Corrosion promotion exposure test method for steel materials

Abstract

To provide a corrosion promotion exposure test method for steel materials that can quantitatively indicate the extent of progress of corrosion promotion of steel materials in a soil environment.SOLUTION: A corrosion promotion exposure test method for steel materials executes a corrosion promotion exposure test including burying a plurality of test pieces 100 at an interval in soil 30 put into a test container 12, intermittently sprinkling a sodium chloride solution L on the soil 30, and repeating drying and moistening the soil, and a corrosion normal exposure test including burying a plurality of test pieces 300 equivalent to the test pieces 100 at an interval in soil 30 put into the test container 212. The method includes: taking out the test pieces 100 and test pieces 300 from the soil 30 for every predetermined exposure days, calculating a promoted corrosion rate of the test pieces 100 and a normal corrosion rate of the test pieces 300, from corrosion weight values of the test pieces 100 and test pieces 300, in accordance with the JIS K 0100, a "testing method for corrosivity of industrial water," and calculating a corrosion promotion multiplication factor of the steel materials from the promoted corrosion rate and the normal corrosion rate.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for accelerating exposure test of steel materials in a soil environment.

Background Art

[0002] Patent Document 1 below discloses a method for soil corrosion test of steel materials using simulated soil, wherein the simulated soil is composed of granular materials having properties of being insoluble in water and hardly soluble in acids and alkalis, and further adjusting the water content in the simulated soil to set the pF value to an arbitrary value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method for soil corrosion test of steel materials described in Patent Document 1 above, it is a comparison of the corrosion characteristics of steel materials for each level of soil. Therefore, it is impossible to quantitatively show to what extent the corrosion characteristics of steel materials can be accelerated by the acceleration test.

[0005] In consideration of the above facts, an object of the present invention is to provide a method for accelerating exposure test of steel materials that can quantitatively show to what extent the corrosion of steel materials in a soil environment progresses.

Means for Solving the Problems

[0006] The corrosion acceleration exposure test method for steel materials according to the first aspect includes embedding a plurality of first steel materials at intervals in the soil placed in a first container, intermittently spraying an aqueous sodium chloride solution on the soil, and repeating the wetting and drying of the soil in a corrosion acceleration exposure test, and conducting a normal corrosion exposure test in which a plurality of second steel materials equivalent to the first steel materials are embedded at intervals in the soil placed in a second container. For each predetermined exposure number of days, the first steel material and the second steel material are taken out of the soil, and according to JIS K 0100 "Test Method for Corrosiveness of Industrial Water", the accelerated corrosion rate of the first steel material and the normal corrosion rate of the second steel material are calculated from the corrosion weight values of the first steel material and the second steel material, and the corrosion acceleration magnification of the steel material is calculated from the accelerated corrosion rate and the normal corrosion rate.

[0007] According to the corrosion acceleration exposure test method for steel materials according to the first aspect, by using the exposure test results of both the corrosion acceleration exposure test and the normal corrosion exposure test, the accelerated corrosion rate and the normal corrosion rate are calculated according to JIS K 0100 "Test Method for Corrosiveness of Industrial Water". Furthermore, by calculating the corrosion acceleration magnification of the steel material from the accelerated corrosion rate and the normal corrosion rate, it is possible to quantitatively show to what extent the corrosion acceleration of the steel material progresses, and a test with reproducibility can be performed.

[0008] The corrosion acceleration exposure test method for steel materials according to the second aspect is the corrosion acceleration exposure test method for steel materials according to the first aspect. Based on the result of calculating the accelerated corrosion rate from the corrosion weight values of the plurality of first steel materials obtained from the start of exposure to the elapsed days of a predetermined period in the corrosion acceleration exposure test, a first approximation formula representing the relationship between the exposure number of days and the accelerated corrosion rate is derived. Based on the result of calculating the normal corrosion rate from the corrosion weight values of the plurality of second steel materials obtained from the start of exposure to the elapsed days of a predetermined period in the normal corrosion exposure test, a second approximation formula representing the relationship between the exposure number of days and the corrosion rate is derived. The corrosion acceleration magnification is calculated by a third formula obtained by dividing the first approximation formula by the second approximation formula.

