Corrosion testing apparatus and corrosion monitoring method

Abstract

To provide a corrosion test system capable of performing corrosion evaluation of a material over time in a splash adhesion environment where corrosion (heterogeneous corrosion) progresses due to intermittent and uneven splashing of corrosive liquid.SOLUTION: The corrosion test system having droplet generating means sequentially measures the current value, voltage value, and temperature of a test piece and evaluates the amount of corrosion from the electrical resistance value. The test piece and splash conditions satisfy the following formulas 1 to 3: a×Dmax≤W (where, 1.0≤a)...formula 1; b×Dmean≤W(where, 2.0≤b)...formula 2; and 0<S / A≤0.5...formula 3; wherein, Dmax: maximum splash diameter [m], Dmean: average splash diameter [m], W: test piece width (effective test piece width) [m2], S: predetermined droplet adhesion area per hour [m2 / H], and A: area of test piece (area of effective evaluation surface) [m2].SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a corrosion testing apparatus and a corrosion monitoring method. [Background technology]

[0002] Several environments can cause corrosion in steel materials due to the adhesion of corrosive liquids. For example, in environments where de-icing salt is spread, it is known that spray containing chloride ions from the road surface is kicked up by vehicles driving, causing corrosion of the undercarriage. In addition, in marine structures, it is known that spray generated by wave collisions adheres to the structure, causing severe corrosion. In such environments where spray adheres, corrosive substances, such as corrosive liquids containing high concentrations of chloride ions, directly adhere to the structure, and repeated wetting and drying further causes severe corrosion. While corrosion prevention measures such as plating, heavy-duty anti-corrosion coatings, and high-alloy corrosion-resistant steel are used against environments where corrosive liquid spray of several millimeters adheres (hereinafter referred to as "splash adhesion environments"), there is a desire to extend the lifespan of steel materials and reduce LCC (Life-Cycle Cost) by simplifying coatings. To develop materials that contribute to LCC reduction, corrosion testing methods that reproduce splash adhesion environments are needed, and several proposals have been made.

[0003] For example, Patent Document 1 proposes a corrosion test method that generates splashes of a test solution using a rotating body. Patent Document 2 proposes a corrosion monitoring method that simultaneously measures the electrical resistance and temperature of a metal piece and reduces the effect of temperature changes on the resistance value based on the relationship between the initial resistance and temperature. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-78615 [Patent Document 2] Japanese Patent Publication No. 2020-20735 [Overview of the project] [Problems that the invention aims to solve]

[0005] The corrosion test apparatus described in Patent Document 1 causes droplets of a corrosive solution such as a snow-melting agent or seawater to adhere to a test piece, and successfully reproduces the droplet adhesion environment. However, since this is a proposal of a batch-type test apparatus, it is not suitable for evaluating the temporal change of corrosion caused by intermittently adhering droplets.

[0006] The corrosion monitoring method described in Patent Document 2 can monitor the change in electrical resistance of a test piece from the change in cross-sectional area of the test piece due to corrosion. On the other hand, non-uniform corrosion progression caused by droplets is not taken into consideration, and it is required to be able to monitor the accurate corrosion phenomenon under droplets.

[0007] Accordingly, the present invention has an object to enable temporal corrosion evaluation even for corrosion (non-uniform corrosion) caused by intermittent and non-uniform droplet adhesion of a corrosive liquid occurring in a droplet adhesion environment, and aims to provide such a corrosion test apparatus and a corrosion test method. [Means for Solving the Problems]

[0008] The present inventors conducted intensive studies to achieve the object of the present invention, and obtained the following findings. (a) The present inventors conceived that by applying electrical resistance monitoring to the test piece of a droplet test apparatus, temporal monitoring of non-uniform corrosion of the test piece becomes possible. However, unless the test piece size and the droplet scattering state are appropriately matched, evaluation of non-uniform corrosion that properly reproduces the droplet adhesion environment cannot be performed. Therefore, the relationship between the droplet diameter distribution and the test piece shape, and the relationship between the preset droplet adhesion area per predetermined time and the area of the surface for evaluating the corrosion of the test piece (effective evaluation surface) were investigated, and the relationship between appropriate droplet conditions and the test piece shape was found. a×D max ≦W (where 1.0≦a) ····Formula 1 b×D mean ≦W (where 2.0≦b) ····Formula 2 0<S / A≦0.5 ····Formula 3 Here, D max : Maximum droplet diameter [m], D mean : Average droplet diameter [m], W: Specimen width (width of effective evaluation surface) [m] S: Area of ​​droplet adhesion per specified time [m²] 2 / H], A: Area of ​​the evaluation surface (effective evaluation surface) of the test specimen [m²] 2 ] indicates.

[0009] (stomach) When applying electrical resistance monitoring, the resistance value of the test specimen (metal plate) is affected by temperature. Therefore, if temperature variations occur within the test specimen, it becomes impossible to accurately evaluate the amount of corrosion. To address this, we found that it is beneficial to position the heater so that it is in contact with the entire test specimen (at least the effective evaluation surface), and to place a temperature buffer plate (e.g., a metal plate such as a Ti plate) between the heater and the test specimen to equalize the temperature. This makes it possible to equalize the temperature of the evaluation surface of the test specimen.

