Corrosion estimation method and apparatus

Abstract

In Step S101, the particle size of soil is measured (particle size measurement step). In Step S102, a color measurement value related to the color of the soil is measured (color measurement step). In Step S103, corrosion of steel buried in the soil is estimated from the particle size and the color measurement value that have been measured (estimation step). In the measuring the color measurement value, a color value is measured as the color measurement value. In the estimating corrosion, a corrosion rate is determined from the measured particle size, a corrosion rate multiplier is determined from the measured color measurement value, the corrosion rate is multiplied by the corrosion rate multiplier to obtain a corrected corrosion rate, and the corrosion of the steel is estimated using the corrected corrosion rate obtained.

Description

[Technical field]

[0001] The present invention relates to a corrosion estimation method and device for estimating corrosion of a structure buried in the ground. [Background technology]

[0002] In order to prevent breakdowns in aging infrastructure equipment, maintenance operations have traditionally been carried out through periodic inspections. However, visual inspections are difficult depending on the location of the equipment, and in many cases, alternative, appropriate inspection methods have not been established. For this reason, for equipment that is difficult or impossible to inspect, there is currently no choice but to adopt a form of time-based maintenance in which equipment that has passed a certain age is uniformly replaced.

[0003] In order to balance the safety and efficiency of equipment that is difficult to inspect visually, research and development into technology that realizes condition-based maintenance by predicting and estimating the deterioration state of equipment has been actively conducted in recent years. If condition-based maintenance can be realized, safety can be ensured by not overlooking and updating objects that deteriorate quickly, and it is expected that cost efficiency will be improved by using objects that deteriorate more slowly for a longer period of time. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Y. Wan et al., "Corrosion Behaviors of Q235 Steel in Indoor Soil", International Journal of Electrochemical Science, vol. 8, pp. 12531-12542, 2013. Summary of the Invention [Problem to be solved by the invention]

[0005] As a representative example of equipment that is difficult to visually inspect, underground equipment can be given. In order to predict soil corrosion, which is the main cause of deterioration of metal materials buried underground, it is necessary to extract the dominant environmental factors and understand their influence. It is known that soil corrosion, like aqueous solution corrosion, progresses based on an oxidation-reduction reaction between water and oxygen. However, unlike aqueous solution corrosion, soil is a special environment in which three phases, solid, gas, and liquid, coexist, and there are multiple environmental factors related to the progress of soil corrosion, so soil corrosion is said to be a particularly complex system (Non-Patent Document 1). Thus, there was a problem that it was not easy to estimate the corrosion of metal materials buried underground.

[0006] The present invention has been made to solve the above problems, and has an object to make it possible to easily estimate the corrosion of metal materials buried underground. [Means for solving the problem]

[0007] The corrosion estimation method of the present invention includes a particle size measurement step of measuring the particle size of soil, a color measurement step of measuring color measurement values ​​related to the color of the soil, and an estimation step of estimating corrosion of steel buried in the soil from the particle size and color measurement values.

[0008] In addition, the corrosion estimation device of the present invention includes a particle size measuring device that measures the particle size of soil, a color measuring device that measures color measurement values ​​related to the color of the soil, and an estimation circuit that estimates the corrosion of steel buried in the soil from the particle size and color measurement values. Effect of the Invention