[0009] According to the corrosion acceleration exposure test method for steel materials according to the second aspect, by calculating the corrosion acceleration magnification by a third formula obtained by dividing the first approximation formula by the second approximation formula, it is possible to quantitatively show to what extent the corrosion acceleration of the steel material progresses.

[0010] In the method for accelerating corrosion exposure test of steel materials according to the third aspect, in the method for accelerating corrosion exposure test of steel materials according to the first aspect, the concentration of the sodium chloride aqueous solution is 2% or more and 5% or less.

[0011] According to the method for accelerating corrosion exposure test of steel materials according to the third aspect, when the concentration of the sodium chloride aqueous solution is in the range of 2% or more and 5% or less, the corrosion rate of the first steel material becomes relatively high compared with the case where it is outside this range. That is, it is possible to suppress a decrease in the corrosion rate of the first steel material as compared with the case where the concentration of the sodium chloride aqueous solution is less than 2%. Also, it is possible to suppress a decrease in the corrosion rate of the first steel material as compared with the case where the concentration of the sodium chloride aqueous solution is greater than 5%.

Effect of the Invention

[0012] According to the method for accelerating corrosion exposure test of steel materials of the present disclosure, it is possible to quantitatively show the degree to which the corrosion of steel materials in the soil environment progresses.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0014] Embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, those having low relevance to the present invention are not shown.

[0015] 〔First Embodiment〕 Using FIGS. 1 to 5, the corrosion acceleration exposure test method for steel materials according to the first embodiment will be described. FIG. 1 is a schematic configuration diagram showing an automatic watering device 10 for carrying out a corrosion acceleration exposure test in the corrosion acceleration exposure test method for steel materials according to the first embodiment. FIG. 2(A) is a perspective view showing a test container 12 of the automatic watering device 10, and FIG. 2(B) is a plan view showing the test container 12.

[0016] <Configuration of Automatic Watering Device> The automatic watering device 10 is a test device for carrying out a corrosion acceleration exposure test on a test piece 100 (see FIGS. 2(A) and (B)). As shown in FIG. 1, the automatic watering device 10 includes a test container 12, a tank 14, a supply unit 16, a watering unit 18, a discharge unit 20, and a control panel 22.

[0017] As shown in FIGS. 1 and 2(A) and (B), in the automatic watering device 10, a plurality of test pieces 100 are buried in the soil 30 placed in the test container 12 at intervals, and an aqueous sodium chloride solution L is intermittently sprayed on the soil 30 to carry out a corrosion acceleration exposure test in which the dry and wet states of the soil 30 are repeated. Here, the test piece 100 is an example of the first steel material, and the test container 12 is an example of the first container.

[0018] As shown in FIGS. 1 and 2(A) and (B), the test container 12 is a box-shaped member with an open top, and includes a bottom 12A and side portions 12B. As an example, the test container 12 is rectangular in plan view, and is formed such that the outer shape of the upper side in the vertical direction of the side portion 12B gradually becomes larger than the outer shape of the lower side in the vertical direction of the side portion 12B. Also, as an example, the test container 12 includes a rectangular bottom 12A and side portions 12B formed by four sides rising from the bottom 12A. Note that the test container 12 is not limited to this shape and can be changed to other shapes.

[0019] Soil 30 is placed inside the test container 12. As an example, for the soil 30, Kanto loam is used, and lumps of soil and gravel are removed by a sieve of a predetermined size (for example, 19 mm) so as to have a uniform particle size distribution.

[0020] A plurality of test pieces 100 are buried in the soil 30 inside the test container 12 at intervals. As an example, the test piece 100 is an SS material, that is, a hot-rolled steel sheet for general structural use. In this embodiment, SS400 is used as the test piece 100. The test container 12 is configured such that a sodium chloride solution is sprayed from above by the sprinkling unit 18 to accelerate the corrosion of the test piece 100 buried in the soil 30.

