Corrosion diagnosis method and corrosion diagnosis system

Abstract

To provide a corrosion diagnosis method for making corrosion diagnosis that reflects changes in a corrosion state of a steel structure.SOLUTION: A corrosion diagnosis method includes the steps of: measuring and recording a corrosion amount of a steel structure using an electric resistance type corrosion sensor attached to the steel structure; and diagnosing a corrosion state of the steel structure on the basis of the corrosion amount of the steel structure. The step of diagnosing a corrosion state includes the steps of: determining a reference time point that is a time point subsequent to a measurement start time point and that is a time point prior to a diagnosis time point; and calculating a corrosion prediction formula from a relationship between lapsed time in an evaluation object period and a corrosion amount, where a period from the reference time point to the diagnosis time point is considered to be the evaluation object period.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a corrosion diagnostic method and a corrosion diagnostic system. [Background technology]

[0002] Steel structures, such as bridges, are designed so that the amount of corrosion during their service life will remain within a range that does not affect their load-bearing capacity. In order to confirm whether the amount of corrosion is as predicted at the time of design, a patch-type exposure test is conducted in which plate-shaped test specimens (patch test specimens) are affixed to bridges and other structures, and these are removed at predetermined intervals (for example, once a year) to determine the amount of corrosion. In addition, data obtained from patch-type exposure tests and other tests is used to perform regression analysis of the relationship between elapsed time and amount of corrosion, and to predict future amounts of corrosion. For example, the elapsed time X and the amount of corrosion Y at elapsed time X are applied to the following equation (1), parameters A and B are estimated, and the amount of corrosion in the future is predicted. Y=AX B (1)

[0003] Japanese Patent No. 6631593 discloses a method for predicting corrosion of weathering steel, which involves determining a period during which the ratio of the amount of corrosion between ordinary steel and weathering steel becomes constant, and calculating a corrosion prediction formula using the amount of corrosion of the weathering steel during that period.

[0004] As a method for measuring the amount of corrosion of a metal, a method for measuring the amount of corrosion based on an increase in electrical resistance that accompanies a decrease in plate thickness is known (see, for example, JP 2016-197102 A and JP 2017-3376 A). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6631593 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-197102 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-3376

[0006] [Non-Patent Document 1] Yuantai Ma et al., "Corrosion of low carbon steel in atmospheric environments of different chloride content", Corrosion Science 51 (2009) 997-1006. Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, corrosion diagnosis of steel structures involves regression analysis of the relationship between elapsed time and the amount of corrosion to predict the amount of corrosion in the future. Furthermore, Equation (1), which represents the corrosion behavior of steel materials, is commonly used to predict the amount of corrosion. Y=AX B (1)

[0008] On the other hand, the parameters A and B in equation (1) may change due to changes in the surface condition of the steel structure or changes in the environment.

[0009] For example, Non-Patent Document 1 describes an example in which parameters A and B change depending on the distance from the coast around 9 months after the start of measurements and around 12 months after the start of measurements. This is said to be due to changes in the surface condition of the steel structure caused by the deposition of chloride ions.

[0010] Furthermore, the inventors investigated the corrosion state of bridges installed in areas where typhoons passed, and found that parameters A and B changed before and after the typhoon. This is thought to be due to salt carried by the typhoon adhering to the bridge and changing the surface condition. In this way, parameters A and B can also change due to the influence of a typhoon.

[0011] Such changes in parameters A and B do not necessarily increase the rate of corrosion; they may sometimes increase the rate of corrosion and sometimes decrease it. When using a regression analysis of the relationship between elapsed time and the amount of corrosion, if parameters change during the measurement period, an appropriate prediction formula cannot be obtained. Therefore, there is a risk that the remaining life may be overestimated or underestimated.

[0012] An object of the present invention is to provide a corrosion diagnosis method and a corrosion diagnosis system that can perform corrosion diagnosis that reflects changes in the corrosion state of a steel structure. [Means for solving the problem]

[0013] A corrosion diagnosis method according to one embodiment of the present invention comprises the steps of measuring and recording the amount of corrosion of a steel structure using an electrical resistance corrosion sensor attached to the steel structure, and diagnosing the corrosion condition of the steel structure based on the amount of corrosion of the steel structure, wherein the step of diagnosing the corrosion condition includes the steps of determining a reference point in time that is later than the measurement start point and earlier than the diagnosis point in time, and setting the period from the reference point in time to the diagnosis point in time as an evaluation period, and calculating a corrosion prediction equation from the relationship between the elapsed time in the evaluation period and the amount of corrosion.

