JP4522289B2 - Corrosion estimation method - Google Patents

Description

  The present invention relates to a corrosion estimation method for estimating a corrosion state (whether or not corrosion has occurred and its degree) of a long metal body at least partially disposed in a medium.

  Currently, various types of piping for supplying utilities such as water and gas into buildings where consumers live are buried in media such as soil and concrete. Such pipes are drawn into the premises of each building as main pipes via main branches (outer pipes) buried under roads, etc., and gas meters that measure gas usage and water supplies that measure water usage It is further drawn into the building via a meter.

  A specific part of the piping as a long metal body, at least a part of which is placed in the soil, is directly or indirectly electrically connected to the reinforcing bars (conductive members) in the concrete forming the building. There are things to do. In this case, since the concrete is alkaline, the reinforcing bar in the concrete shows a potential of about -200 mV (saturated copper sulfate electrode standard. The following potential is also the same standard). On the other hand, when there is a defect in the coating in the soil, the part of the piping that contacts the soil exhibits a potential of about -500 mV to -700 mV. Therefore, a macro cell (battery) having a potential difference of about 300 mV to 500 mV is formed between the pipe and the reinforcing bar, and a corrosion current flows through the pipe due to the DC potential difference. And the corrosion according to the magnitude of a corrosion current generate | occur | produces in the contact part with the soil of piping.

  Conventionally, as a method for estimating the corrosion state of a pipe, a method of actually measuring a corrosion current flowing through the pipe has been proposed. For example, a clamp type DC ammeter is attached to the pipe, and the corrosion current actually flowing is measured (see, for example, Patent Document 1).

No. 7-19007

  However, when trying to measure the direct current corrosion current flowing through the pipe which is a long metal body based on the conventional method, there is a limit. In other words, direct DC current measurement using a clamp-type DC ammeter can only detect currents in the order of milliamps at current levels due to the effects of geomagnetism and piping magnetic fields. Cannot be measured. As a result, when the corrosion current flowing through the pipe is small because the area of the defective portion is small, the corrosion cannot be detected or estimated.

  The present invention has been made in view of the above-mentioned problems, and its purpose is, for example, to properly corrode a longitudinal metal body such as a conductive pipe buried in the ground even when the corrosion current is small. The object is to provide a corrosion estimation method capable of detecting and estimating the degree of corrosion.

The characteristic configuration of the corrosion estimation method according to the present invention for achieving the above object is a corrosion estimation method for estimating a corrosion state of a longitudinal metal body at least partially disposed in a first medium,
Contact with the first medium of the elongated metal body in a state in which a macrocell is formed by contact between the elongated metal body and a conductive member disposed in the same or different second medium as the first medium. An alternating potential difference forming step of forming a set potential difference corresponding to a direct current potential difference existing between the portion and the conductive member between the longitudinal metal body and the conductive member using an alternating potential difference forming means; ,
Performing an alternating current measuring step of measuring an alternating current flowing through the elongated metal body by the alternating potential difference forming step;
The corrosion current flowing in the elongated metal body is estimated based on the alternating current measured in the alternating current measuring step.

According to the above characteristic configuration, in the AC potential difference forming step, the longitudinal metal body and the conductive member in the building come into contact with each other, so that the site of the longitudinal metal body in contact with the first medium and the building interior A set potential difference corresponding to the DC potential difference existing between the conductive member and the conductive member is formed between the longitudinal metal body and the conductive member using AC potential difference forming means. And in the alternating current measurement step, the alternating current flowing through the longitudinal metal body is measured by the alternating potential difference forming step, and the corrosion current flows through the longitudinal metal body based on the alternating current measured in the alternating current measurement step. Can be estimated to a small level.
The present application is supported by new technical knowledge newly found by the inventor and later verified theoretically or experimentally in detail.
That is, a long metal body such as a utility pipe introduced into a building and a conductive member, which is a system as the subject of the present application, are located in a predetermined medium, and a part of the part is between them. In a situation where a macro cell is formed through electrical connection and a longitudinal metal body, a conductive member, and a medium, the grounding resistance between the longitudinal metal body and the medium works preferentially, depending on the macro cell. The direct current corrosion current can be estimated from the alternating current flowing at that time. AC current can be easily measured even when the value is small.
Therefore, in this method, even in a situation where only a relatively small corrosion current that could not be measured conventionally flows, the corrosion current can be estimated by measuring an alternating current that is easy to measure. The corrosion situation can be estimated.

