Electrochemical parameter coupling-based crevice corrosion evaluation method and device
By constructing oxygen concentration cells inside and outside the crevice and analyzing polarization curves, the problems of complexity and high cost in crevice corrosion assessment in existing technologies have been solved, and rapid and accurate crevice corrosion rate assessment has been achieved, which is suitable for crevice corrosion risk assessment of engineering equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUN YAT SEN UNIV
- Filing Date
- 2026-03-10
- Publication Date
- 2026-06-09
AI Technical Summary
Existing technologies are insufficient for quickly and economically assessing the risk of crevice corrosion in complex structures. Experimental testing is time-consuming and costly, while finite element simulation technology is complex and has high barriers to entry, making it difficult to quickly identify and analyze crevice corrosion risks.
A crevice corrosion assessment method based on electrochemical parameter coupling is used to construct oxygen concentration cells inside and outside the crevice, and combine polarization curves and kinetic parameter analysis to quickly calculate the corrosion rate inside the crevice and assess the corrosion impact on the crevice structure.
It enables rapid identification and assessment of crevice corrosion rates, and is applicable to the rapid identification and assessment of crevice corrosion risks in structures of engineering equipment. It features convenience, high repeatability, and accurate results, and is suitable for rapid prediction in the initial stage of crevice corrosion.
Smart Images
Figure CN122171429A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrochemical corrosion assessment technology, and in particular to a crevice corrosion assessment method and apparatus based on electrochemical parameter coupling. Background Technology
[0002] Crevice corrosion is a localized corrosion phenomenon that occurs in metallic materials in narrow gaps or enclosed areas (such as gaps formed by flange connections, bolt tightening, or deposits). Crevice corrosion is concentrated inside the gap, while the external surface remains largely intact, creating a stark contrast of "internal corrosion and external integrity." It is highly concealed and extremely harmful, often leading to sudden failures of engineering structures (such as offshore platforms, chemical equipment, and ship pipelines).
[0003] Currently, crevice corrosion assessment mainly includes two categories: laboratory testing and finite element simulation. Laboratory testing primarily relies on standards such as GB / T 13671-2025 Electrochemical Test Method for Crevice Corrosion of Stainless Steel and GB / T 10127-2002 Test Method for Crevice Corrosion of Ferric Chloride in Stainless Steel. This method involves artificially constructing crevice structures and using immersion tests in specific media to assess the corrosion rate and risk of materials within these structures. However, laboratory testing is time-consuming, costly, and inefficient, applicable to a limited range of materials, and unsuitable for the rapidly evolving corrosion protection design and assessment of current equipment. Furthermore, it struggles to assess the crevice corrosion risk of complex structures. Finite element simulation, on the other hand, utilizes simulation software such as COMSOL to construct multiphysics models of crevice corrosion. It simulates the microscopic material transport and electrochemical reactions within the crevice structure using finite element methods. However, this method requires highly complex modeling and physical field construction processes, resulting in a high technical barrier and hindering the rapid identification and analysis of structural crevice corrosion risks. Summary of the Invention
[0004] This invention provides a crevice corrosion assessment method and apparatus based on electrochemical parameter coupling. It aims to start from the basic theory of crevice corrosion, construct an oxygen concentration cell inside and outside the crevice through the polarization behavior of the material, and combine it with relevant kinetic parameter coupling analysis to quickly calculate the corrosion rate in the internal region of the crevice and assess the influence of the crevice structure on crevice corrosion.
[0005] The crevice corrosion assessment method based on electrochemical parameter coupling provided by this invention includes the following steps: S1, Based on the gap structure, determine the anode and cathode of the oxygen concentration cell, and calculate the surface area of the anode and the surface area of the cathode; S2, The anodic polarization curve and cathodic polarization curve of the gap structure material are obtained by using a three-electrode electrochemical testing device, wherein the anodic polarization curve is measured in an oxygen-deficient medium environment and the cathodic polarization curve is measured in an oxygen-rich environment. S3. Obtain the anode current density-potential relationship based on the anode polarization curve, and obtain the cathode current density-potential relationship based on the cathode polarization curve; S4, Establish the electrochemical equilibrium formula: i c ×A c =i a ×A a ; In the formula, A c A is the surface area of the cathode. a i is the surface area of the anode. a i is the anode current density. c The cathode current density; Calculate the coupling potential E of the oxygen concentration cell based on the electrochemical equilibrium formula. corr,galv If the coupling potential E corr,galv If it is not in the activation region of the anodic polarization curve, then crevice corrosion has not occurred; if the coupling potential E corr,galv If it is in the activation region of the anodic polarization curve, then the coupling potential E is obtained. corr,galv The corresponding anodic current density, at this point is the crevice corrosion current density; S5, calculate the crevice corrosion rate based on the crevice corrosion current density.
