Method for designing corrosion sensor, method for manufacturing corrosion sensor, and method for managing structure
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2025-12-26
- Publication Date
- 2026-08-06
Smart Images
Figure JP2025045831_06082026_PF_FP_ABST
Abstract
Description
Corrosion sensor design method, corrosion sensor manufacturing method, and structural management method
[0001] This invention relates to a method for designing corrosion sensors, a method for manufacturing corrosion sensors, and a method for managing structures.
[0002] To ensure the safe long-term use of structures such as bridges, ports, and buildings; mobile vehicles such as automobiles and trains; and factory equipment such as power plants and steel mills, it is crucial to accurately understand the degree of corrosion progressing in these structures (more specifically, the metal materials that make up the structures).
[0003] Conventionally, electrical resistance type corrosion sensors have been known as a technique for evaluating the corrosion of metal materials. An electrical 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 isolated from the corrosive environment. The amount of corrosion of the sensor part is determined based on the electrical resistance value of the reference part and the electrical resistance value of the sensor part that increases due to corrosion (Patent Document 1).
[0004] International Publication No. 2021 / 235475
[0005] Many of the structures mentioned above are used for long periods of time, and in such cases, the amount of corrosion (corrosion depth) tends to be large. Therefore, it is necessary to accurately measure the amount of corrosion over long periods using corrosion sensors.
[0006] This invention has been made in view of the above points, and aims to provide a corrosion sensor that has excellent corrosion measurement accuracy over a long period of time.
[0007] The inventors, after diligent study, have found that the above objective 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 comprises 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 measures 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, wherein the conductor is made of a metallic material containing a metallic element contained in the target member whose corrosion is to be evaluated, 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). ｉｎｆ ) ... (I) t ｓｅｎｓ ≥ (2.4 × t) ｉｎｆ ) ... (II) t ｉｎｆ : Initial thickness of the above target component [mm] w: Width of the above sensor part [mm] t ｓｅｎｓ : Initial thickness of the sensor part [mm] [2] The design method for the corrosion sensor described in [1] above, wherein the length of the sensor part 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 type corrosion sensor comprising 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 corrosion sensor design method described in [1] or [2] above. [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 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 part.
[0008] According to the present invention, a corrosion sensor with excellent measurement accuracy of the corrosion amount over a long period can be obtained.
[0009] It is a plan view showing a corrosion sensor. It is a sectional view taken along line A - A of FIG. 1. It is a graph showing the relationship between the average corrosion amount and the maximum corrosion amount. It is a graph showing the relationship between the initial thickness of the target member and the initial thickness of the sensor part.
[0010] [Design method of corrosion sensor] Hereinafter, the design method of the corrosion sensor will be described. Note that the following description also serves as an explanation of the manufacturing method of the corrosion sensor.
[0011] 〈Basic configuration of corrosion sensor〉 A preferred example of the basic configuration of an electric resistance type corrosion sensor will be described based on FIGS. 1 to 2. However, the corrosion sensor described based on FIGS. 1 to 2 is an example, and the corrosion sensor is not limited thereto.
[0012] FIG. 1 is a plan view showing a corrosion sensor 1. FIG. 2 is a sectional view taken along line A - A of FIG. 1. The electric resistance type corrosion sensor 1 has a sensor part 11 exposed to an arbitrary environment and a reference part 21 blocked from an arbitrary environment in which the sensor part 11 is exposed.
[0013] The "arbitrary environment" in which the sensor part 11 is exposed is a concept that encompasses various environments, including a "corrosion environment" in which the sensor part 11 corrodes. That is, the corrosion sensor 1 may be used not only in a corrosion environment where the sensor part 11 corrodes but also in an environment where the sensor part 11 does not corrode.
[0014] As shown in FIG. 2, on one surface of a base material 31, a sensor part 11 made of a conductor and a reference part 21 made of a conductor are arranged in parallel via an insulating sheet 41. The cross - sections of the sensor part 11 and the reference part 21 are rectangles (including squares) having a predetermined thickness. Both side surfaces of the sensor part 11 and the reference part 21 are covered with an insulating resin 51. The upper surface side of the reference part 21 is covered with a cover 61.
