Research on the experimental device and method of the influence of HVDC transmission line grounding electrode discharge on buried pipeline interference

Abstract

The present application belongs to the field of corrosion experiment technology and measurement, and relates to an electrochemical experimental device and experimental method for studying the interference of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, which solves the problem that the prior art cannot obtain comprehensive and reliable interference data of high-voltage transmission line grounding electrode discharge on buried pipeline in the laboratory. The corrosion of the cathode area and the anode area caused by the discharge current of the grounding electrode flowing into and out of the pipeline under cathodic protection is simulated by the damage points of the anticorrosion layer in the cathode area electrolytic cell and the anode area electrolytic cell, respectively. The direct current interference system is controlled by a direct current constant current source, the cathode protection system in the cathode area is controlled by a constant potential instrument, the cathode protection system in the anode area is controlled by a constant potential instrument, and the test system in the anode area is controlled by an electrochemical workstation. The device and the experimental method can be used for the simulation research on the electric interference corrosion of the high-voltage direct-current transmission line grounding electrode discharge on the buried pipeline.

Description

Technical Field

[0001] This invention belongs to the field of corrosion testing technology and measurement, and relates to an experimental device and method for studying the interference effect of grounding electrode discharge of high voltage DC transmission lines on buried pipelines. Background Technology

[0002] In recent years, with the rapid development of my country's economy, the rigid demand for energy has continued to rise, leading to the vigorous development of high-voltage power grids and long-distance oil and gas pipelines. High-voltage direct current (HVDC) transmission, with its advantages of long distance, large capacity, low loss, and low cost, has become one of the mainstream technologies for inter-regional power transmission in my country. By the end of 2020, my country had completed 38 HVDC projects, including 15 ultra-high-voltage (UHVDC) projects exceeding ±800 kV. my country has become the country with the largest number of HVDC projects, the highest voltage level, and the largest transmission capacity in the world. HVDC transmission systems have two operating modes: bipolar and unipolar. During normal operation, bipolar mode is used; during maintenance or faults, unipolar mode is used, where the earth forms a circuit, and a working current of several thousand amperes is injected into the earth through the grounding electrode. Meanwhile, the rapid construction of oil and gas storage and transportation pipelines has led to numerous instances of high-power high-voltage / ultra-high-voltage transmission lines intersecting or running parallel to buried oil and gas pipelines. This has resulted in severe electrical interference to the oil and gas pipeline network caused by grounding electrode discharge from high-voltage transmission lines, leading to a series of problems that seriously affect the operational safety of important oil and gas pipelines, such as corrosion and hydrogen damage. In recent years, numerous cases of interference to buried pipelines caused by single-pole operation of grounding electrodes in high-voltage direct current transmission systems have been reported abroad.

[0003] In the initial operation of DC grounding electrode systems, or during faults and maintenance, a single-pole operation mode is often used. In this mode, the system uses one or two conductors to form a loop with the ground. The operating current flows from one grounding electrode into the ground and along the ground to the other grounding electrode. The current flowing into the ground is the system's rated DC current, reaching several thousand amperes. Such a large current, besides generating electrical and thermal effects, causes serious damage to nearby buried pipelines and related equipment: the instantaneous high current can puncture the anti-corrosion layer of the buried pipeline, causing perforation and burning out nearby cathodic protection equipment. According to existing reports, high current will affect the normal operation of the cathodic protection system, leading to arcing and ablation on both sides of the pressure tap insulation sleeve; where the current flows into the pipeline, cathodic corrosion occurs at the metal / electrolyte interface. The cathodic reaction causes the pipeline potential to shift negatively, and excessive cathodic current or lack of oxygen can lead to water decomposition and the production of OH-. - and H, OH - Increasing the pH value on the pipe surface can cause severe hydrogen evolution reaction, leading to cathodic stripping of the anti-corrosion layer; atomic hydrogen dissolving into the metal pipe can cause hydrogen damage to the steel pipe body; stray currents flowing out of the pipe can cause anodic corrosion at the metal / electrolyte interface, resulting in anodic dissolution corrosion; at the same time, interference may cause inadequate cathodic protection, increasing the risk of pipe corrosion.

