Metal corrosion sensor, localized corrosion rate detection device, and localized corrosion rate detection method

Abstract

To provide a metal corrosion sensor capable of calculating a corrosion rate of a metal structure.SOLUTION: The metal corrosion sensor 10 is used to detect a corrosion rate of a pipe (metal structure) through which fresh water (liquid) flows. The metallic corrosion sensor 10 is sandwiched between a first metallic plate 11 and a second metallic plate 12, the first metallic plate 11 being made of the same material as the pipe and having a known thickness t1 and being exposed to fresh water (liquid), and the second metallic plate 12 being made of a different material from the first metallic plate 11 and being shielded from fresh water. A spacer 13 that electrically insulates the first metal plate 11 and the second metal plate 12 from each other, and an ionic crystal 14 that is held by the spacer 13 in a state of being shielded from fresh water, and that is exposed to fresh water when a through-hole is formed in the first metal plate 11 due to local corrosion, thereby electrically connecting the first metal plate 11 and the second metal plate 12, wherein a current flowing between the first metal plate 11 and the second metal plate 12 can be measured.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a metal corrosion sensor, a localized corrosion rate detection device, and a localized corrosion rate detection method. [Background technology]

[0002] An evaluation electrode is known in which an anode (copper piece) covered with corrosion products and a cathode (copper piece) whose liquid-contacting surface is not covered with corrosion products are arranged in an electrically insulated manner (Patent Document 1). The evaluation electrode is immersed in an aqueous system, and the progress of copper pitting corrosion (localized corrosion) is evaluated by measuring the current flowing between the anode and cathode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-214881 Summary of the Invention [Problem to be solved by the invention]

[0004] However, while the above-mentioned technology can evaluate the progress of copper corrosion from the current value between two copper pieces, it cannot calculate the rate at which localized corrosion progresses (corrosion rate), making it difficult to evaluate the lifespan of metals using the above-mentioned technology.

[0005] In consideration of the above circumstances, the present invention provides a metal corrosion sensor, a local corrosion rate detection device, and a local corrosion rate detection method that enable calculation of the corrosion rate of a metal structure. [Means for solving the problem]

[0006] The metal corrosion sensor of the present invention is a metal corrosion sensor used to detect the corrosion rate of a metal structure through which a liquid flows or is stored, and comprises: a first metal plate made of the same or similar metal as the metal structure, having a known thickness, and exposed to the liquid; a second metal plate made of a different metal from the first metal plate, and shielded from the liquid; a spacer sandwiched between the first metal plate and the second metal plate, electrically insulating the first metal plate and the second metal plate; and an ion crystal held by the spacer while shielded from the liquid, which is exposed to the liquid when a through hole is formed in the first metal plate due to localized corrosion, thereby enabling electrical conductivity between the first metal plate and the second metal plate, and making it possible to measure the current flowing between the first metal plate and the second metal plate.

[0007] In this case, it is preferable that the first metal plate and the second metal plate have a potential difference of 50 mV or more.

[0008] The local corrosion rate detection device of the present invention comprises any of the metal corrosion sensors described above, a current measuring unit that measures the current flowing between the first metal plate and the second metal plate, and a recording unit that records the elapsed time since the first metal plate began to be exposed to the liquid and periodically records the current value measured by the current measuring unit.

[0009] The present invention is a local corrosion rate detection method that uses any of the above-mentioned metal corrosion sensors, and includes a through hole detection process that estimates that the through hole has formed in the first metal plate when the current flowing between the first metal plate and the second metal plate increases, and a corrosion rate calculation process that calculates the corrosion rate of the first metal plate by dividing the thickness of the first metal plate by the elapsed time from when the first metal plate began to be exposed to the liquid until the current increased.

[0010] The present invention also provides a local corrosion rate detection method that uses a plurality of any of the above-mentioned metal corrosion sensors, wherein the plurality of metal corrosion sensors each have a first metal plate of a different thickness, and the method includes, for each metal corrosion sensor, a through hole detection process that estimates that a through hole has formed in the first metal plate when the current flowing between the first metal plate and the second metal plate increases, and a second corrosion rate calculation process that calculates a prediction formula for the corrosion rate of the first metal plate based on the relationship between the thickness of each first metal plate and the elapsed time from when each first metal plate begins to be exposed to the liquid until the current increases. [Effects of the Invention]

