JP2011247642A - Method of estimating corrosion state of steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an estimation method capable of accurately and easily estimating a corrosion state when estimating the corrosion state of a steel material in a predetermined composition in a predetermined atmospheric environment.SOLUTION: The estimation method comprises: a steel corrosion index calculation process of calculating the steel corrosion index of the steel material from the amount of two or more elements included in the steel material to be an estimation object; an environmental corrosion index calculation process of calculating the environmental corrosion index of the atmospheric environment from two or more environmental factors indicating the state of the atmospheric environment in which the steel material to be the estimation object is used; and an estimation process of estimating the corrosion state of the steel material to be the estimation object, for a boundary obtained from the relationship of the steel corrosion index and the environmental corrosion index calculated beforehand and the corrosion state, depending on in which area divided by the boundary the steel material corrosion index and the environmental corrosion index are positioned.

Description

  The present invention relates to a method for estimating a corrosion state of a steel material that estimates a corrosion state of a steel material used in a predetermined atmospheric environment, that is, a state of rust generated on the surface of the steel material.

In steel structures such as bridges, steel materials having various compositions are used depending on required mechanical properties and the atmospheric environment of the intended use location. Here, when the steel material is used in an atmospheric environment where it is difficult to corrode, rust (stable rust) serving as a protective film is uniformly generated on the surface of the steel material, and corrosion of the steel material is suppressed. Accordingly, since the steel material can be used for a long time without causing a problem in landscape, maintenance such as corrosion resistance treatment can be minimized in maintaining the steel material.
On the other hand, when the steel material is used in an atmospheric environment where the steel material is easily corroded, the rust generated on the surface of the steel material is peeled off in layers. Therefore, it causes a problem on the landscape and makes it difficult to use the steel material for a long time, so that maintenance such as corrosion resistance treatment is frequently required.

  The corrosion state of such steel materials, that is, the ability to generate rust (stable rust) is determined by the balance between the corrosion resistance (weather resistance) of the steel materials and the atmospheric environment of the intended use location. It is necessary to select a steel material having necessary and sufficient corrosion resistance (weather resistance) according to the environment.

In view of the above circumstances, many methods for estimating the corrosion state and the amount of corrosion of steel materials have been proposed.
For example, Patent Document 1 discloses a method for predicting the rust level of an unpainted weather-resistant steel bridge using bridge structure data, terrain data of bridge positions, and the like. Patent Document 2 discloses a method for evaluating the degree of rust stabilization from the composition and amount of the chemical component of the amorphous part contained in the rust generated on the surface of the steel material.

JP 2007-39970 A (Claim 1) JP 2002-310889 A (Claim 1)

However, since the corrosion resistance (weather resistance) of the steel material is not considered in the first place, the method according to Patent Document 1 cannot accurately predict the corrosion state of the steel material.
In addition, the method according to Patent Document 2 needs to analyze the chemical component of rust generated on the surface of the steel material to be measured. However, since the chemical component of rust changes with time, accurate evaluation is required. In order to do so, it is necessary to expose the steel to the atmospheric environment for a long period of months to years. Therefore, when it was going to estimate the corrosion state of steel materials by the said method, there existed a problem that it took very long time and was not realistic.

  The present invention has been made in view of the above problems, and its object is to provide an estimation method that can easily estimate the corrosion state of a steel material having a predetermined composition in a predetermined atmospheric environment. There is.

  The present inventors, when using a steel material having a predetermined composition in a predetermined atmospheric environment, an index (steel material) representing the corrosion resistance of the steel material determined by using the amount of Cu, Ni, Cr, Ti, etc. contained in the steel material Corrosion index Km) and two indicators of environmental corrosivity (environmental corrosion index Ke) determined using environmental factors such as annual average temperature, annual average humidity, and the amount of electrolysis deposited on the steel surface. Thus, the present inventors have found that it is possible to predict whether or not stable rust generated on the surface of the steel material will cause peeling.