[0009] As described above, according to the present invention, the corrosion of steel materials buried in soil is estimated from the measured particle size and color measurement values, so that the corrosion of metal materials buried underground can be easily estimated. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a flowchart illustrating a corrosion estimation method according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a configuration diagram showing the configuration of a corrosion estimation device according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a configuration diagram showing a partial configuration of a corrosion estimation device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a configuration diagram showing a partial configuration of a corrosion estimation device according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a characteristic diagram showing the time change of the corrosion rate estimated from the soil grain size. [Figure 6] FIG. 6 is a characteristic diagram showing the relationship between the CIELAB L* value and the corrosion rate multiplier. [Figure 7] FIG. 7 is a characteristic diagram showing the relationship between the CIELAB a* value and the corrosion rate multiplier. [Figure 8] FIG. 8 is a characteristic diagram showing the relationship between the CIELAB b* value and the corrosion rate multiplier. [Figure 9] FIG. 9 is a characteristic diagram showing the change over time in the corrosion rate estimated from the particle size and color of soil. [Figure 10] FIG. 10 is a flowchart for explaining in more detail the corrosion estimation method according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a corrosion estimation method according to an embodiment of the present invention will be described with reference to Fig. 1. In this method, first, in step S101, the particle size of soil is measured (particle size measurement step). For measuring the particle size, for example, JIS A 1204:2009 "Soil Particle Size Test Method" can be used. Also, a method conforming to JIS Z 8825:2013 "Particle Size Analysis - Laser Diffraction and Scattering Method" can be used.

[0012] Next, in step S102, color measurement values ​​relating to the color of the soil are measured (color measurement step). In measuring the color measurement values, color values ​​can be measured as the color measurement values. In measuring the color measurement values, for example, a standard soil color book in which standard soil colors are arranged according to the Munsell classification method can be used. In addition, a spectrophotometer can be used to measure the color measurement values.

[0013] Next, in step S103, the corrosion of the steel material buried in the soil is estimated from the measured particle diameter and color measurement value (estimation step). In estimating corrosion, the corrosion rate is calculated from the measured particle diameter, a corrosion rate magnification is calculated from the measured color measurement value, a corrected corrosion rate is calculated by multiplying the corrosion rate by the corrosion rate magnification, and the corrosion of the steel material is estimated from the calculated corrected corrosion rate.

[0014] Next, a corrosion estimation device for carrying out the above-mentioned corrosion estimation method will be described with reference to Fig. 2. This corrosion estimation device includes a particle size measuring device 101 for measuring the particle size of soil, a color measuring device 102 for measuring color measurement values ​​related to the color of the soil, and an estimation circuit 103 for estimating corrosion of steel buried in soil from the measured particle size and the measured color measurement values. The color measuring device 102 measures, for example, a color value as the color measurement value.

[0015] The estimation circuit 103 obtains the corrosion rate from the particle diameter, obtains the corrosion rate magnification from the color measurement value, obtains a corrected corrosion rate by multiplying the corrosion rate by the corrosion rate magnification, and estimates the corrosion of the steel material based on the obtained corrected corrosion rate. The estimation circuit 103 is a computer device equipped with a CPU (Central Processing Unit), a memory, and the like. The CPU operates (executes the program) according to a program deployed in the memory, thereby realizing the above-mentioned function (estimation step). The estimation circuit 103 can also be configured with a programmable logic device (PLD: Programmable Logic Device) such as an FPGA (field-programmable gate array). A program for realizing the operation of the estimation step can be written into the FPGA by connecting a predetermined writing device.

[0016] As mentioned above, soil corrosion is a complex system, so the key to estimating soil corrosion is how to extract and analyze the controlling factors related to corrosion from the solid phase, which is specific to the soil environment.

[0017] One of the important pieces of information about the solid phase is the soil particle size. The structure of the interparticle voids and the packing rate of the particles change depending on the size and distribution of the particles, and this greatly affects the ease of oxygen supply from the soil surface and the wetted area of ​​the metal surface by water captured by capillary action. Soil particle size is the most effective environmental factor for estimating the liquid and gas phase information that governs the occurrence of corrosion in soil corrosion.

[0018] As mentioned above, the particle size of soil can provide information on the occurrence of soil corrosion, but the particle size of soil alone is insufficient to estimate soil corrosion. Even if the climatic conditions such as temperature and humidity of the place where the equipment is installed are similar, for example, in coastal areas and hot spring areas, the corrosion progress rate is generally said to be faster. Therefore, after satisfying the corrosion occurrence conditions, it is necessary to consider the presence or absence of chemical components in the environment that accelerate the corrosion progress.

