JP6764815B2 - How to check the soundness of the corrosion sensor - Google Patents

Description

The present invention relates to a method for confirming the soundness of a capacitance type corrosion sensor.

The steel material in the concrete structure is protected from corrosion by forming a passivation film on the surface of the steel material because the concrete maintains an alkaline environment. However, when corrosive factors such as carbon dioxide in the air, sulfuric acid in sewerage facilities, or chloride ions enter the concrete, this passivation film is destroyed and the water and oxygen in the concrete cause corrosion of the steel material. Start. Further, in structures using steel materials such as iron bridges and plants, protective paints are used to prevent rusting of the steel materials.

When the steel material of a concrete structure corrodes, the volume expansion of the steel material occurs, the expansion pressure causes cracks in the concrete, and the corrosion of the steel material is accelerated by the invasion of corrosive factors and the supply of water and oxygen from the outside through the cracks. Eventually, the function as a concrete structure cannot be maintained. Further, when the steel material is corroded in the steel bridge, the protective coating film is lifted or peeled off due to the volume expansion of the steel material, and the rust preventive effect is lost.

Therefore, the invasion of corrosion factors and the start of corrosion of steel materials are detected before the start of corrosion of steel materials, and for example, measures such as surface coating prevent further intrusion of corrosion factors and water and oxygen to protect the steel materials from corrosion. It is important to take preventive maintenance of the structure. Various corrosion diagnosis methods have been conventionally proposed for this problem. For example, a method of removing a core to analyze a corrosion factor, a method of nondestructively measuring the natural potential and polarization resistance of a steel material, a method of detecting a corrosion factor with a chemical sensor or a gas sensor, and a simulated corrosion member made of iron wire. There is known a method of burying it in concrete and detecting corrosion when a thin wire is broken.

Among these corrosion diagnosis methods, the method of detecting corrosion by disconnection of a thin wire is (a) that the concrete is not damaged such as core removal by embedding a sensor in advance, and (b) between the concrete surface and the steel material. By installing several thin wires according to the depth, it is possible to monitor the time dependence of the invasion of corrosion factors from the surface and facilitate the formulation of maintenance plans. (C) Since iron corrosion is directly captured, It is possible to detect the possibility of corrosion including not only corrosion factors but also the supply state of water and oxygen. (D) Since it captures changes in electrical resistance, it can be detected with extremely low power consumption and is suitable for long-term monitoring. There are merits, and various corrosion diagnosis methods by detecting fine wire cutting have been proposed (for example, Patent Documents 1 to 3). Further, in order to increase the sensitivity and the degree of freedom in design, a corrosion sensor using an iron foil material has also been proposed (Patent Document 4).

Many conventional corrosion sensors capture the electrical resistance of the detector. Iron with a high dielectric constant does not easily change its resistance value unless it breaks, and the sensitivity of the sensor tends to depend on the wire diameter and line width, etc. In addition, it loses its function as a sensor after breaking. There is a proposal to detect a corrosive environment by capturing the capacitance (Patent Document 5). Since this capacitance sensor can detect corrosion by changing the area of the detection unit, it is possible to grasp how much corrosion has progressed in the concrete structure.

Japanese Patent Application Laid-Open No. 8-094557 Japanese Patent Application Laid-Open No. 8-233896 Patent No. 3205291 Japanese Unexamined Patent Publication No. 2012-145330 JP-A-2017-032516

When the corrosion sensor is embedded in concrete, the concrete itself filled around it is a dielectric material, and the dielectric constant changes depending on the water content. Therefore, the waterproof case is used to waterproof the parts other than the detection part. However, in rare cases, if the waterproofing is insufficient, the corrosion sensor may break down due to flooding or the like, or the detection unit and the counter electrode may become conductive and the function of the corrosion sensor may be lost. However, even if the function of the corrosion sensor is lost, it is difficult to confirm the soundness of the corrosion sensor because it is buried in concrete. Therefore, when the electrical characteristics such as capacitance change, it is not possible to determine whether it is due to corrosion or malfunction, or there is no choice but to bury a large number of corrosion sensors to determine. ..