[0006] Optionally, the anode current density-potential relationship is: ; In the formula, i a i is the anode current density. a0 E is the anode exchange current density, and E is the potential. a0 b is the anode equilibrium potential. a The slope of the anode Tafel is given.
[0007] Optionally, in the activation region of the cathode polarization curve, the cathode current density-potential relationship is: ; In the formula, i c i is the cathode current density. c0 E is the cathode exchange current density, and E is the potential. c0 b is the cathode equilibrium potential. c The slope of the cathode Tafel is given.
[0008] Optionally, if the cathode of the oxygen concentration cell exhibits concentration polarization, then the cathode current density i c Represented as: ; In the formula, The limiting diffusion current density is derived from the limiting diffusion current plateau of the polarization curve; If the cathode polarization curve does not show a limiting diffusion current plateau, the limiting diffusion current density is determined using the limiting diffusion current density formula. The limiting diffusion current density formula is: ; In the formula, n is the charge number of oxygen undergoing reduction, F is the Faraday constant, and D is the diffusion coefficient of dissolved oxygen in the medium. C is the thickness of the diffusion layer. O2 This represents the concentration of dissolved oxygen in the medium.
[0009] Optionally, the coupling potential E corr,galv Calculated using the following formula: ; In the formula, R=A c / A a .
[0010] Optionally, the crevice corrosion rate is calculated using the following formula: ; In the formula, V is the corrosion rate, M is the molar mass of the material, n is the number of electrons in the anodic reaction, F is the Faraday constant, ρ is the material density, and i a,corr This represents the crevice corrosion current density.
[0011] Optionally, if Cl is present inside the gap - If ions are enriched, the crevice corrosion rate is corrected as follows: V 修正 =V×k; In the formula, V 修正 The corrected corrosion rate is given by k, which is a correction factor calibrated through short-term immersion experiments.
[0012] Optionally, the slit opening size h of the slit structure satisfies 0.0025mm≤h≤0.25mm.
[0013] Optionally, the oxygen-deficient medium environment is obtained by continuously introducing an inert gas into the medium, and the oxygen-rich medium environment is obtained by continuously introducing air into the medium.
[0014] The crevice corrosion assessment device based on electrochemical parameter coupling provided by this invention includes: The crevice corrosion physical model building unit is used to build a physical model of crevice corrosion based on the actual crevice structure, determine the anode and cathode of the oxygen concentration cell, and calculate the surface area of the anode and the surface area of the cathode. The polarization curve testing unit is used to test the anodic polarization curve and cathodic polarization curve of the gap structure material, wherein the anodic polarization curve is measured in an oxygen-deficient medium environment and the cathodic polarization curve is measured in an oxygen-rich environment. An electrochemical parameter fitting unit is used to obtain the anodic current density-potential relationship based on the anodic polarization curve and the cathode current density-potential relationship based on the cathode polarization curve. An electrochemical coupling equilibrium calculation and corrosion determination unit is used to construct electrochemical equilibrium formulas. i c ×A c =i a ×A a ; In the formula, A c A is the surface area of the cathode. a i is the surface area of the anode. a i is the anode current density. c The cathode current density; The coupling potential E of the oxygen concentration cell was calculated based on the electrochemical equilibrium formula. corr,galv If the coupling potential E corr,galv If it is not in the activation region of the anodic polarization curve, then crevice corrosion has not occurred; if the coupling potential E corr,galv If it is in the activation region of the anodic polarization curve, then the coupling potential E is obtained. corr,galv The corresponding anodic current density, at this point is the crevice corrosion current density; The crevice corrosion rate calculation unit is used to calculate and output the crevice corrosion rate based on the crevice corrosion current density.
