Method and apparatus for determining corrosion allowance of steel structures

Abstract

This invention provides a method for determining the corrosion allowance of steel structures, such as steel sheet piles and steel pipe piles used in underground environments, which can determine the appropriate corrosion allowance for these structures. [Solution] An electrical resistance type corrosion sensor 10 is used, which is buried in the soil where a steel structure is planned to be buried, and comprises a metal piece 11 made of the same type of metal as the metal forming the steel structure, to measure the amount of corrosion Δt of the metal piece from the time the corrosion sensor is buried in the soil until a reference period T0 has elapsed. i A corrosion amount recording process ST1 sequentially calculates and records the corrosion amount of the metal piece, and based on the corrosion amount of the metal piece recorded in the corrosion amount recording process, the corrosion amount Δt of the metal piece after an evaluation period T longer than the reference period has elapsed. a A corrosion amount prediction process ST2 predicts the amount of corrosion of the metal piece predicted in the corrosion amount prediction process, and based on that, the corrosion allowance of the steel structure t a The process includes a corrosion allowance determination step ST3 to determine the corrosion allowance.

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to a corrosion allowance determining method and a corrosion allowance determining device for steel structures, which are capable of determining an appropriate corrosion allowance for steel structures such as steel sheet piles and steel pipe piles used in underground environments. [[BACKGROUND ART]]

[0002] For steel structures such as steel sheet piles and steel pipe piles used in underground environments, it is common that a corrosion allowance corresponding to the corrosion amount expected according to the service period is provided in advance.

[0003] Figure 1 is a diagram showing an example of the results of a survey on the corrosion amount of steel sheet piles, angle steels and steel pipe piles in various underground environments at 33 locations in Japan, which is described in Non-Patent Document 1. The horizontal axis of Figure 1 logarithmically represents the elapsed time after embedding steel sheet piles, angle steels and steel pipe piles, and the vertical axis logarithmically represents the average corrosion amount on one side at each location. As described in Non-Patent Document 1, when σ is the standard deviation of the deviation between each data plotted with "○" shown in Figure 1 and the regression line calculated from each data, it is calculated that the corrosion amount on one side will be about 1 mm after 100 years if the regression line + 2σ is taken as the reference. For this reason, conventionally, it is general that the corrosion allowance on one side of a steel structure is uniformly determined to be 1 mm for 100 years of service without individually considering the underground environment where the steel structure is used.

[0004] However, since the progress of corrosion of steel structures varies depending on the underground environment, when used in a highly corrosive underground environment, the corrosion allowance may be consumed at an early stage, which is not desirable from the viewpoints of the integrity of steel structures and disaster prevention and mitigation. In addition, when used in a low-corrosivity underground environment, it is conceivable that excess corrosion allowance will remain. In this case, although the steel structure still has sufficient residual bearing capacity, unnecessary maintenance work, maintenance and reconstruction work will occur, which is not desirable from the viewpoints of economy and the decrease in working population. Therefore, there is a demand for a method capable of determining an appropriate corrosion allowance for steel structures.

[0005] Patent Document 1 proposes a method for calculating a corrosion prediction formula based on the amount of corrosion of a steel structure measured by an electrical resistance type corrosion sensor, and for determining whether or not repair of the steel structure is necessary based on the corrosion prediction formula, but this is not a method for determining the corrosion allowance of the steel structure. Furthermore, while Patent Documents 2 and 3 propose a soil corrosion monitoring device capable of accurately monitoring the amount of corrosion of metal pieces buried in the soil, it does not provide a method for determining the corrosion allowance of steel structures. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Susumu Moriya, et al., "Statistical Study of the Corrosion Behavior of Steel Piles and Steel Sheet Piles in Soil," Civil Engineering Technical Data, 2005, No. 47, Vol. 3, pp. 52-57. [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-58105 [Patent Document 2] Japanese Patent Publication No. 2024-98860 [Patent Document 3] Japanese Patent Publication No. 2024-126583 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention was made to solve the problems of the prior art described above, and aims to provide a method and apparatus for determining the corrosion allowance of steel structures, such as steel sheet piles and steel pipe piles used in soil environments, which can determine an appropriate corrosion allowance for steel structures. [Means for solving the problem]

[0009] To solve the aforementioned problems, the present invention provides a method for determining the corrosion allowance of a steel structure, comprising: a corrosion amount recording step of sequentially calculating and recording the amount of corrosion of a metal piece formed from the same type of metal as the metal forming the steel structure, using an electrical resistance type corrosion sensor which is buried in the soil where the steel structure is planned to be buried, from the time the corrosion sensor is buried in the soil until a standard period has elapsed; a corrosion amount prediction step of predicting the amount of corrosion of the metal piece after an evaluation period longer than the standard period has elapsed, based on the amount of corrosion of the metal piece recorded in the corrosion amount recording step; and a corrosion allowance determination step of determining the corrosion allowance of the steel structure based on the amount of corrosion of the metal piece predicted in the corrosion amount prediction step.