[0004] At present, the commonly used detection method of the interference influence of grounding electrode discharge on pipeline is divided into two categories, field detection and indoor simulation experiment. The field detection is to monitor and test the cathodic protection potential of the pipeline near the grounding electrode or under the suspected interference condition, the pipe ground potential, the direct current density, the soil resistivity, the polarization test piece burying (corrosion rate) and the like, and to collect data to judge the interference influence degree of the pipeline. The other is to simulate the interference influence parameters indoors, but the anode reaction is simulated. The field detection consumes a large amount of manpower and material resources, and is complex in operation, long in time and high in cost, and is not synchronized with the indoor simulation of the anode reaction, which reduces the reference value of the experimental data on the real influence of the grounding electrode on the buried pipeline.

[0005] The interference influence degree of the grounding electrode discharge of the high-voltage direct current transmission line is much larger than that of the conventional stray current interference source. Under the interference of the high-voltage direct current, the electrochemical polarization law and corrosion behavior of the metal / soil interface at the damaged point of the pipeline coating, the electromigration of the soil water and ions in the electric field, and the electric effect and thermal effect of the soil itself and many other phenomena and problems are not clear. In addition, the polarity of the grounding electrode and the single-pole operation time are uncertain, the high-voltage direct current interference has the characteristics of large interference strength, large influence range and short interference time, and the field detection and research consume time and effort and are difficult to quantitatively study.

[0006] Therefore, it is necessary to develop an experimental device and method, which can simulate the cathodic corrosion reaction of the pipeline at the current inflow point and the anodic corrosion reaction of the pipeline at the current outflow point under the grounding electrode discharge in the laboratory at the same time, quantitatively study and evaluate the corrosion and hydrogen damage behavior and law of the pipeline material under different interference levels, and realize the indoor simulation experiment research on the interference influence of the grounding electrode discharge of the high-voltage direct current transmission line on the pipeline. SUMMARY

[0007] The purpose of the present application is to provide an experimental device and method for studying the interference influence of the grounding electrode discharge of the high-voltage direct current transmission line on the buried pipeline, which solves the problems in the prior art that the cathodic and anodic reactions of the pipeline at the current inflow and outflow points under the grounding electrode discharge cannot be simulated in the laboratory at the same time, the corrosion and hydrogen damage law of the pipeline under different interference levels cannot be quantitatively studied and evaluated, and the comprehensive and reliable interference data of the grounding electrode discharge of the high-voltage transmission line on the buried pipeline cannot be obtained in the laboratory.

[0008] The technical scheme of the present application is:

[0009] An experimental device for studying the interference of HVDC transmission line grounding electrode discharge on buried pipeline, comprising the following components: pipeline, anticorrosive coating, cathode zone anticorrosive coating damage point, cathode zone electrolytic cell, first auxiliary electrode, pH meter, deoxygenation inlet pipe, first constant potential instrument, ammeter, DC constant current source, second constant potential instrument, reference electrode, second auxiliary electrode, anode zone electrolytic cell, anode zone anticorrosive coating damage point, third auxiliary electrode, fourth auxiliary electrode, electrochemical workstation, deoxygenation outlet pipe, fifth auxiliary electrode, computer, and the specific structure is as follows:

[0010] The pipeline surface is coated with an anticorrosive coating, and two anticorrosive coating damage points of the same area are made near the two ends of the pipeline, which are respectively located at the bottom center of the cathode zone electrolytic cell and the anode zone electrolytic cell.

[0011] The cathode zone anticorrosive coating damage point, the first auxiliary electrode, and the second auxiliary electrode are placed in the cathode zone electrolytic cell, and the third auxiliary electrode, the anode zone anticorrosive coating damage point, the fourth auxiliary electrode, and the fifth auxiliary electrode are placed in the anode zone electrolytic cell.

[0012] The cathode zone electrolytic cell and the anode zone electrolytic cell are filled with corrosion medium, the positive electrode of the DC constant current source is connected to the first auxiliary electrode, the negative electrode of the DC constant current source is connected to the ammeter and then to the fourth auxiliary electrode, and the cathode zone anticorrosive coating damage point and the anode zone anticorrosive coating damage point are connected by the pipeline, which together constitute a DC interference system to provide DC current for the two anticorrosive coating damage points and simulate the grounding electrode discharge.

[0013] A pipeline cathode zone test connection point is arranged on the side of the pipeline close to the cathode zone electrolytic cell, the positive electrode of the first constant potential instrument is connected to the second auxiliary electrode, and the negative electrode of the first constant potential instrument is connected to the pipeline cathode zone test connection point to constitute a cathode protection system for the cathode zone anticorrosive coating damage point and simulate the actual pipeline cathode protection.

