Method for evaluating corrosion resistance of metallic materials in environment with deposited powder or granules, method for corrosion management of structure, method for management of steel material, and method for producing structure

Abstract

To provide: a method for evaluating corrosion resistance of metallic materials, the method being simple and highly correlated with corrosion of metallic materials in a real environment with deposited powder or granules; a method for corrosion management of structures; a method for management of steel materials; and a method for producing structures.SOLUTION: The present invention provides a method for evaluating corrosion resistance of metallic materials in an environment with deposited powder or granules. The method includes: a selection step of selecting simulated powder or granules based on electrical conductivity of the powder or granules known beforehand; and a corrosion step of depositing the simulated powder or granules on the metallic materials and supplying moisture to the deposited simulated powder or granules to corrode the metallic materials. In the selection step, the simulated powder or granules are selected using a threshold value of electrical conductivity. In the corrosion step, when simulated powder or granules with an electrical conductivity less than the threshold value of electrical conductivity are employed, the moisture is made to contain anions.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating the corrosion resistance of metallic materials in an environment where powder or granular material is accumulated, a method for managing corrosion of structures, a method for managing steel materials, and a method for manufacturing structures. [Background technology]

[0002] An example of an environment where granular materials are deposited is a steel mill, specifically an environment where granular steel raw materials, i.e., coal, ore, coke, and sintered ore, are deposited singly or in a mixed state (an environment where granular steel raw materials are deposited). Another example of an environment where granular materials are deposited is the soil environment.

[0003] In environments where steel raw materials are piled up, corrosion degradation of steel materials that make up facilities and structures is becoming a problem. Corrosion degradation of steel materials used underground, such as steel pipe piles, has also been reported in soil environments when they come into contact with soil. Therefore, there is a need to evaluate the corrosivity of metal materials that make up facilities and structures used in environments where granular materials are piled up, and to appropriately manage corrosion of these facilities and structures.

[0004] A method for evaluating the corrosion resistance of metallic materials in a soil environment has been disclosed as a corrosion test method for metallic materials to appropriately evaluate the corrosivity of metallic materials in an environment where powder and granular materials are accumulated.

[0005] Patent Document 1 describes a method for evaluating the rate of general corrosion of steel material and the presence or absence of significant corrosion in localized areas of the steel material (macrocell corrosion) after a 10-year buried test of steel plate in real soil.

[0006] Patent Document 2 also discloses a soil corrosion test method for steel materials using simulated soil. Specifically, this method uses granular material that is insoluble in water and poorly soluble in acids and alkalis as the simulated soil, and adjusts the water content of the simulated soil to set the pF value to an arbitrary value. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-336463 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-75477 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the corrosion test method disclosed in Patent Document 1 has the problem that it uses actual soil and therefore cannot predict corrosion resistance when the soil is changed to another type. Another problem is that the test period is long.

[0009] On the other hand, the soil corrosion testing method using simulated soil disclosed in Patent Document 2 can evaluate the soil corrosivity of steel materials in a short period of time, but it was devised based on the fact that the degree of corrosion of steel materials in soil is closely related to the amount of free water in the soil, and it was found that it may not be possible to properly evaluate the corrosion resistance of metal materials in environments where powdery materials other than soil are accumulated.

[0010] The present disclosure has been made in view of the above, and aims to provide a simple method for evaluating the corrosion resistance of metallic materials, a method for managing corrosion of structures, a method for managing steel materials, and a method for manufacturing structures, which have a high correlation with the corrosion of metallic materials in an environment where actual powder and granular materials are accumulated. A high correlation with the corrosion of metallic materials means that the ranking of the corrosion resistance of metallic materials in an actual environment is consistent. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. [1] A method for evaluating the corrosion resistance of a metallic material in an environment where powder or granular material is deposited, comprising: a selection step of selecting a simulated powder or granular material based on the electrical conductivity of the powder or granular material that has been previously determined; a corrosion process of depositing the simulated powder or granular material on a metal material and supplying moisture to the deposited simulated powder or granular material to corrode the metal material; Equipped with In the selection step, When the electrical conductivity of the powder or granular material is equal to or greater than the boundary value of the electrical conductivity, a simulated powder or granular material is selected which has an electrical conductivity equal to or greater than the boundary value of the electrical conductivity and a potential higher than the potential of the metal material; When the electrical conductivity of the powder or granular material is less than the boundary value of the electrical conductivity, a simulated powder or granular material having an electrical conductivity less than the boundary value of the electrical conductivity; an anion based on the type of anion eluted from the powder or granule that is known in advance; In the corrosion step, when a simulated powder or granular material having an electrical conductivity lower than the boundary value of the electrical conductivity is used, the water contains the anions. A method for evaluating the corrosion resistance of metallic materials in an environment where particulate matter is accumulated. [2] When the metal material is steel, the boundary value of the electrical conductivity is 0.01 S / m; A method for evaluating the corrosion resistance of a metal material in an environment where powder or granular material described in [1] is accumulated. [3] A corrosion management method for a structure, which sets a period for inspecting or repairing a structure based on the amount of corrosion of steel obtained by the method for evaluating the corrosion resistance of metal materials in an environment where powder and granular material has accumulated, as described in [2] above. [4] A method for managing steel materials, which sets the usable life of the steel materials based on the amount of corrosion of the steel materials obtained by the method for evaluating the corrosion resistance of metal materials in an environment where powder and granular materials have accumulated, described in [2] above. [5] A method for manufacturing a structure, in which a target corrosion resistance is set in advance based on the amount of corrosion of steel material and the accumulated actual values of the service life of the steel material, and a steel material having the target corrosion resistance is selected based on the amount of corrosion of steel material obtained by the method for evaluating the corrosion resistance of metallic materials in an environment where powder and granular material are accumulated described in [2], and a structure is manufactured using the selected steel material. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide a simple method for evaluating the corrosion resistance of metal materials that is highly correlated with the corrosion of metal materials in an environment where actual powder and granular materials are accumulated. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 shows the relationship between the electrical conductivity of powder and the corrosion rate of steel. [Figure 2] FIG. 2 is a schematic diagram of a cell used to measure the electrical conductivity of powder or granular material. DETAILED DESCRIPTION OF THE INVENTION

[0014] First, the findings of the present inventors will be described. In devising a corrosion resistance evaluation method that can appropriately evaluate the corrosion resistance of metallic materials in an environment where powder and granular materials are accumulated, the corrosion mechanism of steel materials in an environment where steel raw materials from a steel mill are accumulated was first investigated.