Details will be described in detail separately, but the outline of the reason why such processing is possible is as follows. When the longitudinal metal body in contact with the first medium and the conductive member are conductive, the longitudinal metal body is elongated by a DC potential difference caused by the macrocell between the portion of the longitudinal metal body in contact with the first medium and the conductive member. The direct-current corrosion current flowing through the metal body can be generally derived by the quotient of the direct-current potential difference caused by the macro cell and the ground resistance between the longitudinal metal body and the first medium. On the other hand, when an AC potential difference is formed between the portion of the longitudinal metal body that is in contact with the first medium and the conductive member, the AC current that flows through the longitudinal metal body is equal to the AC potential difference, the longitudinal metal body, and the first metal body. It can be derived by the quotient of the ground resistance with the medium.
Thus, both the corrosion current and the alternating current in the longitudinal metal body reflect the ground resistance between the longitudinal metal body and the first medium. Therefore, instead of measuring the direct current corrosion current flowing in the longitudinal metal body by the direct current potential difference (macrocell) existing between the portion of the longitudinal metal body in contact with the first medium and the conductive member, It can be generally replaced by measuring the alternating current flowing in the longitudinal metal body when an alternating potential difference of the same magnitude is formed between the portion of the longitudinal metal body in contact with the first medium and the conductive member. Therefore, when the macrocell is formed, the direct current corrosion current flowing in the longitudinal metal body is such that the AC potential difference exists between the portion of the longitudinal metal body that contacts the first medium and the conductive member. It can be estimated based on the flowing alternating current.
In this case, since it is only necessary to measure the alternating current, in order to know the corrosion current flowing through the elongated metal body, a conventional clamp type DC ammeter that is difficult to measure a current below milliampere due to the influence of geomagnetism or the like. May not be used. As a result, for example, even when a small corrosion current of the order of milliamperes or less flows through the longitudinal metal body, the corrosion current can be estimated by the corrosion estimation method of the present invention, and the degree of corrosion of the longitudinal metal body is estimated. Is possible.

  The characteristic configuration of the corrosion estimation method according to the present invention is to measure a DC potential difference existing between a portion of the elongated metal body that contacts the first medium and the conductive member, and to determine the DC potential difference as the set potential difference. The set potential difference determining step is set as follows.

  When the above characteristic configuration is implemented, first, a direct current potential difference existing between the longitudinal metal body and a conductive member in a building that contacts the longitudinal metal body is actually measured. This direct current potential difference is given as the set potential difference described above, and the alternating current is measured to accurately estimate the corrosion current actually generated in the elongated metal body.

  Another characteristic configuration of the corrosion estimation method according to the present invention is to set an estimated DC potential difference estimated to exist between a portion of the elongated metal body that contacts the first medium and the conductive member as the set potential difference. The set potential difference determining step includes the step of.

  When implementing the above characteristic configuration, the estimated DC potential difference is the DC potential difference actually measured in another longitudinal metal body embedded in the same environment as the longitudinal metal body on which the corrosion current is estimated. In addition, a DC potential difference that is empirically estimated based on a state in which the elongated metal body is embedded in a first medium such as soil is used as an estimated DC potential difference. Then, the estimated DC potential difference obtained in this way is given as the set potential difference described above, and the corrosion current actually generated in the longitudinal metal body is estimated. As a result, the estimated DC potential difference can be used to estimate the corrosion state of the elongated metal body in a specific situation.

  The characteristic configuration of the corrosion estimation method according to the present invention is that it includes a conduction state determination step of determining a conduction state between the longitudinal metal body and the conductive member prior to the alternating current measurement step.

