A method for constructing the cathodic protection electric field of a submarine structure

Abstract

This application relates to the technical field of measuring electrical variables, and specifically relates to a method for constructing a cathodic protection electric field for submarine structures. The method includes: establishing a three-dimensional model of the structure; performing forward calculation of the electric field distribution based on the three-dimensional model; obtaining the three-component data measured by the electric field sensors in the target area; performing linear three-dimensional inversion on the underwater structure based on the three-dimensional model and the three-component data; obtaining the potential distribution and current density distribution on the surface of the underwater structure based on the linear three-dimensional inversion; and evaluating the cathodic protection scheme based on the results of the forward calculation, potential, and current density distribution. This application solves the problem in the prior art that due to the inability to effectively judge the spatial distribution law of the corrosion electric field of underwater complex structures, it is impossible to effectively implement cathodic protection for submarine complex structures.

Description

Technical Field

[0001] This application relates to the technical field of measuring electrical variables, and more particularly, to a method for constructing a cathodic protection electric field for submarine structures. Background Art

[0002] The hydrodynamic conditions of seawater in nearshore wind farms are complex. The interaction between underwater structures and seawater accelerates the corrosion and aging of the structures. Due to the diverse shapes of the structures and the complex seabed environment, the distribution of the corrosion electric field is controlled by multiple factors such as the geometric structure of the structures, the parameters of the cathodic protection system, the physical and chemical conditions of seawater, the characteristics of seabed sediments, and other surrounding metal structures. The physical field control equations are diverse and the coupling relationships are complex. The reconstruction of the intensity and direction of the corrosion current density is very important for the protection of submarine complex structures. However, in the prior art, during the reconstruction of the intensity and direction of the corrosion current density, the spatial distribution law of the corrosion electric field of underwater complex structures cannot be effectively judged, resulting in the inability to effectively protect the cathodes of submarine complex structures. Summary of the Invention

[0003] The purpose of this application is to provide a method for constructing a cathodic protection electric field for submarine structures, which solves the problem in the prior art that due to the inability to effectively judge the spatial distribution law of the corrosion electric field of underwater complex structures, the cathodic protection of submarine complex structures cannot be effectively achieved.

[0004] Technical Solution of this Application

[0005] This application provides a method for constructing a cathodic protection electric field for submarine structures, including:

[0006] Establish a three-dimensional model of the underwater structure in the target area;

[0007] Based on the three-dimensional model, perform forward calculation of the electric field distribution, where the potential equation is:

[0008] ,

[0009] is the corrosion electric field in seawater, is the conductivity of seawater, is the current density vector in seawater, is the volume current density in seawater;

[0010] Obtain the three-component data measured by the electric field sensors in the target area;

[0011] Based on the three-dimensional model and the three-component data, perform linear three-dimensional inversion on the underwater structure;

[0012] Based on linear three-dimensional inversion, the potential distribution and current density distribution on the surface of the underwater structure are obtained;

[0013] Based on the results of forward calculation, potential and current density distribution, the cathodic protection scheme is evaluated.

[0014] Further, in the establishment of the three-dimensional model of the complex structure, the governing equations are discretized by the finite element method to simulate the cathodic protection state of the underwater steel structure in different occurrence environments.

[0015] Further, based on the three-dimensional model, the forward calculation of the electric field distribution is performed. Specifically: different polarization boundary conditions are introduced according to the anode or cathode material and the environment, and a polarization curve graph is obtained. Among them, the calculation formula of the polarization curve is:

[0016]

[0017] Among them, represents the local current density, represents the current density generated by the anode, is the current density generated by the cathode, is the exchange current density during the dissolution of the sacrificial anode, is the charge transfer coefficient in the anode direction, is the charge transfer coefficient in the cathode direction, F is the Faraday constant, is the overpotential of the cathode and anode, R is the gas constant, T is the absolute temperature, is the maximum exchange current density under oxygen limitation.

[0018] Further, the forward calculation of the electric field distribution also includes:

[0019] Simulating the electrochemical charge transfer reaction at the interface between the electrolyte and the structure;

[0020] Based on the dissolution effect of the sacrificial anode during operation, determining the variation parameters of the output of the dissolution effect with time.

[0021] Further, it also includes:

[0022] According to the electric field distribution results, determining the positions of local abnormal hot spots of the complex underwater structure in the target detection area;

[0023] Obtaining the abnormal amplitude parameters of the positions of local abnormal hot spots.