[0021] As an example, the test piece 100 is a plate-shaped member. The dimensions of the test piece 100 are, for example, a length in the vertical direction of 100 mm, a length in the horizontal direction of 50 mm, and a thickness t of 9.0 mm. The surface state of the test piece 100 is a ground finish obtained by removing the mill scale (surface oxide film), surface oil, and deposits, etc. by shot blasting. Shot blasting is an example of a pretreatment for accelerating the corrosion of the test piece 100.

[0022] In order to spray an aqueous sodium chloride solution from above the test container 12 by the watering section 18, a plurality of drain holes 13 for discharging moisture containing the aqueous sodium chloride solution in the soil 30 are provided at the lower part of the side portion 12B of the test container 12. The plurality of drain holes 13 are arranged side by side in the horizontal direction at the lower part of the side portion 12B. The drain holes 13 not only discharge the moisture in the soil 30 but also allow air to pass between the inside and the outside of the test container 12. For example, the water vapor inside the test container 12 can escape to the outside of the test container 12 through the drain holes 13.

[0023] FIG. 3 is an enlarged perspective view showing the lower part of the test container 12. As shown in FIG. 3, the test container 12 includes a plurality of protruding portions 36 that protrude outward along the vertical direction on the side portion 12B. The plurality of protruding portions 36 are provided at intervals in the horizontal direction at the lower part of the side portion 12B. In the test container 12, a plurality of drain holes 13 are provided in the diagonal wall portion 38 arranged between the protruding portions 36. Note that the shape of the test container 12 can be changed. For example, the test container 12 may also be provided with a plurality of drain holes 13 in each protruding portion 36. Further, the test container 12 may be planar without providing the plurality of protruding portions 36.

[0024] As an example, a plurality of drain holes 13 are provided at the lower part of the side portion 12B on the long side of the rectangular shape in the test container 12, but the positions of the plurality of drain holes 13 are not limited to this configuration and can be changed. Further, the drain holes 13 are rectangular in shape that is long in the vertical direction, but the shape of the drain holes 13 is not limited to this and can be changed.

[0025] As an example, the test container 12 is supported on a base 60A provided at the lower part of the support member 60 via a plurality of blocks 62.

[0026] Inside the test container 12, a moisture content sensor 32 for measuring the moisture content in the soil 30 is provided. The moisture content sensor 32 measures the moisture content within a predetermined measurement range 33 in the soil 30. In the present embodiment, the moisture content sensor 32 is embedded in the soil 30 near the corner of the test container 12. As an example, the measurement range 33 is a circle with a predetermined diameter (for example, a diameter of about 60 mm) centered on the moisture content sensor 32.

[0027] Regarding the arrangement of the plurality of test pieces 100 inside the test container 12, it is preferable to provide an appropriate separation (that is, a gap) that does not cause battery action between the test pieces 100. The gap between the test pieces 100 is preferably 80 mm or more and 100 mm or less. For example, the gap between the test pieces 100 is set to 81 mm.

[0028] The tank 14 contains an aqueous sodium chloride solution L inside. In the present embodiment, in order to promote the corrosion of the test piece 100 by the salt content, the aqueous sodium chloride solution L is adopted as the liquid sprayed from the watering section 18. The concentration of the aqueous sodium chloride solution L is preferably 2% or more and 5% or less, more preferably 2.3% or more and 4% or less, and even more preferably 2.5% or more and 3.5% or less. In the present embodiment, the concentration of the aqueous sodium chloride solution L is set to 3%, which corresponds to the salt concentration of seawater. When the concentration of the aqueous sodium chloride solution L is in the range of 2% or more and 5% or less, the corrosion rate of the steel material is relatively higher compared to the case outside this range, and it reaches a maximum near 3%. That is, when the concentration of the aqueous sodium chloride solution L is outside the range of 2% or more and 5% or less, the corrosion rate tends to decrease.

