density I _AC is obtained by dividing the effective value of the probe current measurement value per unit time by the probe cross-sectional area A. The probe AC current density I _AC is obtained in order to evaluate whether or not there is an AC corrosion risk in the pipeline P in the anticorrosion region including the level crossing Lc, and is used as a parameter when the cathodic protection is executed. is not. Then, an average value E _ON per unit time is obtained from the measured value of the probe on potential E (hereinafter, this average value E _{ON is referred} to as a probe on potential).

The following formulas (1) to (3) are used to calculate the probe direct current density I _DC , the probe alternating current density I _AC , and the probe on potential E _ON .

Extracting the minimum value I _DC ^min in the basic section of the probe direct current density I _DC ;
Within the basic measurement section that divides the measurement time every predetermined time, the probe direct current density I _DC obtained per unit time is sequentially compared, and the minimum value in the basic measurement section (referred to as the minimum value within the section). ) ^Determine I _DC ^min . At the same time, the probe-on potential E _ON obtained within the unit time at the time when the in-section minimum value I _DC ^min appears is extracted. Then, (I _DC ^min , E _ON ) extracted in the basic measurement section is saved as one set data, and <measurement time / basic measurement section> pieces of set data are extracted and stored within the measurement time.

FIG. 3 is an explanatory diagram showing an example of a process from the above-described pre-measurement process to extraction / storage of (I _DC ^min , E _ON ) combination data. For example, if the basic measurement interval is set to 10 s with a measurement time of 2 hours, 720 basic measurement intervals are obtained, and one set of (I _DC ^min , E _ON ) is set for each basic measurement interval. Since data is extracted and stored, 720 sets of data are obtained in a measurement time of 2 hours.

The extraction of (I _DC ^min , E _ON ) for each basic measurement section is performed by collecting 200 simultaneous measurement values of (I, E) measured every 0.1 ms for each unit time (20 ms), and the above-described formula. I _DC and E _ON are obtained by (1) and equation (2). Then, the _{I DC} obtained for each unit time as compared with the first basic measurement interval _10s, select the unit _{time I DC} is the minimum value, in the unit time _{(I DC, E ON)} to _{(I DC} ^min , E _ON ). Here, the measurement time and the basic measurement section can be set to arbitrary times. The unit time is set to a time corresponding to one cycle of the commercial power supply frequency (for example, 50 Hz) in order to obtain the probe alternating current density I _AC at the same time.

Correlation confirmation step between the minimum value I _DC ^min in the section and the probe on potential E _ON ;
In the embodiment of the present invention, in the cathodic protection current control step described later, output control of the cathodic protection current is performed using the probe on potential E _ON measured by the control reference electrode as a detection parameter. This is a high negative value between the probe-on potential E _ON of the pipeline P embedded in the anticorrosion area including the level crossing Lc and the probe DC current density of the probe 10 installed in the sheath tube C below the level crossing Lc. It is assumed that there is a correlation.

FIG. 4 shows an example in which (I _DC ^min , E _ON ) extracted within the measurement time is plotted on a correlation diagram in which the horizontal axis is E _ON and the vertical axis is I _DC ^min (I _DC The unit of ^min is A / m ² and the unit of E _ON is V _CSE (potential of saturated copper sulfate electrode reference)). Here, assuming that the measurement time is 2 hours, the set data of (I _DC ^min , E _ON ) is extracted for each basic measurement section of 10 s from the measurement value in the DC electric railway vehicle operation time zone in rainy weather. As shown in the figure, in the DC electric railway vehicle operating time zone, the probe ON potential E _ON of the pipeline P and the minimum value I _DC ^min in the section of the probe DC current density are negative with a very high correlation coefficient of −0.908. Correlation is shown.

