JPH10253524A - Accelerating test method for atmospheric corrosion-resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accelerating and evaluating method for corrosion resistance of metallic materials in a desired atmospheric environment. SOLUTION: After forming a liquid film containing chloride ions all over a surface to be tested of a test piece, continuous temperature change is applied to the test piece to repeat drying and wetting to form one cycle. By performing the cycles formed by the formation of a liquid film and temperature changes, corrosion resistance is evaluated. In this case, the liquid film is formed after the test piece is set at the predetermined minimum temperature, then temperature is raised to the predetermined maximum temperature, and next, temperature is lowered to the above-mentioned minimum temperature to form one cycle. Furthermore, it is prefered to perform one cycle in one day and to maintain changes in atmospheric dew points within ±10 deg.C at the time of repeating drying and wetting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an accelerated test method suitable for evaluating the corrosion resistance of metallic materials in various atmospheric environments.

[0002]

2. Description of the Related Art Durability is the most important performance required for equipment and structures used outdoors, and especially in the case of metal materials, the durability is greatly influenced by corrosion resistance to atmospheric corrosion. The best way to determine the resistance to this atmospheric corrosion is through an air exposure test. However, the air exposure test requires a long period of time to obtain results, and it is necessary to conduct tests at many points in order to understand the environmental impact and the use limit of materials. It requires a great deal of labor and cost.

[0003] In order to solve this problem, various types of accelerated tests have been set as standards and proposed. In general, as an accelerated test method for grasping the corrosion resistance of a metallic material in a humid atmosphere (especially in a beach environment), a salt spray test standardized in JIS Z 2371 and the “Stainless Steel Handbook (Third Edition)” (The Stainless Steel Association, 1995, p.4
69-471) are widely used.

In the salt spray test, a test liquid containing a chloride ion in a material (in many cases, a 5% NaCl aqueous solution is used) is sprayed for a predetermined time to measure the corrosion amount of the material. The cycle corrosion test is sometimes called a combined corrosion test or a combined cycle corrosion test. This method is 5
% NaCl aqueous solution or artificial seawater is sprayed on the test piece, and then dried and wetted (this combination constitutes one cycle)
Is repeated to measure the amount of material corrosion with respect to the number of cycles. In general, the test liquid is sprayed at 35 ° C., the drying is set at a temperature of about 60 ° C. at a humidity of 30% or less, and the wet is set at a humidity of 90% or more and the temperature at about 50 ° C. Further, these tests are characterized in that the temperature and the relative humidity are changed stepwise. The salt spray and the cyclic corrosion test are methods for grasping the difference in corrosion resistance between materials under certain test conditions.

On the other hand, as a test method for grasping the influence of environmental conditions on corrosion, Japanese Patent Application Laid-Open No. 56-104235 discloses a method in which various concentrations of water-soluble salts and solid particles are adhered to the surface of a test piece and dried. And a method of repeating wetting are disclosed. This is to investigate the relationship between the amount of deposits and the amount of corrosion, and to understand the effect of environmental conditions on corrosion resistance.

[0006]

The salt spray test and the cyclic corrosion test have both been proven as accelerated tests, and for a particular atmospheric environment, a correspondence has been found between the test results and the atmospheric exposure test. However, this should be done so that the degree of corrosion is close to the results of long-term air exposure tests.
It is the result of determining the accelerated test conditions such as the order and the number of the wetting process and the temperature and humidity of the drying / wetting process by trial and error. Essentially, these tests evaluate the difference in corrosion resistance between materials while keeping the test conditions constant. Therefore, it is impossible to provide the information originally required for an atmospheric corrosion acceleration test, assuming a certain region or a specific atmospheric environment, and estimating the corrosion resistance and durability of the material there.