[0014] A pipeline anode zone test connection point is arranged on the side of the pipeline close to the anode zone electrolytic cell, the positive electrode of the second constant potential instrument is connected to the third auxiliary electrode, and the negative electrode of the second constant potential instrument is connected to the pipeline anode zone test connection point to constitute an anode protection system for the anode zone anticorrosive coating damage point and simulate the actual pipeline anode protection.

[0015] The electrochemical workstation is connected to the computer, and the three electrodes of the electrochemical workstation are connected to the pipeline anode zone test connection point, the reference electrode, and the fifth auxiliary electrode through lines to form a three-electrode system as an anode test system to realize parameter testing.

[0016] The experimental device for studying the interference of HVDC transmission line grounding electrode discharge on buried pipeline, and the corrosion medium is selected according to the test needs, such as soil type or soil solution.

[0017] The experimental device for studying the interference influence of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, the cathode zone electrolytic cell is provided with a cathode zone electrolytic cell cover plate, and the anode zone electrolytic cell is provided with an anode zone electrolytic cell cover plate.

[0018] The experimental device for studying the interference influence of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, the pH meter, the deoxygenation inlet pipe and the deoxygenation outlet pipe are vertically inserted into the cathode zone electrolytic cell cover plate, the lower end of the pH meter extends to the lower part of the cathode zone electrolytic cell, the lower end of the deoxygenation inlet pipe extends to the lower part of the cathode zone electrolytic cell, and the lower end of the deoxygenation outlet pipe extends to the upper part of the cathode zone electrolytic cell.

[0019] The experimental device for studying the interference influence of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, the reference electrode is vertically inserted into the anode zone electrolytic cell cover plate, and the lower end of the reference electrode extends to the lower part of the anode zone electrolytic cell.

[0020] The experimental device for studying the interference influence of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, the cathode zone electrolytic cell and the anode zone electrolytic cell respectively simulate the corrosion of the cathode zone and the anode zone caused by the grounding electrode discharge current flowing into and out of the pipeline under the cathode protection, the direct-current interference system is controlled by a direct-current constant current source, the cathode protection system of the cathode zone is controlled by a potentiostat, the cathode protection system of the anode zone is controlled by a potentiostat, and the anode zone test system is controlled by an electrochemical workstation.

[0021] The experimental device for studying the interference influence of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, the anticorrosive layer is a three-layer polyethylene anticorrosive coating, the first auxiliary electrode, the second auxiliary electrode, the third auxiliary electrode, the fourth auxiliary electrode and the fifth auxiliary electrode are selected from platinized titanium mesh, and the reference electrode is a saturated calomel electrode.

[0022] An experimental method for studying the interference influence of high-voltage direct-current transmission line grounding electrode discharge on buried pipeline, after installing all the components, the corrosion medium is loaded, and the high-voltage direct-current transmission line grounding electrode discharge interference influence experiment on buried pipeline is carried out according to the following steps:

[0023] (1) Nitrogen is used for cathode zone electrolytic deoxygenation;

[0024] (2) Turn on the first potentiostat and the second potentiostat switch, and set the cathode protection potential value to provide the cathode protection potential for the cathode zone anticorrosive layer damage point and the anode zone anticorrosive layer damage point;

[0025] (3) Turn on the switch of the direct-current constant current source, and set the current value to provide the simulated grounding electrode discharge current for the cathode zone anticorrosive layer damage point and the anode zone anticorrosive layer damage point;

[0026] (4) Open the computer, set the measurement parameters of the electrochemical workstation, and perform open circuit potential electrochemical data test on the anode area coating damage point;

[0027] (5) The pH meter monitors the acidity and alkalinity of the corrosion medium in the cathode area electrolytic cell in real time;

[0028] (6) Disconnect the power supply of all equipment, remove the two electrolytic cells: the cathode area electrolytic cell and the anode area electrolytic cell, and take samples at the two coating damage points for morphology observation and corrosion weight loss test;

[0029] (7) According to the corrosion morphology, corrosion weight loss, and current density curve integral value parameters of the pipeline coating damage point, the corrosion rate of the pipeline material under different interference levels is evaluated; and according to the mechanical performance indicators of the yield strength, tensile strength and elongation of the samples before and after the experiment, the hydrogen damage degree of the pipeline material is evaluated.

[0030] If it is necessary to perform a direct current gradient experiment according to the field feedback information, or to change the coating damage point area, or to change the coating type and thickness, or to replace the soil and solution type, then steps (3) to (6) are repeated.