[0011] According to the present invention, it is possible to calculate the corrosion rate of a metal structure. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a localized corrosion rate detection device according to an embodiment of the present invention. [Figure 2] 1 is a perspective view showing a metal corrosion sensor according to one embodiment of the present invention. [Figure 3] 1 is an exploded perspective view showing a metal corrosion sensor according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram (cross-sectional view) illustrating the operation of a localized corrosion rate detection device (metal corrosion sensor) according to one embodiment of the present invention. [Figure 5] 1 is a flowchart illustrating a method for detecting a localized corrosion rate according to an embodiment of the present invention. [Figure 6] FIG. 2 is a schematic diagram illustrating test conditions for the localized corrosion rate detection device according to one embodiment of the present invention. [Figure 7] 4 is a graph showing the relationship between current value and elapsed time, which is a test result of the localized corrosion rate detection device according to one embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram showing a localized corrosion rate detection device according to a modified embodiment of the present invention. [Figure 9]1 is a flowchart illustrating a method for detecting a localized corrosion rate according to a variation of an embodiment of the present invention. [Figure 10] 10 is a graph showing the relationship between the thickness of three first metal plates of a localized corrosion rate detection device according to a modified example of one embodiment of the present invention and three increase times corresponding to the three metal corrosion sensors. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that in each drawing, the shape and size of each component are not accurate and are shown schematically for the purpose of explanation.

[0014] [Localized corrosion rate detection device] A localized corrosion rate detecting device 1 according to this embodiment will be described with reference to Figures 1 to 4. Figure 1 is a schematic diagram showing the localized corrosion rate detecting device 1. Figure 2 is a perspective view showing a metal corrosion sensor 10. Figure 3 is an exploded perspective view showing the metal corrosion sensor 10. Figure 4 is a schematic diagram (cross-sectional view) explaining the operation of the localized corrosion rate detecting device 1 (metal corrosion sensor 10).

[0015] The local corrosion rate detection device 1 is installed to evaluate the corrosion state of building equipment piping 5 (see FIG. 1 ) through which fresh water 6, such as tap water, flows. Specifically, the local corrosion rate detection device 1 is used in a local corrosion rate detection method for determining the maximum corrosion rate (V) of a metal equivalent to the building equipment piping 5 (steel pipe). The maximum corrosion rate (V) is used to evaluate the lifespan, etc., of the building equipment piping 5. Note that in this specification, the "building equipment piping 5" will be simply referred to as "piping 5," and the "maximum corrosion rate (V)" will be simply referred to as "corrosion rate (V)." Furthermore, in this specification, the fresh water 6 flowing inside the piping 5 is an example of a "liquid" as defined in the claims, and the piping 5 through which the fresh water 6 flows is an example of a "metal structure" as defined in the claims.

[0016] As shown in Figure 1, the local corrosion rate detection device 1 includes a metal corrosion sensor 10 attached to a pipe 5, a current measurement unit 20 electrically connected to the metal corrosion sensor 10, and a recording unit 21 electrically connected to the current measurement unit 20.

[0017] <Metal corrosion sensor> The metal corrosion sensor 10 is used to detect the corrosion rate of a pipe 5 through which fresh water 6 flows. Specifically, the metal corrosion sensor 10 utilizes the principle of galvanic corrosion to detect the occurrence of through holes 7 (corrosion holes) in the same (similar) metal as the pipe 5. As shown in FIGS. 2 and 3, the metal corrosion sensor 10 includes a first metal plate 11, a second metal plate 12, a spacer 13, and an ion crystal 14. In this specification, the "first metal plate 11" and the "second metal plate 12" will be simply referred to as the "metal plates 11, 12" when describing the same. In this specification, the "through hole 7" refers to a hole that penetrates the metal (first metal plate 11) in the thickness direction (see the lower part of FIG. 4).

[0018] (1st metal plate, 2nd metal plate) The first metal plate 11 is made of a metal that is the same as or similar to that of the pipe 5. Specifically, the first metal plate 11 is a cold-rolled steel plate whose surface has been polished with a #400 buff. The first metal plate 11 is formed, for example, in a substantially square plate (sheet) shape, with a thickness t1 of approximately 0.1 mm. The second metal plate 12 is made of a metal (of a different type) from the first metal plate 11, for example, a copper plate. Like the first metal plate 11, the second metal plate 12 is formed in a substantially square plate (sheet) shape. The thickness t2 of the second metal plate 12 is approximately 0.3 mm. Core wires (metal wires) of coated copper wires 15 are soldered to the surfaces of the two metal plates 11 and 12, allowing the current flowing between the first metal plate 11 and the second metal plate 12 to be measured. Note that only one coated copper wire 15 is shown in FIG. 1.