[0010] (cormorant) To improve the accuracy of corrosion assessment, it is preferable to maximize the surface area of ​​the test specimen (effective assessment area) and minimize local influencing factors specific to the testing equipment to a negligible degree. On the other hand, since electrical resistance monitoring evaluates the reduction in cross-sectional area due to corrosion of the test specimen using electrical resistance, a smaller cross-sectional area of ​​the test specimen makes it easier to detect changes and improves accuracy. Therefore, we found that by making slits in the test specimen, we can improve evaluation accuracy while securing a large effective assessment area and reducing the cross-sectional area of ​​the test specimen.

[0011] This invention is based on the above findings, and its gist is as follows. [1] A corrosion testing apparatus for evaluating corrosion of a metal test specimen by applying a splash of test solution to its surface, passing an electric current through the specimen to measure its electrical resistance, and further measuring the temperature of the specimen, A test specimen holding means for holding the test specimen, a droplet generating means for generating droplets of the test solution, a measuring means for measuring the temperature and electrical resistance of the test piece, and a corrosion loss calculating means for calculating the corrosion loss of the test piece from the measured temperature and electrical resistance, wherein the maximum droplet diameter of the droplets adhering to the test piece is defined as D max , the average droplet diameter is defined as D mean , the area of the effective evaluation surface, which is the surface for evaluating corrosion on the surface of the test piece, is defined as A, the width of the effective evaluation surface of the test piece in the direction perpendicular to the current direction is defined as W, and the droplet adhesion area, which is the total area of droplets adhering to the effective evaluation surface of the test piece per predetermined time, is defined as S, the corrosion test apparatus characterized by satisfying the relationship of the following Formulas 1 to 3. a×D max ≦W (where 1.0≦a) ····Formula 1 b×D mean ≦W (where 2.0≦b) ····Formula 2 0<S / A≦0.5 ····Formula 3 [2] The corrosion test apparatus according to [1], wherein the test piece holding means has a heater for heating the test piece, and a temperature buffer plate in contact with the entire back surface of the test piece between the test piece and the heater. [3] The corrosion test apparatus according to [2], wherein the temperature buffer plate is a metal plate. [4] The corrosion test apparatus according to [1] or [2], wherein the test piece has a slit. [5] The width W of the slit slit satisfies the following Formula 4, the corrosion test apparatus according to [4]. D mean <W slit ····Formula 4 [6] A corrosion test method using the corrosion test apparatus according to any one of [1] to [5], comprising: a test piece preparation step of preparing a test piece, A test specimen holding step, in which the prepared test specimen is held, A measurement step comprising generating droplets of the test solution, adhering the droplets to the surface of the test piece, and measuring the temperature and electrical resistance of the test piece, The system includes a corrosion amount calculation step that calculates the amount of corrosion of the test piece from the measured temperature and electrical resistance, In the test specimen preparation step, the diameter of the droplets of the test solution adhering to the test specimen is measured in advance to determine the maximum droplet diameter D. max and average droplet diameter D mean Seeking, Let A be the area of ​​the effective evaluation surface, which is the surface on the surface of the test specimen used to evaluate corrosion. On the effective evaluation surface of the test specimen, the width perpendicular to the current direction is W. When S is the total area of ​​droplets adhering to the effective evaluation surface of the test specimen per predetermined time, A corrosion test method characterized by preparing a test specimen that satisfies the following relationships in equations 1 to 3. a×D max ≤W (where 1.0 ≤ a) ····Equation 1 b×D mean ≤W (where 2.0 ≤ b) ····Equation 2 0 [7] The corrosion test method according to [6], wherein, in order to measure the diameter of the droplets of the test solution adhering to the test piece, a water-sensitive test paper is attached to the surface of the test piece and the diameter of the droplets remaining on the water-sensitive test paper is measured. [Effects of the Invention]

[0012] According to the present invention, it is possible to reproduce a splash adhesion environment and enable time-dependent corrosion evaluation even for non-uniform corrosion caused by intermittent splash adhesion of corrosive liquids. The present invention enables efficient advancement of material and structural development against intermittent non-uniform corrosion. [Brief explanation of the drawing]

[0013] [Figure 1] ​Figure 1 shows an overview of an example of a corrosion testing apparatus according to the present invention. [Figure 2] Figure 2 shows an overview of the cross-section of a test specimen according to the present invention. [Figure 3] Figures 3(a) and 3(b) both show examples of test specimens with slits (effective evaluation surfaces). [Figure 4] Figure 4 shows the relationship between the amount of corrosion and time (cycles) measured in the example. [Modes for carrying out the invention]

[0014] Let me describe one embodiment of the present invention.

[0015] [Corrosion testing equipment] A corrosion testing apparatus works by intermittently applying droplets of a test solution to the surface of a metal test specimen, passing an electric current through the specimen to measure its electrical resistance, and then measuring the temperature of the specimen. The amount of corrosion of the specimen is calculated from these measured electrical resistance and temperature values ​​to evaluate the corrosion. Therefore, the apparatus includes at least a specimen holding means for holding the specimen, a droplet generating means for generating droplets of the test solution, a measuring means for measuring the temperature and electrical resistance of the specimen, and a corrosion amount calculation means for calculating the amount of corrosion from the measured temperature and electrical resistance of the specimen.

[0016] For example, the specimen holding means, droplet generating means, and measuring means may be located within a single enclosed enclosure. For instance, the atmospheric conditions within this enclosed space, such as temperature, humidity, and pressure, may be controlled to reproduce an environment that more closely resembles the actual conditions of droplet adhesion.

