Corrosion sensor design method, corrosion sensor manufacturing method, and structural management method

Abstract

To obtain a corrosion sensor with excellent measurement accuracy of the amount of corrosion over a long period of time. 【Solution means】The corrosion sensor 1 includes a sensor part 11 made of a conductor exposed to an arbitrary environment and a reference part 21 made of a conductor shielded from an arbitrary environment, and measures the amount of corrosion of the sensor part 11 based on the electrical resistance value of the reference part 21 and the electrical resistance value of the sensor part 11. It is an electrical resistance type corrosion sensor. The conductor is made of a metal material containing a metal element contained in the target member whose corrosion is to be evaluated. The width of the sensor part 11 is set to a width that satisfies the following formula (I), and the initial thickness of the sensor part 11 is set to a thickness that satisfies the following formula (II). w≦(0.6×t inf )···(I) t sens ≧(2.4×t inf )···(II) t inf : Initial thickness of the target member [mm] w: Width of the sensor part 11 [mm] t sens : Initial thickness of the sensor part 11 [mm]

Description

Technical Field

[0001] The present invention relates to a method for designing a corrosion sensor, a method for manufacturing a corrosion sensor, and a method for managing a structure.

Background Art

[0002] In order to safely use structures such as bridges, harbors, buildings, etc.; moving bodies such as automobiles, trains, etc.; factory facilities such as power plants, steel mills, etc. for a long period of time, it is important to accurately grasp the degree of progress of corrosion of the structure (more specifically, the metal material constituting the structure).

[0003] Conventionally, as a technique for evaluating the corrosion of a metal material, an electric resistance type corrosion sensor is known. The electric resistance type corrosion sensor has a sensor part (conductor) that is exposed to a corrosive environment and corrodes and a reference part (conductor) that is shielded from the corrosive environment, and obtains the amount of corrosion of the sensor part based on the electric resistance value of the reference part and the electric resistance value of the sensor part that increases due to corrosion (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Many of the above-mentioned structures are used for a long period of time, and in that case, the amount of corrosion (corrosion depth) also tends to be large. Therefore, it is required to accurately measure the amount of corrosion over a long period of time using a corrosion sensor.

[0006] The present invention has been made in view of the above points, and an object thereof is to obtain a corrosion sensor having excellent measurement accuracy of the amount of corrosion over a long period of time.

Means for Solving the Problems

[0007] As a result of intensive studies, the present inventors have found that the above object can be achieved by adopting the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [4]. [1] A method for designing a corrosion sensor, wherein the corrosion sensor includes a sensor part made of a conductor exposed to an arbitrary environment and a reference part made of a conductor shielded from the arbitrary environment, and the amount of corrosion of the sensor part is measured based on the electrical resistance value of the reference part and the electrical resistance value of the sensor part. It is an electric resistance type corrosion sensor, the conductor is made of a metal material containing a metal element contained in a target member that is the object of evaluating corrosion, the width of the sensor part is set to satisfy the following formula (I), and the initial thickness of the sensor part is set to satisfy the following formula (II). A method for designing a corrosion sensor. w ≦ (0.6 × t inf ) ··· (I) t sens ≧ (2.4 × t inf ) ··· (II) t inf : The initial thickness of the target member [mm] w: The width of the sensor part [mm] t sens : The initial thickness of the sensor part [mm] [2] The method for designing a corrosion sensor according to [1] above, wherein the length of the sensor part is set to satisfy the following formula (III). 10 3 ≦ {L / (w × t sens )} × I ··· (III) t sens : The initial thickness of the sensor part [mm] w: The width of the sensor part [mm] L: The length of the sensor part [mm] I: Current value [mA] [3] A method for manufacturing an electric resistance type corrosion sensor including a sensor part made of a conductor exposed to an arbitrary environment and a reference part made of a conductor shielded from the arbitrary environment, wherein the sensor part is designed according to the method for designing a corrosion sensor described in [1] or [2] above. A method for manufacturing a corrosion sensor. [4] A method for managing a structure, comprising measuring the amount of corrosion of the sensor part using a corrosion sensor designed according to the corrosion sensor design method described in [1] or [2] above, and managing the structure having the target member based on the difference between the initial thickness of the target member and the amount of corrosion of the sensor part. [Effects of the Invention]

[0008] According to the present invention, a corrosion sensor can be obtained that exhibits excellent accuracy in measuring the amount of corrosion over a long period of time. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view showing a corrosion sensor. [Figure 2] This is a cross-sectional view along line AA in Figure 1. [Figure 3] This graph shows the relationship between the average corrosion rate and the maximum corrosion rate. [Figure 4] This graph shows the relationship between the initial thickness of the target component and the initial thickness of the sensor part. [Modes for carrying out the invention]

[0010] [Design Method for Corrosion Sensors] The following describes the design method for corrosion sensors. This explanation also serves as a description of the manufacturing method for corrosion sensors.

