Accelerated corrosion testing method for steel materials for bridges

Abstract

To provide an accelerated corrosion test method for bridge steel materials, which accurately simulates a corrosion environment of a specific assessment target portion of a bridge such as a girder end.SOLUTION: An accelerated corrosion test method for bridge steel materials is provided, the method comprising measuring an environmental factor for each of a general portion of a bridge and an assessment target portion of the bridge, quantifying a difference in measured values between the environmental factors of respective portions, and changing existing conditions for an accelerated corrosion test according to the quantified difference to perform the accelerated corrosion test.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an accelerated corrosion test method for steel materials for bridges, and more particularly to an accelerated corrosion test method capable of simulating a severely corrosive environment in a bridge. [Background technology]

[0002] Steel for bridges used outdoors is subject to corrosion due to the atmospheric environment in which it is used, and its initial performance and functionality may deteriorate over time. Therefore, understanding the corrosion resistance (hereinafter also referred to as weathering resistance) of steel for bridges in the atmospheric environment in which it is used is extremely important in terms of quality evaluation, life prediction, material selection, etc. of steel for bridges.

[0003] There are two test methods for evaluating weather resistance: atmospheric exposure tests conducted in an atmospheric environment, and accelerated exposure tests using indoor testing equipment with specific environmental factors in the atmospheric environment as the main factors. The former atmospheric exposure tests are conducted on-site, and are therefore well known to be highly reliable. However, conducting long-term tests on-site is practically difficult. Therefore, the latter accelerated exposure tests are generally used.

[0004] The accelerated exposure test generally involves a cyclic corrosion test (CCT), which is a corrosion test that mainly tests the effects of salinity, temperature, and humidity.Corrosion tests include a continuous spray test using a salt solution or artificial acid rain solution as the test solution, and a combined cycle test that combines spraying of the test solution with cycles of wetting and drying.

[0005] The most commonly prescribed accelerated corrosion test in the Japanese Industrial Standards (hereinafter referred to as JIS) is the neutral salt spray test (JIS Z 2371). This test involves spraying (atomizing) a 5% sodium chloride solution onto the test material, accelerating corrosion, and evaluating corrosion resistance. JIS Z 2371, established in 1955 (Showa 30), is a test method in which the sprayed solution is continuously applied to the test specimen, accelerating corrosion. However, it has the disadvantage of not taking into account the drying time in an atmospheric environment, such as that required for bridges.

[0006] A later developed test method is the combined cycle test method. In this test method, salt water is sprayed for a set period of time, followed by a drying and wetting process, and the salt water spray is not repeated continuously. Examples of combined cycle test methods include the "neutral salt water spray cycle test" specified in JIS H 8502 (corrosion resistance test method for plating) and the "combined cycle corrosion resistance" specified in JIS K 5621, 5600 (general-purpose rust preventive paint).

[0007] The combined cycle test method described above was developed based on the JASO Automotive Standards, a group standard set by the Society of Automotive Engineers of Japan. It is said that the combined cycle test produces test results that are closer to the real-world environment than the neutral salt spray test described above. However, compared to the history of the neutral salt spray test, the combined cycle test has a shorter history, and in setting the test conditions, a lot of trial and error has been done to ensure that the test conditions are appropriate for the location being tested.

[0008] For example, Patent Document 1 proposes the following method as an accelerated corrosion test method for steel materials used in structures such as bridges in highly humid environments, particularly in water leaking areas and narrow spaces: That is, the accelerated corrosion test method for steel materials comprises carrying out the following steps (A), (B), and (C) at least once, and in the step (A), the amount of salt deposition is 0.1 to 100,000 mg / m 2The document also discloses an accelerated corrosion test method for steel in a highly humid environment, characterized in that in the following step (B), the drying step and wetting step are carried out within the following condition ranges: (A) a step of adhering salt containing chloride ions to the surface of the steel, (B) a step of repeating the drying step and wetting step set by changing the temperature and relative humidity on the steel, with one cycle consisting of the drying step and wetting step being repeated, and the relative humidity in the drying step and the wetting rate, as expressed by the following formula, being within the following condition ranges, and carrying out this cycle at least once: drying step relative humidity: more than 40% and 70% or less, wetting step relative humidity: 80% or more, wetting rate = (wetting step holding time / (drying step holding time + wetting step holding time)): 95% or more and 100% or less, (C) a step of washing the surface of the steel with wash water.

[0009] Patent Document 2 also shows that the wetness factor is calculated using the formula: wetness factor = P(RH) × P(T) using a probability coefficient for humidity P(RH) and a probability coefficient for temperature P(T) derived from the annual average relative humidity (RH) and annual average temperature (T) measured near the usage environment.Then, a method for evaluating paint corrosion potential using this wetness factor (wetness factor) is shown. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-139450 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-194314 Summary of the Invention [Problem to be solved by the invention]

[0011] The combined cycle test may produce test results closer to the real environment when compared with the neutral salt spray test mentioned above, but the test conditions do not exactly simulate the corrosive environment of a bridge. The reason for this is that bridges are steel structures with complex shapes, and although the areas where bridges are erected are in the same macroscopic environment, the corrosion conditions are often different between the center of the bridge, where the space under the girders is wide and well-ventilated, and the ends of the girders, where the space under the girders is narrow and poorly ventilated, and in some cases, where vegetation grows thick and sediment accumulates. In reality, it is the ends of the bridge girders that are the problematic areas where corrosion of the steel that makes up the bridge progresses.

[0012] Furthermore, the above-mentioned combined cycle test was developed with reference to automobile standards, and did not take into account the corrosive environment of a bridge. The environment in the center of a bridge is thought to be able to simulate a general atmospheric corrosion environment where automobiles pass through. However, the environmental factors at the ends of bridge girders are unknown, and it cannot be said that they can simulate a general atmospheric corrosion environment where automobiles pass through.