[0015] The corrosion reaction of steel generally progresses through a combination of the following two reactions: (1) a reaction in which iron, the main component of steel, dissolves in a water film formed on the steel surface, generating electrons (anodic reaction); and (2) a reaction in which oxygen dissolved in the water film is reduced on the steel surface, consuming electrons (cathodic reaction). As described above, water, which is essential for the progression of the corrosion reaction of steel, is retained between particles and within pores that make up the powder and granular material in an environment where steel raw materials (granular material) are accumulated, and is supplied to the steel surface. Therefore, in an environment where powder and granular material are accumulated, the water-wet state persists for a longer period than in an environment without powder and granular material accumulation (general atmospheric environment), and the amount of corrosion of steel in an environment with powder and granular material accumulation is greater than in a general atmospheric environment. The present inventors conducted a detailed investigation into the factors that affect the amount of corrosion of steel in an environment with powder and granular material accumulation and found that the electrical conductivity of the powder and granular material is the main influencing factor. Specifically, when the metallic material is steel and the powder has a high electrical conductivity (here, above 0.01 S / m), we found that the corrosion rate of the steel increases significantly with increasing electrical conductivity, as shown in Figure 1. We also found that the potential of the powder is more noble than that of the steel, which is an important factor in the corrosion of steel in an environment where highly conductive powder is deposited. Based on these findings, the mechanism by which steel corrosion is accelerated in an environment where highly conductive powder is deposited is inferred as follows: In a typical atmospheric environment, electrons generated in the dissolution reaction of iron, the main component of steel, are consumed by oxygen reduction reactions on the steel surface. On the other hand, in an environment where highly conductive powder is deposited, if the potential of the powder deposited on the steel is more noble than that of the steel, electrons generated in the dissolution reaction of iron flow within the deposited powder, resulting in oxygen reduction reactions on the surface of the deposited powder as well as the steel surface, resulting in electron consumption. In other words, the cathode area is larger than in a typical atmospheric environment. As a result, it is presumed that the oxygen reduction reaction was accelerated more than in a general atmospheric environment, resulting in an increased amount of corrosion (hereinafter, this type of corrosion will be referred to as galvanic corrosion). On the other hand, if the electrical conductivity of the powder is less than 0.01 S / m, the accumulation of powder does not accelerate corrosion of steel based on the above corrosion mechanism. However, when soluble components are present in the powder accumulated on the steel surface, the anions that make up the soluble components have been found to accelerate corrosion of the steel.

[0016] Based on the above findings, the present inventors have discovered that, when evaluating the corrosion resistance of metallic materials in an environment where powder and granular materials are accumulated at a laboratory level, it is possible to evaluate the corrosion resistance of metallic materials in an environment where powder and granular materials are accumulated by selecting a simulated powder and granular material based on the electrical conductivity of the powder and granular material in the environment to be evaluated and supplying water to the simulated powder and granular material to conduct a corrosion test. Based on this discovery, the present invention has been completed after various studies.

[0017] [Methods for evaluating the corrosion resistance of metallic materials] The corrosion resistance evaluation method for a metallic material according to an embodiment of the present disclosure will be specifically described below. A method for evaluating the corrosion resistance of a metallic material according to an embodiment of the present disclosure is a method for evaluating the corrosion resistance of a metallic material in an environment where powder or granular material is accumulated, and includes a selection process for selecting a simulated powder or granular material based on the electrical conductivity of the powder or granular material, which is known in advance, and a corrosion process for depositing the simulated granular material on a metallic material and supplying moisture to the deposited simulated powder or granular material to corrode the metallic material.

[0018] (metallic material) The metallic material is not particularly limited as long as it is a metallic material that is used in the environment where the powder or granular material to be evaluated is accumulated. When the powder or granular material is a steel raw material, the facilities and structures that handle the steel raw material are often made of steel, and the present method can be suitably applied to the above-mentioned metallic materials, particularly steel.

[0019] (powder) The granular material is a granular material deposited in the environment to be evaluated, and is an aggregate composed of one or more types of granular material. The granular material may be actually deposited granular material. If 80% or more of the actually deposited granular material is composed of one type of granular material A, the granular material may be considered to be granular material A. If the actually deposited granular material is mainly composed of two types of granular material A and granular material B, the granular material may be considered to be a mixture of granular material A and granular material B in a certain ratio. For example, if the environment to be evaluated is a steel mill, granular material containing one or more of the following steel raw materials will be deposited: coal, coke, ore, and sintered ore. Therefore, the granular material may be the main deposited steel raw material, or a mixture of steel raw materials corresponding to the types and ratios of the deposited steel raw materials.

[0020] (Selection process) In the selection step, the simulated powder or granular material is selected based on the electrical conductivity of the powder or granular material. When the electrical conductivity of the powder or granule is high (above the electrical conductivity boundary value), the electrical conductivity becomes the dominant factor in the corrosion of metal materials in an environment where the powder or granule is accumulated, causing galvanic corrosion due to the powder or granule, and the corrosion of the metal material progresses. Therefore, it is appropriate to select a simulated powder or granule with an electrical conductivity above the electrical conductivity boundary value. On the other hand, when the electrical conductivity of the powder or granule is low (below the electrical conductivity boundary value), the influence of galvanic corrosion due to the powder or granule is small, and corrosion depending on the type and amount of anions eluted from the powder or granule becomes dominant. Therefore, it is appropriate to select a simulated powder or granule with an electrical conductivity below the electrical conductivity boundary value. The electrical conductivity boundary value is based on the following idea: when the relationship between the electrical conductivity of the powder or granule and the corrosion amount (or corrosion rate) of the metal material is plotted on a double logarithmic graph, the electrical conductivity at which the corrosion behavior (i.e., the slope) changes toward increasing electrical conductivity is defined as the electrical conductivity boundary value.

[0021] Furthermore, when the electrical conductivity of the powder or granule is high (above the boundary value of electrical conductivity), the potential of the simulated powder or granule must be more noble than the potential of the metallic material, because the corrosion of the metallic material will progress if the potential of the simulated powder or granule is more noble than the potential of the metallic material.

[0022] In this way, the material of the simulated powder or granular material may be selected based on the electrical conductivity of the powder or granular material.

[0023] More specifically, when the metallic material is a steel material, as shown in Figure 1, the corrosion mechanism changes when the electrical conductivity exceeds 0.01 S / m. Therefore, if the electrical conductivity of the powder or granule is 0.01 S / m or higher, a simulated powder or granule with an electrical conductivity of 0.01 S / m or higher should be selected. More preferably, a simulated powder or granule with an electrical conductivity of 0.10 S / m or higher should be selected. Using a simulated powder or granule with an electrical conductivity of 0.10 S / m or higher promotes the corrosion reaction while maintaining the corrosion mechanism of the steel, enabling the corrosion resistance of the metallic material to be evaluated in a shorter period of time. Furthermore, the potential of the simulated powder or granule must be more noble than the potential of the steel. This is because corrosion of the steel progresses when the potential of the simulated powder or granule is more noble than the potential of the steel. Although there is no particular upper limit, the potential of the simulated powder or granule is preferably 0.5 V vs. SSE or less (SSE: saturated KCl / Ag / AgCl electrode, hereinafter referred to as SSE).

