JP2009156707A - Measurement evaluation method and measurement evaluation system of cathode corrosion protection state - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To confirm whether a sacrificial anode has a function satisfying a necessary protective current under influence of AC induction or not, or whether the sacrificial anode has a sufficient AC induction reduction effect or not, when grasping a cathode corrosion protection state of a structure placed in the state of cathode corrosion protection by a sacrificial anode system. <P>SOLUTION: This system is equipped with a current measuring means 11 for measuring a current flowing in a wire connected between the sacrificial anode and a metal structure, and an operation processing means 12 for performing operation processing of a measured value measured by the current measuring means 11. The operation processing means 12 is equipped with a measured value extraction means 12A, a DC current density calculation means 12B, an AC current density calculation means 12C, a commercial frequency identification means 12D, and a cathode corrosion protection state evaluation means 12E. When the commercial frequency identification means 12D confirms to be a sine wave having a unit measuring time as a period, the cathode corrosion protection state evaluation means 12E determines whether or not the maximum value in a measuring period of an AC current density exceeds a reference value set by using a phenomenon that function decline is generated in the sacrificial anode 2 by AC induction as a reference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for measuring and evaluating the cathodic protection status of a metal structure that is cathodic protected by a galvanic anode method, and a system for measuring and evaluating the same.

  In order to prevent corrosion of metal structures existing in electrolytes such as soil, it is necessary to first isolate the metal structure surface from the electrolyte, but the metal structure surface and the electrolyte are in contact. Is known to be the most effective method of cathodic protection, in which a current (anticorrosion current) is allowed to flow into the surface of the metal structure so as not to cause an anode reaction (a cathode reaction is caused to occur on the surface of the metal structure). It has been.

  Cathodic protection methods currently used for metal structures such as soil-buried pipelines can be broadly divided into a galvanic anode method, an external power supply method, and a hybrid method in which both are mixed. In the external power supply system, a DC power supply device is connected between an electrode (anode) and a metal structure (cathode) installed in the electrolyte to apply a DC voltage, and a DC current is applied from the electrode to the metal structure through the electrolyte. This is a method of preventing corrosion by flowing in. In this external power supply system, usually, a section to be protected against corrosion is insulated, a DC power supply having an output corresponding to the section is installed, and a desired cathodic protection situation is obtained by adjusting the output of the DC power supply. I am doing so.

  On the other hand, in the galvanic anode method, a metal having a negative corrosion potential than that of the metal structure is used as an anode (fluidic anode), and this is connected to the metal structure with an electric wire. This is a method for preventing the corrosion of the surface of the metal structure by causing the anticorrosion current generated from the galvanic anode by the metal battery action to flow into the metal structure. In general, Mg anodes are often used as galvanic anodes for steel soil buried pipelines.

  In order to grasp the cathodic protection status of a metal structure that is cathodic-protected by such a galvanic anode method, the current flowing through the wire connecting the galvanic anode and the metal structure is measured periodically, Monitoring of the anticorrosion current generated from the electric anode is performed.

FIG. 1 is an explanatory diagram for explaining the prior art disclosed in Patent Document 1 below. In this prior art, a measuring system provided with a life predictor J12 and an analog measuring instrument J18 while connecting the soil buried pipeline J10 and the galvanic anode (Mg anode) J11 with electric wires J16 and J17 is provided in the terminal box J19. In the life predictor J12, the current monitoring circuit J13 periodically monitors the current value flowing out from the electroplating anode J11, and inputs this measured value to the electric quantity calculation circuit J14. In the measurement circuit J18, the alternating current generated from the galvanic anode J11 is measured, and this value is smoothed and input to the capacitance calculation circuit J14. In the electric capacity calculation circuit J14, the degree of consumption of the electric capacity of the current flowing anode J11 so far, and further the current flowing from the electric capacity of the flowing current anode J11 inputted in advance and the current value including the monitored alternating current. A life prediction value indicating how long the electric anode J11 is to be maintained is calculated and output to the display circuit J15.
Japanese Patent No. 3214778

  When a buried metal structure that is cathodic protected by the galvanic anode method is subjected to AC induction by running a high-voltage AC power transmission line or AC electric railway vehicle, the galvanic anode is a low-grounded body, so an AC current is generated from the galvanic anode. As a result, the AC voltage of the buried metal structure decreases, and the AC corrosion of the buried metal structure can be reduced or ignored. In this case, the galvanic anode prevents the AC corrosion of the buried metal structure by reducing the function of generating the required anticorrosion current for cathodic protection of the buried metal structure and the AC induction affecting the buried metal structure. Both functions as a ground electrode are assumed.

