Experimental device and method for studying the influence of grounding electrode discharge on buried pipeline interference

Abstract

The present invention provides an experimental device and method for studying the interference effect of grounding electrode discharge on buried pipelines. The experimental device includes a pipeline test piece, a grounding electrode DC interference simulation system, a cathodic protection system and an interference test system. The pipeline test piece has coating defects in the cathode area and coating defects in the anode area. The grounding electrode interference simulation system can simulate the grounding electrode discharge current, and then simulate the corrosion cathode area and the corrosion anode area under cathodic protection. The cathodic protection system can provide cathodic protection for the pipeline. The interference test system can perform electrochemical testing of the anode area. The experimental method is carried out using the above-mentioned experimental device. The beneficial effects of the present invention may include: being able to simultaneously simulate the cathode and anode reactions occurring in the pipeline at the current inflow and outflow points in the grounding electrode discharge environment indoors, and providing a reference for the evaluation and prevention of the interference effect of the grounding electrode discharge of high-voltage transmission lines on buried steel oil and gas pipelines.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion simulation experiment and measurement, and in particular to an electrochemical experimental device and an experimental method for studying the interference effect of high-voltage direct current grounding electrode discharge on buried pipelines. Background Art

[0002] my country has a vast territory, with energy mainly distributed in the western region, while the population and industry are mainly concentrated in the eastern region. Therefore, a long-distance, large-capacity, high-efficiency, and low-cost energy transmission strategy has emerged, and high-voltage power grids and long-distance oil and gas pipeline projects have also entered a peak construction period. By the end of 2020, my country has become the country with the largest number of DC transmission projects, the highest voltage level, and the largest transmission capacity in the world. Since the site selection requirements for DC transmission projects and long-distance oil and gas pipelines are very similar, the two may cross or overlap in the transmission path. It is not uncommon for DC grounding electrodes to be adjacent to buried oil and gas pipelines. Buried steel pipelines are inevitably affected by the interference of the DC grounding electrode's ground current.

[0003] In normal operation, the unbalanced current passing through the grounding electrode is only 1% of the rated DC current of the system, and the interference to the surrounding buried pipelines is relatively small. When the transmission system is debugged or a fault occurs, it switches to unipolar operation. At this time, the earth is added to the transmission system as a conductor, and the current flows from the receiving end grounding electrode through the earth and returns to the sending end grounding electrode. At this time, the ground current is the rated DC current of the system, and the value may reach several thousand amperes. The instantaneous large current will break through the coating of the buried pipeline, causing the pipeline to be perforated, and will burn nearby cathodic protection equipment, causing personal injury to the operator. When the current flows into the pipeline, a cathode reaction occurs at the metal / electrolyte interface, causing the pipeline potential to shift negatively. Excessive cathode current or lack of oxygen will cause water to decompose and produce OH - and H, OH - Increasing the pH value on the pipeline surface will cause severe hydrogen evolution reaction, which will cause coating peeling; atomic hydrogen dissolving into metal pipelines will cause hydrogen damage to steel pipes; current flowing out of the pipeline will cause anodic reaction at the metal / electrolyte interface, leading to anodic dissolution corrosion; at the same time, interference may cause cathode under-protection, increasing the risk of pipeline corrosion.

[0004] At present, there are few targeted studies on the influence of DC grounding electrodes on the interference corrosion of metal pipelines. The existing research results generally use field tests and indoor simulation calculations to detect the influence of DC grounding electrode discharge on pipeline interference. Field tests generally conduct cathodic protection effectiveness tests on interference pipelines, corrosion rate detection by test piece method, and remote potential monitoring, etc.; the other is to conduct indoor polarization curve tests on pipeline materials, anode reaction simulation, and interference simulation calculations. The pipeline service site environment is complex. In practice, the discharge polarity of the grounding electrode may be cathode or anode when the grounding electrode is operating in a single pole. The test results of single cathodic protection effectiveness or test piece corrosion rate do not match the indoor simulation test. There is often a large error between the two, resulting in the experimental data not being able to truly reflect the interference effect of the grounding electrode on the buried pipeline.

[0005] The interference caused by high-voltage DC grounding electrode discharge is much greater than that of conventional stray current interference sources. Under large-scale high-voltage DC interference, many phenomena and problems such as the electrochemical polarization law and corrosion behavior of the metal / soil interface at the pipeline coating defects, the electromigration of soil water and ions in the electric field, and the electrical and thermal effects of the soil itself are still unclear; in addition, the polarity of the grounding electrode and the single-pole operation time are uncertain. High-voltage DC interference also has the characteristics of high interference intensity, large impact range, and short interference time. On-site detection and research are time-consuming and labor-intensive, and difficult to quantify.