[0024] On the other hand, if the electrical conductivity of the powder or granule is less than 0.01 S / m, the effect of galvanic corrosion by the powder or granule is small, and corrosion depending on the type and amount of anions eluted from the powder or granule becomes dominant. Therefore, simulated powder or granules with an electrical conductivity of less than 0.01 S / m are selected. This is because if a simulated powder or granule with an electrical conductivity of 0.01 S / m or more is selected, corrosion of the steel material will proceed mainly by a corrosion mechanism different from the corrosion mechanism in the environment to be evaluated, i.e., galvanic corrosion, making it impossible to properly evaluate corrosion resistance.

[0025] When evaluating the corrosion resistance of metallic materials other than steel, the relationship between the corrosion rate of the metallic material and the electrical conductivity of the powder or granule is investigated, as in the case of steel. For example, when plotting a double logarithmic graph where electrical conductivity is x and corrosion rate is y, the point at which the slope (log(corrosion rate y2) - log(corrosion rate y1)) / (log(electrical conductivity x2) - log(electrical conductivity x1)) changes significantly, i.e., the point at which the corrosion behavior changes, can be determined as the boundary value (threshold value) of electrical conductivity. Specifically, the boundary value can be determined, for example, by the following steps (1) to (3). (1) When the measurement points are in the range a≦x≦b, move the point of interest (x=n) from a to b, and calculate the absolute value A1 of the slope of regression line 1 (a≦x≦n) and the absolute value A2 of the slope of regression line 2 (n≦x≦b) at each position (where a and b are constants). (2) The point n when the ratio of A2 to A1 (A2 / A1) is maximum is set as the point where the slope changes sharply, that is, the boundary value of the electrical conductivity. (3) However, if the boundary value of the electrical conductivity obtained in (2) deviates from the value of the electrical conductivity at the intersection of the regression lines 1 and 2, the electrical conductivity values of both are compared, and the smaller electrical conductivity value is set as the boundary value of the electrical conductivity.

[0026] The electrical conductivity used to select the simulated powder or granular material is measured using the following method. The cell shown in the schematic diagram in Figure 2 was used to measure the electrical conductivity. Specifically, carbon steel sheets 10 (SM490A) were fixed to opposite sides of the cell, and the powder or granular material was placed inside. Pure water was then supplied so that the moisture content was 100%. The cell configuration, for example, is such that the electrodes are 30 mm or more in length and 90 mm in width, the distance between the electrodes is 55 mm, and the powder or granular material and pure water 11 are filled to a height of 30 mm. However, these values may be arbitrary. With the cell filled with (powder or granular material and pure water) 11, two carbon steel sheets 10 are used as electrodes, and the electrical resistance between the electrodes is measured using a tester. The electrical conductivity is then calculated from the electrical resistance measured above, the electrode area of the carbon steel sheets 10, and the distance between the electrodes. The reason for using carbon steel 10 here is that it is easily available and has high electrical conductivity (the electrical conductivity of carbon steel 10 is much higher than that of the powder or granular material, and does not affect the measurement results of the electrical conductivity of the powder or granular material). Here, the state of 100% moisture content is defined as follows: 20 g of the powder or granule is immersed in 200 mL of pure water for 3 days, and the weight (W (g)) of the powder or granule obtained after filtration is measured. Here, the weight increase (ΔW 20,100% (g)) is defined as the maximum amount of moisture that can be held by 20 g of the powder or granule. In other words, when the moisture content of the powder or granule is 100%, ΔW A,100% =A(g)xΔW 20,100% This refers to the state in which (g) / 20(g) of water is supplied to powder A(g).

[0027] In addition, when the powder is A (g), the water supplied is ΔW A,X% The moisture content X (%) at (g) is X (%) = (ΔW A,X% (g) / W A,100% )x100···(1)

[0028] The potential of the metallic material and the potential of the simulated powder or granule refer to the respective potentials in a water film formed on the surface of the metallic material, and the evaluation should determine whether the potential of the simulated powder or granule is more noble than the potential of the metallic material. Therefore, any method that can evaluate the relative relationship between the potential of the metallic material in water and the potential of the simulated powder or granule in water is not particularly limited. For example, one method for measuring the potential of the simulated powder or granule in water involves preparing a compact of the simulated powder or granule, using the resulting compact as a sample electrode, an SSE as a reference electrode, and measuring the potential of the compact using a 1 mol / L aqueous potassium chloride solution as the electrolyte. The method for preparing the compact is not particularly limited as long as it can be used to prepare a compact. However, if a compact cannot be prepared using only the simulated powder or granule, for example, a compact can be prepared by mixing PTFE (polytetrafluoroethylene) with the simulated powder or granule. The PTFE content can be set to the minimum amount that allows the compact to be prepared. Regarding the potential of the metallic material, the compact of the sample electrode can be replaced with the metallic material and the potential of the metallic material can be measured under the same conditions as the potential of the compact.

[0029] <Simulated powder> The simulated powder or granular material is not particularly limited in terms of its physical properties and shape, other than its electric potential and electrical conductivity. Examples of simulated powder or granular material with an electrical conductivity of 0.01 S / m or greater include peat, coke, and activated carbon. Examples of simulated powder or granular material with an electrical conductivity of less than 0.01 S / m include silica sand, zircon beads, and glass beads. The simulated powder or granular material may be a single material or a mixture of two or more materials. However, when using a mixture of two or more materials with different electrical conductivities, the mixing ratio is adjusted so that the electrical conductivity of the mixed simulated powder or granular material falls within a predetermined range. When checking the electrical conductivity of a simulated powder or granular material made of a single material or a mixture of two or more materials, the measurement can be performed with the moisture content set to 100%.

[0030] For example, when the powder is a steel raw material whose main component is coke, activated carbon can be used as the simulated powder because the electrical conductivity of the powder is 0.01 S / m or more. On the other hand, when the powder is a steel raw material whose main component is not coke but coal, ore, or sintered ore, the electrical conductivity is less than 0.01 S / m, so silica sand can be used.