[0017] Furthermore, other auxiliary means may be provided. For example, there may be a storage means for saving and creating a database of data measured by another measurement means and data calculated by a corrosion amount calculation means, along with the sampling time data; a corrosion analysis means for analyzing and interpreting the database; and a monitoring means for displaying the data sampling status and the analysis results from the corrosion analysis means. The corrosion amount calculation means, storage means, corrosion evaluation means, and monitoring means do not need to be in the vicinity of the specimen holding means, and may be located anywhere as long as they are connected by a data line or the like.

[0018] The following describes one embodiment of the corrosion testing apparatus according to the present invention, focusing on the splash generation means, test specimen, test specimen holding means, measurement means, and corrosion amount calculation means.

[0019] [Means of generating droplets] The method for generating droplets is not particularly limited. For example, a rotating body such as a rotating brush, as disclosed in Patent Document 1, may be immersed in the test solution, and droplets of the test solution may be scattered by the centrifugal force caused by the rotation. Alternatively, droplets may be scattered by spraying the test solution into droplets using a spray nozzle. Another method is to introduce bubbles (gas bubbles such as air) into the test solution, and the droplets may be scattered when the bubbles burst.

[0020] Hereafter, a corrosion testing apparatus 1 using a rotating brush 2 as a droplet generation means, as shown in Figure 1, will be described as an example. In the corrosion testing apparatus 1 of Figure 1, a portion of the rotating brush 2 is immersed in the test solution 3, and droplets 4 of the test solution are scattered by centrifugal force and adhere to the test piece 5. The shape (particle size) and amount of droplets that adhere to the test piece 5 can be adjusted by the properties of the brush material of the rotating brush 2 (shape, material, number, density, etc. of the brush material (hair-like fibers)), the shape of the rotating brush (overall diameter and width of the rotating brush, etc.), the rotation speed, the properties of the test solution (components, viscosity, etc.), the immersion depth of the rotating brush, and the distance to the test piece.

[0021] [Test piece] In corrosion testing, proper evaluation of non-uniform corrosion caused by intermittent droplets is impossible unless the specimen size and droplet dispersion conditions are appropriately matched. For example, in environments where snowmelt salt is spread or in the droplet zones of offshore structures, droplets do not constantly adhere to the entire surface. Corrosion progresses through repeated adhesion and drying of corrosive liquids. Therefore, optimization of the properties of the droplets, such as particle size, and the specimen is required. The inventors studied actual droplet adhesion environments, such as snowmelt salt spread environments and droplet zone environments of offshore structures, and found that the relationship between the droplet particle size distribution and the specimen shape, as well as the relationship between the droplet adhesion area (total area of ​​droplets adhering per given time) and the area of ​​the surface of the specimen being tested for corrosion (effective evaluation surface), are important.

[0022] First, let's explain the relationship between the width of the corrosion test surface (effective evaluation surface) of the test specimen and the droplet particle size. If the droplet particle size is too large compared to the width of the effective evaluation surface, the droplets will not fit within the effective evaluation surface, making proper evaluation impossible. Therefore, it is preferable that the width W of the effective evaluation surface be greater than the maximum droplet particle size. That is, the width W of the effective evaluation surface of the test specimen should be greater than the maximum droplet particle size D. max It is preferable to make it 1.0 times or more (Equation 1). That is, the coefficient a shown in Equation 1 is preferably 1.0 or more, for example, 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, 4.0 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, 9.0 or more, or 10.0 or more. It is preferable that the coefficient a in Equation 1 be large, and there is no particular upper limit, but it is limited by the shape of the device, etc. a×D max ≤W (where 1.0 ≤ a) ····Equation 1

[0023] Furthermore, it is preferable that droplets are moderately dispersed and adhere to the effective evaluation surface, as this more closely resembles the conditions of an actual droplet adhesion environment. For example, if the width W of the effective evaluation surface of the test specimen is equal to the average particle size D of the droplets, mean It is preferable that it is 2.0 times or more (Equation 2). That is, the coefficient b shown in Equation 2 is preferably 2.0 or more, for example, 3.0 or more, 4.0 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, 9.0 or more, or 10.0 or more. b×D mean≤W (where 2.0 ≤ b) ····Equation 2

[0024] Next, we will explain the relationship between the droplet adhesion area, which is the total area of ​​droplets adhering per predetermined time, and the area of ​​the surface of the test specimen used for corrosion testing (effective evaluation surface). It is preferable to reproduce an actual droplet adhesion environment where droplets adhere in moderation. The inventors conducted numerous experiments and found appropriate conditions for reproducing an actual droplet adhesion environment. If the droplet adhesion area per predetermined time (e.g., 30 minutes or 1 hour, a pre-set time) is too large, the adhesion and drying cycle cannot occur, resulting in constant adhesion and a wet state, thus failing to reproduce an actual droplet adhesion environment. Therefore, the ratio S / A of the droplet adhesion area S and the area A of the surface of the test specimen used for corrosion evaluation (effective evaluation surface) should be 0.50 or less (Equation 3). Preferably, it should be 0.45 or less, 0.40 or less, or 0.35 or less. On the other hand, there is no particular lower limit to the droplet adhesion area. It is sufficient if even a small amount of droplet adheres to the test specimen. Therefore, the droplet adhesion area S should be greater than 0. However, if the area of ​​droplet adhesion is too small, corrosion becomes localized, making it difficult to perform a highly accurate corrosion evaluation. Therefore, it is preferable that the ratio of the area of ​​droplet adhesion S per predetermined time to the area A of the surface of the test piece to be evaluated for corrosion (effective evaluation surface) be 0.03 or greater (Equation 3). More preferably, it is 0.05 or greater, 0.07 or greater, 0.10 or greater, 0.15 or greater, or 0.20 or greater. 0