[0019] The most important factor in estimating the chemical components in soil is the color of the soil. For example, the "soil groups" classified by the agricultural soil classification standard are classified by color based on the soil's chemical components that are important for agricultural practice. For example, black soil, as its name suggests, is black, and contains organic acids derived from humus. Brown soil, yellow soil, and red soil are also classified by the percentage of iron oxide in the soil, and blue-colored gleyed soil is also derived from reduced iron. For these reasons, it is possible to estimate the acceleration of corrosion from the chemical components in the soil based on the color of the soil.

[0020] The particle size of the soil is measured as a factor for estimating whether or not corrosion will occur from information on the solid and liquid phases near the surface of metal materials buried in soil, and the color of the soil is measured as a factor for estimating the chemical components that accelerate corrosion under conditions in which corrosion will occur.From these two measured factors, it is possible to estimate the amount of corrosion of metal materials buried underground.

[0021] Next, the corrosion estimation device will be described in more detail. First, the particle size measuring device 101 will be described with reference to Fig. 3. The particle size measuring device 101 includes a first storage container 111, a dryer 112, a stirrer 113, a particle size measuring unit 114, and a particle size calculation circuit 115. The particle size measuring device 101 performs a test to measure the particle size of soil.

[0022] In the particle size measuring instrument 101, first, the soil in which the steel material for which the amount of corrosion is to be estimated is buried is placed in the first storage container 111. The amount of soil to be placed in the first storage container 111 varies depending on the particle size measuring method described below, but can be a maximum amount of about 500 mL. The shape of the first storage container 111 is not limited as long as it is large enough to hold the amount of soil required for measurement.

[0023] The material constituting the first storage container 111 can be arbitrarily determined by the user. However, if the first storage container 111 is made of a metal material, when moist soil is contained therein, a corrosive reaction may occur between the metal and the moist soil, causing the container to deteriorate, and furthermore, the corrosion products may be mixed into the moist soil, affecting the soil color measurement described below. Therefore, when selecting the material constituting the first storage container 111, it is preferable to avoid metal materials.

[0024] Furthermore, when drying the soil in the first storage container 111 by the dryer 112 is performed by heating, it is preferable to avoid materials that are sensitive to heat. For example, the first storage container 111 can be made of a heat-resistant polymer resin, glass, or the like.

[0025] If the soil stored in the first storage container 111 is wet, soil particle clumps may form due to the capillary action of water trapped in the gaps between the particles. If particle size measurement is performed in the presence of soil particle clumps, a large proportion of particles larger than the actual particle size will be detected, making it difficult to obtain the true particle size. To prevent this, it is important to remove the water in the gaps between the particles, which is the cause of soil particle clumps, and the soil in the first storage container 111 is dried using the dryer 112.

[0026] The dryer 112 dries the stored soil, for example, by applying heat to raise the temperature of the first storage container 111. The dryer 112 can also reduce the pressure inside the first storage container 111 to perform vacuum drying. When applying heat, a material must be selected that can withstand the temperature set by the user for the first storage container 111.

[0027] Furthermore, if the soil contained in first storage container 111 contains humus and is black in color, the organic chemical components will be denatured by heat, causing the black soil to lose its inherent properties and possibly affecting the results obtained by color measuring instrument 102. Therefore, it is preferable to limit the temperature rise inside first storage container 111 to an upper limit of 50°C.

[0028] Furthermore, when drying the soil stored in the first storage container 111 by reducing pressure, it is important that the first storage container 111 is made of a material that can withstand reduced pressure. For example, when drying the soil by reducing pressure, the first storage container 111 is preferably made of glass.

[0029] The drying operation in the dryer 112 ends when the moisture content of the soil stored in the first storage container 111 reaches 0%. For example, it is possible to detect the soil moisture content of the first storage container 111 by installing a soil moisture content sensor in the first storage container 111. The drying method of the dryer 112 is not limited to the above-mentioned method, so long as the dryer 112 has a mechanism that realizes a method that can make the soil moisture content in the first storage container 111 0%.