[0031] The design idea of the present application is:

[0032] The electrical interference of the grounding electrode discharge of the high-voltage direct current transmission line on the oil and gas pipeline is a new problem in recent years. Under such a large high-voltage direct current interference, people lack a deep understanding and understanding of the electrochemical polarization law and corrosion behavior of the metal / soil interface of the pipeline coating damage point, the electric migration of soil water and ions in the electric field, and the electric effect and thermal effect of the soil itself, and many other phenomena and problems. Therefore, field investigation and testing are always carried out after the interference phenomenon is discovered and even corrosion is caused, which is time-consuming and laborious, and it is difficult to quantitatively study and evaluate the corrosion and hydrogen damage behavior and law of the pipeline material under different interference levels. However, the current indoor simulation experiment often only considers the current flowing into or flowing out of the pipeline single corrosion reaction, ignoring the simultaneous corrosion effect caused by the grounding electrode discharge current flowing into and flowing out of the pipeline at different positions. Therefore, in view of the special corrosion environment of the grounding electrode discharge, based on the corrosion prevention idea and the restoration of the field corrosion condition, the present application simultaneously simulates the whole process of the grounding electrode discharge current flowing into and flowing out of the pipeline under cathodic protection, simultaneously exhibits the synergistic corrosion effect of the current flowing into and flowing out of the pipeline and the effectiveness of the cathodic protection under this environment, and quantitatively studies and evaluates the corrosion and hydrogen damage behavior and law of the pipeline material under different interference levels.

[0033] The advantages and beneficial effects of the present application are:

[0034] 1. The device can generate direct current interference current, can simulate cathodic protection, can carry out multi-factor influence experiment of different direct current density, different pipeline material, different anticorrosive layer, different anticorrosive layer damage point area, different corrosion medium, can carry out corrosion simulation experiment of pipeline anode area and cathode area under the joint action of electric interference and cathodic protection, can synchronously evaluate the influence of interference current intensity on pipeline cathode reaction interface pH value, hydrogen evolution degree and interference current intensity, duration, interference period and cathodic protection level on the influence law of anode area pipeline corrosion, provide reference for the evaluation and prevention and control of the interference influence of high-voltage transmission line grounding electrode discharge on oil and gas pipeline.

[0035] 2. The device and the experimental method thereof can be used for the electric interference corrosion simulation research of the discharge of the grounding electrode of the high-voltage direct current transmission line on the buried pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The experimental device structure diagram for studying the interference influence of the discharge of the grounding electrode of the high-voltage direct current transmission line on the buried pipeline.

[0037] Figure 2 The main body top view of the experimental device for studying the interference influence of the discharge of the grounding electrode of the high-voltage direct current transmission line on the buried pipeline.

[0038] Figure 3 The main body side view (cathode area electrolytic cell side) of the experimental device for studying the interference influence of the discharge of the grounding electrode of the high-voltage direct current transmission line on the buried pipeline.

[0039] Figures 4(a)-4(b) It is for applying different direct current density interference experiment; wherein, Fig. 4 (a) is an anode DC interference curve, the abscissa Time represents time (ks), the ordinate Potential represents potential (vs. SCE / V), and Anodic interference represents anode interference; Fig. 4 (b) is a cathode current interference curve, the abscissa Time represents time (ks), and the ordinate Potential represents potential (vs. SCE / V).

[0040] Figure 5 It is the corrosion behavior curve of the pipeline steel HVDC voltage interference sample in acid soil. In the figure, the abscissa Time represents time (s), and the ordinate i DC represents current density (A·m -2 ).

[0041] In the diagram, 1. Pipeline; 2. Anti-corrosion coating; 3. First auxiliary electrode; 4. Damage point of anti-corrosion coating in the cathode area; 5. Second auxiliary electrode; 6. Electrolytic cell in the cathode area; 7. Deoxygenated air inlet pipe; 8. Electrolytic cell cover plate in the cathode area; 9. pH meter; 10. First potentiostat; 11. DC constant current source; 12. Ammeter; 13. Second potentiostat; 14. Electrolytic cell cover plate in the anode area; 15. Reference electrode; 16. Third auxiliary electrode; 17. Electrolytic cell in the anode area; 18. Damage point of anti-corrosion coating in the anode area; 19. Fourth auxiliary electrode; 20. Fifth auxiliary electrode; 21. Corrosive medium; 22. Electrochemical workstation; 23. Computer; 24. Test connection point in the anode area of ​​the pipeline; 25. Test connection point in the cathode area of ​​the pipeline; 26. Deoxygenated air outlet pipe. Detailed Implementation