[0029] The supply section 16 supplies the aqueous sodium chloride solution L in the tank 14 to the watering section 18. Specifically, the supply section 16 includes a pipe 42 connecting the tank 14 and the watering section 18, and a pump 44 provided in the middle of the pipe 42 for sending the aqueous sodium chloride solution L. Further, the supply section 16 includes valves 46 and 48 provided on the upstream side and the downstream side in the feeding direction of the pump 44 in the pipe 42, and a solenoid valve 50 provided on the downstream side of the valve 48 in the pipe 42 and on the upstream side of the watering section 18.

[0030] In the supply unit 16, by opening the solenoid valve 50 and driving the pump 44, the aqueous sodium chloride solution L in the tank 14 is supplied to the watering unit 18 through the pipe 42.

[0031] The watering unit 18 sprays the aqueous sodium chloride solution L onto the soil 30 inside the test container 12. The watering unit 18 includes a cylindrical nozzle 54 arranged along the longitudinal direction of the test container 12, and the pipe 42 of the supply unit 16 is connected to the upstream end of the nozzle 54. The support member 60 supports the base 60A and includes at least two vertical members 60B extending in the vertical direction. The nozzle 54 is horizontally supported by the vertical member 60B and is arranged above the test container 12 at a distance from the test container 12. The lower part of the nozzle 54 is formed in an arc shape and is provided with a plurality of holes 56. The plurality of holes 56 of the nozzle 54 are formed to spray the liquid over a wide range of the soil 30 inside the test container 12. When the aqueous sodium chloride solution L is supplied to the watering unit 18 by the supply unit 16, the aqueous sodium chloride solution L is sprayed from the plurality of holes 56 of the nozzle 54 onto the soil 30 inside the test container 12.

[0032] The control panel 22 controls each part of the automatic watering device 10, for example, controls the opening and closing of the solenoid valve 50 and the driving of the pump 44. By opening the solenoid valve 50 and driving the pump 44, the aqueous sodium chloride solution L is sprayed from the watering unit 18.

[0033] Since the balance between moisture and oxygen is crucial for the corrosion of the test piece 100 in the environment of the soil 30, in this embodiment, a wet-dry cycle is adopted by intermittently spraying the sodium chloride aqueous solution L. In the wet-dry cycle, a cycle in which the soil 30 gets wet by spraying the sodium chloride aqueous solution L and dries while the sodium chloride aqueous solution L is not sprayed is repeated. Here, the balance means a state in which moisture and oxygen are taken into the soil 30 in a well-balanced manner. If either moisture or oxygen is insufficient, or if either moisture or oxygen is excessive, the corrosion of the steel material is less likely to progress. Oxygen is considered to be taken into the soil 30 by the oxygen dissolved in the moisture when the sodium chloride aqueous solution L is sprayed. Also, since the corrosion of the steel material is less likely to progress when the soil 30 is always in a wet state, it is necessary to adopt a wet-dry cycle.

[0034] As an example, the spraying amount and spraying frequency of the sodium chloride aqueous solution L are set so that the water content in the soil 30 is about 0.5 [m 3 / m 3 . For example, when the volume of the test container 12 is 50 L, by spraying 5 L of the sodium chloride aqueous solution L every 7 days with the water spraying unit 18, the water content in the soil 30 is maximized to about 0.5 [m 3 / m 3 .

[0035] The discharge part 20 includes a water receiving tray 72 disposed on the base 60A on the lower side of the test container 12 and a drain pipe 74 through which the liquid flowing down from the water receiving tray 72 flows. The water receiving tray 72 is provided with holes above the drain pipe 74. The moisture in the soil 30 inside the test container 12 flows down from the drain pores 13 to the water receiving tray 72, further drops from the water receiving tray 72 to the drain pipe 74, and is drained by flowing through the drain pipe 74.

