Corrosion monitoring device

Abstract

To provide a corrosion monitoring device capable of accurately monitoring an amount of corrosion of a metal piece and of monitoring a corrosion behavior in a state where corrosion products are deposited.SOLUTION: A corrosion monitoring device 100 according to the present invention comprises: a metal piece 11; electric resistance measuring means 20 that measures an electric resistance value of the metal piece by energizing the metal piece; and calculation means 30 that calculates an amount of corrosion of the metal piece on the basis of the electric resistance value of the metal piece measured by the electric resistance measuring means. The thickness of the metal piece is 0.3 mm or less, and corrosion products CP are previously deposited on the metal piece.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a corrosion monitoring device capable of monitoring the amount of corrosion of a metal piece. In particular, the present invention relates to a corrosion monitoring device capable of monitoring the amount of corrosion of a metal piece with high accuracy and monitoring corrosion behavior in a state where corrosion products have accumulated. [Background technology]

[0002] For predicting the lifespan and maintenance of metal products, or for developing products with excellent corrosion resistance, there is a demand for a device that can monitor the amount of corrosion of metal pieces with high accuracy.

[0003] One means capable of monitoring the amount of corrosion of a metal piece is an electrical resistance type corrosion sensor as described in Patent Documents 1 to 3. An electrical resistance type corrosion sensor measures the amount of corrosion (amount of corrosion thinning) of a metal piece based on an increase in electrical resistance value that accompanies corrosion thinning of the metal piece that constitutes the corrosion sensor.

[0004] In electrical resistance corrosion sensors, the amount of corrosion of a metal piece is calculated by multiplying the initial thickness of the metal piece by a parameter related to the change in the metal piece's electrical resistance. Therefore, the noise width of the calculated corrosion amount (the amplitude of noise that repeatedly increases and decreases over a short period of time) increases with the initial thickness of the metal piece. If the noise width is large, the corrosion behavior of the metal piece cannot be measured accurately, even with signal processing such as smoothing. Therefore, to improve the measurement accuracy of the corrosion sensor, it is necessary to set the initial thickness of the metal piece small.

[0005] On the other hand, if the initial thickness of the metal piece is set small, the corrosion will penetrate the metal piece in the thickness direction early as the corrosion progresses, making it impossible to measure the corrosion amount. In other words, the measurement life will be shortened. Therefore, it is difficult to grasp the corrosion behavior when the corrosion of the metal piece has progressed to a certain extent and corrosion products have accumulated on the metal piece. Since the corrosion behavior of the metal piece changes significantly depending on the presence or absence of corrosion products, it is problematic that it is difficult to grasp the corrosion behavior when corrosion products have accumulated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-3376 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-197102 [Patent Document 3] International Publication No. 2021 / 235475 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the problems of the conventional technology as described above, and has an object to provide a corrosion monitoring device that can monitor the amount of corrosion of metal pieces with high accuracy and can monitor corrosion behavior in a state where corrosion products have accumulated. [Means for solving the problem]

[0008] To solve the above problems, the present inventors conducted extensive research and found that the amount of corrosion of a metal piece can be measured with high accuracy by making the thickness of the metal piece (the initial thickness before corrosion occurs on the metal piece) 0.3 mm or less. They also found that by depositing corrosion products on the metal piece in advance (depositing corrosion products before corrosion occurs on the metal piece), it is possible to understand the corrosion behavior of the metal piece with the corrosion products deposited, even if the thickness of the metal piece is small.

[0009] The present invention was completed based on the above findings of the present inventors. That is, in order to solve the above-mentioned problems, the present invention provides a corrosion monitoring device comprising a metal piece, an electrical resistance measuring means for measuring the electrical resistance value of the metal piece by passing an electric current through the metal piece, and a calculation means for calculating the amount of corrosion of the metal piece based on the electrical resistance value of the metal piece measured by the electrical resistance measuring means, wherein the thickness of the metal piece is 0.3 mm or less and corrosion products have already accumulated on the metal piece.