[0042] like Figure 1 As shown, the experimental apparatus of this invention for studying the interference effect of grounding electrode discharge of high-voltage direct current transmission lines on buried pipelines mainly includes the following systems: pipeline 1, cathode electrolytic cell 6, anode electrolytic cell 17, a DC interference system, a cathode cathodic protection system (CP system), an anode cathodic protection system (CP system), and an anode testing system. The DC interference system simulates the grounding electrode discharge current, the cathode and anode cathodic protection systems provide cathodic protection, and the anode testing system performs electrochemical testing of the anode region. Specifically, cathode electrolytic cell 6 and anode electrolytic cell 17 simulate the corrosion of the cathode and anode regions caused by the grounding electrode discharge current flowing into and out of the pipeline under cathodic protection, respectively. The DC interference system includes a DC constant current source 11, a first auxiliary electrode 3, a fourth auxiliary electrode 19, and an ammeter 12, and is controlled by the DC constant current source. The cathode cathodic protection system includes a second auxiliary electrode 5 and a first potentiostat 10, and is controlled by the potentiostat. The anode cathodic protection system includes a second potentiostat 13 and a third auxiliary electrode 16, and is controlled by the potentiostat. The anode testing system includes a reference electrode 15, a fifth auxiliary electrode 20, an electrochemical workstation 22, and a computer 23. The anode testing system adopts a three-electrode system and is controlled by the electrochemical workstation.

[0043] like Figures 1-3As shown, the experimental device for studying the interference of HVDC transmission line grounding electrode discharge on buried pipeline mainly comprises the following components: pipeline 1, anticorrosive layer 2, first auxiliary electrode 3, cathode zone anticorrosive layer damage point 4, second auxiliary electrode 5, cathode zone electrolytic cell 6, deoxygenation inlet pipe 7, cathode zone electrolytic cell cover plate 8, pH meter 9, first constant potential instrument 10, direct current constant current source 11, ammeter 12, second constant potential instrument 13, anode zone electrolytic cell cover plate 14, reference electrode 15, third auxiliary electrode 16, anode zone electrolytic cell 17, anode zone anticorrosive layer damage point 18, fourth auxiliary electrode 19, fifth auxiliary electrode 20, corrosion medium 21, electrochemical workstation 22, computer 23, pipeline anode zone test wiring point 24, pipeline cathode zone test wiring point 25, deoxygenation outlet pipe 26, etc., and the specific structure is as follows:

[0044] The pipeline 1 is coated with the anticorrosive layer 2, two anticorrosive layer damage points of the same area are manufactured near the two ends of the pipeline 1, i.e. the cathode zone anticorrosive layer damage point 4 and the anode zone anticorrosive layer damage point 18, the cathode zone electrolytic cell 6 is covered on the anticorrosive layer outside the cathode zone anticorrosive layer damage point 4, and the anode zone electrolytic cell 17 is covered on the anticorrosive layer outside the anode zone anticorrosive layer damage point 18, the cathode zone anticorrosive layer damage point 4 is located at the center of the bottom of the cathode zone electrolytic cell 6, and the anode zone anticorrosive layer damage point 18 is located at the center of the bottom of the anode zone electrolytic cell 17; the cathode zone electrolytic cell 6 is provided with the cathode zone electrolytic cell cover plate 8, and the anode zone electrolytic cell 17 is provided with the anode zone electrolytic cell cover plate 14.

[0045] The cathode zone anticorrosive layer damage point 4, the first auxiliary electrode 3 and the second auxiliary electrode 5 are placed in the cathode zone electrolytic cell 6, the pH meter 9, the deoxygenation inlet pipe 7 and the deoxygenation outlet pipe 26 are vertically inserted on the cathode zone electrolytic cell cover plate 8, the lower end of the pH meter 9 extends to the lower part of the cathode zone electrolytic cell 6, the lower end of the deoxygenation inlet pipe 7 extends to the lower part of the cathode zone electrolytic cell 6, and the lower end of the deoxygenation outlet pipe 26 extends to the upper part of the cathode zone electrolytic cell 6. Among them, the deoxygenation inlet pipe 7 and the deoxygenation outlet pipe 26 are used for deoxygenation of the cathode zone electrolytic cell 6, and the pH meter 9 is used for monitoring the pH value of the corrosion medium 21 in the cathode zone electrolytic cell 6.