  In such a case, it is the commercial frequency sine wave that has the greatest influence on the buried metal structure, and this periodic change causes the potential of the galvanic anode to change from positive to negative. It will be. Then, when the buried metal structure is affected by a large alternating current induction, the potential of the galvanic anode connected to the buried metal structure periodically shifts to a large positive value. And the difference between the ground potential of the buried metal structure and the galvanic anode cannot function to generate the anticorrosion current.

  In such a case, in order to properly grasp the cathodic protection status of the buried metal structure that is cathodic protected by the galvanic anode method, the smoothing value of the measured alternating current is added as in the prior art. It is not sufficient to simply calculate the life expectancy of the anode, and it is necessary to confirm whether the galvanic anode has the ability to flow out the required anticorrosion current even when it is affected by AC induction.

  In addition, when the galvanic anode is subjected to AC corrosion, an electrocoating having a high electric resistance may be generated on the surface of the galvanic anode due to the cathodic reaction. According to this, the grounding resistance of the galvanic anode is increased, the anticorrosion current generated from the galvanic anode is reduced, and at the same time, the AC induction reducing effect as the earth electrode is reduced.

  An object of the present invention is to cope with such a situation. In order to grasp the cathodic protection status of a structure that is cathodic protected by the galvanic anode method, the present invention is applied under the influence of alternating current induction. It can be confirmed whether or not the current anode has a function that satisfies the required anticorrosion current, and whether or not the current anode has a sufficient AC induction reduction effect. The anticorrosion target pipeline satisfies the cathodic protection standards, with the premise of satisfying the anticorrosion current, there is no concern about AC corrosion in the anticorrosion target pipeline, and the galvanic anode can be used up to the design life. It is an object of the present invention that it can be confirmed.

  In order to achieve such an object, the present invention includes at least the following features.

  This is a method for measuring and evaluating the cathodic protection status of metal structures that are cathodic-protected by the galvanic anode method. The unit measurement time corresponding to the period of the commercial frequency is set and connected between the galvanic anode and the metal structure. A step of measuring a current flowing through the electric wire, a step of obtaining a direct current density of a current generated from the galvanic anode every unit measurement time from the measured value of the current, a measured value of the current and the direct current A step of obtaining an alternating current density of current generated from the galvanic anode from the density every unit measurement time, and a temporal change in the measurement value is a sine wave having the unit measurement time as a cycle. And a maximum value within the measurement period of the alternating current density when the step is confirmed to be a sine wave having the unit measurement time as a period in the step. A step of determining whether or not a reference value set based on the occurrence of a decrease is exceeded, and when the reference value is exceeded in the step, the cathodic protection status of the metal structure is poor It is characterized by evaluating.

  Further, it is a system for measuring and evaluating the cathodic protection status of a metal structure that is cathodic-protected by the galvanic anode method, and a current measuring means for measuring the current flowing in the electric wire connected between the galvanic anode and the metal structure. And an arithmetic processing means for arithmetically processing the measurement value measured by the current measuring means, wherein the arithmetic processing means extracts the measurement value for each unit measurement time corresponding to a commercial frequency period at a set sampling interval. A measurement value extracting means for performing, a DC current density calculating means for obtaining a DC current density of a current generated from the galvanic anode for each unit measurement time from the extracted measurement value, the extracted measurement value and the AC current density calculating means for obtaining an AC current density of current generated from the galvanic anode at each unit measurement time from the DC current density, and a temporal change in the measured value When the commercial frequency identifying means for confirming that the sine wave has a unit measurement time as a period and the commercial frequency identification means confirms that the sine wave has a period as the unit measurement time, the alternating current A cathodic protection status evaluation unit for determining whether or not a maximum value of the current density within a measurement period exceeds a reference value set based on the fact that a function deterioration occurs in the galvanic anode due to AC induction. Features.