[0019] (Spacer) The spacer 13 is made of, for example, an electrically insulating synthetic resin, and is formed in a substantially circular (cylindrical) shape so as to surround the filling space 13A that is filled with the ion crystals 14. The thickness t3 of the spacer 13 is set to approximately 0.3 mm. The spacer 13 is sandwiched between the first metal plate 11 and the second metal plate 12, and electrically insulates the first metal plate 11 from the second metal plate 12.

[0020] (ionic crystals) The ionic crystals 14 are, for example, powdered sodium chloride, and are filled in the filling space 13A of the spacer 13. The ionic crystals 14 are held by the spacer 13 in a state where they fill the filling space 13A, and are sandwiched between the first metal plate 11 and the second metal plate 12. The ionic crystals 14 are not electrically conductive in a powder (solid) state, and therefore electrically insulate the first metal plate 11 and the second metal plate 12.

[0021] (Resin exterior parts, etc.) The two metal plates 11, 12 and the spacer 13 are bonded together with an adhesive such as a cyanoacrylate adhesive, and the first metal plate 11 is embedded in a synthetic resin such as an epoxy resin, with a portion of the surface of the first metal plate 11 exposed. The embedded synthetic resin forms a substantially cylindrical resin exterior part 16 (see the two-dot chain line in FIG. 2). The boundary between the first metal plate 11 and the resin exterior part 16 is covered with an adhesive such as a vinyl chloride-vinyl acetate copolymer resin adhesive (not shown).

[0022] [Installation of metal corrosion sensor] As shown in FIG. 1 , metal corrosion sensor 10 is attached to pipe 5 with first metal plate 11 facing the inside of pipe 5 (fresh water 6 (corrosive environment)). First metal plate 11 exposed from resin exterior part 16 is exposed to (in contact with) fresh water 6, while second metal plate 12 and spacer 13 are shielded (isolated) from (not in contact with) fresh water 6. Furthermore, ion crystal 14 is held by spacer 13 in a state where it is shielded from fresh water 6.

[0023] [Metal corrosion sensor function] As shown in the upper part of FIG. 4 , when localized corrosion of the first metal plate 11 has not progressed and no through-holes 7 (corrosion holes) have formed in the first metal plate 11, the electrically non-conductive ionic crystals 14 are held by the spacer 13, and no current flows between the first metal plate 11 and the second metal plate 12 (current value (I) ≈ 0 μA). In contrast, as shown in the lower part of FIG. 4 , when localized corrosion of the first metal plate 11 progresses and through-holes 7 (corrosion holes) have formed in the first metal plate 11, fresh water 6 flows through the through-holes 7 into the filling space 13A of the spacer 13. The ionic crystals 14 are then exposed to the fresh water 6 and dissolve into the fresh water 6, becoming an electrolyte 17, establishing electrical continuity between the first metal plate 11 and the second metal plate 12. In other words, when the ionic crystals 14 become the electrolyte 17, a battery is formed, and current flows between the first metal plate 11 and the second metal plate 12 (see the dashed arrow in the lower part of FIG. 4 ). As described above, the basic principle of detecting through hole 7 by metal corrosion sensor 10 is to detect changes in the value of current (I) flowing between two metal plates 11, 12. The premise is that the corrosion state of first metal plate 11, which is made of the same (similar) metal as pipe 5, matches the corrosion state of the inner surface of pipe 5.

[0024] <Current measurement unit, recording unit> The current measuring unit 20 is, for example, a zero-resistance ammeter. As shown in the lower part of FIG. 4, the current measuring unit 20 is connected in series to the two metal plates 11 and 12 via two coated copper wires 15. The current measuring unit 20 measures the current flowing between the first metal plate 11 and the second metal plate 12. The current measuring unit 20 includes a transmitting unit (not shown) that transmits data (current value (I)) using a wired or wireless communication standard such as a local area network (LAN) or Bluetooth (registered trademark). The recording unit 21 is, for example, a personal computer, a smartphone, a tablet, or a data logger. The recording unit 21 is connected to the current measuring unit 20 in a data communication-enabled state. The recording unit 21 includes a receiving unit (not shown) that receives data using the same communication standard as the transmitting unit of the current measuring unit 20.