[0010] According to the present invention, since the thickness of the metal piece is 0.3 mm or less, the amount of corrosion of the metal piece can be monitored with high accuracy, as discovered by the inventors. Furthermore, since corrosion products are already deposited on the metal piece, it is possible to monitor the corrosion behavior of the metal piece even when the thickness is as small as 0.3 mm or less, with corrosion products already deposited. The "thickness of the metal piece" refers to the initial thickness of the metal piece before corrosion occurs (immediately after the metal piece is placed in a corrosive environment). The thickness of the metal piece may be 0.3 mm or less, and is preferably 0.1 mm or less. Furthermore, "corrosion products have already accumulated on the metal piece" means that corrosion products have already accumulated in the early stage before corrosion occurs on the metal piece (immediately after the metal piece is placed in a corrosive environment). The corrosion products may be accumulated on only one surface (top or bottom surface) of the metal piece, or on both surfaces. Furthermore, the corrosion products do not necessarily have to be accumulated on the entire surface of one surface (or both surfaces) of the metal piece, but may be accumulated on only a portion of the surface. Examples of methods for depositing corrosion products include, but are not limited to, a method in which a solvent containing corrosion products is applied to the metal piece and the solvent is dried, a method in which conductive tape is attached to the metal piece, or a method in which the tape is pressed onto the metal piece.

[0011] Preferably, the calculation means smooths the calculated corrosion amount of the metal piece over time.

[0012] According to the above-described preferred configuration, the noise width of the calculated corrosion amount is reduced, and the corrosion amount of the metal piece can be monitored with even higher accuracy. The method of temporal smoothing is not particularly limited, and any method can be applied as long as it can reduce the noise width of the corrosion amount, such as local regression such as LOWESS (locally weighted scatterplot smoothing) or moving average.

[0013] The electrical resistance of a metal piece is temperature dependent. Depending on the measurement environment (the environment in which the metal piece is placed), there may be little temperature change, in which case the temperature dependency of the electrical resistance does not necessarily need to be taken into consideration. However, in order to measure the corrosion amount of the metal piece with even greater accuracy, it is preferable to take into consideration the temperature dependency of the electrical resistance value. A method for taking into account the temperature dependence of electrical resistance, based on the same concepts as those described in Patent Documents 1 to 3, is to provide a reference section, separate from the metal piece used to measure the amount of corrosion, that is isolated from the measurement environment to prevent corrosion, and measure the amount of corrosion of the metal piece based on the electrical resistance of the metal piece and the electrical resistance of the reference section. Specifically, this method considers that changes in the electrical resistance of the reference section are due to temperature changes rather than corrosion, and calculates the change in the electrical resistance of the metal piece excluding the change in electrical resistance due to temperature changes as the change in electrical resistance due to corrosion. For this reason, this method assumes that the temperature of the metal piece and the temperature of the reference section are the same. However, if the reference part is prepared by coating the same metal piece as the metal piece used to measure the amount of corrosion with an anticorrosive paint or the like in order to prevent corrosion of the reference part, this coating may increase the temperature difference between the reference part and the metal piece, and it may not be possible to sufficiently reduce the effect of the temperature dependence of the electrical resistance value. Therefore, in order to measure the corrosion amount of the metal piece with higher accuracy taking into account the temperature dependency of the electrical resistance value, it is preferable to directly measure the temperature of the metal piece instead of providing a reference part.

[0014] That is, in the present invention, it is preferable that the apparatus further includes a temperature measuring means for measuring the temperature of the metal piece, and the calculation means calculates the amount of corrosion of the metal piece based on the electrical resistance value of the metal piece measured by the electrical resistance measuring means and the temperature of the metal piece measured by the temperature measuring means.

