Method for evaluating the severity of atmospheric corrosion in marine environment

Abstract

This invention discloses a method for assessing the severity of atmospheric corrosion in marine environments, comprising the following steps: Step S1: Measuring key influencing factors that induce atmospheric corrosion of metals in the assessed environmental objects; Step S2: Integrating the measured influencing factors to obtain environmental parameters; Step S3: Calculating key parameters for different environmental objects based on the environmental parameters; Step S4: Calculating the equivalent corrosion severity value of the environmental objects based on the key parameters, and comparing the atmospheric corrosivity levels of different environmental objects. This method is applicable to assessing the severity of atmospheric corrosion in environments where temperature, humidity, and salt spray concentration are the main influencing factors, and can provide effective guidance for metal corrosion prediction and prevention.

Description

Technical Field

[0001] This invention relates to the field of metal corrosion and corrosion prevention, and specifically to a semi-quantitative evaluation method for atmospheric corrosion severity based on a mass transfer kinetics model of key environmental factors affecting marine climate. Background Technology

[0002] In marine environments, the combined effects of high-concentration marine salt spray, high temperature and humidity, and highly variable environmental factors make metallic materials highly susceptible to corrosion and deterioration over long periods. This can lead to decreased electrical performance and malfunctions in service products, severely impacting equipment safety and lifespan. Atmospheric corrosion in marine environments begins with the deposition of sea salt particles on the material surface. Influenced by ambient temperature and humidity, the salt deliquesces to form an electrolyte film, subsequently causing electrochemical corrosion. The rate of electrochemical corrosion within the electrolyte film is related to oxygen diffusion and solubility. Changes in environmental factors such as temperature and humidity alter the electrolyte film concentration, thickness, oxygen solubility, and diffusion rate, thus changing the corrosion reaction rate. This invention studies the changes and states of active substance O2 in the electrolyte film under different environmental conditions and establishes a relational model. By calculating the diffusion rate of active substance O2 on the electrode surface, the theoretical rate of atmospheric corrosion of metals under different conditions can be evaluated, thereby achieving an assessment of atmospheric corrosivity based on environmental conditions. Summary of the Invention

[0003] The purpose of this invention is to provide a method for assessing the severity of atmospheric corrosivity in marine environments. This method can conduct a semi-quantitative assessment of the severity of the impact of different (different spatial / temporal) environmental objects on metal corrosion.

[0004] The objective of this invention is achieved through the following technical solution: a method for assessing the severity of atmospheric corrosivity in marine environments, characterized by comprising the following steps:

[0005] Step S1: Measure and evaluate the key influencing factors that induce atmospheric corrosion of metals in the environmental objects.

[0006] The temperature (T / ℃), humidity (RH,%), and salt spray concentration (salt spray deposition rate S) of the environmental object were measured. NaCl / g·m -2 ·day -1 The environmental object refers to the environment of a certain spatial location at different time periods or the environment of different spatial locations at a certain time.

[0007] Step S2: Integrate the measured influencing factors to obtain environmental parameters.

[0008] Temperature and salt spray concentration are integrated using their arithmetic mean to calculate the average temperature. and salt spray concentration

[0009]

[0010]

[0011] Relative humidity data is processed as follows:

[0012] According to RH≥RH sa Filter the relative humidity data, RH sat Find the relative humidity (%) for sodium chloride deliquescence and calculate the time / space wetting ratio K:

[0013]

[0014] Where a represents the relative humidity RH≥RH sat The number of data points, where m is the total number of relative humidity data points;

[0015] At the same time, relative humidity RH≥RH sat value Calculate the average relative humidity

[0016]

[0017] Step S3: Calculate the key parameters for different environmental objects based on the environmental parameters.

[0018] Calculate the oxygen diffusion rate using Fick's Law

[0019]

[0020] Where L is the liquid film thickness during atmospheric corrosion, it is equivalently characterized by the condensation potential l of saline air under marine salt spray atmosphere, and quantified by the following formula:

[0021]

[0022] The concentration of oxygen within the electrolyte film is represented by the equivalent oxygen solubility C in a salt solution, and quantified using the following formula:

[0023] C = 0.255 × exp - 0.360 × T

[0024] D is the diffusion coefficient of oxygen within the electrolyte film, which is quantified by the following formula:

[0025] D = -3.47 × 10 -17 T·RH+3.27×10 -14 RH+3.47×10-15 T+2.05×10 -9 ;

[0026] Substitute the environmental parameters integrated in step S2 into the corresponding environmental objects. and Calculate the key parameters l, C, and D for atmospheric corrosion severity;

[0027] Step S4: Calculate the equivalent corrosion severity value of the environmental object based on the key parameters, and compare the atmospheric corrosivity of different environmental objects.