[0025] The current measuring unit 20 performs A / D conversion (Analog to Digital Conversion) on the measured data (current value (I)) and transmits the data to the recording unit 21 using the function of the transmitting unit. The recording unit 21 receives the data transmitted from the current measuring unit 20 using the function of the receiving unit. The recording unit 21 records (saves) the received data (current value (I)) periodically (at regular intervals). The recording unit 21 also records (saves) the elapsed time (T) since the first metal plate 11 began to be exposed to fresh water 6 using a clock function or the like that is provided as standard.

[0026] [Localized corrosion rate detection method] Next, a method for detecting a local corrosion rate using the metal corrosion sensor 10 (local corrosion rate detecting device 1) will be described with reference to Figures 4 and 5. Figure 5 is a flowchart showing the method for detecting a local corrosion rate.

[0027] 5, the local corrosion rate detection method includes a through hole detection step S1 and a corrosion rate calculation step S2. The local corrosion rate detection method (through hole detection step S1, corrosion rate calculation step S2) may be performed manually by an operator (person) who checks the data (current value (I), elapsed time (T)) recorded in the recording unit 21, automatically by software (program) stored in the recording unit 21, or semi-automatically by collaboration between the operator operating the recording unit 21 and the software. When the local corrosion rate detection method is performed automatically or semi-automatically by software, information such as the dimensions and materials of the components of the metal corrosion sensor 10 is assumed to be stored in the recording unit 21, such as the fact that the first metal plate 11 is a steel plate with a thickness t1.

[0028] <Through-hole detection process> In the through hole detection step S1, the formation of the through hole 7 in the first metal plate 11 is determined based on the current value (I) recorded in the recording unit 21. To explain in more detail, if the first metal plate 11 does not have the through hole 7 and no current flows between the two metal plates 11 and 12 (see the upper part of FIG. 4), the current measuring unit 20 cannot measure the current (to be precise, it measures a current of approximately 0 amperes), and therefore data indicating approximately 0 amperes is recorded in the recording unit 21. In contrast, if the first metal plate 11 has the through hole 7 and a current flows between the two metal plates 11 and 12 (see the lower part of FIG. 4), the current measuring unit 20 measures the current, and data indicating a current value (I) exceeding 0 amperes is recorded in the recording unit 21.

[0029] Using the above principle, in the through hole detection step S1, it is determined whether data indicating a current value (I) exceeding 0 amperes has been recorded in the recording unit 21. If the current value (I) recorded in the recording unit 21 is 0 amperes (NO in S1), the recording unit 21 (or the worker) repeats the determination until the current value (I) exceeds 0 amperes. On the other hand, if the current value (I) recorded in the recording unit 21 increases (changes) (exceeds 0 amperes) (YES in S1), the recording unit 21 (or the worker) estimates (determines) that a through hole 7 has been formed in the first metal plate 11 at the point when the current (current value (I)) flowing between the first metal plate 11 and the second metal plate 12 increases. Note that the current value (I) may be determined to have increased (changed) if it is equal to or greater than a predetermined threshold value (or exceeds the threshold value).

[0030] <Corrosion rate calculation process> After it is estimated (determined) that a through hole 7 has been formed in the first metal plate 11, a corrosion rate calculation step S2 is executed. The thickness t1 of the first metal plate 11 is known, and the elapsed time (T) from the start of exposing the first metal plate 11 to the fresh water 6 until the current (current value (I)) increases (hereinafter also referred to as the "increase time (N)") is also recorded in the recording unit 21. Therefore, it is possible to calculate the corrosion rate (V), which is the change in the amount of decrease in the thickness t1 of the first metal plate 11 over time. In the corrosion rate calculation step S2, the recording unit 21 (or an operator) divides the thickness t1 of the first metal plate 11 by the increase time (N) to calculate the corrosion rate (V) of the first metal plate 11. The calculated corrosion rate (V) may be recorded in the recording unit 21.

[0031] Since the first metal plate 11 is the same as (similar to) the metal that constitutes the pipe 5, the corrosion rate (V) of the first metal plate 11 can be estimated to be the corrosion rate (V) of the pipe 5. This makes it possible to evaluate (estimate) the lifespan of the pipe 5, taking into account the period of use, thickness, etc. of the pipe 5.