[0031] The average particle size of the simulated powder and granules is preferably 2 mm or less. Setting the average particle size of the simulated powder and granules to 2 mm or less facilitates the retention of water between the simulated powder and granules, and facilitates the formation of a thin water film on the metal material surface by the meniscus. As a result, it is possible to more accurately reproduce the characteristic of corrosion in an environment where powder and granules are accumulated, namely, "maintaining a water-wet state on the metal material surface for a longer period than in a typical atmospheric environment." The reason for this longer period is as follows: In a typical atmospheric environment, the metal material surface becomes water-wet at night when the temperature is low and the relative humidity is high. In contrast, the metal material surface is dry during the daytime when the temperature is high and the relative humidity is low. In an environment where powder and granules are accumulated, the powder and granules prevent water from evaporating into the atmosphere, thereby maintaining the water-wet state on the metal material surface for a longer period than in an atmospheric environment, i.e., at least longer than in an atmospheric environment. On the other hand, the average particle size of the simulated powder and granules is preferably 45 μm or more. By making the average particle size of the simulated powder or granular material 45 μm or more, it is possible to ensure the interparticle gaps necessary for oxygen diffusion from the simulated powder or granular material surface, making it easier for the corrosion reaction of the metal material to proceed. Note that the above average particle size is the particle size measured in accordance with JIS Z 8815 6.1.

[0032] Furthermore, it is preferable to select simulated powders and granules with a low content of soluble components. If soluble components are present in the simulated powders and granules, corrosion may be accelerated by anions eluted from the simulated powders and granules, depending on the type of soluble component. When the electrical conductivity of the powders and granules in the environment to be evaluated is equal to or greater than a predetermined electrical conductivity (the boundary value of electrical conductivity), the corrosion-accelerating effect of the electrical conductivity is significant, and the corrosion-accelerating effect of the soluble components (anions) in the simulated powders and granules is small and can be ignored. On the other hand, when the electrical conductivity of the powders and granules in the environment to be evaluated is less than the predetermined electrical conductivity (the boundary value of electrical conductivity), corrosion due to the soluble components eluted from the simulated powders and granules may become the dominant factor, potentially preventing an appropriate evaluation of the corrosion resistance of the metal material. Therefore, during the selection process, it is preferable to simultaneously select anions based on the type of anions eluted from the powders and granules.

[0033] (Corrosion process) In the corrosion process, the simulated powder particles are deposited on a metal material, and water is supplied to the deposited simulated powder particles to corrode the metal material. The detailed flow of the corrosion process will be described below. First, the simulated powder or granular material is deposited on a metal material. Here, the thickness of the simulated powder or granular material from the surface of the metal material is defined as the cover thickness of the simulated powder or granular material. The cover thickness of the simulated powder or granular material is not particularly limited as long as the simulated powder or granular material is deposited on the surface of the metal material, but it is preferably 1 mm or more. By setting the cover thickness of the simulated powder or granular material to 1 mm or more, the total surface area of the simulated powder or granular material increases, i.e., the cathode area increases, and the cathode reaction is promoted. As a result, galvanic corrosion is promoted, making it possible to evaluate the corrosion resistance of the metal material in a shorter period of time. More preferably, the cover thickness of the simulated powder or granular material is 5 mm or more. On the other hand, it is preferable that the cover thickness of the simulated powder or granular material be 300 mm or less. If the cover thickness of the simulated powder or granular material exceeds 300 mm, the diffusion of oxygen supplied from the atmosphere to the metal material surface is inhibited by the simulated powder or granular material, significantly reducing the corrosion rate of the metal material. More preferably, the cover thickness of the simulated powder or granular material is 100 mm or less. As explained in the examples, the above-mentioned covering thickness is the average thickness at 10 locations. The surface of the metal material on which the simulated powder or granular material is deposited is not particularly limited, and the metal material may be placed in the simulated powder or granular material with the orientation for evaluating corrosion resistance appropriately selected depending on the target environment. Specifically, when evaluating an environment in which powder or granular material is deposited on a metal material, the evaluation surface should face up, and when evaluating a steel pipe pile or the like buried in the ground, the evaluation surface should be rotated 90° from the upright orientation.

[0034] Next, moisture is supplied to the simulated powder and granules after they have accumulated on the metal material to corrode the metal material. Here, as described above, unlike typical atmospheric environments, in environments where powder and granules are accumulated, moisture is retained between particles and within pores constituting the powder and granules due to the accumulation of powder and granules on the surface of the metal material, resulting in the supply of moisture to the metal material surface and the progression of corrosion of the metal material. Therefore, to simulate corrosion behavior that correlates with corrosion behavior in environments where powder and granules are accumulated, it is important to deposit simulated powder and granules on the surface of the metal material and supply moisture to the simulated powder and granules to corrode the metal material. In this case, the moisture content of the simulated powder and granules can be set based on the state of the powder and granules in the environment in which the powder and granules are accumulated (i.e., the moisture content of the powder and granules). For example, in soil environments, a high moisture content may be maintained due to the accumulation of rainfall or the inflow of groundwater. Even if the moisture content is high immediately after rainfall, water may be easily discharged, resulting in large fluctuations in moisture content. Therefore, the timing of water supply can be determined by measuring the changes in the moisture content of the soil environment to be evaluated. For example, in an environment where steel raw materials are piled up, a high moisture content state is maintained due to rainfall retention, etc., and then the moisture content drops to a certain lower limit due to evaporation in an environment exposed to sunlight, and then increases again if rain falls, etc. Therefore, it is only necessary to measure the change in moisture content in the environment to be evaluated and set the timing of water supply. Furthermore, when a simulated powder or granular material having an electrical conductivity less than the boundary value of the electrical conductivity is selected, it is preferable to select the anions to be supplied to the metal material based on the type of anions eluted from the powder or granular material that is known in advance, and to supply the water containing the anions to cause corrosion. Furthermore, when the electrical conductivity of the powder or granular material in the environment to be evaluated is equal to or higher than the boundary value of electrical conductivity, the promotion of corrosion by anions eluted from the powder or granular material is hardly observed, but corrosion may be caused by adding anions to the water based on the type of anions eluted from the powder or granular material.

[0035] As described above, when the electrical conductivity of the powder or granule is equal to or greater than the boundary value, the electrical conductivity of the powder or granule becomes the dominant factor in corrosion. Therefore, the corrosion resistance of the metallic material can be appropriately evaluated by using a simulated powder or granule whose electrical conductivity is equal to or greater than the boundary value. On the other hand, when the electrical conductivity of the powder or granule is less than the boundary value, the corrosion-promoting effect due to galvanic corrosion according to the electrical conductivity of the powder or granule is extremely small. However, if the powder or granule contains a component soluble in a water film, anions eluted from the powder or granule may accelerate corrosion. Therefore, to more appropriately evaluate the corrosion resistance of the metallic material in an environment where the powder or granule is accumulated, it is preferable to set the electrical conductivity of the simulated powder or granule to less than 0.01 S / m, select anions to be supplied to the metallic material based on the type of anions eluted from the powder or granule, and then add the selected anions to the water in the corrosion process. Two or more anions may be supplied depending on the evaluation environment.