[0015] According to the above-described preferred configuration, the corrosion amount of the metal piece is calculated using the temperature of the metal piece measured by the temperature measuring means in addition to the electrical resistance value of the metal piece measured by the electrical resistance measuring means, so that the corrosion amount of the metal piece can be measured more accurately than when the temperature dependency of the electrical resistance value is not taken into account (when the temperature change of the metal piece is not taken into account).Furthermore, compared to when a reference part is provided as described in Patent Documents 1 to 3, the corrosion amount of the metal piece can be measured more accurately and the effort and cost of providing a reference part can be reduced. [Effects of the Invention]

[0016] According to the present invention, it is possible to monitor the amount of corrosion of a metal piece with high accuracy, and also possible to monitor the corrosion behavior in a state where corrosion products have accumulated. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a schematic configuration of a corrosion monitoring device according to an embodiment of the present invention. [Figure 2] 1. FIG. 4 is a plan view showing another example of the metal piece shown in FIG. [Figure 3] FIG. 1 is a diagram showing the results of a corrosion test conducted by the present inventors. [Figure 4] FIG. 4 is a diagram showing the change over time in the corrosion rate of the metal piece 11, which is obtained by time differentiating the corrosion amount Δt of the metal piece 11 after smoothing shown in FIG. 3(d). [Figure 5] FIG. 10 shows the results of another corrosion test conducted by the present inventors. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a diagram showing a schematic configuration of a corrosion monitoring device according to one embodiment of the present invention. Fig. 1(a) is a plan view showing the overall configuration, and Fig. 1(b) is an enlarged view of a cross section of a metal piece along the width direction. Fig. 2 is a plan view showing another example of the metal piece shown in Fig. 1. 1, a corrosion monitoring device 100 according to this embodiment includes a corrosion sensor 10, an electrical resistance measurement means 20 that measures the electrical resistance of a metal piece 11 provided in the corrosion sensor 10 by passing an electric current through the metal piece 11, and a calculation means 30 that calculates the amount of corrosion of the metal piece 11. In a preferred embodiment, the corrosion sensor 10 provided in the corrosion monitoring device 100 according to this embodiment also includes a temperature measurement means 40 that measures the temperature of the metal piece 11. The corrosion sensor 10, the electrical resistance measurement means 20, and the calculation means 30 that constitute the corrosion monitoring device 100 will be described below in order.

[0019] <Corrosion Sensor 10> The corrosion sensor 10 comprises a metal piece 11, a substrate 12 on which the metal piece 11 is placed, and a temperature measuring means 40. The metal piece 11 is formed from the same type of metal as the metal product (e.g., steel) to be evaluated. In the example shown in FIG. 1, the shape of the metal piece 11 is rectangular in plan view, but this is not limited thereto. For example, as shown in FIG. 2(a), the metal piece 11 may be a U-shaped metal piece 11A in plan view, or as shown in FIG. 2(b), the metal piece 11 may be a serpentine metal piece 11B in plan view. The metal piece 11 has longitudinal ends 111 and 112 electrically connected to the electrical resistance measuring means 20. Wiring 211 and 221 electrically connecting the ends 111 and 112 of the metal piece 11 to the electrical resistance measuring means 20 are preferably covered with a predetermined covering member 13 to prevent disconnection due to corrosion. The same applies when using metal pieces 11A and 11B.

[0020] Corrosion products CP are deposited in advance on the metal piece 11. In the example shown in Fig. 1(b), the corrosion products CP are deposited only on the upper surface of the metal piece 11. Methods for depositing the corrosion products CP include, but are not limited to, a method of applying a solvent containing the corrosion products CP to the metal piece 11 and drying the solvent, a method of attaching the corrosion products CP to the metal piece 11 using conductive tape, and a method of pressing the corrosion products CP onto the metal piece 11. The thickness of the corrosion products CP is set to, for example, 10 µm to 5000 µm.