[0014] A corrosion diagnosis system according to one embodiment of the present invention comprises an electrical resistance corrosion sensor attached to a steel structure to measure the amount of corrosion of the steel structure, a recording device to record the measured amount of corrosion, and a computing device, wherein the computing device executes the steps of determining a reference point that is a point later than the measurement start point and earlier than the diagnosis point, and designating the period from the reference point to the diagnosis point as an evaluation period, and calculating a corrosion prediction equation from the relationship between the elapsed time and the amount of corrosion in the evaluation period. [Effects of the Invention]

[0015] According to the present invention, corrosion diagnosis can be performed that reflects changes in the corrosion state of a steel structure. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flow diagram of a corrosion diagnosis method according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating the configuration of an example of an electrical resistance corrosion sensor. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a diagram schematically showing the configuration of another example of an electrical resistance corrosion sensor. [Figure 5] FIG. 5 is a diagram showing an example of the relationship between the elapsed time and the amount of corrosion. [Figure 6] FIG. 6 shows an example in which the evaluation period crosses over time point E in the relationship between the elapsed time and the corrosion amount shown in FIG. [Figure 7] FIG. 7 is a diagram showing a schematic diagram of the relationship between the parameters A and B and the endurance time D. In FIG. [Figure 8] FIG. 8 is a flow diagram of a corrosion diagnosis method according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a more specific flow diagram of the step of determining the reference time point in the corrosion diagnosis method of FIG. [Figure 10] FIG. 10 is a block diagram showing the functional configuration of a corrosion diagnosis system according to an embodiment of the present invention. [Figure 11] FIG. 11 is a graph showing the relationship between the elapsed time and the amount of corrosion measured by the electrical resistance corrosion sensor. [Figure 12] FIG. 12 shows the relationship between the elapsed time and the amount of corrosion shown in FIG. 11 in a double logarithmic graph. [Figure 13] FIG. 13 is a diagram showing the relationship between the parameters A and B and the endurance time. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[0018] [Corrosion diagnosis method] [First embodiment] Fig. 1 is a flow diagram of a corrosion diagnosis method according to a first embodiment of the present invention. This corrosion diagnosis method comprises a step of measuring and recording the amount of corrosion of a steel structure (step S1), and a step of diagnosing the corrosion state of the steel structure based on the amount of corrosion of the steel structure (step S2A). This corrosion diagnosis method further comprises steps of issuing a notification when the error between the amount of corrosion calculated from the corrosion prediction formula and the actual measured value during the evaluation period exceeds a predetermined reference value (steps S3A and S4), and a step of determining whether repair is necessary based on the corrosion prediction formula (step S5). Each step will be described in detail below.

[0019] [Process of measuring and recording the amount of corrosion] The amount of corrosion of the steel structure is measured and recorded by an electrical resistance corrosion sensor attached to the steel structure (step S1).

[0020] Steel structures are structures that are the subject of corrosion diagnosis. Examples of steel structures include bridges, port structures, marine structures, steel pipe piles, and sheet piles for river embankments. Materials for steel structures include, but are not limited to, ordinary steel, weathering steel, low-alloy steel, and low-alloy corrosion-resistant steel.

[0021] Fig. 2 is a diagram schematically showing the configuration of a corrosion sensor 1, which is an example of an electrical resistance corrosion sensor. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. The corrosion sensor 1 includes a sensor body 10 and an electrical resistance measuring device 20.

[0022] The sensor body 10 includes a substrate 11, a measurement metal 12, a reference metal 13, and a covering member 14. The measurement metal 12 and the reference metal 13 are formed on the substrate 11. The covering member 14 is formed to cover a portion of the measurement metal 12 and the entire reference metal 13.

[0023] The substrate 11 is, for example, a plastic substrate. The substrate 11 may be a conductor such as a metal. In that case, an insulator may be disposed between the substrate 11 and the measurement metal 12 and between the substrate 11 and the reference metal 13.

[0024] The measurement metal 12 is made of the same material as the measurement target portion of the steel structure. The measurement metal 12 is electrically connected to the electrical resistance measuring instrument 20 via wiring 21a and 22a. The measurement metal 12 has a surface exposed to the measurement environment.

[0025] The reference metal 13 is made of the same material as the measurement metal 12. The reference metal 13 is electrically connected to the electrical resistance measuring instrument 20 via wiring 21a and 23a. The reference metal 13 is isolated from the measurement environment. Specifically, the entire surface of the reference metal 13 except for the surface in contact with the substrate 11 is covered with a covering member 14. Unlike the measurement metal 12, the reference metal 13 does not have a surface exposed to the measurement environment. It is preferable that the reference metal 13 has the same shape and dimensions as the measurement metal 12.

[0026] The coating member 14 is, for example, an anticorrosive paint.

[0027] The electrical resistance measuring device 20 includes a constant current power supply 21 and voltmeters 22 and 23 .

[0028] The constant current power supply 21 is electrically connected to the measurement metal 12 and the reference metal 13 via wiring 21a. The measurement metal 12 and the reference metal 13 are connected in series to the constant current power supply 21. Therefore, current I of the same magnitude flows through the measurement metal 12 and the reference metal 13.

[0029] The voltmeter 22 is electrically connected to the measurement metal 12 via wiring 22a and measures a voltage V1 between measurement positions on the measurement metal 12. The voltage V1 is divided by the current I to obtain the electrical resistance R of the measurement metal 12. mea can be obtained.

[0030] Similarly, the voltmeter 23 is electrically connected to the reference metal 13 via the wiring 23a and measures the voltage V2 between voltage measurement positions on the reference metal 13. The electrical resistance R of the reference metal 13 is calculated by dividing the voltage V2 by the current I. ref can be obtained.