[0032] [Verification of localized corrosion rate detection device (method)] The applicant conducted tests (verification) to confirm the effectiveness of the local corrosion rate detection device 1 (local corrosion rate detection method) described above. Hereinafter, the test conditions and test results for the local corrosion rate detection device 1 (local corrosion rate detection method) will be described with reference to Figs. 6 and 7. Fig. 6 is a schematic diagram illustrating the test conditions for the local corrosion rate detection device 1. Fig. 7 is a graph showing the test results for the local corrosion rate detection device 1, depicting the relationship between current value (I) and elapsed time (T).

[0033] <Test conditions> As shown in Figure 6, tap water (500 ml) as an example of fresh water 6 (liquid) and a stirrer 32 were placed in a beaker 30 (capacity 500 ml), and the beaker 30 was placed on a stirrer 31. In addition, the local corrosion rate detecting device 1 described above was prepared, and the metal corrosion sensor 10 was immersed in the fresh water 6 (tap water) in the beaker 30, and the two coated copper wires 15 extending from the two metal plates 11, 12 were supported by a plug member 34 fixed to a lid member 33 of the beaker 30. In this state, the first metal plate 11 of the metal corrosion sensor 10 was exposed to the fresh water 6 (tap water).

[0034] The fresh water 6 (beaker 30) and the localized corrosion rate detection device 1 were placed in an environment at room temperature of 25°C, and the stirrer 31 was operated with the rotation speed of the stirrer 32 set to 300 rpm, causing the fresh water 6 in the beaker 30 to flow (stir) (start of the test). The recording unit 21 of the localized corrosion rate detection device 1 began measuring the elapsed time (T) from the start of the test (after the metal corrosion sensor 10 was immersed or after stirring began), and recorded the current value (I) measured by the current measurement unit 20 every 30 seconds (periodically).

[0035] <Test Results> As shown in Figure 7, from the start of the test (0 h) to approximately 80 h, the current value (I) was approximately 0 μA, and no current was detected between the two metal plates 11 and 12. In contrast, after approximately 80 h of elapsed time (T) (increase time (N)), an increase (rise) in the current value (I) was confirmed. At this point, observation of the surface of the first metal plate 11 of the metal corrosion sensor 10 confirmed the formation of a through-hole 7 beneath the accumulation of corrosion products. Fresh water 6 flowed into the metal corrosion sensor 10 through the through-hole 7, and the ionic crystals 14 dissolved in the fresh water 6 to form the electrolyte 17, short-circuiting the two metal plates 11 and 12. In other words, a battery was formed, causing the current value (I) to increase (rise).

[0036] As described above, the local corrosion rate detection device 1 (metal corrosion sensor 10) was able to detect the formation of the through hole 7 in the first metal plate 11 as an increase (change) in the current value (I).

[0037] Here, since the thickness t1 of the first metal plate 11 is known, the corrosion rate (V) (10.95 mm / year = 0.1 mm / 80 h) was calculated by dividing the thickness t1 (0.1 mm) by the increase time (N) (80 h), which is the elapsed time (T) at the time when the current value (I) increased (the time when the through hole 7 was formed). As described above, it was confirmed that the local corrosion rate detection device 1 (local corrosion rate detection method) is effective in determining the corrosion rate (V).

[0038] In the metal corrosion sensor 10 according to the present embodiment described above, two different types of metal plates 11 and 12 are combined with an ionic crystal 14 sandwiched therebetween, making it possible to measure the current flowing between the two metal plates 11 and 12. When a through hole 7 is formed in the first metal plate 11 due to the progression of localized corrosion, the ionic crystal 14 dissolves in the fresh water 6 to form the electrolyte 17, short-circuiting the two metal plates 11 and 12. With this configuration, the occurrence of the through hole 7 in the first metal plate 11 can be determined by checking the current generated between the two metal plates 11 and 12. Furthermore, the corrosion rate (V) of the first metal plate 11 can be easily calculated based on the known thickness t1 of the first metal plate 11 and the elapsed time (T) (increased time (N)) from the start of exposure of the first metal plate 11 to the fresh water 6 until the start of current flow. As a result, the state of corrosion and the progress of corrosion of the pipe 5 made of the same (similar) metal as the first metal plate 11 can be estimated, and the life of the pipe 5 can be predicted (evaluated).