Incidentally, when the correlation between the rail ground potential E _{R / S} and I _DC ^min , E _ON measured simultaneously at this time is seen, as shown in FIGS. 5A and 5B, E _{R / S} and I _DC ^{min are obtained.} has high positive correlation (correlation coefficient: _{0.816), E R / S} and _{E ON} is high negative correlation (correlation coefficient: -0.884) is it possible to confirm. Thus, it is confirmed that there is a high positive correlation between E _{R / S} and I _DC ^min , and there is a high negative correlation between E _{R / S} and E _ON , and there is a high negative correlation between I _DC ^min and E _ON. If possible, it can be confirmed that the correlation between I _DC ^min and E _ON is caused by a change in rail-to-ground potential. Therefore, by utilizing the correlation between I _DC ^min and E _ON and performing output control of the cathodic protection current using E _ON as a detection parameter, it is embedded under the rail crossing Lc where the change in rail-to-ground potential E _{R / S} is severe. Thus, it is possible to control the output of the cathodic protection current that efficiently avoids the corrosion risk caused by the change in the rail-to-ground potential ER _{/ S.} At this time, the correlation with the rail ground potential E _{R / S} is sufficient if it can be confirmed once at one site, and the measurement of the rail ground potential E _{R / S} is not required for the subsequent measurement and control. In addition, when there is clearly no metal structure such as another buried pipeline and it can be estimated that the correlation between I _DC ^min and E _ON is caused by the change in rail ground potential, the rail ground potential E _{R / S} and The correlation confirmation can be omitted.

When a significant negative correlation is found between I _DC ^min and E _ON due to the influence of the change in rail-to-ground potential E _{R / S} (that is, the operation of the DC electric railway vehicle), By utilizing a significant negative correlation between _DC ^min and E _ON, it is possible to effectively control the cathodic protection current corresponding to the change in the rail ground potential.

Cathodic protection current control process;
FIG. 2B is an explanatory diagram showing a system configuration for executing a cathodic protection current control step in the cathodic protection method for a pipeline according to the embodiment of the present invention. As described above, the probe 10 installed in the sheath tube C is connected to the pipeline P, and between the wire connecting the pipeline P and the probe 10 and the control reference electrode 12C. A probe-on electrometer 13 is connected. The control reference electrode 12 </ b> C here is installed in a terminal box TB provided outside the underground potential gradient zone by the railroad crossing Lc.

An anode 14 buried near the pipeline P is connected to the pipeline P, and a DC power supply 15 is connected between the wires connecting the anode 14 and the pipeline P. The direct current power supply device 15 includes a power source that is positive on the anode side and negative on the pipeline P side so as to generate a cathodic protection current from the anode 14 and a control unit that controls an output current of the power source. Is configured such that the measured value of the probe-on potential E _ON measured by the probe-on electrometer 13 is input as a detection parameter for control.

The measurement value of the probe on potential E _ON at this time will be described in detail. For example, sampling is performed every 0.1 ms, 200 pieces of data are obtained at 20 ms, and the above-described equation (3) is obtained from the 200 pieces of data. _EON is determined by Then, a measurement interval of 0.5 s is set, and the maximum value E _ON ^max between them is extracted, and this is set as a detection parameter for control. The reason why E _ON ^max is used as a detection parameter for control is that E _ON and I _DC ^min show a negative correlation, so that stricter control is performed with respect to corrosion risk. 0.5 s of the measurement section is an interval necessary and sufficient for detecting a change in the probe-on potential E _ON at the level crossing Lc and feeding it back to the control means.

  In this system, only one anode 14 and DC power supply device 15 are provided in the anticorrosion area including the railroad crossing Lc. That is, the cathodic protection of the buried part below the rail crossing Lc in the pipeline P is cathodic protected by the cathodic protection current flowing out from the anode 14, and the entire anticorrosion region of the pipeline P partitioned by the insulating joint is cathodic protected. Thus, when cathodic protection of the entire anticorrosion region including the railroad crossing portion Lc is performed by one anode 14 and the DC power supply device 15, the railroad crossing portion Lc in which the probe-on potential frequently and greatly changes is efficiently cathodically protected. Therefore, it is necessary to control the entire anticorrosion area so as not to be anticorrosion.

In order to realize such control, the function of the control means in the DC power supply device 15 is that the probe DC current density at the probe 10 is measured by the control reference electrode 12C so as to always pass the cathodic protection standard. Based on the ON potential E _ON , the output current is controlled at a constant potential, and the probe ON potential measured by the control reference electrode 12C so that the average value of the probe DC current density at the probe 10 passes the cathodic protection standard. Regardless of E _ON , the output current is controlled at a constant current. That is, the control means of the DC power supply device 15 has both a constant potential control function responsible for local cathodic protection under the railroad crossing Lc and a constant current control function responsible for cathodic protection of the entire anticorrosion region.