[0031] According to the configuration of the corrosion sensor 1, the electrical resistance R of the measurement metal 12 mea In addition, the electrical resistance R of the reference metal 13 ref This makes it possible to compensate for the influence of temperature changes in the measurement environment. In other words, since the measurement metal 12 and the reference metal 13 are made of the same material, the electrical resistance R mea and electrical resistance R ref By taking the ratio of d0 to R, it is possible to cancel out the influence of temperature change on the resistivity due to the temperature change of the measurement environment. mea_init , the initial electrical resistance of the reference metal 13 is R ref_init When this is the case, the thickness reduction amount Δd of the metal 12 to be measured can be calculated by the following formula.

[0032]

number

[0033] The measurement metal 12 is made of the same material as the measurement target portion of the steel structure. Therefore, the thickness reduction Δd of the measurement metal 12 can be considered to be equivalent to the amount of corrosion (thickness reduction) of the measurement target portion of the steel structure. Therefore, the corrosion amount of the steel structure can be measured using the corrosion sensor 1.

[0034] The amount of corrosion measured by the corrosion sensor 1 is recorded, for example, in a recording device 30. Instead of recording the amount of reduction in plate thickness Δd of the measurement metal 12 as the amount of corrosion, the electrical resistance R mea and electrical resistance R ref Alternatively, voltage V1 and voltage V2 may be recorded.

[0035] The recording method of the recording device 30 may be either digital or analog. The recording device 30 is preferably configured to automatically capture the information output from the electrical resistance measuring device 20.

[0036] 4 is a diagram schematically illustrating the configuration of a corrosion sensor 2, which is another example of an electrical resistance corrosion sensor. The corrosion sensor 2 includes a sensor body 40 and an electrical resistance measuring device 25.

[0037] The sensor body 40 includes a substrate 41 , a measurement metal 42 , and a temperature sensor 43 .

[0038] The measurement metal 42 is disposed on a substrate 41. The substrate 41 and the measurement metal 42 are similar to the substrate 11 and the measurement metal 12 of the corrosion sensor 1 (FIG. 2), respectively.

[0039] The temperature sensor 43 detects the temperature T t The temperature sensor 43 is, for example, a thermocouple. However, the temperature sensor 43 is not limited to this and may be any sensor that can measure the temperature of the measurement metal 42. The temperature sensor 43 may be, for example, an electrical resistance type temperature sensor or a non-contact type temperature sensor such as an infrared radiation thermometer. Furthermore, the measurement by the temperature sensor 43 may be either continuous or intermittent.

[0040] The temperature sensor 43 is fixed to the measurement metal 42 by, for example, insulating tape 43a. The temperature sensor 43 may be fixed by any method, for example, by a magnet or a screw. The temperature sensor 43 may be fixed at any position (temperature measurement position). Multiple temperature sensors 43 may be used to measure multiple positions on the measurement metal 42, and the average value may be used.

[0041] The electrical resistance measuring device 25 includes a constant current power supply 26 and a voltmeter 27 .

[0042] The constant current power supply 26 is electrically connected to the measurement metal 42 via wiring 26a, and applies a constant current to the measurement metal 42. The voltmeter 27 is electrically connected to the measurement metal 42 via wiring 27a, and measures the voltage V between voltage measurement positions on the measurement metal 42. The electrical resistance R of the measurement metal 42 is calculated by dividing the voltage V by the current I. t can be obtained.

[0043] According to the configuration of the corrosion sensor 2, the electrical resistance R of the measurement metal 42 t In addition, the temperature of the metal measured is T t This makes it possible to compensate for the influence of temperature changes in the measurement environment. Specifically, the temperature dependence of the initial resistance of the measurement metal 42 is obtained in advance by measurement or the like, and a temperature dependence function R0(T) that expresses the initial resistance of the measurement metal 42 as a function of temperature T is calculated, and the influence of temperature changes can be corrected based on this. Specifically, when the initial thickness of the measurement metal 42 is d0 and the temperature T=T t The value of the temperature dependent function R0(T) is R0(T t ), the thickness reduction amount Δd of the measurement metal 42 can be calculated by the following formula.

number

[0044] As with corrosion sensor 1, the thickness reduction Δd of measurement metal 42 can be considered to be equivalent to the amount of corrosion (thickness reduction) at the measurement target location of the steel structure. Therefore, corrosion sensor 2 can measure the amount of corrosion of the steel structure. Note that with corrosion sensor 1, if the temperature of the measurement environment changes drastically, a temperature difference may occur between measurement metal 12 and reference metal 13, and the effects of temperature change may not be sufficiently corrected. Corrosion sensor 2 does not have this problem, and therefore can perform measurements with higher accuracy than corrosion sensor 1.

[0045] The amount of corrosion measured by the corrosion sensor 2 is recorded in the recording device 30, for example, in the same manner as in the case of the corrosion sensor 1. Instead of recording the amount of reduction in plate thickness Δd of the measurement metal 42 as the amount of corrosion, the electrical resistance R tand temperature T t , or voltage V and temperature T t may be recorded.

[0046] Unlike the patch-type exposure test, electrical resistance corrosion sensors such as Corrosion Sensor 1 and Corrosion Sensor 2 do not require the collection of test specimens to measure the amount of corrosion. This makes it possible to continuously measure and record the amount of corrosion on steel structures.

[0047] The above-described configurations of the corrosion sensor 1 and the corrosion sensor 2 are merely examples, and the electrical resistance corrosion sensor used in this embodiment is not limited to these. The electrical resistance corrosion sensor used in this embodiment may be any sensor that measures the amount of corrosion of a steel structure by measuring the electrical resistance of the same material as the measurement target location of the steel structure.