[0025] The predetermined time for droplet dispersion to measure the droplet adhesion area should be determined by the droplet adhesion environment that serves as the basis for the corrosion evaluation. However, for typical droplet adhesion environments, such as snowmelt salt spreading environments or droplet zones of marine structures, a predetermined time of 30 minutes is acceptable. Furthermore, equations 1 to 3 described above can be summarized as follows. a×D max ≤W (where 1.0 ≤ a) ····Equation 1 b×D mean ≤W (where 2.0 ≤ b) ····Equation 2 0 D max : Maximum droplet diameter [m],​​ D mean : Average droplet diameter [m], W: Test specimen width (effective test specimen width) [m 2 ], S: Area of ​​droplet adhesion [m²] after a specified time (e.g., 30 minutes) 2 ], A: Area of ​​the test specimen (area of ​​the effective evaluation surface) [m²] 2 ] indicates.

[0026] The material of test piece 5 is not particularly limited as long as it is conductive, since corrosion is evaluated by electrical resistance. Generally, since metal materials are widely used in automobiles and marine structures, the test piece is often made of metal. The material is not particularly limited as long as it is metal. Non-ferrous materials such as Al (aluminum), Ti (titanium), and Cu (copper) can also be used. Furthermore, materials with a metal base material that have been surface-treated, such as plating or coating with corrosion-resistant paint, are also acceptable. For example, steel materials with plating on the surface or steel materials with corrosion-resistant paint coated on the surface are acceptable. This allows for the evaluation of the corrosion resistance of the plating film or corrosion-resistant paint.

[0027] The shape of the test specimen is not particularly limited, as long as it satisfies the relationship with the droplet behavior described above. The test specimen may be flat, rod-shaped, pipe-shaped, or even have a complex shape like a component. It should be determined appropriately depending on the structure being tested. However, when evaluating the corrosion of a material, it is preferable to make the adhesion conditions of the scattered droplets as uniform as possible within the surface, and from this viewpoint, a flat shape is preferable. Also, although the shape of the test specimen is not particularly limited, it is preferable that the width of the effective evaluation surface be as constant as possible. For this reason, a rectangle (including a square) is preferable. The following explanation will assume a rectangular, flat test specimen.

[0028] There are no particular limitations on the size of the test specimen. However, if the surface area where scattered debris adheres and corrosion is evaluated (effective evaluation surface) is too small, local conditions on the test specimen may affect the accuracy of the evaluation, so it is preferable to make the effective evaluation surface as wide as possible. There are no particular limitations on the thickness of the test specimen, but from the viewpoint of uniform temperature within the specimen, it is preferable to make the plate thickness as thin as possible. However, the plate thickness should be determined appropriately based on the expected amount of corrosion and strength.

[0029] Furthermore, as shown in Figure 2, electrode terminals (not shown) are provided at the ends of the effective evaluation surface 10 in the test specimen in order to pass electricity through the test specimen and monitor the electrical resistance of the test specimen 5. Here, the length in the direction of current flow (current direction) on the effective evaluation surface of the test specimen is defined as the length of the test specimen, and the length perpendicular to the current path is defined as the width of the test specimen. The shortest value of the width of the test specimen is defined as the width W of the test specimen. In this specification, when simply referred to as "width of the test specimen," it refers to this shortest width W of the test specimen. Since the electrical resistance of the test specimen is determined from the voltage and current values ​​between these electrode terminals, the range actually evaluated is between the electrode terminals. That is, the area between the electrode terminals is the effective evaluation surface.

[0030] Furthermore, at least one temperature sensor 11 (a thermocouple is depicted in Figure 2) is incorporated into the test specimen 5. It is preferable that the temperature sensor be positioned at least near the center of the effective evaluation surface in order to measure the representative temperature of the test specimen.

[0031] [Means for holding test specimens] As shown in Figure 1, the test specimen 5 is held in the housing 9 of the corrosion test apparatus 1 by the test holding means 6. The method of holding the test specimen is not particularly limited. The test specimen should be positioned and held so that the droplets adhere appropriately to the effective evaluation surface when droplets are scattered. For example, when droplets are scattered by a rotating brush 2 as shown in Figure 1, it is good to position the rotating brush's axis of rotation, the liquid surface of the test solution 3, and the effective evaluation surface of the test specimen 5 so that they are parallel to each other. For example, when droplets are scattered by a spray nozzle, it is good to position the effective evaluation surface of the test specimen so that it is perpendicular to the axis of the spray shape.