As a result, the cathodic protection state under the level crossing Lc is such that the output of the DC power supply device 15 is such that the probe DC current density at the probe 10 always passes the cathodic protection standard according to the tube-to-ground potential state that changes frequently and greatly. Since the current is controlled at a constant potential, the current is always maintained in a good state. Furthermore, cathodic protection state of the entire anticorrosion region, since independent output current is constant current control to the probe on the potential E _ON so that the average value of the probe DC current density to pass the cathodic protection criteria, cathodic protection area This prevents the occurrence of corrosion risk by surely eliminating that the pipeline P becomes non-corrosive. Specific embodiments of constant current control and constant potential control will be described below.

Constant current control value calculation step;
Constant current control by the control means of the DC power supply 15 outputs an independent desired constant current to the probe on the potential E _ON measured by the control reference electrode 12C. That is, a cathodic protection current having a constant current value is output from the anode 14 regardless of the fluctuation of the rail ground potential. Since this constant current becomes a bias current, a constant cathodic protection current is output even when the power supply for constant potential control, which will be described later, is turned off. dont make.

The constant current here is the minimum required probe inflow DC current as the minimum value I _DC ^min in the section on the regression line obtained from the set data (I _DC ^min , E _ON ) obtained within the measurement time in the above-described preliminary measurement process. A density of 0.1 A / m ² is substituted to obtain a reference probe-on potential E _ON . Then, by shifting the constant current value stepwise, the constant current value at which the average probe-on potential E _ON becomes a reference value is determined as the output current value of the constant current control. The minimum required probe inflow DC current density (0.1 A / m ² ) is a lower limit value of the cathodic protection standard in the pipeline using the probe DC current density as an index. When the measured probe direct current density _IDC is equal to or greater than this value and does not cause excessive corrosion protection, the cathode corrosion protection standard is passed. Here, because of the use of the minimum value I _DC ^min in the interval as the value of the probe direct current density I _DC, all I _DC of this value in the interval if the pass cathodic protection standards accepted in cathodic protection criteria Will be.

More specifically, in the example shown in FIG. 4, a regression line of the paired data (I _DC ^min , E _ON ) plotted in the correlation diagram is obtained, and 0.1 A / m ² is substituted as the vertical axis side variable thereof. Then, as shown in the figure, E _ON (0.1 A / m ² ) = − 3.16V _CSE is obtained. This E _ON (0.1 A / m ² ) = − 3.16V _CSE becomes a constant current control value, and the average value of E _ON when a constant current is continuously supplied becomes this value −3.16V _CSE. Set a constant current value.

Constant potential control value calculation step;
On the other hand, the constant current control by the control means of the DC power supply 15, to the frequent and large change tube ground potential state, the probe ON potential E _ON measured by the control reference electrode 12C is compared with a reference value, comparing The constant potential source is turned on / off according to the result. As described above, the control reference electrode 12C used here is installed outside the ground potential gradient zone formed by the crossing Lc. Since the control reference electrode 12C is required to be continuous, a metal electrode such as a zinc reference electrode or a magnesium reference electrode is used.

The reference value (constant potential control value) for performing this constant potential control is the correlation between I _DC ^min and E _ON obtained from all the set data (I _DC ^min , E _ON ) within the measurement time obtained in the preliminary measurement process. Even if the rail-to-ground potential fluctuates greatly, the measured I _DC is all more than the minimum required probe inflow DC current density (0.1 A / m ² ), that is, cathodic protection standards Set E _ON to pass.

More specifically, in the example shown in FIG. 4, a threshold value for E _ON is determined for all sets of data (I _DC ^min , E _ON ) plotted in the correlation diagram. Draw a vertical threshold line (broken line), move this threshold line in the negative direction of the horizontal axis (E _ON ), and I _DC ^min is less than 0.1 A / m ^{2 for} the set data on the negative side of the threshold line The maximum threshold line (threshold value) at which no value set data exists is obtained. That is, the set data (I _DC ^min , E _ON ) having the probe on potential E _ON on the minus side of the set threshold value all have I _DC ^{min equal} to or higher than the minimum required probe inflow DC current density (0.1 A / m ² ). A threshold value (E _ON (constant potential control value)) is determined. In the example of FIG. 4, E _ON (constant potential control value) = − 4.2V _CSE .