[0010] According to the present invention, in the corrosion amount recording process, an electrical resistance type corrosion sensor is used, which is buried in the soil where the steel structure is planned to be buried and is equipped with a metal piece made of the same type of metal as the metal forming the steel structure. The amount of corrosion of the metal piece is calculated sequentially from the time the corrosion sensor is buried in the soil until a standard period (e.g., 1 year) has elapsed. Because an electrical resistance type corrosion sensor is used, the amount of corrosion of the metal piece can be calculated with high accuracy, and because the corrosion sensor is buried in the soil where the steel structure is planned to be buried, an appropriate amount of corrosion of the metal piece can be calculated according to the soil environment. Next, according to the present invention, in the corrosion amount prediction step, the corrosion amount of the metal piece after a longer evaluation period (e.g., 100 years) than the reference period is predicted based on the corrosion amount of the metal piece recorded in the corrosion amount recording step. Specifically, for example, an approximation method such as the least squares method can be applied to the recorded corrosion amount of the metal piece to calculate an approximation formula such as a power function that takes the elapsed time since the corrosion sensor was buried in the soil as input and outputs the corrosion amount, and the output when the evaluation period is input to this approximation formula can be used as the predicted value of the corrosion amount. Finally, according to the present invention, in the corrosion allowance determination step, the corrosion allowance of the steel structure is determined based on the amount of corrosion of the metal piece predicted in the corrosion amount prediction step. The corrosion allowance may be the same value as the predicted amount of corrosion of the metal piece, or it may be a value obtained by multiplying the predicted amount of corrosion of the metal piece by a coefficient greater than 1, or by adding a predetermined offset to the predicted amount of corrosion of the metal piece, in order to provide a margin. As described above, according to the present invention, an appropriate amount of metal fragment corrosion can be calculated according to the soil environment in which the steel structure is planned to be buried, thereby predicting an appropriate amount of metal fragment corrosion after the evaluation period has elapsed, and thereby determining an appropriate corrosion allowance for the steel structure.

[0011] In the present invention, preferably, a first corrosion sensor in which the metal piece is formed from carbon steel and a second corrosion sensor in which the metal piece is formed from corrosion-resistant steel are used as the corrosion sensor, and the corrosion amount recording step, the corrosion amount prediction step and the corrosion allowance determination step are performed to determine the corrosion allowance when the steel structure is formed from carbon steel and the corrosion allowance when the steel structure is formed from corrosion-resistant steel.

[0012] Generally, when steel structures are buried in the ground for the same period of time, structures made from carbon steel will corrode more than structures made from corrosion-resistant steel. Therefore, when both types of steel structures are used for the same period, the corrosion allowance for structures made from carbon steel must be greater than that for structures made from corrosion-resistant steel. According to the preferred method described above, the corrosion allowance when the steel structure is made of carbon steel is determined by using a first corrosion sensor in which the metal piece is made of carbon steel, and the corrosion allowance when the steel structure is made of corrosion-resistant steel is determined by using a second corrosion sensor in which the metal piece is made of corrosion-resistant steel. Therefore, it is possible to determine an appropriate corrosion allowance according to the material of the steel structure. Furthermore, it is possible to select an appropriate material for the steel structure by taking into account the differences in costs such as material costs of the steel structure that arise from differences in material and the determined corrosion allowance.

[0013] In the present invention, preferably, as the evaluation period used in the corrosion amount prediction step, a first evaluation period for the first corrosion sensor and a second evaluation period for the second corrosion sensor are set, and the first and second evaluation periods are calculated when the corrosion allowance when the steel structure is formed from carbon steel and the corrosion allowance when the steel structure is formed from corrosion-resistant steel are the same, determined by executing the corrosion amount recording step, the corrosion amount prediction step and the corrosion allowance determination step, and the calculated first evaluation period is set as the service life when the steel structure is formed from carbon steel, and the calculated second evaluation period is set as the service life when the steel structure is formed from corrosion-resistant steel.

[0014] Generally, given the same corrosion allowance, steel structures made from carbon steel lose their corrosion allowance more quickly than steel structures made from corrosion-resistant steel. Therefore, if the corrosion allowances of both types of steel structures are the same, steel structures made from carbon steel require replacement or maintenance sooner. According to the preferred method described above, when the corrosion allowance for a steel structure made of carbon steel and the corrosion allowance for a steel structure made of corrosion-resistant steel are the same (in other words, when the corrosion amount of the metal piece predicted in the corrosion amount prediction process is the same), the first evaluation period (evaluation period for the first corrosion sensor when the metal piece is made of carbon steel) and the second evaluation period (evaluation period for the second corrosion sensor when the metal piece is made of corrosion-resistant steel) are calculated. The first evaluation period is set as the service life when the steel structure is made of carbon steel, and the second evaluation period is set as the service life when the steel structure is made of corrosion-resistant steel. Therefore, it is possible to select an appropriate material for the steel structure, taking into account the cost differences such as the material cost of the steel structure due to the difference in material and the construction cost due to the difference in the calculated service life.

