An in-situ corrosion electrochemical test system and test method suitable for low conductivity media pipelines

Abstract

The application relates to an in-situ corrosion electrochemical test system and test method suitable for low-conductivity medium pipelines, and belongs to the technical field of corrosion electrochemical testing. In the system, sapphire windows are arranged on the two sides of a reaction kettle, a microelectrode system and a built-in U-shaped coil are arranged in the reaction kettle, a temperature and pressure system realizes accurate and stable temperature and pressure environment through PID control, a micro three-electrode system is adopted in an electrochemical test unit, electrochemical noise measurement is supported, and the electrochemical test unit is suitable for high-impedance media; and a high-speed camera system can in-situ observe thin liquid film formation and evolution behavior on an electrode surface. The application can simulate low-conductivity corrosion working conditions of CO2, hydrogen, hydrogen-doped natural gas, liquid ammonia, methanol, natural gas and the like pipelines, realizes synchronous collection and analysis of corrosion electrochemical signals and micro corrosion phenomena, and provides an effective means for solving corrosion monitoring and safety evaluation of new energy pipelines in harsh environments.

Description

Technical Field

[0001] This invention belongs to the field of corrosion electrochemical testing technology, specifically relating to an in-situ corrosion electrochemical testing system and method suitable for pipelines carrying low-conductivity media. This invention is particularly applicable to experimental needs in new energy pipeline transportation systems such as carbon dioxide, hydrogen, liquid ammonia, and methanol pipelines, for studying the in-situ corrosion electrochemical behavior of pipelines and the dynamic development of droplets and the evolution of corrosion behavior induced by changes in pipeline transportation conditions. Background Technology

[0002] With the profound adjustment of the global energy structure and the continuous advancement of low-carbon transformation, pipeline transportation systems for new energy sources such as carbon dioxide (CO2), hydrogen, liquid ammonia, and methanol have become an important component of national energy infrastructure construction. Compared with traditional refined oil or gathering and transportation pipelines, the internal media of these pipelines are typically in a low-water-content condition and possess extremely low electrical conductivity. For example, in the process of supercritical carbon dioxide pipeline transportation, the water content of the medium is extremely low (usually less than 200 ppmv), resulting in its conductivity being far lower than that of conventional electrolyte environments.

[0003] Under the aforementioned low moisture content and low conductivity environments, the internal corrosion mechanism and corrosion kinetics of pipeline materials exhibit significant unique characteristics. Traditional electrochemical corrosion testing methods (such as potentiodynamic polarization curves and electrochemical impedance spectroscopy) are primarily based on three-electrode systems. However, in practical engineering assessments, existing testing technologies and devices face the following significant technical challenges when used for corrosion detection in low moisture content and low conductivity environments: First, signal distortion is caused by the high impedance of the medium. In low-conductivity media, the ohmic voltage drop generated by conventional three-electrode systems is extremely high due to the huge solution resistance, making it difficult for electrochemical workstations to obtain accurate electrode potential signals. Existing electrolytic cell designs often neglect the local continuous liquid film process formed by trace water precipitation, resulting in measurement results that cannot truly reflect the corrosion state of the pipe's inner wall.

[0004] Second, there is a conflict between pressure conditions and electrode layout. Pressure pipeline environments place high demands on the sealing and pressure-bearing capacity of the testing equipment. Traditional laboratory electrochemical reactors are large in volume, slow in response, and have a large spatial span between the three electrodes, which further amplifies measurement noise in low conductivity environments. Currently, there is a lack of a precision testing configuration that can be optimized for pipeline transport conditions, shorten electrode spacing, and reduce dielectric resistance interference.

[0005] Third, the corrosion evolution process lacks multi-physics correlation. Corrosion within pipelines is often induced by the precipitation, migration, and coalescence of droplets, accompanied by complex dynamic evolution of the liquid film. Existing in-situ monitoring methods mostly focus on the acquisition of single electrochemical signals, lacking the ability to couple and observe microscopic electrochemical responses with macroscopic physical morphologies (such as droplet dynamic evolution and corrosion product film formation) in real time and synchronously. This makes it difficult for researchers to establish the intrinsic logical relationship between "operating condition fluctuations - droplet behavior - corrosion response".

[0006] Therefore, there is an urgent need to develop a new testing system that can adapt to complex working conditions with low conductivity and has the functions of high-sensitivity electrochemical signal acquisition and in-situ optical image synchronous monitoring, so as to solve the problem of accurate evaluation of corrosion in new energy pipelines.

[0007] The establishment of this system will help deepen the understanding of the corrosion mechanism of new energy pipelines under real working conditions, provide key data support for pipeline material selection, safety evaluation and protection technology development, and is of great significance for ensuring the safety of energy transmission systems and promoting the development of clean energy. Summary of the Invention

[0008] The purpose of this invention is to address the problems in existing technologies regarding electrochemical signal acquisition distortion, difficult electrode layout, and lack of synchronous monitoring of microstructures in low-conductivity media environments (such as CO2, hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, and natural gas). This invention provides an in-situ electrochemical corrosion testing system and method suitable for pipelines operating in low-conductivity media. The invention aims to achieve in-situ, synchronous, and accurate measurement of the dynamic evolution process of trace droplets and the electrochemical corrosion response under pipeline transportation conditions.