[0046] The third auxiliary electrode 16, the anode zone anticorrosive layer damage point 18, the fourth auxiliary electrode 19 and the fifth auxiliary electrode 20 are placed in the anode zone electrolytic cell 17, the reference electrode 15 is vertically inserted on the anode zone electrolytic cell cover plate 14, and the lower end of the reference electrode 15 extends to the lower part of the anode zone electrolytic cell 17.

[0047] The anticorrosive layer 2 is a three-layer polyethylene (3PE) anticorrosive coating, the areas of the cathode zone anticorrosive layer damage point 4 and the anode zone anticorrosive layer damage point 18 are both 6.5 cm 2The first auxiliary electrode 3, the second auxiliary electrode 5, the third auxiliary electrode 16, the fourth auxiliary electrode 19 and the fifth auxiliary electrode 20 are made of platinized titanium mesh, and the reference electrode 15 is a saturated calomel electrode.

[0048] The cathode zone electrolytic cell 6 and the anode zone electrolytic cell 17 are filled with the corrosion medium 21, which can be soil solution or soil according to the test requirement. The positive pole of the direct current constant current source 11 is connected to the first auxiliary electrode 3, the negative pole of the direct current constant current source 11 is connected to the fourth auxiliary electrode 19 through the ammeter 12, and the cathode zone anticorrosion layer damage point 4 and the anode zone anticorrosion layer damage point 18 are connected by the pipeline 1, which together constitute a direct current interference system to provide direct current for the two anticorrosion layer damage points (the cathode zone anticorrosion layer damage point 4 and the anode zone anticorrosion layer damage point 18) to simulate the grounding pole discharge.

[0049] The pipeline cathode zone test connection point 25 is arranged on the side of the pipeline 1 close to the cathode zone electrolytic cell 6, the positive pole of the first constant potential instrument 10 is connected to the second auxiliary electrode 5, and the negative pole of the first constant potential instrument 10 is connected to the pipeline cathode zone test connection point 25 to constitute a cathode protection system for the cathode zone anticorrosion layer damage point 4 to simulate the actual pipeline cathode protection.

[0050] The pipeline anode zone test connection point 24 is arranged on the side of the pipeline 1 close to the anode zone electrolytic cell 17, the positive pole of the second constant potential instrument 13 is connected to the third auxiliary electrode 16, and the negative pole of the second constant potential instrument 13 is connected to the pipeline anode zone test connection point 24 to constitute an anode protection system for the anode zone anticorrosion layer damage point 18 to simulate the actual pipeline cathode protection.

[0051] The electrochemical workstation 22 is connected to the computer 23, the three electrodes of the electrochemical workstation 22 are connected to the pipeline anode zone test connection point 24, the reference electrode 15 and the fifth auxiliary electrode 20 through lines to form a three-electrode system as an anode zone test system to realize parameter test.

[0052] As shown in Figures 1-3 After the installation of the components, the cathode zone electrolytic cell 6 and the anode zone electrolytic cell 17 are filled with the corrosion medium 21, and the experiment of the interference of the grounding pole discharge of the high-voltage direct current transmission line on the buried pipeline is carried out according to the following steps:

[0053] (1) The nitrogen is used to remove oxygen in the cathode zone electrolytic cell 6;

[0054] (2) The switches of the first constant potential instrument 10 and the second constant potential instrument 13 are turned on, the cathode protection potential value (generally -1.05V CSE ) is set, and the cathode protection potential is provided for the cathode zone anticorrosion layer damage point 4 and the anode zone anticorrosion layer damage point 18;

[0055] (3) Turn on the switch of DC constant current source 11, set the current value, and provide simulated grounding electrode discharge current for the cathode anti-corrosion layer damage point 4 and the anode anti-corrosion layer damage point 18.

[0056] (4) Turn on the computer 23, set the measurement parameters of the electrochemical workstation 22, and perform electrochemical data tests such as the open circuit potential of the anodic anti-corrosion layer damage point 18;

[0057] (5) pH meter 9 monitors the acidity and alkalinity of the corrosive medium in the cathode electrolytic cell 6 in real time;

[0058] (6) Disconnect all equipment power supply and remove two electrolytic cells: cathode electrolytic cell 6 and anode electrolytic cell 17. Take samples at the two anti-corrosion layer damage points (cathode anti-corrosion layer damage point 4 and anode anti-corrosion layer damage point 18) for morphological observation, corrosion weight loss and other tests.