[0015] As shown in Fig. 2, when the corrosion sensor 1 is viewed in cross section, both side surfaces and upper and lower surfaces of the rectangular reference portion 21 are covered with respective members. Therefore, even when the corrosion sensor 1 is in an arbitrary environment, the reference portion 21 is blocked from this arbitrary environment.
[0016] On the other hand, as shown in Fig. 2, when the corrosion sensor 1 is viewed in cross section, both side surfaces and the lower surface of the rectangular sensor portion 11 are covered with respective members, but the upper surface is exposed. Therefore, when the corrosion sensor 1 is in an arbitrary environment, the upper surface of the sensor portion 11 is exposed to this arbitrary environment. Corrosion progresses in the thickness direction (the direction from the upper surface side to the lower surface side) of the sensor portion 11 whose upper surface is exposed.
[0017] The material of the insulating sheet 41 is not particularly limited, and conventionally known materials can be used. Examples include PET (polyethylene terephthalate), polyimide, and the like. The thickness of the insulating sheet 41 (the distance in the vertical direction in Fig. 2 (the same shall apply hereinafter)) may be any thickness that can insulate the base material 31 from the sensor portion 11 and the reference portion 21. For example, it is 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 easier 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. Examples include epoxy resin, acrylic resin, and the like. The thickness of the resin 51 conforms to the thicknesses of the sensor portion 11 and the reference portion 21.
[0019] As the material of the cover 61, there is no particular limitation as long as it is a material (insulating material) that can prevent the corrosion of the reference portion 21. For example, silicone sealant, natural resin, etc. can be mentioned. From the viewpoint of suppressing the generation of the 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 preferable thickness of the cover 61 varies depending on the material, but 5 to 200 μm is preferable. The cover 61 is preferably adhered so that there is no gap 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 wash 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) that 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, or a building; a moving body such as an automobile or a train; a factory facility such as a power plant or a steel mill; etc., and is made of a metal material containing a metal element. The target member is, for example, a flat member having a predetermined thickness (t ｉｎｆ )
[0022] The conductor constituting the sensor portion 11 and the reference portion 21 and the target member are preferably made of the same metal material. Examples of such a metal material include iron or an iron alloy. The iron content in the iron alloy is preferably 90% by mass or more. Examples of the elements other than iron contained in the iron alloy include at least one element selected from the group consisting of carbon, silicon, manganese, phosphorus, and sulfur; elements such as copper and nickel that improve corrosion resistance; etc.
[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 As a 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 portion of the sensor unit 11 near terminal 11b and the portion of the reference unit 21 near terminal 21b are connected by a connecting portion 35. Preferably, the connecting portion 35 is made of the same conductive material as the conductive material that constitutes the sensor unit 11 and the reference unit 21. Preferably, the sensor unit 11, the reference unit 21 and the connecting portion 35 are integrally molded.
[0027] In such a corrosion sensor 1, the electrical resistance values of the sensor unit 11 and the reference unit 21 are determined by applying a constant current from the current source 71 and measuring the voltage. At this time, if the sensor unit 11 gradually corrodes due to exposure to an arbitrary environment, the electrical resistance value of the sensor unit 11 gradually increases from its initial value. On the other hand, since the reference unit 21 is isolated from the arbitrary 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 part 11 is related to the increase in electrical resistance is generally considered to be as follows: As corrosion progresses, the conductor constituting the sensor part 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, their conductivity is much lower than that of 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 part 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 {(R ｒｅｆ，ｉｎｉｔ / R ｓｅｎｓ，ｉｎｉｔ ) - (R ｒｅｆ / R ｓｅｎｓ )}...(IV) CD: Amount of corrosion (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 part [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 assumptions. For example, 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 of the sensor unit 11 (R 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 of 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 providing a communication function to the corrosion sensor 1, data such as electrical resistance values can be collected from the corrosion sensor 1 at any 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, and data can be collected from each slave unit to the master unit.