[0015] In the present invention, preferably, in the corrosion amount recording step, the corrosion amount of the metal pieces provided by each of the multiple corrosion sensors is sequentially calculated and recorded using a plurality of corrosion sensors from the time the plurality of corrosion sensors are each buried at different three-dimensional positions in the soil until the reference period has elapsed; in the corrosion amount prediction step, the corrosion amount of the metal pieces provided by each of the plurality of corrosion sensors after the evaluation period has elapsed is predicted based on the corrosion amount of the metal pieces provided by each of the plurality of corrosion sensors recorded in the corrosion amount recording step; and in the corrosion allowance determination step, the corrosion allowance for each of the three-dimensional positions of the steel structure when the steel structure is buried in the soil is determined based on the corrosion amount of the metal pieces provided by each of the plurality of corrosion sensors predicted in the corrosion amount prediction step.

[0016] Even within the same soil, corrosiveness can differ depending on the three-dimensional location (horizontal and depth directions). Therefore, even if the elapsed time since a steel structure was buried in the soil is the same, the amount of corrosion may differ depending on the three-dimensional location of the buried steel structure, which may result in different appropriate corrosion allowances. According to the preferred method described above, by burying multiple corrosion sensors at different three-dimensional locations in the soil, the amount of corrosion of metal pieces at each three-dimensional location can be calculated, and consequently, the amount of corrosion after the evaluation period at each three-dimensional location can be predicted. Therefore, the corrosion allowance for each three-dimensional location of a steel structure when it is buried in the soil can be determined. This makes it possible to determine a more appropriate corrosion allowance according to the soil environment in which the steel structure is buried.

[0017] Furthermore, in order to solve the above problems, the present invention is also provided as a corrosion allowance determination device for a steel structure, comprising: an electrical resistance type corrosion sensor that is buried in the soil where a steel structure is planned to be buried and comprises a metal piece made of the same type of metal as the metal forming the steel structure; an electrical resistance measuring means for measuring the electrical resistance value of the metal piece by applying an electric current to the metal piece; 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; a recording means; and a prediction means, wherein the calculation means performs a corrosion amount recording step of sequentially calculating the amount of corrosion of the metal piece from the time the corrosion sensor is buried in the soil until a standard period has elapsed and recording it in the recording means; and the prediction means performs a corrosion amount prediction step of predicting the amount of corrosion of the metal piece after an evaluation period longer than the standard period has elapsed based on the amount of corrosion of the metal piece recorded in the recording means; and a corrosion allowance determination step of determining the corrosion allowance of the steel structure based on the amount of corrosion of the metal piece predicted in the corrosion amount prediction step. [Effects of the Invention]

[0018] According to the present invention, it is possible to determine the appropriate corrosion allowance for steel structures such as steel sheet piles and steel pipe piles used in soil environments. [Brief explanation of the drawing]

[0019] [Figure 1] This figure shows an example of the results of a survey on the amount of corrosion of steel sheet piles, angle steel, and steel pipe piles in various soil environments at 33 locations in Japan, as described in Non-Patent Literature 1. [Figure 2] This figure schematically shows the general configuration of a corrosion allowance determination device for steel structures according to one embodiment of the present invention. [Figure 3] This is a flowchart illustrating the steps involved in a method for determining the corrosion allowance of a steel structure according to one embodiment of the present invention. [Figure 4] Figure 3 is a schematic diagram illustrating the corrosion amount recording process ST1 and the corrosion amount prediction process ST2 shown. [Figure 5] This figure schematically illustrates the method for determining the corrosion allowance in Modification Example 1. [Figure 6] This figure schematically illustrates the method for determining the corrosion allowance in modified example 2. [Figure 7] This figure schematically illustrates the method for determining the corrosion allowance in modified example 3. [Modes for carrying out the invention]

[0020] An embodiment of the present invention will be described below with reference to the attached drawings as appropriate.

[0021] <Corrosion allowance determination device> Figure 2 is a schematic diagram showing the general configuration of a corrosion allowance determination device for steel structures according to one embodiment of the present invention. As shown in Figure 2, the corrosion allowance determination device 100 according to this embodiment includes an electrical resistance type corrosion sensor 10 that is buried in the soil where steel structures such as steel sheet piles and steel pipe piles are planned to be buried, an electrical resistance measuring means 20 that measures the electrical resistance value of a metal piece 11 by applying current to the metal piece 11 provided by the corrosion sensor 10, a calculation means 30 that calculates the amount of corrosion of the metal piece 11, a recording means 40, and a prediction means 50. Furthermore, the corrosion sensor 10 provided in the corrosion allowance determination device 100 according to this embodiment includes a temperature measuring means 60 that measures the temperature of the metal piece 11. The corrosion sensor 10, electrical resistance measuring means 20, calculation means 30, recording means 40, and prediction means 50 that constitute the corrosion allowance determination device 100 will be described in order below.

[0022] [Corrosion Sensor 10] The corrosion sensor 10 comprises a metal piece 11, a substrate 12 on which the metal piece 11 is placed on the upper surface, and a temperature measuring means 60. The metal piece 11 is made of the same type of metal as the metal forming the steel structure. In the example shown in Figure 2, the shape of the metal piece 11 is rectangular in plan view, but it is not limited to this, and it may be a U-shaped metal piece in plan view, or a serpentine metal piece in plan view. The longitudinal ends 111 and 112 of the metal piece 11 are electrically connected to the electrical resistance measuring means 20, respectively. The wiring 211 and 221 that electrically connect the ends 111 and 112 of the metal piece 11 to the electrical resistance measuring means 20 is preferably covered with a predetermined covering member 13 to prevent disconnection due to corrosion.