[0039] In the localized corrosion rate detection device 1 according to the present embodiment described above, the current measurement unit 20 measures the current flowing between the two metal plates 11 and 12, and the recording unit 21 records the elapsed time (T) since the first metal plate 11 began to be exposed to the fresh water 6, and periodically records the current value (I) measured by the current measurement unit 20. With this configuration, the increase (change) in the current value (I) and the elapsed time (T) at the time of the increase are recorded (saved) in the recording unit 21. Therefore, simply by referring to the record in the recording unit 21, it is possible to determine the occurrence of a through hole 7 in the first metal plate 11 and calculate the corrosion rate (V) of the first metal plate 11. This reduces the effort and cost required to retrieve the metal corrosion sensor 10 from the fresh water 6 to evaluate the progress of localized corrosion (pitting corrosion).

[0040] According to the local corrosion rate detection method of this embodiment described above, it is possible to ascertain the occurrence of a through hole 7 in the first metal plate 11 by checking an increase in the current value (I) recorded in the recording unit 21. Furthermore, the corrosion rate (V) of the first metal plate 11 (piping 5) can be obtained by a simple calculation in which the known thickness t1 of the first metal plate 11 is divided by the elapsed time (T) (increase time (N)) at the point in time when the current value (I) recorded in the recording unit 21 increased.

[0041] [Variations] Next, a local corrosion rate detecting device 2 (local corrosion rate detecting method) according to a modified example of this embodiment will be described with reference to FIGS. 8 to 10. FIG. 8 is a schematic diagram showing the local corrosion rate detecting device 2 according to the modified example. FIG. 9 is a flowchart showing the local corrosion rate detecting method according to the modified example. FIG. 10 is a graph showing the relationship between the thicknesses t1A, t1B, and t1C of the three first metal plates 11A, 11B, and 11C of the local corrosion rate detecting device 2 according to the modified example and the three increase times (NA, NB, and NC) corresponding to the three metal corrosion sensors 10A, 10B, and 10C. Note that components that are the same as or correspond to those in the local corrosion rate detecting device 1 (local corrosion rate detecting method) described above are designated by the same reference numerals, and their description will be omitted.

[0042] While the local corrosion rate detecting device 1 according to the present embodiment described above includes one metal corrosion sensor 10, the present invention is not limited to this and may include one or more metal corrosion sensors 10. For example, as shown in FIG. 8 , a local corrosion rate detecting device 2 according to a modified example includes multiple (e.g., three) metal corrosion sensors 10A, 10B, and 10C. The three metal corrosion sensors 10A, 10B, and 10C are attached to a pipe 5 at intervals along the flow direction of fresh water 6. The three metal corrosion sensors 10A, 10B, and 10C include first metal plates 11A, 11B, and 11C, respectively, having different thicknesses. The thickness t1B of the first metal plate 11B is thicker than the thickness t1A of the first metal plate 11A, and the thickness t1C of the first metal plate 11C is thicker than the thickness t1B of the first metal plate 11B. The thicknesses t1A, t1B, and t1C of the three first metal plates 11A, 11B, and 11C are each known and may be stored in the recording unit 21. In this specification, in explanations common to the three metal corrosion sensors 10A, 10B, and 10C, only Arabic numerals are used for the symbols. The same applies to the first metal plates 11A, 11B, and 11C. Similarly, the thicknesses t1A, t1B, and t1C and the increase times (NA, NB, and NC) may also be simply referred to as "thickness t1" and "increase time (N)."

[0043] Each of the three metal corrosion sensors 10 is connected to a current measurement unit 20 via a coated copper wire 15. The current measurement unit 20 measures the current generated in each of the metal corrosion sensors 10A, 10B, and 10C. The recording unit 21 records (saves) data (current value (I)) corresponding to each of the metal corrosion sensors 10A, 10B, and 10C. Note that FIG. 8 shows only one coated copper wire 15 corresponding to each of the metal corrosion sensors 10A, 10B, and 10C.

[0044] As shown in Figure 9, the local corrosion rate detection method using multiple metal corrosion sensors 10 includes a second corrosion rate calculation step S3 in addition to a through hole detection step S1 and a corrosion rate calculation step S2. In the through hole detection step S1, for each metal corrosion sensor 10, it is estimated that a through hole 7 has formed in the first metal plate 11 at the time when the current (current value (I)) flowing between the first metal plate 11 and the second metal plate 12 increases (changes). In the corrosion rate calculation step S2, the corrosion rate (V) of the first metal plate 11 is calculated for each metal corrosion sensor 10 by dividing the thickness t1 of the first metal plate 11 by the time (N) of increase. In the local corrosion rate detection method, the through hole detection step S1 and the corrosion rate calculation step S2 are repeated for all metal corrosion sensors 10 until a through hole 7 has formed and the corrosion rate (V) has been calculated (NO in step S4).