  By executing this step, it is possible to confirm the contact state between the elongated metal body and the conductive member, that is, the possibility of forming a macro cell in question.

The corrosion estimation method according to the present invention will be described below with reference to the drawings.
[Corrosion target]
In the following embodiment, the conductive metal pipe 2 (elbow 2a, pipe 2b, pipe 2c) to which an insulating coating is applied at least in the soil 1 is illustrated as the longitudinal metal body. FIG. 1 shows a state in which conductive pipes (elbow 2 a, pipe 2 b, pipe 2 c) are arranged from a ground building composed of concrete 3 and reinforcing bars 4 to underground soil 1. ing.
In this system, the conductive pipe 2 corresponds to a long metal body, the reinforcing bar 4 corresponds to a conductive member, the soil 1 corresponds to the “first medium” of the present invention, and the concrete 3 corresponds to the present invention. The rebar 4 in the concrete 3 corresponds to a conductive member.

[Macro cell]
The conductive pipe 2 may be electrically connected to the reinforcing bar 4 provided in the concrete 3 of the building in the region A. In this case, the potential of the reinforcing bar 4 is about -200 mV (saturated copper sulfate electrode standard. The following potential is also the same standard). In addition, for example, a coating defect (indicated by “x” in the drawing) that may become a corroded portion may occur in the elbow 2a that is provided with an insulating coating. In this case, the metal portion of the elbow 2a Only exposed and comes into contact with the soil 1. And the potential of about -500 mV-about -700 mV arises in the elbow 2a of the site | part which contacts the soil 1 by the occurrence of a coating defect according to the environment of the soil 1. As a result, a macro cell (battery) having a direct current potential difference of about 300 mV to about 500 mV is formed between the coating defect portion in contact with the soil 1 of the conductive pipe 2 and the reinforcing bar 4 in the concrete 3 of the building. Thus, a direct current corrosion current as shown by a one-dot chain line in FIG. The corrosion current flows out from the reinforcing bar 4 to the soil 1 through the conductive pipe 2 and flows into the reinforcing bar 4 through the concrete 3, whereby the corrosion progresses. The present application is intended to accurately estimate the direct current corrosion current.

[Corrosion estimation method]
The corrosion estimation method according to the present invention will be described with reference to FIGS.
FIG. 1 shows the configuration of a corrosion estimation system for estimating a direct current corrosion current flowing in the conductive pipe 2. FIG. 2 shows a configuration of a measurement system that measures a DC potential difference required in the previous stage when performing corrosion estimation in the present application. FIG. 3 shows a confirmation system for determining a conduction state between the conductive pipe 2 and the reinforcing bar 4 before performing the corrosion estimation in order to confirm the possibility of the macro cell corrosion that is a problem in the present application. It is the composition.

[Corrosion estimation system]
In the configuration of the corrosion estimation system shown in FIG. 1, the AC potential difference forming unit 12 generates a set potential difference corresponding to a DC potential difference existing between the coating defect portion in contact with the soil 1 of the conductive pipe 2 and the reinforcing bar 4. , Formed between the conductive pipe 2 and the reinforcing bar 4 (AC potential difference forming step), the current measuring means 11 measures the AC current flowing through the conductive pipe 2 by the AC potential difference formed by the AC potential difference forming means 12. Then, the information processing apparatus 10 estimates the corrosion current flowing through the conductive pipe 2 based on the alternating current measured by the current measuring means 11.

  The AC potential difference forming means 12 shown in FIG. 1 includes a voltmeter 12a, an AC power source 12b, and a magnetic field forming means 12c. When a magnetic field surrounding the pipe 2c is formed by the magnetic field forming unit 12c driven by the AC power source 12b, an AC potential difference for flowing an AC current through the pipe 2c is formed. The AC potential difference can be measured using a voltmeter 12a. That is, the AC potential difference forming means 12 adjusts the output of the AC power supply 12b, thereby forming a predetermined AC potential difference between the coating defect portion in contact with the soil 1 of the conductive pipe 2 and the reinforcing bar 4. A potential difference forming step is executed.