On the other hand, the test method disclosed in Japanese Patent Application Laid-Open No. 56-104235 is to obtain the relationship between environmental conditions and corrosion resistance by changing the amount of attached salt and repeating drying and wetting. However, the corrosion resistance and corrosion behavior in an outdoor atmospheric environment largely depend not only on the amount of attached salt, but also on the condition of dew condensation and the conditions of dry and wet repetition. Therefore, the results obtained by this method, which does not specify the method of simulating dew condensation or the method of repeating wet and dry, do not provide corrosion resistance in an actual atmospheric environment.

[0008] As described above, at present, a truly appropriate atmospheric corrosion acceleration test method has not yet been developed. Therefore,
The present invention provides a method for promoting and evaluating the corrosion resistance of a metal material in a desired atmospheric environment.

[0009]

The present inventor has analyzed the atmospheric corrosion phenomenon of metallic materials and the meteorological characteristics of the atmospheric environment that cause it, and as a result, found that chlorides generated due to dew condensation in an outdoor atmospheric environment. By faithfully simulating the formation of a liquid film containing ions and the drying and moisture absorption processes of the liquid film, we have obtained a completely new finding that the corrosion resistance of metallic materials under atmospheric conditions with different environmental conditions can be grasped.

The present invention has been made based on the above findings. After a liquid film containing chloride ions is formed on the entire test surface of a test piece, a continuous temperature change is applied to the test piece to repeat drying and wetting. This is defined as one cycle, and the cycle consisting of the formation of the liquid film and the temperature change is repeated to evaluate the corrosion resistance.
At this time, it is preferable to set a test piece to a predetermined minimum temperature, form a liquid film, then increase the temperature to a predetermined maximum temperature, and then decrease the temperature to the predetermined minimum temperature in one cycle. Furthermore, one cycle is one day,
It is preferable to keep the fluctuation of the dew point of the atmosphere during the repetition of the drying and humidity within ± 10 ° C.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the test conditions constituting the present invention will be described in detail below. First, the test liquid adheres to the test surface of the material.In order to properly evaluate the corrosion resistance of metallic materials in the air environment, the liquid should be applied to the entire test surface instead of a droplet like a salt spray test. It is necessary to form a film. Here, the liquid film refers to a state where the liquid covers the entire test surface except for a meniscus portion formed at an end of the test surface. This is not a state where a large number of droplets are distributed on the test surface or a state where a liquid film is formed only on a part of the test surface.

When the liquid is in the form of droplets, it is not possible to evaluate the corrosion resistance of the portion where the liquid has not adhered, and to determine the droplet adhesion form determined by the surface tension of the metal material surface and spray conditions. Changes the form of corrosion. Therefore, the performance of the material cannot be accurately determined. On the other hand, when a liquid film is used, it is possible to evaluate the corrosion resistance of all portions of the material surface.

Further, in order to reproduce the corrosion form and corrosion behavior in an actual atmospheric environment, it is necessary to repeat a drying and a wet by giving a continuous temperature change to a test piece after forming a liquid film. The way the liquid film dries during the process of drying the liquid film depends on the non-uniformity of the corrosion characteristics of the material surface. For example, a porous corrosion product is generated and absorbs a liquid in a portion where erosion has locally progressed on the surface of the test piece, so that the liquid is less likely to dry, and only that portion is further corroded. As a result, the non-uniformity of corrosion, which is a characteristic of atmospheric corrosion, and the non-uniform dry state can be accurately reproduced. Furthermore, by creating a wet state after drying, corrosion products and chlorides absorb moisture, and the corrosion regrows preferentially only in that part, and the uneven corrosion phenomenon in atmospheric corrosion as in the case of drying Can be faithfully reproduced.