[0006] Therefore, it is necessary to develop a set of experimental equipment and methods that can synchronously simulate the cathode reaction of the pipeline at the point where the grounding electrode discharge current flows into the pipeline and the anode reaction of the pipeline at the point where the current flows out of the pipeline indoors, quantitatively study and evaluate the corrosion behavior and hydrogen damage characteristics and laws of pipeline materials under different interference levels, and realize indoor simulation experimental research on the interference effect of grounding electrode discharge of high-voltage DC transmission lines on buried steel pipelines. Summary of the invention

[0007] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, the anode reaction simulated indoors is not synchronized with the on-site detection, which reduces the reference value of the actual impact of the grounding electrode on the buried pipeline. For another example, the indoor interference impact parameter simulation test only simulates the anode reaction.

[0008] In order to achieve the above-mentioned purpose, one aspect of the present invention provides an experimental device for studying the interference effect of grounding electrode discharge on buried pipelines, characterized in that the grounding electrode is a grounding electrode of a high-voltage DC transmission line, and the device includes a pipeline test piece, a grounding electrode DC interference simulation system, a cathodic protection system, and a grounding electrode interference test system. Among them, the surface of the pipeline test piece is coated with a coating, and the coating is a three-layer polyethylene anti-corrosion coating, an epoxy powder anti-corrosion layer or a petroleum asphalt anti-corrosion layer, and the coating has a cathode area coating defect and an anode area coating defect. The grounding electrode DC interference simulation system includes a DC power supply control, a cathode area electrolytic cell, and an anode area electrolytic cell. The DC power supply is used to simulate the grounding electrode discharge current and can control the current intensity. The positive electrode of the DC power supply is connected to the cathode area electrolytic cell, and the negative electrode is connected to the anode area electrolytic cell. The cathode area electrolytic cell is filled with a corrosive medium, and the corrosive medium is in contact with the cathode area coating defect. The cathode area electrolytic cell can simulate the corrosion cathode area caused by the grounding electrode discharge current flowing into the pipeline under cathodic protection. The anode electrolytic cell is filled with a corrosive medium, and the corrosive medium contacts the anode coating defect. The anode electrolytic cell can simulate the corrosive anode area caused by the discharge current of the grounding electrode flowing out of the pipeline under cathodic protection. The cathodic protection system can provide cathodic protection for the pipeline. The interference test system includes a reference electrode, a test counter electrode, an electrochemical workstation and a computer. The electrochemical workstation can test electrochemical parameters. The computer is connected to the electrochemical workstation and can record the electrochemical parameters. The three electrodes of the electrochemical workstation are respectively connected to the test wiring point, the reference electrode, and the test counter electrode through lines to form a three-electrode system. The test wiring point is located on the pipeline and is between the cathode electrolytic cell and the anode electrolytic cell and is closer to the anode electrolytic cell and closer to the anode electrolytic cell. The end of the reference electrode not connected to the electrochemical workstation is set in the corrosive medium of the anode electrolytic cell, and the test counter electrode is set in the corrosive medium of the anode electrolytic cell. The electrochemical parameters include the open circuit potential of the anode coating defect.

[0009] In an exemplary embodiment of the present invention, the DC power supply is connected to the cathode region electrolytic cell through a first pair of electrodes, and the first pair of electrodes is arranged in the corrosive medium of the cathode region electrolytic cell, and the DC power supply is connected to the anode region electrolytic cell through a fourth pair of electrodes, and the fourth pair of electrodes is arranged in the corrosive medium of the anode region electrolytic cell.

[0010] In an exemplary embodiment of the present invention, the experimental device further comprises a pH meter, which is capable of monitoring the pH value of the corrosive medium in the cathode electrolytic cell.

[0011] In an exemplary embodiment of the present invention, the experimental device further comprises a deoxygenation device, which is capable of removing oxygen from the cathode electrolytic cell.

[0012] In an exemplary embodiment of the present invention, the corrosive medium is soil or soil solution.

[0013] In an exemplary embodiment of the present invention, the area of ​​the cathode coating defect is 7 to 10 cm 2 The area of ​​the coating defect in the anode region is 7 to 10 cm 2 .

[0014] In an exemplary embodiment of the present invention, the area of ​​the cathode coating defect is 6.5 cm 2 The area of ​​the coating defect in the anode region is 6.5 cm 2 .

[0015] In an exemplary embodiment of the present invention, the area of ​​the cathode coating defect is equal to the area of ​​the anode coating defect.