[0048] The step of measuring and recording the amount of corrosion (step S1) is preferably performed periodically. The intervals (sampling intervals) for measuring and recording the amount of corrosion vary depending on the purpose of the diagnosis and are not particularly limited. The step of measuring and recording the amount of corrosion (step S1) may be performed, for example, once every few minutes or more frequently, or conversely, once every few days or less frequently. However, from the perspective of utilizing the advantage of the electrical resistance corrosion sensor, which is that it is capable of continuous measurement, the step of measuring and recording the amount of corrosion (step S1) is preferably performed at least once a day, and more preferably at least once an hour.

[0049] [Process for diagnosing corrosion conditions] The corrosion state of the steel structure is diagnosed based on the amount of corrosion of the steel structure (step S2A).

[0050] The step of diagnosing the corrosion state (Step S2A) is preferably performed periodically. The intervals at which the corrosion state is diagnosed vary depending on the purpose of the diagnosis and are not particularly limited. The step of diagnosing the corrosion state (Step S2A) may or may not be synchronized with the step of measuring and recording the amount of corrosion (Step S1). That is, the step of diagnosing the corrosion state (Step S2A) may be performed every time new data is recorded in the step of measuring and recording the amount of corrosion (Step S1), or every time a predetermined amount of data is recorded. The step of diagnosing the corrosion state (Step S2A) may be performed, for example, once every few days or more frequently, or conversely, once every few months or less frequently. The step of diagnosing the corrosion state (Step S2A) is preferably performed at least once a month, and more preferably at least once a week.

[0051] The process of diagnosing the corrosion condition (step S2A) includes a process of determining a reference point (step S2A-1) that is a point later than the start point of measurement of the steel structure but earlier than the diagnosis point, and a process of calculating a corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion in the evaluation period, which is the period from the reference point to the diagnosis point (step S2A-2).

[0052] First, a reference time point is determined, which is a time point after the start of measurement of the steel structure and before the diagnosis time point (step S2A-1).

[0053] In this embodiment, the method of determining the reference time point is to determine a time point a predetermined time before the time of diagnosis as the reference time point. That is, a time point a predetermined time before the time of diagnosis is determined as the reference time point. For example, one month before the time of diagnosis is determined as the reference time point.

[0054] In this method, the predetermined time is the length of the evaluation period. If the evaluation period is too short or too long, the corrosion condition may not be properly evaluated. The lower limit of the evaluation period is preferably one week, and more preferably one month. The upper limit of the evaluation period is preferably six months, and more preferably three months.

[0055] If the reference point is set to one month before the diagnosis point, the corrosion condition is not diagnosed during the one month period from the start of measurement, but the process of measuring and recording the amount of corrosion (step S1) is carried out.

[0056] Next, the period from the reference time point to the diagnosis time point is set as the evaluation period, and a corrosion prediction formula is calculated from the relationship between the elapsed time and the amount of corrosion in the evaluation period (step S2A-2).

[0057] The corrosion prediction formula may be, for example, the following formula (1). Y=AX B (1) Here, X is the elapsed time, Y is the amount of corrosion, and A and B are parameters.

[0058] When formula (1) is used as the corrosion prediction formula, the step of calculating the corrosion prediction formula (step S2A-2) can be performed by applying the relationship between the elapsed time X in the evaluation period and the corrosion amount Y at the elapsed time X to formula (1) to estimate the parameters A and B.

[0059] FIG. 5 is a diagram showing an example of the relationship between elapsed time and the amount of corrosion. FIG. 5 is a double logarithmic graph with the horizontal axis representing the logarithm of elapsed time and the vertical axis representing the logarithm of the amount of corrosion. This diagram shows a case where the relationship between elapsed time and the amount of corrosion follows equation (1) in the short term. When the relationship between elapsed time and the amount of corrosion follows equation (1), the relationship between elapsed time and the amount of corrosion becomes a straight line on the double logarithmic graph.

[0060] In the example of Figure 5, the corrosion amount behaves in accordance with equation (1), that is, it behaves as a straight line on a double logarithmic graph from the start of measurement to point E. After the corrosion amount increases sharply at point E, the rate of increase slows down, and the corrosion amount again behaves in accordance with equation (1).

[0061] In this embodiment, the corrosion prediction equation is calculated from the relationship between the elapsed time during the evaluation period and the amount of corrosion. That is, the corrosion prediction equation is calculated using only data during the evaluation period. In other words, data from the period between the start of measurement and the reference time point is not used in calculating the corrosion prediction equation. By extrapolating the corrosion prediction equation obtained here, it is possible to predict the amount of corrosion at a point in time after the diagnosis time point, i.e., in the future.

[0062] In the above example, when the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion during the evaluation period is plotted on Figure 5, the result is line L1. On the other hand, when the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion over the entire period from the start of measurement to the time of diagnosis is plotted on Figure 5, the result is line L0. Comparing line L1 and line L0, line L1 is considered to more accurately reflect the corrosion state of the steel structure at the time of diagnosis. In other words, it is considered that calculating the corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion during the evaluation period will result in a corrosion prediction formula that more accurately reflects the corrosion state of the steel structure at the time of diagnosis than calculating the corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion over the entire period.

