Experimental device for simulating alternating-current stray current corrosion of buried metal pipeline

Abstract

The utility model provides an experimental device for simulating alternating-current stray current corrosion of a buried metal pipeline, and belongs to the field of alternating-current corrosion. Comprising an alternating-current power supply, a direct-current power supply, an alternating-current stray current monitoring system, a saturated copper sulfate reference electrode, a graphite electrode, soil, a metal pipeline and a plastic box. The AC stray current monitoring system mainly comprises a signal conditioning circuit, an A / D conversion circuit, a monitoring device, a display screen and an ESP8266 remote communication module. According to the utility model, by simulating the alternating stray current corrosion of the buried metal pipeline, the real-time pipe-to-ground potential is monitored, and the corrosion area and the corrosion degree of the buried metal pipeline after corrosion for a period of time are observed; the corrosion influence of factors such as alternating voltage and a pipeline laying angle on the alternating stray current of the buried metal pipeline under the interference of the alternating stray current is researched.

Description

Technical Field

[0001] The utility model relates to the field of AC corrosion, in particular to an experimental device for simulating AC stray current corrosion of buried metal pipelines. Background Art

[0002] Stray current is also called stray current. Since the track cannot be completely insulated, part of the railway traction current flows into the earth instead of returning directly to the traction substation along the track. This current that flows into the earth through the track is called stray current. When stray current flows out of the buried metal structure, it may cause electrochemical corrosion and even accelerate corrosion. Buried metal pipeline corrosion can be divided into DC corrosion and AC corrosion according to the different sources of stray current interference. Among them, the main sources of AC stray current interference are electrified railways and high-voltage transmission lines.

[0003] Since the rails are not completely insulated from the ground, part of the AC current will leak into the ground along the rails. The interference caused by this part of the current flowing into the ground to the buried metal structure is called resistive coupling. Resistive coupling will interfere with the cathodic protection system due to the leakage current and the pipeline's own voltage, and may even damage the equipment because the pipeline surface is no longer polarized. When a fault occurs, the fault current flowing into the ground will generate a strong magnetic field, and the generated arc will cause the anti-corrosion layer to peel off.

[0004] Current density is an important indicator for measuring the corrosion risk of buried metal pipelines. However, it is difficult to directly detect the current density on the surface of buried metal pipelines in actual working environments. Usually, the pipe-to-ground potential, which is easier to measure, is used to indirectly reflect the corrosion degree and corrosion risk of the metal surface. Therefore, a reference electrode is used as a reference comparison electrode, and the pipe-to-ground potential is obtained by measuring the potential difference between the reference electrode in the soil and the buried metal pipeline.

[0005] Currently, most experimental devices for studying AC corrosion of buried metal pipelines use electrochemical measurement, weight loss method and surface analysis technology, and all of them use tiny specimens for research, which is quite different from the actual pipeline. It is impossible to consider the influence of AC stray current leakage points and return points in the actual working environment and the relative position between the pipeline and the leakage point, and it is also impossible to monitor the hazards of AC corrosion in real time through changes in pipe-to-ground potential.

[0006] The prior art with publication number CN116858755A discloses a stray current corrosion detection device for metal pipes along the local subway, including: two sets, on which through holes matching the metal pipes are arranged; two circular insulating pads are arranged in the through holes; a first sleeve and a second sleeve are both arranged on the metal pipe and can move laterally or rotate relative to the metal pipe; a plurality of balls are rotatably arranged on the first sleeve and the second sleeve respectively; a driving device is arranged on the two sets for driving the first sleeve and the second sleeve to rotate or move laterally on the metal pipe at the same time; a control device is used to indirectly control the operation of the driving device; an industrial camera is arranged on the second sleeve; and a wireless communication module. Its structure is complex and inconvenient to use, and it is not possible to obtain corrosion status information in real time. Utility Model Content

[0007] In view of the shortcomings of the existing technology, an experimental device is provided for simulating AC stray current corrosion of buried metal pipelines. Experiments on buried metal pipelines under simulated AC stray current interference are carried out, and the pipe-to-ground potential is monitored in real time, so as to judge the AC corrosion risk of buried metal pipelines. The structure is simple, practical and convenient.