[0024] Further, for the linear three-dimensional inversion of the underwater structure, among them, the inversion calculation formula is:

[0025]

[0026] is the observed data, is the forward model for calculating predicted data, is the observation error diagonal matrix, 、 is the model weighting matrix, and is the weighted least squares matrix.

[0027] Furthermore, the three-dimensional model of the complex structure is established by laser three-dimensional scanning or three-dimensional sonar, and the surface of the structure is reconstructed through echo data.

[0028] Furthermore, the linear three-dimensional inversion of the underwater structure is performed as follows:

[0029] The inversion grid is discretized at the three-dimensional boundary;

[0030] Reduce the solution freedom of the inversion parameter ;

[0031] Optimize the observation path of the ROV.

[0032] Furthermore, based on the results of forward calculation, potential and current density distribution, the cathodic protection scheme is determined as follows:

[0033] The formula for the remaining life of the sacrificial anode is:

[0034]

[0035] Where:

[0036]

[0037] In the formula is the remaining life of the anode, is the initial net weight of the anode, is the utilization rate, is the consumption of the anode material, is the anode current obtained by inversion, is the anode consumption rate, is the year of investigation, is the installation year of the anode.

[0038] The technical solution of this application has at least the following advantages and beneficial effects:

[0039] The present application provides a method for constructing a cathodic protection electric field for a submarine structure. By calculating the spatial distribution of the corrosion electric field vector in seawater in the target area, forward calculation, and linear three-dimensional inversion, the spatial distribution characteristics of the corrosion electric field response of the complex structure are obtained, the health status of the cathodic protection system is determined, the main controlled factors of the corrosion electric field morphology are judged, the long-term stability and dynamic change law of the corrosion electric field under the coupling action of multiple factors are determined, and effective support is provided for reconstructing the intensity and direction of the corrosion current density. Furthermore, the cathodic protection of the complex submarine structure is realized, and the problem in the prior art that the cathodic protection of the complex submarine structure cannot be effectively realized due to the inability to effectively judge the spatial distribution law of the corrosion electric field of the underwater complex structure is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic flow chart of the construction method of the present application;

[0041] Figure 2 is a schematic diagram of the surface polarization process of the cathodic protection electrode in the embodiment of the present application;

[0042] Figure 3 is a schematic diagram of the result of the forward calculation of the simple pipe pile model in the embodiment of the present application;

[0043] Figure 4 is a schematic diagram for evaluating the surface potential distribution of the simulated structure in the embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0045] Embodiment

[0046] Please refer to Figures 1-4 together. The present application provides a method for constructing a cathodic protection electric field for a submarine structure, including:

[0047] Establish a three-dimensional model of the underwater structure in the target area;

[0048] Based on the three-dimensional model, perform forward calculation of the electric field distribution, where the potential equation is:

[0049] ,

[0050] is the corrosion electric field in seawater, is the conductivity of seawater, is the current density vector in seawater, is the volume current density in seawater;

[0051] Obtain the three-component data measured by the electric field sensor in the target area;

[0052] Based on the three-dimensional model and the three-component data, perform a linear three-dimensional inversion on the underwater structure;

[0053] Based on the linear three-dimensional inversion, obtain the potential distribution and current density distribution on the surface of the underwater structure;

[0054] Evaluate the cathodic protection scheme based on the results of forward calculation, potential, and current density distribution.

[0055] It should be noted that in this embodiment, by calculating the spatial distribution of the corrosion electric field vector in the seawater of the target area, forward calculation, and linear three-dimensional inversion, the spatial distribution characteristics of the corrosion electric field response of complex structures are obtained, the health status of the cathodic protection system is determined, the main controlled factors of the corrosion electric field morphology are judged, the long-term stability and dynamic change law of the corrosion electric field under the coupling action of multiple factors are determined, which provides effective support for reconstructing the intensity and direction of the corrosion current density, and further realizes the protection of the cathode of complex underwater structures, solving the problem in the prior art that due to the inability to effectively judge the spatial distribution law of the corrosion electric field of complex underwater structures, the cathodic protection of complex underwater structures cannot be effectively realized.

[0056] It should be noted that in the potential equation, is the corrosion electric field in seawater, specifically referring to the potential gradient, and its unit is V / m; is the conductivity of seawater, and its unit is S / m; is the current density vector in seawater, and its unit is A / m 2 ; is the volume current density in seawater, and its unit is A / m 3 . Specifically, when considering anodic dissolution, The value is described by the Nenst-Planck equation. Assuming the seawater is electrically neutral, the current source in seawater , and the potential equation in seawater is obtained as: . Specifically, this formula describes the distribution of the electric field vector inside the electrolyte domain, and the local current density at the interface between the electrolyte and the electrode is described by the polarization boundary condition.