[0023] The metal piece 11 has a surface that is exposed to the soil. That is, at least a portion of the metal piece 11 is exposed without being covered. In the example shown in Figure 2, the top surface and side surfaces of the metal piece 11 (more precisely, the portion of the side surfaces other than the portion in contact with the covering member 13) are exposed to the soil. However, the present invention is not limited to this, and it is also possible to adopt a configuration in which the side surfaces of the metal piece 11 are covered with resin or the like, and only the top surface is exposed.

[0024] Furthermore, in order to accurately calculate the amount of corrosion of the metal piece 11 in the soil, it is preferable to set the width of the metal piece 11 (the dimension in the direction perpendicular to the direction of current flow and the thickness direction of the metal piece 11) to 11 mm or more, as described in Patent Document 2. Also, in order to accurately calculate the amount of corrosion of the metal piece 11 in the soil over a long period of time, it is preferable to set the thickness of the metal piece 11 to 1.5 mm or more, as described in Patent Document 3.

[0025] For example, a plastic substrate, which is an insulator, can be used as the substrate 12. However, it is not limited to this, and a substrate made of a conductor such as metal may also be used as the substrate 12, in which case an insulator should be placed between the substrate 12 and the metal piece 11.

[0026] In this embodiment, a thermocouple 61 is used as the temperature measuring means 60 to measure the temperature of the metal piece 11. It is preferable to cover the thermocouple 61 with a predetermined covering member 62 to prevent it from breaking due to corrosion. In the example shown in Figure 2, the tip of the thermocouple 61 is fixed to the lower surface of the metal piece 11 with insulating tape 63. The method of fixing the thermocouple 61 is arbitrary; for example, it can be fixed with a magnet or with a screw. The fixing position (temperature measurement position) of the thermocouple 61 is also arbitrary. Multiple thermocouples 61 may be used to measure the temperature of multiple positions on the metal piece 11, and the average value may be used as the temperature of the metal piece 11 in the calculation means 30 described later.

[0027] Furthermore, the temperature measuring means 60 is not limited to a thermocouple 61, and any configuration can be used, such as an electrical resistance temperature sensor, as long as it can measure the temperature of the metal piece 11 buried in the soil. Also, since direct sunlight does not reach the metal piece 11 in the soil, it is possible to measure the temperature of the soil and use that value as the temperature of the metal piece 11. In addition, the temperature measurement by the temperature measuring means 60 may be continuous or intermittent.

[0028] [Electrical resistance measurement means 20] The electrical resistance measuring means 20 comprises a constant current power supply 21, a voltmeter 22, and an electrical resistance value calculation means 23 for measuring the electrical resistance 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 wiring 211, and supplies a constant current from end 111 to end 112 of the metal piece 11. The voltmeter 22 is electrically connected to ends 111 and 112 of the metal piece 11 by wiring 221, and measures the voltage between ends 111 and 112 of the metal piece 11. The electrical resistance calculation means 23 calculates the electrical resistance 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 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 the measurement of the electrical resistance of the metal piece 11 by the electrical resistance measuring means 20 and the timing of the measurement of the temperature of the metal piece 11 by the temperature measuring means 60 are synchronized.

[0029] Furthermore, in order to accurately measure the electrical resistance of the metal piece 11, it is preferable to take measures to eliminate measurement noise caused by thermoelectric power due to the temperature difference between the connection point between the end 111 of the metal piece 11 and the wirings 211 and 221, and between the connection point between the end 112 of the metal piece 11 and the wirings 211 and 221. Possible noise reduction measures include, for example, (1) increasing the voltage measured by the voltmeter 22 by increasing the current supplied from the constant current power supply 21, (2) using the voltage measured by the voltmeter 22 when the current supplied from the constant current power supply 21 is stopped as the voltage used to calculate the electrical resistance, (3) reversing the polarity of the current supplied from the constant current power supply 21 and using the average of the absolute values ​​of the voltages measured when currents of each polarity are supplied as the voltage used to calculate the electrical resistance, and (4) making the current supplied to the metal piece 11 an alternating current (preferably in the low frequency range of 100 kHz or less, taking the skin effect into consideration). Furthermore, it is preferable to use coaxial cables or stranded cables for the wiring 211 and 221. This reduces the influence of external electromagnetic fields generated by the wiring 211 and 221, and reduces measurement noise caused by induced electromotive force.

[0030] The electrical resistance measuring means 20 is not limited to the configuration described above. For example, it is also possible to employ a configuration in which a constant voltage is applied between the ends 111 and 112 of the metal piece 11, and the electrical resistance of the metal piece 11 is measured by measuring the current flowing from the end 111 to the end 112 of the metal piece 11.

[0031] [Calculation means 30] The calculation means 30 is electrically connected to the electrical resistance value calculation means 23 and the temperature measurement means 60, 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 and the temperature of the metal piece 11 measured by the temperature measurement means 60. Specifically, the calculation means 30 has a temperature-dependent function R0(T) pre-stored, which is the relationship between the initial electrical resistance value R0 of the metal piece 11 and the temperature T. The initial electrical resistance value R0 of the metal piece 11 is the electrical resistance value at the time before corrosion occurs in the metal piece 11, or in other words, the initial thickness (t, described later) of the metal piece 11 before corrosion occurs throughout the entire piece. ini This is the electrical resistance value at the point in time when it has ).