[0008] In order to achieve the above technical purpose, an experimental device for simulating AC stray current corrosion of buried metal pipelines of the present invention comprises an environment simulation device, an AC stray current generating device and an AC stray current detecting device;

[0009] The environmental simulation device includes a plastic box with soil inside, and the metal pipe to be tested is buried horizontally in the soil;

[0010] The AC stray current generating device includes an AC power source 3 and graphite electrodes No. 1, No. 2 and No. 3 for simulating leakage points and backflow points of AC stray current in a soil environment. The ends of graphite electrodes No. 1, No. 2 and No. 3 are inserted into the soil of a plastic box, wherein the ends of graphite electrodes No. 1 and No. 3 are connected to the negative pole of the AC power source through a wire, and the end of graphite electrode No. 2 is connected to the positive pole of the AC power source through a wire;

[0011] The AC stray current detection device includes an AC stray current monitoring system for real-time monitoring of pipe-to-ground potential signals. The AC stray current monitoring system is connected to a DC power supply. The AC stray current monitoring system includes a signal conditioning circuit for collecting AC signals. The negative pole of the AC stray current monitoring system is connected to a saturated copper sulfate reference electrode for measuring the pipe-to-ground potential AC signal through a wire. The end of the saturated copper sulfate reference electrode is placed on the soil surface or in the soil where the metal pipeline is buried. The positive pole of the AC stray current monitoring system 2 is connected to the metal pipeline buried in the soil through a wire.

[0012] Furthermore, both ends of the metal pipe are provided with plugs to prevent liquid from invading the interior.

[0013] Furthermore, the soil is a soil sample collected on-site in the simulation area to simulate the corrosive electrolyte environment of AC stray current; or water and sodium chloride are added to the soil to adjust the soil resistivity.

[0014] Furthermore, the AC power supply is a STG-200W voltage-stabilized power supply with a frequency of 50 Hz, and the AC voltage is adjusted according to the simulation needs.

[0015] Furthermore, graphite electrode No. 1, graphite electrode No. 2, and graphite electrode No. 3 are all vertically inserted into the soil with an insertion depth of 80 mm, wherein graphite electrode No. 1, graphite electrode No. 2, and graphite electrode No. 3 are evenly distributed in the length direction of the soil domain, and their positions are 80 mm, 380 mm, and 680 mm, respectively.

[0016] Furthermore, the AC stray current monitoring system 2 includes a signal conditioning circuit, an A / D conversion circuit, an STM32F103ZET6 monitoring device, a display screen, and an ESP8266 remote communication module connected in sequence, wherein the signal conditioning circuit includes a signal amplification circuit and an effective value conversion circuit; the STM32F103ZET6 monitoring device 22 sends data to the display screen. Beneficial Effects

[0017] The utility model discloses a method of establishing an AC stray current corrosion environment and an AC stray current monitoring system, thereby achieving real-time monitoring of the pipe-to-ground potential under AC interference and observing the AC corrosion morphology of the buried metal pipeline after a period of time. The utility model can also explore the influence of different factors on the corrosion of the pipeline by changing the AC voltage and the position of the buried metal pipeline in the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The utility model is a schematic diagram of an experimental device for simulating AC stray current corrosion of buried metal pipelines.

[0019] Figure 2 This is the connection diagram of the experimental device of AC stray current monitoring system.