[0028] Based on the metal corrosion reaction rate v under cathodic control corr With oxidant diffusion rate Related to the establishment of the reaction rate v with metal corrosion. corr Equivalent corrosion severity quantification model S:

[0029]

[0030] By substituting relevant parameters K, l, C, and D, the atmospheric corrosion severity of different environmental objects is quantified for comparative evaluation.

[0031] Beneficial effects:

[0032] Based on the theory of material transport dynamics in atmospheric corrosion of metals, this paper analyzes the environmental factors that play a major role in atmospheric corrosion of metals and presents a method for evaluating the severity of atmospheric corrosion. This method is applicable to the comprehensive evaluation of atmospheric corrosivity under the influence of marine climate through multiple key influencing factors (temperature, humidity, and salt spray concentration). It can achieve a semi-quantitative comparative evaluation of the ability of environmental objects to induce metal corrosion at different time periods at a certain spatial location or at different spatial locations at a certain time, and can provide effective guidance for metal corrosion prediction and prevention. Attached Figure Description

[0033] Figure 1 Key climatic and environmental influencing factors under different conditions and attribute states;

[0034] Figure 2 Integrate parameters for key climate and environmental influencing factors under different conditions and attributes;

[0035] Figure 3 This is a schematic diagram of the steady-state distribution (diffusion) of oxygen in an electrolyte film.

[0036] Figure 4 The relationship between atmospheric corrosion and the thickness of thin films on metal surfaces. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0038] The present invention provides a method for assessing the severity of atmospheric corrosivity in marine environments, comprising the following steps:

[0039] Step S1: Measure and evaluate the key influencing factors that induce atmospheric corrosion of metals in the environmental objects.

[0040] The assessment of the severity of atmospheric corrosivity in marine environments aims to evaluate the strength of atmospheric-induced metal corrosion in environmental objects at different times or geographical locations. It can be conducted at different time periods at a specific location or at different locations at a specific time, thereby assessing the changes in atmospheric corrosivity caused by temporal or geographical differences.

[0041] Different environmental objects can be labeled, such as environmental objects at different time periods at a certain spatial location, or environmental objects at different spatial locations at a certain time as A1, A2, ... A n n = 1, 2, 3… According to the theory of metal corrosion, the key environmental factors inducing atmospheric corrosion of metals mainly include temperature (T / ℃), humidity (RH,%), and salt spray concentration (salt spray deposition rate S). NaCl / g·m -2 ·day -1 ),like Figure 1 As shown, environment objects A1, A2, ... A are obtained respectively. n Data sets of air temperature, relative humidity, and salt spray concentration that are spatially distributed or change over time.

[0042] Step S2: Integrate the measured influencing factors to obtain environmental parameters.

[0043] Temperature and salt spray concentration are integrated using their arithmetic mean to calculate the average temperature. and salt spray concentration

[0044]

[0045]

[0046] Relative humidity data is processed as follows, based on RH≥RH sa Filter the relative humidity data and calculate the time / space wetting ratio K:

[0047]

[0048] Where a represents the relative humidity RH≥RH sat The number of data points, where m is the total number of relative humidity data points. RH sat The relative humidity (%) for sodium chloride deliquescence is RH. sat With temperature (T) i The relationship between / ℃) satisfies the following formula:

[0049] RH sat，i =-0.03T i +76

[0050] At the same time, the relative humidity value Calculate the average relative humidity

[0051]

[0052] Depend on Figure 1 Environmental parameters obtained by integrating influencing factors, such as Figure 2 As shown.

[0053] Step S3: Calculate the key parameters for different environmental objects based on the environmental parameters.

[0054] Atmospheric corrosion in marine environments begins with the deposition of sea salt particles on the material surface. Affected by changes in ambient temperature and humidity, the salt deliquesces to form an electrolyte film, which then leads to electrochemical corrosion. The reaction rate is controlled by the diffusion rate of the oxidant (oxygen) within the electrolyte film.