[0032] The temperature-dependent function R0(T) differs depending on the type of metal forming the metal piece 11. Therefore, it is necessary to determine the temperature-dependent function R0(T) for each type of metal being measured for corrosion. The temperature-dependent function R0(T) can be determined by conducting tests at different temperatures each time the corrosion amount is measured, or it can be obtained from past measurements or recorded in a database. Alternatively, it can be theoretically determined from the chemical composition and microstructure of the metal.

[0033] When determining the temperature-dependent function R0(T) of the metal piece 11 by actual measurement, it is preferable to perform the measurement in a dry environment where the metal piece 11 does not corrode. In the temperature range in soil, the electrical resistance of metals generally shows 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 temperature points and approximate the measurement results linearly to obtain the temperature-dependent function R0(T). However, this is not the only option; the temperature-dependent function R0(T) may also be a function of order two or higher of temperature T, or it may be presented in a table format that records the correspondence between the initial electrical resistance R0 and temperature T.

[0034] The calculation means 30 uses the temperature-dependent function R0(T) described above and the electrical resistance value R of the metal piece 11 measured by the electrical resistance value calculation means 23. t The temperature T of the metal piece 11, as measured by the temperature measuring means 60.t to calculate the corrosion amount Δt of the metal piece 11. Specifically, the calculation means 30 calculates, based on the temperature-dependent function R0(T), the measured temperature T t the initial electrical resistance value R0(T t ) of the metal piece 11 at. Next, the calculation means 30 calculates the calculated initial electrical resistance value R0(T t ) and the measured electrical resistance value R t which is the ratio of R0(T t ) / R t is calculated. Next, the calculation means 30 calculates, based on the calculated ratio R0(T t ) / R t , the residual thickness t' of the metal piece 11 at the time of measurement by the following formula (1). t'=t ini ×R0(T t ) / R t ···(1) In the above formula (1), 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 by the following formula (2). Δt=t ini -t' ···(2)

[0035] In the present embodiment, the configuration in which the calculation means 30 calculates the corrosion amount Δt of the metal piece 11 by using the temperature T of the metal piece 11 measured by the temperature measurement means 60 t has been described. However, in a soil environment, unlike an atmospheric environment, the soil environment is not exposed to direct sunlight and has less temperature change, so it is not necessarily necessary to consider the temperature dependence of the electrical resistance value. When the temperature dependence of the electrical resistance value is not considered, in the above formula (1), as R0(T t ), an initial electrical resistance value R0 (fixed value) measured at a representative temperature in soil may be used. Furthermore, based on the same concept as in Patent Document 1, it is also possible to adopt a configuration in which a reference section is provided, separate from the metal piece 11 for measuring the amount of corrosion, which is isolated from the soil environment to prevent corrosion, and 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 section. In this case, the initial thickness of the reference section is t ref_ini The initial electrical resistance value of the metal piece 11 is R ini R t The initial electrical resistance value of the reference section is R ref_ini R is the electrical resistance value of the reference part at the time of measurement. ref_t Therefore, the amount of corrosion Δt of the metal piece 11 at the time of measurement can be calculated using the following equation (3). Δt=t ref_ini ×(R ref_ini / R ini -R ref_t / R t ) ···(3)

[0036] [Recording means 40] The recording means 40 is electrically connected to the calculation means 30, and the recording means 40 records the amount of corrosion Δt from the time the corrosion sensor 10 is buried in the soil until the reference period T0 described later has elapsed, which is sequentially calculated by the calculation means 30. i This is recorded. Δt i This represents the amount of corrosion Δt of the metal piece 11, which is calculated sequentially at predetermined time intervals, and i is an integer such that 0 ≤ i ≤ N (N = T0 / time interval).

[0037] [Prediction means 50] The prediction means 50 is electrically connected to the recording means 40, and the amount of corrosion Δt of the metal piece 11 recorded in the recording means 40 is recorded. i Based on this, the amount of corrosion Δt of the metal piece 11 after the evaluation period T, which is longer than the reference period T0, has elapsed (in this specification, the amount of corrosion Δt predicted by the prediction means 50 is Δt a The prediction means 50 predicts the amount of corrosion Δt of the predicted metal piece 11. a Based on this, the corrosion allowance of steel structures t a This is determined. The specific calculations of the prediction means 50 will be described later.

[0038] The calculation means 30, recording means 40, and prediction means 50 described above are comprised of a computer equipped with, for example, a hardware processor such as a CPU, and memory such as RAM, ROM, and hard disk. Various calculations are performed when a program stored in the computer's memory is executed by the hardware processor. As a result, the computer functions as the calculation means 30, recording means 40, and prediction means 50. The calculation means 30, recording means 40, and prediction means 50 may be installed near the location where the corrosion sensor 10 is buried, or they can be installed in a remote location far from the location where the corrosion sensor 10 is buried by wirelessly connecting the corrosion sensor 10 and the calculation means 30. Furthermore, for example, the calculation means 30, recording means 40, and prediction means 50 can be configured from a cloud server, and the corrosion amount Δt recorded in the recording means 40 can be used to determine the corrosion amount. i or the amount of corrosion Δt predicted by the prediction means 50 a It is also possible to configure it so that it can be viewed by accessing a cloud server.

