Loop experiment device for simulating corrosion in natural gas pipeline in deep sea environment

Abstract

The invention discloses a loop experimental device for simulating corrosion in a natural gas pipeline in a deep sea environment, relates to the field of marine oil and gas gathering and transportation experimental equipment, and solves the problems that an existing device is incomplete in working condition simulation and difficult in sample and data acquisition. According to the device, a gas source system, a pressurization and pressure stabilization system, a loop circulation system, a corrosion test box system and a data acquisition system are connected through a high-pressure corrosion resistant pipeline to form a closed loop, wherein the gas source system can be configured with a multi-element experimental medium to regulate and control the gas-liquid ratio; a pressurization system stabilizes the deep sea pressure of 0.1 MPa to 30 MPa; the loop system comprises an experimental pipeline and a gas-liquid mixed transportation control system and can control various flow patterns; the corrosion test box synchronously simulates high pressure, ocean current impact and axial temperature gradient through a high-pressure bin, an eccentric weight assembly and a temperature adjusting structure; the data acquisition system comprehensively acquires corrosion related parameters by means of two sensors and an image acquisition component. According to the device, the actual corrosion environment can be precisely restored, and a reliable platform is provided for deep sea pipeline internal corrosion mechanism research, anti-corrosion material screening and corrosion inhibitor evaluation.

Description

Technical Field

[0001] This patent relates to the technical field of experimental equipment for oil and gas engineering under extreme conditions, specifically a ring-shaped experimental device for simulating internal corrosion of natural gas pipelines in deep-sea environments. This device can reproduce key operating conditions in deep-sea environments such as high pressure, temperature distribution, unidirectional ocean current impact, gas-liquid mixed transport with multiple flow patterns, and uniform mixing of complex media. It is suitable for experiments such as studying the internal corrosion mechanism of deep-sea natural gas pipelines, verifying anti-corrosion materials, and evaluating the performance of corrosion inhibitors, providing experimental support for the safe operation of deep-sea pipelines. Background Technology

[0002] As deep-sea oil and gas resource development extends to deeper waters, the corrosion of subsea natural gas pipelines, as core transportation facilities, directly impacts the safety and economics of gas field development. The deep-sea environment is characterized by high pressure, significant temperature gradients, directional ocean currents, complex gas-liquid mixed flow patterns within pipelines, and diverse media components. These factors work synergistically to create extremely complex corrosion mechanisms within pipelines, placing stringent demands on the comprehensiveness and accuracy of experimental simulation devices.

[0003] Existing experimental devices for simulating pipeline corrosion have several technical shortcomings: First, most devices cannot simulate the multi-flow conditions of gas-liquid mixing in actual deep-sea pipelines, and can only achieve single-phase medium transport. This results in significant deviations from the actual flow patterns of alternating slug flow and annular flow in pipelines, failing to reflect the impact of different flow patterns on corrosion rates. Second, pressure regulation capabilities are limited, with most devices designed for fixed pressure values ​​(e.g., 14 MPa), making it difficult to cover the pressure range from shallow seas (approximately 0.1 MPa) to ultra-deep seas (approximately 30 MPa). This leads to poor adaptability and fails to meet experimental requirements at different deep-sea depths. Third, the medium mixing methods are simple, relying on natural circulation or mechanical stirring. The mixing uniformity of natural gas, chemical agents, and high-mineralized water is insufficient, easily leading to local concentration deviations and failing to reproduce the actual medium distribution in pipelines. Fourth, temperature simulations often employ overall isothermal control or axial single-segment heating, resulting in low precision in temperature gradient control. Furthermore, they do not utilize the combination of spiral circulating water pipes and heating belts to achieve accurate temperature distribution simulation, leading to significant deviations from the actual temperature field of deep-sea pipelines. Summary of the Invention

[0004] This patent aims to overcome the shortcomings of existing technologies and provide a circular experimental device for simulating corrosion inside natural gas pipelines in deep-sea environments. It is suitable for simulating corrosion inside pipelines under multiple complex operating conditions, and can explore the corrosion behavior of different media and materials under conditions such as deep-sea high pressure, temperature gradient, ocean current impact, and gas-liquid mixed transport with multiple flow patterns. It can comprehensively evaluate the corrosion resistance of pipelines and provide precise experimental support for the study of corrosion mechanisms inside deep-sea pipelines, the verification of anti-corrosion materials, and the evaluation of corrosion inhibitors, thus ensuring the safe service of deep-sea pipelines.