In order to solve the above-mentioned problems, the method for estimating the corrosion state of a steel material according to the present invention includes a steel material corrosion index indicating the ease of corrosion of the steel material from the viewpoint of the properties of the steel material itself (such as the amount of elements contained in the steel material). And the environmental corrosion index indicating the susceptibility to corrosion of the steel from the characteristics of the atmospheric environment in which the steel is used (annual average temperature, annual average humidity, etc.) A corrosion state estimation method for estimating the corrosion state of the steel material, the steel material corrosion index calculating step for calculating the steel material corrosion index of the steel material from the amount of two or more elements contained in the steel material to be estimated, An environmental corrosion index calculating step of calculating an environmental corrosion index of the atmospheric environment from two or more environmental factors indicating the state of the atmospheric environment in which the steel material to be estimated is used, and a plurality of atmospheric environments having different environmental corrosion indexes In said steel material When a plurality of steel materials having different corrosion indexes are used, the steel material corrosion is compared with the boundary obtained from the relationship between the steel material corrosion index, the environmental corrosion index, and the corrosion state calculated in advance by observing the corrosion state of each steel material. An estimation step of estimating the corrosion state of the steel material to be estimated according to which region the steel material corrosion index and the environmental corrosion index calculated by the index calculation step and the environmental corrosion index calculation step are located in the boundary. It is characterized by including.
Moreover, it is preferable that the said corrosion state is the presence or absence of peeling of the rust formed in the surface of the said steel material in the corrosion state estimation method of the steel material which concerns on this invention.

  As described above, the method for estimating the corrosion state of the steel material according to the present invention was calculated by the steel material corrosion index calculation step and the environmental corrosion index calculation step based on the relationship between the steel material corrosion index and the environmental corrosion index calculated in advance. By applying the steel material corrosion index and the environmental corrosion index, the corrosion state of the steel material can be easily estimated. Therefore, it is possible to estimate the corrosion state of a steel material even in a steel material having a composition that has never been subjected to a corrosion experiment or the like, or even in an atmospheric environment that has not actually been subjected to a corrosion experiment. . That is, in estimating the corrosion state of the steel material to be estimated, a corrosion experiment or the like of the steel material becomes unnecessary.

  In the method for estimating the corrosion state of a steel material according to the present invention, the steel material corrosion index is preferably a value calculated from two or more kinds of Cu, Ni, Cr and Ti contained in the steel material. . In the method for estimating the corrosion state of a steel material according to the present invention, the steel material corrosion index is calculated by a linear function having two or more kinds of Cu, Ni, Cr and Ti contained in the steel material as variables. It is preferable.

  As described above, the method for estimating the corrosion state of a steel material according to the present invention has a significant effect on the corrosion state of the steel material (whether rust generated on the steel material surface is stably formed as a protective layer or peels off in layers). Since the steel material corrosion index calculated based on the addition amount of Cr, Ti is used, the corrosion state of the steel material can be accurately estimated.

  Further, in the method for estimating the corrosion state of a steel material according to the present invention, the environmental corrosion index is calculated by a calculation formula using two or more kinds of annual average temperature, annual average humidity, and attached electrolytic mass in the atmospheric environment as variables. The attached electrolytic mass is preferably the amount of electrolyte that adheres to the unit area of the steel material during a unit time.

  As described above, the method for estimating the corrosion state of a steel material according to the present invention has an annual average temperature that greatly affects the corrosion state of the steel material (whether rust generated on the surface of the steel material is stably formed as a protective layer or peels into a layer). Further, since the environmental corrosion index calculated based on two or more of the annual average humidity and the attached electrolytic mass is used, the corrosion state of the steel material can be estimated more accurately.

  Further, in the method for estimating the corrosion state of a steel material according to the present invention, when the environmental corrosion index calculated in the environmental corrosion index calculation step is calculated using at least the attached electrolytic mass, the environmental corrosion index calculation step The attached electrolytic mass used for calculating the environmental corrosion index is determined by calculating the amount of the electrolyte from the amount of the electrolyte contained in the aqueous solution attached to each steel material after a plurality of steel materials are installed at different angles with respect to the horizontal direction. The electrolytic mass is determined for each angle with respect to the horizontal direction of the steel material, the electrolytic mass measurement step for determining the correspondence between the attached electrolytic mass and the angle with respect to the horizontal direction of the steel material, and the correspondence relationship determined by the electrolytic mass measurement step. From the inside, an electrolytic mass selection step of selecting the adhered electrolytic mass according to the angle with respect to the horizontal direction of the steel material to be estimated is calculated from It is preferable that.