[0045] If through holes 7 have been formed and the corrosion rate (V) has been calculated for all metal corrosion sensors 10 (YES in step S4), a second corrosion rate calculation step S3 is executed. In the second corrosion rate calculation step S3, the recording unit 21 (or an operator) calculates a prediction formula F for the corrosion rate (V) of the first metal plate 11 based on the relationship between the thicknesses t1A, t1B, and t1C of each of the first metal plates 11A, 11B, and 11C and the increase times (NA, NB, and NC) from the start of exposure of each of the first metal plates 11A, 11B, and 11C to the start of an increase in current. Figure 10 was obtained by plotting the thicknesses t1A, t1B, and t1C of the three first metal plates 11A, 11B, and 11C and the three increase times (NA, NB, and NC) (elapsed time). The corrosion rate (V) prediction formula F can be calculated by, for example, using the least squares method to find a function that approximates the three pieces of data obtained. The corrosion rate (V) can be calculated as the slope of the prediction formula F.

[0046] In the local corrosion rate detecting device 2 (local corrosion rate detecting method) according to the modified example of this embodiment described above, a prediction formula F for the corrosion rate (V) of fresh water 6 is calculated using multiple metal corrosion sensors 10 having first metal plates 11 with different thicknesses t1A, t1B, and t1C. This configuration makes it possible to predict a corrosion rate (V) more accurately than a corrosion rate (V) calculated using each individual metal corrosion sensor 10. This allows the progress of corrosion in the pipe 5 to be accurately estimated, thereby enabling the lifespan of the pipe 5 to be predicted (evaluated) with high accuracy.

[0047] Although the local corrosion rate detecting device 2 according to the modified example is provided with three metal corrosion sensors 10, the number is not limited to this, and three or more metal corrosion sensors 10 may be provided (not shown).

[0048] Furthermore, in the local corrosion rate detecting device 2 (local corrosion rate detecting method) according to the modified example, three corrosion rates (V) are calculated in the corrosion rate calculation step S2, but the present invention is not limited to this. For example, the average of three (multiple) corrosion rates (V) may be calculated and used as the corrosion rate (V) in freshwater 6 (corrosive environment). Alternatively, for example, the corrosion rate calculation step S2 may be omitted, and the local corrosion rate detecting method may be composed of a through hole detection step S1 and a second corrosion rate calculation step S3 (not shown). In this case, in step S4, it is preferable to determine whether or not a through hole 7 has been formed for all of the metal corrosion sensors 10.

[0049] In the localized corrosion rate detection devices 1 and 2 according to the present embodiment (including modified examples, the same applies below), the metal corrosion sensor 10 is attached to a pipe 5 made of steel. However, the present invention is not limited to this. The metal corrosion sensor 10 may be attached to, for example, an iron pipe or a lead pipe. Alternatively, the metal corrosion sensor 10 may be attached to a pipe 5 made of cast iron, copper, zinc, aluminum, or an alloy containing these metals, or a metal (alloy) whose base material is subjected to a surface treatment such as painting. The metal corrosion sensor 10 may also be attached to a tank (another example of a metal structure) that contains (retains) a liquid such as fresh water 6. In other words, the metal corrosion sensor 10 may be attached to a metal structure that circulates or retains a liquid. Furthermore, the first metal plate 11 of the metal corrosion sensor 10 may be made of a metal that is the same as or similar to the metal structure, such as the pipe 5 or a tank. For example, if the first metal plate 11 is made of carbon steel, it means that the carbon content of the first metal plate 11 is slightly different from that of the metal structure, and the two metals can be considered almost identical. Furthermore, the liquid inside the metal structure is not limited to fresh water 6, but may also be salt water, alcohol, or the like.

[0050] Furthermore, in the metal corrosion sensor 10 of the localized corrosion rate detection devices 1 and 2 according to this embodiment, the first metal plate 11 is an iron plate and the second metal plate 12 is a copper plate. However, the types of the two metal plates 11 and 12 are not particularly limited. The first metal plate 11 and the second metal plate 12 may be made of different metals, and preferably, they are selected so as to have a potential difference of 50 mV or more in a liquid (corrosive environment). With this configuration, by setting the potential difference between the two metal plates 11 and 12 to 50 mV or more, the current flowing between the two metal plates 11 and 12 can be increased when the ionic crystals 14 become the electrolyte 17. This makes it easier to confirm the increase in the current value (I), making it possible to clearly determine the occurrence of a through hole 7 in the first metal plate 11 and the elapsed time (T) (increase time (N)) until the current generation.