At this time, the acceleration of the accelerated test of the present invention is 1
It becomes higher as the number of times of drying and wetting (the number of temperature maximum points) in the cycle increases. However, if the acceleration is excessively increased, there is a tendency that the form of corrosion, the order of corrosion resistance between materials, and the like are difficult to match with the actual outdoor atmospheric environment. For this reason,
It is preferable to repeat drying and wetting once in one cycle. By the way, the formation of a water film on the surface of a material in an actual outdoor atmospheric environment is due to condensation. Condensation occurs at night when the temperature of the material or the temperature drops. Therefore, when drying in one cycle is one time,
After setting the test piece at a predetermined minimum temperature, a liquid film containing chloride ions is formed on the surface to be tested of the test piece, then the temperature is raised to a predetermined maximum temperature, and then the temperature is lowered to the predetermined minimum temperature. It is desirable that this be one cycle. By using this method, the outdoor atmospheric corrosion behavior can be accelerated and evaluated with high accuracy. It should be noted that the maximum and minimum temperatures during repeated wet and dry cycles need to be changed depending on the simulated atmospheric environment and area, and cannot be uniquely determined. It is preferable to match the air temperature or the daily minimum temperature of the material. The maximum temperature will be described later.

Next, when these drying and wetting are performed, if the temperature is changed stepwise and the drying or wetting is performed instantaneously, the time required for the corrosion is not secured, so that the form of the corrosion is the actual atmospheric environment. Will be different. Therefore, in order to properly evaluate the corrosion resistance of a material, it is necessary to continuously change the temperature. In this case, it is preferable that the temperature increase / decrease rate is slower. In particular, in order to accurately predict the rust form and the degree of occurrence, the formation of the liquid film is performed once a day at a temperature of 1 day, as in the actual outdoor atmospheric environment. It is necessary to change the day continuously as one cycle. What governs the atmospheric corrosion behavior of metal materials is the chloride ion concentration in the liquid film during condensation and the temperature and humidity conditions during repeated drying and drying. By accelerating the cycle of liquid film formation and temperature cycling, which are the repetition conditions of dry and wet, as close as possible to the actual outdoor environment, the acceleration factor of the accelerated test can be limited to the chloride ion concentration and the maximum and minimum temperatures. Applicable salt adhesion amount and maximum and minimum temperature (environmental conditions) can be grasped.

By the way, at the time of repetition of wet and dry, it is most desirable to reproduce the time change of the actual material temperature in the outdoor environment to be simulated. However, this is impossible when the place or region where the metal material is used is not specified or when the temperature change cannot be measured. However, even in such a case, in order to evaluate the corrosion resistance in the environment with sufficient validity, first determine the atmospheric environment to be simulated and the dew point of the local atmosphere, and then determine the ambient air around the test specimen. It is necessary to keep the moisture content within ± 10 ° C. of this dew point, to continuously change the temperature, and to repeat the wet and dry.

Hereinafter, the reason for this and a specific implementation method will be described. FIG. 1 shows the relationship between the relative humidity of the atmosphere and the temperature measured in the coastal area of Gushito Village, Okinawa Prefecture and the rural area of Kimitsu City, Chiba Prefecture. These are measurements performed continuously for three days at intervals of 2 minutes and 30 seconds in a hundred-leaf box placed at a height of 1 m and 50 cm from the ground. The solid line shown in the figure shows the relative humidity when only the air temperature changes, with the dew point of the air being constant (water vapor amount being constant). As can be seen from FIG. 1, the dew point of the atmosphere hardly changes,
It is constant within the range of ± 10 ° C. Therefore, in order to accurately simulate dryness and wetness in a specific atmospheric environment, first determine the average dew point of the atmosphere to be simulated, and keep the dew point constant within ± 10 ° C. Changing the temperature is essential.

By the way, as shown in FIG. 1, the dew point of the atmosphere is constant within a range of several days, but changes according to the season when viewed over a long period such as one year. The dew point is high in summer and low in winter. Generally, in an outdoor structure or the like, the higher the dew point, the more easily dew condensation occurs, and the higher the corrosiveness as an environment. Therefore, when testing the durability of a material for a long period of time or evaluating the performance of the material on the dangerous side, keep the dew point within ± 10 ° C based on the assumed summer dew point in the usage area. It is desirable to control it. For example, based on FIG. 1, the dew point in summer is 28 ° C. on the beach of Gushiga-son, Okinawa Prefecture (1995).
August 29-September 1). Therefore, in order to simulate the atmospheric corrosion environment in this area and evaluate the corrosion resistance of the material for a long time, it is desirable to repeat the dry and wet at a dew point of 28 ° C. ± 10 ° C.