[0016] Another aspect of the present invention provides an experimental method for studying the interference effect of grounding electrode discharge on buried pipelines. The method uses the above-mentioned experimental device for studying the interference effect of grounding electrode discharge on buried pipelines, and includes the following steps: deoxygenation: removing oxygen in the cathode electrolytic cell; cathodic protection: turning on the cathodic protection system to provide cathodic protection for the cathode coating defects and the anode coating defects; simulated discharge: turning on the DC power supply and setting the current value to provide simulated grounding electrode discharge current for the cathode coating defects and the anode coating defects; testing: turning on the computer, setting the measurement parameters of the electrochemical workstation, and measuring the electrochemical parameters; sampling and observation: disconnecting all power supplies, removing the cathode electrolytic cell and the anode electrolytic cell, sampling at the cathode coating defects and the anode coating defects, and testing the grounding electrode discharge interference data on the buried pipeline. The grounding electrode discharge interference data on the buried pipeline includes any one or more of the electrochemical parameters, the corrosion morphology at the cathode coating defects and the anode coating defects of the pipeline coating, the corrosion weight loss, the current density curve integral, the yield strength, the tensile strength and the elongation.

[0017] In an exemplary embodiment of the present invention, the method further includes: repeating the experiment: changing any one of the DC current intensity, coating type, coating thickness, corrosive medium type, cathode coating defect area, and anode coating defect area according to the results of sampling observation, and then repeating the simulated discharge, testing and sampling observation steps for the cathode coating defect and the anode coating defect until sufficient data on the interference of grounding electrode discharge on the buried pipeline is obtained.

[0018] Compared with the prior art, the beneficial effects of the present invention may include: (1) being able to simultaneously simulate the cathode and anode reactions of the pipeline at the current inflow and outflow points under the grounding electrode discharge environment indoors; (2) being able to quantitatively study and evaluate the corrosion and hydrogen damage laws of the pipeline under different interference levels; (3) being able to obtain comprehensive and reliable simulated interference data of the grounding electrode discharge of high-voltage transmission lines on buried pipelines indoors; (4) being able to simultaneously carry out simulation experiments on the corrosion of the anode and cathode areas of the pipeline under the combined action of electrical interference and cathodic protection, and simultaneously evaluate the influence of the interference current intensity on the pH value of the pipeline cathode reaction interface, the degree of hydrogen evolution and the influence of the interference current intensity, duration, interference period and cathodic protection level on the corrosion of the anode area pipeline; (5) being able to provide a reference for the evaluation and prevention of the interference effect of the grounding electrode discharge of high-voltage transmission lines on oil and gas pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic structural diagram of an experimental device for studying the interference effect of ground electrode discharge on buried steel pipelines in an exemplary embodiment of the present invention is shown;

[0020] Figure 2 The figure shows an anode DC interference curve applied in an exemplary embodiment of the present invention, where the horizontal axis Time represents time (s), the vertical axis Potential represents potential (vs. SCE / V), and Anodic interference represents anode interference;

[0021] Figure 3 The cathode current interference curve in an exemplary embodiment of the present invention is shown, where the abscissa Time represents time (s), and the ordinate Potential represents potential (vs. SCE / V);

[0022] Figure 4 The figure shows the corrosion behavior curve of the HVDC voltage interference sample of pipeline steel in acidic soil in an exemplary embodiment of the present invention, where the horizontal axis Time represents time (s) and the vertical axis iDC represents current density (A·m -2 ).

[0023] Markings in the figure:

[0024] 1- pipeline test piece, 2- coating, 3- coating defect in cathode area, 4- coating defect in anode area, 5- electrolytic cell in cathode area, 6- electrolytic cell in anode area, 71- first pair of electrodes, 72- second pair of electrodes, 73- third pair of electrodes, 74- fourth pair of electrodes, 75- test pair of electrodes, 81- deoxygenation inlet pipe, 82- deoxygenation outlet pipe, 9- pH meter, 10- constant potentiostat, 11- DC power supply, 12- ammeter, 13- reference electrode, 14- electrochemical workstation, 15- computer, 16- test connection point. DETAILED DESCRIPTION

[0025] In the following, the experimental device and method for studying the interference effect of ground electrode discharge on buried pipelines of the present invention will be described in detail in combination with exemplary embodiments. In this article, "first", "second", "third", "fourth", etc. are only for the convenience of description and distinction, and cannot be understood as indicating or implying relative importance or having a strict order.

[0026] Detailed illustrative embodiments are disclosed in the present invention. However, for the purpose of describing the exemplary embodiments, the specific structural and functional details disclosed in the present invention are merely representative. However, the present invention can be implemented in many alternative forms and should not be construed as being limited to the embodiments set forth in the present invention.