[0009] To achieve the above objectives, the present invention provides the following technical solution: As a first aspect of the present invention, an in-situ corrosion electrochemical testing system suitable for pipelines containing low-conductivity media is provided, comprising: A reaction vessel, including the reaction vessel body and the reaction vessel lid; An electrochemical testing system is installed on the reactor. The electrochemical testing system includes an electrochemical noise testing device, which includes two working electrodes and one reference electrode. Electrode leads connected to the two working electrodes and one reference electrode are connected to an electrochemical workstation outside the reactor. The system includes an automatic temperature and pressure control system, comprising a heating / cooling U-shaped coil installed inside the reactor as a heat exchanger for heating and cooling the medium; and a temperature sensor, a pressure sensor, and a control system. The temperature sensor and pressure sensor monitor the temperature and pressure inside the reactor in real time, and the control system uses the U-shaped coil to maintain the temperature and pressure inside the reactor stable according to the set values.

[0010] In some embodiments of the present invention, the electrochemical testing system employs a miniature three-electrode system, comprising two working electrodes made of the same material as the pipe under test and a platinum wire reference electrode, arranged in an equilateral triangle with a spacing of 1 mm ± 0.05 mm. The electrodes are led to the outside of the reaction vessel via double-shielded low-noise wires and connected to an electrochemical workstation. This system supports electrochemical noise electrochemical testing methods and has undergone signal-to-noise ratio optimization specifically for high-impedance systems, enabling real-time monitoring of corrosion electrochemical signals.

[0011] In some embodiments of the present invention, the electrochemical testing system includes two 1cm² pipeline steel working electrodes and a 1mm diameter platinum wire reference electrode.

[0012] In some embodiments of the present invention, the temperature sensor is a thermocouple temperature sensor.

[0013] In some embodiments of the present invention, the automatic temperature and pressure control system further includes an external coil disposed outside the reactor, which is connected to a heating / cooling U-shaped coil inside the reactor to achieve rapid temperature regulation of the U-shaped coil.

[0014] The system monitors the internal environmental parameters of the reactor in real time using thermocouple temperature and pressure sensors. The control system adjusts the temperature and flow rate of the heat exchange medium within the external coils and the internal heating / cooling U-shaped coils to achieve high-precision temperature control (±0.5℃) and pressure stability (±0.1%FS). The system supports programmed heating and cooling as well as long-term isothermal tests, accurately simulating actual pipeline temperature and pressure fluctuations.

[0015] In some embodiments of the present invention, the reactor body is made of Hastelloy C276, which has good corrosion resistance, hydrogen embrittlement resistance and high temperature stability.

[0016] Furthermore, the in-situ corrosion electrochemical testing system for pipelines with low conductivity media also includes sapphire windows symmetrically arranged on both sides of the reactor body for in-situ observation of electrode surface phenomena.

[0017] Furthermore, the in-situ corrosion electrochemical testing system for pipelines with low electrical conductivity also includes a high-speed microscopic imaging system and an illumination system. These consist of a high-speed camera and a coaxial LED light source, respectively positioned on either side of the sapphire window. The system can record in real-time dynamic processes such as droplet precipitation, migration, coalescence, and thin film formation on the working electrode surface, with a frame rate exceeding 1000 fps and a spatial resolution better than 2 μm. Combined with synchronously acquired electrochemical noise data, correlation analysis between corrosion phenomena and electrochemical responses can be achieved.

[0018] Furthermore, in the in-situ corrosion electrochemical testing system for pipelines with low electrical conductivity media, the electrochemical workstation includes a data acquisition and analysis unit that simultaneously records electrochemical signals and optical images, and performs time-domain and frequency-domain analysis on the electrochemical noise data, including fast Fourier transform, thereby revealing the corrosion mechanism and development trend.

[0019] The testing system provided by this invention includes a high-temperature, high-pressure reactor: the main body has a U-shaped coil structure to simulate the flow state and medium distribution in an actual pipeline; it is equipped with a high-precision viewing window, allowing for in-situ optical observation. This structure can effectively maintain the stability of low-conductivity media under pipeline transport pressure, providing a reliable operating environment for electrochemical testing.

[0020] The testing system and method provided by this invention use high-sensitivity thermocouple temperature sensors and pressure sensors to achieve precise monitoring and closed-loop control of temperature and pressure inside the reactor, and can simulate the effects of different delivery pressures, temperatures and fluid states on the corrosion behavior of materials.

[0021] The testing system and method provided by this invention, in conjunction with a high-speed microscopic imaging device, can perform in-situ, dynamic, and high-resolution observation and recording of the formation, distribution, evolution behavior of thin liquid films on material surfaces and their correlation with phase transition processes.