[0036] Although illustration is omitted, in the automatic sprinkler device 10, a plurality of test containers 12 and sprinkling units 18 are provided, and the pipe 42 from the tank 14 is branched into a plurality and connected to each sprinkling unit 18. Further, the solenoid valves 50 are provided for each of the plurality of sprinkling units 18. Thereby, by embedding a plurality of test pieces 100 in the soil 30 inside each of the plurality of test containers 12, a corrosion acceleration exposure test of the plurality of test pieces 100 can be carried out under the same conditions in each test container 12.

[0037] <Configuration of a normal test apparatus for performing a normal exposure corrosion test> Next, in the corrosion acceleration exposure test method for steel materials of the first embodiment, a normal test apparatus for performing a normal exposure corrosion test will be described.

[0038] FIG. 4(A) is a perspective view showing a normal test apparatus 200 for performing a normal exposure corrosion test on a test piece 300, and FIG. 4(B) is a plan view showing the normal test apparatus 200 for performing a normal exposure corrosion test on the test piece 300. Note that the same reference numerals may be given to the same components as those of the automatic sprinkler device 10, and the description thereof may be omitted.

[0039] As shown in FIGS. 4(A) and 4(B), the normal test apparatus 200 includes a test container 212. The test container 212 is a box-shaped member with an open top, and includes a bottom 12A and side portions 12B. As an example, the test container 212 has the same configuration as the test container 12 (see FIG. 2) for the corrosion acceleration exposure test. A plurality of drain holes 13 are provided at the lower part of the side portion 12B of the test container 212 in the same manner as the test container 12 (see FIG. 2), but a configuration without the drain holes 13 may also be used.

[0040] Inside the test container 212, soil 30 is placed in the same way as in the test container 12 (see Fig. 2) for the corrosion-accelerated exposure test, and a plurality of test pieces 300 are embedded in the soil 30 inside the test container 212 at intervals. The test piece 300 is an example of a second steel material, and the test container 212 is an example of a second container. The test piece 300 has the same configuration as the test piece 100 in the corrosion-accelerated exposure test. For example, the test piece 300 is set to the same material and dimensions as the test piece 100, and the same pretreatment as the test piece 100 is performed. Also, the intervals between the plurality of test pieces 300 embedded in the soil 30 are set in the same way as the plurality of test pieces 100 in the corrosion-accelerated exposure test.

[0041] In the normal test apparatus 200, a corrosion normal exposure test is carried out by embedding a plurality of test pieces 300 at intervals in the soil 30 inside the test container 212. In the corrosion normal exposure test, an aqueous sodium chloride solution is not sprayed on the soil 30 inside the test container 212. Also, as an example, intermittent spraying of water (for example, pure water or ion-exchanged water, etc.) on the soil 30 inside the test container 212 is not performed.

[0042] <Method for Corrosion-Accelerated Exposure Test of Steel Material> Next, the corrosion-accelerated exposure test method of the steel material of the first embodiment will be described. In the corrosion-accelerated exposure test method of the steel material, a corrosion-accelerated exposure test of the test piece 100 and a corrosion normal exposure test of the test piece 300 are carried out, the accelerated corrosion rate of the test piece 100 is calculated from the corrosion weight value of the test piece 100, and the normal corrosion rate of the test piece 300 is calculated from the corrosion weight value of the test piece 300. Further, in the corrosion-accelerated exposure test method of the steel material of the first embodiment, the corrosion acceleration magnification of the steel material is calculated from the accelerated corrosion rate and the normal corrosion rate.

[0043] (Corrosion-Accelerated Exposure Test) First, the corrosion-accelerated exposure test will be described.

[0044] In the automatic sprinkler device 10 (see FIGS. 1 and 2), as described above, a plurality of test pieces 100 are buried in the soil 30 placed in the test container 12 at intervals, and the sodium chloride aqueous solution L is intermittently sprinkled on the soil 30 to repeat the wet and dry cycles of the soil 30, thereby conducting a corrosion acceleration exposure test. In the corrosion acceleration exposure test, every predetermined number of exposure days, the test piece 100 is taken out from the soil 30, and in accordance with JIS K 0100 "Industrial Water Corrosivity Test Method", the corrosion weight of the test piece 100 is measured. The measurement of the corrosion weight is carried out for each of the test pieces 100 taken out from the soil 30 every predetermined number of exposure days.