The current measuring means 11 shown in FIG. 1 is a clamp-type AC ammeter including an ammeter 11a and a clamp part 11b. When an alternating current flows through the pipe 2c, a current is induced in the clamp portion 11b by a magnetic field induced by the alternating current. The current can be measured using an AC ammeter 11a. That is, the current measuring unit 11 executes an AC current measuring process in which the AC potential difference forming unit 12 measures the AC current flowing through the conductive pipe 2 by forming an AC potential difference.
Therefore, in this corrosion estimation system, an alternating current can be generated based on a previously known DC potential difference and an alternating current generated in that state can be obtained.

The information processing apparatus 10 illustrated in FIG. 1 can be realized using a general computer or another arithmetic processing apparatus. And the information processing apparatus 10 estimates the corrosion current which flows into the piping 2c based on the alternating current measured by the current measurement means 11 in the alternating current measurement process mentioned above.
The information processing apparatus 10 stores a correlation index newly created by the inventor. The index may be a chart as shown in FIG. 4, may be based on a certain correlation equation, or may take the form of a numerical table.
In FIG. 4, the horizontal axis is the alternating current (actual value) measured by the current measuring means 11, and the vertical axis is the direct current corrosion current (actually measured value in the simulation test) flowing through the pipe 2c when the macro cell is formed. ). The information processing apparatus 10 flows into the pipe 2c based on the measured alternating current by utilizing the fact that the alternating current and the direct current corrosion current have a certain strong correlation as shown by the solid line in FIG. Estimate the corrosion current. For example, when the alternating current measured by the current measuring means 11 is 10 μA as indicated by an arrow in the figure, it can be estimated that the corrosion current is about 7 μA.

The above is the core of the corrosion estimation method according to the present application. The corrosion estimation system executes an estimation method that gives an AC potential difference corresponding to a DC potential difference and estimates a corrosion current based on an AC current amount measured in that state. Although it is the outline, hereinafter, the corrosion estimation according to the present application will be described according to the work procedure.
This work procedure is, for example,
1 Judgment of conduction state with conductive member with longitudinal metal body (conduction state judgment step),
2 DC potential difference measurement (set potential difference determination process),
3. Proceed in the order of corrosion estimation using the corrosion estimation system (AC potential difference formation process / AC current measurement process).
Hereinafter, it demonstrates in this order.

1 Judgment of conduction state between longitudinal metal body and conductive member (conduction state judgment step)
In this determination step, continuity is confirmed by the confirmation system shown in FIG.
The resistance measuring means 18 of the confirmation system shown in FIG. 3 includes an AC power source 18a that applies an AC voltage between a contact 19 electrically connected to the conductive pipe 2 and a counter electrode 20 inserted in the soil 1, and a conductive An ampere meter 18b for measuring the current flowing through the conductive pipe 2, and a voltmeter 18c for measuring a potential difference existing between the reference electrode 21 inserted in the soil 1 and the contact point 19. Furthermore, a current measuring means 16 for measuring the current flowing inside at a position closer to the reinforcing bar 4 than the contact 19 is provided. Then, the information processing apparatus 110 determines whether the conductive pipe 2 and the reinforcing bar 4 are based on the potential difference existing between the conductive pipe 2 and the reference electrode 21 measured by the resistance measuring unit 18 and the current flowing through the potential difference. The continuity of is determined. This determination method can be based on the measurement value of the current measurement means 16 or the resistance measurement means 18 provided in the confirmation system.

In the case of using the current measuring means 16 In this example, the electric current is measured based on the current flowing through the conductive pipe 2 from the contact point 19 to the conduction part A, which is measured using the current measuring means 16. The continuity between the conductive pipe 2 and the reinforcing bar 4 is determined. As shown in FIG. 3, the current measuring means 16 is a clamp-type AC ammeter provided with a clamp portion 16b and an ammeter 16a arranged around the pipe 2c. For example, the determination is based on a voltmeter 18c provided in the resistance measuring means 18 in a state where an AC voltage is applied between the contact 19 and the counter electrode 20, as shown in FIG. The resistance flowing through the circuit indicated by is obtained. And when resistance of the circuit X derived | led-out based on the measurement result of the ammeter 16a is small (for example, less than 10 ohms), it can determine with the electroconductive piping 2 and the reinforcing bar 4 being electrically connected. If it is high, it can be determined that the continuity is not established.
This measurement method can be applied regardless of the presence or absence of the insulation state between the conductive pipe 2 and the soil 1.