[0005] To address the background technical problems, this patent adopts the following technical solution: It includes a natural gas mixing tank, a main pipeline, a corrosion test chamber, a detachable experimental pipeline, a control system cabinet, a computer, a gas-liquid mixing control system, an atomizer assembly, and an eccentric hammer striking assembly. The natural gas mixing tank and the corrosion test chamber form a circulation loop through the main pipeline. A circulation pump, valves, a flow sensor, and a pressure sensor are sequentially installed on the main pipeline, and a gas-liquid mixing control system is located near the corrosion test chamber. An atomizer assembly is installed inside the natural gas mixing tank. The detachable experimental pipeline inside the corrosion test chamber is connected to the main pipeline through a sealed connection assembly. A circulating water pipe is spirally wound around the outside of the pipeline, and a heating belt is wrapped around it. Three temperature sensors and a corrosion sensor are axially spaced. An eccentric hammer striking assembly is located on the outside of the corrosion test chamber, and a drive motor drives the eccentric hammer to periodically strike the chamber through a transmission rod. All components are connected to the control system cabinet, and the control system cabinet communicates with the computer.

[0006] The detachable experimental pipeline features a modular design, with at least one segmented corrosion test tube, all connected to the main pipeline via quick-release compression fittings. Quick-release flanges and locating pins are provided at both ends for precise docking and pre-fixation.

[0007] The sealing connection assembly includes nuts, front and rear sealing gaskets, and connecting bolts, and adopts a squeeze thread connection. High-pressure sealing can reach 35MPa.

[0008] The circulating water pipe is made of a high-pressure corrosion resistant material, and the S-shaped spiral winding ensures uniform temperature regulation. The heating belt works in conjunction with the circulating water control temperature, and three temperature sensors monitor the axial temperature gradient in real time.

[0009] The gas-liquid mixing control system can quickly switch between slug flow, annular flow and other flow patterns with a response time of ≤5s; the gas-liquid ratio of the atomizer component can be adjusted from 1:1 to 10:1, and the atomized particle size is 5 to 50μm, which improves the uniformity of medium mixing.

[0010] The eccentric hammer striking component has a striking frequency of 0.2Hz~3Hz and the force can be infinitely adjusted to accurately simulate the impact of ocean currents of different intensities in a single direction.

[0011] The corrosion sensor includes an electrochemical probe and an ultrasonic probe. The probe is evenly arranged around the circumference of the pipe wall, enabling non-contact corrosion monitoring. The lead wire interface is waterproof and sealed.

[0012] The detachable experimental piping can be made of X65 / X70 grade pipeline steel, 316L stainless steel, and titanium alloy, etc., to suit different experimental needs.

[0013] The control system cabinet integrates various control modules, and the panel is equipped with multiple monitoring and adjustment components. The pressure adjustment range is 0.1MPa~30MPa, the stability accuracy is ±0.05MPa, and the operation is intuitive and convenient.

[0014] The beneficial effects of this patent are: it comprehensively simulates the complex working conditions of deep-sea pipelines, accurately reproducing key environments such as high pressure, temperature gradient, and ocean current impact through the collaborative work of multi-functional modules; the modular design of the experimental pipeline makes it easy to disassemble and assemble, and the materials are optional, adapting to different experimental scenarios; dual signal acquisition and dedicated software analysis ensure comprehensive and accurate corrosion data; the device has a simple structure, is easy to operate, has a wide range of applications, and the obtained data is reliable, enabling real-time monitoring and mechanism research of corrosion inside pipelines, filling the gap in existing experimental technologies, and providing strong support for the research and development of corrosion protection technology for deep-sea pipelines. Attached Figure Description