[0036] The amount of anions supplied to the water in the corrosion step may be set to a value equivalent to the amount of anions eluted from the powder or granular material to be evaluated, or, for the purpose of promoting corrosion and shortening the evaluation time, may be determined based on the relationship between the amount of anions eluted from the powder or granular material to be evaluated and the corrosion resistance of the metal material. For example, when the amount of anions is set to a value equivalent to the amount of anions eluted from the powder or granular material to be evaluated, it may be determined by the following method.

[0037] First, the amount of anions eluted from the powder or granule to be evaluated into water is measured. Specifically, 20 g of powder or granule is immersed in 200 mL of pure water for three days, and the filtrate obtained after filtration is analyzed by ICP or ion chromatography. The amount of anions contained per weight of powder or granule, M2 (mol / kg), is calculated from the obtained anion concentration, M1. Next, the amount of anions eluted from the powder and attached to the metal surface per unit area, M3 (mol / cm 2 Here, when the cover thickness of the simulated powder is h (cm), the anion adhesion amount M3 (mol / cm) is determined so that the same amount of anions is supplied to the simulated powder as the amount of anions that is supplied when the powder is deposited on the surface of a metal material at a cover thickness of h (cm). 2 ) is determined. 2 ) is the bulk density of the powder or granular material, ρ (kg / cm 3 ), it is calculated using the following formula (2). M3(mol / cm 2 ) = M2 (mol / kg) × ρ (kg / cm 3 )×h(cm)···(2) The resulting anion attachment amount M3 (mol / cm 2 ), the amount of anions to be added to the water supplied in the corrosion process, i.e., the anion concentration M4 (mol / L) in the water supplied in the corrosion process, is determined. Here, it is assumed that the total amount of anions contained in the amount of water V (L) supplied to the simulated powder deposited on the metal material surface to achieve a specified moisture content is supplied to the metal material surface, and the anion concentration M4 (mol / L) in the water supplied in the corrosion process is calculated using the following equation (3). M4 (mol / L) = M3 (mol / cm 2 )×S(cm 2 ) / V(L)···(3) Here, S(cm 2 ) is the opening area of the container used to deposit the simulated powder on the surface of the metal material in the corrosion process.

[0038] An aqueous solution to which anions have been added so as to achieve the anion concentration M4 thus obtained is prepared, and the resulting aqueous solution may be used as the water to be supplied in the corrosion step. The amount of anions (mol / cm) dissolved into water from the powder or granules obtained above 2 ) is an example of the measurement required when the surface to be evaluated is installed facing upward.

[0039] For example, when the simulated powder was steel, it was found that sulfate ions, bicarbonate ions, and chloride ions were mainly eluted from the steel raw material. Furthermore, an evaluation of the relationship between the corrosion behavior of steel and the amount of each anion attached showed that sulfate ions have a large effect on steel corrosion, with an average of 10 ―7 mol / cm 2 Therefore, when the simulated powder is mainly composed of materials other than coke, powder with an electrical conductivity of less than 0.01 S / m is used, and sulfate ions are applied to the steel surface at a rate of 10 -7 mol / cm 2 To achieve this, sulfate ions may be added to the water supplied in the corrosion process.

[0040] The water used for the water supply is preferably pure water, specifically distilled water or ion-exchanged water. By reducing the impurities in the water, it is possible to reduce the effect of ions contained in the water supplied to the simulated powder on the corrosion resistance of the metal material, allowing for highly reproducible and appropriate evaluation of the corrosion resistance of the metal material.

[0041] The environment in which the metallic material is placed after the simulated powder or granular material has been deposited may be selected depending on the environment in which the powder or granular material to be evaluated has been deposited.

[0042] For example, if the environment in which the powder or granular material to be evaluated is an environment in which steel raw materials are deposited, such as in a steel mill, the deposited steel raw materials are surrounded by an atmospheric environment and are affected by changes in temperature and relative humidity (temperature and humidity) between day and night. Therefore, a combined cycle test or the like can be performed by placing the metal material on which the simulated powder or granular material has been deposited in a testing machine that can realize combined cycle test conditions simulating the changes in temperature and humidity between day and night. Specifically, the metal material on which the simulated powder or granular material has been deposited is placed in a thermo-hygrostat, and a known test method, such as the wet-dry cycle conditions disclosed in Patent Document 3, can be performed (the dew point fluctuation between the drying step and the wetting step is set to within ±5°C, the drying step time is equal to or longer than the wetting step time, and the drying step is performed at a temperature of 40 to 60°C, a relative humidity of 40% or less, and a holding time of 2 to 12 hours, and the wetting step is performed at a temperature of 20 to 60°C, a relative humidity of 80 to 96%, and a holding time of 2 to 12 hours).

[0043] Furthermore, if the environment in which the powder or granular material to be evaluated is deposited is a soil environment, although the surrounding soil is an atmospheric environment, the soil environment (inside the soil) often does not exhibit a day-night temperature and humidity change cycle, so the metal material after the deposition of the simulated powder or granular material can be placed in a testing machine that can realize an environment with constant temperature and humidity conditions, and the temperature and humidity can be kept constant. The specific temperature and relative humidity values can be set appropriately depending on the soil environment to be evaluated. [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-77260

[0044] (Corrosion resistance evaluation) The method for evaluating the corrosion resistance of metallic materials is not particularly limited as long as it allows the ranking of corrosion resistance to be determined. For example, corrosion resistance can be evaluated by observing the state of corrosion on the surface of the metallic material after a predetermined period of time, or by quantitatively measuring the amount of corrosion, which is the difference between the mass of the metallic material before the test and the mass of the metallic material after the test after the rust has been removed. In other words, the amount of corrosion can be evaluated as the amount of metallic material that has turned into rust, and the superiority or inferiority of corrosion resistance is determined based on the amount of corrosion.

[0045] <Corrosion control methods for structures> The method for evaluating the corrosion resistance of a metallic material according to the embodiment can also be applied to a method for managing corrosion of a structure, in which a period for inspecting or repairing the structure is set based on the amount of corrosion of the steel material obtained by the method for evaluating the corrosion resistance of a metallic material.

[0046] In the corrosion management method for a structure according to the embodiment, the corrosion level of a steel material used in the structure in an environment where, for example, powdered steel raw materials, such as coal, ore, coke, and sintered ore, are deposited singly or in a mixed state in a steelworks or the like where the structure is installed or is installed, is evaluated using a corrosion resistance evaluation method for metallic materials. This makes it possible to evaluate the corrosion level of a steel structure made of steel materials.