  As described above, the corrosion state estimation method for steel materials according to the present invention calculates the adhesion electrolysis mass for each installation angle (angle with respect to the horizontal direction) of the steel materials, and therefore more accurately estimates the corrosion state of the steel materials. Can do.

  According to the method for estimating the corrosion state of a steel material according to the present invention, in order to estimate the corrosion state of the steel material to be estimated, a corrosion experiment or the like of the steel material becomes unnecessary, and therefore the corrosion state of the steel material can be simply estimated. Can do.

It is a graph which shows the relationship between a steel material corrosion index, an environmental corrosion index, and a corrosion state.

  Hereinafter, the form for implementing the corrosion state estimation method of the steel materials concerning this invention is demonstrated in detail, referring drawings suitably.

[Steel]
The steel material to be estimated by the method for estimating the corrosion state of the steel material according to the present invention may have any shape and size as long as the corrosion state needs to be estimated.
The steel material to be measured may be used for any structure used in the atmospheric environment. For example, a steel material used for a bridge exposed to the air for a long period of time may be used. It becomes a target.

[Atmospheric environment]
Also, the atmospheric environment in which the steel material is used is not particularly limited, and any atmospheric environment may be used as long as the annual average temperature and the annual average humidity are known (or can be measured).
For example, the method for estimating the corrosion state of a steel material according to the present invention can be used regardless of the distance from the coast or the riverbank.

[Method of estimating the corrosion state of steel]
Next, an embodiment of a steel material corrosion state estimation method according to the present invention will be described with reference to FIG.
The steel material corrosion state estimation method according to the present embodiment includes a steel material corrosion index calculating step of calculating a steel material corrosion index of the steel material from the amount of two or more elements contained in the steel material to be estimated, and the estimation object. An environmental corrosion index calculating step for calculating an environmental corrosion index of the atmospheric environment from two or more environmental factors indicating the state of the atmospheric environment in which the steel material is used, and the steel materials in a plurality of atmospheric environments having different environmental corrosion indexes When a plurality of steel materials having different corrosion indexes are used, the steel material corrosion is compared with the boundary obtained from the relationship between the steel material corrosion index, the environmental corrosion index, and the corrosion state calculated in advance by observing the corrosion state of each steel material. Depending on which region the steel material corrosion index and the environmental corrosion index calculated by the index calculation step and the environmental corrosion index calculation step are located at the boundary, Characterized in that it comprises an estimation step of estimating the corrosion state of the steel to be serial estimation target.
Hereinafter, the steel material corrosion index calculation process, the environmental corrosion index calculation process, and the estimation process will be described.

(Steel corrosion index calculation process)
The steel material corrosion index calculating step is a step of calculating the steel material corrosion index of the steel material from the amount of two or more elements contained in the steel material to be estimated.
In addition, this element is an element which affects the corrosion of steel materials.

The steel material corrosion index is an index determined by the composition of the steel material and an index indicating the ease of corrosion of the steel material from the viewpoint of the characteristics of the steel material itself (amount of elements contained in the steel material, etc.). In addition, the amount of Cu, Ni, Cr and Ti contained in the steel material has a great influence on the corrosion state of the steel material (whether rust generated on the steel material surface is stably formed as a protective layer or peeled off in layers). Therefore, the steel material corrosion index is preferably a value calculated from two or more kinds of Cu, Ni, Cr, and Ti contained in the steel material.
Two or more types are used because there is no meaning for obtaining the steel material corrosion index in the case of one type.

  Furthermore, it is preferable that the said steel material corrosion index | exponent is calculated by the linear function which makes 2 or more types of quantity a variable among Cu, Ni, Cr, and Ti contained in steel materials. The steel material corrosion index is more preferably a value calculated by adding the amounts of Si and Mn in addition to Cu, Ni, Cr and Ti and adding the variables.

For example, specifically, the steel material corrosion index Km can be calculated based on the following formula (1). In addition, [% M] in the following formula (1) indicates an addition amount (% by weight) of the additive element M in the steel material. Further, the items [% Si] and [% Mn] in the following formula (1) may not be provided, but the steel corrosion index Km can be calculated more accurately by providing the items.
Km = [% Si] + [% Mn] + [% Cu] + [% Ni] + [% Cr] + [% Ti] (1)

  Further, the steel material corrosion index Km may be calculated by multiplying a variable indicating the amount of each element ([% M] in the above formula (1)) by a predetermined coefficient according to the degree of influence of each element on the corrosion. . For example, for an element having a large influence on corrosion, a coefficient of a variable indicating the amount of the element may be set to a larger value than a coefficient of a variable indicating the amount of another element.