[0011] <Basic configuration of a corrosion sensor> A preferred example of the basic configuration of an electrical resistance type corrosion sensor will be explained based on Figures 1 and 2. However, the corrosion sensor described based on Figures 1 and 2 is just one example, and corrosion sensors are not limited to this.

[0012] Figure 1 is a plan view showing the corrosion sensor 1. Figure 2 is a cross-sectional view taken along line AA of Figure 1. The electrical resistance type corrosion sensor 1 has a sensor unit 11 that is exposed to any environment and a reference unit 21 that is isolated from any environment to which the sensor unit 11 is exposed.

[0013] The "arbitrary environment" to which the sensor unit 11 is exposed is a concept that encompasses various environments, including a "corrosive environment" that causes the sensor unit 11 to corrode. In other words, the corrosion sensor 1 may be used not only in a corrosive environment where the sensor part 11 corrodes, but also in an environment where the sensor part 11 does not corrode.

[0014] As shown in Figure 2, a sensor section 11 made of a conductive material and a reference section 21 made of a conductive material are arranged in parallel on one surface of the substrate 31, separated by an insulating sheet 41. The cross-sections of the sensor section 11 and the reference section 21 are rectangular (including square) with a predetermined thickness. Both sides of the sensor section 11 and the reference section 21 are covered with an insulating resin 51. The upper side of the reference section 21 is covered by the cover 61.

[0015] As shown in Figure 2, when the corrosion sensor 1 is viewed in cross-section, both sides and the top and bottom surfaces of the rectangular reference section 21 are covered by the respective components. Therefore, even if the corrosion sensor 1 is in any environment, the reference section 21 is isolated from that environment.

[0016] On the other hand, as shown in Figure 2, when the corrosion sensor 1 is viewed in cross-section, both sides and the bottom surface of the rectangular sensor portion 11 are covered by the respective components, but the top surface is exposed. Therefore, when the corrosion sensor 1 is in any environment, the top surface of the sensor portion 11 is exposed to that environment. When the top surface of the sensor portion 11 is exposed, corrosion progresses in the thickness direction (from the top side to the bottom side).

[0017] The material of the insulating sheet 41 is not particularly limited, and conventionally known materials can be used, such as PET (polyethylene terephthalate) and polyimide. The thickness of the insulating sheet 41 (the vertical distance in Figure 2 (hereinafter the same)) should be such that it can insulate the base material 31 from the sensor part 11 and the reference part 21, for example, 5 μm or more. The upper limit is not particularly limited, but the thickness of the insulating sheet 41 is preferably 200 μm or less because it is easy to make the thermal history of the reference portion 21 the same as that of the sensor portion 11.

[0018] The material of the resin 51 is not particularly limited, and conventionally known materials can be used. For example, epoxy resins, acrylic resins, etc. can be mentioned. The thickness of the resin 51 conforms to the thicknesses of the sensor portion 11 and the reference portion 21.

[0019] The material of the cover 61 is not particularly limited as long as it can prevent the corrosion of the reference portion 21 (insulating material). For example, silicone sealants, natural resins, etc. can be mentioned. From the viewpoint of suppressing the generation of a temperature difference between the sensor portion 11 and the reference portion 21, a material with high thermal conductivity is preferable. If the cover 61 is too thick, the thermal conductivity is likely to deteriorate. On the other hand, if it is too thin, the corrosion of the reference portion 21 is likely to occur. The suitable thickness of the cover 61 varies depending on the material, but is preferably 5 to 200 μm. The cover 61 is preferably adhered so that no gap occurs between it and the reference portion 21. This is because if a gap occurs, the thermal conductivity is likely to be impaired. For this reason, it is preferable to crimp the cover 61 and the reference portion 21 with sufficient force, or to bond the two using a thermally conductive adhesive. At this time, it is preferable to thoroughly clean the dirt, etc. between the cover 61 and the reference portion 21 and then adhere the two.