[0047] The corrosion management method for structures according to the embodiment described above enables corrosion management, which manages the corrosion state of steel structures for each environment. Specifically, the corrosion state of a structure can be reflected in the setting of inspection periods and repair periods, allowing corrosion inspections and repairs associated with corrosion to be planned and efficiently set, which can be useful for cost reduction. Furthermore, it can be useful for preventing breakdowns and disasters caused by the collapse of equipment and buildings. Furthermore, the corrosion management method for structures according to the embodiment can be used to design corrosion allowances using data on the amount of corrosion, which can be useful for reducing investment.

[0048] <Steel material management method> The corrosion resistance evaluation method for a metallic material according to the embodiment can also be applied to a steel management method, in which the usable life of the steel is set based on the amount of corrosion of the steel.

[0049] According to the steel management method of the embodiment described above, it is possible to evaluate the amount of corrosion of steel materials that make up structures used in environments where powdered steel raw materials, such as coal, ore, coke, and sintered ore, are deposited alone or in a mixture at steelworks where the structures are installed, thereby optimizing corrosion management of steel structures.

[0050] <Method of manufacturing the structure> The corrosion resistance evaluation method for metallic materials according to the embodiment can also be applied to a method for manufacturing a structure. In this case, in the method for manufacturing a structure according to the embodiment, a steel material having a predetermined corrosion resistance is selected based on the corrosion rate of the steel material in an environment where powdered steel raw materials, i.e., coal, ore, coke, and sintered ore, are deposited singly or mixedly in a steelworks or other facility where the structure is to be installed, and the structure is manufactured using the selected steel material. Having the predetermined corrosion resistance refers to a state in which the steel material has corrosion resistance that allows it to be used until a predetermined target service life is reached. The target corrosion resistance is set in advance based on the accumulated actual values of the corrosion rate of the steel material and the service life of the steel material, and a steel material having the predetermined corrosion resistance is selected based on the obtained corrosion rate of the steel material using this test method.

[0051] According to the method for manufacturing a structure according to the embodiment described above, it is possible to manufacture a structure that has a predetermined corrosion resistance in an environment where powdered steel raw materials, i.e., coal, ore, coke, and sintered ore, are deposited alone or in a mixed state in a steelworks or the like where the structure is to be installed. [Example]

[0052] Hereinafter, the present invention will be specifically explained with reference to examples in which steel is used as the metallic material, but the present invention is not limited to these examples. Example 1 (Environment where granular material is accumulated) In Example 1, an environment in which granular iron and steel raw materials are piled up in a steelworks was selected as the environment in which granular materials are piled up to be evaluated. The environment in which granular iron and steel raw materials are piled up selected in Example 1 (location (1)) is a location where the iron and steel raw materials are mainly coke.

[0053] (metallic material) In Example 1, three types of flat steel materials (steel material A, steel material B, and steel material C) shown in Table 1 were used as the metal materials, and test pieces for evaluating corrosion resistance were prepared. First, steel materials A to C were cut to obtain test pieces with a width of 70 mm and a length of 150 mm. Next, the obtained test pieces were immersed in a mixed solvent of toluene and ethanol, and degreased by ultrasonic cleaning, and the weight of the test pieces was measured. Thereafter, the back and side surfaces of the surface to be evaluated of the test pieces were covered with masking tape, and the area (exposed area) for evaluating corrosion resistance was set to 6.0 × 10 3 mm 2 (50mm x 120mm).

[0054] (powder) The powder or granular material in Example 1 was powder or granular material (1) collected from a location (1) selected as an environment where the powder or granular material to be evaluated had accumulated. The electrical conductivity and potential in water of the powder / granule (1) were measured using the methods described in the embodiment. The amount of anions M2 (mol / kg) in the soluble components of the powder / granule (1) was also measured using the method described in the embodiment. The results are shown in Table 2.

[0055] (Selection process) In Example 1, steel is used as the metallic material. The boundary value of electrical conductivity when steel is used as the metallic material is determined as the electrical conductivity at which the corrosion behavior (i.e., the slope) changes as the electrical conductivity increases when the relationship between the electrical conductivity of various powders and the corrosion amount (or corrosion rate) of the metallic material is plotted on a double logarithmic graph. That is, as shown in Figure 1, the boundary value of electrical conductivity for steel is 0.01 S / m. Therefore, to evaluate the corrosion resistance of steel at location (1), we selected simulated powders with an adjusted ratio of activated carbon and silica sand mixtures to achieve an electrical conductivity of 0.01 S / m or higher, which is the boundary value for electrical conductivity of steel, based on the electrical conductivity of powder (1) of 0.15 S / m. It was also confirmed that the potential of the selected simulated powders was more noble than the potential of the steel (Table 3, Nos. 1–4 and 6–9). For comparison, we also conducted an evaluation using silica sand, whose electrical conductivity is less than the boundary value for electrical conductivity of steel (0.01 S / m) (Table 3, No. 5). The electrical conductivities, potentials in water, and average particle sizes of the simulated silica sand and the activated carbon / silica sand mixture are shown in Table 3. The potentials in water of the test specimens Steel A, Steel B, and Steel C are also shown in Table 3. The electrical conductivity and electric potential in water were measured using the methods described in the embodiments. The average particle size of the simulated powder or granular material was as follows. Sieving was performed in accordance with JIS Z 8815 6.1 (dry sieving test). Sieving was performed using sieves with larger openings, and the opening of the sieve where 50% or more of the total mass remained on the sieve was defined as the average particle size.

[0056] (Corrosion process) First, the selected simulated powder or granule was deposited on the surface of the test specimen. Specifically, a container (effective inner diameter: width 299 mm x depth 196 mm x height 300 mm, material: polypropylene) was prepared, and the simulated powder or granule was poured into the container to a height of 37 mm. The resulting test specimen was placed on the simulated powder or granule with the surface to be evaluated facing upward, and the simulated powder or granule was then deposited on the test specimen until the cover thickness of the simulated powder or granule was reached as shown in Table 3. The cover thickness was measured at 10 points, and the average value of the 10 points was calculated.

[0057] Next, moisture was supplied to the simulated powder and granules after they had been piled up, and the container was placed in a constant temperature and humidity chamber to corrode the test piece.