[0032] A heater (heater) 8 may be installed on the back surface of the test specimen 5 (the surface opposite the effective evaluation surface) to ensure uniform temperature throughout the specimen. The heater 8 allows the temperature of the test specimen to be set according to the test environment. From the viewpoint of uniformly heating and maintaining the temperature of the entire test specimen, a flat heater is preferred. For example, a mica heater that can be heated electrically and is easy to control is preferred. Non-contact heating such as electromagnetic induction may also be applied. In addition, a temperature buffer plate 7 may be placed between the test specimen 5 and the heater 8 to prevent temperature unevenness within the test specimen caused by temperature unevenness in the heater being transmitted to the test specimen. This temperature buffer plate should be placed so as to be in contact with the back surface of the test specimen, preferably the entire back surface. The temperature buffer plate makes the heat transfer from the heater 8 uniform, suppressing uneven temperature distribution within the test specimen 5 due to factors such as temperature unevenness in the heater 8. The material of the temperature buffer plate 7 is not particularly limited, but a metal plate is preferred from the viewpoint of processability and corrosion resistance. As for the material of the metal plate, Ti or Al, which have corrosion resistance and good heat conductivity, are preferred.

[0033] [Measurement means] The means for measuring the temperature and electrical resistance of the test specimen are not particularly limited, but as mentioned above, electrode terminals (not shown) are provided at both ends of the effective evaluation surface 10 of the test specimen 5, and the voltage and current values ​​between the terminals are measured, and a temperature sensor is placed at least near the center of the effective evaluation surface for measurement.

[0034] For temperature measurement, for example, a temperature sensor 11 can be placed on the back surface of the test specimen 5 to measure the temperature. It is desirable for the temperature to be uniform throughout the entire test specimen, so one temperature sensor may suffice, but it is preferable to install multiple sensors if possible. Thermocouples and infrared radiation thermometers can be used as temperature sensors 11. Thermocouples are preferred because they have less disturbance and are highly reliable.

[0035] As mentioned above, the electrical resistance of test piece 5 can be determined at any time by measuring the current and voltage across the test piece terminals when electricity is passed directly through the test piece.

[0036] Figure 2 shows a conceptual diagram of the installation of a thermocouple as a temperature sensor 11 and an ammeter 13 and voltmeter 12 for determining electrical resistance in a cross-section of the test specimen 5. It is desirable to place the terminals for current measurement and the terminals for voltage measurement at both ends in the longitudinal direction of the effective evaluation surface 10 of the test specimen 5. This is because the corrosion state in the area between these two terminals can be monitored. In Figure 2, electricity flows from the left end to the right end of the test specimen 5, and the electrical resistance between the voltage terminals is calculated from the voltage and current values ​​measured by the voltmeter 12 and ammeter 13. In Figure 2, the upper part of the drawing is the surface of the test specimen 5 where corrosion is actually evaluated (effective evaluation surface 10), and the temperature sensor 11, current terminals, and voltage terminals are provided on the back side of it. The areas other than the effective evaluation surface are coated 14 with resin or the like to prevent the test solution from directly adhering to the sensors and terminals. The coating 14 should preferably have insulating properties and resistance to the test solution (corrosion resistance, chemical resistance, etc.).

[0037] [Corrosion amount calculation means: Corrosion amount calculation step] The corrosion calculation means (corrosion calculation step) calculates the amount of corrosion of the test specimen from the temperature, current value, and voltage value measured by the measurement means (measurement step). For the sake of simplicity, the following explanation assumes that the temperature remains constant throughout the corrosion test period (from the start to the end of the corrosion test).

[0038] In a corrosion test, corrosion progresses as droplets of the test solution intermittently and unevenly adhere to the test specimen, followed by drying. As corrosion occurs, the cross-sectional area of ​​the test specimen in the corroded portion decreases, and consequently, the electrical resistance increases. It is well known that the electrical resistance of conductors such as metals is inversely proportional to the cross-sectional area of ​​the current path (Equation 5). That is, since the length L of the effective evaluation surface and the resistivity ρ of the material are constant, the product of the electrical resistance R and the cross-sectional area A is constant. R = V / I = ρL / A ..... Equation 5 R: Electrical resistance value V: Voltage I: Current ρ: Resistivity of the material L: Conductor length (effective evaluation surface area of ​​the test specimen) A: Conductor (effective evaluation surface of the test piece) cross-sectional area In other words, when the electrical resistance R is measured at any given time point, the cross-sectional area A of the test specimen at that time can be calculated using Equation 6. A=A0×R0 / R...Equation 6 R0: Electrical resistance value of the test specimen (effective evaluation surface) in its initial state before corrosion testing. A0: Cross-sectional area of ​​the test specimen (effective evaluation surface) in the initial state. Furthermore, assuming that the entire effective evaluation surface is uniformly corroded, with width W and thickness d of the test specimen (effective evaluation surface), the average corrosion amount Δd can be calculated using Equation 7. Δd = A0 / WA / W =(A0 / W)×(1-R0 / R) =d0(1-R0 / R)...Equation 7 d0: Thickness of the test specimen (effective evaluation surface) in the initial state. The corrosion resistance of the test specimen can be evaluated using the average corrosion amount Δd obtained as described above.