[0013] Patent Document 1 proposes a technique for an accelerated corrosion test method for steel materials used in structures such as bridges, but does not necessarily simulate the corrosive environment at the ends of bridge girders.

[0014] Patent Document 2 suggests using annual average relative humidity and annual average temperature measured near the usage environment. While it is convenient to use values ​​from a data set, such as data from the Japan Meteorological Agency, in reality, as will be described later, the temperature and humidity of bridge parts change from moment to moment, with large daily fluctuations, resulting in significant differences in the annual average relative humidity and annual average temperature measured near the usage environment. Furthermore, the actual bridge environment (WET ratio) is not simple enough to be uniquely determined given average temperature and average humidity, and it cannot be said that bridge parts are properly evaluated. In other words, until now, there has been no laboratory corrosion test method that simulates the corrosive environment of bridge girder ends, and there has been a lack of appropriate evaluation methods for developing highly corrosion-resistant steel for bridges.

[0015] The present invention has been made in consideration of the above circumstances, and its object is to provide an accelerated corrosion testing method for steel materials for bridges that accurately simulates the corrosive environment of specific evaluation targets such as the girder ends of bridges, and to provide a method for evaluating the corrosion resistance of steel materials for bridges using the accelerated corrosion testing method. [Means for solving the problem]

[0016] Aspect 1 of the present invention is A corrosion accelerated testing method for steel materials for bridges, comprising: a step of measuring environmental factors in each of the general portion of the bridge and the evaluation target portion of the bridge; Quantifying the differences in the measured values ​​of the environmental factors of each part; and changing the conditions of an existing accelerated corrosion test based on the quantified difference, and then conducting the accelerated corrosion test.

[0017] Aspect 2 of the present invention is In the accelerated corrosion test method for steel materials for bridges according to aspect 1, the environmental factors of each part are measured at intervals of 1 to 60 minutes, including the surface temperature of the steel material and the drying or wetting time of the surface of the steel material, and the salt content is measured at monthly intervals.

[0018] Aspect 3 of the present invention is In the measurement of the dry or wet time, the current value on the surface of the steel material is measured with an ACM-type corrosion sensor, and the time during which the current value is 0.1 μA or less is defined as the dry time, and the time during which the current value is more than 0.1 μA is defined as the wet time. This is the accelerated corrosion test method for steel materials for bridges according to aspect 1 or 2.

[0019] A fourth aspect of the present invention is The existing accelerated corrosion test is a combined cycle test including a salt spray process of spraying salt water onto a steel material, a drying process of drying the steel material to which chlorides have adhered in the salt spray process, and a wetting process of wetting the steel material. This is the accelerated corrosion test method for steel materials for bridges according to aspect 1.

[0020] A fifth aspect of the present invention is The combined cycle test is the accelerated corrosion test method for bridge steel materials according to aspect 4, which is carried out under the operating conditions of JIS-K-5600 Cycle D.

[0021] A sixth aspect of the present invention is The accelerated corrosion test method for steel materials for bridges according to aspect 4 or 5, wherein the concentration of salt water used in the salt water spraying step is 5 mass % or less, which is one-tenth of the amount of airborne salt measured in an actual environment.

[0022] A seventh aspect of the present invention is The accelerated corrosion testing method for steel materials for bridges according to aspect 4 or 5, wherein when the difference, as expressed by the following formula, between the steel surface temperature of the general part of the bridge and the steel surface temperature of the part of the bridge to be evaluated is 30% or more, the modified test temperatures for the salt spray process, the drying process, and the wetting process of the combined cyclic test are set to (existing test temperature × (steel surface temperature of the part of the bridge to be evaluated / steel surface temperature of the general part of the bridge)): Temperature difference (%) = [(Temperature of the bridge part being evaluated - Temperature of the general part of the bridge) / (Temperature of the general part of the bridge)] x 100

[0023] Aspect 8 of the present invention is Calculate the ratio of the drying time of the evaluated part of the bridge to the drying time of the general part of the bridge, multiplying the existing drying time of the combined cycle test by the percentage to obtain a corrected drying time; and 6. The accelerated corrosion test method for bridge steel materials according to aspect 4 or 5, wherein a difference obtained by subtracting a corrected drying time from an existing drying time in the combined cyclic test is added to the existing wetting time in the combined cyclic test to obtain the corrected wetting time.

[0024] A ninth aspect of the present invention is The salt spray time in the salt spray process is 15 minutes to 30 minutes, the corrected drying time in the drying process is 30 minutes or more, and the corrected wetting time in the wetting process is 30 minutes or more, The total time of the salt spray time, the modified drying time, and the modified wetting time is 5 to 7 hours, and further, The method for accelerated corrosion testing of a steel material for bridges according to aspect 4 or 5, wherein the WET ratio represented by the following formula (1) is set to 34% to 66%: WET rate = [(salt spray time + wetting time) / (salt spray time + drying time + wetting time)] × 100 (1)

[0025] A tenth aspect of the present invention is Aspect 10 is the accelerated corrosion testing method for a steel material for bridges according to aspect 9, wherein the wet rate is set to 40% to 60%.