[0020] In the figure: 1. DC power supply, 2. stray current monitoring system, 3. AC power supply, 4. saturated copper sulfate reference electrode, 5. No. 1 graphite electrode, 6. No. 2 graphite electrode, 7. No. 3 graphite electrode, 8. metal pipe, 9. soil, 10. plastic box;

[0021] 20. Signal conditioning circuit, 21. A / D conversion circuit, 22. STM32F103ZET6 monitoring device, 23. ESP8266 remote communication module, 24. Display screen. DETAILED DESCRIPTION

[0022] The content of the utility model is further described below in conjunction with the accompanying drawings:

[0023] See also Figure 1 , Figure 2 .in, Figure 1 The utility model provides an experimental device for simulating AC stray current corrosion of buried metal pipelines. Figure 2 This is the connection diagram of the experimental device for the AC stray current monitoring system.

[0024] The plastic box 10 is used to contain the soil 9, and the soil resistivity is kept at a constant value by adding water.

[0025] The AC power source 3 is used to output AC signals with a frequency of 50 Hz and different voltages to simulate stray currents of different AC voltages.

[0026] Three graphite electrodes 5, 6, and 7 of the same model are buried vertically in the soil, and the distance between two adjacent electrodes is the same. The upper ends of the three graphite electrodes 5, 6, and 7 are connected to the AC power supply 3 through wires, and the middle graphite electrode No. 2 6 is connected to one end of the power supply to simulate the leakage source of stray current, and the graphite electrodes No. 1 and No. 3 5 and 7 at both ends are connected to the other end of the AC power supply to simulate the return point.

[0027] The saturated copper sulfate reference electrode 4 is used to measure the corrosion results. The utility model adopts the ground reference method to measure the pipe ground potential, thereby reducing the experimental error. The specific method is: the saturated copper sulfate reference electrode 4 is placed on the surface of the soil 9 just above the measurement point. Example

[0028] The metal pipeline 8 has an inner diameter of 25 mm, an outer diameter of 35 mm, and a length of 750 mm, and is used to simulate an underground metal pipeline for oil and gas transportation under actual working conditions;

[0029] Soil 9, with a volume of 760 mm × 550 mm × 255 mm, was used to simulate the corrosive electrolyte;

[0030] Sodium chloride, used to simulate a corrosive environment and change the conductivity of the soil;

[0031] AC current source 3, using STG-200W voltage stabilizer with a frequency of 50Hz, is used to simulate AC stray current;

[0032] Graphite electrodes, with a diameter of 8 mm and a length of 00 mm, are used to simulate the inflow and outflow points of AC stray current;

[0033] A plastic box 10, with a volume of 860 mm×630 mm×480 mm, is used to hold soil;

[0034] The plug, upper diameter: 29 mm, height: 28 mm, lower diameter: 22 mm, seals the pipe from both sides and prevents AC current from flowing into the pipe from the inside.

[0035] DuPont cable, model 40P, used to connect the AC voltage source and the monitoring device;

[0036] Wire, national standard RV, used to connect to the positive and negative poles of the power supply to draw out AC current;

[0037] The monitoring device, STM32F103ZET6 single-chip microcomputer, provides A / D conversion module and realizes data transmission;

[0038] The data cable uses a USB to Type-C data cable to achieve data communication between the monitoring device and the display screen;

[0039] AD620 module, used to amplify the received signal;

[0040] AD637 module, used for effective value conversion, converting AC signals into DC signals;

[0041] Saturated copper sulfate reference electrode 4, used to measure the tube-to-ground potential;

[0042] ESP8266, wireless communication module, used to connect to WIFI signals and realize wireless communication;

[0043] The specific working method is: the reference electrode and the buried metal pipe to be measured are respectively connected to the signal conditioning circuit 20 through wires. First, the pipe-to-ground potential is amplified by the signal conditioning circuit 20 and the AC signal is converted into a DC effective value. Then, the potential difference generated between the two is converted into a digital signal through the A / D conversion circuit 21. The monitored potential signal is transmitted to the display screen 24 through wifi through the STM32F103ZET6 monitoring device 22 to realize the display and storage functions of the potential. At the same time, the ESP8266 remote communication 23 is used to transmit the signal to OneNET through WIFI, so as to perform remote monitoring through the display screen.