[0015] The present invention has the following beneficial effects: The crevice corrosion assessment method based on electrochemical parameter coupling proposed in this invention starts from the basic theory of crevice corrosion. Through simple polarization curve analysis, crevice structure size analysis, construction of oxygen concentration cells inside and outside the crevice, and coupling analysis of relevant kinetic parameters, it can achieve rapid identification and assessment of the corrosion rate of materials in the crevice. It has the characteristics of being convenient, fast, highly repeatable, and relatively accurate. It is suitable for rapid prediction of the initial stage of crevice corrosion, and is especially suitable for rapid identification and assessment of crevice corrosion risk in structures of engineering equipment. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram illustrating the principle of crevice corrosion in engineering structures.
[0018] Figure 2 The flowcharts are for some embodiments of the crevice corrosion assessment method based on electrochemical parameter coupling of the present invention. Figure 3 This is a schematic diagram of the physical model of the crevice structure in some embodiments of the crevice corrosion assessment method based on electrochemical parameter coupling of the present invention; Figure 4 This is a theoretical schematic diagram of the crevice corrosion assessment method based on electrochemical parameter coupling of the present invention. Detailed Implementation
[0019] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0020] The terms “comprising” and “having” and any variations thereof in this invention are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product or device.
[0021] For the principle of crevice corrosion, please refer to [reference needed]. Figure 1 In narrow gaps or enclosed areas, the chemical properties of the solution (oxygen concentration, pH value, ion concentration, etc.) inside and outside the gap on the metal surface are significantly different, which leads to accelerated corrosion inside the gap. Since the crevice corrosion is concentrated inside the gap, the external surface is basically intact, forming a stark contrast of "internal corrosion and external integrity". When the corrosion is severe, it may cause perforation of the metal inside the gap, while the overall appearance of the metal component is not obviously abnormal.
[0022] For crevice corrosion to occur, the crevice must be narrow enough (usually between 0.025 mm and 0.25 mm in width) to impede the convection and diffusion of the solution inside and outside the crevice, thus forming a "closed cell." This is a prerequisite for crevice corrosion. In the mechanism of crevice corrosion, the "closed cell" is the core electrochemical unit that drives the corrosion process to start, develop, and self-accelerate. It does not refer to a battery with a certain physical structure, but describes an electrochemical corrosion system with anodic and cathodic regions formed by environmental differences (mainly oxygen concentration differences) inside and outside the crevice. It is also called an "oxygen concentration cell."
[0023] The anodic reaction of the oxygen concentration cell is: M-ne - =M n+ M represents metal, e - Represents electrons; the cathode reaction is O2 + 2H2O + 4e-. - =4OH - .
[0024] This invention predicts crevice corrosion rates through polarization curve analysis, crevice structure size analysis, construction of oxygen concentration cells inside and outside the crevice, and coupled analysis of related kinetic parameters. The core of this invention is the extraction of electrochemical kinetic parameters from polarization curves for coupled analysis. (See also...) Figure 2 In this embodiment of the invention, the crevice corrosion assessment method based on electrochemical parameter coupling includes steps S1 to S5: S1. Based on the gap structure, determine the anode and cathode of the oxygen concentration cell, and calculate the surface area of the anode and the surface area of the cathode.
[0025] Specifically, for structures at risk of crevice corrosion, the dimensional parameters inside and outside the crevice and the opening size of the crevice are determined through surveying or 3D modeling, based on the actual morphology of the crevice in the engineering structure (such as pipe flange joints, bolt-to-base gaps, and lap joint gaps); see reference. Figure 3 In this embodiment of the invention, the inside of the crevice is the anode (a), and the outside of the crevice is the cathode (c). The crevice opening size (h) satisfies 0.0025 mm ≤ h ≤ 0.25 mm. The crevice opening size is highly correlated with the sensitivity to crevice corrosion. If the crevice opening size (h) is greater than 0.25 mm, it is difficult to form an oxygen concentration cell inside and outside the crevice, and the crevice corrosion effect is weak. If the crevice opening size is less than 0.0025 mm, it is difficult for the solution to enter the crevice, and the crevice corrosion effect is difficult to form. The surface area of the anode is the surface area of the material in contact with the electrochemical medium inside the crevice, denoted as A. a The surface area of the cathode is the surface area of the material exposed to the electrochemical medium outside the slit, denoted as A. c The ratio of the inner and outer areas of the gap is R=A c / A a This ratio is a key parameter affecting the distribution of cathode polarization current, and R is usually much greater than 1.