Control execution process;
The control of the cathodic protection current by the DC power supply device 15 is a control in which the constant current control for outputting the constant current described above is superimposed on the constant potential control using the threshold value as a constant potential control value. That is, when the probe-on potential E _ON measured by the control reference electrode 12C is on the minus side of the aforementioned threshold value (E _ON (constant potential control value)), the constant potential generation source is turned off and constant current control is performed. When the probe-on potential E _ON measured by the control reference electrode 12C is on the plus side of the aforementioned threshold value (E _ON (constant potential control value)), the output of the constant potential generating source is output. A cathodic protection current obtained by adding a constant current value of constant current control to the current value is output from the anode 14.

Such output control of the cathodic protection current is always performed when the DC power supply 15 is in operation. For example, at the time of regular inspection every year, the above-described preliminary measurement process is newly performed, and the above-described correlation diagram between I _DC ^min and E _ON is obtained based on the newly extracted set data (I _DC ^min , E _ON ). The control is performed after updating E _ON (0.1 A / m ² ) and E _ON (constant potential control value) described above. At the time of such an update, it is not necessary to measure the rail ground potential or confirm the correlation with the rail ground potential in the preliminary measurement process.

In the method of cathodic protection of pipeline P according to the embodiment of the present invention having such a feature, the probe 10 is installed in the sheath tube C under the crossing Lc, and the probe current I and the probe on potential E are measured simultaneously. Then, using the high correlation between the probe DC current density I _DC and the probe ON potential E _ON obtained from the probe current I, the control reference electrode 12C is used so that the probe DC current density I _DC always passes the cathodic protection standard. Based on the probe on potential E _ON measured by the above, the output current of the DC power supply 15 is controlled at a constant potential. As a result, the cathodic protection current can be supplied while evaluating the cathodic protection status under the level crossing Lc, and the corrosion risk of the pipeline P embedded so as to cross the level crossing Lc of the DC electric railway can be assured. It can be avoided.

Further, the output control of the DC power supply 15 while detecting the tube voltage to ground state of the crossing portion Lc under which changes by operating situation of the DC electric railcars by the measurement probe on the potential E _ON via the control reference electrode 12C Therefore, the cathodic protection current can be efficiently supplied without causing problems such as over-corrosion prevention with respect to the pipeline P and direct current interference with other buried pipelines.

Only one probe 10 is arranged in the sheath pipe C arranged under the level crossing Lc, and the reference electrode is not arranged in the sheath pipe C or in the ground potential gradient zone. Thus, the probe-on potential can be stably measured. Accordingly, the cathodic protection current output is accurately obtained while accurately grasping the state of cathodic protection and potential change under the level crossing Lc for the pipeline P laid through the inside of the sheath pipe C disposed under the level crossing Lc. Can be controlled. The probe-on potential E _ON detected for controlling the cathodic protection current output is measured by installing the control verification electrode 12C outside the ground potential gradient zone, and therefore, a metal electrode is used as the control verification electrode 12C. Can be used to perform stable and continuous measurement.

Since the probe 10 is installed in the sheath C below the level crossing Lc and the probe current is measured, it is possible to evaluate the AC corrosion risk by the probe AC current density I _AC which is the AC component of the probe current. is there. Therefore, when it is evaluated that the AC corrosion risk is high, it is possible to control the output of the cathodic protection current after taking risk reduction measures such as connection of AC induction reducing means.

  In addition, since the measurement of rail-to-ground potential at the time of cathodic protection current supply can be omitted, it is possible to avoid difficult situations such as permitting DC electric railway managers and avoiding operation of DC electric railway vehicles, and an easy-to-implement method Can be provided.