The present invention has been made in view of such circumstances, and it is possible to confirm the soundness of the corrosion sensor non-destructively even when it is buried in concrete, and to accurately grasp the corrosive environment. It is an object of the present invention to provide a method for confirming the soundness of a corrosion sensor.

(1) In order to achieve the above object, the present invention has taken the following measures. That is, the method for confirming the soundness of the corrosion sensor of the present invention includes a detection unit made of a corrosive metal and a counter electrode formed of a corrosion resistant metal and provided at a position facing the detection unit. This is a method for confirming the soundness of a corrosion sensor including a dielectric provided between the detection unit and the counter electrode, wherein the detection unit is a concrete surface. A step of embedding the corrosion sensor in concrete so as to be located on the side, a step of installing an external electrode on the concrete surface at a position facing the position where the corrosion sensor is embedded, and the detection unit and the external electrode. A step of measuring the capacitance Cx between the detection unit and the counter electrode, a step of measuring the capacitance Cy between the detection unit and the counter electrode, and a capacitance Cz between the external electrode and the counter electrode. It is characterized by including at least a step of measuring and a step of determining whether or not the measurement result of each capacitance satisfies a predetermined relational expression.

In this way, the corrosion sensor is embedded in the concrete so that the detection unit is located on the concrete surface side, the external electrode is installed at the position facing the position where the corrosion sensor is embedded on the concrete surface, and the detection unit and the external electrode are installed. The capacitance Cx between the two is measured, the capacitance Cy between the detection unit and the counter electrode is measured, the capacitance Cz between the external electrode and the counter electrode is measured, and each capacitance is measured. Since it is determined whether or not the measurement result of the above satisfies a predetermined relational expression, the soundness of the corrosion sensor can be confirmed even when the corrosion sensor is embedded in the concrete structure. Since the state can be grasped only by installing an external electrode on the surface of concrete and measuring the capacitance, the state of the corrosion sensor can be easily checked at low cost and non-destructively.

(2) Further, in the method for confirming the soundness of the corrosion sensor of the present invention, it is determined whether or not the capacitance Cx, the capacitance Cy, and the capacitance Cz satisfy the following equation. ..

As described above, when the corrosion sensor is sound, the capacitance Cx, the capacitance Cy, and the capacitance Cz can be regarded as a series circuit, so that the equation (1) holds. Therefore, the soundness of the corrosion sensor can be confirmed even when the corrosion sensor is embedded in concrete. This relationship holds even if the detection unit is corroded, as long as the sensor is in a healthy state.

According to the present invention, the soundness of the corrosion sensor can be confirmed non-destructively even when it is buried in concrete, and the corroded environment can be accurately grasped.

It is a top view which shows the schematic structure of the corrosion sensor which concerns on this embodiment. It is sectional drawing when the corrosion sensor shown in FIG. 1 is cut by AA. It is a top view which shows the schematic structure of the corrosion sensor which concerns on this embodiment. It is a flowchart which shows the manufacturing method of the corrosion sensor which concerns on this embodiment. It is a figure which shows the outline of this corrosion sensor embedded in mortar or concrete. It is a figure which shows the principle of the soundness confirmation method of the corrosion sensor which concerns on this embodiment. It is a figure which shows the outline of the capacitance value measuring method using an external electrode. It is a figure seen from the top to the bottom with respect to the paper surface of FIG. It is a figure which shows the measurement result of the capacitance Cx, the capacitance Cy, and the capacitance Cz.

[Measurement principle of corrosion sensor]
The dielectric loss tangent increases with increasing resistance. In addition, the capacitance changes due to a defect in the electrode (detection unit). Therefore, by detecting the dielectric loss tangent, the initial corrosion generated on the surface of the corrosion sensor can be detected. In addition, electrical characteristics such as reactance and equivalent parallel resistance also change due to corrosion. Here, it is desirable to measure the change in dielectric loss tangent in a high frequency region of 10 kHz or more. Furthermore, by comprehensively judging the progress of corrosion with the degree of decrease in capacitance, it is possible to grasp the corrosion state with higher accuracy.