[0039] <Method for determining corrosion allowance> The following describes a method for determining the corrosion allowance using the corrosion allowance determination device 100 having the above configuration. Figure 3 is a schematic flowchart showing the steps of a corrosion allowance determination method for steel structures according to one embodiment of the present invention. As shown in Figure 3, the corrosion allowance determination method according to this embodiment includes a corrosion amount recording step ST1, a corrosion amount prediction step ST2, and a corrosion allowance determination step ST3. Steps ST1 to ST3 will be described below.

[0040] [Corrosion amount recording process ST1] Figure 4 schematically illustrates the corrosion amount recording process ST1 and the corrosion amount prediction process ST2. Figure 4(a) illustrates the corrosion amount recording process ST1 and the corrosion amount prediction process ST2, and Figure 4(b) illustrates the corrosion amount prediction process ST2. As shown in Figure 4(a), in the corrosion amount recording process ST1, the corrosion amount Δt of the metal piece 11 is recorded using the corrosion sensor 10 (specifically, using the corrosion sensor 10, electrical resistance measuring means 20, and calculation means 30) from the time the corrosion sensor 10 is buried in the soil until the reference period T0 has elapsed. i The values ​​(shown by solid lines in Figure 4(a)) are calculated sequentially at predetermined time intervals and recorded in the recording means 40. The reference period T0 is not limited to this, but for example, it is set to one year as shown in Figure 4(a). The time interval is not limited to this, but for example, it is set to a constant time interval of 30 minutes.

[0041] [Corrosion amount prediction process ST2] In the corrosion amount prediction step ST2, the prediction means 50 predicts the corrosion amount Δt of the metal piece 11 recorded by the recording means 40 in the corrosion amount recording step ST1. i Based on this, the amount of corrosion Δt of the metal piece 11 after an evaluation period T longer than the reference period T0 has elapsed. a This predicts the following. The evaluation period T is not limited to this, but for example, it is set to 100 years, as shown in Figure 4(b). Specifically, as shown in Figure 4(a), the prediction means 50 determines the amount of corrosion Δt of the recorded metal piece 11. i By applying an approximation method such as the least squares method, the power function Δt = A·X is output when the elapsed time X since the corrosion sensor 10 was buried in the soil is taken as input and the amount of corrosion Δt is output. B An approximate formula (shown as a dashed line in Figure 4(a)) is calculated, such as (A and B are predetermined constants). Then, as shown in Figure 4(b), the prediction means 50 outputs the predicted value Δt of corrosion when the evaluation period T is input to this approximate formula. a Let's assume that in the example shown in Figure 4(b), Δt a =A·T B Therefore, the amount of corrosion Δt of the metal piece 11 after T = 100 years has elapsed. a It is predicted that this will be approximately 0.4 mm.

[0042] [Corrosion allowance determination process ST3] In the corrosion allowance determination step ST3, the prediction means 50 determines the corrosion amount Δt of the metal piece 11 predicted in the corrosion amount prediction step ST2. aBased on this, the corrosion allowance of steel structures t a Determine the corrosion allowance t. a This is the predicted amount of corrosion Δt of the metal piece 11. a It may be set to the same value, or to allow for a margin, the predicted corrosion amount Δt of the metal piece 11 may be set. a Multiply by a coefficient greater than 1, or the predicted corrosion amount Δt of the metal piece 11. a The value may be obtained by adding a predetermined offset to this value. Corrosion allowance t a Corrosion amount Δt a If we set it to the same value, in the example shown in Figure 4(b), the corrosion allowance t a This will be determined to be approximately 0.4 mm.

[0043] According to the corrosion allowance determination device 100 and corrosion allowance determination method using the present embodiment described above, in the corrosion amount recording step ST1, an electrical resistance type corrosion sensor 10 is used, so the corrosion amount Δt of the metal piece 11 i It can accurately calculate the corrosion amount Δt of the metal piece 11 according to the soil environment, as the corrosion sensor 10 is to be buried in the soil where the steel structure is planned to be embedded. i Therefore, in the corrosion amount prediction process ST2, the appropriate corrosion amount Δt of the metal piece 11 after the evaluation period T has elapsed can be calculated. a This is predicted, and in the corrosion allowance determination process ST3, the appropriate corrosion allowance t of the steel structure is determined. a It is possible to determine this.

[0044] The following describes some modified examples of the corrosion allowance determination method according to this embodiment.

[0045] <Example 1> Figure 5 is a schematic diagram illustrating the method for determining the corrosion allowance according to Modification Example 1. In the corrosion allowance determination method according to Modification 1, a first corrosion sensor, in which a metal piece 11 is formed from carbon steel, and a second corrosion sensor, in which a metal piece 11 is formed from corrosion-resistant steel, are used as corrosion sensors 10, and the corrosion amount recording step ST1, corrosion amount prediction step ST2, and corrosion allowance determination step ST3 are performed. It is preferable that the first corrosion sensor and the second corrosion sensor be buried in the soil at the same time.