[0020] The conductor constituting the sensor portion 11 and the conductor constituting the reference portion 21 are each made of a metal material containing a metal element (for example, iron) contained in a target member (not shown) which is the object to be evaluated for corrosion.

[0021] The target member is, for example, a member constituting a structure such as a building such as a bridge, a harbor, a building; a moving body such as an automobile, a train; factory equipment such as a power plant, a steel mill; etc., and is made of a metal material containing a metal element. The target member is, for example, a flat plate-like member having a predetermined thickness (t inf ).

[0022] It is preferable that the conductor constituting the sensor section 11 and the reference section 21 and the target member are made of the same metal material. Examples of such metallic materials include iron or iron alloys. The iron content in the iron alloy is preferably 90% by mass or more. Other elements to be included in the iron alloy include, for example, at least one element selected from the group consisting of carbon, silicon, manganese, phosphorus, and sulfur; elements that improve corrosion resistance, such as copper and nickel; and other elements.

[0023] The base material 31 on which the sensor unit 11 and the reference unit 21 are arranged is preferably made of the same metal material as the target member. The base material 31 is, for example, a flat plate-shaped member having a predetermined thickness, as shown in Figure 2, and may be the target member itself. In this case, the thickness of the base material 31 (the vertical distance in Figure 2) is equal to the initial thickness t of the target member. inf This is the result. Since the base material 31 is the target component itself, the thermal history of the sensor unit 11 and the reference unit 21 will be the same as that of the target component. In this case, it is preferable that the insulating sheet 41 placed between the base material 31 and the sensor unit 11 and the reference unit 21 is not too thick.

[0024] The sensor section 11 and the reference section 21 are preferably elongated with a certain length. For example, as shown in Figure 1, a meandering shape with bends at regular intervals is preferred. This makes it easier to ensure the electrical resistance value necessary for detection.

[0025] A voltage measuring unit 81 is connected to terminal 11a at one end of the sensor unit 11 and terminal 11b at the other end, and a voltage measuring unit 91 is connected to terminal 21a at one end of the reference unit 21 and terminal 21b at the other end. A current source 71 is connected to terminal 11a of the sensor unit 11 and terminal 21a of the reference unit 21.

[0026] The sensor unit 11 and the reference unit 21 are electrically connected. More specifically, as shown in Figure 1, the part of the sensor unit 11 near terminal 11b and the part of the reference unit 21 near terminal 21b are connected by a connecting part 35. Preferably, the connecting part 35 is made of the same conductive material as the conductive materials that make up the sensor unit 11 and the reference unit 21. It is preferable that the sensor unit 11, the reference unit 21, and the connection unit 35 are integrally molded.

[0027] In such a corrosion sensor 1, a constant current is supplied from the current source 71 and the voltage is measured to determine the electrical resistance values ​​of the sensor unit 11 and the reference unit 21, respectively. In this case, if the sensor unit 11 gradually corrodes due to exposure to any environment, the electrical resistance value of the sensor unit 11 will gradually increase from its initial value. On the other hand, since the reference unit 21 is isolated from the environment to which the sensor unit 11 is exposed, corrosion does not progress, and the electrical resistance value of the reference unit 21 remains basically unchanged from its initial value, except for changes caused by temperature changes, which will be described later.

[0028] The reason why the progression of corrosion in the sensor unit 11 is related to the increase in electrical resistance is generally thought to be as follows. As corrosion progresses, the conductor constituting the sensor unit 11 thins in the thickness direction, starting from the area exposed to the environment. The thinned conductor is either lost from the surface or remains on the surface replaced by corrosion products. These corrosion products are often insulators, or, if they are conductors, have significantly lower conductivity compared to the original conductor. As a result, the increase in electrical resistance due to corrosion is considered to be due to the thinning of the conductor constituting the sensor unit 11.

[0029] In this way, the corrosion sensor 1 determines the electrical resistance values ​​of the sensor unit 11 and the reference unit 21 at arbitrary fixed intervals, and calculates (converts) the amount of corrosion (corrosion depth) of the sensor unit 11 based on the determined electrical resistance values. The conversion formula for the amount of corrosion is expressed in more detail by the following formula (IV). CD=t sens {(Rref,init / R sens,init )-(R ref / R sens )}···(IV) CD: Corrosion amount (corrosion depth) [μm] t sens Initial thickness of the sensor part [μm] R ref,init : Initial electrical resistance value of the reference part [Ω] R sens,init Initial electrical resistance value of the sensor [Ω] R ref : Electrical resistance value [Ω] of the reference part during measurement. R sens : Electrical resistance value [Ω] of the sensor unit during measurement.