[0022] The testing system and method provided by this invention integrate a three-electrode system consisting of a micro reference electrode and two micro working electrodes. Combined with an external electrochemical workstation, it can simultaneously conduct electrochemical noise testing in a low conductivity environment, and realize real-time acquisition and analysis of corrosion electrochemical parameters.

[0023] Through the synergistic effect of the above-mentioned components, the system of this invention can simultaneously realize in-situ observation of the thin liquid film behavior at the material / medium interface and corrosion electrochemical testing and analysis under simulated low conductivity conditions of actual pipelines, significantly improving the multi-dimensional understanding of the corrosion mechanism of new energy pipelines in extreme environments and the reliability of experimental data.

[0024] This invention solves the technical bottleneck of existing technologies that cannot simultaneously perform in-situ visual observation and electrochemical measurement in real low conductivity environments, and can provide key experimental means for material safety evaluation and life prediction of pipelines such as CO2, hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, and natural gas.

[0025] As a second aspect of the present invention, a method for in-situ electrochemical testing of corrosion in pipelines containing low-conductivity media is provided, comprising the following steps: Step 1: Install the three-electrode electrochemical noise testing device into the reaction vessel to complete the assembly of the in-situ corrosion electrochemical testing system for pipelines with low conductivity media as described in the first aspect. Seal the reaction vessel, evacuate it, and then fill it with test gas to the target pressure; Inject an appropriate amount of deionized water using a micro-pump to bring the water vapor content in the system to the set value. Adjust the temperature to the test conditions; After the temperature and pressure stabilize, the high-speed camera system is turned on to focus on the surface of the working electrode and record the behavior of the condensate in real time. The electrochemical workstation was started simultaneously to measure electrochemical noise and monitor corrosion response; Step 2: Detect the electrochemical noise test results under different moisture contents; Step 3: Fast Fourier Transform of Electrochemical Noise Signal.

[0026] In step 1, the test gas includes CO2, hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, or natural gas, etc., to simulate the internal media environment of various energy transmission pipelines.

[0027] In step 2, the water content is adjusted, and under constant pressure and temperature, a dual-electrode noise measurement mode is used to collect electrochemical noise data at a sampling frequency of 10 Hz for 3600 seconds. After removing DC drift from the electrochemical noise time-domain data, the noise resistance was calculated. R n ); The noise resistance is calculated using the following formula, which indicates the corrosion resistance of the sample: ; In the formula, σ I The standard deviation of current noise. σ E The standard deviation of potential noise. S This represents the exposed area of ​​the sample.

[0028] In step 2, the data acquisition and analysis unit performs time-domain and frequency-domain analysis on the electrochemical noise data. In the measured electrochemical noise time-domain spectrum, obvious transient peaks indicate an increase in the frequency of local corrosion.

[0029] In step 3, noise data under specific water content conditions is extracted from the measured electrochemical noise time-domain spectrum, and a Fast Fourier Transform (FFT) is performed to obtain a frequency range of 10. -2 -10 2 Spectral distribution within Hz.

[0030] In step 3, the spectrum shows an upward trend in the low-frequency region (<0.1Hz), which is consistent with the characteristics of typical local corrosion; the noise level in the high-frequency region is low, indicating that the background noise of the system is well controlled.

[0031] As a third aspect of the invention, it provides the application of the in-situ corrosion electrochemical testing method for pipelines with low conductivity media described in the second aspect in identifying supercritical-liquid CO2 phase transition processes.

[0032] In some embodiments of the present invention, the step of identifying the supercritical-liquid CO2 phase transition process is as follows: under a fixed pressure, the temperature is gradually reduced, and electrochemical noise signals are collected simultaneously and the power spectral density amplitude is calculated in order to identify the phase transition sensitive corrosion region.

[0033] Compared with the prior art, this application has the following beneficial effects: This invention provides an in-situ corrosion electrochemical testing system suitable for pipelines carrying low-conductivity media. Its core lies in integrating pipeline transportation environment simulation, multi-parameter precision control, in-situ microscopic observation and electrochemical testing into one system. It can realize multi-scale in-situ research on material corrosion behavior under the conditions of simulating actual pipeline transportation of low-conductivity media (such as CO2, hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, natural gas, etc.).

[0034] An integrated three-electrode system consisting of a micro-reference electrode and a micro-working electrode minimizes the distance between electrodes, thereby maximally compensating for the ohmic voltage drop generated by low-conductivity media. Combined with an external electrochemical workstation, it can simultaneously conduct electrochemical noise testing in low-conductivity environments, enabling real-time acquisition and analysis of corrosion electrochemical parameters.