[0044] Among them, the signal conditioning circuit 20 mainly includes: a signal amplification circuit and an effective value conversion circuit. Since the measured pipe-to-ground potential signal is a weak signal, a signal amplification circuit is required to amplify the measured pipe-to-ground potential signal. AD620 is an operational amplifier with low price and high measurement accuracy, which can reach one thousandth, and can meet the needs of signal amplification. When measuring the pipe-to-ground potential, the AC voltage cannot be directly converted into analog digital through the A / D conversion circuit, and the AC voltage value needs to be converted into a DC voltage through an AC voltage effective value conversion circuit. AD637 is a DC converter that can accurately calculate the effective value of various waveforms. The power supply voltage range of AD637 is: ±5 V~±15 V, so an external output positive and negative voltage step-up and step-down power supply module is required to output the DC power supply voltage as a positive and negative voltage drop to meet the power supply requirements of AD637. At this time, the LM358 chip is used, which is a low-power dual operational amplifier used in a wide voltage range and powered by a single power supply. The operating voltage range of the amplifier is 3 V~32 V, and it can output positive and negative voltages at the same time.

[0045] The voltage signal measured by the measuring end needs to be converted into a digital signal by the A / D conversion circuit 21. At this time, the ADC analog signal and digital signal converter inherent in the STM32F103 chip is used.

[0046] The communication method between serial devices adopts serial port communication, which uses the serial port in STM32F103ZET6. The chip can provide up to 5 serial ports.

[0047] WIFI wireless transmission technology is mainly realized through ESP8266 remote communication 23. WIFI module realizes wireless communication, and OneNET realizes online monitoring, storage and query of data. The information is transferred through wireless signals, which has the advantages of fast transmission speed, high security and no need for wiring, meeting the requirements of long-distance transmission of monitoring data.

[0048] Real-time data transmission is achieved through remote communication between the display screen 24 and the STM32F103ZET6 monitoring device 22. The main functions of the display screen 24 are to send commands and collect data, process the data and display it on images and in tables, and save the measured data and call it when needed.

[0049] The specific method of using the saturated copper sulfate reference electrode 4 is as follows: first, open the upper cover of the saturated copper sulfate reference electrode 4, then add distilled water until the water level reaches about 2 cm above the copper sulfate particles, then cover the upper cover, shake the electrode fully, so that the copper sulfate particles are completely dissolved in the distilled water, and then soak the microporous leakage end at the lower end of the reference electrode. Place the end of the saturated copper sulfate reference electrode on the soil surface or in the soil where the metal structure is buried, connect the reference electrode to the input end of the measuring device, connect the measured metal component to the output end of the measuring device, read the potential and record the data.

[0050] The monitoring system 2 is used to monitor the pipe-to-ground potential in real time. The specific method is: a wire is connected to the upper end of the buried metal pipe 8 and the reference electrode 4, and they are connected to the monitoring system 2 through the wire. The monitoring device realizes data communication with the display screen 24 through wifi. When the AC current is stable, the pipe-to-ground potential can be measured in real time.

[0051] The DC power supply 1 provides power to the monitoring system 2 to ensure the normal operation of the AC monitoring system.

[0052] AC stray current monitoring system such as Figure 2 As shown, it is used to monitor the AC signal of pipe-to-ground potential, and mainly includes: a reference electrode, a signal conditioning circuit 20, an A / D conversion module 21, an STM32F103ZET6 monitoring device 22, an ESP8266 wireless communication module 23, a display screen and other key components.

[0053] This embodiment provides an experimental device for simulating AC stray current corrosion of buried metal pipelines. In actual operation, the device mainly includes the following steps:

[0054] Step 1: build a simulated AC stray current experimental environment, pour soil 9 into a plastic box 10, mix it with water and sodium chloride, and adjust the soil resistivity to a fixed value.

[0055] Step 2: Polish the metal pipe 8 to a bright finish, plug both ends of the pipe with plugs to prevent AC stray current from directly leaking into the pipe, and then bury the metal pipe 8 in the soil with a burial depth of 100 mm. The burial position is on the symmetry axis in the width direction of the soil domain 9 and is parallel to the length direction of the soil domain 9.