[0058] Specifically, because the piled steel raw materials at location (1) were surrounded by an atmospheric environment, the container containing the simulated powder and granules was placed in a constant temperature and humidity chamber capable of conducting a combined cycle test simulating the temperature and humidity change cycle during day and night. The combined cycle test consisted of a drying process (temperature: 40°C, relative humidity: 35% RH, holding time: 6 hours), a wetting process (temperature: 25°C, relative humidity: 95% RH, holding time: 6 hours), a transition process 1 from the drying process to the wetting process (transition time: 6 hours), and a transition process 2 from the wetting process to the drying process (transition time: 6 hours). One cycle consisted of the drying process → transition process 1 → wetting process → transition process 2. In this example, 28 cycles of testing were conducted, and corrosion resistance was evaluated based on the amount of corrosion on the test specimens. However, the temperature and relative humidity were continuously changed during the transition process.

[0059] In addition, water is supplied so that the water content is 100% before the start of the cycle, and the total mass w of the container containing the simulated powder, water, and test specimen is 100 After measuring the mass (g), the container was placed in the constant temperature and humidity chamber. After each completion of the transition process 2, the container was taken out of the constant temperature and humidity chamber, the mass w of the container was measured, and the moisture content C M The container mass was measured in a short time, and no time was set aside in the cycle for weight measurement. C M (%)=1‐{w 100 (g)-w(g)} / W(g) W (g) is the mass of water initially supplied to make the moisture content 100%. After each cycle, if the moisture content calculated by the above method was less than 70%, moisture was supplied so that the moisture content reached 100%, and the container was then placed back in the thermo-humidistat chamber. This reproduces the behavior in which the moisture content reaches 100% after rainfall, and if there is a period of no rainfall, it decreases to about 70%, after which the rate of decrease slows and no significant decrease is observed, and then the moisture content returns to 100% with the next rainfall.

[0060] <Moisture> Distilled water was used as the moisture and was supplied during the corrosion process. Furthermore, since sulfate ions were mainly detected as a soluble component in powder (1), a test was also conducted in which distilled water to which sulfate ions had been added was used to supply water during the corrosion process (Table 3, No. 4). Sulfate ions were supplied using sodium sulfate. The concentration of sulfate ions was calculated by the amount of sulfate ions in powder (1), M2(SO4 2- ) (mol / kg), using the above equations (2) and (3), M4(SO4 2- ) (mol / L) was calculated and determined. S (cm 2 ) is (299 x 196) mm 2 and V(L) was the amount at which the moisture content determined by the above method for each simulated powder / granule was 100%.

[0061] (Corrosion resistance evaluation) The corrosion resistance of steel materials was evaluated by the amount of corrosion. Three specimens were tested under each condition, and the average corrosion depth of the three specimens was recorded as the corrosion depth. Specifically, after the test, the masking tape was removed from the back and sides of each specimen. The specimen was then immersed in a pickling solution containing concentrated hydrochloric acid and ion-exchanged water (volume ratio: 1:1) with 3.5 g / L of hexamethylenediamine added as an inhibitor to completely remove corrosion products. The specimen was then neutralized by immersion in a sodium bicarbonate aqueous solution, dried in a hot air oven, and weighed. The average corrosion depth (mm) was calculated from the difference between the weight of the specimen before and after pickling (weight loss) using the following formula (4). Here, the corrosion of the specimens was assumed to be uniform. The average corrosion depth of the three specimens was then calculated and recorded as the corrosion depth. The resulting corrosion depth is shown in Table 3. Average corrosion depth (mm) = Weight loss (g) / Exposed area of test piece (mm 2 ) / Density of test piece (g / mm 3 )···(4) To determine whether corrosion resistance highly correlated with corrosion of metallic materials in an actual environment with accumulated powder and granular material was achieved, three specimens each of steel A, B, and C were placed at location (1) for 12 months, and the amount of corrosion of steel A, B, and C was evaluated, and a judgment was made as to whether the ranking of the amount of corrosion could be reproduced. The ranking of the amount of corrosion of the steel at location (1) when placed at the above location (1) for 12 months was (high) steel A > steel B > steel C (low). If the ranking of the amount of corrosion of the steel was the same as when placed at the above location (1) for 12 months, the corrosion resistance evaluation results were judged to be consistent, and if the ranking differed, it was judged to be inconsistent.

[0062] In Example 1, the electrical conductivity of the powder / granular material (1) (0.15 S / m) is equal to or greater than the boundary value (0.01 S / m) for electrical conductivity of steel. Therefore, when a simulated powder / granular material having an electrical conductivity of 0.01 S / m or greater and a potential higher than the potential of the test piece was selected, the corrosion resistance evaluation results were consistent as shown in Nos. 1 to 4 and 6 to 9 in Table 3. However, when a simulated powder / granular material having an electrical conductivity of less than 0.01 S / m was selected, the corrosion resistance evaluation results were inconsistent as shown in No. 5 in Table 3. From this, it can be seen that by selecting an appropriate simulated powder / granular material based on the electrical conductivity of the powder / granular material, corrosion behavior highly correlated with corrosion of metallic materials in an environment where actual powder / granular material is deposited can be evaluated, and corrosion resistance can be appropriately evaluated. Furthermore, when the electrical conductivity is 0.01 S / m or higher, the results of Nos. 3 and 4 in Table 3 show that even when anions eluted from powder or granular material are supplied to the water, corrosion is promoted while the corrosion resistance evaluation results remain consistent.

[0063] <Example 2> (Evaluation environment) In Example 2, an environment in which powdered and granular steel raw materials are piled up in a steelworks was selected as the environment in which the powdered and granular steel raw materials are piled up (evaluation target environment) to be evaluated. The environment in which the steel raw materials are piled up selected in Example 2 (location (2)) is a location where the steel raw materials are mainly composed of steel raw materials other than coke.

[0064] (metallic material) In Example 2, a test piece prepared under the same conditions as in Example 1 was used as the metal material.

[0065] (powder) The powder or granular material in Example 2 was powder or granular material (2) collected from a place (2) selected as an environment where the powder or granular material to be evaluated had accumulated. The electrical conductivity and potential in water of the powder / granule (2) were measured using the methods described in the embodiment. The amount of anions M2 (mol / kg) in the soluble components of the powder / granule (2) was also measured using the method described in the embodiment. The results are shown in Table 2.

[0066] (Selection process) In Example 2, steel was used as the metallic material. The boundary value of electrical conductivity when steel was used as the metallic material was determined as the electrical conductivity at which the corrosion behavior (i.e., the slope) changed as the electrical conductivity increased when the relationship between the electrical conductivity of various powders and the corrosion amount (or corrosion rate) of the metallic material was plotted on a double logarithmic graph. That is, as shown in Figure 1, the boundary value of electrical conductivity for steel was 0.01 S / m.