[0035] The device of this invention, through the coordinated operation of the above-mentioned systems, realizes in-situ, real-time, and multi-dimensional monitoring of material corrosion behavior in low conductivity environments, providing a reliable technical means for the safety evaluation and life prediction of new energy pipelines. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0037] Figure 1 This is a schematic diagram of the optical path and layout of a high-frequency microscopic observation system; the light source and camera device are shown in the figure. Figure 2 This is an axial cross-sectional view of the main body of the reactor in the electrochemical testing system. Figure 3 This is a top-view layout diagram of the main body of the reaction vessel in the electrochemical testing system. Figure 4 This is a rendering of the main body of the reactor in the electrochemical testing system, where A is a side view, B is an axial cross-sectional view, and C is an isometric view. Figure 5 This is a schematic diagram of the electrochemical noise testing device in an embodiment of the present invention; Figure 6 This is a schematic diagram of an overall electrochemical testing system applicable to pipeline systems with low conductivity and high impedance, as described in an embodiment of the present invention. Figure 7 The electrochemical noise time-domain spectra measured by this device under different water contents (2000, 3000, 5000 ppmv) in a supercritical / liquid CO2 environment are shown. Among them, A is 8 MPa 35℃ 2000 ppmv, B is 8 MPa 35℃ 3000 ppmv, C is 8 MPa 35℃ 5000 ppmv, D is 8 MPa 25℃ 2000 ppmv, E is 8 MPa 25℃ 3000 ppmv, and F is 8 MPa 25℃ 5000 ppmv.

[0038] Figure 8 The frequency domain spectra obtained after performing a Fast Fourier Transform (FFT) on the electrochemical noise data are shown below; where A is 8 MPa 35℃ 2000 ppmv, B is 8 MPa 35℃ 3000 ppmv, C is 8 MPa 35℃ 5000 ppmv, D is 8 MPa 25℃ 2000 ppmv, E is 8 MPa 25℃ 3000 ppmv, and F is 8 MPa 25℃ 5000 ppmv.

[0039] Figure 9 The graph shows the change in electrochemical potential noise response during the transition of CO2 from the supercritical state to the liquid state; where A represents the transition from the supercritical state to the dense phase at 8 MPa and 2000 ppmv, B represents the transition from the supercritical state to the dense phase at 8 MPa and 3000 ppmv, and C represents the transition from the supercritical state to the dense phase at 8 MPa and 5000 ppmv.

[0040] Figure 10 The graph shows the change in electrochemical current noise response during the transition of CO2 from the supercritical state to the liquid state; where A represents the transition from the supercritical state to the dense phase at 8 MPa and 2000 ppmv, B represents the transition from the supercritical state to the dense phase at 8 MPa and 3000 ppmv, and C represents the transition from the supercritical state to the dense phase at 8 MPa and 5000 ppmv.

[0041] Among them, 1-three-wire connector; 2-U-shaped coil; 3-clamp; 4-reamer cover; 5-fastening bolt; 6-rubber sealing gasket; 7-thermocouple temperature sensor; 8-external coil; 9-rear view of the reactor; 10-front view of the reactor; 11-reamer cover gripper; 12-exhaust / drain valve; 13-electrochemical workstation; 14-air inlet; 15-liquid injection port; 16-exhaust port; 17-pressure sensor; 18-high-speed camera; 19-coaxial LED light source.

[0042] 101 - Reference electrode, 102 - Working electrode.

[0043] 601 - CO2 injection pump, 602 - Control device, 603 - Temperature controller. Detailed Implementation

[0044] The following will describe in detail, with reference to the accompanying drawings and specific embodiments, an in-situ corrosion electrochemical testing device and system suitable for pipelines with low electrical conductivity media according to the present invention, but the implementation of the present invention is not limited thereto.

[0045] Low conductivity medium environment: an environment in which a continuous ion conduction loop cannot be formed in the bulk medium, and the corrosion current must rely on locally deposited trace electrolytes (such as condensed water droplets, thin liquid films) for conduction. The medium includes, but is not limited to, CO2 (supercritical, dense phase, etc.), hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, natural gas, etc., which meet the pipeline transportation standards.

[0046] Figures 1 to 5 As shown, this embodiment provides an in-situ corrosion electrochemical testing system suitable for pipelines with low electrical conductivity media. The system includes a corrosion-resistant high-pressure reactor, a precision temperature and pressure control system, a high-speed camera observation system, a microelectrode electrochemical testing system, and a data acquisition and analysis unit. It can simulate a low electrical conductivity medium environment and realize in-situ observation and electrochemical analysis of the corrosion process.

[0047] like Figures 1-6 As shown, the in-situ corrosion electrochemical testing system for pipelines with low electrical conductivity includes the following structure: 1. High-temperature and high-pressure reactor The reactor includes the reactor body and reactor cover 4. The reactor body is machined from Hastelloy C276, a high-corrosion-resistant alloy, and is designed for a pressure of 30 MPa and a temperature of 300℃. Symmetrical through holes are provided at the front and rear of the reactor body for mounting such... Figure 1 and Figure 3 The rear viewing window 9 and front viewing window 10 of the reactor shown (50 mm in diameter, linear transmittance > 90%) have excellent high-pressure sealing and optical transmission performance, allowing visible and near-infrared light to pass through efficiently, meeting the requirements of high-definition microscopic imaging.