[0027] Therefore, although the example embodiments are capable of various modifications and alternative forms, these embodiments are shown in the accompanying drawings by way of example and are described in detail herein. However, it should be understood that the example embodiments should not be limited to the specific forms disclosed. On the contrary, the example embodiments cover all modifications, equivalents and alternatives falling within the scope of the present disclosure. In the entire description of the accompanying drawings, the same reference numerals represent the same elements.

[0028] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0029] Exemplary Embodiment 1

[0030] In a first exemplary embodiment of the present invention, Figure 1 As shown in, the experimental device for studying the interference effect of grounding electrode discharge on buried pipelines may include a pipeline test piece 1, a grounding electrode DC interference simulation system, a cathodic protection system, and an interference test system. Here, the buried pipeline is a buried steel pipeline. Here, Figure 1 The schematic diagram of the structure of the experimental device for studying the interference effect of ground electrode discharge on buried pipelines in this embodiment is shown.

[0031] The surface of the pipeline test piece 1 is coated with a coating 2, the pipeline test piece 1 is made of the same material as the research pipeline, which can be X65, X70 or X80, etc., and the coating 2 has a cathode coating defect 3 and an anode coating defect 4. Here, the coating 2 can be a three-layer polyethylene anti-corrosion coating, an epoxy powder anti-corrosion layer or a petroleum asphalt anti-corrosion layer.

[0032] The area of ​​the cathode coating defect 3 can be 6.5 cm 2 The area of ​​the anode coating defect 4 can be 6.5 cm 2 .

[0033] The area of ​​the cathode coating defect 3 can also be 7 to 10 cm 2 , for example, 7.5cm 2 、8cm 2 、8.5cm 2 、9cm 2 , or 9.5cm 2 The area of ​​the anode coating defect 4 can be 7 to 10 cm 2 , for example, 7.5cm 2 、8cm 2 、8.5cm 2 、9cm 2 , or 9.5cm 2 .

[0034] The cathode coating defect 3 and the anode coating defect 4 may have the same area or different areas. For example, the cathode coating defect 3 and the anode coating defect 4 are both 7.5 cm 2 , so as to get as close as possible to the maximum defect area of ​​the pipeline coating. The consistency of the coating defect area can create the same corrosion reaction parameters, and is also helpful as a benchmark comparison data for the test of changing the coating defect area parameters.

[0035] The grounding electrode DC interference simulation system includes a DC power supply 11, a cathode electrolytic cell 5 and an anode electrolytic cell 6. The DC power supply 11 is used to simulate the grounding electrode discharge current of the high-voltage DC transmission line, and can control the current intensity, thereby simulating the corrosion cathode area and the corrosion anode area on the pipeline test piece 1 under cathodic protection. The positive electrode of the DC power supply 11 is connected to the cathode electrolytic cell 5, and the negative electrode is connected to the anode electrolytic cell 6.

[0036] In an exemplary embodiment of the present invention, for example Figure 1 As shown, the grounding electrode DC interference simulation system may further include an ammeter 12 for testing the current size of the DC power supply 11 .

[0037] The cathode electrolytic cell 5 is filled with a corrosive medium, and the corrosive medium can contact the cathode coating defect 3, and the cathode electrolytic cell 5 can simulate the corrosion cathode area caused by the grounding electrode discharge current flowing into the pipeline test piece 1 under cathodic protection. The anode electrolytic cell 6 is also filled with a corrosive medium, and the corrosive medium is in contact with the anode coating defect 4, and the anode electrolytic cell 6 can simulate the corrosion anode area caused by the grounding electrode discharge current flowing out of the pipeline test piece 1 under cathodic protection. Here, the corrosive medium can be soil or soil solution according to test needs, and the type of soil or soil solution can also be selected according to test needs.

[0038] In an exemplary embodiment of the present invention, for example Figure 1 As shown, the cathode electrolytic cell 5 may be provided with a cathode electrolytic cell cover plate, and the anode electrolytic cell 6 may be provided with an anode electrolytic cell cover plate to avoid external interference.

[0039] For example, the DC power supply 11 can be connected to the cathode electrolytic cell 5 through the first pair of electrodes 71, and the first pair of electrodes 71 is arranged in the corrosive medium of the cathode electrolytic cell 5, and the DC power supply 11 is connected to the anode electrolytic cell 6 through the fourth pair of electrodes 74, and the fourth pair of electrodes 74 is arranged in the corrosive medium of the anode electrolytic cell 6, for providing a DC current to the cathode coating defect 3 and the anode coating defect 4 of the coating 2 to simulate ground electrode discharge. Here, the first pair of electrodes 71 and the fourth pair of electrodes 74 can be cathode electrode materials such as platinum-plated titanium mesh, platinum sheet or stainless steel sheet.