[0030] The agitator 113 performs agitation work on the soil in the first storage container 111, whose soil moisture content has become 0% due to drying by the dryer 112, in order to break up the soil particle clumps. The agitator 113 is not limited as long as it has a mechanism that can break up all the soil particle clumps. For example, it can be configured with a mechanism that stirs two rod-shaped stirrers in a circular motion. Also, a mechanism similar to that of an automatic agitator used in food factories and the like can be used.

[0031] The particle size measuring unit 114 performs particle size measurement on the soil in the first storage container 111, which has been pretreated by the dryer 112 and the mixer 113. As a method for measuring particle size, JIS A 1204:2009 "Soil Grain Size Test Method" can be used. In addition, the particle size can be measured in accordance with JIS Z 8825:2013 "Particle Size Analysis - Laser Diffraction and Scattering Method."

[0032] For example, when carrying out a soil grain size test, metal mesh sieves as specified in JIS Z 8801-1 are used with openings of 75 mm, 53 mm, 37.5 mm, 26.5 mm, 19 mm, 9.5 mm, 4.75 mm, 2 mm, 850 μm, 425 μm, 250 μm, 106 μm, and 75 μm. Soil is placed into the metal mesh sieves and sieved, and the particle size distribution is calculated from the proportion of soil particles remaining on each sieve.

[0033] For particle sizes of 75 μm or less, the soil particle sedimentation method using hydrometer is used to calculate the particle size. It is possible to calculate the particle size distribution by combining the results of the sieve method for soil particles of 75 μm or more and the sedimentation method for soil particles of less than 75 μm. In order to carry out the soil grain size test method, about 500 mL of soil needs to be stored in the first storage container 111.

[0034] Particle size analysis - laser diffraction and scattering method, which is another measurement technology that can measure particle size, involves irradiating soil particles with laser light, generating diffracted and scattered light of different intensities depending on the size of the particle, and calculating the particle size distribution by analyzing the light intensity distribution pattern formed from the diffracted and scattered light.

[0035] Particle size measurement by the laser diffraction and scattering method can be performed using a commercially available analytical device. In order to perform particle size analysis by the laser diffraction and scattering method, the amount of soil stored in the first storage container 111 can be about 50 mL. The soil used for measurement by the particle size measurement unit 114 can be discarded as is, or can be reused by the color measurement device 102. When discarding the soil, it is necessary to prepare an additional amount of soil that allows measurement by the color measurement device 102. When reusing the soil by the color measurement device 102, it is not necessary to prepare an additional amount of soil, but since the soil measured by the particle size measurement unit 114 is in a wet state, it is necessary to perform drying work by the dryer 112 and removal of soil lumps by the mixer 113 again.

[0036] The particle diameter measurement results obtained by the particle diameter measurement unit 114 are sent to a particle diameter calculation circuit 115, which derives a particle diameter distribution based on the measurement results. The particle diameter distribution obtained by the particle diameter calculation circuit 115 is, for example, a graph with particle diameters on the horizontal axis and frequency % or cumulative frequency % of each particle diameter on the vertical axis.

[0037] Next, the color measuring instrument 102 will be described with reference to FIG. 4. In the color measuring instrument 102, a test is carried out to measure the color of the soil. First, soil is transferred from the first storage container 111 of the particle size measuring instrument 101 to the second storage container 121. The shape and material of the second storage container 121 are not particularly limited as long as soil color measurement is possible. However, whether a measuring device is used as the soil color measurement means or the measurer visually checks, it is essential that the soil color can be distinguished from the outside of the first storage container 111, so it is preferable that the top of the container is largely open, such as a petri dish, or that the entire container is made of a transparent material.

[0038] The soil color measurement unit 122 measures the color of the soil in the second storage container 121, and the soil color judgment circuit 123 judges the measured soil color. For example, a standard soil color book in which standard soil colors are arranged according to the Munsell classification method can be used to measure the soil color in the soil color measurement unit 122. Also, a spectrophotometer can be used to measure the soil color in the soil color measurement unit 122.