[0046] Specifically, as shown in Figure 5, by using the first corrosion sensor to perform the corrosion amount recording process ST1 and the corrosion amount prediction process ST2, the approximate formula Δt = A1·X shown by the dashed line is obtained. B1 (A1 and B1 are predetermined constants) are calculated, and when the evaluation period T is input into this approximation formula, the output is the predicted corrosion amount Δt. a1 It is said that, by performing the corrosion allowance determination process ST3, the corrosion allowance t when the steel structure is formed from carbon steel is determined. a1 However, for example, the predicted amount of corrosion Δt a1 It is determined to be the same value as [the other value]. On the other hand, by using the second corrosion sensor to perform the corrosion amount recording process ST1 and the corrosion amount prediction process ST2, the approximate formula Δt = A2·X shown by the solid line in Figure 5 is obtained. B2 (A2 and B2 are predetermined constants) are calculated, and the output when the evaluation period T is input to this approximation formula is the predicted corrosion amount Δt. a2 It is said that, by performing the corrosion allowance determination process ST3, the corrosion allowance t when the steel structure is formed from corrosion-resistant steel is determined. a2 However, for example, the predicted amount of corrosion Δt a2 It is determined to be the same value as [the other value].

[0047] According to the corrosion allowance determination method described in Modification 1, it is possible to determine an appropriate corrosion allowance according to the material of the steel structure. Furthermore, it is possible to select an appropriate material for the steel structure by considering the differences in costs such as material costs for the steel structure that arise from differences in material and the determined corrosion allowance.

[0048] <Modification 2> Figure 6 is a schematic diagram illustrating the method for determining the corrosion allowance related to Modification Example 2. In the corrosion allowance determination method according to Modification 2, similar to the corrosion allowance determination method according to Modification 1, a first corrosion sensor in which the metal piece 11 is made of carbon steel and a second corrosion sensor in which the metal piece 11 is made of corrosion-resistant steel are used as the corrosion sensor 10. As shown in Figure 6, in the corrosion allowance determination method according to Modification 2, a first evaluation period T1 for the first corrosion sensor and a second evaluation period T2 for the second corrosion sensor are set as evaluation periods used in the corrosion amount prediction process ST2. Then, the first evaluation period T1 and the second evaluation period T2 are calculated when the corrosion allowance when the steel structure is formed from carbon steel and the corrosion allowance when the steel structure is formed from corrosion-resistant steel are the same, as determined by executing the corrosion amount recording process ST1, the corrosion amount prediction process ST2, and the corrosion allowance determination process ST3.

[0049] Specifically, as shown in Figure 6, by using the first corrosion sensor to perform the corrosion amount recording process ST1 and the corrosion amount prediction process ST2, the approximate formula Δt = A1·X shown by the dashed line is obtained. B1 The following is calculated, and by performing the corrosion amount recording process ST1 and the corrosion amount prediction process ST2 using the second corrosion sensor, the approximate formula Δt = A2·X shown by the solid line is obtained. B2 If these calculations are performed, the output of these approximation formulas will be the same predicted value Δt for the amount of corrosion. a (In the example shown in Figure 6, the same corrosion allowance t) a =Δt a (This is how it works.) Then, calculate the first evaluation period T1 and the second evaluation period T2, which are the inputs to each approximation formula. Furthermore, in the corrosion allowance determination method related to Modification 2, the calculated first evaluation period T1 is set as the service life when the steel structure is made from carbon steel, and the calculated second evaluation period T2 is set as the service life when the steel structure is made from corrosion-resistant steel.

[0050] According to the corrosion allowance determination method of Modification 2, it is possible to select an appropriate material for the steel structure by taking into account the differences in costs such as the material cost of the steel structure due to the difference in material and the construction cost due to the difference in the calculated useful life.

[0051] <Variation 3> Figure 7 is a schematic diagram illustrating the corrosion allowance determination method according to Modification 3. Figure 7(a) is a plan view showing the corrosion sensor 10 buried in the soil S, and Figure 7(b) is a longitudinal cross-sectional view showing the corrosion sensor 10 buried in the soil S. In Figure 7, the X direction means one horizontal direction, the Y direction means another horizontal direction perpendicular to the X direction, and the Z direction means the depth direction (vertical direction) perpendicular to the X and Y directions. As shown in Figure 7, in the corrosion allowance determination method according to Modification 3, in the corrosion amount recording step ST1, multiple corrosion sensors 10 are used to measure the corrosion amount Δt of the metal pieces 11 provided by each of the multiple corrosion sensors 10 from the time the multiple corrosion sensors 10 are buried at different three-dimensional positions in the soil S (positions in the horizontal plane (positions in the XY plane) and positions in the depth direction (Z direction), i.e., different three-dimensional coordinates (X, Y, Z)) until the reference period T0 has elapsed. i The corrosion amount Δt is calculated sequentially and recorded in the recording means 40. Then, in the corrosion amount prediction step ST2, the corrosion amount Δt of the metal piece 11, which is provided by each of the multiple corrosion sensors 10 recorded in the corrosion amount recording step ST1, is calculated. i Based on this, the amount of corrosion Δt of the metal piece 11, which is measured by each of the multiple corrosion sensors 10, is determined when the evaluation period T has elapsed. a Finally, in the corrosion allowance determination step ST3, the corrosion amount Δt of the metal piece 11, which is measured by each of the multiple corrosion sensors 10 predicted in the corrosion amount prediction step ST2, is predicted. a Based on this, the corrosion allowance t for each three-dimensional position of a steel structure when it is buried in soil S is a To decide.