[0055] According to Fick's law, the diffusion coefficient is the mass or number of moles of a substance that diffuses perpendicularly through a unit area per unit time under a unit concentration gradient along the diffusion direction. The diffusion process of oxygen under the liquid film after reaching steady state is as follows: Figure 3 As shown, the O2 concentration and diffusion rate within the liquid film are mainly affected by the environment, with the oxygen diffusion rate perpendicular to the metal surface being... Calculations can be performed according to Fick's rules:

[0056]

[0057] Where L is the liquid film thickness during atmospheric corrosion, it is equivalently characterized by the condensation potential (i.e., salt spray deposition and deliquescence) of salt-containing air under marine salt spray atmosphere, and then quantified by the following formula:

[0058]

[0059] This indicates the concentration of the oxidant (oxygen) within the electrolyte membrane. It can be equivalently characterized based on the oxygen solubility C in the salt solution, and then quantified using the following formula:

[0060] C = 0.255 × exp - 0.360 × T

[0061] D is the diffusion coefficient of the oxidant (oxygen) within the electrolyte film, which can be quantified by the following formula:

[0062] D = -3.47 × 10 -17 T·RH+3.27×10-14 RH+3.47×10 -15 T+2.05×10 -9 .

[0063] Corresponding to different environment objects (A1, A2, ... A n Substitute the integrated environmental parameters (e.g., n = 1, 2, 3...) into the set of parameters. Figure 2 As shown, that is, in step S2 and ) Calculate the key parameters l, C, and D for atmospheric corrosion severity.

[0064] Step S4: Calculate the equivalent corrosion severity value of the environmental object based on the key parameters, and compare the atmospheric corrosivity of different environmental objects.

[0065] Based on the metal corrosion reaction rate v under cathodic control corr With oxidant diffusion rate Related:

[0066]

[0067] Establish the reaction rate v with metal corrosion corr Equivalent corrosion severity quantification model S:

[0068]

[0069] Substituting the relevant parameters K, l, C, and D, the environmental atmospheric corrosion severity S, which is equivalent to the corrosion rate, is quantified. The strength of the atmospheric-induced metal corrosion ability is directly proportional to the calculated severity value S.

[0070] For different environmental objects (A1, A2, ... A n Substitute the values ​​of n (n = 1, 2, 3, ...) into the key parameters in step S3 to calculate the corresponding severity values. A comparative evaluation can then be conducted.

[0071] Sea salt particles deposited on equipment surfaces absorb moisture and deliquesce to form an electrolyte film, making the atmosphere in nearshore and offshore areas highly corrosive. As sea salt particles deposit on material surfaces, changes in external temperature and humidity cause the deposited salt to deliquesce, generating an electrolyte film, which in turn leads to electrochemical corrosion of metals and material aging. The concentration and settling velocity of salt spray in the air are important environmental factors for the classification and assessment of atmospheric corrosivity. Therefore, the key environmental factors for atmospheric corrosivity in marine environments are: relative humidity, temperature, and salt spray (sea salt particle) concentration.

[0072] Beneath the liquid film, the metal acting as the anode loses electrons while oxygen, acting as the cathode, gains electrons, leading to corrosion and destruction of the metal structure. In the atmospheric environment, influenced by factors such as relative humidity, sunlight, rainfall, and condensation, the water film layer causing electrochemical corrosion on the metal surface cannot persist indefinitely; atmospheric corrosion of the metal surface is accompanied by a cycle of alternating wet and dry conditions. Among environmental factors, relative humidity, temperature, and the amount of deposited salt work together to alter the state of the deliquescent liquid film (concentration / thickness, etc.), thus affecting the corrosion reaction. Furthermore, in a constantly changing environmental system, drastic temperature / humidity changes can cause the liquid film to dry rapidly or deliquesce within a short period; the accelerated drying process of the liquid film increases the rate of material transfer, thus increasing the corrosion rate. Therefore, evaluating the atmospheric corrosivity of marine environments requires long-term / large-scale data collection, and the severity of atmospheric corrosion needs to be determined based on continuous periodic reactions.

[0073] Tomashov proposed a qualitative study in the 1940s on the effect of liquid film thickness on the atmospheric corrosion rate of metals. Figure 4 Based on Tomashov's corrosion model, research reports indicate that the corrosion rate of metals under a liquid film is affected by the diffusion rate of oxygen within the liquid film. In a constantly changing environment, drastic temperature / humidity changes can cause the liquid film to dry rapidly or deliquesce within a short period. During the accelerated drying process of the liquid film, the material transfer rate increases, and simultaneously, as the atmospheric temperature rises, the solubility of O2 gradually decreases, thus affecting the oxygen depolarization reaction at the cathode and altering the corrosion process. Wetting conditions are a fundamental prerequisite for determining whether corrosion occurs. Therefore, the concept of the time / space wetting ratio K is proposed and incorporated into the model. Determining the conditions for wetting requires considering the characteristics of the marine atmospheric environment: in marine environments, surface wetting is mostly caused by salt spray deposition and deliquescence; the deliquescent characteristics of salt in saline air, i.e., the deliquescent humidity of salt, are used to filter relative humidity data and calculate K.