[0039] When measuring soil color using a standard soil color book, it is preferable that the person who performs the measurement is always the same person in order to minimize measurement errors when measuring soil color for multiple soils. The person who performs soil color measurement using a standard soil color book completes the measurement by recording the color values ​​of hue, lightness, and saturation written on the standard soil color book. When using a standard soil color book for soil color measurement, it is preferable to prepare at least about 20 mL of soil in the second storage container 121 in order to judge the soil color visually.

[0040] Next, a case where a spectrophotometer is used to measure soil colors in the soil color measuring unit 122 will be described. A spectrophotometer is a type of photometer, and can obtain information about a color by measuring the wavelength intensity of each color. When a spectrophotometer is used as the soil color measuring unit 122, the second storage container 121 needs to be a transparent spectrophotometer cell that enables measurement.

[0041] As described above, the color information stored after the measurement is sent to the soil color determination circuit 123 and converted into some color value. * a * b * ) color space (CIELAB). In CIELAB, the lightness of a color is expressed as L * , which represents the positions of red and green * , b represents the position of yellow and blue * Color values ​​are described as three coordinates: * , a * , b * The value of can be calculated by the soil color determination circuit 123 and used as the soil color measurement result.

[0042] Next, the estimation circuit 103 will be described in detail. The estimation circuit 103 estimates the amount of corrosion of the steel buried in the measured soil based on the results obtained by the particle size measuring instrument 101 and the color measuring instrument 102. First, the particle size measurement results (particle size distribution) obtained by the particle size calculation circuit 115 and the soil color measurement results (soil color judgment results) obtained by the soil color judgment circuit 123 are sent to the memory of the estimation circuit 103. The estimation circuit 103 calculates and outputs the corrosion amount estimation result using each measurement result stored in the memory. Information on the corrosion rate due to soil corrosion is obtained from the particle size measurement results (particle size distribution) obtained by the particle size calculation circuit 115 in the particle size measuring instrument 101.

[0043] As mentioned above, the progress of corrosion reaction is determined by the wetted area of ​​the metal surface buried in the soil and the oxygen partial pressure. The wetted area depends on the capillary force of water trapped in the particle gaps, which can be calculated from the particle gap size, i.e., the particle size distribution.

[0044] Similarly, after the gaps between particles are filled with water from rain, etc., the water penetrates and diffuses deep underground as gravity water, and oxygen diffuses from the surface layer into the ground and is supplied to the metal surface. The supplied oxygen can dissolve in water and reach the metal surface as dissolved oxygen, but the diffusion rate of dissolved oxygen is 10 times slower than the diffusion rate of gaseous oxygen. 4 Since oxygen is diffusing through the soil as a gas, the longer the distance it diffuses through the soil, the easier it is to supply the oxygen necessary for the corrosion reaction. In other words, the speed at which water in the soil penetrates and diffuses is linked to the distance that gaseous oxygen can diffuse, and the water permeation diffusion speed is also determined by the particle size distribution.

[0045] As a result, information on the time change of corrosion rate can be obtained from the particle size distribution. As an example of information on the time change of corrosion rate, the time change of corrosion rate estimated from the results of measuring particle size in soil of various conditions is shown in Figure 5.

[0046] In the graph shown in Figure 5, at the point of time elapsed of 0 on the horizontal axis, all the gaps between the soil particles are filled with water and in a wet state, and as time passes, the soil dries out due to the permeation and diffusion of water. As the soil dries out, the corrosion rate increases and at a certain point it reaches its maximum corrosion rate. This is because as the soil dries out, oxygen can be supplied to the area near the metal surface, maintaining the balance of water and oxygen necessary for the corrosion reaction to progress. After reaching the maximum corrosion rate, the corrosion rate decreases. This is because as the soil dries out further, a sufficient amount of oxygen necessary for the corrosion reaction is supplied, but the wetted area of ​​the metal surface decreases.