[0052] According to the corrosion allowance determination method of modified example 3, by burying multiple corrosion sensors 10 at different three-dimensional positions (three-dimensional coordinates (X, Y, Z)) in the soil S, the amount of corrosion Δt of the metal piece 11 at each three-dimensional position is determined. i This allows us to calculate the amount of corrosion Δt at each 3D position after the evaluation period T has elapsed. a Because it can predict the corrosion allowance t for each three-dimensional position of a steel structure when it is buried in soil S, a This allows for the determination of a more appropriate corrosion allowance t according to the environment of the soil S in which the steel structure is buried. aIt is possible to determine this. [Explanation of Symbols]

[0053] 10. Corrosion sensor 11...metal piece 20. Electrical resistance measurement means 30...Arithmetic means 40. Recording means 50... Prediction methods 100...Corrosion allowance determination device ST1... Corrosion amount recording process ST2...Corrosion amount prediction process ST3... Corrosion allowance determination process T0 ··Reference period T...evaluation period

Claims

1. A corrosion amount recording step involves using an electrical resistance type corrosion sensor, which is buried in the soil where a steel structure is planned to be buried, and which has a metal piece made of the same type of metal as the metal forming the steel structure, to sequentially calculate and record the amount of corrosion of the metal piece from the time the corrosion sensor is buried in the soil until a standard period has elapsed, and A corrosion amount prediction step, which predicts the corrosion amount of the metal piece after an evaluation period longer than the reference period has elapsed, based on the corrosion amount of the metal piece recorded in the corrosion amount recording step, A corrosion allowance determination step, which determines the corrosion allowance of the steel structure based on the corrosion amount of the metal piece predicted in the corrosion amount prediction step, A method for determining the corrosion allowance of a steel structure, comprising the characteristics of a steel structure.

2. A method for determining the corrosion allowance of a steel structure according to claim 1, wherein the corrosion sensor comprises a first corrosion sensor whose metal piece is made of carbon steel and a second corrosion sensor whose metal piece is made of corrosion-resistant steel, respectively, and the corrosion amount recording step, corrosion amount prediction step, and corrosion allowance determination step are performed to determine the corrosion allowance when the steel structure is made of carbon steel and the corrosion allowance when the steel structure is made of corrosion-resistant steel.

3. As the evaluation period used in the corrosion amount prediction process, a first evaluation period for the first corrosion sensor and a second evaluation period for the second corrosion sensor are set, A method for determining the corrosion allowance of a steel structure according to claim 2, wherein the corrosion allowance when the steel structure is formed from carbon steel and the corrosion allowance when the steel structure is formed from corrosion-resistant steel are the same, determined by performing the corrosion amount recording step, the corrosion amount prediction step, and the corrosion allowance determination step, the first evaluation period and the second evaluation period are calculated, the first evaluation period calculated is set as the service life when the steel structure is formed from carbon steel, and the second evaluation period calculated is set as the service life when the steel structure is formed from corrosion-resistant steel.

4. In the corrosion amount recording step, using a plurality of corrosion sensors, the amount of corrosion of the metal pieces provided by each of the plurality of corrosion sensors is sequentially calculated and recorded from the time the plurality of corrosion sensors are buried at different three-dimensional positions in the soil until the reference period has elapsed. In the corrosion amount prediction step, based on the amount of corrosion of the metal piece provided by each of the multiple corrosion sensors recorded in the corrosion amount recording step, the amount of corrosion of the metal piece provided by each of the multiple corrosion sensors after the evaluation period has elapsed is predicted. A method for determining the corrosion allowance of a steel structure according to claim 1 or 2, wherein in the corrosion allowance determination step, the corrosion allowance for each of the three-dimensional positions of the steel structure when the steel structure is buried in the soil is determined based on the amount of corrosion of the metal piece provided by each of the plurality of corrosion sensors predicted in the corrosion amount prediction step.

5. An electrical resistance type corrosion sensor is buried in the soil where a steel structure is planned to be buried, and comprises a metal piece made of the same type of metal as the metal forming the steel structure, An electrical resistance measuring means for measuring the electrical resistance of the metal piece by passing an electric current through the metal piece, 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, Recording means and Equipped with a prediction means, The calculation means performs a corrosion amount recording step, in which it sequentially calculates the amount of corrosion of the metal piece from the time the corrosion sensor is buried in the soil until a standard period has elapsed, and records the result in the recording means. The prediction means is A corrosion amount prediction step, which predicts the amount of corrosion of the metal piece after an evaluation period longer than the reference period has elapsed, based on the amount of corrosion of the metal piece recorded in the recording means, A corrosion allowance determination step is performed to determine the corrosion allowance of the steel structure based on the corrosion amount of the metal piece predicted in the corrosion amount prediction step. A device for determining the corrosion allowance of steel structures.

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