[0057] It should be noted that in this embodiment, by combining forward modeling and inverse modeling, the corrosion state of offshore engineering structures is sensed through the electric field, providing an effective method for building a solution to extend the service life of offshore wind power and other offshore engineering, and providing an efficient and comprehensive health detection solution for later operation and maintenance. On the other hand, in this embodiment, by considering inversion strategies such as non-uniform variation of resistivity and sparse constraints in inverse imaging to locate local anomalies, more accurate data support is provided for establishing the complex three-dimensional structure and variable occurrence environment of underwater structures.

[0058] Furthermore, in the establishment of the three-dimensional model of complex structures, the governing equations are discretized by the finite element method to simulate the cathodic protection state of underwater steel structures in different occurrence environments. Specifically, the simulation scenarios at least include: the fully submerged area, the sediment-covered area.

[0059] Furthermore, based on the three-dimensional model, a forward calculation of the electric field distribution is performed. Specifically: different polarization boundary conditions are introduced according to the anode or cathode material and the environment, and a polarization curve graph is obtained, where: the calculation formula of the polarization curve is:

[0060]

[0061] where, represents the local current density, represents the current density generated by the anode, is the current density generated by the cathode, is the exchange current density during the dissolution of the sacrificial anode, is the charge transfer coefficient in the anode direction, is the charge transfer coefficient in the cathode direction, F is the Faraday constant, is the overpotential of the cathode and anode, R is the gas constant, T is the absolute temperature, is the maximum exchange current density under oxygen-limited conditions.

[0062] It should be noted that, the exchange current density during the dissolution of the sacrificial anode is defined as a positive current density (i.e., a current source). On the surface of the protected metal structure, an oxygen reduction reaction occurs. When the oxygen concentration is limited, the lack of oxygen supply will inhibit the exponential growth of the overpotential on the cathode surface. When the current density is too high, it no longer grows exponentially but approaches the limiting current density , which is defined as a negative current density (i.e., a current sink). The polarization curves of sacrificial anode dissolution and cathode polarization are as shown in Figure 2As shown in the figure, in the figure, Ecorr is the corrosion equilibrium potential of the structure, Jcorr is the cathodic corrosion equilibrium current of the structure, and log(Jcorr) is the logarithmic operation of the cathodic corrosion equilibrium current of the structure. Specifically, the polarization curve is not only related to the inherent properties of the electrode material itself, but also affected by the surrounding environment. For example, the polarization characteristics of submarine structures made of the same material are different in a seawater environment with a high chloride ion concentration or in a marine mud environment with a low oxygen concentration. Therefore, the corrosion characteristics and evolution laws of submarine structures in different zones of seawater can be simulated by changing the input of the polarization curve.

[0063] Furthermore, the forward calculation of the execution of the electric field distribution further includes:

[0064] Simulating the electrochemical charge transfer reaction at the interface between the electrolyte and the structure;

[0065] Based on the dissolution effect of the sacrificial anode during operation, determining the parameters of the output of the dissolution effect varying with time.

[0066] It should be noted that the forward calculation described in this embodiment requires constructing a forward model and performing forward simulation; the inversion requires constructing an inversion model, performing inversion simulation, and inversion imaging. Specifically, when the sacrificial anode method is used to implement cathodic protection for metal components, the sacrificial anode is electrically connected to the metal component to be protected in the electrolyte environment. The alloy serving as the sacrificial anode preferentially dissolves, and the released current polarizes the metal component cathodically to the protection potential to achieve protection. The forward simulation calculates the spatial distribution of the corrosion electric field vector (i.e., the potential gradient) in seawater based on the local current density distribution on the surfaces of the sacrificial anode and the cathode.

[0067] It should be noted that to analyze the feasibility of the potential gradient measurement method for underwater structures, in this embodiment, based on the spatial distribution of the corrosion electric field vector, a multi-physics simulation software COMSOL is used to establish an underwater pipe pile model for the forward calculation of the electric field distribution. Please refer to Figure 3 .. The forward calculation obtains the electrolyte potential distribution caused by the sacrificial anode and coating damage. Potential and potential gradient measurement lines are respectively set at 10 cm, 30 cm, 50 cm, and 70 cm outside the pipe pile, so as to determine the characteristics of potential gradient data measurement: the abnormal directions caused by the anode and coating damage are opposite, and the potential gradient amplitude is within the scale of zero point several microvolts per centimeter. The forward simulation can determine the abnormal size by using the gradient measurement method. Therefore, the forward simulation is carried out on this basis.