[0021] The metal piece 11 on which the corrosion products CP are deposited has a surface exposed to the measurement environment. That is, at least a portion of the metal piece 11 on which the corrosion products CP are deposited is exposed without being covered. In the example shown in Fig. 1, the side surfaces of the metal piece 11 are covered with a resin or the like (not shown), and only the top surface on which the corrosion products CP are deposited is exposed to the measurement environment (it is actually the top surface of the corrosion products CP that is exposed). However, the present invention is not limited to this, and it is also possible to adopt a configuration in which the upper surface (upper surface of the corrosion product CP) and side surfaces of the metal piece 11 (more precisely, the portions of the side surfaces other than those in contact with the covering member 13) are exposed to the measurement environment. Furthermore, when the metal piece 11 is placed on the lower surface of the substrate 12 and the corrosion products CP are deposited only on the lower surface of the metal piece 11, it is also possible to adopt a configuration in which only the lower surface of the metal piece 11 (lower surface of the corrosion product CP) is exposed to the measurement environment, or a configuration in which the lower surface (lower surface of the corrosion product CP) and side surfaces of the metal piece 11 are exposed to the measurement environment. Furthermore, when only the ends 111, 112 of the metal piece 11 are supported by the substrate 12 and the corrosion products CP are deposited on the upper and lower surfaces of the metal piece 11, it is also possible to adopt a configuration in which the upper surface (upper surface of the corrosion product CP) and lower surface (lower surface of the corrosion product CP) of the metal piece 11 are exposed to the measurement environment, or a configuration in which the upper surface (upper surface of the corrosion product CP), lower surface (lower surface of the corrosion product CP), and side surfaces of the metal piece 11 are exposed to the measurement environment. The same applies when the metal pieces 11A and 11B are used.

[0022] For example, a plastic substrate, which is an insulator, is used as the substrate 12. However, the present invention is not limited to this, and a substrate made of a conductor such as metal may also be used as the substrate 12. In this case, an insulator may be disposed between the substrate 12 and the metal piece 11. The same applies when the metal pieces 11A and 11B are used.

[0023] In this embodiment, a thermocouple 41 that measures the temperature of the metal piece 11 is used as the temperature measurement means 40. It is preferable to cover the thermocouple 41 with a predetermined covering member 42 to prevent the thermocouple 41 from breaking due to corrosion. In the example shown in FIG. 1(a), the tip of the thermocouple 41 is fixed to the underside of the metal piece 11 with insulating tape 43. The thermocouple 41 can be fixed in any manner, and for example, it can be fixed with a magnet or a screw. The fixing position of the thermocouple 41 (temperature measurement position) can also be arbitrary. Multiple thermocouples 41 can be used to measure temperatures at multiple positions on the metal piece 11, and the average value can be used as the temperature of the metal piece 11 used by the calculation means 30 described below. The same applies when metal pieces 11A and 11B are used.

[0024] The temperature measuring means 40 is not limited to the thermocouple 41, and any configuration such as an electrical resistance temperature sensor can be used as long as it can measure the temperature of the metal piece 11. The temperature measurement by the temperature measuring means 40 may be continuous or intermittent. The same applies when using the metal pieces 11A and 11B.

[0025] <Electrical resistance measuring means 20> The electrical resistance measuring means 20 includes a constant current power supply 21 , a voltmeter 22 , and an electrical resistance value calculating means 23 in order to measure the electrical resistance value of the metal piece 11 . The constant current power supply 21 is electrically connected to the ends 111 and 112 of the metal piece 11 by a wire 211 , and applies a constant current from the end 111 to the end 112 of the metal piece 11 . The voltmeter 22 is electrically connected to the ends 111 and 112 of the metal piece 11 by a wire 221 , and measures the voltage between the ends 111 and 112 of the metal piece 11 . The electrical resistance value calculation means 23 calculates the electrical resistance value of the metal piece 11 by dividing the voltage measured by the voltmeter 22 by the current supplied from the constant current power supply 21 . The measurement of the electrical resistance value of the metal piece 11 by the electrical resistance measuring means 20 may be continuous or intermittent. However, it is preferable that the timing of measuring the electrical resistance value of the metal piece 11 by the electrical resistance measuring means 20 and the timing of measuring the temperature of the metal piece 11 by the temperature measuring means 40 are synchronized. The same applies when the metal pieces 11A and 11B are used.