[0039] Regarding the method for compensating for electrical resistance due to temperature changes, the method described in Patent Document 2 can be applied. Briefly, since the electrical resistance R of the test piece is a function of temperature, this can be expressed as a temperature-dependent function R F (T) is denoted as (T). Since the temperature dependence of electrical resistance differs depending on the metal material, a temperature-dependent function R is defined in advance according to the material of the test piece. F Let (T) be determined. If the initial temperature is T0, and the temperature measured at any point during the corrosion evaluation test is T and the electrical resistance is R, then the measured electrical resistance R is equal to the electrical resistance R at temperature T0. T0 This can be calculated using Equation 8. In this way, the electrical resistance R measured at any given time can be converted to the electrical resistance R at the initial temperature T0. T0 By comparing the results, the effects of temperature changes can be compensated for, and the amount of corrosion can be determined. R T0 =R×{R F (T0) / R F (T)} ...Formula 8

[0040] The measured electrical resistance R is converted to the initial temperature T0 using Equation 8. T0 By substituting this value into R in Equation 7, the effect of temperature can be offset, and the average corrosion rate can be determined with high accuracy. Of course, the electrical resistance value R0 at the initial state (temperature T0) can also be converted to the temperature (T) at the time of measurement and substituted into Equation 7. Since both methods yield the same value, there is no problem in using either conversion method.

[0041] [Test specimen preparation steps] [Droplet particle size, droplet adhesion area] As mentioned above, in corrosion testing, if the droplet dispersion pattern and the test specimen are not appropriately matched, it is impossible to properly evaluate non-uniform corrosion caused by intermittent droplets. Therefore, optimization of the properties of the droplets, such as particle size, and the test specimen is required, and it was shown that the relationship between the droplet particle size distribution and the shape of the test specimen, and the relationship between the area of ​​droplet adhesion per predetermined time and the area of ​​the surface of the test specimen to be tested for corrosion (effective evaluation surface) are important. Accordingly, in order to determine the shape of the test specimen, the properties of the droplets, such as particle size, in the testing apparatus are measured in advance.

[0042] [Measurement of droplet size] The droplet particle size can be measured using water-sensitive test paper. The water-sensitive test paper is attached to the corrosion test surface (effective evaluation surface) of the test specimen, and droplets of the test solution are scattered in the same manner as in the corrosion test. The droplet adhesion is then observed to measure the particle size. Water-sensitive test paper changes color when moisture adheres to it, and the discolored area remains unchanged even after drying, allowing for post-test confirmation of droplet adhesion marks. By scattering droplets for a predetermined time and observing the adhesion marks left on the water-sensitive test paper, the maximum droplet particle size, average droplet particle size, and particle size distribution can be determined. Furthermore, by attaching water-sensitive test paper to the entire effective evaluation surface, the droplet adhesion area can also be measured. For example, the droplet particle size distribution and droplet adhesion area can be easily determined by binarization using image processing. Measurements may be taken across the entire effective evaluation surface of the test specimen, or three or more observation areas of a 10 mm square (or, if the width of the effective evaluation surface is 10 mm or less, a square with sides of a length equal to or less than that width) may be arbitrarily selected from the effective evaluation surface, and the maximum particle size, average particle size, and droplet adhesion area ratio of droplets may be measured within these observation areas, and these values ​​may be calculated by arithmetic mean.

[0043] [slit] To improve the accuracy of evaluating the amount of corrosion on the effective evaluation surface of a test specimen, it is preferable to make the area of ​​the test specimen (effective evaluation area) as large as possible and to evaluate it in a way that minimizes the local influencing factors inherent to the test equipment to the point where they can be ignored. On the other hand, electrical resistance monitoring evaluates the reduction in cross-sectional area due to corrosion of the test specimen using electrical resistance, and accuracy improves as the cross-sectional area of ​​the test specimen decreases. Therefore, as shown in Figures 3(a) and 3(b) as an example, a slit 31 may be made in the test specimen 5. By making a slit, it is possible to improve evaluation accuracy by narrowing the width of the effective evaluation surface and reducing the cross-sectional area while securing a large effective evaluation area. Specifically, it is preferable to make a slit in the effective evaluation surface of the test specimen and increase the current path length (the length over which the current flows). There are no particular limitations on how the slit is made, but it is preferable to make the slit so that the width W of the effective evaluation surface is as constant as possible (an example is shown in Figures 3(a) and 3(b)).

[0044] Furthermore, while there is no particular limit to the slit width, if it is too narrow, a current path may be formed when droplets adhere to it, potentially causing an electrical short circuit. On the other hand, even if a short circuit occurs in the slit due to droplets (liquid), the electrical conductivity of the metal test piece is extremely high, so even if a short circuit occurs in the slit due to a small amount of droplet adhesion, the impact is small and negligible. Therefore, the slit width W slit The average particle size of droplets is D mean It is desirable to make it wider (Equation 4). Preferably, the average particle size D mean It is recommended to multiply it by 1.2 times or more, 1.4 times or more, or 1.5 times or more. D mean <W slit ...Formula 4 W slit : Slit width Furthermore, if there is sufficient effective evaluation area in the test specimen and a sufficient slit width can be secured, the slit width (W slit ) with maximum particle size (D max It is preferable to make it wider than )

[0045] Although the area of ​​the effective evaluation surface of the test specimen may decrease by making a slit, it is assumed that the same non-uniform corrosion is occurring as in the effective evaluation surface before making the slit (shown by the dotted line in Figure 3), so there is no problem in the same non-uniform corrosion evaluation. Furthermore, since the thickness does not change, the width W of the effective evaluation surface becomes narrower, the cross-sectional area becomes smaller, and the accuracy of the corrosion evaluation is improved, which is effective. Although the area of ​​the effective evaluation surface of the test specimen decreases by the amount of the slit, it is assumed that the same non-uniform corrosion is occurring as in the effective evaluation surface before making the slit (shown by the dotted line in Figure 3), so the accuracy of the same non-uniform corrosion evaluation can be improved. To confirm that the same non-uniform corrosion is occurring, when a slit is made, it is preferable to increase the lower limit of the ratio of the area of ​​droplet adhesion to the area of ​​the effective evaluation surface (S / A in Equation 3) at a predetermined time, preferably 0.10 or higher, more preferably 0.20 or higher, and even more preferably 0.30 or higher.