To know the dew point in a certain area, it is necessary to measure the temperature and the relative humidity. Although small measuring instruments that operate on dry batteries are commercially available, it is not always feasible to go out to various places and perform actual measurements, which requires a great deal of labor and cost. In such a case, the value of the daily minimum temperature in the area is treated as equivalent to the average dew point. On the other hand, the dew point is kept constant within a range of ± 10 ° C, and the corrosion resistance is repeated by drying and wetting. Can be evaluated. In general, the temperature decreases at night due to radiant cooling. Then, condensation starts when the temperature reaches the dew point of the atmosphere. However, during the dew condensation, the water vapor liquefies, generating latent heat, and the air temperature and the temperature of the material surface slightly rise. For this reason, at the time of dew condensation, the temperature does not drop significantly beyond the dew point, and the daily minimum temperature substantially matches the average dew point of the atmosphere on that day. Fig. 1 also shows the August 1995
The minimum temperature from 29th of September to 1st of September is about 25 ° C. The minimum dew point during this period is 25 ° C and the average dew point is about 28 ° C
And the minimum temperature is almost equal to the average dew point. Strictly speaking, the daily minimum temperature coincides with the daily minimum dew point. However, the change in dew point during the day is small, so that the daily minimum dew point substantially matches the average dew point,
The average dew point can be determined from the daily minimum temperature.
In FIG. 1, even in other periods, the minimum temperature is almost equal to the average dew point.

Incidentally, daily minimum temperatures not only in Japan but also around the world are disclosed in statistical data and various data collections issued by the Japan Meteorological Agency, and according to the method of the present invention, based on these data, Accelerated tests can be performed assuming the dew point of the atmospheric environment. In addition, the maximum and minimum temperatures at the time of repetition of the wet and dry conditions are not particularly defined in the present invention. However, drying refers to a state in which salt has precipitated on the surface of the test piece, and refers to a state in which the remaining of water droplets cannot be confirmed visually. The term “wet” refers to a state in which the salt absorbs moisture, part or all of the salt is dissolved as an aqueous solution, and droplets are present on the surface of the test piece.

In an outdoor environment, the material is heated to a temperature higher than the temperature by direct sunlight. Therefore, the maximum temperature at the time of drying should be determined in consideration of the usage form such as the thickness of the material and the positional relationship with the heat insulating material, and cannot be uniquely determined. However, for example, when a roof or a wall of a building is assumed, it is appropriate that the maximum temperature be 50 to 80 ° C. Further, it is preferable that the minimum temperature is made to coincide with the average dew point or the minimum dew point of the environment to be simulated as described above. The temperature pattern (heating rate, cooling rate, etc.) at the time of repetition of the drying and wet conditions is only required to continuously change the temperature in the present invention, and other conditions are not particularly defined. Conditions relating to the repetition of dry and wet conditions, such as the ratio of daytime to nighttime and shade in the sun, vary depending on the area of use and components, and cannot be uniquely determined. However, for example, to simulate the environment of a member exposed to direct sunlight in a mid-latitude area such as Japan,
In terms of faithful simulation of the outdoor environment, the temperature changes to the predetermined maximum temperature in about 6 hours after the wet state at a low temperature equivalent to nighttime has been performed for about 12 hours according to the time change of the actual day and night. A pattern of raising the temperature and lowering the temperature in about 6 hours is preferable.