[0074] In the high-salt-fog marine environment, when the interior of electrical equipment is penetrated by salt spray, the sea salt particles deposited on the equipment surface will deliquesce and become wetted under low relative humidity. Sea salt particles exhibit drastically different deliquescing states under different temperature and humidity conditions. Hygroscopicity is an important physicochemical property of marine aerosols, affecting their life cycle and atmospheric behavior. The ability of salts to absorb moisture varies under different temperatures and relative humidity levels, and the hygroscopicity of aerosols is influenced by factors such as particle size, chemical composition, and mixing state. Sea salt aerosols are hydrophilic aerosols; after deliquescing due to moisture absorption, sea salt particles can be approximated as small droplets containing solute. Sea salt accounts for 3.5% of the mass of seawater, of which 85% is NaCl. Therefore, the main component of sea salt particles is NaCl, leading to an investigation into the physical properties of sodium chloride.

[0075] Sea salt particles deliquesce under low relative humidity. Different types of salt exhibit drastically different deliquescing characteristics under varying temperature and humidity conditions. According to the laws of thermodynamics, the deliquescing characteristics of salts are as follows:

[0076] a) The microdroplets formed by deliquescence start with salt crystallization, and the thickness / amount of the liquid film formed mainly depends on the relative humidity and the amount of deposited salt.

[0077] b) The concentration of the electrolyte solution formed by deliquescence decreases linearly with increasing relative humidity;

[0078] c) The solubility of salt in water increases with increasing temperature, while the density, concentration, and equilibrium RH of the saturated solution decrease.

[0079] By preparing sodium chloride solutions with different known salinities, and using a temperature and humidity chamber to control the ambient temperature, a measurement device was built using temperature and humidity sensors and chloride ion concentration measuring equipment as standard instruments to measure the equilibrium relative humidity of NaCl solutions at different temperatures, as well as the relationship between NaCl deliquescence and water vapor partial pressure (relative humidity) at different temperatures. The changes in equilibrium relative humidity (deliquescence humidity) and solution density of NaCl aqueous solutions / deliquates under different solubilities / saturation states at different temperatures were observed. The deliquescence humidity of NaCl decreased with increasing temperature, showing a linear relationship.

[0080] Through experiments, empirical formulas for the physical properties of salts / salt solutions were derived:

[0081] RH sat , i =-0.03T i +76

[0082] C = 0.255 × exp - 0.360 × T

[0083] D = -3.47 × 10 -17 T·RH+3.27×10 -14 RH+3.47×10 -15 T+2.05×10 -9

[0084] Based on the changes in key environmental factors (temperature / humidity and salt deposition), it is necessary to observe the corrosion rate under different instantaneous states, obtain the relationship between the corrosion rate under different states and the environmental factors under each state, and study the ability of different factors to affect corrosion. The corrosion of metals is generally a reaction between the metal and the oxidant (O2). Generally, depending on the type of metal and the reaction time, the density of the metal oxide film varies, resulting in different levels of protection and robustness. For example, the oxide film of copper gradually becomes denser over time, and the corrosion rate is inhibited by the oxide film, changing with time t in a parabolic manner (ISO 9224 standard).

[0085]

[0086] The strength of metal corrosion induced by the actual environment, i.e., the strength of atmospheric corrosivity, depends only on the various properties and conditions of the environment. When evaluating using standard metals, the inherent characteristics of the metal itself are naturally substituted, thus limiting the application range of time t in the standard model. This invention patent aims to establish a more widely applicable atmospheric corrosion model. Based on the fundamental principles of metal corrosion, namely the electrochemical corrosion reaction occurring under the electrolyte film on the metal surface, the reaction steps can be divided into the following two stages:

[0087] 1. Oxygen diffusion in electrolyte solutions

[0088] 2. Electrochemical reactions occur at the solution / metal interface.