(Environmental corrosion index calculation process)
The environmental corrosion index calculating step is a step of calculating the environmental corrosion index of the atmospheric environment from two or more environmental factors indicating the state of the atmospheric environment where the steel material to be estimated is used.
The environmental factor is a numerical value of an environmental condition such as annual average temperature and annual average humidity.

The environmental corrosion index is an index determined by the environmental factors of the air environment, and the steel material in the air environment in terms of the characteristics of the air environment in which the steel material is used (annual average temperature, annual average humidity, etc.). It is an index indicating the ease of corrosion.
Here, environmental factors such as the temperature of the steel material, the time covered (wet) by the water film formed on the steel material surface, and the concentration of the aqueous electrolyte solution in the water film formed on the steel material surface contribute to the corrosion state of the steel material. These environmental factors have a great influence and depend largely on the values of the annual average temperature, the average humidity, and the deposited electrolytic mass (amount of electrolyte that adheres to the unit area of steel during unit time) of the atmospheric environment Yes. Therefore, the environmental corrosion index is preferably calculated based on two or more of the annual average temperature, the annual average humidity, and the attached electrolytic mass in the atmospheric environment.
Two or more types are used because it is meaningless to obtain an environmental corrosion index in the case of one type.

For example, the environmental corrosion index Ke can be calculated based on the following formula (2). T in the following formula (2) is the annual average temperature (° C.) of the atmospheric environment where the steel material to be estimated is arranged, H is the annual average humidity (% RH) of the atmospheric environment, and V is the unit time (for example, 30) shows the amount of electrolytic electrolyte (mg / m ² ) that is the amount of electrolyte that adheres to the unit area of the steel material.
Ke = 1000 / (0.5 × T + H + 63 × V) (2)

In addition, each coefficient of the annual average temperature T (° C.), the annual average humidity H (% RH), and the adhesion electrolytic mass V (mg / m ² ) in the above formula (2) is the influence of each environmental factor on the corrosion state of the steel material. It is determined based on the degree.

The annual average temperature T (° C) and annual average humidity H (% RH) may be obtained by actual measurements using a 100-leaf box installed in the atmospheric environment where the steel is to be used. It may be obtained using the data of the meteorological observation point.
As the electrolyte of the adhered electrolysis mass, chlorides, sulfates, carbonates, etc. that affect the corrosion of steel materials are preferable. Among these, chlorides that have the greatest effect and are easy to analyze due to the large amount of adhesion are the most. preferable.

Here, if the amount of electrolyte flying to the place where the corrosion state is estimated is calculated, for example, it is calculated by the method prescribed in Reference 2 or Reference 3 of JIS Z2381 (General Rules for Outdoor Exposure Test Methods) Can do. In the method of Reference 3 relating to the measurement of the amount of sulfur oxides or the amount of sea salt particles, first, the gauze is cut into a size of 120 mm × 240 mm, the chloride is sufficiently leached with pure water, and then dried well. Then, the gauze is folded in half and fitted into a wooden frame having an inner dimension of 100 mm × 100 mm. By chemically analyzing the ion content ^- which were exposed to 1 month perpendicular to best of direct rain it does not strike ventilation air quality is expected to steel is used, after exposure, to remove the gauze from crate Cl Measurement may be performed according to

  However, the amount of electrolyte that actually adheres to the steel material dominates the corrosion state of the steel material. Even in the same atmospheric environment, the attached electrolytic mass varies slightly depending on the installation angle (angle of the steel material surface relative to the horizontal direction). Therefore, in order to more accurately estimate the corrosion state of the steel material, it is preferable to calculate the adhesion electrolytic mass at the installation angle planned when the steel material to be estimated is installed.

  Specifically, the attached electrolytic mass is determined by calculating the attached electrolytic mass from the amount of the electrolyte contained in the aqueous solution attached to each steel material after the plurality of steel materials are installed at different angles with respect to the horizontal direction. From each of the correspondences obtained by the electrolytic mass measurement step for obtaining the correspondence between the attached electrolytic mass and the angle with respect to the horizontal direction of the steel material, and the correspondence obtained by the electrolytic mass measurement step. It is preferably calculated from an electrolytic mass selection step of selecting an attached electrolytic mass according to an angle of the steel material with respect to the horizontal direction.