[0063] [Process to notify if there is a large error] It is determined whether the error between the amount of corrosion calculated from the corrosion prediction formula and the actual measured value during the evaluation period is equal to or greater than a predetermined reference value (step S3A), and if it is equal to or greater than the reference value, a notification is made (step S4).

[0064] The corrosion prediction formula calculated in step S2A-2 is compared with the actual measured values ​​to determine whether the error during the evaluation period is equal to or greater than a predetermined reference value (step S3A). The error is evaluated using only data during the evaluation period. In other words, data from the start of measurement to the reference point is not used in the error evaluation. Various indicators of the magnitude of the error can be used, for example, the sum of squares of the difference between the amount of corrosion calculated from the corrosion prediction formula and the actual measured values, or the square root of that difference.

[0065] If the error is equal to or greater than a predetermined reference value, a notification is sent (step S4). The recipient of the notification is not particularly limited, but may be, for example, the manager of the steel structure. A large error means that the prediction formula and the actual measured values ​​do not match well during the evaluation period, and ultimately means that the relationship between the amount of corrosion and the actual measured values ​​during the evaluation period deviates from the functional form of the prediction formula used in step S2A-2 (e.g., equation (1)).

[0066] Figure 6 shows an example of the relationship between elapsed time and corrosion amount shown in Figure 5 when the evaluation period crosses over time point E. Line L3 plots the corrosion prediction formula calculated from the relationship between elapsed time and corrosion amount during the evaluation period. In this example, the relationship between elapsed time and corrosion amount during the evaluation period cannot be well reproduced using formula (1), so the error between the corrosion amount calculated from the corrosion prediction formula and the actual measured value during the evaluation period is large. If the error between the corrosion amount calculated from the corrosion prediction formula and the actual measured value during the evaluation period is large, as in this example, it is possible that the corrosion condition of the steel structure has changed during the evaluation period. In other words, by evaluating the error between the corrosion amount calculated from the corrosion prediction formula and the actual measured value during the evaluation period, it may be possible to detect changes in the corrosion condition of the steel structure.

[0067] [Process to determine whether repairs are necessary] Whether or not repair is necessary is determined based on the corrosion prediction formula obtained in step S2A-2 (step S5). The determination of whether or not repair is necessary can be made, for example, as follows, although not limited to this.

[0068] When the relationship between the elapsed time and the amount of corrosion follows Equation (1), the durability time D until the amount of corrosion reaches the allowable weight loss Y0 can be obtained from the following Equation (2). D = (Y0 / A) 1 / B (2)

[0069] Figure 7 is a diagram schematically showing the relationship between the parameters A and B and the durability time D. In Figure 7, the trajectories of A and B for which the durability time D becomes D1, D2, and D3 (where D1 < D2 < D3) are shown. As shown in Figure 7, on the graph with A and B as the horizontal and vertical axes respectively, the closer to the origin O, the greater the durability time D.

[0070] Here, referring again to Figure 5, consider the change in the durability time of the steel structure before and after the time point E in the example of Figure 5. The straight line L2 is a plot on Figure 5 of the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion during the period from the start time of measurement to the time point E.

[0071] In this example, the amount of corrosion increases rapidly at the time point E, but thereafter, the rate of increase in the amount of corrosion decreases, and the slope of the straight line L1 is smaller than the slope of the straight line L2. As a result, the durability time based on the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion during the evaluation target period is longer than the durability time based on the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion during the period up to the time point E.

[0072] The change in the durability time of the steel structure before and after the time point E in the example of Figure 5 will be explained using Figure 7. The point P₂ in Figure 7 plots the positions of A and B of the straight line L2, and the point P₁ plots the positions of A and B of the straight line L1. Along with the rapid increase in the amount of corrosion at the time point E, the value of A increases for the straight line L1. On the other hand, along with the decrease in the slope of the straight line L1, the value of B decreases. In the example of Figure 5, the contribution due to the decrease in B is greater than the contribution due to the increase in A, and as a result, the durability time is longer. In this case, it can be judged that the need for repair is relatively low.

[0073] In this way, as an example of a method for determining whether repair is necessary, it may be determined that repair is not necessary if the durability time has become longer compared to before the change in corrosion condition occurred, and conversely, it may be determined that repair is necessary if the durability time has become shorter.

[0074] As another example of a method for determining whether repair is necessary, the durability time may be calculated from the corrosion prediction formula obtained in step S2A-2, and the remaining durability time may be calculated by subtracting the elapsed time at the time of diagnosis from the durability time, and if the remaining durability time is less than a predetermined time, it may be determined that repair is necessary.

[0075] The corrosion diagnosis method according to the first embodiment of the present invention has been described above. In this embodiment, an electrical resistance corrosion sensor is used, which enables continuous measurement and recording of the amount of corrosion of a steel structure. Furthermore, in this embodiment, the period from a reference point in time to the time of diagnosis is set as an evaluation period, and a corrosion prediction equation is calculated from the relationship between the elapsed time and the amount of corrosion in the evaluation period. This makes it possible to obtain a corrosion prediction equation that more accurately reflects the corrosion state of the steel structure at the time of diagnosis than if the corrosion prediction equation were calculated from the relationship between the elapsed time and the amount of corrosion over the entire period. Therefore, according to this embodiment, corrosion diagnosis that reflects changes in the corrosion state of the steel structure can be performed.