[0045] Regarding the measurement of the corrosion amount after the corrosion acceleration exposure test, pickling of the test piece 100 is carried out in accordance with JIS K 0100 "Industrial Water Corrosivity Test Method". Specifically, after immersing in hydrochloric acid with a volume percentage concentration of 15% for 15 seconds, running water washing and scrubbing of the test piece 100 with a non-metallic brush are carried out to remove the corrosion products. Then, after wiping off the moisture of the test piece 100 with a paper towel, visually confirm the removal of the corrosion products on the test piece 100. If the removal of the corrosion products is insufficient, immerse the test piece 100 in the same hydrochloric acid again and carry out pickling for 5 minutes. Repeat this until the corrosion products on the test piece 100 can be removed. After the pickling is completed, dry the test piece 100 thoroughly with a blower. During the weight measurement, +0.02 mg is corrected to the measured weight for the number of pickling times.

[0046] Then, the corrosion weight of the test piece 100 is measured from the difference between the mass of the initial test piece 100 and the weight of the test piece 100 from which the corrosion products have been removed (i.e., the mass reduction). Further, the accelerated corrosion rate of the test piece 100 is calculated from the corrosion weight value of the test piece 100.

[0047] Here, the method for measuring the corrosion weight of the test piece 300 and the method for calculating the accelerated corrosion rate of the test piece 100 are shown in Equation 1. Evaluation is carried out using the corrosion weight M, the plate thickness consumption T, and the average corrosion rate P obtained from Equations 4-1, 4-2, and 4-3 shown in Equation 1.

Equation

[0048] In Equation 1, M1 is the initial weight [g], M2 is the weight [g] after pickling, S is the surface area [mm 2 , d is the density [g / cm 3 , and D is the number of exposure days [day].

[0049] (General corrosion exposure test) Next, the general corrosion exposure test will be described.

[0050] In the general test apparatus 200 (see Fig. 4), as described above, a general corrosion exposure test is carried out in which a plurality of test pieces 100 are buried in the soil 30 placed in the test container 12 at intervals. Similarly, in the general corrosion exposure test, every predetermined number of exposure days, the test piece 300 is taken out from the soil 30, and in accordance with JIS K 0100 "Test Method for Corrosiveness of Industrial Water", the corrosion weight of the test piece 300 is measured. The measurement of the corrosion weight is carried out for each of the test pieces 300 taken out from the soil 30 every predetermined number of exposure days. Further, the accelerated corrosion rate of the test piece 300 is calculated from the corrosion weight value of the test piece 300.

[0051] The method for measuring the corrosion weight of the test piece 300 and the method for calculating the general corrosion rate of the test piece 300 are the same as the method for measuring the corrosion weight of the test piece 100 and the method for calculating the general corrosion rate of the test piece 100 described above.

[0052] (Calculation of corrosion acceleration ratio) Next, in the corrosion accelerated exposure test method of the steel material of the first embodiment, a method for calculating the corrosion acceleration ratio of the steel material from the accelerated corrosion rate and the general corrosion rate will be described.

[0053] Based on the result of calculating the accelerated corrosion rate from the corrosion weight values of a plurality of test pieces 100 obtained from the start of exposure to the elapsed days of a predetermined period in the corrosion accelerated exposure test, a first approximation formula representing the relationship between the exposure days and the accelerated corrosion rate is derived.

[0054] FIG. 5 shows an example of a graph showing the relationship between the exposure days and the corrosion rate, which is the result of a corrosion-accelerating exposure test (i.e., embedding and saltwater wet-dry cycle). Specifically, as shown in FIG. 5, for a plurality of test pieces 100, the numerical values of the accelerated corrosion rate with respect to the exposure days are plotted on the graph respectively, and a first approximation formula 120 representing the relationship between the exposure days and the corrosion rate is derived.