When the resistance measuring means 18 can be used, it can be confirmed that the portion of the conductive pipe 2 in the soil 1 includes an insulating joint and the like, and the ground resistance between the conductive pipe 2 and the soil 1 is secured. In this case, since the current flowing through the circuit Y shown in FIG. 3 is considered to be sufficiently small based on the results of the ammeter 18b and the voltmeter 18c provided in the resistance measuring means 18, the conductive pipe 2 is reduced from the resistance in the circuit X. And the rebar 4 can be determined. That is, if the resistance of the circuit X derived by the resistance measuring means 18 is small (for example, less than 100Ω), it is determined that the conductive pipe 2 and the reinforcing bar 4 are conductive, and on the other hand, the resistance of the circuit X Is larger (for example, 100Ω or more), it is determined that the conductive pipe 2 and the reinforcing bar 4 are not electrically connected.
In this way, it is possible to determine whether or not the macro cell corrosion is a problem depending on whether or not the conductive pipe 2 and the reinforcing bar 4 are electrically connected. Only when it is determined that there is continuity, the following work is performed.

2 DC potential difference measurement (set potential difference determination process)
As the AC potential difference formed in the pipe 2 by the AC potential difference forming means 12 provided in the corrosion estimation system shown in FIG. 1, when using the estimation method of the present application, the DC potential difference measured by the measurement system shown in FIG. Use.
In the measurement system shown in FIG. 2, the information processing apparatus 100 includes a contact 14 electrically connected to the conductive pipe 2 and an electrode 15 inserted into the soil 1 (with the same metal material as the pipe) by a voltmeter 13. And a DC potential difference existing between and corresponding to coating defects) is measured.

3 Corrosion estimation using the corrosion estimation system (AC potential difference formation process / AC current measurement process)
Through the above steps, the corrosion estimation system according to the present application uses the DC potential difference measured by the above method. That is, in the corrosion estimation system shown in FIG. 1, the information processing apparatus 10 sets the measured DC potential difference as the set potential difference. In this case, an AC potential difference corresponding to the DC potential difference measured by the voltmeter 13 can be applied by adjusting the output of the AC power source 12 b based on the measurement result of the voltmeter 12 a provided in the AC potential difference forming unit 12. It becomes possible.
Then, in a state where the predetermined AC potential difference is formed, the current measuring means 11 measures the AC current value, and the information processing apparatus 10 determines the AC current based on the correlation index shown in FIG. 4 described above. The corrosion current value is obtained from the value. As a result, the corrosion current can be obtained quantitatively.

Furthermore, the information processing apparatus 10 can derive the corrosion mass rate of the conductive pipe 2 based on the estimated corrosion current, and can estimate the degree of corrosion of the coating defect portion of the conductive pipe 2. .
For example, when the estimated corrosion current is 100 μA and the material of the conductive pipe 2 is iron, the corrosion mass rate for iron eluted (corroded) from the conductive pipe 2 to the soil 1 by the corrosion current is 0.9 g. / Year. However, the anode reaction when iron ions are eluted from the conductive pipe 2 to the soil 1 is the following chemical reaction formula.

