Method for determining cathode protection current demand quantity of tank bottom plate of built storage tank

Abstract

The invention discloses a method for determining cathode protection current demand quantity of a tank bottom plate of a built storage tank, and belongs to the technical field of corrosion protection of storage tanks. According to the technical scheme, the on-off potential of the peripheral area of the storage tank is determined, a geometric model of a storage tank bottom plate is established, and the polarization curve of the storage tank and the soil resistivity around the storage tank are tested; calculating the polarization potential of each storage tank peripheral recording point; then the calculated potential of each recording point is compared with the actually measured power-off potential in sequence, and the final cathode boundary corresponding to the storage tank is obtained by adjusting the coating surface; and calculating the whole potential distribution condition of the tank bottom plate of the storage tank, and determining the cathode protection current demand quantity of the tank bottom plate of the storage tank in combination with the condition of a field feed experiment. The method has the beneficial effects that the cathode protection current demand quantity of the bottom plate of the built storage tank can be accurately determined, the effectiveness of cathode protection design is ensured, the corrosion risk of the outer side of the bottom plate of the storage tank is effectively controlled, and the treatment cost, the environment and other adverse effects caused by corrosion leakage of the storage tank are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion protection of storage tanks. It aims to solve the problem of installing cathodic protection on existing storage tanks and helps to improve the accuracy of the current demand of the cathodic protection system installed on existing storage tanks. In particular, it relates to a method for determining the current demand of the cathodic protection of the bottom plate of an existing storage tank. Background Art

[0002] Steel oil tanks are crucial facilities in the extraction, storage, transportation, and processing of oil. During operation, tanks are often subject to corrosion from both internal and external media, severely impacting their safety and lifespan. Corrosion of the tank bottom is particularly severe. According to relevant data analysis, bottom plate corrosion accounts for 80% of tank corrosion. Cathodic protection, an effective method for preventing or mitigating corrosion of buried metal structures, has been widely used in buried pipelines, such as those for oil and gas transmission, achieving excellent corrosion protection results. It also provides an effective method for protecting tank bottom plates. In recent years, many new tanks have incorporated cathodic protection systems on the outside of the tank bottom during the design and construction phases. However, a significant number of existing tanks were not designed with cathodic protection technology in mind. As operation progresses, the risks of corrosion become increasingly apparent, making the addition of cathodic protection technology a pressing need for safe production. For new tanks, the cathodic protection current density of the tank bottom plate can be determined and the protection current requirement calculated according to relevant standards. However, for existing storage tanks, there is currently no effective method to accurately determine the cathodic protection current demand for existing storage tanks due to the unclear condition of the anti-corrosion layer on the outer side of the tank bottom plate and the corrosion environment under the tank. This has become a difficult problem that restricts the effective design of cathodic protection for existing storage tanks. Summary of the Invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a method for determining the current demand for cathodic protection of the bottom plate of an existing storage tank, providing accurate data support for determining the current demand for installing a cathodic protection system on an existing storage tank, solving the problem that the current demand cannot be accurately calculated when a cathodic protection system is installed on an in-service station, realizing effective cathodic protection of the storage tank, and ensuring the inherent safety of the operation of the station tank.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for determining the cathodic protection current requirement for the bottom plate of an existing storage tank comprises the following steps:

[0006] S1. Obtain basic information about the storage tank, verify its accuracy on-site, and use a power feed test to determine the on-off potential of the tank's peripheral area.

[0007] S2. Based on the basic information of step S1, a geometric model of the tank bottom plate is established;

[0008] S3. Based on the basic information from step S1, test the polarization curve of the storage tank and the resistivity of the soil around the storage tank;

[0009] S4. Using the geometric model of step S2 and the polarization curve of step S3 as the cathode boundary, the boundary element solution method is used to calculate the polarization potential of each recording point on the periphery of the tank; then, the calculated potential of each recording point is compared with the actual measured power-off potential. If the difference between the two exceeds 10%, the simulation is considered unqualified. The cathode boundary is adjusted by adjusting the coating surface resistivity and damage rate until the difference between the two is within 10%, thereby obtaining the final cathode boundary corresponding to the tank;

[0010] S5. Calculate the entire potential distribution of the tank bottom plate, including the center position of the tank bottom plate, using a boundary element solution method based on the final cathode boundary of the tank obtained in step S4;

[0011] S6. Determine the cathode protection current requirement of the tank bottom plate according to the potential distribution of the tank bottom plate obtained in step S5 and the results of the on-site power feeding experiment in step S1.