[0089] Stage 2 involves the inherent reaction characteristics of the metal, while Stage 1 is entirely determined by environmental conditions. Stage 1 is the diffusion process of the substance (oxidant). Substituting Fick's second law, the diffusion process of oxygen under the liquid film after reaching steady state is as follows: Figure 3 As shown, the O2 concentration and diffusion rate within the liquid film are mainly affected by the environment, with the oxygen diffusion rate perpendicular to the metal surface being... Calculations can be performed using Fick's second law:

[0090] J = -DC / L

[0091] It is evident that the diffusion rate J is directly proportional to the concentration of substances on the liquid film surface and the diffusion coefficient of substances within the electrolyte liquid film, and inversely proportional to the liquid film thickness. The liquid film thickness represents the surface state of the metal, not the environmental state. When the liquid film on the metal surface is caused by natural phenomena (condensation, salt spray deposition, deliquescence), the environmental conditions inducing this phenomenon can be used to calculate the state of the liquid film (ignoring the influence of the metal surface microstructure). In marine environments, liquid films are mostly caused by salt spray deposition and deliquescence. The concept of the condensation potential of saline air is proposed, representing the thickness of the liquid film formed under steady-state conditions after a metal placed in this air environment undergoes salt spray deposition and deliquescence. The thickness of the liquid film formed by deliquescence is related to the salt spray deposition rate, temperature, and humidity. An empirical formula is fitted:

[0092]

[0093] The severity of atmospheric corrosion, S, determines the rate of corrosion when metal corrosion is induced and the corrosion is in stage 1 (diffusion control occurs when a dense oxide film has not yet formed on the metal, i.e., in the initial stage of the corrosion reaction).

[0094] Corrosion reaction rate ∝ diffusion rate J

[0095] A corrosion severity quantification model S, equivalent to the metal corrosion reaction rate, is established. It is directly proportional to the time / space wetting ratio K, the concentration of substances on the liquid film surface C, and the expansion coefficient D of substances in the electrolyte liquid film, and inversely proportional to the condensation potential l of salt-containing air.

[0096]

[0097] The above is a description of the principles of this invention. The specific embodiments of this invention are not limited thereto. Based on the above content, and according to common technical knowledge and conventional methods in the field, without departing from the basic technical concept of this invention, various other equivalent modifications, substitutions, or alterations can be made to this invention, all of which should fall within the protection scope of this invention.

Claims

1. A method for assessing the severity of atmospheric corrosivity in marine environments, characterized in that, Includes the following steps: Step S1: Measure and evaluate the key influencing factors that induce atmospheric corrosion of metals in the environmental objects: The temperature (T) and humidity (RH) of the environmental object are measured as a percentage, and the salt spray concentration is also measured. Unit: g·m -2 ·day -1 The environmental object refers to the environment of a certain spatial location at different time periods or the environment of different spatial locations at a certain time. Step S2: Integrate the measured influencing factors to obtain environmental parameters: Temperature and salt spray concentration are integrated using their arithmetic mean to calculate the average temperature. and average salt spray concentration : ； ； Relative humidity data is processed as follows: According to RH≥RH sat Filter the relative humidity data, RH sat The relative humidity for sodium chloride deliquescence is expressed as a percentage, and the time / space wetting ratio K is calculated: ； Where a represents the relative humidity RH≥RH sat The number of data points, where m is the total number of relative humidity data points; At the same time, relative humidity RH≥RH sat value Calculate the average relative humidity : ； Step S3: Calculate the key parameters for different environmental objects based on the environmental parameters: Calculate the oxygen diffusion rate using Fick's Law : ； Where L represents the liquid film thickness during atmospheric corrosion, and is used as the condensation potential of saline air under marine salt spray conditions. Perform equivalent characterization and quantify using the following formula: ; The concentration of oxygen within the electrolyte film is represented by the equivalent oxygen solubility C in a salt solution, and quantified using the following formula: ； D is the diffusion coefficient of oxygen within the electrolyte film, which is quantified by the following formula: ； Substitute the environmental parameters integrated in step S2 into the corresponding environmental objects. , and Calculate the key parameters l, C, and D for atmospheric corrosion severity; Step S4: Calculate the equivalent corrosion severity value of the environmental object based on the key parameters, and compare the atmospheric corrosivity of different environmental objects: Based on the metal corrosion reaction rate under cathodic control With oxidant diffusion rate Related to the establishment of reaction rates with metal corrosion Equivalent corrosion severity quantification model S: ； By substituting relevant parameters K, l, C, and D, the atmospheric corrosion severity of different environmental objects is quantified for comparative evaluation.

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