[0015] Figure 1 is a schematic diagram of the overall structure of the experimental device of this patent; Figure 2 is an enlarged view of the structure of the detachable experimental pipe and the sealing connection assembly; Figure 3 is an enlarged view of the eccentric hammer impact assembly (simulating ocean current impact); Figure 4 is a schematic diagram of the connection structure between the gas-liquid mixing transport control system and the main pipeline; Figure 5 is an enlarged view of the atomizer assembly structure; Figure 6 is a schematic diagram of the installation and replacement structure of the corrosion test section; In Figure 1: 1-Natural gas mixing tank, 2-Circulating pump, 3-Main pipeline, 4a, 4b, 4c, 4d-Butterfly valves, 5-Flow sensor, 6-Pressure sensor, 7-Sealing connection assembly, 8-Temperature control related components (circulating water pipe + heating belt), 9-Corrosion sensor (9a-Electrochemical probe, 9b-Ultrasonic probe), 10-Corrosion test chamber, 11a, 11b-Ball valves, 12-Removable experimental pipeline (for ease of observation, the experimental pipeline is twice the size of the main pipeline, but the actual pipe diameter is the same), 17-Sensor lead interface, 18-Control system cabinet, 19-Computer, 20-Gas-liquid mixed transport control system, 21-Atomizer assembly, 22-Eccentric hammer impact assembly, 23-Circulating water tank, 24a, 24b, 24c-Temperature sensors, 25-Natural gas and carbon dioxide mixing tank, 26-Corrosion inhibitor tank; In Figure 2: 12-Removable experimental pipe, 13-Nut, 14-Internal rear sealing gasket, 15-Internal front sealing gasket, 16-Connecting bolt; In Figure 3: 22a - buffer block, 22b - hammer, 22c - connecting rod, 22d - eccentric cam, 22e - servo motor; In Figure 4: 3-main pipeline, 20-gas-liquid mixed transport control system (including 20a-flow distribution valve, 20b-flow pattern monitoring module, 20c-control unit); In Figure 6: 12-Removable test pipe, 27-Quick-release flange, 28-Sealing lock, 29-Positioning pin; The above figures are intended to clearly illustrate: the quick-release structure of the detachable experimental pipeline, the installation position of the elastic sealing gasket, and the distribution of locking components; the spiral winding method of the circulating water pipe, the wrapping state of the heating belt, and the installation positions of the three temperature sensors; the assembly position of the gas-liquid mixing and transport control system on the main pipeline and the composition of its core components; the connection relationship between the eccentric hammer impact assembly and the corrosion test chamber; the structural details of the atomizer assembly; and the installation and positioning structure and process of the corrosion test section. Detailed Implementation

[0016] Referring to the accompanying drawings, this patent specifically adopts the following implementation method: It includes a natural gas mixing tank (1), a main pipeline (3), a corrosion test chamber (10), a detachable experimental pipeline (12), a control system cabinet (18), a computer (19), a gas-liquid mixing control system (20), an atomizer assembly (21), and an eccentric hammer striking assembly (22). The natural gas mixing tank (1) and the corrosion test chamber (10) are connected by the main pipeline (3) to form a circulation loop. The main pipeline (3) is sequentially equipped with a circulation pump (2), a valve (4), a flow sensor (5), and a pressure sensor (6). The gas-liquid mixing control system (20) is located near the inlet of the corrosion test chamber (10) on the main pipeline (3). An atomizer assembly (21) is located at the inlet end of the natural gas mixing tank (1). A detachable experimental pipeline (12) is located inside the corrosion test chamber (10). The detachable experimental pipeline (12) is connected to the main pipeline (3) via a sealing connection assembly (7). The outer spiral is wound with a circulating water pipe (23), and the outer layer of the circulating water pipe (23) is wrapped with a heating belt. Three temperature sensors (24a, 24b, 24c) and a corrosion sensor (9) are arranged axially on the detachable experimental pipe (12). The corrosion test chamber (10) is provided with an eccentric hammer striking assembly (22) on the outside corresponding to the detachable experimental pipe (12). The assembly includes an eccentric hammer, a drive motor and a transmission rod. The drive motor is connected to the eccentric hammer through the transmission rod and drives it to periodically strike the side wall of the corrosion test chamber (10). The circulating pump (2), valve (4), flow sensor (5), pressure sensor (6), corrosion sensor (9), temperature sensors (24a, 24b, 24c), drive motor, gas-liquid mixing control system (20), and atomizer assembly (21) are respectively connected to the control system cabinet (18) through wires. The control system cabinet (18) is connected to the computer (19) through wires.

[0017] The installation, monitoring, and replacement system for the corrosion test section: The detachable test pipeline (12) adopts a modular design with a single section length of 300mm~800mm and an inner diameter consistent with the actual deep-sea pipeline (DN50~DN200). It can be combined into 1~3 sections according to experimental requirements. The test section is equipped with standardized quick-release flanges (27) at both ends, which, together with positioning pins (29), achieve precise docking. The sealing lock (28) can quickly complete the pre-fixation, and finally achieve high-pressure sealing (sealing pressure up to 35MPa) through the sealing connection assembly (7).