[0076] The above description has focused on an example in which equation (1) is used as the corrosion prediction equation. However, the corrosion prediction equation used in step S2A-2 is not limited to equation (1), and any prediction equation can be used. Furthermore, the above description has been given as an example in which the corrosion condition changes significantly at a certain point in time (point in time E). However, the corrosion diagnosis method according to this embodiment can also be applied to cases in which the corrosion condition changes gradually.

[0077] The steps of issuing a notification when the error between the corrosion amount calculated from the corrosion prediction formula and the actual measured value during the evaluation period exceeds a predetermined reference value (steps S3A and S4), and the step of determining whether repair is necessary based on the corrosion prediction formula (step S5) are both optional steps. Depending on the purpose of the diagnosis, one or both of these steps may be omitted.

[0078] [Second embodiment] 8 is a flow diagram of a corrosion diagnosis method according to a second embodiment of the present invention. This corrosion diagnosis method comprises a step of measuring and recording the amount of corrosion of a steel structure (step S1), and a step of diagnosing the corrosion state of the steel structure based on the amount of corrosion of the steel structure (step S2B). This corrosion diagnosis method further comprises steps of issuing a notification when the difference between a reference point and a reference point determined during the previous diagnosis exceeds a predetermined threshold (steps S3B and S4), and a step of determining whether repair is necessary based on a corrosion prediction equation (step S5).

[0079] The corrosion diagnosis method according to the second embodiment differs from the corrosion diagnosis method according to the first embodiment (FIG. 1) in the step of diagnosing the corrosion state of a steel structure (step S2B). Also, the corrosion diagnosis method according to the second embodiment differs in the step of determining whether or not to perform the notification step (step S4) (step S3B). These steps will be explained in order below.

[0080] The process of diagnosing the corrosion condition (step S2B), similar to the corrosion diagnosis method of the first embodiment, includes a process of determining a reference point (step S2B-1) that is a point later than the start point of measurement of the steel structure but earlier than the diagnosis point, and a process of calculating a corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion in the evaluation period, which is the period from the reference point to the diagnosis point (step S2B-2).

[0081] In this embodiment, the reference time point is determined based on the error between the corrosion amount calculated from the corrosion prediction formula and the actual measurement value. Specifically, the reference time point is determined so that the error between the corrosion amount calculated from the corrosion prediction formula and the actual measurement value during the evaluation period is less than a predetermined reference value.

[0082] FIG. 9 is a more specific flow diagram of the step of determining the reference time point (step S2B-1).

[0083] First, a tentative reference time point is set (step S2B-1-1). The period from this tentative reference time point to the diagnosis time point is set as a tentative evaluation period, and a corrosion prediction formula is calculated from the relationship between the elapsed time and the amount of corrosion in this tentative evaluation period (step S2B-1-2). The calculation of this corrosion prediction formula can be performed in the same way as described in step S2A-2 of the first embodiment.

[0084] Next, it is determined whether the error between the corrosion amount calculated from the corrosion prediction formula and the actual measurement value during the provisional evaluation period is less than a predetermined reference value (step S2B-1-3). The error evaluation can be performed in the same manner as described in step S3A of the first embodiment. If the error is less than the predetermined reference value, the initially set provisional reference time point is determined to be the reference time point (step S2B-1-4). If the error is equal to or greater than the predetermined reference value, another reference time point is set, and the above procedure is repeated until the error becomes less than the predetermined reference value.

[0085] Methods for searching for the reference time point include, but are not limited to, searching from the measurement start time point toward the diagnosis time point, and searching from the diagnosis time point toward the measurement start time point. However, if the evaluation period is too short or too long, the corrosion condition may not be properly evaluated. If the reference time point is searched from the measurement start time point toward the diagnosis time point, the evaluation period may become too long. If the reference time point is searched from the diagnosis time point toward the measurement start time point, the evaluation period may become too short. Therefore, even if a reference time point is found that makes the error less than the predetermined reference value, it is preferable to repeat the above procedure until the evaluation period becomes an appropriate length.

[0086] Next, the period from the reference time point to the diagnosis time point is set as the evaluation period, and a corrosion prediction formula is calculated from the relationship between the elapsed time in the evaluation period and the amount of corrosion (step S2B-2). This step is the same as step S2A-2 in the first embodiment.

[0087] In this embodiment, whether to perform the notification step (step S4) is determined based on the difference between the reference time point determined in step S2B-1 and the reference time point determined at the time of the previous diagnosis (step S3B). Specifically, it is determined whether the difference between the reference time point determined in step S2B-1 and the reference time point determined at the time of the previous diagnosis is equal to or greater than a predetermined threshold (step S3B), and if it is equal to or greater than the threshold, notification is performed (step S4).

[0088] If the reference point has changed significantly from the reference point determined in the previous diagnosis, it is possible that the corrosion condition of the steel structure has changed between the reference point determined in the previous diagnosis and the reference point determined this time. In other words, by evaluating the change in the reference point from the previous diagnosis, it may be possible to detect a change in the corrosion condition of the steel structure.