[0026] In addition, in order to accurately measure the electrical resistance value of metal piece 11, it is preferable to take measures to remove measurement noise caused by thermoelectric power due to the temperature difference between the connection part between end 111 of metal piece 11 and wiring 211, 221 and the connection part between end 112 of metal piece 11 and wiring 211, 221. Possible noise removal measures include, for example, (1) increasing the current flowing from constant current power supply 21 to increase the voltage measured by voltmeter 22, (2) subtracting the voltage measured by voltmeter 22 when the current flowing from constant current power supply 21 is stopped from the voltage measured by voltmeter 22 when current is flowing from constant current power supply 21, and using the resulting value as the voltage when calculating the electrical resistance value, (3) reversing the polarity of the current flowing from constant current power supply 21, and using the average of the absolute values ​​of the voltages measured when current of each polarity is flowing as the voltage when calculating the electrical resistance value, and (4) using an AC current (preferably in the low frequency range of 100 kHz or less, taking into account the skin effect) flowing through metal piece 11. Furthermore, it is preferable to use a coaxial cable or a twisted cable as the wiring 211, 221. This reduces the influence of external electromagnetic fields generated by the wiring 211, 221, and makes it possible to reduce measurement noise due to induced electromotive force.

[0027] The electrical resistance measuring means 20 is not limited to the above-described configuration. For example, it is also possible to employ a configuration in which a constant voltage is applied between the end 111 and the end 112 of the metal piece 11, and the current flowing from the end 111 to the end 112 of the metal piece 11 is measured, thereby measuring the electrical resistance value of the metal piece 11.

[0028] <Calculation means 30> The calculation means 30 is composed of, for example, a computer in which a program for performing the calculations described below is stored, and calculates the amount of corrosion of the metal piece 11 based on the electrical resistance value of the metal piece 11 measured by the electrical resistance value calculation means 23. In a preferred embodiment, the calculation means 30 of this embodiment calculates the amount of corrosion of the metal piece 11 based on the electrical resistance value of the metal piece 11 measured by the electrical resistance value calculation means 23 and the temperature of the metal piece 11 measured by the temperature measurement means 40. Specifically, the calculation means 30 stores in advance a temperature-dependent function R0(T) that is the relationship between the initial electrical resistance R0 of the metal piece 11 and the temperature T. The initial electrical resistance R0 of the metal piece 11 is the electrical resistance value at a point in time before corrosion occurs in the metal piece 11, in other words, the initial thickness (t ini ) is the electrical resistance value at the point where

[0029] The temperature-dependent function R0(T) differs depending on the type of metal constituting the metal piece 11. Therefore, it is necessary to determine the temperature-dependent function R0(T) for each type of metal for which the amount of corrosion is to be measured. The temperature-dependent function R0(T) may be determined by actual measurement performed by changing the temperature each time the amount of corrosion is measured, or it may be determined by using a function obtained from a previous measurement or a function recorded in a database. Alternatively, a function theoretically determined from the chemical composition and structure of the metal may be used.

[0030] When actually measuring the temperature-dependent function R0(T) of the metal piece 11, it is preferable to measure it in a dry environment where the metal piece 11 will not corrode. In a normal temperature range, the electrical resistance of a metal generally exhibits a nearly linear relationship with temperature. For this reason, for example, it is conceivable to measure the initial electrical resistance R0 of the metal piece 11 at two or more temperatures and linearly approximate the measurement results to obtain the temperature-dependent function R0(T). However, this is not a limitation, and the temperature-dependent function R0(T) may be a quadratic or higher function of the temperature T, or may be represented in the form of a table that records the correspondence between the initial electrical resistance R0 and the temperature T.

[0031] The calculation means 30 calculates the temperature-dependent function R0(T) described above and the electrical resistance R of the metal piece 11 measured by the electrical resistance calculation means 23. t and the temperature T of the metal piece 11 measured by the temperature measuring means 40. t The corrosion amount Δt of the metal piece 11 is calculated using the above. Specifically, the calculation means 30 calculates the measured temperature T based on the temperature-dependent function R0(T). t The initial electrical resistance value R0(T t Next, the calculation means 30 calculates the calculated initial electrical resistance value R0(T t ) and the measured electrical resistance R t R0(T t ) / R t Next, the calculation means 30 calculates the calculated ratio R0(T t ) / R t Based on this, the remaining thickness t' of the metal piece 11 at the time of measurement is calculated by the following formula (A). t'=t ini ×R0(T t ) / R t (A) In the above formula (A), t ini is the initial thickness of the metal piece 11. Finally, the calculation means 30 calculates the corrosion amount Δt of the metal piece 11 at the time of measurement using the following formula (B). Δt=t ini -t' (B)