[0018] The material of the test section can be flexibly changed. The standard configuration is X65 grade pipeline steel, and X70 grade pipeline steel (suitable for deeper sea conditions), 316L stainless steel (suitable for high sulfur content media) and titanium alloy (for special corrosive environments) can also be selected. The replacement process is as follows: 1) Close the valves (11a, 11b) at the front and rear ends of the corrosion test chamber (10), and release the pressure in the test chamber to normal pressure through the pressure relief valve; 2) Remove the connecting bolts (16) of the sealing connection assembly (7), unlock the sealing lock (28), and guide the old test section out through the positioning pin (29); 3) Connect the new test section to the main pipeline (3) through the positioning pin (29), fasten the sealing lock (28), and install the internal front sealing gasket (15), internal rear sealing gasket (14) and nut (13) in sequence. Tighten the connecting bolts (16) to the preset torque (150N·m~250N·m depending on the material); 4) Close the pressure relief valve, slowly open the valves (11a, 11b) to conduct a pressure test, and proceed with the test process after ensuring there is no leakage.

[0019] The monitoring system for the experimental section is integrated into the inner and outer walls of the pipe. Three sets of electrochemical probes (9a) (spaced 120° apart) are evenly arranged along the circumference of the inner wall, corresponding axially to three temperature sensors (24a, 24b, 24c). The probe heads are flush with the inner wall of the pipe to avoid interfering with the flow pattern. An ultrasonic corrosion monitoring probe (9b) is installed at the corresponding position on the outer wall to achieve non-contact monitoring of corrosion thickness. All sensor leads are led out through the sensor lead interface (17) at the end of the pipe. The interface adopts a waterproof and sealed design to prevent media leakage.

[0020] Corrosion Signal Acquisition and Interpretation System: This device adopts a "dual signal synchronous acquisition" mode to ensure the comprehensiveness and accuracy of corrosion data. The specific acquisition methods and information types are as follows: Electrochemical probe signals: A three-electrode system was used (working electrode: experimental section material; reference electrode: Ag / AgCl; auxiliary electrode: platinum sheet). Linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and polarization curves were acquired via an electrochemical workstation at a sampling frequency of 1 time / minute. The signal types were weak current signals (nA level) and voltage signals (mV level). This signal can reflect the instantaneous corrosion rate and corrosion mechanism changes of the pipeline inner wall in real time. The LPR signal is directly used to calculate the corrosion rate (using the Stern-Geary equation), and the EIS signal is used to analyze the impedance characteristics of the corrosion product film.

[0021] Ultrasonic probe signal: The ultrasonic probe uses a 5MHz focusing probe to acquire pipe wall thickness data via pulse reflection method, with a sampling interval of 5mm (axial) × 10. o (Circumferential direction), the signal type is ultrasonic reflection signal. This signal can generate a three-dimensional map of the corrosion morphology of the inner wall of the pipe, accurately locate the position and depth of local corrosion (such as pitting corrosion), and the measurement accuracy can reach 0.01mm.

[0022] The interpretation of corrosion signals is achieved through dedicated software built into the computer (19), which includes: 1) Data preprocessing module: filtering (removing high-frequency noise), baseline correction (eliminating the influence of temperature drift) and normalization of the acquired raw signals; 2) Corrosion rate calculation module: calculating the instantaneous corrosion rate (unit: mm / a) based on the LPR signal and calculating the local corrosion rate based on ultrasonic data; 3) Corrosion mechanism analysis module: determining whether the corrosion process is controlled by charge transfer or diffusion by fitting the equivalent circuit of the EIS spectrum, and analyzing the influence of the medium on the corrosion type by combining the corrosion potential and passivation range of the polarization curve; 4) Visualization module: superimposing and displaying parameters such as corrosion rate, corrosion morphology, flow pattern, and pressure to generate a multi-dimensional correlation spectrum.

[0023] Experimental parameters and expected results design: The experimental duration of this device is set according to the experimental objectives. The basic corrosion rate test duration is 72 hours (3 complete cycles), the material comparison test duration is 168 hours (7 days), the corrosion inhibitor performance evaluation test duration is 336 hours (14 days), and the long-term corrosion mechanism study test duration can be extended to 720 hours (30 days). During the experiment, complete data is automatically stored once per hour. After key operating condition changes (such as flow pattern changes, pressure adjustments), sampling is intensified to once per 10 minutes.