[0026] An eleventh aspect of the present invention is A method for evaluating the corrosion resistance of a steel material for bridges using the accelerated corrosion test method for a steel material for bridges according to the first or second aspect. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide an accelerated corrosion testing method for steel materials for bridges that accurately simulates the corrosive environment of specific evaluation targets such as the girder ends of bridges, and to provide a method for evaluating the corrosion resistance of steel materials for bridges using the accelerated corrosion testing method. [Brief explanation of the drawings]

[0028] [Figure 1] Figure 1 shows the relationship between the WET rate and the amount of corrosion over two months for the general section and girder end of a bridge in an actual environment. [Figure 2] FIG. 2 is a diagram showing the shape and installation method of the steel test piece in the example. [Figure 3] FIG. 3 is a diagram showing the results of measuring current values ​​using an ACM sensor in the example. [Figure 4] FIG. 4 is a diagram showing the relationship between the wet rate and the amount of corrosion in the examples. [Figure 5] FIG. 5 is a diagram comparing FIG. 1 and FIG. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present inventors have conducted extensive research to realize an accelerated corrosion test that simulates the severe corrosive environment of bridge girder ends, which has not been sufficiently reproduced until now, as an evaluation target area. a process of measuring environmental factors in each of the general part of the bridge and the part of the bridge to be evaluated; Quantifying the differences in the measured values ​​of the environmental factors of each part; The authors discovered that an accelerated corrosion test method for steel materials can be achieved by modifying the conditions of an existing accelerated corrosion test based on the quantified difference and then conducting the accelerated corrosion test. Each step is explained below. The "evaluation target portion of the bridge" refers to the location where the corrosive environment is to be simulated in the accelerated corrosion test.

[0030] [Process of measuring environmental factors in both the general section of the bridge and the section of the bridge to be evaluated] [Process to quantify the differences in the measured values ​​of environmental factors in each part] Using measuring equipment installed in a real environment, environmental factors are measured in both the "real environment of the general part (center) of the bridge," which can be simulated by existing cyclic corrosion tests, and the "real environment of the part of the bridge being evaluated," which cannot be simulated by existing cyclic corrosion tests, such as the severe corrosive environment of the girder end of the bridge mentioned above. By measuring environmental factors, it is possible to quantitatively evaluate the differences from the general part of the bridge, and by reflecting these differences in existing cyclic corrosion tests, it is possible to perform a corrosion resistance evaluation that is more in line with the real environment. Furthermore, measuring environmental factors makes it possible to clarify which environmental factors have a significant impact on corrosion.

[0031] The measured values ​​of environmental factors for the "actual environment of the general part (central part) of the bridge" and the "actual environment of the part of the bridge being evaluated" are compared, and the differences in the measured values ​​of the environmental factors for each part are quantified.The environmental factors to be measured include the steel surface temperature, humidity, and the wetness of the steel surface (such as the time it takes for the steel surface to dry or wet), the amount of salt, etc.

[0032] The conditions for the combined cycle test include the operating conditions of JIS-K-5600 Cycle D shown in Table 1 below. However, the conditions for existing accelerated corrosion tests are not limited to these, and other standards such as JIS K 5621 can also be used.

[0033] In this specification, the term "general part of a bridge" refers to a location with a large, well-ventilated space under the girder, such as the center of a bridge. While there is no clear definition of the term, the term "general part of a bridge" refers to the area including the center of the bridge, excluding the girder ends (described below), and occupies approximately 80% of the bridge's length. Hereinafter, the term "general part of a bridge" may be referred to as the "general bridge part." Meanwhile, the term "bridge girder end" refers not only to the bridge itself, but also to areas with severe corrosive environments, such as areas near abutments where vegetation is overgrown, where sediment has accumulated, and in some cases, areas near expansion joints or leaking areas. Examples include areas with leaking areas, stagnant water, high temperatures, high humidity, high salinity, and poor ventilation. Hereinafter, the term "bridge girder end" may be referred to as the "bridge girder end." However, the reason why the corrosive environment at the "bridge girder ends" is severe is because the space under the girders is narrow, and in bridges with narrow space under the girders or bridges with piers, the general part (center part) may also experience a corrosive environment similar to that at the girder ends. Furthermore, "existing accelerated corrosion tests" are not limited to JIS-K-5600 Cycle D shown in Table 1, for example, that were known at the time of filing this application, and refer to accelerated corrosion tests that are conducted uniformly without taking into account the differences in the corrosive environments between "general parts of bridges" and "bridge girder ends."

[0034] In other words, the evaluation target portion of a bridge is not particularly limited as long as it is a bridge. An example of an evaluation target portion that cannot be simulated under the conditions of existing accelerated corrosion tests such as the JIS-K-5600 Cycle D is the end of a bridge girder. The conditions in existing accelerated corrosion tests shown in Table 1 below are expressed as, for example, "existing salt spray time," "existing wetting time," and the following hot air drying and warm air drying times are collectively referred to as "existing drying time," and are to be distinguished from these times corrected by the method of the present invention.

[0035] [Table 1]

[0036] Below, we will explain the environmental factors, such as the amount of salt, drying / wetting time, and temperature, of each part of the general bridge section and the bridge section to be evaluated, as well as an existing accelerated corrosion test, a combined cycle test that includes a salt spray process in which salt water is sprayed onto the steel, a drying process in which the steel that has chlorides attached in the salt spray process is dried, and a wetting process in which the steel is wetted, as well as an existing combined cycle test conducted under the operating conditions of JIS-K-5600 Cycle D.

[0037] (Measurement of salt content) The amount of salt in the actual environment was measured for both the general bridge section and the bridge evaluation section. Even in mountainous areas far from the sea, antifreeze agents containing salt may be sprayed, and this dispersion causes airborne salt. Airborne salt is easily washed away by wind and rain in the general bridge section, but due to the intricate structure of the bridge girder ends, it is thought that airborne salt is more likely to accumulate.

[0038] The salt content may be NaCl. The interval for measuring the salt content is not particularly limited, but is preferably about once a month. This allows for more accurate calculation of the salt content. If possible, it is preferable to perform measurements once a month for one year. The method for measuring the salt content is not particularly limited, and existing methods can be used. For example, the dry gauze method, in which gauze is placed in the actual environment to measure the amount of airborne salt, the wet candle method or other airborne salt measurement methods specified in JIS-Z-2382, the airborne salt measurement method in which the steel surface is wiped with gauze, and the method in which a titanium plate is placed in the actual environment to measure the amount of adhered salt can be used. Although either the amount of airborne salt or the amount of adhered salt can be measured, it is preferable to measure the amount of airborne salt from the standpoint of accuracy. However, if it is difficult to measure the amount of airborne salt, the amount of adhered salt can be used instead.