[0030] Here, the amount of corrosion is calculated based on the above formula (IV), under certain assumptions. For example, if the initial thickness of both the sensor part 11 and the reference part 21 is "100 μm", and the initial electrical resistance value of the reference part 21 is (R ref,init ) and the initial electrical resistance value (R) of the sensor unit 11 sens,init Both values ​​are "0.1Ω", and the electrical resistance value (R) of the reference unit 21 at the time of measurement is... ref The initial value remained unchanged at "0.1Ω", but on the other hand, corrosion of the sensor part 11 progressed, causing the electrical resistance value (R sens If the Ω value increased to "0.11Ω", the amount of corrosion can be calculated from the above formula (IV) as 100 × {(0.1 / 0.1) - (0.1 / 0.11)}, resulting in "9.1 μm".

[0031] By the way, when determining the amount of corrosion in the sensor unit 11, for example, the corrosion sensor 1 is accessed to collect the electrical resistance values ​​of the sensor unit 11 and the reference unit 21. However, depending on the installation location of the corrosion sensor 1, it may be difficult to access the corrosion sensor 1 periodically. Therefore, for example, by adding a communication function to the corrosion sensor 1, data such as electrical resistance values ​​can be collected from the corrosion sensor 1 at any desired time. If there are many corrosion sensors 1, one corrosion sensor 1 may be designated as a master unit and the remaining corrosion sensors 1 as slave units, with data collected from each slave unit and sent to the master unit.

[0032] In the corrosion sensor 1, it is preferable to perform temperature compensation. In other words, when measuring the amount of corrosion, if the electrical resistance value of the reference unit 21 changes, it is preferable to assume that this change is due to a temperature change and to correct the measured amount of corrosion based on this change. Generally, the electrical resistivity of metals increases with increasing temperature. Therefore, for example, under the above assumption, if the temperature has risen from the initial temperature, the electrical resistance value of the sensor unit 11 at the time of measurement (R sens Suppose the resistance was not "0.11Ω" but "0.121Ω", which is 10% higher. In this case, if we calculate from equation (IV) above as 100 × {(0.1 / 0.1)-(0.1 / 0.121)}, the corrosion amount becomes "17μm", which is significantly different from the original corrosion amount of "9.1μm". However, at this time, for example, the electrical resistance value (R) of the reference unit 21 ref Similarly, if the resistance changes from "0.1Ω" to "0.11Ω" (a 10% increase) due to the rise in temperature, the amount of corrosion can be corrected based on this change. That is, the amount of corrosion can be calculated from the above formula (IV) as 100 × {(0.1 / 0.1) - (0.11 / 0.121)}, resulting in "9.1 μm", which is the same result as when there was no temperature change.

[0033] <Thickness of the sensor part> The thickness (initial thickness) of the sensor unit 11 will be explained. sens ) represents the vertical distance of the sensor unit 11 in Figure 2. It is preferable that the sensor unit 11 does not become perforated by corrosion during the period of corrosion measurement. The inventors measured the average corrosion rate and the maximum corrosion rate over time for a steel sensor unit 11 exposed to a corrosive environment in the atmosphere, and plotted them on a graph. Figure 3 is a graph showing the relationship between the average corrosion rate and the maximum corrosion rate.

[0034] The target component is a flat steel component, and the sensor unit 11 was manufactured using the same metal material as this target component.

[0035] The corroded surface of the sensor unit 11 (the exposed surface where corrosion progresses) is actually an uneven surface. The amount of corrosion of the sensor unit 11 when this corroded surface is considered as a flat surface is called the "average corrosion amount." The amount of corrosion (corrosion depth) of the deepest recess on the corroded surface of the sensor unit 11 is called the "maximum corrosion amount." When the average corrosion amount of the sensor part 11 reaches the plate thickness of the target member, the maximum corrosion amount of the sensor part 11 must exceed the thickness of the sensor part 11; in other words, the sensor part 11 must not be penetrated by corrosion.