[0059] (7) If it is necessary to conduct a DC current gradient experiment based on the on-site feedback information, or change the area of ​​the damaged point of the anti-corrosion layer, or change the type and thickness of the anti-corrosion layer, or change the soil and solution type, etc., and other parameters affect the experiment, then repeat steps (3) to (6).

[0060] (8) Evaluate the corrosion rate of pipeline materials under different interference levels based on parameters such as corrosion morphology, corrosion weight loss, and integral (electric charge) value of current density curve at the point of failure of pipeline anti-corrosion layer; evaluate the degree of hydrogen damage to pipeline materials based on mechanical property parameters such as yield strength, tensile strength and elongation of samples before and after the experiment.

[0061] Using the apparatus and method of this invention, indoor simulation experiments were conducted, including experiments with different DC current density gradient interference and corrosion experiments on pipeline steel samples subjected to HVDC voltage interference in acidic soil. The following patterns were obtained:

[0062] 1) Polarization pattern at the damaged point of the pipeline coating: As shown in Figure 4(a), when anodic DC interference is applied, the steel potential shifts in the positive direction; as shown in Figure 4(b), when cathodic current interference is applied, the steel potential shifts in the negative direction, and the shift increases with the interference current density.

[0063] 2) such as Figure 5 As shown, the corrosion behavior of pipeline steel samples subjected to HVDC voltage interference in acidic soil exhibits a trend of first increasing and then decreasing with increasing interference potentials at DC interference potentials of 10V, 100V, 200V, 300V, and 400V. This is related to the change in current density in the soil. The integral (electrical quantity) value of the current density curve can be used to evaluate the corrosion rate of the pipeline.

[0064] The results show that the indoor simulation experiment research on the interference influence of the grounding electrode discharge of the high voltage direct current transmission line on the pipeline can be realized by the cathode corrosion reaction and the current outflow point pipeline anode corrosion reaction of the grounding electrode discharge current inflow point pipeline.

Claims

1. An experimental device for studying the influence of HVDC line ground electrode discharge on buried pipeline interference, characterized in that, The device comprises the following components: a pipeline, a corrosion protection layer, a cathode zone corrosion protection layer damage point, a cathode zone electrolytic cell, a first auxiliary electrode, a pH meter, an oxygen removal inlet pipe, a first constant potential instrument, an ammeter, a direct current constant current source, a second constant potential instrument, a reference electrode, a second auxiliary electrode, an anode zone electrolytic cell, an anode zone corrosion protection layer damage point, a third auxiliary electrode, a fourth auxiliary electrode, an electrochemical workstation, an oxygen removal outlet pipe, a fifth auxiliary electrode, and a computer, and the specific structure is as follows: The pipeline surface is coated with a corrosion protection layer, and two corrosion protection layer damage points with the same area are manufactured near the two ends of the pipeline, and the corrosion protection layer damage points are respectively located at the bottom center of the cathode zone electrolytic cell and the anode zone electrolytic cell. The cathode zone corrosion protection layer damage point, the first auxiliary electrode, and the second auxiliary electrode are arranged in the cathode zone electrolytic cell, and the third auxiliary electrode, the anode zone corrosion protection layer damage point, the fourth auxiliary electrode, and the fifth auxiliary electrode are arranged in the anode zone electrolytic cell. The cathode zone electrolytic cell and the anode zone electrolytic cell are filled with a corrosion medium, the positive electrode of the direct current constant current source is connected to the first auxiliary electrode, the negative electrode of the direct current constant current source is connected to the ammeter and then connected to the fourth auxiliary electrode, the cathode zone corrosion protection layer damage point and the anode zone corrosion protection layer damage point are connected by the pipeline, and the above together constitute a direct current interference system, which provides a direct current for the two corrosion protection layer damage points to simulate the discharge of the grounding electrode. A pipeline cathode zone test connection point is arranged on one side of the pipeline near the cathode zone electrolytic cell, the positive electrode of the first constant potential instrument is connected to the second auxiliary electrode, and the negative electrode of the first constant potential instrument is connected to the pipeline cathode zone test connection point to constitute a cathode protection system for the cathode zone corrosion protection layer damage point to simulate the actual pipeline cathode protection. A pipeline anode zone test connection point is arranged on one side of the pipeline near the anode zone electrolytic cell, the positive electrode of the second constant potential instrument is connected to the third auxiliary electrode, and the negative electrode of the second constant potential instrument is connected to the pipeline anode zone test connection point to constitute an anode protection system for the anode zone corrosion protection layer damage point to simulate the actual pipeline cathode protection. The electrochemical workstation is connected to the computer, and the three electrodes of the electrochemical workstation are connected to the pipeline anode zone test connection point, the reference electrode, and the fifth auxiliary electrode through lines to form a three-electrode system as an anode test system to realize parameter testing. A cathode zone electrolytic cell cover plate is arranged on the cathode zone electrolytic cell, and an anode zone electrolytic cell cover plate is arranged on the anode zone electrolytic cell. The cathode zone electrolytic cell and the anode zone electrolytic cell respectively simulate the corrosion of the cathode zone and the anode zone caused by the flow of the grounding electrode discharge current into and out of the pipeline under cathode protection, the direct current interference system is controlled by the direct current constant current source, the cathode protection system is controlled by the constant potential instrument, the anode protection system is controlled by the constant potential instrument, and the anode test system is controlled by the electrochemical workstation.