[0089] The corrosion diagnosis method according to the second embodiment of the present invention has been described above. This embodiment also makes it possible to perform corrosion diagnosis that reflects changes in the corrosion state of a steel structure.

[0090] The steps of issuing a notification when the difference between the reference time point and the reference time point determined in the previous diagnosis is equal to or greater than a predetermined threshold (steps S3B and S4), and the step of determining whether repair is necessary based on the corrosion prediction formula (step S5) are both optional steps, and one or both of these steps may be omitted depending on the purpose of the diagnosis.

[0091] [Corrosion diagnosis system] 10 is a block diagram showing the functional configuration of a corrosion diagnosis system 100 according to one embodiment of the present invention. The corrosion diagnosis system 100 includes a corrosion sensor 1, which is an electrical resistance corrosion sensor that is attached to a steel structure and measures the amount of corrosion of the steel structure, a recording device 30 that records the measured amount of corrosion, and a computing device 50.

[0092] The calculation device 50 receives information on the amount of corrosion of the steel structure from at least one of the corrosion sensor 1 and the recording device 30. The corrosion diagnosis system 100 may be configured so that the information on the amount of corrosion measured by the corrosion sensor 1 is recorded in the recording device 30 via the calculation device 50, or may be configured so that the information on the amount of corrosion measured by the corrosion sensor 1 is recorded in the recording device 30 without going through the calculation device 50, and then the calculation device 50 receives the information on the amount of corrosion by referring to the recording device 30.

[0093] The computing device 50 executes a step of diagnosing the corrosion state of a steel structure based on the amount of corrosion of the steel structure. Specifically, the computing device executes the steps of determining a reference time point that is later than the measurement start time of the steel structure but earlier than the diagnosis time point, and setting the period from the reference time point to the diagnosis time point as an evaluation period, and calculating a corrosion prediction formula from the relationship between the elapsed time in the evaluation period and the amount of corrosion. These steps are the same as those described in the step of diagnosing the corrosion state (step S2A) of the corrosion diagnosis method according to the first embodiment (FIG. 1) and the step of diagnosing the corrosion state (step S2B) of the corrosion diagnosis method according to the second embodiment (FIG. 8).

[0094] The computing device 50 may further execute a step of issuing a notification when the error between the amount of corrosion calculated from the corrosion prediction equation and the actual measurement value during the evaluation period exceeds a predetermined reference value. This step is similar to the steps (steps S3A and S4) of issuing a notification when the error between the amount of corrosion calculated from the corrosion prediction equation and the actual measurement value during the evaluation period exceeds a predetermined reference value in the corrosion diagnosis method according to the first embodiment (FIG. 1).

[0095] The computing device 50 may further execute a step of issuing a notification when the difference between the reference time point and the reference time point determined during the previous diagnosis becomes equal to or greater than a predetermined threshold. This step is similar to the steps (steps S3B and S4) of issuing a notification when the difference between the reference time point and the reference time point determined during the previous diagnosis becomes equal to or greater than a predetermined threshold in the corrosion diagnosis method according to the second embodiment (FIG. 8).

[0096] The computing device 50 may further execute a step of determining whether or not repair of the steel structure is necessary based on the corrosion prediction equation, similar to the step of determining whether or not repair is necessary (step S5) in the corrosion diagnosis method according to the first embodiment (FIG. 1).

[0097] The corrosion diagnosis system 100 according to one embodiment of the present invention has been described above. In the above embodiment, the corrosion diagnosis system 100 is described as including corrosion sensor 1 as an electrical resistance type corrosion sensor. The corrosion diagnosis system 100 may be provided with corrosion sensor 2 instead of corrosion sensor 1. The corrosion diagnosis system 100 may also be provided with any electrical resistance type corrosion sensor other than corrosion sensor 1 and corrosion sensor 2. [Example]

[0098] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0099] Electrical resistance corrosion sensors were installed on bridges within the steelworks premises to monitor corrosion conditions. The electrical resistance corrosion sensors used had a configuration similar to Corrosion Sensor 2 (Fig. 4).

[0100] Figure 11 is a graph showing the relationship between the amount of corrosion measured with an electrical resistance corrosion sensor and the elapsed time. Figure 11 shows that the typhoon passed on September 9th, and the amount of corrosion increased sharply at this point.

[0101] Figure 12 is a double logarithmic graph showing the relationship between the elapsed time and the amount of corrosion shown in Figure 11. Line L4 is a plot of the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion for the period from August 18 to September 5. Line L5 is a plot of the corrosion prediction formula calculated from the relationship between the elapsed time and the amount of corrosion for the period from September 23 to October 11. Comparing line L4 and line L5, line L5 is considered to more accurately reflect the corrosion state of the steel structure at the time of the diagnosis.

[0102] Figure 13 is a diagram showing the relationship between parameters A and B and durability time. Point P4 in Figure 13 is a plot of the positions of A and B on line L4, and point P5 is a plot of the positions of A and B on line L5. Figure 13 shows that, on the bridge that was the subject of the assessment, the amount of corrosion temporarily increased due to the passage of the typhoon, but at the time of the assessment, the corrosion condition had changed in a direction that would actually lengthen durability time.