[0040] The cathodic protection system can provide cathodic protection for the pipeline test piece 1, and further provide cathodic protection potential for the cathode coating defect 3 and the anode coating defect 4 on the pipeline test piece 1, simulating actual pipeline cathodic protection.

[0041] The cathodic protection system may include a constant potential instrument 10, a second pair of electrodes 72 and a third pair of electrodes 73, the positive pole of the constant potential instrument 10 is connected to the second pair of electrodes 72 and the third pair of electrodes 73, the second pair of electrodes 72 is arranged in the corrosive medium of the cathode electrolytic cell 5, the third pair of electrodes 73 is arranged in the corrosive medium of the anode electrolytic cell, and the negative pole of the constant potential instrument 10 is connected to the pipeline test piece 1, providing a cathodic protection potential for the cathode coating defect 3 and the anode coating defect 4 on the pipeline test piece 1, simulating actual pipeline cathodic protection.

[0042] Here, the second pair of electrodes 72 and the third pair of electrodes 73 can be made of platinum-plated titanium mesh, platinum sheet or stainless steel sheet and other cathode electrode materials. Here, the cathodic protection current of the cathodic protection system is controlled by the constant potential instrument 10. For example, the cathodic protection current of the cathodic protection subsystem in the cathode area is -1.05V CSE . Platinum-coated titanium mesh is available.

[0043] The interference test system includes a reference electrode 13, a test counter electrode 75, an electrochemical workstation 14 and a computer 15. The electrochemical workstation 14 is capable of testing electrochemical parameters. The computer 15 is connected to the electrochemical workstation 14 and is capable of recording the electrochemical parameters. The three electrodes of the electrochemical workstation 14 are respectively connected to the test wiring point 16, the reference electrode 13 and the test counter electrode 75 through lines to form a three-electrode system. One end of the reference electrode 13 is arranged in the corrosive medium of the anode electrolytic cell 6, and the other end is connected to the electrochemical workstation 14 through a circuit. The test wiring point 16 is located on the pipeline test piece 1 and is between the cathode electrolytic cell 5 and the anode electrolytic cell 6 and is closer to the coating defect in the anode area. The test counter electrode 75 is arranged in the corrosive medium of the anode electrolytic cell 6.

[0044] Here, the electrochemical parameter includes the open circuit potential of the anode region coating defect 4. The reference electrode 13 can be vertically inserted in the anode region electrolytic cell 6, and one end of the reference electrode 13 extends to the lower part of the anode region electrolytic cell 6. Further, when the anode region electrolytic cell 6 is sealed by the anode region electrolytic cell 6 cover, the reference electrode 13 can be vertically inserted on the anode region electrolytic cell 6 cover. The test counter electrode 75 can be a platinum-plated titanium mesh.

[0045] In an exemplary embodiment of the present invention, the experimental device further includes a pH meter 9. The pH meter 9 is used to monitor the pH value (acidity and alkalinity) of the corrosive medium in the cathode electrolytic cell 5, and to assist in evaluating the influence of the interference current intensity on the pH value of the pipeline cathode reaction interface. Figure 1 As shown, the lower end of the pH meter 9 extends to the lower part of the cathode electrolytic cell 5 to measure the pH value of the corrosive medium in the cathode electrolytic cell 5.

[0046] In an exemplary embodiment of the present invention, the experimental device further includes a deoxygenation device, which can remove oxygen in the cathode electrolytic cell 5 to maintain the actual pH value in the electrolytic cell during the reaction process. The deoxygenation device may include a deoxygenation inlet pipe 81 and a deoxygenation outlet pipe 82, for example Figure 1 As shown, the deoxygenation air inlet pipe 81 and the deoxygenation air outlet pipe 82 are vertically inserted on the cover plate of the cathode area electrolytic cell 5, and chemically inactive gases such as nitrogen are introduced into the cathode area corrosive medium through the deoxygenation air inlet pipe 81 to discharge oxygen in the corrosive medium of the cathode area electrolytic cell 5, such as oxygen in the soil and oxygen dissolved in the soil solution.