[0032] In the corrosion sensor 1, it is preferable to perform temperature compensation. That is, 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 as the temperature rises. Therefore, for example, in 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 ｓｅｎｓSuppose the value of (R) is not "0.11Ω" but 10% higher, "0.121Ω". In this case, if we calculate from the above formula (IV) 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, in this case, for example, the electrical resistance value of the reference part 21 (R 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 part 11 will be explained. Thickness of the sensor part 11 (initial thickness t ｓｅｎｓ ) is the vertical distance of the sensor unit 11 in Figure 2. It is preferable that the sensor unit 11 is not penetrated by corrosion during the corrosion measurement period. The inventors measured the average corrosion amount and the maximum corrosion amount 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 amount and the maximum corrosion amount.
[0034] The target component is a flat steel member, and the sensor unit 11 was manufactured using the same metal material as this target component.
[0035] The corroded surface of the sensor part 11 (the exposed surface where corrosion progresses) is actually an uneven surface. The amount of corrosion of the sensor part 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 part 11 is called the "maximum corrosion amount." When the average corrosion amount of the sensor part 11 reaches the 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] Incidentally, since corrosion progresses significantly in the thickness direction of the sensor unit 11, the unevenness in the thickness direction becomes very large, and as a result, the electrical resistance value increases locally, which may affect the measurement accuracy of the corrosion sensor 1. Here, let's consider the case where 50% of the corroded surface of the sensor unit 11 shows the maximum amount of corrosion (at which time the increase in local electrical resistance value is maximum). 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 material. This error changes depending on the initial thickness of the sensor unit 11 (unit: mm) and the initial thickness of the target material (unit: mm).
[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 member 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%, so the initial thickness of the sensor unit 11 (t ｓｅｎｓ ) as the initial thickness (t) of the target member. ｉｎｆ The thickness is set to be 2.4 times or more than the initial thickness of the sensor unit 11. That is, the initial thickness of the sensor unit 11 is set to a thickness that satisfies the following formula (II). 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 Sensor Section> The width of the sensor section 11 will be explained. The width (w) of the sensor section 11 is the distance in the left-right direction in Figure 2. One of the factors that causes corrosion of the target material is chloride ions. In particular, under harsh conditions over a long period of time, chloride ion nests (rust layers containing a lot of iron chloride) are formed on the surface (corroded surface) of the target material, and recesses with a depth:diameter (width) ratio of approximately 1:1 are formed. Here, in the sensor section 11, the average amount of corrosion is equal to the initial thickness (t) of the target material. 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 it is 0.7 times the difference in thickness (t) (see 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). 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 member in question. 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 the sensor unit 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 Sensor Section> The length of the sensor section 11 will be explained. As shown in Figure 1, the length of the sensor section 11 is the distance of the center line passing through the center of the width of the sensor section 11. As mentioned above, the amount of corrosion of the sensor section 11 is measured by the voltage when a constant current is passed through it. The longer the sensor section 11, the greater the electrical resistance. That is, the voltage increases, so the accuracy of measuring the amount of corrosion is improved. The voltage also changes depending on the current value of the constant current. Here, the general formula "E = IR" can be converted to the formula "E = {ρ × L / (w × t)} × I", and further converted to "E / ρ = {L / (w × t)} × I" (E: voltage value, R: resistance value, I: current value, t: thickness of the sensor section 11, ρ: electrical resistivity of the sensor section 11). Taking into account the general value of ρ (electrical resistivity) of the sensor section 11, and considering an E (voltage value) that is high enough to obtain good measurement accuracy, the value of "E / ρ" is 10 ３ This can be derived. 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 unit 11 [mm] L: Length of sensor unit 11 [mm] I: Current value [mA]
[0045] [Structural Management Method] Next, the structural management method will be explained. In general terms, a corrosion sensor 1 designed according to the design method described above is used to measure the amount of corrosion of 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 of the sensor part 11. A specific example will be explained below.
[0046] First, the difference between the initial thickness of the target member and the amount of corrosion of the sensor part 11 is determined as the remaining thickness of the target member. 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. There are various methods for FEM analysis, from simple methods using mechanical calculations to advanced methods using simulations, but they can be appropriately selected according to the acceptable accuracy, and are not particularly limited. Furthermore, 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 having 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 period until the building collapses due to the progression of corrosion is calculated.