[0056] Step 3: bury three graphite electrodes 5, 6, and 7 of exactly the same size and shape directly above the pipeline 8, with a burial depth of 80 mm and evenly distributed in the length direction of the pipeline. Connect the middle graphite electrode 6 No. 1 to the positive pole of the AC power supply 3 through a wire to simulate the AC stray current leakage point, and connect the graphite electrodes 5 and 7 No. 2 and No. 3 on both sides to the negative pole of the AC power supply 3 to simulate the stray current return point.

[0057] Step 4: Connect the modules in the monitoring system 2 in the order of signal conditioning circuit 20, A / D conversion circuit 21, STM32F103ZET6 monitoring device 22, ESP8266 remote communication 23, and display screen 24 to realize real-time monitoring of the pipe-to-ground potential AC signal, thereby evaluating the corrosion risk of the buried metal pipeline.

[0058] Step 5: Place the saturated copper sulfate reference electrode 4 on the surface of the soil 9 at the location to be measured, and lead out a wire.

[0059] Step six, a conductor is led out from one side of the buried metal pipe 8 and connected to the AC stray current monitoring system 2 together with the conductor led out from the saturated copper sulfate reference electrode 4, thereby providing the monitoring system with a pipe-to-ground potential signal.

[0060] Step 7: When the AC current is stable, the corrosion risk can be determined by observing the pipe-to-ground potential displayed on the display screen 24. After a period of simulated AC corrosion, the corrosion area and degree of corrosion can be determined by observing the corrosion morphology of the metal pipe 8.

[0061] Therefore, the utility model provides an experimental device for simulating AC stray current corrosion of buried metal pipelines, which is suitable for simulating the corrosion effect of AC stray current interference on buried metal pipelines. It can be used to explore the effects of different applied AC currents, different laying angles of buried metal pipelines, soil resistivity and other factors on the corrosion of buried metal pipelines, and provides an experimental device in the laboratory for studying AC stray current interference. The specific method is as follows:

[0062] Keep the buried depth at 100 mm, and adjust the applied AC voltage with a frequency of 50 Hz to 10 V, 20 V, 30 V and 40 V respectively. The middle graphite electrode 1 6 is located in the middle of the pipeline length direction, and the two return points graphite electrode 2 5 and graphite electrode 3 7 are located at 0.08 m and 0.68 m respectively. When the AC voltage is stable, observe the changes in the pipe-to-ground potential at different measuring points;

[0063] Keeping the applied AC voltage at 30 V (50 Hz), the graphite electrode 6 was moved to different positions along the straight line where the pipeline 8 was located to conduct experimental research, monitor the pipe-to-ground potential distribution at different positions and observe the corrosion morphology after AC interference for a period of time;

[0064] The angles between the buried metal pipe 8 and the connecting lines of the No. 1, No. 2, No. 3 graphite electrodes 5, 6, 7 are set to 0°, 15° and 30°, and the experimental device of the utility model is used to conduct experimental research, monitor the pipe-to-ground potential distribution at different positions and observe the corrosion morphology after AC interference for a period of time;

[0065] The buried depth of the buried metal pipeline 8 is set to 100 mm, and the horizontal distances between the No. 1 graphite electrode 5, the No. 2 graphite electrode 6, the No. 3 graphite electrode 7 and the parallel pipeline 8 are changed to 0, 100 mm, and 200 mm, respectively. The experimental device of the utility model is used to conduct experimental research to observe the corrosion area and corrosion degree of the pipeline surface after corrosion for a period of time.

[0066] The experiment changes the soil resistivity by changing the soil water content and sodium chloride content, and can explore the pipe-to-ground potential distribution when the soil resistivity is different. The soil environment, as the electrolyte environment for the corrosion of buried metal pipelines, directly affects the corrosion rate. The pipe-to-ground potential distribution under three conditions of soil resistivity of 100 Ω·m, 50 Ω·m and 33 Ω·m was studied respectively. The soil resistivity can be measured by the four-electrode method or the soil resistivity meter.