[0036] Referring to the graph in Figure 3, the maximum corrosion amount (unit: mm) was 1.2116 times the average corrosion amount (unit: mm). Therefore, considering safety, the initial thickness (t) of the sensor part 11 was reduced. sens ) as the initial thickness (t) of the target member. inf Set the thickness to 1.3 times or more than the specified value.

[0037] However, since corrosion progresses significantly in the thickness direction of the sensor section 11, the unevenness in the thickness direction becomes very large, which may result in a localized increase in electrical resistance and affect the measurement accuracy of the corrosion sensor 1. Here, consider the case where 50% of the corroded surface in the sensor unit 11 shows the maximum amount of corrosion (at which point the increase in local electrical resistance is maximized). In this case, an error occurs between the amount of corrosion measured by the corrosion sensor 1 and the actual amount of corrosion in the target member. This error varies depending on the initial thickness (unit: mm) of the sensor unit 11 and the initial thickness (unit: mm) of the target member.

[0038] Therefore, the initial thickness of the sensor unit 11 when the corrosion error was 5%, 10%, or 15% was plotted together with the initial thickness of the target member. Figure 4 is a graph showing the relationship between the initial thickness of the target component and the initial thickness of the sensor unit 11. Referring to the graph in Figure 4, when the initial thickness of the sensor unit 11 was 1.8259 times the initial thickness of the target member, the error was 15%, but when it was 2.3751 times, the error was 5%. From the viewpoint of obtaining good measurement accuracy, it is preferable to keep the error within 5%, therefore the initial thickness (t) of the sensor part 11 is sens ) as the initial thickness (t) of the target member. inf Set the thickness to 2.4 times or more than the standard thickness. In other words, the initial thickness of the sensor unit 11 is set to a thickness that satisfies the following equation (II). t sens ≥(2.4 × t) inf )···(II) t inf : Initial thickness of the target component [mm] t sens Initial thickness of sensor unit 11 [mm]

[0039] The initial thickness of the sensor unit 11 is not particularly limited to an upper limit, but from the viewpoint of improving measurement accuracy, it is preferable that it be 10.0 times or less the initial thickness of the target member, and more preferably 5.0 times or less.

[0040] <Width of the sensor section> The width of the sensor unit 11 will now be explained. The width (w) of the sensor unit 11 is the distance in the left-right direction in Figure 2. One of the factors causing corrosion of the target material is chloride ions. In particular, under harsh conditions over long periods, chloride ion nests (rust layers containing a large amount of iron chloride) form on the surface (corroded surface) of the target material, creating depressions with a depth:diameter (width) ratio of approximately 1:1. Here, in the sensor unit 11, the average corrosion amount is determined to be the initial thickness (t) of the target member. inf Assume that it has reached ). At this time, the thickness of the sensor part 11 at the position showing the maximum amount of corrosion (t sens, max ) is the initial thickness (t) of the target member. inf ) is 1.3 times, and the thickness of the sensor part 11 at the position showing the minimum amount of corrosion (t sens, min ) is the initial thickness (t) of the target member. inf The inventors have found that this is 0.7 times (see the formula below). Furthermore, the inventors have found that the maximum depth of the recess formed by the chloride ion nest is the difference in thickness (t sens, max -t sens, min We found that it can be obtained by (see the formula below). t sens, max = 1.3 × t inf t sens, max = 0.7 × t inf t sens, max -t sens, min = 0.6 × t inf

[0041] Therefore, the average corrosion amount is equal to the initial thickness (t) of the target member. inf When it reaches ), the depth of the recess is 0.6 × t inf This is the result. At this time, as described above, a recess is formed with a depth:diameter (width) ratio of approximately 1:1, so the width (w) of the sensor part 11 is equal to the initial thickness (t) of the target member. inf If the thickness is 0.6 times or less, even if a recess is formed in the sensor part 11 when viewed in cross-section, the overall thickness is reduced in the width direction, making it less likely for variations to occur.

[0042] In other words, the width of the sensor unit 11 is set to a width that satisfies the following equation (I). w≦(0.6×t inf )···(I) t inf : Initial thickness of the target component [mm] w: Width of sensor section 11 [mm]

[0043] The width of the sensor portion 11 is not particularly limited to a lower limit, but from the viewpoint of ease of machining, it is preferably 50 μm or more, and more preferably 100 μm or more.