  According to these characteristics, the cathodic protection situation when a metal structure that is cathodic-protected by the galvanic anode method is affected by AC induction is based on the functional degradation of the galvanic anode caused by AC induction. It becomes possible to measure and evaluate. According to this, it becomes possible to quantitatively manage the galvanic anode corresponding to the change in the surrounding situation.

  When a buried pipeline as a metal structure is subject to anticorrosion, the galvanic anode satisfies the required anticorrosion current, there is no concern about AC corrosion in the anticorrosion target pipeline, and the galvanic anode is used to the design life. It is possible to confirm that the pipeline to be protected against corrosion satisfies the cathodic protection standard.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, a pipeline embedded in the ground as a metal structure will be described as an example. However, the embodiment of the present invention is not particularly limited to this, and a pipe installed in water. This applies to metal structures such as lines that are covered with electrolyte and that have a risk of stray current corrosion.

  As shown in FIG. 2, in order to prevent cathodic protection of the pipeline 1 by the galvanic anode method, a galvanic anode (for example, Mg anode) 2 is embedded in the vicinity of the pipeline 1. The other end of the electric wire L1 having one end connected to the galvanic anode 2 is pulled up to the ground in a terminal box TB provided at a predetermined interval (for example, 250 m interval) along the pipeline 1, for example. The other end of the electric wire L2 having one end connected to 1 is also pulled up to the ground, and the pipeline 1 and the galvanic anode 2 are electrically connected via the electric wires L1 and L2.

  In the terminal box TB, a verification electrode 3 (for example, a saturated copper sulfate electrode) and a probe 4 are provided as equipment for grasping the cathodic protection status of the pipeline 1. The probe 4 is deployed as necessary. The reference electrode 3 is generally provided in the terminal box TB at the time of inspection. The reference electrode 3 is a reference electrode that is installed on the ground surface in the terminal box TB and has a constant potential. One end of the reference electrode 3 is connected to the pipeline 1 and the other end is pulled up to the ground in the terminal box TB. L3 is electrically connected to the pipeline 1 via electric wires L4 and L5, and a tube-to-ground potential (potential difference between the verification electrode 3 and the pipeline 1) is obtained by a DC voltmeter 5 connected between the electric wires L4 and L5. It is to be measured. The probe 4 is a test piece having a predetermined area of the same metal material as that of the pipeline 1, and the tip thereof is provided close to the pipeline 1 so as to simulate the coating defect portion of the pipeline 1. It is electrically connected to the pipeline 1 via the electric wires L6, L4, L3, and is connected to the probe DC current (DC current flowing into the pipeline 1 from the probe 4) by the DC ammeter 6 connected between the electric wires L3, L4. ).

  When installing a galvanic anode for a pipeline, normally, when the pipeline is embedded in an environment where the required corrosion protection current of the pipeline is small and the electrical resistivity is low, cathodic protection is mainly performed by an external power supply method. However, when cathodic protection is applied to a short insulated section where this cathode current does not reach, it is cathodic protected if it is used to locally protect the thinned part of the pipeline where the bare or coating is considerably deteriorated. The pipeline that is subject to DC interference where the anti-corrosion current to be supplied to the pipeline is flowing into the other pipeline is in metal touch with the pipeline that is cathodic-proof, and the metal touch portion In order to prevent both types of corrosion, even if the above-mentioned metal touch part is revealed, the pipeline is not suitable for the complicated burial condition of the pipeline. In cases where mutual insulation measures cannot be taken immediately, the pipeline is affected by AC induction, and there is a case where a galvanic anode is installed as a low grounding body (earth electrode) to reduce AC induction. .