  In addition to the installation angle (the angle of the steel surface relative to the horizontal direction), the adhesion electrolysis mass is calculated for each installation orientation (direction in which the steel surface is facing) (electrolytic mass measurement step), You may select (electrolytic mass selection process).

  In addition, when calculating the adhesion electrolysis mass considering the installation angle and installation orientation, for example, use a surface salinity meter that measures the concentration of adhering salt from the change in electrical conductivity, or wipe off gauze as follows: You may measure by a method.

In this method, first, a test panel (predetermined steel material) is exposed to an atmospheric environment where the steel material is to be used so as to have a planned installation angle and installation orientation. Here, if the exposure period of the test panel is too short, the attached electrolytic mass is small and the measurement error is large, so that it is preferably 3 days or more, and more preferably 5 days or more. Further, there is no problem even if the exposure period is long, and for example, it may be about 30 days.
Note that the size of the test panel is preferably 30 cm × 30 cm or more, because if the test panel is too small, the amount of attached electrolysis is small and the measurement error increases. In consideration of handling of the test panel, 100 cm × 100 cm or less is preferable.

And the electrolyte of the test panel surface is dissolved in the water | moisture content contained in the said gauze by wiping off the test panel surface after exposure with the gauze moistened with the pure water. Thereafter, the gauze is immersed in pure water with a known capacity, the concentration of the electrolyte is measured by chemical analysis, and the amount of the electrolyte substance adhering to the test panel surface is calculated.
In addition, it is also possible to wash | clean the test panel surface after exposure with a pure water, and to measure the density | concentration of electrolyte by a chemical analysis using the collect | recovered said wash water as a test solution.

In addition, this environmental corrosion index calculation process calculates the environmental factors (annual average temperature, annual average humidity, adhesion electrolysis mass) of the atmospheric environment where the steel is to be used, and then calculates the environmental corrosion index based on each environmental factor. May be.
In addition, if data related to multiple environmental factors (annual average temperature, annual average humidity, adhesion electrolysis mass) associated with a location are entered in the database in advance and the location where the steel is to be used is entered, The environmental factor of the place corresponding (same or approximate) is selected, and the environmental corrosion index may be calculated based on the selected environmental factor.
In addition, for the electrolytic electrolytic mass, enter not only the location but also the data related to the installation angle and installation orientation in the database, and enter the location, installation angle and installation orientation where the steel will be used. Thus, it may be configured such that a more accurate attached electrolytic mass can be selected.

(Estimation process)
The estimation process means that the steel corrosion index and the environmental corrosion calculated in advance by observing the corrosion state of each steel material when a plurality of steel materials having different steel corrosion indexes are used in a plurality of atmospheric environments having different environmental corrosion indexes. With respect to the boundary obtained from the relationship between the index and the corrosion state, the steel material corrosion index and the environmental corrosion index calculated by the steel material corrosion index calculation process and the environmental corrosion index calculation process are located in any region divided by the boundary. This is a step of estimating the corrosion state of the steel material to be estimated depending on whether or not

  Here, the relationship between the steel material corrosion index, the environmental corrosion index, and the corrosion state means that the steel material having a predetermined steel material corrosion index is observed in a corrosive state in an atmospheric environment having a predetermined environmental corrosion index. From the observation results, three relationships among the steel material corrosion index, the environmental corrosion index, and the corrosion state are clarified.

Specifically, the relationship is such that the environmental corrosion index Ke is taken on the X axis, the steel material corrosion index Km is taken on the Y axis, and the observation results of a plurality of corrosion states are plotted on the XY plane, so that the rust is stably protected. The relationship shown in the graph of FIG. 1 showing the region formed as “No rust peeling” in FIG. 1 and the region where rust peels in layers (“With rust peeling” in FIG. 1). It is.
In addition, a boundary is a dotted line which divides | segments the area | region where rust is stably formed as a protective layer in FIG. 1, and the area | region where rust peels in layers.