[0026] S2. The anodic and cathodic polarization curves of the gap structure material were obtained using a three-electrode electrochemical testing device. The anodic polarization curve was measured in an oxygen-deficient medium environment, and the cathodic polarization curve was measured in an oxygen-rich environment.
[0027] In this step, a conventional three-electrode system is used. Different dielectric environments are designed according to the actual working conditions of the engineering structure to test the polarization curve data of the target material. The three-electrode system is the most standard and commonly used test system in electrochemical testing. It consists of a working electrode, a reference electrode, a counter electrode, an electrolyte, and an electrochemical workstation. It is used to accurately measure parameters such as the polarization curve, corrosion sites, and current density of the material, which will not be elaborated here. The scanning rate of the polarization curve is set to ≤0.5mV / s to reduce polarization hysteresis error and obtain the current density-potential relationship curve of the material.
[0028] In this embodiment of the invention, the cathodic polarization curve and anodic polarization curve of the target material are measured separately. When testing the anodic polarization curve, an inert gas (preferably nitrogen) is continuously introduced into the electrochemical medium during the test to make the medium in an oxygen-deficient state, so as to simulate the oxygen-deficient environment inside the gap. When testing the cathodic polarization curve, air is continuously introduced into the electrochemical medium during the test to make the medium in an oxygen-rich state, so as to simulate the oxygen-rich environment outside the gap.
[0029] S3. Obtain the anodic current density-potential relationship from the anodic polarization curve, and obtain the cathode current density-potential relationship from the cathode polarization curve.
[0030] Specifically, in this embodiment of the invention, the target material is subjected to anodic polarization scanning in an oxygen-deficient environment to obtain the current density-potential curve of the metal dissolution reaction, i.e., the anodic polarization curve, which satisfies the Tafel equation: ; In the formula, i a i is the anode current density. a0 E is the anode exchange current density, and E is the potential. a0 b is the anode equilibrium potential. a The slope of the anode Tafel is given.
[0031] Cathodic polarization scanning of the target material in an oxygen-rich environment yields the current density-potential curve of the oxygen reduction reaction, i.e., the cathodic polarization curve. The low-current region (activation region) of the cathodic polarization curve conforms to the Tafel equation. ; The equation can be simplified to: ; In the formula, i c i is the cathode current density. c0 E is the cathode exchange current density, and E is the potential. c0 b is the cathode equilibrium potential. c The slope of the cathode Tafel is given.
[0032] In actual corrosion, cathodic polarization typically includes activation polarization and concentration polarization. Under oxygen-rich conditions, activation polarization usually dominates, and the polarization curve satisfies the aforementioned cathodic Tafel equation, such as... Figure 4 The conventional cathodic polarization curve is shown in the figure; however, under conditions of insufficient oxygen and poor diffusion, the corrosion current no longer increases with potential, that is, the cathodic reaction rate is limited by the diffusion rate of dissolved oxygen. The high-current region of the cathodic polarization curve is limited by concentration polarization. In this case, the ideal concentration polarization curve shows a limiting diffusion current plateau at high current, as shown in the figure. Figure 4 As shown in the diffusion-controlled cathode polarization curve, the limiting diffusion current plateau corresponds to the limiting diffusion current density i L This value is directly derived from the polarization curve.
[0033] However, in actual corrosion processes, if the polarization curves obtained from the tests do not fully reflect the differences in oxygen concentration (e.g., insufficient oxygen enrichment in the experiment), and the actual tested polarization curves do not show a limiting diffusion current plateau, then the limiting diffusion current density i needs to be calculated using the following formula. L : ; In the formula, i L Let be the limiting diffusion current density, n be the charge number (value 4) of oxygen undergoing reduction, F be the Faraday constant, and D be the diffusion coefficient of dissolved oxygen in the medium. The diffusion layer thickness (under natural convection, the diffusion layer thickness for oxygen reduction reactions is typically between 0.1 and 0.5 mm, which can be precisely measured using a rotating disk electrode; in engineering, 0.3 can also be used as an empirical value), C O2 This represents the concentration of dissolved oxygen in the medium.
[0034] Among the parameters involved in the above formulas, the anodic equilibrium potential E of the target material is... a0 and cathode equilibrium potential E c0 These are thermodynamic parameters and can be directly obtained from electrochemical corrosion handbooks; the anodic exchange current density i of the target material. a0 and cathode exchange current density i c0 This is a theoretical value, which can be obtained by consulting relevant research literature or technical manuals; anode Tafel slope b a and cathode Tafel slope b c It can be obtained by fitting the polarization curve.