  In particular, according to the embodiment of the present invention, the pipeline 1 is affected by AC induction, and the installed current-flow anode 2 functions as a low grounding body for reducing AC induction, and the pipeline 1 has an anticorrosion current. The purpose is to properly grasp the cathodic protection status of the pipeline 1 under the condition of supplying

  The cathodic protection status measurement / evaluation apparatus 10 is connected between the electric wires L1 and L2, and the cathode of the pipeline 1 is monitored while monitoring the electric current flowing through the electric wires L1 and L2, that is, the anticorrosion current generated from the galvanic anode 2. Corrosion protection is measured and evaluated.

  The cathodic protection status measurement / evaluation apparatus 10 includes a current measuring unit (ammeter) 11 that measures the current flowing through the electric wires L1 and L2, and an arithmetic processing unit 12 that performs arithmetic processing on the measurement value measured by the current measuring unit 11. ing. Moreover, the arithmetic processing means 12 can also process the measured values of the probe DC current and the tube-to-ground potential measured by the DC ammeter 6 and the DC voltmeter 5 as required.

  The arithmetic processing means 12 includes at least a measurement value extraction means 12A, a direct current density calculation means 12B, an alternating current density calculation means 12C, a commercial frequency identification means 12D, and a cathodic protection status evaluation means 12E. Each of these means can be formed by software for controlling the operation of the arithmetic processing means 12.

  The measurement value extraction unit 12A extracts a measurement value measured by the current measurement unit 11 for each unit measurement time corresponding to a commercial frequency period at a set sampling interval. If the commercial frequency is 50 Hz, the unit measurement time is 20 msec, and the sampling interval set within the unit measurement time can be set to 0.1 msec, for example. Here, the technical idea of measurement and evaluation is how AC corrosion of the flowing current anode 2 affects the current generated by the flowing current anode 2. Since it is known that alternating current induction resulting from the traveling of an alternating current electric railway vehicle has the greatest influence, attention is paid to the commercial frequency as the frequency.

  The direct current density calculation means 12B obtains the direct current density of the current generated from the flowing current anode 2 every unit measurement time from the extracted measurement value by the current measurement means 11. The alternating current density calculating means 12C is an alternating current of current generated from the galvanic anode 2 per unit measurement time from the measured value obtained by the extracted current measuring means 11 and the direct current density obtained by the direct current density calculating means 12B. The density is calculated.

When the commercial frequency is 50 Hz, the unit measurement time is 20 msec, and the measurement value is extracted at the data sampling interval of 0.1 msec, the direct current density (I _DC ) can be obtained by the following formula (1), Further, the alternating current density (I _AC ) can be obtained by the following formula (2).

  The commercial frequency identification unit 12D confirms that the temporal change in the measurement value measured by the current measurement unit 11 is a sine wave having a unit measurement time as a cycle. More specifically, the difference in the appearance time between the maximum value and the minimum value of the measurement value within the unit measurement time is ½ of the unit measurement time (10 msec when the unit measurement time is 20 msec), and within the unit measurement time. It is confirmed that the difference between the maximum value and the average value is equal to the difference between the average value and the minimum value within the unit measurement time.

Specifically, a value (I _AC ^max ) that maximizes the alternating current density (I _AC ) is specified from the entire measurement period. Then, the measurement value I (t) of the unit measurement time indicating the maximum value (I _AC ^max ) is extracted. FIG. 3 is an explanatory diagram showing a time change of 200 measurement values I (t) at a unit measurement time t _s : 20 msec and a sampling interval t ₀ : 0.1 msec. Then, it is confirmed that the illustrated time difference Δt = 10 msec and ΔI1 ((maximum value) − (average value)) = ΔI2 ((average value) − (minimum value)) (I _max (t) in the drawing). Is the maximum measurement value within the unit measurement time, I _min (t) is the minimum measurement value within the unit measurement time, I _ave (t) is the average value within the unit measurement time, T1 is the appearance time of I _max (t), T2 is the appearance time of I _min (t)). Here, the confirmation process was performed for the measurement value indicating the maximum value of the alternating current density (I _AC ) from the entire measurement period. However, in addition to the maximum value, several measurement values are selected in descending order, and the same as described above. The confirmation process may be performed.