[Formula 1]
Fe → Fe ²⁺ + 2e ⁻

The above is a description of the corrosion estimation method according to the present application, but it is used in the information processing apparatus to verify the validity of the present application estimation method.
Regarding verification of the validity, the inventors tried theoretical verification and also performed verification in field tests.
Theoretical verification In the circuit shown in FIG. 5A, the conductive pipe 2 having a coating defect and the reinforcing bar 4 in contact with the concrete 3 are electrically connected to each other. A current path is formed from the soil 1, the concrete 3, and the reinforcing bar 4 to the conductive pipe 2, and a direct current potential difference between the coating defect part and the reinforcing bar 4 that contacts the soil 1 of the conductive pipe 2. : DC equivalent circuit diagram when V is present.
In the current path of the direct current, when the direct current flows, when the conductive pipe 2 corrodes and the metal ions flow out into the soil, which occurs between the coating defective portion of the conductive pipe 2 and the soil 1. The anode reaction resistance of R ₂ , the electric double layer capacity between the coating defect portion of the conductive pipe 2 and the soil 1: C ₂ , and the coating defect portion of the conductive pipe 2 and the soil 1 Between the ground resistance: R _S2 and the cathode reaction resistance which is a reduction reaction of oxygen occurring between the reinforcing bar 4 and the concrete 3: R ₄ , Electric double layer capacity between the reinforcing bar 4 and the concrete 3: C ₄ , And there exists ground resistance: R _S4 between the reinforcing bar 4 and the concrete 3. Considering that the current flowing in this circuit is a direct current, the electrical resistance for this direct current is the anode reaction resistance: R ₂ , ground resistance: R _S2 , ground resistance: R _S4 , and cathode reaction Resistance: R ₄ can be considered.

  Further, for example, when the conductive pipe 2 is iron (Fe) and the reinforcing bar 4 functions as a cathode, the anodic reaction and the cathodic reaction that are generated respectively are represented by the following chemical formulas.

[Formula 2]
Anode reaction: Fe → Fe ²⁺ + 2e ⁻
Cathode reaction: 1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻

However, since the conductive pipe 2 contains a large amount of Fe atoms, the anode reaction is likely to occur, and the anode reaction resistance R ₂ can be regarded as very small. Similarly, since the reinforcing bar 4 has a very large surface area and a very small current density, the cathode reaction resistance R ₄ is very small. Furthermore, since the reinforcing bar 4 and the concrete 3 are in contact with each other in a large area, the grounding resistance R _S4 between the reinforcing bar 4 and the concrete 3 is also very small.
Therefore, the direct current I flowing in the equivalent circuit diagram shown in FIG. 5A is the quotient of the ground resistance R _S2 between the coating defect portion of the conductive pipe 2 and the soil 1 with respect to the DC potential difference V. V / R _S2 can generally be derived.

FIG. 5B shows that the conductive pipe 2 having a coating defect and the reinforcing bar 4 are electrically connected to each other, so that the coating defective part, the soil 1, the reinforcing bar 4 and the conductive pipe of the conductive pipe 2 are connected. 2 and an equivalent circuit of an alternating current when an alternating potential difference: v exists between the coating defect portion and the reinforcing bar 4 in contact with the soil 1 of the conductive pipe 2. is there.
Similarly to the current path of the alternating current shown in FIG. 5A, the anode reaction resistance: R ₂ , the electric double layer capacity: C ₂ , the ground resistance: R _S2, and the cathode Although there is a reaction resistance: R ₄ , the electric double layer capacitance: C ₄ , and the ground resistance: R _S4 , the frequency of this alternating current is considered considering that the alternating current flows through this circuit. Increases, the impedance in the electric double layer capacitors C ₂ and C ₄ becomes almost zero. Further, since the reinforcing bars 4 and the concrete 3 are in contact with each other over a large area, the ground resistance: R _S4 is very small. As a result, it can be considered that the electric resistance for the alternating current is the ground resistance: R _S2 .
Therefore, the alternating current i flowing in the equivalent circuit shown in FIG. 5B is the ground resistance between the coating defect portion of the conductive pipe 2 and the soil with respect to the alternating potential difference: v: the quotient of R _S2 : v / R _S2 can be derived.