[0035] S4, Establish the electrochemical equilibrium formula: i c ×A c =i a ×A a ; In the formula, A cA is the surface area of the cathode (i.e., the metal surface area outside the gap). a i is the surface area of the anode (i.e., the metal surface area within the gap). a i is the anode current density. c This represents the cathode current density.
[0036] Specifically, the oxygen concentration inside the gap is much lower than the oxygen concentration outside the gap. In this embodiment of the invention, the cathode current inside the gap can be ignored (the gap is regarded as a pure anode), and only the cathode current is provided outside the gap. At electrochemical equilibrium, the total cathode current generated by the cathode reaction outside the gap is equal to the total anode current generated by the anode reaction inside the gap.
[0037] In some specific embodiments, substituting the Tafel equation satisfied by the anodic and cathodic polarization curves into the above electrochemical equilibrium formula yields: ; Taking the logarithm of both sides of the equation and rearranging, we can solve for the potential E to obtain the coupling potential E of the oxygen concentration cell formed inside and outside the gap. corr,galv We obtain the following formula: ; In the formula, R=A c / A a .
[0038] It should be noted that under conditions of insufficient oxygen and poor diffusion, the corrosion current no longer increases with potential (concentration polarization). (See [reference needed]). Figure 4 An ideal cathode polarization curve exhibits a limiting diffusion current plateau. At this point, the high-current region of the cathode polarization curve is limited by concentration polarization (approaching the limiting diffusion current density i). L Cathode current density =i L i L This can be directly derived from the cathodic polarization curve; if the cathodic polarization curve outside the slit intersects with the anodic polarization curve inside the slit at the limiting diffusion current plateau (coupled in the concentration polarization region), then the above electrochemical equilibrium formula can be expressed as: ; Depend on Figure 4 It can be seen that the larger the surface area outside the gap, i.e., the larger R, the higher the limiting diffusion current density i. L The larger the value, the greater the crevice corrosion current.
[0039] If the polarization curve obtained from the test does not fully reflect the difference in oxygen concentration, and the actual measured polarization curve does not show a limiting diffusion current plateau, then i can be calculated using the limiting diffusion current density calculation formula mentioned above. L : ; The coupling potential E was calculated. corr,galv Next, first check whether the coupling potential is in the activation region of the anodic polarization curve. If the coupling potential E corr,galv If it is not in the activation region of the anodic polarization curve, then crevice corrosion has not occurred; if the coupling potential E corr,galv For metals in the active region of the anodic polarization curve (where the relationship between current density and potential satisfies the Tafel equation; for metals without passivation properties, their anodic polarization curve has no critical passivation potential and no passivation region; therefore, the entire potential range is assumed to be the active region; crevice corrosion is determined to occur as long as the coupling potential is higher than the metal's self-corrosion potential), the anodic current density i can be obtained by solving the Tafel equation of the anodic polarization curve or by directly looking up the current density corresponding to the coupling potential from the measured anodic polarization curve. a,corr Anode current density i a,corr This refers to the crevice corrosion current density.
[0040] S5, calculate the crevice corrosion rate based on the crevice corrosion current density.
[0041] The crevice corrosion rate is calculated using the following formula: ; In the formula, V is the corrosion rate (unit: mm / year), M is the molar mass of the material (g / mol), n is the number of electrons in the anodic reaction, F is the Faraday constant (96485 C / mol), and ρ is the material density (g / cm³). 3 ), i a,corr This represents the crevice corrosion current density.
[0042] The aforementioned embodiments did not consider the decrease in pH and Cl within the gaps. - Subsequent acidification effects, such as ion enrichment, are considered in the initial risk assessment of crevice corrosion based solely on the initial oxygen concentration cell; furthermore, the presence of Cl within the crevice is taken into account. - The "autocatalytic acceleration" caused by ion (chloride ion) enrichment (chloride ion enrichment promotes the hydrolysis and acidification of metal ions, causing a decrease in the pH value inside the crevice, resulting in an increase in the actual crevice corrosion rate) can be corrected by introducing a correction factor k, and the crevice corrosion rate calculation formula can be modified as follows: V 修正 =V×k; In the formula, V 修正 The corrected corrosion rate is given by k, which is a correction factor calibrated through short-term immersion experiments. The value of k typically ranges from 1.2 to 3.0. - The higher the concentration and the higher the temperature, the larger the k value.