When the commercial anti-corrosion status evaluation means 12E confirms that the commercial frequency identification means 12D is a sine wave having a unit measurement time as a period, the maximum value (I _AC ^max ) within the measurement period of the alternating current density (I _AC ). ) Exceeds the reference value. As the maximum value (I _AC ^max ) within the measurement period of the alternating current density (I _AC ), the value obtained by the commercial frequency identification means 12D can be used, and this value is compared with a preset reference value within the measurement period. When the maximum value exceeds the reference value, it is determined that the cathodic protection situation is poor.

The reference value here is a reference value that is set on the basis that the function degradation occurs in the galvanic anode 2 due to AC induction. The phenomenon of the function deterioration of the galvanic anode due to AC induction will be explained using an example of the Mg anode. When the Mg anode is subjected to AC corrosion, a reaction of 1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻ occurs as a cathode reaction. Mg ²⁺ flows out from one Mg anode as a supply of anticorrosion current to the pipeline. When Mg ²⁺ flowing out from the Mg anode and 2OH ⁻ generated by the above-described cathode reaction are combined, Mg (OH) ₂ is generated and precipitated on the surface of the Mg anode. Mg (OH) ₂ is a high resistance body called electrocoating, and when this electrocoating is generated on the surface of the Mg anode, the ground resistance of the Mg anode becomes high. As a result, the anticorrosion current generated from the Mg anode is reduced, and at the same time, the AC induction reduction effect as the ground electrode is also reduced. This is an example of a mechanism of functional degradation due to AC induction of the galvanic anode.

In order not to cause such a decrease in function of the galvanic anode, it is necessary to monitor the influence of the AC induction acting on the galvanic anode. In the embodiment of the present invention, The AC component is monitored so that the AC component does not exceed the reference value. When the Mg anode is used and AC induction occurs at a commercial frequency of 50 Hz, the function of the Mg anode is empirically maintained by setting the above-described AC current density I _AC to less than 1 A / m ^2. Is confirmed.

  FIG. 4 is a flowchart showing a method for measuring and evaluating the cathodic protection situation according to the embodiment of the present invention. The following method can be realized by the system configuration described above.

  When the measurement is started, the current flowing through the electric wires L1 and L2 (I (t): galvanic anode generation current) is measured by the current measuring means 11, and the tube-to-ground potential is further measured by the DC voltmeter 5 as necessary. The probe direct current is measured by the direct current ammeter 6 (S1). The measurement is executed until a predetermined measurement period, and when the measurement period ends (S2), the process proceeds to the next arithmetic processing step.

When the current I (t) flowing through the electric wires L1 and L2 is measured, the measurement value extracting unit 12A uses the unit measurement time (for example, 20 msec) described above at a predetermined sampling interval (for example, 0.1 msec). Each is sequentially extracted (S3). Then, the DC current density calculating unit 12B is, by equation (1) described above, calculates the direct current density I _DC per unit measurement time (S4), the alternating current density calculating unit 12C is, by the aforementioned equations (2) The AC current density I _AC is calculated every unit measurement time (S5).

  At the stage where the measurement period ends, the arithmetic processing means 12 performs the following processing by the commercial frequency identification means 12D, the cathodic protection status evaluation means 12E, and the processing means associated therewith.

First, it extracts the maximum value _I ^{DC max} the maximum value _I ^{AC max} of the AC current density _{I AC} DC current density _{I DC} in the measurement period (S6). Here, the extraction of the maximum values I _DC ^max and I _AC ^max is performed by storing all of the calculated I _DC and I _AC and the measured value I (t) in the storage means, and all the I _DC and I _AC are stored in the storage unit. Can be executed by extracting the maximum values I _DC ^max and I _AC ^max and the corresponding measured value I (t).