  Even when the probe-on potential under the level crossing Lc changes frequently and greatly, the cathodic protection current so that the probe DC current density passes the cathodic protection standard (above the minimum required probe inflow DC current density) in all states. In addition, a constant cathodic protection current is output so that the probe DC current density always passes the cathodic protection standard on average regardless of the tube ground potential state below the level crossing Lc. Even under the rail crossing Lc where the ground potential state frequently and greatly changes, it is possible to always maintain a good cathodic anticorrosion state and not to create an anticorrosion state in which the DC power supply 15 is turned off. As a result, the crossing portion Lc can be applied to the pipeline P embedded so as to cross under the crossing portion Lc while properly performing local cathodic protection under the crossing portion Lc with one DC power supply device 15. The cathodic protection current can always be supplied to the entire predetermined anticorrosion area.

It is explanatory drawing which shows the underground electric potential gradient in a level crossing part. It is explanatory drawing which showed the system configuration | structure for implementing the cathodic protection method of the pipeline which concerns on embodiment of this invention. In an embodiment of the present invention, it is an explanatory view showing the pre-measurement step (I DC min, E ON) the example process until extracting and storing the set data of. It is an example of a correlation diagram in which the horizontal axis plotting (I DC min , E ON ) extracted within the measurement time is E ON and the vertical axis is I DC min . It is an example of the correlation diagram of (E R / S , I DC min ) and (E R / S , E ON ) extracted within the measurement time.

Explanation of symbols

10: Probe,
11: Probe ammeter,
12: Reference electrode (saturated copper sulfate electrode), 12C: Control reference electrode (metal electrode),
13: Probe-on electrometer
14: anode,
15: DC power supply,
P: pipeline, Pc: coating,
Lc: level crossing, L: rail,
C: sheath tube

Claims (5)

A cathode anticorrosion method for a pipeline that is buried so as to cross under a level crossing of a DC electric railway and is laid through a sheath pipe disposed under the level crossing,
The only probe that is installed at the center of the railroad crossing in the sheath pipe and that simulates a coating defect portion of the pipeline is connected to the pipeline, and the probe current in the probe and the probe within the set measurement time Having a pre-measurement step of simultaneously measuring the probe-on potential in the probe,
Using the high correlation between the probe DC current density obtained from the measured probe current and the probe-on potential, the reference value and the crossing section set so that the probe DC current density always passes the cathodic protection standard In the constant potential control for controlling the output current of the DC power supply device connected to the pipeline by comparing the probe-on potential measured by the control reference electrode installed outside the ground potential gradient area in the pipeline, the pipeline The control is performed by superimposing a constant current control for controlling an output current of a DC power supply device connected to a constant current value set so that an average value of the probe DC current density passes a cathodic protection standard. To prevent cathodic protection of pipeline. A cathode anticorrosion method for a pipeline that is buried so as to cross under a level crossing of a DC electric railway and is laid through a sheath pipe disposed under the level crossing,
The only probe installed in the center of the railroad crossing in the sheath pipe and simulating the coating defect part of the pipeline is connected to the pipeline, and the probe current in the probe is set within the set measurement time. A pre-measurement step of simultaneously measuring a probe-on potential in the probe;
A probe DC current density is obtained from the measured probe current, a minimum value within the section of the probe DC current density is obtained for each basic section within the measurement time, and the probe-on potential at the appearance time and the minimum value within the section. As a single set of data, the correlation between the minimum value in the section and the probe-on potential is obtained from all the set data at the measurement time,
When there is a significant correlation between the minimum value in the section and the probe-on potential, the section data having the probe-on potential on the minus side of the set threshold are all equal to or higher than the minimum required probe inflow DC current density. A threshold value having the smallest value is defined,
When controlling the output current of the DC power supply device connected to the pipeline, the probe-on potential measured by the control reference electrode installed outside the ground potential gradient zone at the railroad crossing with the threshold as a reference value A cathode cathodic protection method for a pipeline, characterized in that control is performed by superimposing constant current control for outputting a desired constant current on constant potential control for controlling so that becomes a reference value .   The pipeline cathodic protection method according to claim 1 or 2, wherein the preliminary measurement step is performed in rainy weather when the DC electric railway is operated.   The constant current is an output current value for obtaining a probe-on potential obtained by substituting the minimum required probe inflow DC current density as the minimum value in the section into the regression line obtained by the set data within the measurement time. 4. The method of cathodic protection for pipelines according to claim 2 or 3,   The pipeline cathodic protection method according to any one of claims 1 to 4, wherein the pipeline is a steel pipeline provided with a high resistivity coating.

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