[0048] The top side wall of the reactor body is also sequentially provided with an air inlet 14, a liquid injection port 15, and an exhaust port 16. The air inlet 14 is located at the sealed end of the reactor body and is used to introduce test gas, which can be CO2, hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, natural gas, etc. The liquid injection port 15 is used to introduce a small amount of pure water. The exhaust port 16 is used to exhaust gas. During the test preparation stage, closing the liquid injection port 15 and opening the air inlet 14 and exhaust port 16 can achieve the purpose of purging and removing air. At the start of the test, opening the liquid injection port 15 and closing the air inlet 14 and exhaust port 16 can achieve conditions such as water injection to ensure the water content in the test conditions. Then, closing the liquid injection port 15 and exhaust port 16 and opening the air inlet 14 can achieve pressurization. After the test, closing the air inlet 14 and liquid injection port 15 and opening the exhaust port 16 can achieve depressurization. A pressure sensor 17 is installed at the air inlet 14, and a gas injection pump is installed on the air delivery pipeline connected to the air inlet 14. In this embodiment, taking CO2 as an example, the gas injection pump is a CO2 injection pump 601.

[0049] A lid handle 11 is provided on the reactor lid 4 for opening and closing the reactor lid 4.

[0050] The reactor has an integrated electrode mounting module, such as... Figure 2 As shown, the device includes a clamp 3 for fixing the electrochemical noise testing device and the corrosion sample. After the clamp 3 holds the electrochemical noise testing device, the wires of the electrochemical noise testing device are connected to the internal part of the reaction vessel of the three-wire connector 1.

[0051] 2. Automatic temperature and pressure control system In a typical embodiment, such as Figure 6 As shown, the system temperature and pressure are controlled in the following manner: The in-situ corrosion electrochemical testing system includes: a control device 602 connected to a pressure sensor 17 and a CO2 injection pump 601, which receives pressure signals from inside the reactor and controls the operation of the CO2 injection pump 601; it also includes a thermocouple temperature sensor 7 installed on the reactor, a heating / cooling controller (jacket) installed on the reactor body, and a temperature controller 603 connected to the temperature sensor 7 and the heating / cooling controller. The temperature controller 603 receives temperature signals from the temperature sensor 7 and controls the heating / cooling controller to control the temperature of the reactor.

[0052] In a typical embodiment, as a further optimization of the structure, an automatic temperature and pressure control system is also provided. For example... Figure 2 and Figure 3As shown, the automatic temperature and pressure control system includes an external coil 8, an internal heating / cooling U-shaped coil 2 connected to the external coil 8, a thermocouple temperature sensor 7, a pressure sensor 17, and a control system. The thermocouple temperature sensor 7 and the pressure sensor 17 monitor the temperature and pressure inside the reactor in real time. The control system automatically adjusts the working state of the U-shaped coil 2, which serves as both a heating and cooling element, according to set values ​​to maintain stable temperature and pressure inside the reactor.

[0053] The control system is a PID control system.

[0054] In this embodiment, an externally mounted electric heating mantle (0-300℃±0.5℃), a semiconductor cooler, a back pressure valve (0.1-30MPa±0.1%FS), and a micro-injection pump (0-5mL / min) are also included, equipped with an H2S / CO2 gas mixing module to support the construction of corrosive media environments.

[0055] This system is responsible for high-precision dynamic control of the internal environment of the reactor, mainly including: Temperature control unit: The U-shaped coil 2 is connected to the electric heating mantle and the semiconductor cooler respectively through the external coil 8. The electric heating mantle and the semiconductor cooler regulate the temperature of the external coil 8 by heating and cooling it, thereby further regulating the U-shaped coil 2 connected to the external coil 8. This structure can achieve rapid heating and cooling of the U-shaped coil 2, while reducing the space of the temperature control unit inside the reactor. The built-in U-shaped coil 2 is coordinated with the electric heating mantle and the semiconductor cooler of the external coil 8. The K-type thermocouple temperature sensor 7 (accuracy ±0.1℃) monitors the temperature inside the reactor in real time. The three-way PID controller realizes the programmed heating and cooling or constant temperature control. The temperature control range is 0-300℃, and the stability is better than ±0.5℃.

[0056] Pressure control unit: A back pressure valve is installed on the pipeline where pressure sensor 17 is located; the pressure is monitored by pressure sensor 17 (range 0–30MPa, accuracy 0.1%FS), and automatic pressure stabilization is achieved by electric back pressure valve, with a control accuracy of ±0.1% of full scale; Media environment control system: The liquid injection port 15 is equipped with a micro injection pump (flow range 0–5 mL / min) for precise injection of liquid water; the air inlet port 14 is connected to a gas mixing module for adding corrosive additives (such as H2S, CO2, etc.) into the reactor body to create a mixed atmosphere containing corrosive components, simulating the actual pipeline impurity environment.