As described above, the AC current i flowing in the equivalent circuit shown in FIG. 5B is equal to the DC current I flowing in the equivalent circuit shown in FIG. It can be said that this reflects the ground resistance between the portion and the soil 1: R _S2 . Therefore, instead of measuring the direct current corrosion current flowing through the conductive pipe 2 due to the direct current potential difference (macrocell) existing between the coating 4 and the reinforcing defect 4 in contact with the soil 1 of the conductive pipe 2, the direct current Theoretically, the alternating current flowing in the conductive pipe 2 is measured when an AC potential difference of the same magnitude as that of the potential difference is formed between the reinforcing bar 4 and the coating defect portion in contact with the soil 1 of the conductive pipe 2. Above is no problem.

The verification by verification tests this test, the test piece 24 surface area simulating a 10 mm ² ～13750Mm ² coating-covering conductive pipe 2 defects created intentionally, and the actual conductive corrosion occurs during embedded A pipe piece was used as a test piece 24 embedded in soil. Then, both the direct current and the alternating current are measured for the same test piece 24 using the systems shown in FIGS. 6 and 7, and the relationship between the direct current and the alternating current measured for each of the same test pieces 24 is illustrated. Plotted on 4.

The system shown in FIG. 6 embeds a test piece 24 in the soil 1 and provides a conductive wire 22 that electrically connects the test piece 24 and the pipe 2c. In this state, the direct current flowing in the conductive wire 22 (corresponding to the corrosion current flowing through the macrocell generated in the conductive pipe 2) is measured by the ammeter 23, whereby the direct current in each test piece 24 is measured. did.
On the other hand, for each of the prepared test pieces 24, the AC potential difference forming means 12 and the current shown in FIG. 1 are connected in a state where the test piece 24 and the pipe 2c are connected by the conductive wire 22 as in the system shown in FIG. Using the AC potential difference forming unit 27 and the current measuring unit 26 having the same configuration as that of the measuring unit 11, the DC potential difference existing between the portion where the coating defect portion of the test piece 24 contacts the soil 1 and the reinforcing bar 4. A set potential difference corresponding to (this is previously measured by the measurement system shown in FIG. 2 in advance) was formed, and the alternating current flowing through the conductive wire 22 was measured.
When the results obtained for each test piece 24 as described above are plotted on FIG. 4, a strong correlation is recognized between the direct current and the alternating current measured according to the method of the present application, and the alternating current according to the method of the present application is observed. It can be seen that the direct current, which is a corrosion current, can be estimated well by measuring the value.

Therefore, for example, it can be said that the corrosion current estimated based on the correlation shown by the solid line in FIG. 4 is reliable. In addition, the corrosion current can be accurately estimated on the order of microamperes. The direct current corrosion current (DC current) shown on the vertical axis is slightly smaller than the alternating current shown on the horizontal axis. The anode reaction resistance at the coating defect portion of the conductive pipe 2 which is not completely zero: R ₂ and the cathode reaction resistance at the reinforcing bar ₄ : R ₄ are the coating defect portion of the conductive pipe 2 and the soil. It is considered that this is because it is added to the grounding resistance between 1 and R _S2 (strictly, R _S2 + R _S4 ).

<Another embodiment>
<1>
In the above embodiment, the execution sequence of the series of corrosion estimation methods including the AC potential difference forming step and the AC current measuring step, the set potential difference determining step, and the conduction state determining step is not particularly described. It is preferable to execute in order of description of the state determination step, the set potential difference determination step, and the corrosion estimation method. The execution order of the conduction state determination step and the set potential difference determination step may be reversed. Furthermore, the conduction state determination step may be performed prior to the alternating current measurement step.

<2>
In the said embodiment and said another embodiment, although the case where a conduction | electrical_connection state determination process is performed was demonstrated, when it was known that the electroconductive piping 2 and the reinforcing bar 4 are conducting, it showed in FIG. The conduction state determination step may not be performed.

<3>
In the above-described embodiment, in the set potential difference determining step described with reference to FIG. 2, the direct current potential difference due to the macrocell existing between the portion where the coating defect portion of the conductive pipe 2 and the soil 1 are in contact with the reinforcing bar 4. However, the DC potential difference caused by the macro cell may be determined by estimation without actually measuring.
For example, a direct current potential difference that has already been actually measured in another conductive pipe embedded in the same environment as the conductive pipe 2 that is the object of measurement of the corrosion current is used as the estimated direct current potential difference, or the conductive pipe 2 The DC potential difference due to the macro cell may be estimated based on the estimated DC potential difference that is empirically estimated based on the state where the cell is embedded in the soil. Further, statistical processing such as averaging a plurality of the estimated DC potential differences may be performed.