[0103] Although the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be appropriately modified and carried out without departing from the spirit of the present invention. [Explanation of symbols]

[0104] 1,2 Electrical resistance corrosion sensor 10,40 Sensor body 11,41 PCB 12,42 Measuring Metals 13 Reference metal 14 Covering material 43 Temperature Sensor 20,25 Electrical Resistance Measuring Instrument 21,26 constant current power supply 22, 23, 27 Voltmeter 30 Recording Device 50 Arithmetic unit 100 Corrosion Diagnostic System

Claims

1. a step of measuring and recording the amount of corrosion of the steel structure using an electrical resistance corrosion sensor attached to the steel structure; and diagnosing the corrosion state of the steel structure based on the amount of corrosion of the steel structure, The step of diagnosing the corrosion state includes: determining a reference time point that is later than the start of measurement and earlier than the diagnosis time point; a step of setting a period from the reference time point to the diagnosis time point as an evaluation period, and calculating a corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion in the evaluation period, the step of determining the reference time point includes a step of determining a time point that is earlier than the diagnosis time point by a predetermined time as the reference time point; The corrosion diagnosis method further comprises a step of issuing a notification when an error between the amount of corrosion calculated from the corrosion prediction formula and the actual measured value during the evaluation period becomes equal to or greater than a predetermined reference value.

2. A step of measuring and recording the amount of corrosion of a steel structure using an electrical resistance corrosion sensor attached to the steel structure; and diagnosing the corrosion state of the steel structure based on the amount of corrosion of the steel structure, The step of diagnosing the corrosion state includes: determining a reference time point that is later than the start of measurement and earlier than the diagnosis time point; a step of setting a period from the reference time point to the diagnosis time point as an evaluation period, and calculating a corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion in the evaluation period, The corrosion diagnosis method includes determining the reference time point such that an error between the amount of corrosion calculated from the corrosion prediction equation and an actual measurement value during the evaluation period is less than a predetermined reference value.

3. The corrosion diagnostic method according to claim 2, The corrosion diagnosis method further comprises a step of issuing a notification when a difference between the reference time point and a reference time point determined during a previous diagnosis becomes equal to or greater than a predetermined threshold.

4. The corrosion diagnosis method according to any one of claims 1 to 3, The corrosion diagnosis method, wherein the step of calculating the corrosion prediction equation includes a step of estimating parameters A and B by applying the relationship between an elapsed time X in the evaluation period and an amount of corrosion Y at the elapsed time X to the following equation (1): Y=AX Ｂ (1)

5. The corrosion diagnosis method according to any one of claims 1 to 4, The electrical resistance corrosion sensor comprises: A measurement metal made of the same material as the measurement target portion of the steel structure; an electrical resistance measuring device for measuring the electrical resistance of the measurement metal; a temperature sensor for measuring the temperature of the measurement metal.

6. The corrosion diagnosis method according to any one of claims 1 to 5, The corrosion diagnosis method further comprises a step of determining whether or not repair of the steel structure is necessary based on the corrosion prediction equation.

7. an electrical resistance corrosion sensor attached to a steel structure to measure the amount of corrosion of the steel structure; a recording device for recording the measured corrosion amount; a computing device, The computing device determining a reference time point that is later than the start of measurement and earlier than the diagnosis time point; a step of setting a period from the reference time point to the diagnosis time point as an evaluation period, and calculating a corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion in the evaluation period, the step of determining the reference time point includes a step of determining a time point that is earlier than the diagnosis time point by a predetermined time as the reference time point; The corrosion diagnosis system further includes a step of issuing a notification when an error between the amount of corrosion calculated from the corrosion prediction equation and the actual measured value during the evaluation period becomes equal to or greater than a predetermined reference value.

8. An electrical resistance corrosion sensor attached to a steel structure to measure the amount of corrosion of the steel structure; a recording device for recording the measured corrosion amount; a computing device, The computing device determining a reference time point that is later than the start of measurement and earlier than the diagnosis time point; a step of setting a period from the reference time point to the diagnosis time point as an evaluation period, and calculating a corrosion prediction formula from the relationship between the elapsed time and the amount of corrosion in the evaluation period, a corrosion diagnosis system, wherein the step of determining the reference point includes a step of determining the reference point so that an error between the amount of corrosion calculated from the corrosion prediction equation and an actual measurement value during the evaluation period is less than a predetermined reference value.

9. A corrosion diagnostic system according to claim 8, The corrosion diagnosis system further includes a step in which the computing device issues a notification when a difference between the reference time point and a reference time point determined during a previous diagnosis becomes equal to or greater than a predetermined threshold.

10. The corrosion diagnostic system according to any one of claims 7 to 9, The step of calculating the corrosion prediction equation includes a step of estimating parameters A and B by applying the relationship between the elapsed time X in the evaluation period and the corrosion amount Y at the elapsed time X to the following equation (1): Y=AX Ｂ (1)

11. The corrosion diagnostic system according to any one of claims 7 to 10, The electrical resistance corrosion sensor comprises: A measurement metal made of the same material as the measurement target portion of the steel structure; an electrical resistance measuring device for measuring the electrical resistance of the measurement metal; a temperature sensor for measuring the temperature of the measurement metal.

12. The corrosion diagnosis method according to any one of claims 7 to 11, The corrosion diagnosis system further comprises a step of determining whether or not repair of the steel structure is necessary based on the corrosion prediction equation.

Images