[0057] 3. Electrochemical testing apparatus In this embodiment, the electrochemical testing device is an electrochemical noise testing device, and its structure is as follows: Figure 5As shown, it includes a three-wire connector 1 and three electrodes fixed on the three-wire connector 1 in an equilateral triangle arrangement (vertex spacing 1mm ± 0.05mm): including two electrodes with an area of ​​1cm². 2 The reactor consists of a working electrode 102 made of pipeline steel and a reference electrode 101 made of platinum wire with a diameter of 1 mm. The two working electrodes 102 and the platinum wire reference electrode 101 are led out from the reactor lid 4 via double-shielded low-noise cables (contact resistance <0.1Ω) through-wall terminals and connected to an electrochemical workstation 13. The electrochemical workstation 13 provides constant potential, constant current, and electrochemical impedance spectroscopy testing functions, and records electrochemical noise signals. A Gamry Interface 5000E electrochemical workstation is used, supporting EN / LEIS / EIS multi-mode measurements. Low-noise connectors are employed; the structure uses double-shielded cables with a contact resistance <0.1Ω. This workstation features electrochemical noise (EN) measurement capabilities, with optimized signal stability and signal-to-noise ratio under high-impedance conditions. The sampling frequency of the electrochemical noise signal is adjustable, up to 100Hz, suitable for capturing early localized corrosion events.

[0058] This system supports electrochemical noise electrochemical testing methods, with signal-to-noise ratio optimized specifically for high-impedance systems, enabling real-time monitoring of corrosion electrochemical signals. In the described micro-three-electrode system, "micro" refers to the millimeter-level spatial layout that maximizes the compression of ion transport paths in high-impedance media. Specifically, the working electrode and reference electrode are arranged in an equilateral triangle, with the center-to-center distance limited to within 1 mm ± 0.05 mm, and the electrode area limited to within 1 cm². The electrodes are isolated from each other by insulating and corrosion-resistant sealing materials, such as polytetrafluoroethylene (PTFE) or epoxy resin. This precise spatial constraint ensures that even in environments with extremely low conductivity, the originally enormous ohmic potential drop is reduced to within the measurable range of the electrochemical workstation, thus guaranteeing the authenticity of the test data.

[0059] Optimizing the signal-to-noise ratio (SNR) of high-impedance systems primarily involves coordinated improvements in three areas: hardware shielding, high input impedance matching, and digital signal processing. At the hardware level, double-shielded Faraday cages and low-noise coaxial cables are required to isolate external electromagnetic interference and reduce background noise. At the connection points, ultra-low contact resistance connectors reduce signal loss. At the algorithm level, dynamic sampling frequency adjustment combined with digital filtering effectively eliminates background noise generated by low-conductivity media, ensuring that even nanoampere-level weak corrosion current signals are clearly extracted.

[0060] 4. High-speed microscopic imaging and illumination system This system is used for in-situ dynamic observation of processes such as thin liquid film behavior, droplet coalescence, and phase transitions occurring on electrode surfaces, mainly including: The front viewing window 10 of the reactor is a sapphire window, and the rear viewing window 9 of the reactor is a sapphire window.

[0061] The high-speed microscopy and illumination system includes a high-speed camera 18, a microscope lens, and a light source. The microscope lens is mounted on the high-speed camera 18 and aligned with the front viewing window 10 of the reaction vessel. The light source is located to one side of the rear viewing window 9 of the reaction vessel, providing uniform illumination. The high-speed camera can record the dynamic process of droplets on the working electrode at a high frame rate, observing the spreading and coalescence behavior of droplets in a single phase or during phase changes.

[0062] High-speed camera 18: Equipped with a long working distance microscope objective, with a maximum frame rate of no less than 1000fps, a spatial resolution better than 2μm, and supports bright field and differential interference (DIC) imaging modes. Coaxial LED light source 19: placed outside the rear viewing window 9 of the reactor, providing uniform high-intensity illumination and avoiding glare and reflection interference; It also includes image acquisition and analysis software: it can record and analyze parameters such as droplet morphology, area, and spreading rate in real time, enabling quantitative tracking of micro-region changes in the corrosion interface.

[0063] Example 1: An in-situ electrochemical testing device and system suitable for pipelines with low conductivity media. like Figures 1 to 6 As shown, it mainly includes the reaction vessel body, electrochemical testing unit, temperature and pressure control and microscopic observation system.

[0064] The reactor body is made of Hastelloy C276 to simulate a low-conductivity corrosive environment. The electrochemical testing device is installed inside the reactor via clamp 3, with the three-wire connector 1 connected to an external electrochemical workstation 13 through a sealed interface, forming an electrochemical noise detection circuit. The reactor lid 4 is fixed to the reactor body with fastening bolts 5, and a high-pressure seal is achieved using a rubber sealing gasket 6. The lid gripper 11 is connected to the top of the reactor lid 4 for easy disassembly and installation. The rear viewing window 9 and the front viewing window 10 are symmetrically installed on the front and rear side walls of the reactor body, welded together to form a single unit. The viewing windows have a three-tiered hollow structure: the first tier is a cylindrical interface connecting to the reactor body; the second tier is a flared transition section; and the third tier is a large-diameter observation area, ensuring high-definition light transmission and structural strength. The temperature control system includes a built-in U-shaped coil 2 and an external coil 8 connected to the internal U-shaped coil, both connected to an external PID temperature control module. Water or other hot media can be introduced into the coil to achieve high-precision heating and cooling of the internal media. Thermocouple temperature sensor 7 monitors the temperature inside the reactor in real time and feeds it back to the control system. Exhaust / drain valve 12 is located at the bottom of the reactor body and is used for vacuuming before the test, replacing the medium, and draining after the test.