[0039] (Quantifying the difference in salt content and modifying the conditions of existing accelerated corrosion tests based on the difference in salt content) When measuring the amount of airborne salt as the amount of salt, the amount of airborne salt measured in the bridge evaluation target section is the salt amount that cannot be used as bare weathering steel for bridges: 0.05 mdd (mg / dm 2 First, an evaluation is made to see whether the salt concentration is equal to or greater than the amount of salt in the air (wt. / day). Depending on this evaluation, the salt concentration used in the salt spray process can be set to 5.0 mass% or less, and to one-tenth of the amount of salt in the air measured in an actual environment. The details are as follows:

[0040] The amount of salt that has come into contact with the bridge evaluation area is 0.05mdd (mg / dm 2 / day), it is assumed that there is no difference in the salt content from the general bridge section, and the conditions of the existing accelerated corrosion test are adopted. In this case, the salt concentration of the saltwater used in the salt spray process of the combined cyclic test should be 5.0 mass%, the same as the salt concentration in the salt spray process of JIS-K-5600 Cycle D in Table 1 above. The reason for this is that the inventors separately investigated the relationship between the amount of corrosion and salt content in an actual environment, and found that the effect of salt content on the amount of corrosion in an actual environment is small, and that increasing the salt concentration does not have a significant effect on the corrosion rate.

[0041] On the other hand, the amount of salt that had flowed into the bridge evaluation area was 0.05 mdd (mg / dm 2 / day), the salt concentration of the saltwater used in the salt spray process of the combined cycle test can be appropriately changed, for example, to a concentration within the range of 5.0 mass% or less, which is one-tenth of the amount of airborne salt measured in an actual environment. For example, if the amount of airborne salt in the bridge evaluation section is 0.005 mdd, the salt concentration of the saltwater used in the salt spray process can be set to 0.5 wt%.

[0042] When the bridge evaluation target part is a girder end, the girder end is considered to be in an environment where the amount of corrosion is advanced, i.e., an environment of 0.05 mdd or more. Therefore, the salt concentration of the saltwater used in the salt spray process of the combined cycle test is set to 5.0 mass%, the same as the salt concentration in the salt spray process of JIS-K-5600 Cycle D in Table 1 above.

[0043] (Measurement of dry and wet time) The dry time and wet time during a certain period are determined by measuring the ratio of wet time per certain period on the steel surface of the general bridge section and the bridge evaluation section. The following measurement method can be used: The current value on the steel surface is measured using an ACM (Atmospheric Corrosion Monitor) corrosion sensor, and the time when the current value is 0.1 μA or less is considered to be the dry state of the steel surface, and the time when the current value is over 0.1 μA is considered to be the wet state of the steel surface. There are various theories about the current value that indicates the dry state of the steel, but in the above, a current value of 0.1 μA or more is considered to be the wet state of the steel surface.

[0044] The measurement of the drying or wetting time of the steel surface, i.e., the measurement of the current value, can be carried out, for example, at intervals of 1 to 60 minutes. Although more data is better, from the viewpoint of keeping the amount of data down and facilitating analysis, intervals of 1 minute or more are preferred. Furthermore, from the viewpoint of responding to weather changes, measurements are preferably taken at intervals of 60 minutes or less, and more preferably at intervals of 5 to 10 minutes. It is preferable to take measurements at the above intervals for 30 days or more.

[0045] (Quantification of the difference between dry and wet times) The total drying time within a certain period is calculated for both the general bridge section and the bridge evaluation section, and the ratio (%) of the total drying time for the bridge evaluation section to the total drying time for the general bridge section is calculated.

[0046] For example, if measurements are taken over a 30-day period and the total drying time for the general part of the bridge is 28 days and the total drying time for the part of the bridge subject to evaluation is 21 days, then the ratio (%) of the total drying time for the part of the bridge subject to evaluation to the total drying time for the general part of the bridge is (21 / 28) x 100 = 75%.

[0047] (Changes to existing accelerated corrosion test conditions based on differences in drying and wetting times) The corrected drying time is obtained by multiplying the quantitative difference by the above percentage and the existing drying time (total of 4 hours) for JIS-K-5600 Cycle D in Table 1. Furthermore, the difference obtained by subtracting the corrected drying time from the existing drying time in the combined cycle test is added to the existing wetting time in the combined cycle test to obtain the corrected wetting time.

[0048] For example, in the case of the above measurement results, the corrected drying time is the drying time (total of 4 hours) x 0.75 = 3 hours for JIS-K-5600 Cycle D shown in Table 1. Also, the difference between the existing drying time and the corrected drying time, 4 hours - 3 hours = 1 hour, is added to the existing wetting time of 1.5 hours, resulting in a corrected wetting time of 1.5 hours + 1 hour = 2.5 hours.

[0049] (Changes in the conditions of existing accelerated corrosion tests using wet rates based on dry and wet times) It is said that salt has a large effect in the case of general corrosion, but in the case of special and severe corrosion environments such as bridge girder ends, it has been found that wetness has a greater effect as an influencing factor than salt. When the inventors investigated the effect of environmental factors on the amount of corrosion, they found that the WET ratio, calculated from the above-mentioned dry time and wet time in the following formula (1), has a large effect on the amount of corrosion, as shown in Figure 1. Figure 1 shows the results of measuring the amount of corrosion over two months on a general bridge section and a bridge girder end in an actual environment. WET rate = [(salt spray time + wetting time) / (salt spray time + drying time + wetting time)] × 100 (1)

[0050] When evaluating the end of a bridge girder as the part of the bridge to be evaluated, it is possible to perform an evaluation that is in line with the actual environment of the end of a bridge girder by setting the WET ratio calculated using the formula below more preferably within the range of 40% to 60%. In other words, when evaluating the end of a bridge girder as the part of the bridge to be evaluated, the WET ratio has a greater effect on corrosion than the amount of salt or temperature as environmental factors, and therefore the corrosive environment of the end of a bridge girder can be adequately simulated simply by controlling the time of each process so as to satisfy the above WET ratio.