The dielectric loss tangent tan δ of the parallel flat conductor (detection unit) has the following relationship with ω: angular frequency, C: capacitance, and R: series equivalent resistance.
tan δ = ωCR ・ ・ ・ (2)

The capacitance C of the parallel plate conductor (detection unit) has the following relationship between the area S of the parallel plate conductor and the distance d between the parallel plate conductors.
C = Q / V = εS / d [F] ... (3)
Here, ε is the permittivity.

The corrosion sensor according to this embodiment uses this principle. That is, when the surface of the iron foil is corroded by the corrosion factor in the detection part of the sensor, the electric resistance increases. Therefore, the dielectric loss tangent increases proportionally. After that, the corrosion of the iron foil progresses, leading to a decrease in defects in the iron foil portion, and the capacitance begins to decrease. By grasping the degree of decrease in capacitance, it is possible to grasp the degree of decrease in the area of the detection unit and the degree of progress of the corrosive environment. The electrostatic tangent will decrease if the decrease in capacitance outweighs the increase in resistance.

Therefore, if the increase in the dielectric loss tangent captures the initial slight start of corrosion, and then the decrease in the dielectric loss tangent or the decrease in capacitance is observed, it is expected that the iron foil portion is chipped. It is possible to detect that the progress of corrosion is progressing.

[Corrosion sensor configuration]
FIG. 1 is a plan view showing a schematic configuration of a capacitance type corrosion sensor (hereinafter, corrosion sensor) according to the present embodiment. FIG. 2 is a cross-sectional view of the corrosion sensor 1 shown in FIG. 1 when it is cut by AA. The corrosion sensor 1 is manufactured by rolling a corrosive metal such as iron, and has an iron foil portion 3 as a detection portion having a thickness of 3 μm or more and 0.1 mm or less, a dielectric 7, and a lead wire 9. , The counter electrode 10 is provided.

The reason why the thickness of the iron foil portion 3 is set to 3 μm or more and 0.1 mm or less is that if it is too thin, cracks are likely to occur when handling the sensor, and if it is too thick, the sensitivity of the sensor may decrease. Further, the area of the iron foil portion 3 may be small because the initial slight start of corrosion can be captured by the dielectric loss tangent, but it is large when the progress of corrosion is grasped stepwise by the capacitance. Is preferable. By setting the area of the iron foil portion 3 to preferably 300 mm ² or more, it is possible to suppress the rapid progress of the corrosion reaction of the iron foil portion 3 and measure it as a sensor for a long period of time.

The iron foil portion 3 may be a thin film formed by vapor deposition or plating, or may be formed in a plate shape. The shape of the iron foil portion 3 may be rectangular, but if the iron foil portion 3 is rectangular, stress due to the difference in the coefficient of thermal expansion of each material is concentrated and adhered to the corner portion after the corrosion sensor 1 is installed. A circular shape is more preferable because it may cause cutting.

The iron foil portion 3 is provided with a plurality of through holes 5 and is formed in a mesh shape. Each through hole 5 may be formed in a mesh shape or a slit shape. By providing a plurality of through holes 5 in the iron foil portion 3, corrosion easily progresses, and even if a part of the through holes 5 is partially corroded and defective, the iron foil portion 3 may be left in an island shape. The amount of electrical continuity is ensured, and the amount of decrease in the area of the detection unit can be accurately captured by the change in capacitance.

Further, the planar shape of each through hole 5 is circular from the viewpoint of formation accuracy and yield in the formation by etching, but is not limited to this. For example, it may be a rectangle (square) or another shape. In etching, when a corner is formed as the shape of the object to be formed, the stress of metal dissolution in the etching causes a crack in the corner portion, the etching solution convects the corner portion, and the metal dissolution progresses locally, and a predetermined value is obtained. The shape may not be formed. When the through hole is circular, such stress is easily dispersed and retention at the corners does not occur, so that the formation accuracy and yield in the production of the through hole of the metal foil portion are improved. As a result, it becomes possible to contribute to quality stabilization and cost reduction.