As another extraction method, first, 200 measurement values I (t) extracted in the first unit measurement time are stored in the storage means, and I _DC and I _AC are calculated from the measurement values. These are stored in the storage means. Next, 200 measurement values I (t) extracted in the next unit measurement time are stored in another storage means, I _DC and I _AC are calculated from the measurement values, and I _DC , I _AC and the current calculated _{I DC,} the _{I AC} respectively compared, larger _{I DC,} and stores the _{I AC,} measured value I and the corresponding (t) will retain stored, smaller _{I DC, IAC} and the corresponding measurement value I (t) erase the data. Furthermore, 200 measurement values I (t) extracted in the next unit measurement time are stored in the storage means from which the previous data has been erased, and I _DC and I _AC are calculated from the measurement values, and the previous calculation is performed. The I _DC and I _AC are compared with the I _DC and I _AC calculated this time, respectively, the larger I _DC and I _AC are stored, and the corresponding measured value I (t) is stored, and the smaller one is stored. I _DC and I _AC and the corresponding measured value I (t) erase data. By repeating this process, the maximum values I _DC ^max and I _AC ^max and the corresponding measurement value I (t) are stored in the storage unit at the end of the measurement period.

Then, it is confirmed that the maximum value I _DC ^max is less than the reference value (S7). The reference value here is a reference value for confirming whether or not the required anticorrosion current can continue to flow until the life of the galvanic anode is designed. On the assumption that this is satisfied, the following processing is performed. I do.

In the next process, the commercial frequency identification unit 12D described above determines whether or not the measured value I (t) corresponding to I _AC ^max is a sine wave of the commercial frequency. If it is determined that this is not a commercial frequency sine wave, it is determined that no countermeasure is required (S8A). If it is determined that this is a commercial frequency sine wave, the above-described cathodic protection status evaluation means 12E The process is executed (S9).

As described above, the cathodic protection status evaluation unit 12E evaluates the cathodic protection status depending on whether or not the maximum value I _AC ^max is less than the reference value. As described above, the reference value here is a reference value based on the function deterioration of the galvanic anode. If the reference value is exceeded, the function of the galvanic anode may be deteriorated. Is determined to be defective, and a countermeasure instruction for a low grounding measure is added by adding an electroplated anode (for example, Mg anode) (S10). If it is less than the reference value, it is determined that the function degradation of the galvanic anode due to AC induction can be ignored, and the cathodic protection status for the normal pipeline 1 is confirmed. That is, it is confirmed whether or not the measured value of the tube ground potential or the probe current density passes the cathodic protection standard using the tube ground potential or the probe current density as an index (S9A).

  According to such an embodiment of the present invention, the cathodic protection situation when the pipeline 1 that is cathodic protected by the galvanic anode method is affected by alternating current induction is the function of the galvanic anode 2 generated by alternating current induction. Measurement and evaluation can be performed based on the decrease. According to this, it becomes possible to perform management of the galvanic anode 2 corresponding to changes in the surrounding situation from a viewpoint completely different from the life prediction of the galvanic anode 2 as in the prior art. That is, when a high-voltage AC transmission line is newly laid or added around the location where the current-carrying anode 2 is installed, or when an AC electric railway is newly laid or added, the surrounding situation changes. The adverse effect on the galvanic anode 2 can be grasped quantitatively, and appropriate measures can be taken based on this.

It is explanatory drawing of a prior art. It is explanatory drawing which shows the system configuration | structure which concerns on embodiment of this invention. Unit measurement time _t s: sampling interval at 20 msec _t 0: is an explanatory view showing a time variation of 200 measured values I (t) at 0.1 msec. It is a flowchart which shows the measurement evaluation method of the cathodic protection condition which concerns on embodiment of this invention.