[0051] Corrosion is significantly affected by moisture, specifically the wetness of the steel surface. Moderate wetness allows for a smooth supply of oxygen, promoting corrosion. From this perspective, it is preferable to increase the wetness ratio, which quantifies the degree of wetness. The wetness ratio is preferably 34% or more, and more preferably 40% or more. On the other hand, if the steel surface is too wet, the corrosion environment tends to be less severe. This is because corrosion factors such as salt present on the steel surface are easily washed away, and the amount of oxygen supplied is reduced. Furthermore, once rust has formed, repeated exposure to dry and wet conditions further accelerates the formation of rust, but if the steel remains wet, rust is less likely to form and the amount of corrosion is likely to decrease.

[0052] As described above, from the viewpoint of promoting corrosion, it is desirable that dry and wet states be alternated, and therefore the wet ratio is preferably 66% or less, and more preferably 60% or less.

[0053] For example, in the case of the above measurement results, the WET ratio at the end of the bridge girder is 3 hours when the salt spray time (0.5 hours) + corrected wet time (2.5 hours) in the combined cycle test is 3 hours, and the salt spray time (0.5 hours) + corrected dry time (3 hours) + corrected wet time (2.5 hours) is 6 hours, so 3 ÷ 6 × 100 = 50%, which is an optimal corrosive environment.

[0054] (Temperature measurement) Thermometers are installed in the general part of the bridge and the part of the bridge to be evaluated, and the temperature is measured every 1 to 60 minutes, preferably every 5 to 10 minutes. There are no particular limitations on the thermometers.

[0055] (Quantifying temperature differences and modifying existing accelerated corrosion test conditions based on temperature) The difference between the steel surface temperature of the general part of the bridge and the steel surface temperature of the part of the bridge being evaluated is calculated using the following formula. Temperature difference (%) = [(Temperature of the bridge part being evaluated - Temperature of the general part of the bridge) / (Temperature of the general part of the bridge)] x 100

[0056] If the difference is 30% or greater, the modified test temperatures for the salt spray, drying, and wetting processes of the combined cycle test can be calculated as follows: (Existing Test Temperature) × (Steel Surface Temperature of the Bridge's Target Area / Steel Surface Temperature of the General Bridge Area). For example, if the temperature of the general bridge area is 20°C and the temperature of the target bridge area is 28°C, the temperature difference is [(28 - 20) / 20] × 100 = 40%. Thus, if the difference is 30% or greater, the existing JIS test temperature is 30°C, but the test can be performed at 30°C × 28 / 20 = 42°C. However, for example, the temperature difference between the general bridge area and the girder end is not significant, and there are no guidelines in Japan for high-temperature environments that could affect corrosion. Therefore, the existing JIS test temperature of 30°C can generally be maintained. When the target bridge area is the girder end, the temperature difference from the center is often less than 30%, so the existing JIS test temperature of 30°C can be maintained.

[0057] [A step of changing the conditions of the existing accelerated corrosion test based on the quantitative difference obtained in the previous step and performing an accelerated corrosion test] The cyclic dry-wet test according to the present invention is a wet-dry cycle process that includes a step of spraying salt water onto a steel specimen, a step of drying the specimen to which chlorides have adhered in the salt water spraying step, and a wetting step of wetting the steel specimen. The corrosion resistance is evaluated based on the amount of corrosion after repeating the cycle one or more times.

[0058] In this combined cyclic test, the test can be conducted in accordance with the test conditions of JIS-K-5600 Cycle D listed in Table 1, except that the test conditions are modified from those of the existing accelerated corrosion test based on the quantitative differences found in the above steps. The approximate times for each step are as follows: A salt spray time of 5 minutes or more is required to sufficiently wet the test specimen. However, even if the salt spray time is 30 minutes or more, the effects of salt are thought to saturate. Therefore, the salt spray time should be 5 to 30 minutes. The salt spray time is more preferably 15 to 30 minutes.

[0059] In the wetting process, the modified wetting time is preferably 5 minutes or more to ensure a sufficiently uniform atmosphere in the test chamber. The modified wetting time is more preferably 30 minutes or more. The hot air drying time is also preferably 15 minutes or more to ensure a sufficiently uniform atmosphere in the test chamber and to thoroughly dry the test specimens. The hot air drying time is also preferably 15 minutes or more to ensure a sufficiently uniform atmosphere in the test chamber and to thoroughly dry the test specimens. Based on the above, within the range that satisfies the WET ratio value, the salt spray time is preferably 5 to 30 minutes, more preferably 15 to 30 minutes, the modified wetting time is preferably 5 minutes or more, more preferably 30 minutes or more, and the total modified drying time is preferably 30 minutes or more. Furthermore, it is preferable that the total time of the salt spray time, the modified drying time, and the modified wetting time is 5 to 7 hours.

[0060] The transition time to each process should be short. The transition time to each process should be about 1 to 10 minutes, depending on the capacity of the equipment, and it is desirable to set each condition within 5 minutes of switching to each process.

[0061] As will be shown in the examples below, in the case of the girder ends of bridges, for example, the wetness conditions (dry time and wet time) have a greater effect on corrosion than the amount of salt, so it is sufficient to only control the wetness conditions (dry time and wet time).To more accurately simulate the amount of corrosion at the ends of bridge girder, the steel plate surface temperature, humidity, and salt content can also be determined from actual environmental values, in addition to the wetness conditions (dry time and wet time).