As is clear from the equations (1) and (2), since the magnitude of the dielectric constant greatly contributes to the dielectric loss tangent and the change in capacitance, the dielectric 7 is a dielectric having a dielectric constant of 3 or more. It is desirable that the thickness is 0.05 mm to 2 mm, and a dielectric material that does not change much with temperature is desirable. This makes it possible to improve the measurement sensitivity of the sensor. As the dielectric 7, a polyimide film having a dielectric constant of 3.3 is preferable.

The counter electrode 10 is preferably a metal having high corrosion resistance. In order to capture the decrease due to corrosion of the iron foil by the electrical characteristics, it is premised that the area of the counter electrode 10 does not change. The counter electrode 10 is a metal having a lower ionization tendency than the target metal, including precious metals such as gold, platinum, and palladium, and has conductivity. When iron is the target, palladium, copper, nickel, and the like are used. Can be used. In addition to rolling, there is also a method of forming a film by sputtering, vapor deposition, plating, or the like. The thickness of the counter electrode 10 does not matter.

Further, as shown in FIG. 3, the iron foil portion 3 including the lead wire 9 may be provided with a corrosion prevention film 30 made of a non-corrosive material, and for example, a metal such as resin or platinum can be used. Above all, it is preferable to use an insulator such as resin in order to grasp the progress of corrosion step by step. This resin may be applied or a sticker may be attached. On the other hand, in the case of a metal, in addition to gold or platinum, it is possible to use a metal such as palladium, copper, lead, tin, nickel, or an alloy thereof, which is noble from the detector which is the material of the coating film, and is wet. A foil layer can be formed by plating, dry plating, or vapor deposition. When a metal is used, a potential difference with the detection unit is generated and corrosion progresses quickly, which is useful when early corrosion detection is desired.

[Manufacturing method of corrosion sensor]
FIG. 4 is a flowchart showing a method of manufacturing a corrosion sensor according to the present embodiment. First, iron as a detection unit is rolled to produce an iron foil (step S101). The iron foil shall have a thickness of 3 μm or more and 0.1 mm or less. Here, the iron foil may be a thin film formed by vapor deposition or plating, or may be formed in a plate shape.

Next, the iron foil material and the polyimide material are bonded together (step S102), and the sensor pattern is resist-printed (step S103). Next, chemical etching is performed (step S104). Here, through holes are also formed. Next, a counter electrode plate as a counter electrode is formed (step S105). Here, for example, sputtering, metal vapor deposition, plating, metal paint, attachment of a metal plate / metal foil, or the like can be used. Next, the lead wires are connected and waterproofed (step S106), and the sensor is exteriorized such as by adhering the case (step S107).

[Installation of corrosion sensor]
When applying a protective paint to a metal structure to be measured for corrosion, for example, a steel bridge, plant equipment, street lights, underground pipes, tanks, ships, etc., the above description is given on the surface of the metal material before application. The corrosion sensor according to this embodiment is attached with an adhesive or the like. When affixed, it may be affected by the electrical condition of the structure, so it is preferable to insulate with a resin tape, a seal, or the adhesive itself. The detection unit of the sensor can be replaced with the same material for which the corrosion state is to be measured, and the iron foil may be replaced with a metal such as stainless steel or aluminum. Then, the protective paint is applied in the same manner as the metal structure. The cable may or may not be exposed to the protective paint. If the cable is not taken out, the sensor is embedded under the coating film as it is, and when measuring, the coating film covering the sensor is peeled off and the measuring instrument is directly connected to measure the electrical signal due to corrosion. To do. Further, the measurement may be performed electromagnetically by using a wireless method. As a result, the sensor can be installed without causing defects in the coating film that occur when the cable is pulled out.