[0043] The crevice corrosion assessment method based on electrochemical parameter coupling proposed in this invention starts from the basic theory of crevice corrosion. Through simple polarization curve analysis, crevice structure size analysis, construction of oxygen concentration cells inside and outside the crevice, and coupling analysis of related kinetic parameters, it can achieve rapid identification and assessment of the corrosion rate of materials in the crevice. It is convenient, fast, highly repeatable, and accurate. It is suitable for rapid prediction of the initial stage of crevice corrosion, especially for rapid identification and assessment of crevice corrosion risk in structures of engineering equipment. It is applicable to qualitative / semi-quantitative analysis scenarios such as material screening and process parameter optimization.
[0044] Based on the above embodiments, in order to illustrate the technical solution of the present invention in more detail, the present invention also proposes the following specific embodiments. It should be noted that the following specific embodiments are merely exemplary and are not intended to limit the scope of protection of the present invention in any way.
[0045] Example 1
[0046] Construct a physical model of the gap structure, such as Figure 3 As shown, the material of the engineering structure is 304 stainless steel, and the anode surface area A in the gap is... a =0.1cm 2 The surface area of the outer cathode in the slit is A c =10cm 2 R=A c / A a =100; consult the electrochemical corrosion handbook to obtain the cathode exchange current density i c0 =1×10 -7 A / cm 2 Cathode equilibrium potential E c0 =0.2V, anode exchange current density i a0 =1×10 -8 A / cm 2 Anode equilibrium potential E a0 =-0.4V.
[0047] A three-electrode testing device was used to obtain the anodic and cathodic polarization curves of 304 stainless steel. During the testing of the anodic polarization curve, nitrogen gas was continuously introduced into the electrochemical medium to make the medium oxygen-deficient. During the testing of the cathodic polarization curve, air was continuously introduced into the electrochemical medium to make the medium oxygen-rich.
[0048] The cathode polarization curve is fitted to obtain the cathode Tafel slope b. c =-0.12V / dec, the anodic Tafel slope b is obtained by fitting the anodic polarization curve. a =0.06V / dec.
[0049] Substitute the above parameters into the coupling potential calculation formula: ; E was calculated corr,galv ≈-0.32V.
[0050] Substituting E = -0.32V into the Tafel equation for the anodic polarization curve: ; The anode current density i was calculated. a,corr ≈2.15×10 -7 A / cm 2 .
[0051] The molar mass of 304 stainless steel is M = 55.85 g / mol (based on iron), the number of electrons in the anodic reaction is n = 2, and the material density is ρ = 7.87 g / cm³. 3 Substitute into the formula for calculating crevice corrosion rate: ; In the formula, V is the corrosion rate (unit: mm / year), M is the molar mass of the material (g / mol), n is the number of electrons in the anodic reaction, F is the Faraday constant (96485 C / mol), and ρ is the material density (g / cm³). 3 ), i a,corr This represents the crevice corrosion current density.
[0052] The calculated corrosion rate inside the crevices of the 304 stainless steel creviced structure is V≈2.6×10⁻⁶. -3 mm / a (unit: millimeters per year), which is consistent with the trend of the experimental results of mild crevice corrosion.
[0053] The present invention also provides a crevice corrosion assessment device based on electrochemical parameter coupling. The device includes a crevice corrosion physical model establishment unit, a polarization curve testing unit, an electrochemical parameter fitting unit, an electrochemical coupling equilibrium calculation and corrosion determination unit, and a crevice corrosion rate calculation unit.
[0054] The crevice corrosion physical model establishment unit is used to establish a physical model of crevice corrosion based on the actual crevice structure, determine the anode and cathode of the oxygen concentration cell, and calculate the surface area of the anode and the surface area of the cathode.
[0055] The polarization curve testing unit is used to test the anodic and cathodic polarization curves of the gap structure material. The anodic polarization curve is measured in an oxygen-deficient medium environment, and the cathodic polarization curve is measured in an oxygen-rich environment.
[0056] In some specific embodiments, the polarization curve testing unit uses a conventional three-electrode system to perform anodic polarization scanning and cathodic polarization scanning on the target material, respectively. The three-electrode system consists of a working electrode, a reference electrode, a counter electrode, an electrolyte, and an electrochemical workstation.