[0047] The corrosion rate of steel buried underground shows a time-varying behavior as shown in Figure 5, and the timing at which the corrosion rate increases and the value of the maximum corrosion rate change depending on the particle size distribution. Therefore, by investigating the relationship between the particle size distribution and the time-varying behavior of the corrosion rate in advance, storing this result in the memory of the estimation circuit 103, and comparing it with the results obtained by the particle size measuring device 101, the time-varying behavior of the corrosion rate can be easily obtained (extracted).

[0048] The corrosion rate can be quantitatively measured using an electrochemical measurement method. Measurements using the electrochemical measurement method can be repeated until the wet soil dries, and the graph in FIG. 5 can be obtained in advance according to each particle size distribution. In addition, if it is desired to save the effort of acquiring the time-varying behavior of the corrosion rate, it is also possible to store only the maximum corrosion rate in the memory of the estimation circuit 103.

[0049] Next, the estimation circuit 103 calculates the corrosion rate multiplication factor from the results obtained by the color measurement instrument 102. * This is an example of a graph showing the relationship between the CIELAB L value and the corrosion rate factor. * The value represents the lightness of the color, L * =0 is black, L * = 100 indicates a white diffuse color. Therefore, L * The closer to 0, the more organic acids derived from humus the soil contains.

[0050] Acid is a factor that accelerates corrosion, so L * The corrosion rate multiplier is determined based on the value of L, and the true corrosion rate in each soil can be obtained by multiplying the corrosion rate value in Figure 5 by the corrosion rate multiplier. * The relationship between the corrosion rate and the corrosion rate factor is as follows: L * You can set a graph in which the closer to 0 the magnification is, the higher it will be. * It is possible to investigate the relationship between the corrosion rate factor and

[0051] Figure 7 shows the a * 1 is a graph showing the relationship between the corrosion rate factor and the * The values ​​indicate the positions of red and green, and a * Green for negative values, a * A positive value indicates that the soil is red. Soil that shows red color contains a lot of iron oxide. If there is a lot of iron oxide produced as a corrosion product in the environment, the corrosion reaction will be slower from the viewpoint of chemical equilibrium, and the corrosion rate factor will be lower. Therefore, a * Figure 7 can be set so that the corrosion rate multiplication factor is lower when the value is positive, and * It is possible to investigate the relationship between the value and the corrosion rate multiplier.

[0052] Figure 8 shows the CIELAB b * 1 is a graph showing the relationship between the corrosion rate factor and the value of b. * The value indicates the position of yellow and blue, and b * Negative values ​​are blue, b * A positive value indicates that the soil is yellow. Soil that shows blue color contains a lot of reduced iron, and there are many electron acceptors required for the corrosion reaction to proceed, so the corrosion rate is significantly faster. Therefore, b * Figure 8 can be set so that the corrosion rate multiplier is higher when the value is negative, and b * It is possible to investigate the relationship between the value and the corrosion rate multiplier.

[0053] The estimation circuit 103 multiplies the time change in corrosion rate or the maximum corrosion rate obtained from the results obtained by the particle size measuring instrument 101 by the corrosion rate multiplication factor obtained from the results obtained by the color measuring instrument 102 to calculate a corrected corrosion rate. This calculation completes the acquisition of all information related to the corrosion rate. Next, the estimation circuit 103 performs an estimation calculation of the amount of corrosion from the corrosion rate information.

[0054] When the change in corrosion rate over time is extracted from the results obtained by the particle size measuring device 101, this indicates the change in corrosion rate over time from one rain to the next, so it is possible to calculate the amount of corrosion that progresses with one rain by integrating the extracted change over time. Therefore, rainfall information is obtained for the area where the soil used was buried, and the amount of corrosion that progresses with one rain is added up for each number of rains to determine the amount of corrosion that progresses in one year R.

[0055] In addition, when the maximum corrosion rate is extracted by the particle size measuring device 101, the amount of corrosion R that progresses in one year from the maximum corrosion rate is similarly calculated. From the calculated amount of corrosion R, the power law "D=RT n ...(1)" may also be used. D is the amount of corrosion [mm], T is the age of the buried metal material [years], and n is the corrosivity evaluation value of the material. However, since the value of n is empirically said to be 0.4 to 0.6, the intermediate value of 0.5 can be used. It is possible to estimate the amount of corrosion of a buried metal material by introducing the age value, which describes how many years have passed since the buried metal material for which the amount of corrosion is to be estimated, into T in equation (1).