FIG. 5 is a diagram showing an outline of a corrosion sensor according to the present embodiment embedded in mortar or concrete. The corrosion sensor 1 is provided with a rubber plate 15 at a distance from the case 13, and is adhered to the case 13 with an epoxy resin 17. In order to measure the electrostatic positive contact and the capacitance of the corrosion sensor 1, the lead wire 9 is soldered so that only the iron foil portion 3 is exposed on the surface so that the connection portion of the lead wire 9 is not corroded. The case 13 is used for exterior, and the inside of the case is filled with resin 21.

The reason for this configuration is to prevent rust on the lead wire 9 and to avoid the influence of the dielectric material of the concrete filled around the lead wire 9 because the dielectric constant varies depending on the water content. It also has the meaning of protecting the corrosion sensor 1 from the impact during concrete filling. Further, although a case is used, this is not always necessary, and as long as the above object can be achieved, for example, resin alone may be used without using the case.

[How to check the soundness of the corrosion sensor]
Next, a method for confirming the soundness of the corrosion sensor will be described. FIG. 6 is a diagram showing the principle of a method for confirming the soundness of a corrosion sensor. The corrosion sensor is embedded in the concrete so that the detection part is located on the concrete surface side and the detection part is substantially parallel to the concrete surface. The corrosion sensor includes an iron foil portion 3, a dielectric 7, and a counter electrode 10. Since the structure of the corrosion sensor is as described above, detailed description thereof will be omitted here.

The external electrode 41 uses a copper electrode or the like and is installed at a position corresponding to the position where the corrosion sensor is embedded on the concrete surface. The corrosion sensor and the external electrode are connected to the measuring device 43, and the capacitance is measured by applying an AC voltage.
The external electrode 41 may have a size substantially equal to or smaller than that of the iron foil portion 3. When the external electrode 41 is made smaller than the iron foil portion 3, it is possible to identify the location where the corrosion environment has occurred in a sound state of the corrosion sensor.

As shown in FIG. 6, regarding the capacitance between each electrode, the capacitance between the concrete surface electrode (copper electrode) and the iron foil electrode is Cx, and the capacitance between the corrosion sensor (iron foil electrode and the gold electrode) is the capacitance. Is Cy, and the capacitance between the concrete surface electrode (copper electrode) and the gold electrode is Cz. Since the capacitance Cx and the capacitance Cy form a series circuit capacitor, the capacitance Cx , The relationship between the capacitance Cy and Cz can be expressed by the equation (4).

That is, if the capacitors showing the capacitance Cx and the capacitance Cy are functioning correctly, the capacitance Cz uses the capacitance Cx and the capacitance Cy as shown in the equation (5). It can be expressed as the product of the sums of the sums.

On the other hand, if a conduction portion or the like is generated in a part of the corrosion sensor, it is conceivable that a part of the corrosion sensor becomes a capacitor of the parallel circuit instead of the capacitor of the series circuit. In this case, as shown in the equation (6), a part of the corrosion sensor becomes the combined capacitance of the capacitor of the parallel circuit, and the total capacitance Cz becomes large.

The combined capacitance of the part that became the capacitor of the parallel circuit is simply the sum of the individual capacitances, and the value of the total capacitance is measured as a large value, so the soundness of the corrosion sensor itself (water leakage) Etc.) can be confirmed. Therefore, when the capacitance of the corrosion sensor changes, by implementing the soundness confirmation method of the present invention, it is possible to determine whether the corrosion environment is really detected or whether the malfunction is due to a failure.

[Capacitance value measurement]
FIG. 7 is a diagram showing an outline of a capacitance value measuring method actually using an external electrode. First, the casing corrosion sensor 100 is embedded in concrete so that the detection unit is located on the concrete surface side and the detection unit is substantially parallel to the concrete surface.

In the corrosion sensor 100, an iron foil having a thickness of 53 × 35 mm was adhered onto a polyimide film having a thickness of 0.105 mm, and a through hole 5 was formed by chemical etching. Further, gold was formed by sputtering on the opposite surface of the polyimide film as the dielectric 7.