[0047] Exemplary Embodiment 2

[0048] In an exemplary embodiment of the present invention, the experimental method for studying the interference effect of ground electrode discharge on buried pipelines uses the experimental device for studying the interference effect of ground electrode discharge on buried pipelines described in exemplary embodiment 1, and the method includes the following steps: deoxygenation: removing oxygen in the cathode electrolytic cell 5; cathodic protection: turning on the cathodic protection system to provide cathodic protection for the cathode coating defect 3 and the anode coating defect 4; simulated discharge: turning on the DC power supply 11 and setting the current value to provide simulated ground electrode discharge current for the cathode coating defect 3 and the anode coating defect 4; test: turning on the meter Computer 15 sets the measurement parameters of electrochemical workstation 14 and measures electrochemical parameters; sampling observation: disconnect all power supplies, remove cathode electrolytic cell 5 and anode electrolytic cell 6, sample at cathode coating defect 3 and anode coating defect 4, and test the interference data of grounding electrode discharge on buried pipeline, the interference data of grounding electrode discharge on buried pipeline includes the electrochemical parameters, corrosion morphology at cathode coating defect 3 and anode coating defect 4 of pipeline coating, corrosion weight loss, current density curve integral, yield strength, tensile strength and elongation. Here, the grounding electrode is the grounding electrode of the high voltage DC transmission line.

[0049] Here, the deoxygenation step is to remove oxygen in the cathode electrolytic cell 5. Here, nitrogen can be introduced into the cathode electrolytic cell 5 through the deoxygenation inlet pipe 81 to remove oxygen in the corrosive medium of the cathode electrolytic cell 5.

[0050] The cathodic protection step is to start the cathodic protection system to provide cathodic protection for the coating defect 3 in the cathode region and the coating defect 4 in the anode region. Here, the cathodic protection potential value can be set by turning on the constant potential instrument 10 (for example, setting the cathodic protection point potential to -1.05V). CSE ), providing cathodic protection potential for the coating defect 3 in the cathode region and the coating defect 4 in the anode region.

[0051] The test step is: start the computer 15 and set the measurement parameters of the electrochemical workstation 14 to measure the electrochemical parameters. The electrochemical parameters include the open circuit potential of the coating defect 4 in the anode area. Furthermore, the test step can simultaneously obtain the acidity and alkalinity of the corrosive medium in the cathode area electrolytic cell 5 monitored in real time by the pH meter 9.

[0052] The sampling and observation steps include: disconnecting all power supplies, removing the cathode electrolytic cell 5 and the anode electrolytic cell 6, sampling at the cathode coating defect 3 and the anode coating defect 4, and testing the interference data of the grounding electrode discharge on the buried pipeline. The interference data of the grounding electrode discharge on the buried pipeline include the electrochemical parameters, the corrosion morphology of the cathode coating defect 3 and the cathode coating defect 3, the corrosion weight loss, the current density curve integral, the yield strength, the tensile strength, the elongation, etc.

[0053] In an exemplary embodiment of the present invention, the experimental method for studying the interference effect of grounding electrode discharge on buried pipelines also includes repeating the experimental steps. The repeated experimental steps are: performing a DC current gradient test on the cathode area coating defect 3 and the anode area coating defect 4 according to the results of sampling observation, changing any one of the type of coating 2, the thickness of coating 2, the type of corrosive medium, the area of ​​the cathode area coating defect 3, and the area of ​​the anode area coating defect 4, and repeating the steps of simulating discharge, testing and sampling observation until sufficient data on the interference of grounding electrode discharge on buried pipelines are obtained. The sufficient data on the interference of grounding electrode discharge on buried pipelines can be judged based on experience according to field feedback information.

[0054] In order to better understand the above exemplary embodiments of the present invention, they are further described below with reference to specific examples.

[0055] Example 1

[0056] like Figure 1 The experimental device is installed as shown, the cathode electrolytic cell 5 and the anode electrolytic cell 6 are respectively filled with corrosive media, and the interference effect of the grounding electrode discharge of the high-voltage direct current transmission line on the buried pipeline is tested according to the following steps:

[0057] S1, using nitrogen to deoxygenate the cathode electrolytic cell 5;

[0058] S2. Turn on the potentiostat 10 switch and set the cathode protection potential value to -1.05V CSE , providing a cathodic protection potential for the coating defect 3 in the cathode region and the coating defect 4 in the anode region;

[0059] S3, turn on the switch of the DC power supply 11, set the current value, and provide a simulated grounding electrode discharge current for the coating defect 3 in the cathode region and the coating defect 4 in the anode region;

[0060] S4, turn on the computer 15, set the measurement parameters of the electrochemical workstation 14, and perform electrochemical parameter tests such as the open circuit potential of the coating defect 4 in the anode area;

[0061] S5, using a pH meter 9 to monitor and record the pH of the corrosive medium in the cathode electrolytic cell 5 in real time;

[0062] S6. Disconnect all equipment power supplies, remove two electrolytic cells: cathode electrolytic cell 5 and anode electrolytic cell 6, and take samples at two coating defects (cathode coating defect 3 and anode coating defect 4) for morphology observation, corrosion weight loss and other tests;

[0063] S7. If it is necessary to conduct a DC current gradient experiment according to the on-site feedback information, or if it is necessary to change the coating defect area according to the on-site feedback information, or if it is necessary to change the coating type and thickness according to the on-site feedback information, or if it is necessary to change the soil and solution type according to the on-site feedback information, etc., repeat steps S3 to S6.