[0032] In this embodiment, the calculation means 30 calculates the temperature T of the metal piece 11 measured by the temperature measurement means 40. t However, in a measurement environment where there is little temperature change, it is not necessary to take into account the temperature dependency of the electrical resistance value. When the temperature dependency of the electrical resistance value is not taken into account, in the above formula (A), R0(T t ) can be the initial electrical resistance R0 (fixed value) measured at a representative temperature in the measurement environment. Furthermore, based on the same concept as in Patent Documents 1 to 3, it is also possible to provide a reference part (a reference part having the same shape as the metal piece 11) that is isolated from the measurement environment so as not to cause corrosion, separate from the metal piece 11 for measuring the amount of corrosion, and to adopt a configuration in which the amount of corrosion of the metal piece 11 is measured based on the electrical resistance value of the metal piece 11 and the electrical resistance value of the reference part. In this case, the temperature measuring means 40 is not necessary, and the initial thickness of the reference part is set to t ref_ini (= initial thickness t of metal piece 11 ini ), the initial electrical resistance of the metal piece 11 is R ini , the electrical resistance value of the metal piece 11 at the time of measurement is R t , the initial electrical resistance of the reference section is R ref_ini , the electrical resistance value of the reference part at the time of measurement is R ref_t Then, the corrosion amount Δt of the metal piece 11 at the time of measurement can be calculated by the following formula (C). Δt=t ref_ini ×(R ref_ini / R ini -R ref_t / R t ) ···(C)

[0033] In the corrosion monitoring device 100 having the above-described configuration, the initial thickness t ini is set to 0.3 mm or less. The reason for this setting is explained below.

[0034] The inventors have fabricated a metal piece 11 made of carbon steel (SM490A) with a width W (the dimension in the direction perpendicular to the current-carrying direction and the thickness direction of the metal piece 11, see FIG. 1) of 10 mm, a length (the dimension in the current-carrying direction of the metal piece 11) of 100 mm, and an initial thickness t ini A corrosion test was carried out using rectangular metal pieces 11 (metal pieces 11 on which no corrosion product CP had previously accumulated) with diameters of 0.1 mm, 0.3 mm, and 1.0 mm in plan view. Specifically, in a sealed atmosphere at 25°C, each metal piece 11 was sprayed with a magnesium chloride aqueous solution with a concentration of 0.5 mol / L for 2 hours, and then held for 16 hours. The corrosion monitoring device 100 was used to calculate the change over time in the amount of corrosion Δt of each metal piece 11 over the 16 hours.

[0035] FIG. 3 shows the results of the corrosion test. ini The corrosion amount Δt calculated for the metal piece 11 of 0.1 mm is shown in Fig. 3(b). ini The corrosion amount Δt calculated for the metal piece 11 of 0.3 mm is shown in Fig. 3(c). ini 3(d) shows the amount of corrosion Δt calculated for a metal piece 11 with a diameter of 1.0 mm. Also, FIG. 3(d) shows the result of smoothing the amount of corrosion Δt calculated for each metal piece 11 over time. Specifically, the result shown in FIG. 3(d) is the result of smoothing the amount of corrosion Δt calculated for each metal piece 11 using LOWESS (locally weighted scatterplot smoothing), a type of local regression. Also, FIG. 4 shows the change in the corrosion rate of the metal piece 11 over time, obtained by time-differentiating the amount of corrosion Δt of the metal piece 11 after smoothing shown in FIG. 3(d). As can be seen from FIGS. 3(a) to 3(c), the initial thickness t ini As the value of Δt increases, the noise width of the corrosion amount Δt (the amplitude value of the noise that repeatedly increases and decreases in a short period of time) also increases. As can be seen from Fig. 3(d) and Fig. 4, even if the calculated corrosion amount Δt is smoothed over time to reduce the noise width, t iniFor the metal piece 11 with a diameter of 1.0 mm, there is a time when the corrosion rate Δt decreases, which is not possible in reality (in FIG. 4, there is a time when the corrosion rate is a negative value), and it can be said that the corrosion behavior of the metal piece 11 cannot be measured accurately. This is because the actual corrosion rate should increase monotonically with the passage of time.