The materials used for concrete are as shown in Table 1.

Next, the composition of concrete is as shown in Table 2.

The installation depth of the corrosion sensor 100 was set to 3 cm from the concrete surface. The concrete was sealed and cured for 14 days after casting, and four surfaces other than the two immersion surfaces were covered with epoxy resin. Then, 20 ° C. 60% R. H. The concrete was placed in a corrosive environment from 21 days of age (drying with a 5% NaCl aqueous solution at 40 ° C. for 2 days and drying at 40 ° C. and 60% RH for 5 days was repeated for 16 cycles).

Next, an external electrode (copper: φ20 mm, thickness 0.1 mm) 41 is installed on the concrete surface at a position corresponding to the position where the corrosion sensor 100 is embedded. The measurement was carried out in a wet state after immersion in a 5% NaCl aqueous solution at 40 ° C. (after 16 cycles). In order to improve the conductivity and adhesion to concrete, a solution prepared by mixing cellulose with a 10% NaCl aqueous solution was applied to the concrete surface to bring the concrete surface into close contact with the copper plate.

FIG. 8 is a view seen from the top to the bottom with respect to the paper surface of FIG. 7. External electrodes 41 are installed at each position (1 to 16) on the concrete surface at the position corresponding to the buried position of the corrosion sensor 100, and the capacitance Cx between the concrete surface electrode (copper electrode) and the iron foil electrode, The capacitance Cy of the corrosion sensor (between the iron foil electrode and the gold electrode) and the capacitance Cz between the concrete surface electrode and the gold electrode were measured at 16 points. The measurement voltage was an AC voltage of 1 V, and the measurement frequency was 100 kHz.

9 (a) to 9 (c) are a summary of the measurement results of the capacitance Cx, the capacitance Cy and the capacitance Cz. In addition, Table 3 is a table summarizing the soundness confirmation results of the corrosion sensor based on the measurement results.

In FIG. 9A, the value of the capacitance Cz is an assumed value and shows a value satisfying the equation (4). That is, it can be determined that the corrosion sensor is in a normal state. On the other hand, FIGS. 9 (b) and 9 (c) show that the value of the capacitance Cz is larger than the assumed value, and does not satisfy the equation (4). That is, it can be determined that the corrosion sensor has some trouble and is not in a normal state. In this way, the state of the corrosion sensor can be determined depending on whether or not the capacitance Cx, the capacitance Cy, and the capacitance Cz satisfy the equation (4).

As described above, according to the present embodiment, the soundness of the corrosion sensor can be confirmed even in the state of being buried in concrete.

1 Corrosion sensor 3 Iron foil part 5 Through hole 7 Dielectric 9 Lead wire 10 Opposing electrode 13 Case 15 Rubber plate 17 Epoxy resin 21 Resin 30 Corrosion prevention film 41 External electrode 43 Measuring device

Claims (2)

It is provided between a detection unit made of a corrosive metal, a counter electrode formed of a corrosion resistant metal and provided at a position facing the detection unit, and the detection unit and the counter electrode. It is a method of confirming the soundness of a corrosion sensor that confirms the soundness of a capacitance type corrosion sensor equipped with a dielectric.
The step of embedding the corrosion sensor in concrete so that the detection unit is located on the concrete surface side,
A step of installing an external electrode on the concrete surface at a position facing the position where the corrosion sensor is embedded, and
A step of measuring the capacitance Cx between the detection unit and the external electrode,
A step of measuring the capacitance Cy between the detection unit and the counter electrode,
A step of measuring the capacitance Cz between the external electrode and the counter electrode,
A method for confirming the soundness of a corrosion sensor, which comprises at least a step of determining whether or not the measurement result of each capacitance satisfies a predetermined relational expression. The method for confirming the soundness of a corrosion sensor according to claim 1, wherein it is determined whether or not the capacitance Cx, the capacitance Cy, and the capacitance Cz satisfy the following equation.

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