[0064] S8. Evaluate the corrosion rate of pipeline materials under different interference levels based on the corrosion morphology of pipeline coating defects, corrosion weight loss, and current density curve integral (electricity) value; evaluate the degree of hydrogen damage to pipeline materials based on mechanical performance index parameters such as yield strength, tensile strength and elongation of the samples before and after the experiment.

[0065] By using the device and method of the present invention, indoor simulation experiments were carried out to conduct pipeline steel corrosion tests under cathode and anode DC interference with different current densities, and the following laws were obtained:

[0066] 1) Interference with the polarization law of pipeline coating defects: Figure 2 As shown in Figure 1, when anode DC interference is applied, the steel potential shifts positively; Figure 3 As shown, when cathode current interference is applied, the steel potential shifts negatively, and the offset increases with the interference current density. Figure 2 In the figure, the horizontal axis Time represents time (s), the vertical axis Potential represents potential (vs. SCE / V), and Anodic interference represents anodic interference. Figure 3 In the figure, the horizontal axis Time represents time (s), and the vertical axis Potential represents potential (vs. SCE / V).

[0067] 2) If Figure 4 As shown in the figure, the steady-state polarization potential of the anode area (a) and cathode area (b) of pipeline steel under direct current interference in acidic soil. The potential of the anode area becomes more positive as the current density increases; the potential of the cathode area is more negative at a higher current density. Figure 4 In the figure, the DC current density represents the DC interference current density (mA·cm -2 ), the vertical axis Potential represents the potential (vs. SCE / V).

[0068] The results show that the present invention can simulate indoor synchronously the cathode corrosion reaction of the pipeline at the inflow point of the grounding electrode discharge current and the anode corrosion reaction of the pipeline at the outflow point of the current under cathodic protection, and realize the indoor simulation experimental research on the interference effect of the grounding electrode discharge of the high-voltage direct current transmission line on the pipeline.

[0069] In summary, the beneficial effects of the present invention may include:

[0070] (1) It can generate DC interference current, simulate cathodic protection, and conduct experiments on multiple factors such as different DC current density, different pipeline materials, different coatings, different coating defect areas, and different corrosive media;

[0071] (2) It can simulate the cathode corrosion reaction of the pipeline at the point where the grounding electrode discharge current flows in and the anode corrosion reaction of the pipeline at the point where the current flows out under cathodic protection indoors, and realize the indoor simulation experimental study on the interference effect of the grounding electrode discharge of the high-voltage direct current transmission line on the pipeline;

[0072] (3) It can simultaneously evaluate the influence of interference current intensity on the pH value of the pipeline cathode reaction interface, the influence of hydrogen evolution degree and interference current intensity, duration, interference cycle and cathodic protection level on the corrosion of the anode area pipeline, and provide a reference for the evaluation and prevention of the interference effect of grounding electrode discharge of high-voltage transmission lines on oil and gas pipelines;

[0073] (4) It can quantitatively study and evaluate the corrosion and hydrogen damage laws of pipelines under different interference levels, and provide a reference for the evaluation and prevention of the interference effects of grounding electrode discharge of high-voltage transmission lines on oil and gas pipelines.