[0051] Furthermore, in the metal corrosion sensor 10 of the localized corrosion rate detection devices 1 and 2 according to the present embodiment, the metal plates 11 and 12 are formed in a substantially square plate shape. However, this is not limited thereto and may be other shapes, such as a disk shape (not shown). Furthermore, the spacer 13 is formed from an electrically insulating synthetic resin. However, this is not limited thereto and may be any electrically insulating material, such as ceramics or glass. Furthermore, the spacer 13 is formed in a substantially circular ring shape. However, this is not limited thereto and may be other shapes, such as a rectangular ring shape (not shown). Furthermore, the ionic crystals 14 are sodium chloride. However, this is not limited thereto and may be other electrolytes. Furthermore, the ionic crystals 14 are powder. However, this is not limited thereto and may be granular or other shapes that are easily soluble in a solute, such as fresh water 6.

[0052] Furthermore, although the local corrosion rate detecting devices 1 and 2 according to the present embodiment are provided with the recording unit 21 that records various data including the current value (I), elapsed time (T) (increase time (N)), corrosion rate (V), thickness t1, etc., the present invention is not limited to this. For example, the recording unit 21 may be omitted (not shown), in which case an operator may periodically visually check the current measuring unit 20 and manually perform the local corrosion rate detection method (through hole detection step S1, corrosion rate calculation step S2, second corrosion rate calculation step S3).

[0053] The above-described embodiment shows one aspect of the metal corrosion sensor, the local corrosion rate detection device, and the local corrosion rate detection method according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit and scope of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0054] 1,2 Localized corrosion rate detection device 5 Building equipment piping (metal structures) 6 Fresh water (liquid) 7 Through holes 10 Metal Corrosion Sensor 11 First metal plate 12 Second metal plate 13 Spacer 14 Ionic Crystals 20 Current measurement section 21 Recording Section F prediction formula S1 Through-hole detection process S2 Corrosion rate calculation process S3 Second corrosion rate calculation process

Claims

1. A metal corrosion sensor used to detect the corrosion rate of a metal structure through which a liquid flows or is stored, a first metal plate made of the same or similar metal as the metal structure, having a known thickness, and exposed to the liquid; a second metal plate made of a different metal from the first metal plate and shielded from the liquid; a spacer sandwiched between the first metal plate and the second metal plate to electrically insulate the first metal plate from the second metal plate; an ionic crystal that is held by the spacer in a state shielded from the liquid, and that is exposed to the liquid when a through-hole is formed in the first metal plate due to local corrosion, thereby electrically connecting the first metal plate and the second metal plate; A metal corrosion sensor capable of measuring the current flowing between the first metal plate and the second metal plate.

2. 2. The metal corrosion sensor according to claim 1, wherein the first metal plate and the second metal plate have a potential difference of 50 mV or more.

3. The metal corrosion sensor according to claim 1 or 2; a current measuring unit that measures the current flowing between the first metal plate and the second metal plate; a recording unit that records the elapsed time since the first metal plate began to be exposed to the liquid and that periodically records the current value measured by the current measuring unit.

4. A method for detecting a local corrosion rate using the metal corrosion sensor according to claim 1 or 2, a through-hole detection step of estimating that the through-hole has been formed in the first metal plate when the current flowing between the first metal plate and the second metal plate increases; a corrosion rate calculation step of calculating the corrosion rate of the first metal plate by dividing the thickness of the first metal plate by the elapsed time from when the first metal plate begins to be exposed to the liquid until the current increases.

5. A method for detecting a local corrosion rate using a plurality of metal corrosion sensors according to claim 1 or 2, The plurality of metal corrosion sensors each have the first metal plate with a different thickness, a through hole detection step of estimating, for each of the metal corrosion sensors, that the through hole has been formed in the first metal plate when the current flowing between the first metal plate and the second metal plate increases; and a second corrosion rate calculation step of calculating a prediction formula for the corrosion rate of the first metal plate based on the relationship between the thickness of each of the first metal plates and the elapsed time from when each of the first metal plates begins to be exposed to the liquid until the current increases.

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