[0055] Equation 2 is an example of the first approximation formula 120. In Equation 2, P1 is the corrosion rate of the corrosion-accelerating exposure test (i.e., embedding and saltwater wet-dry cycle), and D is the exposure days.

Equation

[0056] Similarly, based on the result of calculating the normal corrosion rate from the corrosion weight values of a plurality of test pieces 300 obtained from the start of exposure to the elapsed days of a predetermined period in the normal corrosion exposure test, a second approximation formula representing the relationship between the exposure days and the corrosion rate is derived.

[0057] FIG. 5 shows an example of a graph showing the relationship between the exposure days and the corrosion rate, which is the result of a normal corrosion exposure test (i.e., embedding). Specifically, as shown in FIG. 5, for a plurality of test pieces 300, the numerical values of the accelerated corrosion rate with respect to the exposure days are plotted on the graph respectively, and a second approximation formula 320 representing the relationship between the exposure days and the corrosion rate is derived.

[0058] Equation 3 is an example of the second approximation formula 320. In Equation 3, P2 is the corrosion rate of the normal corrosion exposure test (i.e., embedding), and D is the exposure days.

Equation

[0059] Furthermore, the corrosion acceleration multiple of the steel material is calculated by a third formula obtained by dividing the first approximation formula 120 by the second approximation formula 320.

[0060] The number 4 is an example of the third formula. In the number 4, A is the corrosion acceleration ratio.

Number

[0061] By using the third formula, the acceleration ratio at the third year (1095 days) is calculated to be about 14 times. Since it is assumed that the corrosion rate after the third year does not change significantly, by conducting a corrosion acceleration exposure test and a corrosion numerical exposure test for 5 years using the steel material corrosion acceleration exposure test method of the first embodiment, it has been shown that exposure test results equivalent to 70 years can be obtained.

[0062] <Actions and Effects> Next, the actions and effects of the first embodiment will be described.

[0063] In the steel material corrosion acceleration exposure test method, a plurality of test pieces 100 are buried in the soil 30 placed in the test container 12 at intervals, and a sodium chloride aqueous solution L is intermittently sprinkled on the soil to perform a corrosion acceleration exposure test in which the dry and wet states of the soil 30 are repeated. In addition, a normal corrosion exposure test is performed in which a plurality of test pieces 300 equivalent to the test pieces 100 are buried in the soil 30 placed in the test container 212 at intervals.

[0064] Furthermore, every predetermined number of exposure days, the test pieces 100 and the test pieces 300 are taken out from the soil 30, and in accordance with JIS K 0100 "Industrial Water Corrosion Test Method", the accelerated corrosion rate of the test pieces 100 and the normal corrosion rate of the test pieces 300 are calculated from the corrosion weight values of the test pieces 100 and the test pieces 300, and the corrosion acceleration ratio of the steel material is calculated from the accelerated corrosion rate and the normal corrosion rate.

[0065] In the above steel material corrosion acceleration exposure test method, by using the exposure test results of both the corrosion acceleration exposure test and the normal corrosion exposure test, the accelerated corrosion rate and the normal corrosion rate are calculated in accordance with JIS K 0100 "Industrial Water Corrosion Test Method". Furthermore, by calculating the corrosion acceleration ratio of the steel material from the accelerated corrosion rate and the normal corrosion rate, it is possible to quantitatively show the degree to which the corrosion acceleration of the steel material progresses, and a test with reproducibility can be performed.

[0066] In the corrosion-accelerated exposure test method for steel materials, based on the result of calculating the accelerated corrosion rate from the corrosion weight values of a plurality of test pieces 100 obtained from the start of exposure to the elapsed days of a predetermined period in the corrosion-accelerated exposure test, a first approximation formula (for example, the first approximation formula 120 shown in Equation 2) representing the relationship between the exposure days and the accelerated corrosion rate is derived.