[0065] Example 2, typical experimental operation example: Taking the experiment simulating corrosion induced by a thin liquid film in a CO2 pipeline transportation environment as an example: 1. Operation process: After sanding, cleaning and drying the surfaces of the three electrodes in sequence, they were installed into the reactor. Seal the reactor, evacuate it, and then fill it with high-purity CO2 to the target pressure (e.g., 10 MPa). Inject an appropriate amount of deionized water using a micro-pump to bring the water vapor content in the system to the set value (e.g., 100 ppmv). Adjust the temperature to the test conditions (e.g., 35°C); After the temperature and pressure stabilize, the high-speed camera system is turned on to focus on the surface of the working electrode and record the behavior of the condensate in real time. The electrochemical workstation was started simultaneously to measure electrochemical noise and monitor corrosion response; In other embodiments of the present invention, after the experiment is completed, image sequences and electrochemical data can be analyzed simultaneously to establish the correlation between thin film evolution and electrochemical parameters.

[0066] The system described in this invention can be used not only for CO2 pipelines, but also for the study of corrosion electrochemical mechanisms in various low-conductivity media such as hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, and natural gas, providing an advanced platform for the realistic simulation and accurate evaluation of material corrosion behavior under harsh working conditions.

[0067] 2. Electrochemical noise test results under different moisture contents Operating procedure: In a supercritical / liquid CO2 environment, the water content was adjusted to 2000, 3000, and 5000 ppmv, respectively, while maintaining a constant pressure of 15 MPa and a temperature of 35°C. A dual-electrode noise measurement mode was used, with a sampling frequency of 10 Hz and continuous data acquisition for 3600 seconds.

[0068] Calculation method: After removing DC drift from the electrochemical noise time-domain data, the noise resistance is calculated. R n ).

[0069] The noise resistance, calculated using the formula shown below, indicates the corrosion resistance of the sample: ; In the formula, σ I The standard deviation of current noise. σ E The standard deviation of potential noise. S This represents the exposed area of ​​the sample.

[0070] Test results: such as Figure 7As shown in Figures A through F, the amplitude of electrochemical noise increases significantly with increasing water content, indicating enhanced corrosion activity. A distinct transient peak is visible at 5000 ppmv, suggesting an increased frequency of localized corrosion.

[0071] 3. Fast Fourier Transform of Electrochemical Noise Signals Operation method: Extract Figure 7 Noise data at 5000 ppmv was subjected to FFT transformation to obtain a frequency range of 10. -2 -10 2 Spectral distribution within Hz.

[0072] Test results: such as Figure 8 As shown in Figures A through F, the spectrum shows an upward trend in the low-frequency region (<0.1Hz), which is consistent with typical local corrosion characteristics; the noise level in the high-frequency region is low, indicating that the system's background noise is well controlled.

[0073] 4. Detection of electrochemical noise response during supercritical-liquid CO2 phase transition process Operating method: Under a fixed pressure of 15 MPa, the temperature is gradually reduced from 50℃ (supercritical state) to 25℃ (liquid state) at a cooling rate of 0.5℃ / h, and electrochemical noise signals are collected simultaneously.

[0074] Test results: such as Figure 9 and Figure 10 As shown, under different moisture contents, the potential noise during the phase change process exhibited varying degrees of initial decrease followed by increase, indicating that the open-circuit potential first shifted negatively and then positively. Under unsaturated moisture content conditions, the increase in potential noise and current noise during the rising phase was not significant. Figure 9 A, B and Figure 10 (A, B) However, under supersaturated moisture content conditions, the potential noise showed a significant increase ( Figure 9 C and Figure 10 In the case of C), the open circuit potential shifted positively by approximately 50mV.

[0075] Near the critical point of phase transition, the noise potential fluctuations are significantly amplified, indicating that the change in the physical properties of the medium during the phase transition causes abrupt changes in the interfacial corrosion behavior, which can be used to identify the phase transition-sensitive corrosion range.

[0076] The severity of noise potential fluctuations can be quantitatively characterized by the noise potential standard deviation and power spectral density (PSD), while the determination of a phase transition relies on the "threshold mutation" of the signal. Typically, when a medium transitions from a supercritical state to an unsteady state where a thin liquid film precipitates, the noise potential standard deviation will increase significantly by more than three times compared to the stable reference value, or the open circuit potential (OCP) will exhibit an instantaneous shift exceeding 20 mV within a narrow temperature and pressure window. Furthermore, a frequency domain indicator for quantitatively determining a phase transition is that the power spectral density amplitude in the low-frequency region (less than 0.1 Hz) increases by one order of magnitude or more compared to the dry condition. This can serve as an accurate basis for determining the formation of a continuous electrolyte film on the electrode surface and a fundamental change in corrosion kinetics.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An in-situ electrochemical corrosion testing system suitable for pipelines containing low-conductivity media, characterized in that, include: A reaction vessel, including the reaction vessel body and the reaction vessel lid; An electrochemical testing system is installed on the reactor. The electrochemical testing system includes an electrochemical noise testing device, which includes two working electrodes and one reference electrode. Electrode leads connected to the two working electrodes and one reference electrode are connected to an electrochemical workstation outside the reactor. And an automatic temperature and pressure control system, used to adjust the temperature and pressure inside the reactor and maintain the temperature and pressure inside the reactor stable.