[0062] In the above explanation, JIS-K-5600 Cycle D was used as the standard condition for the existing accelerated corrosion test. However, as mentioned above, the conditions for the existing accelerated corrosion test are not limited to this, and for example, JIS K 5621 or the like can also be used as the standard.

[0063] In contrast to the present invention, the test conditions in Patent Document 1 are not set by quantitatively comparing the conditions of existing accelerated corrosion tests with the environment to be evaluated, and therefore it cannot be said that the combined cycle test sufficiently simulates the actual environment.

[0064] The test method of the present invention is not limited to any particular steel type as long as it is for bridges, and can be applied to steel materials such as ordinary steel, low-alloy steel, and stainless steel, as well as aluminum materials, plated steel sheets, clad steel sheets, etc. Examples of ordinary steel and low-alloy steel include ordinary steel and low-alloy steel materials conforming to the JIS-SMA and JIS-SM standards used for bridges.

[0065] The corrosion resistance evaluation method for steel materials for bridges is also included, which uses the accelerated corrosion test method for steel materials for bridges. The corrosion resistance evaluation method is not limited as long as the accelerated corrosion test method is carried out as described above, and conditions that are usually used can be adopted. [Example]

[0066] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

[0067] (Measured in a real environment) At the girder end of an actual bridge in Miyagi Prefecture and in a general area several meters away, temperature and humidity sensors were installed to measure temperature and humidity every 10 minutes, Atmospheric Corrosion Monitor (ACM) corrosion sensors (commonly known as ACM sensors) to directly measure the electrochemical corrosion current of metals generated by environmental factors every 10 minutes, steel test specimens (50 mm x 50 mm) known as patch test specimens, a gauze-based airborne salt measurement device, and titanium plates for measuring deposited salt. Measurements of corrosion weight loss, salt content, current values ​​measured by the ACM sensors, and temperature were conducted over a six-month period. The patch test specimens were installed as shown in Figure 2. One to three steel test specimens (N = 1–3) were used per condition. The steel plate test specimens were installed in the same position as the titanium plates for measuring deposited salt. To prevent the ACM sensors, batteries, and other precision equipment from getting wet, the precision equipment was protected in a white box (waterproof case).

[0068] [Measurement of corrosion amount] The weight of the steel test specimens was measured before and after the test to determine the corrosion weight loss, and the plate thickness loss, converted as described below, was taken as the amount of corrosion. The test results showed that there was a large difference in the corrosion weight loss of the steel test specimens (patch test specimens) between the girder ends and the general section. Several meteorological factors were thought to be the cause of this difference. In this case, there was no significant difference in temperature or humidity (monthly average) between the general section and the girder ends. There was a difference in the absolute values ​​of the amount of deposited salt and the amount of airborne salt, but in both cases, the amount of salt in winter was higher than in summer, and higher at the girder ends than in the general section. This was thought to be the effect of the spraying of antifreeze.

[0069] Figure 3 shows the results of measuring the current values ​​using the ACM sensor. In Figure 3, the ACM output on the vertical axis represents the current value, and the arrow indicates the rainfall period. From Figure 3, the time period when the ACM output value was 0.1 μA or less was determined to be the drying time. As a result, it was calculated that the girder ends were nearly dry for approximately 20 days and the general parts for approximately 28 days during the extracted 30-day period. The drying time of the steel surface for the general parts was 27.94 days during the 30-day period, indicating that the steel surface was essentially wet only during the rainfall periods indicated by the arrows. On the other hand, the drying time of the steel surface for the girder ends was only 21.52 days, indicating that the surface was wet even outside of the rainfall periods. In other words, the ratio (%) of the total drying time of the bridge girder ends to the total drying time of the general parts of the bridge was (21.52 / 27.94) x 100 = 77%.

[0070] As mentioned above, the drying time for the bridge girder ends was 77% of that for the general area. This difference cannot be observed with a hygrometer. From a macroscopic perspective, the temperature, humidity, and amount of airborne and adhered salt in the bridge construction area should be the same, but microscopic observation of each bridge section revealed that the wet time, i.e., the wetting time, and the drying time differ significantly. This difference is thought to be due to the fact that, although the humidity may be the same, local meteorological factors such as sunlight exposure and wind direction and speed differ for each bridge section, as well as changes due to spatial and structural conditions. From the ACM output values, it was estimated that corrosion was progressing while the surface was wet, and it was thought that the wetness of the surface affected the above-mentioned difference in corrosion rate.

[0071] (Changes to existing accelerated corrosion test conditions) To evaluate these differences depending on the part of the bridge in a laboratory, it is necessary to use test conditions that reflect the micro-environmental factors of the bridge. Therefore, in this example, the typical test conditions of JIS-K-5600 Cycle D were adopted as the conditions for existing accelerated corrosion tests, and these test conditions were modified to reflect the micro-environmental factors of the bridge.

[0072] [Drying and wetting time] First, the total drying time, including the hot air drying time and warm air drying time specified in the JIS standard, was reduced to 77%. In practice, this was set at 75%, taking into consideration the programming of the test equipment, and the drying time was changed from the previous 4 hours to 3 hours. In addition, the wetting time was increased in conjunction with the change in drying time. Specifically, the difference between the existing drying time and the corrected drying time (4 hours - 3 hours = 1 hour) was added to the existing wetting time of 1.5 hours, resulting in a corrected wetting time of 1.5 hours + 1 hour = 2.5 hours. [WET rate] The general WET rate for the bridge was 2 ÷ 6 × 100 = 33%, as the existing salt spray time + existing wetting time in Table 1 was 2 hours, and the existing salt spray time + existing dry time + existing wetting time was 6 hours. On the other hand, the WET rate at the bridge girder end was 3 ÷ 6 × 100 = 50%, as the salt spray time + corrected wetting time in the combined cycle test was 3 hours, and the salt spray time + corrected dry time + corrected wetting time was 6 hours.