[0067] In the normal corrosion exposure test, based on the result of calculating the normal corrosion rate from the corrosion weight values of a plurality of test pieces 300 obtained from the start of exposure to the elapsed days of a predetermined period, a second approximation formula (for example, the second approximation formula 320 shown in Equation 3) representing the relationship between the exposure days and the corrosion rate is derived.

[0068] Furthermore, the corrosion acceleration magnification is calculated by a third formula (for example, the third formula shown in Equation 4) obtained by dividing the first approximation formula by the second approximation formula.

[0069] In the above corrosion-accelerated exposure test method for steel materials, by calculating the corrosion acceleration magnification by the third formula obtained by dividing the first approximation formula by the second approximation formula, it is possible to quantitatively show to what extent the corrosion acceleration of the steel material progresses.

[0070] In the corrosion-accelerated exposure test method for steel materials, the concentration of the sodium chloride aqueous solution L is 2% or more and 5% or less.

[0071] In the above corrosion-accelerated exposure test method for steel materials, when the concentration of the sodium chloride aqueous solution L is in the range of 2% or more and 5% or less, the corrosion rate of the test piece 100 becomes relatively high compared to the case outside this range. For this reason, it is possible to suppress a decrease in the corrosion rate of the test piece 100 compared to the case where the concentration of the sodium chloride aqueous solution is less than 2%, and it is also possible to suppress a decrease in the corrosion rate of the test piece 100 compared to the case where the concentration of the sodium chloride aqueous solution is greater than 5%.

[0072] 〔Others〕 In the above embodiment, the configuration of the automatic sprinkler device 10 can be changed as long as it can intermittently spray an aqueous sodium chloride solution onto the soil.

[0073] Also, in the above embodiment, the configuration of the normal test device 200 can be changed.

[0074] Although the present invention has been described in detail with respect to specific embodiments, it is obvious to those skilled in the art that the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention.

Explanation of Reference Numerals

[0075] 12 Test container (first container) 30 Soil 34 Test container (modified example of the first container) 100 Test piece (first steel material) 120 First approximation formula 212 Test container (second container) 300 Test piece (second steel material) 320 Second approximation formula 340 Third formula L Aqueous sodium chloride solution

Claims

1. A plurality of first steel materials are embedded in the soil in the first container at intervals, and a corrosion acceleration exposure test is performed in which an aqueous sodium chloride solution is intermittently sprinkled on the soil to repeat the wet and dry states of the soil, and a corrosion normal exposure test is performed in which a plurality of second steel materials equivalent to the first steel material are embedded in the soil in the second container at intervals. Every predetermined exposure days, the first steel material and the second steel material are taken out from the soil, and according to JIS K 0100 "Industrial Water Corrosion Test Method", from the corrosion weight values of the first steel material and the second steel material, the accelerated corrosion rate of the first steel material and the normal corrosion rate of the second steel material are calculated, and the corrosion acceleration magnification of the steel material is calculated from the accelerated corrosion rate and the normal corrosion rate. A corrosion acceleration exposure test method for steel materials.

2. Based on the result of calculating the accelerated corrosion rate from the corrosion weight values of the plurality of first steel materials obtained from the start of exposure to the elapsed days of a predetermined period in the corrosion acceleration exposure test, a first approximation formula representing the relationship between the exposure days and the accelerated corrosion rate is derived. Based on the result of calculating the normal corrosion rate from the corrosion weight values of the plurality of second steel materials obtained from the start of exposure to the elapsed days of a predetermined period in the corrosion normal exposure test, a second approximation formula representing the relationship between the exposure days and the corrosion rate is derived. The corrosion acceleration magnification is calculated by a third formula obtained by dividing the first approximation formula by the second approximation formula. The corrosion acceleration exposure test method for steel materials according to Claim 1.

3. The corrosion acceleration exposure test method for steel materials according to Claim 1, wherein the concentration of the aqueous sodium chloride solution is 2% or more and 5% or less.

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