When evaluating the corrosion resistance of a material under various environments having different amounts of sea salt particles, it is necessary to change the concentration of chloride ions in the liquid film according to the sea salt adhesion condition in the assumed environment. Can be dealt with. In the accelerated test, when the liquid film dries, the mass (g / m ² ) of chloride ions deposited on the surface of the test piece and the amount (g / m ² ) of sea salt particles adhering to the material surface in an assumed outdoor atmospheric environment By matching m ² ), the corrosion resistance of the material in the environment can be evaluated. By the way, the amount of chloride ion adhering to stainless steel structures such as roofs and walls in the beach area of Japan is as follows:
It is about 0.1 mg / cm ² .

Various methods are conceivable for producing a liquid film, and the present invention does not particularly define the method. However, in order to produce a liquid film on a large number of test pieces at a time with good reproducibility, it is preferable to place the test pieces so that the surface to be tested is horizontal, and spray the test liquid into a fine mist. When spraying is performed for a long time, the test liquid which is initially in the form of droplets becomes a liquid film as shown in FIG. If the spraying is continued even after the liquid film is formed, the liquid film swells up to the shape of the meniscus determined by the surface tension of the liquid and the test piece, and the test liquid beyond this spills. Therefore, by performing the spraying for a sufficiently long time, a liquid film can be simultaneously formed on a large number of test pieces with good reproducibility. However, since the thickness of the liquid film depends on the surface tension of the test piece, a preliminary study should be conducted in advance to determine how thick the liquid film will be formed on the test piece used for the test. There is a need.

The atmospheric corrosion of the metal material occurs in an environment where sea salt particles alone or coexist with sea salt particles and air pollutants. Therefore, it is necessary to use a test solution containing chloride ions as an atmospheric corrosion test for metal materials. Chloride ions are NaCl, MgCl ₂ , CaCl
₂ , FeCl _3, etc., may be supplied, but it is preferable to use seawater (including artificial seawater) or a diluted or concentrated seawater.

The relationship between the number of cycles in the accelerated test of the present invention and the number of years elapsed in an outdoor atmospheric environment depends on the amount of chloride ion deposited and the conditions of repetition of wet and dry conditions, and there is no unique simple relationship. . However, the atmospheric corrosion rate of a metal material follows the parabolic law, and the corrosion progresses greatly in the initial stage, but the corrosion degree hardly changes after several years. In particular, in a material such as stainless steel or aluminum that causes pitting-type atmospheric corrosion, the progress of the corrosion almost stops in one to two years. Therefore, the accelerated test of the present invention can be performed to select the final corrosion state in the outdoor atmospheric environment and the applicable material when the amount of corrosion does not depend on the number of cycles. Incidentally, assuming a general beach environment in Japan, 10 cycles of the accelerated test of the present invention are equivalent to about 1 year and 6 months, and 20 cycles are equivalent to about 3 years. For example, a general-purpose SUS304 (18Cr-8N
i) In the case of stainless steel, the corrosion resistance and the degree and form of corrosion in the outdoor atmospheric environment can be determined in 10 to 20 cycles.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. SUS304 (18C
r-8Ni), SUS430 (16.5Cr) and 2
Three types of stainless steel plates of 2Cr steel (22.5Cr-1.5Mo) were used. Table 1 shows the chemical compositions of these test pieces. These were cut into 60 mm × 40 mm, and only the test surface was polished with wet No. 600 emery paper, degreased with acetone, and then used for the test. For the test, a salt spray tester (commonly referred to as a composite corrosion tester) having a temperature / humidity control function was used.

[0027]

[Table 1]

In the embodiment of the present invention, the test piece was placed horizontally with the test surface facing upward, and artificial seawater (ASTM D-1141-52) diluted 1/20 was used as the test solution. . The temperature pattern used is that shown in FIG. With 24 hours as one cycle, dew point is 28 ± 10
° C range, with a minimum temperature of 28 ° C and a maximum temperature of 55 ° C.
The temperature was varied in the range of ° C. FIG. 3 also shows the change over time of the relative humidity uniquely determined from the dew point and the temperature. The test liquid was sprayed for 4 hours (14.4 ks) while maintaining the temperature at 28 ° C.
Next, the temperature was kept at 28 ° C. and the humidity was kept at 90% for 4 hours and 36 minutes (16.56 ks).
2 hours 22 minutes (8.52 ks) while keeping the temperature within 10 ° C
Over a period of 1 hour and 40 minutes (6 ks) to a humidity of 54% at 25%, and then over a period of 1 hour and 22 minutes (4.92 ks) to a humidity of 24% at 55 ° C. Then, the temperature was lowered and the low temperature and high humidity were maintained in the reverse pattern over about 12 hours.