[0046] [Corrosion Test Method] The corrosion testing method using the corrosion testing apparatus described above will now be explained.

[0047] [Test specimen holding step] Prior to the corrosion test, the characteristics of the droplets of the test solution adhering to the test specimen are determined. To determine the droplet characteristics, as described above, water-sensitive test paper is attached to the test specimen, and droplets are allowed to adhere to it for a predetermined time, similar to the actual corrosion test. The droplet characteristics (maximum particle size D) are then determined from the residue left on the water-sensitive test paper. max , average particle size D mean Determine the following: Also, determine the ratio of the area S of droplet adhesion to the effective evaluation surface (effective evaluation surface) on the surface of the test specimen used for corrosion testing to the area A of the effective evaluation surface.

[0048] Next, the maximum particle size D obtained max and average particle size D mean The splash generating means of the test apparatus is adjusted so that the width W of the effective evaluation surface of the test specimen and the ratio S / A of the adhesion area S per predetermined time to the area A of the effective evaluation surface are within a predetermined range.

[0049] Ultimately, the maximum particle size D max and average particle size D mean After confirming that the width W of the effective evaluation surface of the test specimen and the ratio S / A of the adhesion area S per predetermined time to the area A of the effective evaluation surface are within the predetermined range, the test specimen is attached to the test specimen holding means and the corrosion test is started.

[0050] [Measurement Steps] After the corrosion test begins, a droplet generating device is used to scatter droplets of the test solution onto the test specimen, and a measuring device measures the temperature, current, and voltage values. The measured data is then sent to a corrosion calculation device.

[0051] [Corrosion Amount Calculation Step] From the temperature, current, and voltage data obtained in the measurement step, the corrosion amount calculation means calculates the electrical resistance of the test specimen at the time of measurement, and then calculates the average corrosion amount from there. The corrosiveness can be evaluated from the calculated electrical resistance and average corrosion amount.

[0052] Furthermore, the data calculated by the corrosion amount calculation means may be stored together with time data in the storage means and created a database. This database may also be used for analysis by the corrosion evaluation means. Additionally, the monitoring means may display data collection status and data analysis results. The corrosion amount calculation means, storage means, corrosion evaluation means, and monitoring means do not need to be in the vicinity of the specimen holding means; they can be located anywhere as long as they are connected by a data line or similar means.

[0053] By repeatedly performing the above measurement step and corrosion amount calculation step, the non-uniform corrosion of the test specimen can be evaluated over time. [Examples]

[0054] A corrosion test was conducted using a rotary brush type corrosion test apparatus (this corrosion test apparatus) as shown in Figure 1, reproducing a splash environment in which corrosive liquid is intermittently scattered. The details of the corrosion test are as follows: • Test specimen material: Carbon steel (SM490A) • Effective evaluation surface size of the test specimen: 0.5t × 10w × 100L (mm) • Test cycle: Table 1 shows the cycle conditions assuming two droplet dispersions per day (24 hours) to accelerate corrosion, with one cycle defined as one day (24 hours). The rotation speed of the rotating brush, the temperature of the test specimen, and the maximum droplet particle size (D max ) and average particle size (D mean Table 1 shows the specifications for the test prerequisites. • Test solution: Artificial seawater (Aquamarine, manufactured by Yashima Pharmaceutical Co., Ltd.). The components of the test solution (artificial seawater) are shown in Table 2. • Test solution replacement frequency: Replace every 2-4 cycles. • Test period: 30 cycles (equivalent to 30 days) As shown in Figure 2, the temperature sensor and terminals were installed on the back side of the effective evaluation surface of the test specimen. The voltage and current terminals were installed at both ends along the longitudinal direction of the effective evaluation surface, and the thermocouple for the temperature sensor was installed approximately in the center of the effective evaluation surface. The measured temperature, current, and voltage data were input into a computer (not shown), processed to calculate the electrical resistance value, and the average corrosion amount Δd was determined accordingly. • Before starting the corrosion test, water-sensitive test paper was attached to the test specimen to adjust the droplet characteristics and adhesion area. At this time, droplets were allowed to adhere for 30 minutes, and the droplet particle size (droplet size) and adhesion area ratio (S / A) measured by binarizing the droplet traces remaining on the water-sensitive test paper are also shown in Table 1.

[0055] Furthermore, to confirm that the sensors were functioning correctly, the weight of the test specimens was measured before the test, and after 30 cycles, the weight was measured again after removing the corrosion products formed on the surface of the specimens. The average amount of corrosion was also calculated from the weight change before and after the test (gravimetric method). Table 3 shows the amount of corrosion measured with this corrosion testing apparatus for each test, and the amount of corrosion measured by the conventional gravimetric method.

[0056] Figure 4 shows an example of the measurement results of the change in the amount of corrosion over time during non-uniform corrosion of the obtained test specimens (test condition 1). Figure 4 also shows the amount of corrosion after 30 cycles, which was determined by the gravimetric method (indicated by circles in the figure).