[0012] Furthermore, in step S1, a potentiostat is used to test the on-off potential of the periphery of the storage tank, which is achieved by the following steps:

[0013] S11. Select a test point with a corresponding underground metal structure;

[0014] S12. Select test points evenly distributed around the tank;

[0015] S13. Use a constant potential instrument and a temporary anode bed to build a temporary cathodic protection system, and record the anode output and the potential of the test point in a timely manner.

[0016] Furthermore, in step S11, the ground or pipeline around the storage tank is selected as a test point.

[0017] Furthermore, in step S12, a test point is selected every 45 degrees around the center of the tank body.

[0018] Furthermore, in step S1, the basic information of the storage tank includes specifications, materials, and cathodic protection status.

[0019] Furthermore, in step S3, the polarization curve of the storage tank is tested using an electrochemical workstation and a three-electrode method.

[0020] Furthermore, in step S3, a resistance tester and the Wenner quadrupole method are used to test the soil resistivity around the storage tank.

[0021] Furthermore, in step S6, the conditions of the on-site power feeding experiment include the position of the anode and the output current.

[0022] Beneficial effects of the present invention:

[0023] Compared with the prior art, the method for determining the cathodic protection current demand of the bottom plate of an existing storage tank described in the present invention can accurately determine the cathodic protection current demand of the bottom plate of an existing storage tank, ensure the effectiveness of the cathodic protection design, achieve effective control of the corrosion risk of the outer side of the tank bottom plate, and reduce the treatment costs and environmental and other adverse effects caused by corrosion and leakage of the tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort. Among them:

[0025] Figure 1 A flowchart of the method for determining the cathodic protection current requirement of the outer wall of the bottom plate of an existing storage tank according to the present invention;

[0026] Figure 2 This is a diagram of the main body of the system after the design of the present invention is completed;

[0027] Figure 3 This is a schematic diagram of a three-dimensional geometric model of a station in an embodiment of the present invention;

[0028] Figure 4 Schematic diagram of station grid division in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Figure 1-2 The method for determining the cathodic protection current requirement for the bottom plate of an existing storage tank is further explained.

[0030] 1. The method for determining the cathodic protection current requirement of the bottom plate of an existing storage tank includes the following steps:

[0031] 1. Search for information and check the basic information of the storage tank, including specifications, materials, and cathodic protection status. Then conduct an on-site inspection to verify the accuracy of the basic information and use a power supply test to determine the on-off potential of the area surrounding the storage tank.

[0032] 2. Based on the basic information in step 1, establish the geometric model of the tank bottom plate;

[0033] In this embodiment, based on the previous data query and on-site verification information for the Tuozili station, a three-dimensional geometric model and grid division for numerical simulation of the regional cathodic protection system of the Liaohe Oilfield station were established. The geometric model is as follows: Figure 3 As shown, the grid is divided as Figure 4 shown.

[0034] 3. Based on the basic information from step 1, use an electrochemical workstation and the three-electrode method to test the polarization curve of the storage tank; and use a resistance tester and the Wenner quadrupole method to test the soil resistivity around the storage tank;

[0035] The polarization characteristics of the coated pipeline are adjusted by continuously changing the coating surface resistivity and damage rate, and the power-off potential test data obtained from the feeding test is used as a comparison condition to finally obtain the polarization boundary conditions of the coated pipeline.

[0036] Fourth, based on the geometric model of step 2 and the polarization curve of step 3 as the cathode boundary, the boundary element solution method is used to calculate the polarization potential of each recording point on the periphery of the tank; then, the calculated potential of each recording point is compared with the actual measured power-off potential. If the difference between the two exceeds 10%, the simulation is considered unqualified. The cathode boundary is adjusted by adjusting the coating surface resistivity and damage rate until the difference between the two is within 10%, and the final cathode boundary corresponding to the tank is obtained;

[0037] After specific modeling and simulation, the relative error between the power-off potential calculated by numerical simulation and the power-off potential tested in three power-feed tests is within 10%. This numerical simulation model can simulate the actual cathodic protection level effect of the Liaohe Oilfield station.

[0038] 5. Based on the final cathode boundary of the tank obtained in step 4, the entire potential distribution of the tank bottom plate, including the center position of the tank bottom plate, is calculated using the boundary element solution method.