[0044] <Length of the sensor part> The length of the sensor unit 11 will now be explained. As shown in Figure 1, the length of the sensor unit 11 is the distance of the center line passing through the center of the width of the sensor unit 11. As described above, the amount of corrosion in the sensor unit 11 is measured by the voltage when a constant current is applied. The longer the sensor unit 11, the greater the electrical resistance. That is, the voltage increases, resulting in better accuracy in measuring the amount of corrosion. The voltage also changes depending on the current value of the constant current. Here, the general formula "E=IR" can be transformed into the formula "E={ρ×L / (w×t)}×I", and further into "E / ρ={L / (w×t)}×I" (E: voltage value, R: resistance value, I: current value, t: thickness of sensor part 11, ρ: electrical resistivity of sensor part 11). Taking into account typical values ​​for the electrical resistivity (ρ) of the sensor unit 11, and considering a sufficiently high voltage (E) to obtain good measurement accuracy, the value of "E / ρ" is 10 3 It can lead to that. In other words, for the reason that the measurement accuracy of the amount of corrosion is better, it is preferable to set the length of the sensor part 11 to a length that satisfies the following formula (III). 10 3 ≤{L / (w×t sens )} × I···(III) t sens Initial thickness of sensor unit 11 [mm] w: Width of sensor section 11 [mm] L: Sensor section length [mm] I: Current value [mA]

[0045] [Methods for managing structures] Next, we will explain the methods for managing structures. In general terms, a corrosion sensor 1 designed according to the design method described above is used to measure the amount of corrosion in the sensor part 11, and the structure containing the target member is managed based on the difference between the initial thickness of the target member and the amount of corrosion in the sensor part 11. The following are specific examples.

[0046] First, the difference between the initial thickness of the target component and the amount of corrosion of the sensor part 11 is determined as the remaining thickness of the target component. Next, the remaining load-bearing capacity is calculated based on the determined remaining thickness. The remaining load-bearing capacity is calculated, for example, using finite element method (FEM) analysis. While there are various FEM analysis methods, ranging from simple methods using mechanical calculations to advanced methods using simulations, the appropriate method can be selected depending on the acceptable level of accuracy, and there are no particular limitations. Incidentally, future corrosion (thickening) can be estimated from the change in the amount of corrosion over time. Therefore, the remaining load-bearing capacity of the target member (and by extension, the structure containing the target member) is calculated from the current remaining thickness and the change in the amount of corrosion over time. For example, if the structure is a factory building, the time until the building collapses due to the progression of corrosion can be calculated.

[0047] Subsequently, based on the calculated remaining load-bearing capacity, the timing and methods of maintenance and preservation work for the structure containing the target member are determined. Then, the structure is managed according to the determined content; that is, maintenance and preservation work is carried out. In this case, the remaining load-bearing capacity of each of the multiple structures may be calculated, and maintenance and preservation work may be carried out in order of the urgency of the structure. Urgency can be arbitrarily determined based on the remaining load-bearing capacity as well as the extent of damage in the event of collapse or destruction of the structure. Furthermore, the method of preservation, whether to use partial repair or complete replacement, may be determined based on the severity of the corrosive environment, which can be judged from the change in the amount of corrosion over time, and the future service life of the structure (e.g., building). [Examples]

[0048] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below.

[0049] <Fabrication of corrosion sensors> A corrosion sensor 1 was fabricated based on the information in Figures 1 and 2. More specifically, first, an insulating sheet 41 made of polyimide (thickness: 12 μm) was placed on one surface of a flat substrate 31, and then the sensor unit 11 and reference unit 21, connected by a connecting unit 35, were placed on top of it. The sensor unit 11 and the reference unit 21 were made to have the same shape as each other. Next, epoxy resin 51 was spread evenly on the insulating sheet 41 to the thickness of the sensor part 11 and the reference part 21, covering both sides of the sensor part 11 and the reference part 21. Furthermore, silicone sealant was applied to the reference part 21 (and the resin 51 placed on both sides thereof) to form a cover 61 (thickness: approximately 100 μm) that covers the reference part 21.

[0050] The base material 31 consists of weather-resistant hot-rolled steel (SMA490 material) for welded structures as specified in JIS G 3114, with an initial thickness t as shown in Table 1 below. inf A flat plate-shaped target member having dimensions (in mm) was used. The sensor unit 11, the reference unit 21, and the connection unit 35 were integrally molded using the same SMA490 material as the base material 31 (target member).

[0051] The initial thickness t of the sensor part 11 of the fabricated corrosion sensor 1 sens Table 1 below shows the dimensions (in mm), width w (in mm), and length L (in mm).