[0073] [Temperature / Humidity] There was no significant difference in temperature or humidity between the JIS conditions and the measurement results for the general part of the bridge, nor was there a significant difference between the measurement results for the general part of the bridge and the girder end, i.e. the difference was less than 30%, so the JIS conditions were followed.

[0074] [Salt content] Regarding salt, salt spraying is essential due to the effects of antifreeze. Since the amount of salt that was blown in was 0.05mdd or more, the JIS requirements were followed.

[0075] Taking into account the differences in the above environmental factors, the conditions for the accelerated corrosion test were set as follows.

[0076] The salt spray process involved spraying 5.0 mass % NaCl at 30°C for 30 minutes (0.5 hours). Although strict temperature control is recommended, the tolerance was set to ±2°C, taking into account variations within the test chamber.

[0077] The wetting process was carried out at 30°C and 95% RH for 150 minutes (2.5 hours). Humidity control should be strict, but considering variations within the test chamber, a tolerance of ±3% was set.

[0078] The hot air drying process was carried out for 90 minutes (1.5 hours) at 50°C. Humidity control should be strictly controlled, but considering variations within the test chamber, the tolerance was set at ±2°C.

[0079] The hot air drying process was carried out for 90 minutes (1.5 hours) at 30°C. Humidity control should be carried out strictly, but considering variations within the test chamber, the tolerance was set at ±2°C.

[0080] These conditions are shown in Table 2.

[0081] [Table 2]

[0082] The specimen was made of 150mm x 50mm x 6mm steel, with a 5mm width on each side of the surface, the sides, and the back sealed. Only the 140mm x 40mm portion of the surface was corroded, and the test was carried out for 14 days.

[0083] Twelve test pieces were used to account for variations. The accelerated corrosion test was conducted under the same conditions as the existing accelerated corrosion test (JIS-K-5600 Cycle D), except for some changes to the conditions for each step as shown in Table 2 above. For comparison, a test was also conducted under the existing accelerated corrosion test conditions (33% wet ratio).

[0084] After the test, the corrosion products were removed and weighed, and the corrosion weight loss was calculated from the difference in weight before and after the test. The corrosion rate was calculated from the 14-day test results and converted to a one-month rate. The results converted to the amount of plate thickness loss after a one-month test are shown in Figure 4, with the amount of corrosion on the vertical axis and the wet rate on the horizontal axis, along with the results of a test under existing accelerated corrosion test conditions (wet rate 33%).

[0085] As shown in Figure 4 above, under the existing accelerated corrosion test conditions, the plate thickness loss was approximately 0.005 mm, whereas under the new conditions, it was 0.015 to 0.025 mm, which was 3 to 5 times the amount of corrosion compared to the existing accelerated corrosion test. In other words, the existing accelerated corrosion test method was unable to precisely evaluate a severely corrosive environment such as the end of a bridge girder, making it difficult to distinguish the amount of corrosion from a mildly corrosive environment. However, under the test conditions of this embodiment, even for the same test period, it was possible to obtain a corrosion amount that accurately reflected the conditions of a severely corrosive environment. The inventors conducted experiments in which the wet ratio was changed to 33%, 50%, and 66%, and found that the largest amount of corrosion was observed when the wet ratio was 50%.

[0086] Furthermore, to confirm whether the accelerated corrosion test of the present invention simulates the corrosion conditions of an actual bridge, the results of two months of corrosion in the actual environment of Figure 1 were compared with those of Figure 4, and are shown in Figure 5. In Figure 5, "A" shows the results for the severely corroded areas, and "B" shows the results for the general areas. Figure 5 shows that, with the accelerated corrosion test of the present invention, the amount of corrosion equivalent to two months on an actual bridge can be evaluated in one month under the new conditions. Furthermore, a good correlation was observed in the amount of corrosion for the general areas and girder ends in the laboratory and real-world test results, demonstrating that the present invention can simulate an actual environment.

[0087] The present invention includes the following aspects. Aspect 1a of the present invention is A corrosion accelerated testing method for steel materials for bridges, comprising: a step of measuring environmental factors in each of the general portion of the bridge and the evaluation target portion of the bridge; Quantifying the differences in the measured values ​​of the environmental factors of each part; and changing the conditions of an existing accelerated corrosion test based on the quantified difference, and then conducting the accelerated corrosion test.

[0088] Aspect 2a of the present invention is In the accelerated corrosion test method for steel materials for bridges according to aspect 1a, the environmental factors of each part are measured at intervals of 1 to 60 minutes, namely, the steel surface temperature and the drying or wetting time of the steel surface, and the salt content is measured at intervals of one month.

[0089] Aspect 3a of the present invention is In the measurement of the dry or wet time, the current value on the steel surface is measured with an ACM-type corrosion sensor, and the time during which the current value is 0.1 μA or less is defined as the dry time, and the time during which the current value is more than 0.1 μA is defined as the wet time. This is the accelerated corrosion test method for steel materials for bridges according to aspect 1a or 2a.

[0090] Aspect 4a of the present invention is The existing accelerated corrosion test is a combined cycle test including a salt spray step of spraying salt water onto a steel material, a drying step of drying the steel material to which chlorides have adhered in the salt spray step, and a wetting step of wetting the steel material, in accordance with any one of Aspects 1a to 3a.

[0091] Aspect 5a of the present invention is The combined cycle test is the accelerated corrosion test method for bridge steel materials according to aspect 4a, which is carried out under the operating conditions of JIS-K-5600 Cycle D.

[0092] Aspect 6a of the present invention is The accelerated corrosion test method for steel materials for bridges according to aspect 4a or 5a, wherein the concentration of salt water used in the salt spray step is 5 mass % or less, which is one-tenth of the amount of airborne salt measured in an actual environment.