  Further, the relationship may be shown by a graph as shown in FIG. 1, or may be shown by a mathematical expression or a table. In the case of using mathematical formulas and tables, as in the case of using the graph of FIG. 1, the boundary is obtained from the relationship between the steel corrosion index, the environmental corrosion index, and the corrosion state. What is necessary is just to estimate a corrosion state by judging in which area | region divided by (1).

The more observation results, the more the area where rust is stably formed as a protective layer (“no rust peeling” in FIG. 1) and the area where rust peels in layers (“rust” in FIG. 1). ”), And the corrosion state of the steel material at the boundary portion can be estimated more accurately.
Therefore, the observation result in the vicinity of the boundary between “without rust peeling” and “with rust peeling” is preferably 3 or more, and more preferably 5 or more.

  In calculating the relationship between the steel corrosion index, the environmental corrosion index, and the corrosion state, use the observation results (corrosion state of the steel material) after a certain period of time after installing the predetermined steel material in the predetermined atmospheric environment. It may be determined based on the estimated period (elapsed period from installation) required for the steel material to be measured. For example, if you want to estimate the corrosion state after 5 years from the installation of the steel material to be measured, the observation results when calculating the relationship between the steel corrosion index, the environmental corrosion index, and the corrosion state (corrosion state of the steel material) It is preferable to use the result of 5 years or more after installation.

All the above steps can be performed by processing means provided in a computer or the like.
Specifically, when the steel composition, the planned use location of the steel material, the installation angle and orientation of the steel material are input using input means such as a keyboard and a mouse, the processing means calculates the steel material corrosion index Km based on the input data. In addition, the environmental corrosion index Ke is calculated (environmental corrosion index calculating process). In calculating the environmental corrosion index Ke, the location entered from the data stored in the database (location, installation angle, annual average temperature associated with the installation orientation, annual average humidity, attached electrolytic mass) In addition, the processing means may be configured to perform a process of selecting an annual average temperature, an annual average humidity, and an attached electrolytic mass corresponding (identical or approximate) to the installation angle and installation orientation.
The calculated steel material corrosion index Km and environmental corrosion index Ke are stored in the database in any region (rust is stably formed as a protective layer) on the boundary (dotted line) on the XY plane of FIG. The processing means determines whether the region corresponds to the region where the rust is peeled off or the region where the rust peels in layers, and the result is displayed on an output unit such as a monitor.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the design can be appropriately changed without departing from the gist of the present invention described in the claims.

Next, the method for estimating the corrosion state of the steel material of the present invention will be specifically described with reference to examples.
At five locations in Japan (AE), the corrosion state of four types of steel materials (test steel materials) (M1-M4), that is, whether or not rust causes peeling was verified and verified. As the annual average temperature T and the annual average humidity H of the predetermined place, data of a point closest to the predetermined place is used in the public data of the Japan Meteorological Agency. Moreover, the adhesion electrolysis mass V was measured by the following method.

30 cm x 30 cm coated steel sheet (thickness 2 mm) coated with epoxy resin paint (thickness 250 μm) is exposed to a predetermined place as a test panel for 30 days, and the amount of salt (Cl ⁻ ion) attached by gauze wiping method Was measured. In addition, the roof was provided in the place where the test panel was installed, and it installed so that rain might not hit a test panel directly.

[Steel corrosion index and environmental corrosion index]
In the examples, the steel material corrosion index Km and the environmental corrosion index Ke were calculated based on the following formulas (1) and (2). In the following formula, [% M] indicates the amount of additive element M added (% by weight), T is the average annual temperature (° C.) at a predetermined location, and H is the annual average humidity (% RH) at a predetermined location. , V represents the electrolysis mass (mg / m ² ) obtained by the measurement method.
Km = [% Si] + [% Mn] + [% Cu] + [% Ni] + [% Cr] + [% Ti] (1)
Ke = 1000 / (0.5 × T + H + 63 × V) (2)

  Table 1 below shows the chemical composition (%) and steel corrosion index Km of each test steel, and Table 2 below shows the environmental factors (annual average temperature, annual average humidity, adhesion electrolytic mass) at a predetermined location. ) And the environmental corrosion index Ke.