As described above, the salt spray was performed for 4 hours out of 24 hours, and a liquid film was formed on the surface of the test piece. FIG. 4 shows the state of the liquid film formed at this time. The liquid is evenly placed on the surface of the test piece (the state of light reflection indicates that a meniscus is formed at the end of the test piece). At this time, a preliminary test confirmed that an average of 0.06 mg / cm ² of chloride ion was attached to the combination of the stainless steel piece and the test solution used in the test. These test conditions are conditions set in order to evaluate the corrosion resistance in the seaside atmospheric environment of Gushizu-mura, Okinawa, which will be described later. That is, the dew point is first
Is the summer dew point at this point, and the chloride ion concentration was adjusted to match the sea salt particle deposition actually measured at the exposure point. The test was performed up to 20 cycles.

As comparative examples, a cycle corrosion test and an atmospheric exposure test were performed. The cycle corrosion test was performed by spraying a test liquid (35 ° C., 4 hours), drying (60 ° C., relative humidity 20)
% Or less, 2 hours) and wet (50 ° C., relative humidity of 95% or more, 2 hours) as 1 cycle to 1 to 60
A cycle was performed. As the test liquid, artificial seawater was used. Under these test conditions, the dew point in the drying process is 28 ° C. or less, and the dew point in the wet process is 49-50 ° C. The test piece was placed at an angle of 60 degrees with respect to the horizontal, and the test liquid was attached in the form of droplets.

The air exposure test was carried out on the beach at Gushizu Village, Okinawa Prefecture. As shown in FIG. 1, the average dew point in summer at this point is 28 ° C. The test piece is 30
Exposure was performed with a degree gradient. During the exposure period, test specimens were collected every other month for the first year and every two months thereafter. At this exposure point, the amount of sea salt particles attached to stainless steel was 0.06 mg / cm ^{2 in} terms of the amount of chloride ions.
Met.

The corrosion state in the accelerated test and the comparative test of the present invention was evaluated by measuring the area ratio of rust occurrence and the density of rust occurrence points (the number of occurrence points per unit area) by image processing. FIG. 5 shows the relationship between the area ratio of rust and the density of rust occurrence points in an air exposure test. It can be seen that the number of rusts (density) mainly increases in the first few months, then the number of rusts and the area ratio both increase, and finally the time when the area ratio increases but the number decreases. The first period is a period in which point-like rust increases in number over time, and is called a rust onset period. In the area where both the area ratio and the number increase next, this is a period during which a new rust generation point is generated and the area of the rust generated up to that time is increased, and is called a rust growth period. Finally, the area where the number of rusts decreases is a rust coalescence period in which rust points grow large and coalesce with each other, and the apparent number decreases. However, SUS30
In No. 4, although the rust coalescence stage did not appear, it was found that atmospheric corrosion progressed through such a characteristic process in the seaside atmospheric environment. Further, it was found that the density of rust generation points in the rust growth period was higher in SUS430 than in SUS304. Table 2 shows the rust occurrence area ratio when the air exposure test was performed for 20 months. Rust is slightly generated even with 22Cr steel.

FIG. 6 shows the rust generation behavior in the cycle corrosion test. In terms of the fact that corrosion progresses through the rust onset, growth and coalescence phases, it has successfully simulated the outdoor environment. However, in this cycle corrosion test, in the rust growth period, the density of rust occurrence points was smaller in SUS430 than in SUS304, and the rust form was different from that in the outdoor environment. I understand that there is no. Further, Table 2 shows the results obtained by arranging the rust generation area ratio when the 60 cycle test was performed. In the atmospheric exposure test, it was 22Cr steel with a slight rust, but it did not corrode at all in the cyclic corrosion test, indicating that the cyclic corrosion test did not properly evaluate the corrosion resistance in the outdoor atmospheric environment. .