Explanation of symbols

1: pipeline (metal structure), 2: galvanic anode (Mg anode), 3: reference electrode (saturated copper sulfate electrode), 4: probe, 5: DC voltmeter, 6: DC ammeter,
10: Cathodic protection status measurement and evaluation device, 11: Current measurement means,
12: arithmetic processing means,
12A: Measurement value extraction means,
12B: DC current density calculating means,
12C: AC current density extraction means,
12D: commercial frequency identification means,
12E: Cathodic protection status evaluation means,
L1 to L6: Electric wire, TB: Terminal box

Claims (6)

A method of measuring and evaluating the cathodic protection status of a metal structure that is cathodic protected by a galvanic anode method,
Setting a unit measurement time corresponding to the cycle of the commercial frequency and measuring the current flowing in the electric wire connected between the galvanic anode and the metal structure;
From the measured value of the current, obtaining a direct current density of the current generated from the galvanic anode every unit measurement time,
From the measured current value and the direct current density, obtaining an alternating current density of current generated from the galvanic anode every unit measurement time;
Confirming that the temporal change of the measurement value is a sine wave with the unit measurement time as a cycle;
When it is confirmed that the step is a sine wave having the unit measurement time as a cycle, the maximum value within the measurement period of the alternating current density is based on the fact that the function deterioration occurs in the galvanic anode by alternating current induction. And determining whether or not the reference value set in is exceeded,
When the said reference value is exceeded at the said process, it evaluates that the cathodic protection condition of the said metal structure is unsatisfactory, The measurement evaluation method of the cathodic protection condition characterized by the above-mentioned. When the measurement value is extracted at a commercial frequency of 50 Hz and the unit measurement time is 20 msec and the data sampling interval is 0.1 msec, the direct current density (I _DC ) is obtained by the following equation (1). The method for measuring and evaluating the cathodic protection status according to claim 1, wherein the alternating current density (I _AC ) is obtained by the following formula (2).

  The step of confirming that the temporal change of the measurement value is a sine wave having the unit measurement time as a cycle is that the difference between the time when the maximum value and the minimum value of the measurement value appear within the unit measurement time is The difference between the maximum value and the average value of the measurement values within the unit measurement time and the difference between the average value and the minimum value of the measurement values within the unit measurement time that is 1/2 of the unit measurement time The method for measuring and evaluating the cathodic protection status according to claim 1 or 2, wherein the two are confirmed to be equal to each other. A system for measuring and evaluating the cathodic protection of metal structures that are cathodic protected by the galvanic anode method,
A current measuring means for measuring the current flowing in the electric wire connected between the galvanic anode and the metal structure;
An arithmetic processing means for arithmetically processing the measurement value measured by the current measuring means,
The arithmetic processing means is
A measurement value extracting means for extracting the measurement value every unit measurement time corresponding to a commercial frequency period at a set sampling interval;
DC current density calculating means for obtaining a DC current density of a current generated from the galvanic anode from the extracted measurement value every unit measurement time;
AC current density calculation means for obtaining an AC current density of current generated from the galvanic anode every unit measurement time from the extracted measurement value and the DC current density;
Commercial frequency identifying means for confirming that the temporal change in the measured value is a sine wave with the unit measurement time as a cycle;
When it is confirmed by the commercial frequency identification means that it is a sine wave having the unit measurement time as a cycle, the maximum value of the alternating current density within the measurement period is reduced in function of the galvanic anode by alternating current induction. A cathodic protection status evaluation means for determining whether or not a reference value set on the basis of occurrence is exceeded,
A cathodic protection situation measurement and evaluation system characterized by comprising: When the measurement value is extracted at a commercial frequency of 50 Hz and the unit measurement time is 20 msec and the data sampling interval is 0.1 msec, the direct current density (I _DC ) is obtained by the following equation (1). The alternating current density (I _AC ) is obtained by the following formula (2),
The said cathodic protection status evaluation means evaluates that the cathodic protection status of a metal structure is bad when the said alternating current density ( _IAC ) exceeds the said reference value. Measurement and evaluation system for cathodic protection.

The commercial frequency identification means includes
The difference in appearance time between the maximum value and the minimum value of the measurement value within the unit measurement time is ½ of the unit measurement time, and the maximum value and the average value of the measurement value within the unit measurement time 6. The measurement and evaluation system for a cathodic protection situation according to claim 4, wherein a difference between the difference between the average value and the minimum value of the measurement values within the unit measurement time is equal.

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