[0057] As can be seen from Table 3 and Figure 4, the corrosion rate obtained using this corrosion testing machine was in good agreement with the results of weight change measurements (gravimetric method) of the test specimens before and after the test. This confirms that the corrosion testing apparatus used in this study was able to accurately monitor corrosion in a splash-adhering environment.

[0058] Figure 4 shows that the rate of corrosion accelerates slightly over time. Although not shown in the figures, similar acceleration of corrosion over time has been confirmed under other test conditions. In other words, in the case of non-uniform corrosion such as in a splash environment, it was confirmed that the corrosion rate gradually increases over time. With conventional evaluations that only measure weight loss before and after testing, it was not possible to grasp that the corrosion rate was changing, and it was only possible to assume a constant corrosion rate. However, by adopting the corrosion test apparatus and corrosion measurement method according to the present invention, it became possible to measure the change in corrosion over time, and it was confirmed that the corrosion rate actually accelerates over time.

[0059] Furthermore, observation of the surface of the test specimen after rust removal (effective evaluation surface) revealed that the entire surface of the test specimen was covered with non-uniform corrosion, confirming that the corrosion progressed due to droplets with a particle size of several millimeters. Thus, it was confirmed that the corrosion testing apparatus and corrosion testing method according to the present invention can be used to analyze in detail what is happening in non-uniform corrosion.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3] [Industrial applicability]

[0063] This invention can be used for material development and material selection for structures used in splash-adhering environments where corrosive liquid splashes adhere and cause uneven corrosion. The materials developed in this way can be used in a wide range of industries, including the construction, power, and shipbuilding industries, as well as in various fields such as addressing environmental issues. [Explanation of Symbols]

[0064] 1. Corrosion testing apparatus 2 Rotating Brushes 3. Test solution 4. Droplets 5 Test specimens 6. Test specimen holding means 7 Temperature buffer plate 8. Heater (heating means) 9 cabinets 10 Effectiveness Evaluation Aspects 11. Temperature sensor (thermocouple) 12 Voltmeter 13 Ammeter 14 Coating 21 Splash marks 31 slits

Claims

1. A corrosion testing apparatus for evaluating corrosion of a metal test specimen by applying a splash of test solution to its surface, passing an electric current through the specimen to measure its electrical resistance, and further measuring the temperature of the specimen, A test specimen holding means for holding the test specimen, A droplet generating means for generating droplets of the test solution, A measuring means for measuring the temperature and electrical resistance of the test specimen, The system includes a corrosion amount calculation means for calculating the amount of corrosion of the test piece from the measured temperature and electrical resistance, The maximum droplet diameter of the droplets adhering to the aforementioned test piece is D. ｍａｘ , average droplet diameter D ｍｅａｎ year, Let A be the area of ​​the effective evaluation surface, which is the surface on the surface of the test specimen used to evaluate corrosion. Let W be the width of the effective evaluation surface of the test specimen in the direction perpendicular to the current direction. When S is the droplet adhesion area, which is the total area of ​​droplets adhering to the effective evaluation surface of the test specimen per predetermined time, A corrosion testing apparatus characterized by satisfying the following relationships between equations 1 to 3. a×D ｍａｘ ≤ W (where 1.0 ≤ a) ... Equation 1 b x D ｍｅａｎ ≤ W (where 2.0 ≤ b) ... Equation 2 0<S / A≦0.5...Formula 3

2. The corrosion testing apparatus according to claim 1, wherein the specimen holding means comprises a heater for heating the specimen and a temperature buffer plate between the specimen and the heater that is in contact with the entire back surface of the specimen.

3. The corrosion testing apparatus according to claim 2, wherein the temperature buffer plate is a metal plate.

4. The corrosion testing apparatus according to claim 1 or 2, wherein the test piece has a slit.

5. W is the width of the slit. ｓｌｉｔ The corrosion testing apparatus according to claim 4, wherein the following formula 4 is satisfied. D ｍｅａｎ <W ｓｌｉｔ ・・・・Form 4

6. A corrosion test method using the corrosion test apparatus described in claim 1 or 2, The specimen preparation step involves preparing the test specimen, A test specimen holding step, in which the prepared test specimen is held, A measurement step comprising generating droplets of the test solution, adhering the droplets to the surface of the test piece, and measuring the temperature and electrical resistance of the test piece, The system includes a corrosion amount calculation step that calculates the amount of corrosion of the test piece from the measured temperature and electrical resistance, in the test piece preparation step, the diameter of the droplets of the test solution adhering to the test piece is measured in advance to obtain the maximum droplet diameter D ｍａｘ and the average droplet diameter D ｍｅａｎ , Let A be the area of ​​the effective evaluation surface, which is the surface on the surface of the test specimen used to evaluate corrosion. On the effective evaluation surface of the test specimen, the width in the direction perpendicular to the current direction is W. When S is the total area of ​​droplets adhering to the effective evaluation surface of the test specimen per predetermined time, A corrosion test method characterized by preparing a test specimen that satisfies the following relationships in equations 1 to 3. a×D ｍａｘ ≤ W (where 1.0 ≤ a) ... Equation 1 b x D ｍｅａｎ ≤ W (where 2.0 ≤ b) ... Equation 2 0<S / A≦0.5...Formula 3

7. The corrosion test method according to claim 6, wherein, when pre-measuring the diameter of the droplets of the test solution adhering to the test piece, a water-sensitive test paper is attached to the surface of the test piece, and the diameter of the droplets remaining on the water-sensitive test paper is measured.

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