[0052] <test> Using the fabricated corrosion sensor 1, a test was conducted in accordance with "JIS K5600-7-9" "Cycle Corrosion Test Method - Salt Spray / Drying / Wetting". More specifically, each corrosion sensor 1 was subjected to repeated cycles of salt spraying (35°C, 5% NaCl concentration, 2 hours) → drying (60°C, 25% humidity, 4 hours) → wetting (50°C, 95% humidity, 2 hours) and left undisturbed for the number of days shown in Table 1 below. During the test, a constant current of the current value I (unit: mA) shown in Table 1 below (10mA in No. 1) was applied from the current source 71 at 10-minute intervals to determine the electrical resistance values ​​of the sensor unit 11 and the reference unit 21. Based on the above equation (IV), the amount of corrosion (corrosion depth) of the sensor unit 11 was measured.

[0053] The degree of discrepancy (in %) between the corrosion amount measured by corrosion sensor 1 and the corrosion amount of the target component at the end of the test was determined. Three similar tests were conducted (Tests 1-3). The results are shown in Table 1 below. If the sensor unit 11 was disconnected during the test, "Disconnected" was noted in the corresponding section of Table 1 below.

[0054] Table 1 below indicates that if the deviation was less than ±5% in any of Tests 1 to 3, it was marked "A," and if the deviation was ±5% or more in any of Tests 1 to 3, or if a break occurred, it was marked "B." "A" indicates excellent accuracy in measuring the amount of corrosion. Table 1 below also indicates whether or not the corrosion sensor 1 satisfies equations (I) to (III) described above. "A" is written if it satisfies the equation, and "B" is written if it does not.

[0055] [Table 1]

[0056] <Summary of Evaluation Results> As shown in Table 1 above, when equations (I) and (II) are satisfied, the degree of deviation in the amount of corrosion is "A", and the accuracy of corrosion measurement was good over a long period of time. In contrast, if at least one of equations (I) and (II) is not satisfied, the degree of deviation in the amount of corrosion is "B," indicating insufficient accuracy in measuring the amount of corrosion. [Explanation of symbols]

[0057] 1: Corrosion sensor 11: Sensor section 11a, 11b: Terminals of the sensor section 21:Reference section 21a, 21b: Terminals of the reference section 31: Base material (target component) 35: Connection part 41: Insulating sheet 51: Resin 61: Cover 71: Current source 81: Voltage measurement section 91: Voltage measurement section

Claims

1. A method for designing a corrosion sensor, The corrosion sensor is an electrical resistance type corrosion sensor comprising a sensor part made of a conductor exposed to any environment and a reference part made of a conductor shielded from the any environment, and measuring the amount of corrosion of the sensor part based on the electrical resistance value of the reference part and the electrical resistance value of the sensor part. The aforementioned conductor is made of a metallic material containing metallic elements contained in the target member whose corrosion is to be evaluated. The width of the sensor section is set to satisfy the following formula (I): A corrosion sensor design method, wherein the initial thickness of the sensor portion is set to a thickness that satisfies the following equation (II). w≦(0.6×t ｉｎｆ )・・・(I) t ｓｅｎｓ ≧().××= ｉｎｆ (II) t ｉｎｆ : Initial thickness of the aforementioned target member [mm] w: Width of the sensor part [mm] t ｓｅｎｓ : Initial thickness of the sensor part [mm]

2. A method for designing a corrosion sensor according to claim 1, wherein the length of the sensor portion is set to a length that satisfies the following formula (III). 10 ３ ≦{L / (w×t) ｓｅｎｓ )}×I・・・(III) t ｓｅｎｓ : Initial thickness of the sensor part [mm] w: Width of the sensor part [mm] L: Length of the sensor part [mm] I: Current value [mA]

3. A method for manufacturing an electrical resistance corrosion sensor comprising a sensor part made of a conductor exposed to any environment, and a reference part made of a conductor isolated from the environment, A method for manufacturing a corrosion sensor, comprising designing the sensor portion according to the corrosion sensor design method described in claim 1 or 2.

4. Using a corrosion sensor designed according to the corrosion sensor design method described in claim 1 or 2, the amount of corrosion in the sensor part is measured. A method for managing a structure, comprising managing a structure having the target member based on the difference between the initial thickness of the target member and the amount of corrosion of the sensor portion.

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