[0074] Although the present invention has been described above in conjunction with the exemplary embodiments and the accompanying drawings, it should be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. An experimental device for studying the interference effect of grounding electrode discharge on buried pipelines, characterized in that: The grounding electrode is a grounding electrode of a high-voltage direct current transmission line, and the device includes a pipeline test piece, a grounding electrode interference simulation system, a cathodic protection system, and an interference test system, wherein: The surface of the pipeline test piece is coated with a coating, wherein the coating is a three-layer structure of a polyethylene anti-corrosion coating, an epoxy powder anti-corrosion layer or a petroleum asphalt anti-corrosion layer, and the coating has a cathode coating defect and an anode coating defect; The grounding electrode interference simulation system includes a DC power supply control, a cathode electrolytic cell and an anode electrolytic cell; The DC power supply is used to simulate the grounding electrode discharge current and can control the current intensity. The DC power supply is connected to the cathode electrolytic cell through a first pair of electrodes, and the first pair of electrodes is arranged in the corrosive medium of the cathode electrolytic cell. The DC power supply is connected to the anode electrolytic cell through a fourth pair of electrodes, and the fourth pair of electrodes is arranged in the corrosive medium of the anode electrolytic cell. The cathode electrolytic cell is filled with a corrosive medium, and the corrosive medium is in contact with the cathode coating defect, and the cathode electrolytic cell can simulate the corrosion cathode area caused by the grounding electrode discharge current flowing into the pipeline under cathodic protection; the anode electrolytic cell is filled with a corrosive medium, and the corrosive medium is in contact with the anode coating defect, and the anode electrolytic cell can simulate the corrosion anode area caused by the grounding electrode discharge current flowing out of the pipeline under cathodic protection; The cathodic protection system can provide cathodic protection for the pipeline test piece, and the cathodic protection system includes a constant potential instrument, a second pair of electrodes and a third pair of electrodes. The negative electrode of the constant potential instrument is connected to the pipeline test piece to provide cathodic protection for the pipeline test piece, and the positive electrode of the constant potential instrument is connected to the second pair of electrodes and the third pair of electrodes respectively; the second pair of electrodes is arranged in the corrosive medium of the cathode electrolytic cell, and the third pair of electrodes is arranged in the corrosive medium of the anode electrolytic cell; The interference test system includes a reference electrode, a counter electrode, an electrochemical workstation and a computer. The electrochemical workstation can test electrochemical parameters. The computer is connected to the electrochemical workstation and can record the electrochemical parameters. The three electrodes of the electrochemical workstation are respectively connected to the test wiring point, the reference electrode and the counter electrode through lines to form a three-electrode system, wherein the test wiring point is located on the pipeline and is between the cathode electrolytic cell and the anode electrolytic cell and is closer to the anode electrolytic cell. The end of the reference electrode not connected to the electrochemical workstation is set in the corrosive medium of the anode electrolytic cell. The test counter electrode is set in the corrosive medium of the anode electrolytic cell. The electrochemical parameters include the open circuit potential of the coating defect in the anode area. The experimental device also includes a pH meter, which can monitor the pH value of the corrosive medium in the cathode electrolytic cell.

2. The experimental device for studying the interference effect of ground electrode discharge on buried pipelines according to claim 1 is characterized in that: The experimental device also includes a deoxygenation device, which can remove oxygen in the cathode electrolytic cell.

3. The experimental device for studying the interference effect of ground electrode discharge on buried pipelines according to claim 1 is characterized in that: The corrosive medium is soil or soil solution.

4. The experimental device for studying the interference effect of ground electrode discharge on buried pipelines according to claim 1 is characterized in that: The area of ​​the cathode coating defect is 7 to 10 cm 2 The area of ​​the coating defect in the anode region is 7 to 10 cm 2 .

5. The experimental device for studying the interference effect of ground electrode discharge on buried pipelines according to claim 4 is characterized in that: The area of ​​the cathode coating defect is equal to the area of ​​the anode coating defect.

6. The experimental device for studying the interference effect of ground electrode discharge on buried pipelines according to claim 1 is characterized in that: The area of ​​the cathode coating defect is 6.5 cm 2 The area of ​​the coating defect in the anode region is 6.5 cm 2 .

7. An experimental method for studying the interference effect of grounding electrode discharge on buried pipelines, characterized in that: The grounding electrode is a grounding electrode of a high voltage direct current transmission line. The method uses an experimental device for studying the influence of grounding electrode discharge on the interference of buried pipelines as claimed in any one of claims 1 to 6, and comprises the following steps: Deoxygenation: remove oxygen from the cathode electrolytic cell; Cathodic protection: Turn on the cathodic protection system to provide cathodic protection for coating defects in the cathode area and coating defects in the anode area; Simulated discharge: Turn on the DC power supply and set the current value to provide simulated grounding electrode discharge current for the coating defects in the cathode area and the coating defects in the anode area; Test: Turn on the computer, set the measurement parameters of the electrochemical workstation, and measure the electrochemical parameters; Sampling and observation: disconnect all power supplies, remove the cathode electrolytic cell and the anode electrolytic cell, take samples at the cathode coating defects and the anode coating defects, and test the interference data of the grounding electrode discharge on the buried pipeline. The interference data of the grounding electrode discharge on the buried pipeline include any one or more of the electrochemical parameters, the corrosion morphology of the pipeline test pieces at the cathode coating defects and the anode coating defects, the corrosion weight loss, the current density curve integral, the yield strength, the tensile strength and the elongation.

8. The experimental method for studying the interference effect of ground electrode discharge on buried pipelines according to claim 7 is characterized in that: The method further comprises: Repeat the experiment: according to the results of sampling observation, change any one of the DC current intensity, coating type, coating thickness, corrosive medium type, cathode coating defect area, and anode coating defect area, and repeat the simulated discharge, test, and sampling observation steps for the cathode coating defects and the anode coating defects until enough data on the interference of grounding electrode discharge on buried pipelines are obtained.

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