[0068] It should be noted that in the forward simulation, it is necessary to simulate the electrochemical charge transfer reaction at the interface between the electrolyte and the structure; based on the dissolution effect of the sacrificial anode during operation, the variation parameters of the dissolution effect output with time are determined. Specifically, in practical applications, complex models such as multiple pile foundations, offshore platforms, and large underwater equipment need to be faced, so it is necessary to establish discrete grids more precisely and reasonably, and thus the accuracy of the solution can be ensured by discretizing the control equations.

[0069] Furthermore, it also includes determining the positions of local abnormal hotspots of complex underwater structures in the target detection area according to the electric field distribution results; obtaining the abnormal amplitude parameters of the positions of the local abnormal hotspots.

[0070] It should be noted that the positions of local abnormal hotspots of the structure are determined through the three-dimensional overall potential distribution results, and these positions can be in the high-potential area or current sinks. These hotspot positions often have coating defects and are located in unprotected areas. Then, the abnormal amplitude parameters of the positions of the local abnormal hotspots are obtained. The abnormal amplitude parameters refer to the magnitude of the abnormality generated at the positions of the abnormal hotspots. According to these abnormal amplitude parameters, the degree of protection, the degree of corrosion influence, the working state of the sacrificial anode, the expected life of the anode, and the rationality of the overall sacrificial anode layout system at this location are further determined, thereby providing data support for the construction of the subsequent cathodic protection scheme. Please refer to Figure 4 , in Figure 4 , the existing sacrificial anodes are working normally, new anodes need to be added in the under-protected areas, and coating protection needs to be taken at the hotspots.

[0071] Furthermore, the linear three-dimensional inversion of the underwater structure is performed, where the inversion calculation formula is:

[0072]

[0073] is the observed data, is the forward model for calculating the predicted data, is the observed error diagonal matrix, , is the model weighting matrix, and are the weighted least squares matrices.

[0074] It should be noted that the inversion described in this embodiment estimates the source current density distribution on the surface of the structure from incomplete observed data and further converts it into a potential distribution, which is an optimization process. Specifically, prior information is introduced before inversion, and the prior information at least includes the conductivity distribution of seawater, the three-dimensional structure of underwater components, etc.

[0075] Furthermore, the complex structure three-dimensional model is established by laser three-dimensional scanning or three-dimensional sonar, in which the surface of the structure is reconstructed through echo data. Specifically, to obtain observation data with a high sampling density, the optimal three-dimensional scanning path is determined according to the density of the electric field and the geometric structure of the structure, so as to obtain high-density multi-component electric field data.

[0076] Furthermore, the linear three-dimensional inversion of the underwater structure is specifically as follows:

[0077] The inversion grid is discretized at the three-dimensional boundary;

[0078] Reduce the degrees of freedom for solving the inversion parameters ;

[0079] Optimize the observation path of the ROV.

[0080] It should be noted that by constructing the objective functional of the three-component observation data, then performing unstructured grid meshing on the surface of the structure, then using the conjugate gradient method to update the model correction amount, and at the same time using the adjoint method to implicitly solve the sensitivity matrix to accelerate the solution, and finally by introducing constraint conditions such as resistivity constraint, sparse norm constraint, and distance weighting, the resolution of the inversion model is improved, and the current density vector distribution on the surface of the structure is finally obtained by inversion, providing effective data support for the subsequent determination of the corrosion state and the formation of the cathodic protection scheme for the complex underwater structure.

[0081] It should be noted that the inversion grid is only discretized at the three-dimensional boundary, and the degrees of freedom for solving the inversion parameters are greatly reduced. At the same time, by optimizing the observation path of the ROV and increasing the sampling density of the observation data, the time for inversion optimization will be shortened and the multi-solution property of the inversion problem will be reduced.

[0082] Furthermore, based on the results of the forward calculation, potential and current density distribution, the cathodic protection scheme is determined, specifically:

[0083] The formula for the remaining life of the sacrificial anode is:

[0084]

[0085] Where:

[0086]

[0087] In the formula is the remaining life of the anode, is the initial net weight of the anode, is the utilization rate, is the consumption of the anode material, is the anode current obtained by inversion, is the anode consumption rate, is the year of investigation, is the installation year of the anode.