[0047] Subsequently, based on the calculated remaining load-bearing capacity, the timing and method 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. At this time, the remaining load-bearing capacity of multiple structures may be calculated for each, and maintenance and preservation work may be carried out in order of the structure with the highest urgency. 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 according to the severity of the corrosive environment that can be judged from the change in the amount of corrosion over time, and the future lifespan of the structure (e.g., building).
[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 Sensor> The corrosion sensor 1 described with reference to Figures 1 and 2 was fabricated. More specifically, first, an insulating sheet 41 (thickness: 12 μm) made of polyimide was placed on one surface of a flat substrate 31, and the sensor part 11 and reference part 21 connected by a connecting part 35 were placed on top of it. The sensor part 11 and the reference part 21 were made to be the same shape as each other. Next, epoxy resin 51 was spread flat 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 part 11, reference part 21, and connecting part 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 (unit: mm), width w (unit: mm), and length L (unit: mm).
[0052] <Test> Using the fabricated corrosion sensor 1, a test was conducted in accordance with the "Cycle Corrosion Test Method - Salt Spray / Drying / Wetting" of "JIS K5600-7-9". More specifically, each corrosion sensor 1 was subjected to repeated cycles of salt spray (35°C, NaCl concentration 5%, 2 hours) → drying (60°C, humidity 25%, 4 hours) → wetting (50°C, humidity 95%, 2 hours) and left for the number of days shown in Table 1 below. During the test, a constant current (10 mA for No. 1) with the current value I (unit: mA) shown in Table 1 below was applied from the current source 71 at 10-minute intervals to determine the electrical resistance values of the sensor part 11 and the reference part 21, and the amount of corrosion (corrosion depth) of the sensor part 11 was measured based on the above formula (IV).
[0053] The degree of deviation (in %) between the corrosion amount of the corrosion sensor 1 and the corrosion amount of the target component at the end of the test was determined. The same test was performed three times (Test 1 to Test 3). The results are shown in Table 1 below. If the sensor unit 11 was disconnected during the test, "Disconnected" was written in the corresponding section of Table 1 below.
[0054] Table 1 below indicates "A" if the deviation was less than ±5% in any of Tests 1 to 3, and "B" if the deviation was ±5% or more in any of Tests 1 to 3 or if a break occurred. "A" indicates excellent accuracy in measuring the amount of corrosion. Table 1 below also indicates whether the corrosion sensor 1 satisfies the above-mentioned equations (I) to (III). "A" is indicated if it satisfies the equations, and "B" is indicated if it does not.
[0055]
[0056] <Summary of Evaluation Results> As shown in Table 1 above, when equations (I) and (II) were satisfied, the degree of deviation in the amount of corrosion was "A", indicating good accuracy in measuring the amount of corrosion over a long period of time. In contrast, when at least one of equations (I) and (II) was not satisfied, the degree of deviation in the amount of corrosion was "B", indicating insufficient accuracy in measuring the amount of corrosion.
[0057] 1: Corrosion sensor 11: Sensor part 11a, 11b: Terminals of the sensor part 21: Reference part 21a, 21b: Terminals of the reference part 31: Base material (target component) 35: Connection part 41: Insulating sheet 51: Resin 61: Cover 71: Current source 81: Voltage measurement part 91: Voltage measurement part
Claims
1. A method for designing a corrosion sensor, wherein the corrosion sensor comprises an electrical resistance type corrosion sensor comprising 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 measures 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, wherein the conductor is made of a metallic material containing a metallic element contained in the target member whose corrosion is to be evaluated, 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). ｉｎｆ ) ... (I) t ｓｅｎｓ ≥ (2.4 × t) ｉｎｆ ) ... (II) t ｉｎｆ : Initial thickness of the 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 type corrosion sensor comprising a sensor portion made of a conductor exposed to any environment and a reference portion made of a conductor shielded from the any environment, wherein the sensor portion is designed according to the corrosion sensor design method described in claim 1 or 2.
4. A method for managing a structure, comprising measuring the amount of corrosion of the sensor portion using a corrosion sensor designed according to the corrosion sensor design method described in claim 1 or 2, 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 portion.