2. The in-situ corrosion electrochemical testing system for pipelines with low conductivity media according to claim 1, characterized in that, The electrochemical testing system adopts a miniature three-electrode system, including two working electrodes made of the same material as the pipe under test and a platinum wire reference electrode, arranged in an equilateral triangle with a spacing of 1 mm ± 0.05 mm, and connected to the electrochemical workstation.

3. The in-situ corrosion electrochemical testing system for pipelines with low conductivity media according to claim 1, characterized in that, The automatic temperature and pressure control system also includes: An external coil is installed outside the reactor and connected to the heating / cooling U-shaped coil inside the reactor to achieve rapid temperature regulation of the U-shaped coil.

4. The in-situ corrosion electrochemical testing system for pipelines with low conductivity media according to claim 1, characterized in that, It also includes sapphire windows symmetrically arranged on both sides of the reactor body for in-situ observation of electrode surface phenomena; It also includes a high-speed microscopic imaging system and an illumination system, including a high-speed camera and a coaxial LED light source respectively set on both sides of the sapphire window, to record in real time the dynamic process of droplet precipitation, migration, coalescence and thin film formation on the surface of the working electrode.

5. The in-situ electrochemical corrosion testing system for pipelines with low conductivity media according to claim 1, characterized in that, The electrochemical workstation includes a data acquisition and analysis unit that simultaneously records electrochemical signals and optical images, and performs time-domain and frequency-domain analysis on electrochemical noise data to reveal corrosion mechanisms and development trends.

6. An in-situ electrochemical testing method for corrosion of pipelines containing low-conductivity media, characterized in that, Includes the following steps: Step 1: Install the three-electrode electrochemical noise testing device into the reaction vessel to complete the assembly of the in-situ corrosion electrochemical testing system for pipelines with low conductivity media as described in claim 1. Seal the reaction vessel, evacuate it, and then fill it with test gas to the target pressure; Inject an appropriate amount of deionized water using a micro-pump to bring the water vapor content in the system to the set value. Adjust the temperature to the test conditions; After the temperature and pressure stabilize, the high-speed camera system is turned on to focus on the surface of the working electrode and record the behavior of the condensate in real time. The electrochemical workstation was started simultaneously to measure electrochemical noise and monitor corrosion response; Step 2: Detect the electrochemical noise test results under different moisture contents; Step 3: Fast Fourier Transform of Electrochemical Noise Signal.

7. The in-situ electrochemical corrosion testing method for pipelines with low electrical conductivity media according to claim 6, characterized in that, In step 1, the test gas includes CO2, hydrogen, hydrogen-blended natural gas, liquid ammonia, methanol, or natural gas.

8. The in-situ electrochemical corrosion testing method for pipelines with low conductivity media according to claim 6, characterized in that, In step 2, the water content is adjusted, and under constant pressure and temperature, electrochemical noise data is collected using a dual-electrode noise measurement mode. After removing DC drift from the electrochemical noise time-domain data, the noise resistance was calculated. Rn ; The noise resistance is calculated using the following formula, which indicates the corrosion resistance of the sample: ； In the formula, σ I The standard deviation of current noise. σ E The standard deviation of potential noise. S This represents the exposed area of ​​the sample. In step 2, the data acquisition and analysis unit performs time-domain and frequency-domain analysis on the electrochemical noise data. In the measured electrochemical noise time-domain spectrum, obvious transient peaks indicate an increase in the frequency of local corrosion.

9. The in-situ electrochemical corrosion testing method for pipelines with low conductivity media according to claim 6, characterized in that, In step 3, noise data under specific water content conditions is extracted from the measured electrochemical noise time-domain spectrum, and a fast Fourier transform is performed to obtain a frequency range of 10. -2 -10 2 Spectral distribution within Hz.

10. The application of the in-situ corrosion electrochemical testing method for pipelines with low electrical conductivity media as described in claim 6 in identifying supercritical-liquid CO2 phase transition processes, characterized in that... The steps for identifying the supercritical-liquid CO2 phase transition process are as follows: under a fixed pressure, the temperature is gradually reduced, and electrochemical noise signals are collected simultaneously and the power spectral density amplitude is calculated to identify the phase transition-sensitive corrosion region. The frequency domain index for quantitatively determining phase transition is: the power spectral density amplitude in the low-frequency region (below 0.1 Hz) is increased by one order of magnitude or more compared to the dry operating condition.

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