[0088] It should be noted that by analyzing the spatio-temporal distribution characteristics of the potential and potential gradient in seawater during the dissolution process of sacrificial anodes, and simulating the corrosion electric field response laws under different aging and damage degrees of the coating, more effective and accurate data can be provided for corrosion electric field observation. Further, for the spatial distribution characteristics of the corrosion electric field response of complex structures obtained, it can help to understand the main controlled factors of the corrosion electric field morphology and reveal the long-term stability and dynamic change laws of the corrosion electric field under the coupling action of multiple factors.

[0089] It should be noted that a quantitative relationship between the current density vector (magnitude and direction), the sacrificial anode life, and the degree of corrosion damage is established to evaluate the health status of the cathodic protection system through the imaging results. On the other hand, using the current inversion results to further simulate and predict the cathodic protection status in the entire wind farm area in the next few years and predict the remaining service life of underwater structures.

[0090] It should be noted that according to data such as the cathode steel pile material and the sacrificial anode material, the current density distribution obtained by inversion is used to predict the remaining life of each sacrificial anode in the current cathodic protection system:

[0091] Optionally, through pool experiments combined with a three-component electric field measurement device, the electromagnetic interference characteristics of the ROV body on the AgCl electrode array are analyzed, and the low-noise installation of the electric field sensor is achieved by reasonably arranging the sensor positions.

[0092] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for constructing a cathodic protection electric field for a submarine structure, characterized in that: include: Establish complex 3D models of underwater structures in the target area; Based on the three-dimensional model, the forward calculation of the electric field distribution is performed, where the potential equation is: ， ; is the corrosion electric field in seawater, is the electrical conductivity of seawater, is the current density vector in seawater, is the volume current density in seawater; Different polarization boundary conditions are introduced according to the anode or cathode materials and the environment to obtain the polarization curve diagram; The forward calculation of the electric field distribution also includes: simulating the electrochemical charge transfer reaction at the interface between the electrolyte and the structure; determining the time-varying parameters of the output of the dissolution effect based on the dissolution effect of the sacrificial anode during operation; Acquire three-component data measured by electric field sensors in the target area; Perform linear 3D inversion of underwater structures based on 3D models and three-component data; Based on linear 3D inversion, the potential distribution and current density distribution on the surface of underwater structures are obtained; Based on the results of forward calculations, potential and current density distribution, the cathodic protection scheme is evaluated, specifically: The remaining life of the sacrificial anode is calculated as follows: ; in: ; In the formula is the remaining life of the anode, is the initial net weight of the anode, is the utilization rate, is the consumption of anode material, is the anode current obtained by inversion, is the anode consumption rate, is the year of the survey, is the year the anode was installed.

2. The construction method according to claim 1, characterized in that: In the establishment of the three-dimensional model of the complex structure, the control equation is discretized by the finite element method to simulate the cathodic protection state of the underwater steel structure under different occurrence environments.

3. The construction method according to claim 1, characterized in that: The forward calculation of the electric field distribution is performed based on the three-dimensional model, and the calculation formula of the polarization curve is: ; in, represents the local current density, is the current density generated by the anode, is the current density generated at the cathode, is the exchange current density when the sacrificial anode dissolves, is the charge transfer coefficient in the anode direction, is the charge transfer coefficient in the cathode direction, F is the Faraday constant, are the overpotentials of the cathode and anode, R is the gas constant, T is the absolute temperature, is the maximum exchange current density under oxygen limitation.

4. The construction method according to claim 1, characterized in that: Also includes: According to the electric field distribution results, determine the location of local abnormal hot spots of complex underwater structures in the target detection area; Get the anomaly amplitude parameters of the local anomaly hotspot location.

5. The construction method according to claim 1, characterized in that: The linear three-dimensional inversion is performed on the underwater structure, wherein the inversion calculation formula is: ; is the observation data, is the forward model for calculating the predicted data, is the observation error diagonal matrix, , is the model weight matrix, and is the weighted least squares matrix.

6. The construction method according to claim 1, characterized in that: The three-dimensional model of the complex structure is established by three-dimensional laser scanning or three-dimensional sonar, wherein the surface of the structure is reconstructed through echo data.

7. The construction method according to claim 1, characterized in that: The linear three-dimensional inversion of underwater structures is performed as follows: The inversion grid is discretized at the three-dimensional boundary; Reduce the inversion parameters The degrees of freedom for solving ; Optimize the ROV's observation path.

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