Four kinds of test steel materials shown in Table 1 were exposed to a predetermined place, and the corrosion state was investigated. The size of the exposed test steel is 150 mm × 70 mm × 5 mm. The exposed location of the test steel was a location adjacent to the location where the test panel for measuring the attached electrolyte was installed, and a roof was provided so that the test steel was not directly exposed to rain. Three test steels are installed for each type at a predetermined location, and when no rust peeling is observed on all three sheets, “no rust peeling” is assumed, and one or more of the three pieces are rust peeled. The case where rust was observed was evaluated as “with rust peeling”.
The test results are as shown in Table 3 below, and the rust peeling state differs depending on the steel material corrosion index Km and the environmental corrosion index Ke. In Table 3, “◯” indicates no rust peeling, “×” indicates rust peeling, and “−” indicates that the test was not performed. The elapsed time (year) is the number of years from when the test steel material is installed to when the corrosion state is confirmed.

FIG. 1 is a plot of the test results in Table 3, with the environmental corrosion index Ke on the X axis and the steel material corrosion index Km on the Y axis. As shown in FIG. 1, the region without rust peeling and the region with rust peeling could be clearly separated (dotted line in FIG. 1).
According to this embodiment, by using the relationship in which the steel corrosion index, the environmental corrosion index, and the corrosion state shown in FIG. 1 are associated, the corrosion of the steel material is calculated from the environmental corrosion index Ke and the steel corrosion index Km of the steel material to be estimated. It was found that the state can be estimated accurately. In addition, by using the relationship shown in FIG. 1, it is not necessary to conduct a corrosion experiment or the like of the steel material when estimating the corrosion state of the steel material to be estimated, so the corrosion state of the steel material can be estimated extremely simply. I found out that

Claims (6)

Using a steel corrosion index indicating the ease of corrosion of the steel material from the characteristics of the steel material itself and an environmental corrosion index indicating the ease of corrosion of the steel material from the characteristics of the atmospheric environment in which the steel material is used A corrosion state estimation method for estimating the corrosion state of steel used in the atmospheric environment,
A steel corrosion index calculating step of calculating a steel corrosion index of the steel material from the amount of two or more elements contained in the steel material to be estimated;
From two or more environmental factors indicating the state of the atmospheric environment in which the steel material to be estimated is used, an environmental corrosion index calculating step of calculating an environmental corrosion index of the atmospheric environment;
The steel corrosion index, the environmental corrosion index, and the corrosion state calculated in advance by observing the corrosion state of the steel materials when using a plurality of steel materials having different steel corrosion indexes in a plurality of atmospheric environments having different environmental corrosion indexes. With respect to the boundary obtained from the relationship, the steel material corrosion index and the environmental corrosion index calculated by the steel corrosion index calculation step and the environmental corrosion index calculation step, depending on which region is divided by the boundary, A corrosion state estimation method comprising an estimation step of estimating a corrosion state of a steel material to be estimated.   The said corrosion state is the presence or absence of peeling of the rust formed in the surface of the said steel materials, The corrosion state estimation method of Claim 1 characterized by the above-mentioned.   3. The steel material corrosion index is a value calculated from two or more kinds of Cu, Ni, Cr and Ti contained in the steel material. The corrosion state estimation method described in 1.   4. The steel material corrosion index is calculated by a linear function having two or more kinds of Cu, Ni, Cr and Ti contained in the steel material as variables. Corrosion state estimation method. The environmental corrosion index is a value calculated by a calculation formula using two or more of annual average temperature, annual average humidity, and attached electrolytic mass in the atmospheric environment as variables,
The corrosion state estimation method according to any one of claims 1 to 4, wherein the attached electrolytic mass is an amount of an electrolyte attached to a unit area of the steel material during a unit time. In the case where the environmental corrosion index calculated in the environmental corrosion index calculation step is calculated using at least the attached electrolytic mass,
The attached electrolytic mass used for calculating the environmental corrosion index in the environmental corrosion index calculation step is:
After installing a plurality of steel materials at different angles with respect to the horizontal direction, from the amount of electrolyte contained in the aqueous solution attached to each steel material, the attached electrolytic mass is determined for each angle with respect to the horizontal direction of the steel material, the attached electrolyte Electrolytic mass measurement step for determining the correspondence between the amount and the angle of the steel material with respect to the horizontal direction;
From the correspondence obtained by the electrolytic mass measurement step, an electrolytic mass selection step of selecting an adhesion electrolytic mass according to an angle with respect to the horizontal direction of the steel material to be estimated is calculated. The corrosion state estimation method according to claim 5, wherein the corrosion state is estimated.

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