<4>
In the said embodiment, although the case where the coating defect existed in the elbow 2a of the electroconductive piping 2 as a longitudinal metal body was demonstrated, the coating defect exists in the other part which comprises the electroconductive piping 2. FIG. However, the corrosion estimation method of the present invention can be applied. Further, the longitudinal metal body may be a steel pipe that is not coated as described above.

<5>
In the said embodiment, in order to determine the conduction | electrical_connection state whether the electroconductive piping 2 and the reinforcing bar 4 are conducting, the form which investigates the resistance between the electroconductive piping 2 and the soil 1 or the reinforcing bar 4 was demonstrated. However, whether or not the conductive pipe 2 and the reinforcing bar 4 are electrically connected by examining the potential difference between the simulated defect and the reinforcing bar 4 and the current flowing from the reinforcing bar 4 to the simulated defect as a considerable amount in addition to the resistance. Such a conduction state may be determined.

<6>
In the above embodiment, the soil 1 is exemplified as the first medium and the concrete 4 is exemplified as the second medium. However, when the long metal body and the conductive member are provided in the soil or another medium other than the concrete. The present invention can also be applied to. Moreover, although the said embodiment demonstrated the case where a 1st medium (soil 1) and a 2nd medium (concrete 3) were different materials, the state by which a macrocell is formed in an elongate metal body and an electroconductive member. If so, the first medium and the second medium may be the same material.

  The corrosion estimation method according to the present invention can be used to estimate the corrosion state of a long metal body such as a gas pipe, a water pipe, or a building material embedded in a medium such as soil, concrete, or water. Furthermore, based on the estimated corrosion state, it can be used to know the replacement time of those elongated metal bodies.

Corrosion estimation system configuration diagram when performing the corrosion estimation method Measurement system configuration diagram when performing the corrosion estimation method Confirmation system configuration diagram when performing the corrosion estimation method Diagram showing the correlation between AC current (actual value) and corrosion current (estimated value) Equivalent circuit diagram when the conductive piping is connected to the reinforcing bar in the building System configuration diagram for measuring corrosion current, which is direct current System configuration diagram for measuring AC current according to the method of this application

Explanation of symbols

1 soil (first medium)
2 Conductive piping (longitudinal metal body)
3 Concrete (second medium)
4 Rebar (conductive member)
12 AC potential difference forming means

Claims (4)

A corrosion estimation method for estimating a corrosion state of a longitudinal metal body at least partially disposed in a first medium,
Contact with the first medium of the elongated metal body in a state in which a macrocell is formed by contact between the elongated metal body and a conductive member disposed in the same or different second medium as the first medium. An alternating potential difference forming step of forming a set potential difference corresponding to a direct current potential difference existing between the portion and the conductive member between the longitudinal metal body and the conductive member using an alternating potential difference forming means; ,
Performing an alternating current measuring step of measuring an alternating current flowing through the elongated metal body by the alternating potential difference forming step;
The corrosion estimation method which estimates the corrosion current which flows into the said elongate metal body based on the alternating current measured in the said alternating current measurement process.   A set potential difference determining step of measuring a DC potential difference existing between a portion of the elongated metal body that contacts the first medium and the conductive member, and setting the measured DC potential difference as the set potential difference The corrosion estimation method according to claim 1.   The corrosion according to claim 1, further comprising a set potential difference determining step of setting an estimated DC potential difference estimated to exist between a portion of the elongated metal body that contacts the first medium and the conductive member as the set potential difference. Estimation method. Prior to the alternating current measurement step,
The corrosion estimation method as described in any one of Claims 1-3 including the conduction | electrical_connection state determination process which determines the conduction | electrical_connection state of the said elongate metal body and the said electroconductive member.

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