[0036] In contrast, as can be seen from Figs. 3(d) and 4, t ini For the metal pieces 11 with thicknesses of 0.1 mm and 0.3 mm, there is no time during which the corrosion amount Δt decreases (in Figure 4, the corrosion rate is always a positive value), and the changes in the corrosion amount Δt over time for both pieces are almost the same, so it is thought that the corrosion behavior of the metal pieces 11 can be measured with high accuracy. For the reasons explained above, in the corrosion monitoring device 100 of this embodiment, the initial thickness t ini The initial thickness t of the metal piece 11 is set to 0.3 mm or less. ini is preferably 0.01 mm or more.

[0037] The inventors also developed a 10 mm wide, 100 mm long, and 100 mm thick carbon steel (SM490A) tube. iniA corrosion test was conducted using rectangular metal pieces 11 (metal pieces 11 on which corrosion products CP had previously accumulated and metal pieces 11 on which corrosion products CP had not previously accumulated) with a diameter of 0.1 mm in plan view. Specifically, 1000 μL of a magnesium chloride aqueous solution with a concentration of 0.5 mol / L was dropped and deposited on the top surface of each metal piece 11 using a micropipette, and then the metal pieces 11 were placed in a thermo-hygrostat chamber with an internal temperature of 30°C. A total of four-hour cycles were repeated: maintaining the humidity at 90% RH for one hour, decreasing the humidity from 90% RH to 50% RH for one hour, maintaining the humidity at 50% RH for 0.5 hours, and increasing the humidity from 50% RH to 90% RH for 1.5 hours. The corrosion amount Δt of each metal piece 11 was calculated every 10 hours using the corrosion monitoring device 100. For the metal pieces 11 on which the corrosion product CP had already accumulated, a mixture of ethanol and γ-FeOOH was applied to the upper surface of the metal pieces 11 before the corrosion test, and the ethanol was allowed to dry naturally, thereby depositing γ-FeOOH to a thickness of 500 μm as the corrosion product CP.

[0038] FIG. 5 shows the results of the above corrosion test. As can be seen from FIG. 5, the corrosion amount Δt increases monotonically with the passage of time for all metal pieces 11. Furthermore, the corrosion progresses faster for metal pieces 11 on which corrosion products CP have already accumulated than for metal pieces 11 on which corrosion products CP have not already accumulated. These results can be said to be consistent with actual corrosion behavior. Therefore, with the corrosion monitoring device 100 according to this embodiment (a device equipped with metal pieces 11 on which corrosion products CP have already accumulated), the initial thickness t of the metal pieces 11 can be monitored. ini By setting the thickness to 0.3 mm or less (0.1 mm in the example shown in FIG. 5), it is possible to monitor the amount of corrosion of the metal piece 11 with high accuracy, and also to monitor the corrosion behavior in a state where the corrosion product CP has accumulated. [Explanation of symbols]

[0039] 10. Corrosion sensor 11, 11A, 11B...Metal piece 20. Electrical resistance measurement means 30...Arithmetic means 100 Corrosion monitoring device CP...Corrosion products

Claims

1. Metal pieces and an electrical resistance measuring means for measuring the electrical resistance of the metal piece by passing a current through the metal piece; a calculation means for calculating the corrosion level of the metal piece based on the electrical resistance value of the metal piece measured by the electrical resistance measurement means, The thickness of the metal piece is 0.3 mm or less, Corrosion products have already accumulated on the metal piece; Corrosion monitoring equipment.

2. the calculation means smooths the calculated corrosion amount of the metal piece over time. The corrosion monitoring device according to claim 1 .

3. Further provided is a temperature measuring means for measuring the temperature of the metal piece, the calculation means calculates the amount of corrosion of the metal piece based on the electrical resistance value of the metal piece measured by the electrical resistance measurement means and the temperature of the metal piece measured by the temperature measurement means. The corrosion monitoring device according to claim 1 or 2.

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