[0067] Therefore, to evaluate the corrosion resistance of steel at location (2), we selected simulated powders and granules with an electrical conductivity of less than 0.01 S / m, or simulated powders and granules with an activated carbon and silica sand mixture adjusted to achieve an electrical conductivity of less than 0.01 S / m, based on the electrical conductivity of 0.008 S / m for powder and granules (2). These simulated powders and granules were selected based on the electrical conductivity of 0.008 S / m for steel, which is the boundary value for electrical conductivity of less than 0.01 S / m (Table 3, Nos. 10–14). For comparison, we also conducted an evaluation using a mixture of activated carbon and silica sand, with an electrical conductivity above the boundary value for electrical conductivity of 0.01 S / m for steel (Table 3, No. 15). The electrical conductivity, underwater potential, and average particle size of the simulated powders and granules, including the silica sand and activated carbon / silica sand mixture, are shown in Table 3. The underwater potentials of the test specimens, Steels A, B, and C, are also shown in Table 3. The electrical conductivity and electric potential in water were measured using the methods described in the embodiments. The average particle size of the simulated powder or granular material was as follows. Sieving was performed in accordance with JIS Z 8815 6.1 (dry sieving test). Sieving was performed using sieves with larger openings, and the opening of the sieve where 50% or more of the total mass remained on the sieve was defined as the average particle size.

[0068] (Corrosion process) First, the selected simulated powder was deposited on the test piece under the same deposition conditions as in Example 1.

[0069] Next, moisture was supplied to the simulated powder and granules after they had been piled up, and the container was placed in a constant temperature and humidity chamber to corrode the test piece. Specifically, since the area around the piled steel raw materials at location (2) was an atmospheric environment, the container after the piled powder and granules were placed in a constant temperature and humidity chamber in which a combined cycle test simulating the temperature and humidity change cycle between day and night could be performed. The combined cycle test conditions were the same as those in Example 1. The conditions for supplying water were the same as in Example 1.

[0070] <Moisture> Distilled water was used as the moisture and was supplied during the corrosion process. In addition, sulfate ions, chloride ions, and bicarbonate ions were detected as soluble components in the powder (2), so distilled water to which sulfate ions or chloride ions had been added was used to supply water in the corrosion process. Sulfate ions were supplied by sodium sulfate. Chloride ions were supplied by sodium chloride. The concentration of sulfate ions was calculated by the amount of sulfate ions in the powder (2), M2(SO4 2- ) (mol / kg), using the above equations (2) and (3), M4(SO4 2- ) (mol / L) was calculated and determined. Similarly, the chloride ion concentration was determined by calculating the amount of chloride ions in the powder (2), M2 (Cl - ) (mol / kg), using the above equations (2) and (3), M4(Cl - ) (mol / L) was calculated and determined. S (cm 2 ) is (299 x 196) mm 2 and V(L) was the amount at which the moisture content determined by the above method for each simulated powder / granule was 100%.

[0071] (Corrosion resistance evaluation) The corrosion resistance of the steel material was evaluated based on the amount of corrosion. The evaluation conditions were the same as in Example 1. To determine whether corrosion resistance highly correlated with corrosion of metallic materials in an actual environment with accumulated powder and granular material was achieved, three specimens each of steels A, B, and C were placed at location (2) for 12 months, and the amount of corrosion of steels A, B, and C was evaluated, and a judgment was made as to whether the ranking of corrosion amounts could be reproduced. The ranking of corrosion amounts of steels at location (2) after 12 months of placement was (high) steel A > steel C > steel B (low). If the ranking of corrosion amounts of steels was the same as when placed at location (2) for 12 months, the corrosion resistance evaluation results were deemed to be consistent, and if the ranking differed, it was deemed to be inconsistent.

[0072] In Example 2, the electrical conductivity of the powder / granular material (2) (0.008 S / m) was less than the boundary value for electrical conductivity (0.01 S / m) for steel materials. Therefore, when a simulated powder / granular material having an electrical conductivity of less than 0.01 S / m was selected and anions eluted from the powder / granular material were added to the water to be supplied, the corrosion resistance evaluation results were consistent as shown in Nos. 10 to 14 in Table 3. However, when a simulated powder / granular material having an electrical conductivity of 0.01 S / m or more was selected, the corrosion resistance evaluation results were inconsistent as shown in No. 15 in Table 3. From this, it can be seen that by selecting an appropriate simulated powder / granular material based on the electrical conductivity of the powder / granular material and adding anions eluted from the powder / granular material to the water to be supplied, it is possible to evaluate corrosion behavior that is highly correlated with the corrosion of metallic materials in an environment where actual powder / granular material is deposited, and thus it is possible to appropriately evaluate corrosion resistance.

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3] [Explanation of symbols]

[0076] 10 Carbon steel 11 Powder + pure water

Claims

1. A method for evaluating corrosion resistance of a metallic material in an environment where powder or granular material is accumulated, comprising: a selection step of selecting a simulated powder or granular material based on the electrical conductivity of the powder or granular material that has been previously determined; a corrosion process of depositing the simulated powder or granular material on a metal material and supplying moisture to the deposited simulated powder or granular material to corrode the metal material; Equipped with In the selection step, When the electrical conductivity of the powder or granular material is equal to or greater than the boundary value of the electrical conductivity, a simulated powder or granular material is selected which has an electrical conductivity equal to or greater than the boundary value of the electrical conductivity and a potential higher than the potential of the metal material; When the electrical conductivity of the powder or granular material is less than the boundary value of the electrical conductivity, a simulated powder or granular material having an electrical conductivity less than the boundary value of the electrical conductivity; an anion based on the type of anion eluted from the powder or granule that is known in advance; In the corrosion step, when a simulated powder or granular material having an electrical conductivity lower than the boundary value of the electrical conductivity is used, the water contains the anions. A method for evaluating the corrosion resistance of metallic materials in an environment where particulate matter is accumulated.

2. When the metal material is a steel material, the boundary value of the electrical conductivity is 0.01 S / m. A method for evaluating corrosion resistance of a metallic material in an environment where the powder or granular material according to claim 1 is accumulated.

3. A corrosion management method for a structure, which sets a period for inspecting or repairing a structure based on the amount of corrosion of steel obtained by the method for evaluating the corrosion resistance of metal materials in an environment where powder or granular material has accumulated as described in claim 2.

4. A method for managing steel materials, which determines the usable life of the steel materials based on the amount of corrosion of the steel materials obtained by the method for evaluating the corrosion resistance of metallic materials in an environment where powder or granular material has accumulated as set forth in claim 2.

5. A method for manufacturing a structure, comprising: setting a target corrosion resistance in advance from accumulated actual values of the amount of corrosion of a steel material and the useful life of the steel material; selecting a steel material having the target corrosion resistance based on the amount of corrosion of the steel material obtained by the method for evaluating the corrosion resistance of metallic materials in an environment where powder or granular material is accumulated as described in claim 2; and manufacturing the structure.

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