2. The experimental apparatus for investigating the effect of HVDC line ground electrode discharge on buried pipeline according to claim 1, characterized in that, The corrosion medium is selected according to the test requirements, and the type of soil or soil solution.

3. The experimental apparatus for investigating the effect of HVDC line ground electrode discharge on buried pipeline according to claim 1, characterized in that, The pH meter, the oxygen removal inlet pipe, and the oxygen removal outlet pipe are vertically inserted into the cathode zone electrolytic cell cover plate, the lower end of the pH meter extends to the lower part of the cathode zone electrolytic cell, the lower end of the oxygen removal inlet pipe extends to the lower part of the cathode zone electrolytic cell, and the lower end of the oxygen removal outlet pipe extends to the upper part of the cathode zone electrolytic cell.

4. The experimental apparatus for investigating the effect of HVDC line ground electrode discharge on buried pipeline according to claim 1, characterized in that, The reference electrode is inserted vertically on the cover plate of the anode area electrolytic cell, and the lower end of the reference electrode extends to the lower part of the anode area electrolytic cell.

5. The experimental apparatus for investigating the effect of HVDC line ground electrode discharge on buried pipeline according to claim 1, characterized in that, The anticorrosive layer is a three-layer polyethylene anticorrosive coating, the first auxiliary electrode, the second auxiliary electrode, the third auxiliary electrode, the fourth auxiliary electrode and the fifth auxiliary electrode are made of platinum-coated titanium mesh, and the reference electrode is a saturated calomel electrode.

6. A test method for investigating the effect of HVDC ground electrode discharge on buried pipelines using the apparatus of any one of claims 1 to 5, characterized in that, After installing all the components, the corrosion medium is loaded, and the following steps are performed for the high-voltage DC transmission line grounding electrode discharge interference influence experiment on the buried pipeline: (1) Nitrogen is used for cathode area electrolysis oxygen removal; (2) Turn on the first constant potential instrument and the second constant potential instrument switch, and set the cathodic protection potential value to provide cathodic protection potential for the cathode area anticorrosion layer damage point and the anode area anticorrosion layer damage point; (3) Turn on the switch of the direct current constant current source, and set the current value to provide simulated grounding electrode discharge current for the cathode area anticorrosion layer damage point and the anode area anticorrosion layer damage point; (4) Turn on the computer and set the measurement parameters of the electrochemical workstation to test the open circuit potential electrochemical data of the anode area anticorrosion layer damage point; (5) The pH meter monitors the acidity and alkalinity of the corrosion medium in the cathode area electrolytic cell in real time; (6) Disconnect all device power supplies, remove the two electrolytic cells: the cathode area electrolytic cell and the anode area electrolytic cell, and take samples at the two anticorrosion layer damage points for morphology observation and corrosion weight loss test; (7) According to the corrosion morphology, corrosion weight loss, and current density curve integral value parameters of the pipeline anticorrosion layer damage point, evaluate the corrosion rate of the pipeline material under different interference levels; according to the mechanical performance indicators of the yield strength, tensile strength and elongation of the samples before and after the experiment, evaluate the hydrogen damage degree of the pipeline material.

7. The experimental method for investigating the effect of HVDC line ground electrode discharge on buried pipeline interference according to claim 6, characterized in that, If it is necessary to perform a direct current gradient experiment according to the field feedback information, or to change the anticorrosion layer damage point area, or to change the anticorrosion layer type and thickness, or to replace the soil and solution type, then repeat steps (3) to (6).

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