[0093] Aspect 7a of the present invention is The accelerated corrosion testing method for steel materials for bridges according to any one of Aspects 4a to 6a, wherein, when the difference, as expressed by the following formula, between the steel surface temperature of the general part of the bridge and the steel surface temperature of the part of the bridge to be evaluated is 30% or more, the modified test temperatures for the salt spray process, drying process, and wetting process of the combined cycle test are set to the existing test temperature × (steel surface temperature of the part of the bridge to be evaluated / steel surface temperature of the general part of the bridge). Temperature difference (%) = [(Temperature of the bridge part being evaluated - Temperature of the general part of the bridge) / (Temperature of the general part of the bridge)] x 100

[0094] Aspect 8a of the present invention is Calculate the ratio of the drying time of the evaluated part of the bridge to the drying time of the general part of the bridge, multiplying the existing drying time of the combined cycle test by the percentage to obtain a corrected drying time; and The accelerated corrosion test method for steel materials for bridges according to any one of Aspects 4a to 7a, wherein a difference obtained by subtracting a corrected drying time from the existing drying time of the combined cyclic test is added to the existing wetting time of the combined cyclic test to obtain the corrected wetting time.

[0095] Aspect 9a of the present invention is The salt spray time in the salt spray process is 15 minutes to 30 minutes, the corrected drying time in the drying process is 30 minutes or more, and the corrected wetting time in the wetting process is 30 minutes or more, The total time of the salt spray time, the modified drying time, and the modified wetting time is 5 to 7 hours, and further, The accelerated corrosion testing method for a steel material for bridges according to any one of Aspects 4a to 8a, wherein the WET ratio represented by the following formula (1) is set to 34% to 66%: WET rate = [(salt spray time + wetting time) / (salt spray time + drying time + wetting time)] × 100 (1)

[0096] Aspect 10a of the present invention is The accelerated corrosion testing method for a steel material for bridges according to Aspect 9a, wherein the wet rate is set to 40% to 60%.

[0097] Aspect 11a of the present invention is A method for evaluating the corrosion resistance of a steel material for bridges, using the accelerated corrosion testing method for a steel material for bridges according to any one of Aspects 1a to 10a. [Industrial Applicability]

[0098] This will enable the development of new highly weather-resistant steel materials that can withstand the corrosive environment at the ends of bridge girders, which could not be simulated using conventional evaluation methods.

Claims

1. A corrosion accelerated testing method for steel materials for bridges, comprising: a step of measuring environmental factors in each of the general portion of the bridge and the evaluation target portion of the bridge; Quantifying the differences in the measured values ​​of the environmental factors of each part; and a step of changing the conditions of an existing accelerated corrosion test based on the quantified difference and conducting the accelerated corrosion test.

2. 2. The accelerated corrosion test method for steel materials for bridges according to claim 1, wherein the environmental factors of each part are measured by measuring the steel surface temperature and the drying or wetting time of the steel surface at intervals of 1 to 60 minutes, and measuring the salt content at intervals of one month.

3. 3. The accelerated corrosion test method for bridge steel materials according to claim 2, wherein, in measuring the drying or wetting time, the current value on the surface of the steel material is measured with an ACM-type corrosion sensor, and the time when the current value is 0.1 μA or less is defined as the drying time, and the time when the current value is more than 0.1 μA is defined as the wetting time.

4. 2. The accelerated corrosion test method for bridge steel materials according to claim 1, wherein the existing accelerated corrosion test is a combined cycle test including a salt spray process of spraying salt water onto a steel material, a drying process of drying the steel material to which chlorides have adhered in the salt spray process, and a wetting process of wetting the steel material.

5. 5. The accelerated corrosion test method for bridge steel materials according to claim 4, wherein the combined cycle test is carried out under operating conditions of JIS-K-5600 Cycle D.

6. 6. The accelerated corrosion test method for bridge steel materials according to claim 4 or 5, wherein the concentration of salt water used in the salt water spraying step is 5 mass% or less, which is one-tenth of the amount of airborne salt measured in an actual environment.

7. 6. The accelerated corrosion testing method for steel materials for bridges according to claim 4 or 5, wherein, when a difference, as expressed by the following formula, between the steel surface temperature of the general part of the bridge and the steel surface temperature of the part of the bridge to be evaluated is 30% or more, the modified test temperatures for the salt spray process, the drying process, and the wetting process of the combined cyclic test are set to the existing test temperature × (steel surface temperature of the part of the bridge to be evaluated / steel surface temperature of the general part of the bridge). Temperature difference (%) = [(Temperature of the bridge part being evaluated - Temperature of the general part of the bridge) / (Temperature of the general part of the bridge)] x 100

8. Calculate the ratio of the drying time of the evaluated part of the bridge to the drying time of the general part of the bridge, multiplying the existing drying time of the combined cycle test by the percentage to obtain a corrected drying time; and 6. The accelerated corrosion test method for bridge steel materials according to claim 4 or 5, wherein a difference obtained by subtracting a corrected drying time from an existing drying time in the combined cyclic test is added to the existing wetting time in the combined cyclic test to obtain the corrected wetting time.

9. The salt spray time in the salt spray step is 15 minutes to 30 minutes, the corrected drying time in the drying step is 30 minutes or more, and the corrected wetting time in the wetting step is 30 minutes or more, The total time of the salt spray time, the modified drying time, and the modified wetting time is 5 to 7 hours, and further The accelerated corrosion test method for bridge steel materials according to claim 4 or 5, wherein the WET ratio represented by the following formula (1) is 34% to 66%: WET rate = [(salt spray time + wetting time) / (salt spray time + drying time + wetting time)] × 100 (1)

10. The accelerated corrosion test method for bridge steel materials according to claim 9, wherein the WET rate is 40% to 60%.

11. A method for evaluating the corrosion resistance of steel materials for bridges, using the accelerated corrosion test method for steel materials for bridges according to claim 1 or 2.

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