FIG. 7 shows the results obtained by using the accelerated test of the present invention.
It is a summary of the relationship between the rust generation area ratio and the generation point density of US304 and SUS430. The figure also shows the results of an air exposure test conducted in Gushizu Village, Okinawa Prefecture. In this accelerated test, the area ratio and the spot density of the rust agree with the results of the outdoor atmospheric test. Moreover, SUS in the rust growth period
The difference between the rust generation point density of 430 and SUS304 was almost completely simulated, indicating that the accelerated test method of the present invention is appropriate as an atmospheric corrosion evaluation method and can simulate the environment with considerable accuracy. Table 2 shows the area ratio of rusting after 20 cycles. According to this table, 22Cr
It can be seen that the same rust generation area ratio as that of the outdoor air environment can be obtained for steel. That is, even if the material is a high corrosion resistant material that cannot be evaluated by the cycle corrosion test, the accelerated test method of the present invention can appropriately evaluate the corrosion resistance against atmospheric corrosion.

[0035]

[Table 2]

[0036]

By using the method of the present invention, it is possible to promote and evaluate the corrosion resistance of a metallic material in a desired atmospheric environment. As a result, it is possible to evaluate and predict the long-term corrosion resistance of various new or improved corrosion-resistant materials with extremely close reliability. In addition, by using the method of the present invention, it is possible to extremely quickly grasp the atmospheric limit condition of the applicable limit of the material, which could be grasped only by the air exposure test until now, thereby facilitating data accumulation. It is to be. This type of data greatly contributes to extending the life of social capital, such as various buildings and civil engineering structures, and maintaining and managing it.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the relative humidity of the atmosphere and the temperature measured in the seaside region of Gushito Village, Okinawa Prefecture and in the rural region of Kimitsu City, Chiba Prefecture.

FIG. 2 is a schematic diagram showing a state in which a liquid changes from a liquid droplet to a liquid film over time when a test liquid is sprayed on a test piece placed horizontally.

FIG. 3 shows temperature control conditions in an accelerated test devised to evaluate the corrosion resistance of a material in a seaside atmospheric environment in Gushigashira Village, Okinawa Prefecture.

FIG. 4 shows a state of a liquid film formed on a test piece placed horizontally.

FIG. 5 is a graph showing the relationship between the rust occurrence area ratio and the density of rust occurrence points in an air exposure test performed in a beach area of Gushigashira Village, Okinawa Prefecture.

FIG. 6 is a graph showing a relationship between a rust occurrence area ratio and a density of rust occurrence points in a cycle corrosion test.

FIG. 7 is a graph showing the relationship between the area ratio of rust and the density of rust occurrence points in the accelerated test of the present invention.

Claims (4)

[Claims] 1. One cycle of forming a liquid film containing chloride ions on the entire surface of a test piece of a test piece and then subjecting the test piece to continuous temperature changes to repeat drying and wetting is defined as one cycle. A test method for accelerating atmospheric corrosion, characterized by evaluating the corrosion resistance by repeating a cycle consisting of temperature and temperature changes. 2. A cycle wherein setting a test piece to a predetermined minimum temperature, forming a liquid film, thereafter increasing the temperature to a predetermined maximum temperature, and then lowering the temperature to the predetermined minimum temperature is one cycle. The accelerated atmospheric corrosion test method according to claim 1, wherein 3. The method for testing accelerated atmospheric corrosion according to claim 1, wherein one cycle is one day. 4. The method for accelerated test for atmospheric corrosion according to claim 1, wherein the fluctuation of the dew point of the atmosphere is maintained within ± 10 ° C.