[0056] FIG. 9 is an example of a graph showing the amount of corrosion estimated from the results of FIGS. 5, 6, 7, and 8 versus the number of years that have passed, and is an example of a graph that diagrammatically shows equation (1), which is an empirical model for predicting the progression of corrosion.

[0057] A more detailed corrosion estimation method will be described below with reference to the flowchart in Fig. 10. First, in step S201, soil is introduced into the corrosion estimation device, and the soil is stored in the first storage container 111 of the particle size measuring instrument 101. Next, in step S202, the dryer 112 is operated for the soil stored in the first storage container 111, and a soil drying process is performed on the soil. Next, in step S203, the mixer 113 is operated for the soil that has been dried, and a mixing process is performed to remove soil debris.

[0058] Next, in step S204, the particle diameter measurement unit 114 is operated to measure particle diameters. Next, in step S205, the particle diameter calculation circuit 115 calculates a particle diameter distribution based on the measured particle diameters. Next, in step S206, the soil color measurement unit 122 measures the color of the soil in the second storage container 121. Next, in step S207, the soil color determination circuit 123 determines the measured soil color.

[0059] Next, in step S208, the estimation circuit 103 calculates the corrosion rate of the steel material buried in the measurement soil based on the results obtained by the particle size measuring instrument 101. Next, in step S209, the estimation circuit 103 calculates the corrosion rate magnification from the results obtained by the color measuring instrument 102. Next, in step S210, the estimation circuit 103 multiplies the corrosion rate value by the corrosion rate magnification to obtain a corrosion rate (corrected corrosion rate). Thereafter, in step S211, the estimation circuit 103 estimates the corrosion (corrosion curve) of the metal material buried underground from the obtained corrosion rate.

[0060] As described above, according to the present invention, the corrosion of steel materials buried in soil is estimated from the measured particle size and color measurement values, making it easy to estimate the corrosion of metal materials buried underground.

[0061] According to the present invention, by estimating soil corrosion, which is a complex corrosion system, from solid phase information alone, with a small number of tests and in a short time, corrosion estimation can be performed easily and at low cost, making it possible to realize condition-based maintenance of metal structures buried underground, and ensuring economy and safety through high efficiency.

[0062] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0063] 101...particle size measuring device, 102...color measuring device, 103...estimation circuit.

Claims

1. A particle size measurement step of measuring the particle size of the soil, A color measurement step of measuring a color measurement value related to the color of the soil, An estimation step of estimating the corrosion of the steel material embedded in the soil from the particle size and the color measurement value, comprising: In the estimation step, a corrosion rate is obtained from the particle size, a corrosion rate magnification is obtained from the color measurement value, a corrected corrosion rate is obtained by multiplying the corrosion rate by the corrosion rate magnification, and the corrosion of the steel material is estimated based on the obtained corrected corrosion rate. A corrosion estimation method.

2. In the corrosion estimation method according to Claim 1, the color measurement step is characterized by measuring a color value as the color measurement value. A corrosion estimation method.

3. A particle size measuring device for measuring the particle size of the soil, A color measuring device for measuring a color measurement value related to the color of the soil, An estimation circuit for estimating the corrosion of the steel material embedded in the soil from the particle size and the color measurement value, comprising: The estimation circuit obtains a corrosion rate from the particle size, obtains a corrosion rate magnification from the color measurement value, obtains a corrected corrosion rate by multiplying the corrosion rate by the corrosion rate magnification, and estimates the corrosion of the steel material based on the obtained corrected corrosion rate. A corrosion estimation device.

4. In the corrosion estimation device according to Claim 3, the color measuring device is characterized by measuring a color value as the color measurement value. A corrosion estimation device.

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