[0067] The above description is only a preferred embodiment of the present utility model and does not limit the present utility model. Any modification and application made by utilizing the principle and spirit of the present utility model should be included in the patent protection scope of the present utility model.

Claims

1. An experimental device for simulating AC stray current corrosion of buried metal pipelines, characterized by: include Environmental simulation device, AC stray current generating device and AC stray current detecting device; The environmental simulation device comprises a plastic box (10) containing soil (9) therein, wherein a metal pipe (8) to be tested is horizontally buried in the soil (9); The AC stray current generating device comprises an AC power source (3) and a No. 1 graphite electrode (5), a No. 2 graphite electrode (6), and a No. 3 graphite electrode (7) for simulating leakage points and return points of AC stray current in a soil environment, wherein the ends of the No. 1 graphite electrode (5), the No. 2 graphite electrode (6), and the No. 3 graphite electrode (7) are inserted into the soil (9) of a plastic box (10), wherein the ends of the No. 1 graphite electrode (5) and the No. 3 graphite electrode (7) are connected to the negative electrode of the AC power source (3) through a wire, and the end of the No. 2 graphite electrode (6) is connected to the positive electrode of the AC power source (3) through a wire; The AC stray current detection device comprises an AC stray current monitoring system (2) for real-time monitoring of pipe-to-ground potential signals. The AC stray current monitoring system (2) is connected to a DC power supply (1). The AC stray current monitoring system (2) collects signals through a built-in signal conditioning circuit (20). Its negative electrode is connected to a saturated copper sulfate reference electrode (4) through a wire, and its positive electrode is connected to a buried metal pipe (8) for measuring pipe-to-ground potential AC signals. The end of the saturated copper sulfate reference electrode (4) is placed on the soil surface or in the soil where the metal pipe (8) is buried. The positive electrode of the AC stray current monitoring system (2) is connected to the metal pipe (8) buried in the soil (9) through a wire.

2. The experimental device for simulating AC stray current corrosion of buried metal pipelines according to claim 1 is characterized in that: Both ends of the metal pipe (8) are plugged to prevent liquid from invading the interior.

3. The experimental device for simulating AC stray current corrosion of buried metal pipelines according to claim 1 is characterized in that: The soil (9) is a soil sample collected on-site in the simulation area to simulate the corrosive electrolyte environment of the AC stray current; or water and sodium chloride are added to the soil (9) to adjust the soil resistivity.

4. The experimental device for simulating AC stray current corrosion of buried metal pipelines according to claim 1 is characterized in that: The AC power supply (3) is a STG-200W voltage stabilizer with a frequency of 50 Hz, and the AC voltage is adjusted according to the simulation requirements.

5. The experimental device for simulating AC stray current corrosion of buried metal pipelines according to claim 1, characterized in that: Graphite electrode No. 1 (5), graphite electrode No. 2 (6), and graphite electrode No. 3 (7) are all vertically inserted into the soil (9) with an insertion depth of 80 mm. Graphite electrode No. 1 (5), graphite electrode No. 2 (6), and graphite electrode No. 3 (7) are evenly distributed in the length direction of the soil (9) domain, and are located at 80 mm, 380 mm, and 680 mm, respectively.

6. The experimental device for simulating AC stray current corrosion of buried metal pipelines according to claim 1, characterized in that: The AC stray current monitoring system (2) comprises a signal conditioning circuit (20), an A / D conversion circuit (21), an STM32F103ZET6 monitoring device (22), a display screen (24), and an ESP8266 remote communication module (23) which are connected in sequence, wherein the signal conditioning circuit (20) comprises a signal amplification circuit and an effective value conversion circuit; and the STM32F103ZET6 monitoring device (22) sends data to the display screen (24).

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