[0057] The electrochemical parameter fitting unit is used to obtain the anodic current density-potential relationship based on the anodic polarization curve and the cathode current density-potential relationship based on the cathode polarization curve.
[0058] The anodic polarization curve satisfies the Tafel equation: ; In the formula, i a i is the anode current density. a0 E is the anode exchange current density, and E is the potential. a0 b is the anode equilibrium potential. a The slope of the anode Tafel is given.
[0059] The low-current region of the cathode polarization curve conforms to the Tafel equation: ; The equation can be simplified to: ; In the formula, i c i is the cathode current density. c0 E is the cathode exchange current density, and E is the potential. c0 b is the cathode equilibrium potential. c The slope of the cathode Tafel is given.
[0060] The high-current region of the cathode polarization curve is limited by concentration polarization, resulting in a current plateau. The current plateau in the cathode polarization curve corresponds to the limiting diffusion current density i. L This value can be directly obtained from the polarization curve.
[0061] In actual corrosion processes, if the measured polarization curve does not show a current plateau, the limiting diffusion current density i can be calculated using the following formula. L : ; In the formula, i L Let be the limiting diffusion current density, n be the charge number (value 4) of oxygen undergoing reduction, F be the Faraday constant, and D be the diffusion coefficient of dissolved oxygen in the medium. C is the thickness of the diffusion layer. O2 This represents the concentration of dissolved oxygen in the medium.
[0062] The electrochemical coupling equilibrium calculation and corrosion determination unit is used to construct the electrochemical equilibrium formula and calculate the coupling potential E of the oxygen concentration cell based on the electrochemical equilibrium formula. corr,galv If the coupling potential E corr,galv If it is not in the activation region of the anodic polarization curve, then crevice corrosion has not occurred; if the coupling potential E corr,galv If it is in the activation region of the anodic polarization curve, then the coupling potential E is obtained. corr,galv The corresponding anodic current density, at this point is the crevice corrosion current density; The electrochemical equilibrium formula is: i c ×A c =i a ×A a ; In the formula, A c A is the surface area of the cathode. a i is the surface area of the anode. a i is the anode current density. c This represents the cathode current density.
[0063] In some embodiments, the coupling potential E corr,galv Calculated using the following formula: ; In the formula, R=A c / A a .
[0064] The crevice corrosion rate calculation unit is used to calculate and output the crevice corrosion rate based on the crevice corrosion current density. In some embodiments, the crevice corrosion rate is calculated using the following formula: ; In the formula, V is the corrosion rate (unit: mm / year), M is the molar mass of the material (g / mol), n is the number of electrons in the anodic reaction, F is the Faraday constant (96485 C / mol), and ρ is the material density (g / cm³). 3 ), i a,corr This represents the crevice corrosion current density.
[0065] In other embodiments, Cl inside the gap is considered. - The "autocatalytic acceleration" caused by ion (chloride ion) enrichment introduces a correction factor k, which modifies the formula for calculating the crevice corrosion rate as follows: V 修正 =V×k; In the formula, V 修正 The corrected corrosion rate is given by k, which is a correction factor calibrated through short-term immersion experiments.
[0066] In the embodiments provided by this invention, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.
[0067] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0068] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.
[0069] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for executing all or part of the steps of the methods described in the various embodiments of the present invention through a computer device (which may be a personal computer, a server, or a network device, etc.). The aforementioned storage medium includes: USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media capable of storing program code.
[0070] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A crevice corrosion assessment method based on electrochemical parameter coupling, characterized in that, Including the following steps: S1, Based on the gap structure, determine the anode and cathode of the oxygen concentration cell, and calculate the surface area of the anode and the surface area of the cathode; S2, The anodic polarization curve and cathodic polarization curve of the gap structure material are obtained by using a three-electrode electrochemical testing device, wherein the anodic polarization curve is measured in an oxygen-deficient medium environment and the cathodic polarization curve is measured in an oxygen-rich medium environment. S3. Obtain the anode current density-potential relationship based on the anode polarization curve, and obtain the cathode current density-potential relationship based on the cathode polarization curve; S4, Establish the electrochemical equilibrium formula: i c ×A c =i a ×A a ; In the formula, A c A is the surface area of the cathode. a i is the surface area of the anode. a i is the anode current density. c The cathode current density; Calculate the coupling potential E of the oxygen concentration cell based on the electrochemical equilibrium formula. corr,galv If the coupling potential E corr,galv If it is not in the activation region of the anodic polarization curve, then crevice corrosion has not occurred; if the coupling potential E corr,galv If it is in the activation region of the anodic polarization curve, then the coupling potential E is obtained. corr,galv The corresponding anodic current density, at this point is the crevice corrosion current density; S5, calculate the crevice corrosion rate based on the crevice corrosion current density.
2. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 1, characterized in that, The anode current density-potential relationship is as follows: ； In the formula, i a i is the anode current density. a0 E is the anode exchange current density, and E is the potential. a0 b is the anode equilibrium potential. a The slope of the anode Tafel is given.
3. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 2, characterized in that, In the activation region of the cathode polarization curve, the cathode current density-potential relationship is: ； In the formula, i c i is the cathode current density. c0 E is the cathode exchange current density, and E is the potential. c0 b is the cathode equilibrium potential. c The slope of the cathode Tafel is given.
4. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 2, characterized in that, If the cathode of the oxygen concentration cell exhibits concentration polarization, then the cathode current density i c Represented as: ； In the formula, The limiting diffusion current density is derived from the limiting diffusion current plateau of the polarization curve; If the cathode polarization curve does not show a limiting diffusion current plateau, the limiting diffusion current density is determined using the limiting diffusion current density formula. The limiting diffusion current density formula is: ； In the formula, n is the charge number of oxygen undergoing reduction, F is the Faraday constant, and D is the diffusion coefficient of dissolved oxygen in the medium. C is the thickness of the diffusion layer. O2 This represents the concentration of dissolved oxygen in the medium.
5. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 3, characterized in that, The coupling potential E corr,galv Calculated using the following formula: ； In the formula, R=A c / A a .
6. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 1, characterized in that, The crevice corrosion rate is calculated using the following formula: ； In the formula, V is the corrosion rate, M is the molar mass of the material, n is the number of electrons in the anodic reaction, F is the Faraday constant, ρ is the material density, and i a,corr This represents the crevice corrosion current density.
7. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 6, characterized in that, If Cl is present inside the gap - If ions are enriched, the crevice corrosion rate is corrected as follows: In 修正 =V×k; In the formula, V 修正 The corrected corrosion rate is given by k, which is a correction factor calibrated through short-term immersion experiments.
8. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 1, characterized in that, The slit opening size h of the slit structure satisfies 0.0025mm≤h≤0.25mm.
9. The crevice corrosion assessment method based on electrochemical parameter coupling according to claim 1, characterized in that, The oxygen-deficient medium environment is obtained by continuously introducing an inert gas into the medium, and the oxygen-rich medium environment is obtained by continuously introducing air into the medium.
10. A crevice corrosion assessment device based on electrochemical parameter coupling, characterized in that, include: The crevice corrosion physical model building unit is used to build a physical model of crevice corrosion based on the actual crevice structure, determine the anode and cathode of the oxygen concentration cell, and calculate the surface area of the anode and the surface area of the cathode. The polarization curve testing unit is used to test the anodic polarization curve and cathodic polarization curve of the gap structure material, wherein the anodic polarization curve is measured in an oxygen-deficient medium environment and the cathodic polarization curve is measured in an oxygen-rich medium environment. An electrochemical parameter fitting unit is used to obtain the anodic current density-potential relationship based on the anodic polarization curve and the cathode current density-potential relationship based on the cathode polarization curve. An electrochemical coupling equilibrium calculation and corrosion determination unit is used to construct electrochemical equilibrium formulas. i c ×A c =i a ×A a ; In the formula, A c A is the surface area of the cathode. a i is the surface area of the anode. a i is the anode current density. c The cathode current density; The coupling potential E of the oxygen concentration cell was calculated based on the electrochemical equilibrium formula. corr,galv If the coupling potential E corr,galv If it is not in the activation region of the anodic polarization curve, then crevice corrosion has not occurred; if the coupling potential E corr,galv If it is in the activation region of the anodic polarization curve, then the coupling potential E is obtained. corr,galv The corresponding anodic current density, at this point is the crevice corrosion current density; The crevice corrosion rate calculation unit is used to calculate and output the crevice corrosion rate based on the crevice corrosion current density.