[0039] 6. Based on the potential distribution of the tank bottom plate obtained in step 5 and the situation of the on-site power feeding experiment in step 1 (mainly the position of the anode and the output current), determine the cathode protection current demand of the tank bottom plate.

[0040] 2. According to the above method for determining the cathodic protection current requirement of the bottom plate of an existing storage tank, it is characterized in that in step 1, the on-off potential of the periphery of the storage tank is tested using a potentiostat, which is achieved by the following method:

[0041] (1) The selected test points should correspond to underground metal structures, such as grounding or pipelines around the tank; at the same time, they should reflect the potential distribution around the tank as completely as possible. Therefore, the test points should be selected as evenly around the tank as possible, such as selecting a test point every 45 degrees around the center of the tank.

[0042] (2) The selected test points should reflect the potential distribution around the tank as completely as possible. Therefore, the test points should be selected as evenly as possible around the tank, such as selecting a test point every 45 degrees around the center of the tank.

[0043] (3) Use a constant potential instrument and a temporary anode bed to build a temporary cathodic protection system, and record the anode output and the potential of the test point in a timely manner.

[0044] This method can be used to accurately determine the cathodic protection current demand of the bottom plate of an existing storage tank, ensure the effectiveness of the cathodic protection design, effectively control the corrosion risk of the outer side of the tank bottom plate, and reduce the treatment costs and environmental and other adverse effects caused by tank corrosion and leakage.

[0045] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for determining the cathodic protection current requirement of the bottom plate of an existing storage tank, characterized in that: Here are the steps: S1. Obtain basic information about the storage tank, verify its accuracy on-site, and use a power feed test to determine the on-off potential of the tank's peripheral area. S2. Based on the basic information of step S1, a geometric model of the tank bottom plate is established; S3. Based on the basic information from step S1, test the polarization curve of the storage tank and the resistivity of the soil around the storage tank; S4. Using the geometric model of step S2 and the polarization curve of step S3 as the cathode boundary, the boundary element solution method is used to calculate the polarization potential of each recording point on the periphery of the tank; then, the calculated potential of each recording point is compared with the actual measured power-off potential. If the difference between the two exceeds 10%, the simulation is considered unqualified. The cathode boundary is adjusted by adjusting the coating surface resistivity and damage rate until the difference between the two is within 10%, thereby obtaining the final cathode boundary corresponding to the tank; S5. Calculate the entire potential distribution of the tank bottom plate, including the center position of the tank bottom plate, using a boundary element solution method based on the final cathode boundary of the tank obtained in step S4; S6. Determine the cathode protection current requirement of the tank bottom plate according to the potential distribution of the tank bottom plate obtained in step S5 and the results of the on-site power feeding experiment in step S1.

2. The method for determining the cathodic protection current demand of the bottom plate of an existing storage tank according to claim 1, characterized in that: In step S1, a potentiostat is used to test the on-off potential of the periphery of the storage tank, which is achieved by the following steps: S11. Select a test point with a corresponding underground metal structure; S12. Select test points evenly distributed around the tank; S13. Use a constant potential instrument and a temporary anode bed to build a temporary cathodic protection system, and record the anode output and the potential of the test point in a timely manner.

3. The method for determining the cathodic protection current demand of the bottom plate of an existing storage tank according to claim 2, characterized in that: In step S11, the ground or pipeline around the storage tank is selected as a test point.

4. The method for determining the cathodic protection current demand of the bottom plate of an existing storage tank according to claim 2, characterized in that: In step S12, a test point is selected every 45 degrees around the center of the tank body.

5. The method for determining the cathodic protection current demand of the bottom plate of an existing storage tank according to claim 1, characterized in that: In step S1, the basic information of the storage tank includes specifications, materials, and cathodic protection status.

6. The method for determining the cathodic protection current requirement of the bottom plate of an existing storage tank according to claim 1, characterized in that: In step S3, the polarization curve of the storage tank is tested using an electrochemical workstation and a three-electrode method.

7. The method for determining the cathodic protection current requirement of the bottom plate of an existing storage tank according to claim 1, characterized in that: In step S3, the soil resistivity around the storage tank is tested using a resistance tester and the Wenner quadrupole method.

8. The method for determining the cathodic protection current requirement of the bottom plate of an existing storage tank according to claim 1, characterized in that: In step S6, the conditions of the on-site power feeding experiment include the position of the anode and the output current.

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