[0024] To quantify the impact of different parameters on corrosion, a specific sensitivity experiment was designed. The specific scheme and expected results are as follows: The experiment investigated the effects of flow pattern and PTQV parameters. Flow pattern (slug flow / annular flow / laminar flow), liquid holdup (10%~80%), and liquid phase velocity (0.5~3 m / s) were used as variable parameters, while pressure (10 MPa), temperature gradient (5℃~20 ℃), CO2 content (5%), and salinity (35000 mg / L) were set as fixed parameters. The expected results of this experiment were that the corrosion rate of slug flow was the highest, 2~3 times higher than that of laminar flow, and the corrosion was most severe at a liquid holdup of 50%. A correlation model between PTQV parameters (pressure P, temperature T, flow rate Q, fluid volume V) and corrosion rate was also established.

[0025] The experiment focusing on the effects of corrosive media on relevant parameters used CO2 content (1%–15%), H2S content (0–5%), salinity (10,000–100,000 mg / L), and pH value (3–8) as variable parameters. Fixed parameters were set as follows: pressure 20 MPa, temperature 25 °C, laminar flow, and liquid phase velocity 1 m / s. The experiment anticipated a synergistic corrosion effect between CO2 and H2S, with the corrosion rate being 1.5 times higher than that of a single medium. The corrosion rate tended to stabilize after salinity exceeded 50,000 mg / L. For every 1 degree decrease in pH value, the corrosion rate increased by approximately 40%.

[0026] The material sensitivity experiment used the material of the test section (X65 / X70 / 316L / titanium alloy) as the core variable, with fixed parameters including pressure of 15 MPa, temperature gradient of 10℃~30℃, slug flow, CO2 content of 8%, and mineralization of 40000 mg / L. The expected results were that titanium alloy had the lowest corrosion rate (≤0.01 mm / a), X65 had the highest corrosion rate (0.15~0.2 mm / a), and 316L showed a significant advantage in high-sulfur environments, with a corrosion rate 80% lower than X70.

[0027] The experiment investigating the effects of ocean current impact used impact frequency (0.2–3 Hz) and impact force (low / medium / high) as variable parameters, while maintaining fixed experimental conditions including a pressure of 25 MPa, a temperature of 15 °C, annular current, a CO2 content of 10%, and a salinity of 50,000 mg / L. The experiment was expected to show that the corrosion rate peaked at an impact frequency of 2 Hz, 1.8 times higher than in the no-impact state; impact force was positively correlated with the corrosion rate and increased the incidence of localized corrosion by 40%.

[0028] Through the above sensitivity experiments, the following objectives are expected to be achieved: to clarify the influence weight of each key parameter in the deep-sea environment on the corrosion inside natural gas pipelines, and to establish a corrosion rate prediction model; to screen out the optimal pipeline material and corrosion inhibitor type suitable for different deep-sea depths (0~3000m); to reveal the corrosion mechanism under complex flow patterns such as slug flow, and to provide a theoretical basis for the design of corrosion protection for pipelines; and to form a standardized experimental method for simulating corrosion inside deep-sea pipelines, filling the gap in existing experimental techniques.

[0029] The removable experimental pipe (12) is at least one section, which is connected to the main pipe (3) or an adjacent experimental pipe through a sealing connection assembly (7). The sealing connection assembly (7) includes a nut (13), an inner rear sealing gasket (14), an inner front sealing gasket (15), and a connecting bolt (16). The nut (13) and the inner rear sealing gasket (14) are sequentially fitted into the removable experimental pipe (12). The small-diameter end of the inner front sealing gasket (15) is embedded in the removable experimental pipe (12). The connecting bolt (16) and the nut (13) are threadedly connected under compression. The removable experimental pipe (12) is made of X65 grade pipeline steel, which is consistent with the material commonly used in actual deep-sea pipelines, which can improve the reference value of the experimental results.

[0030] The circulating water pipe (23) is made of high-pressure corrosion resistant material, which can avoid corrosion by the experimental medium during long-term use. After spiraling forward in an S-shape to the bottom, it returns in an S-shape from the bottom to ensure full contact with the pipe to achieve uniform temperature regulation. The temperature regulation range of the heating belt is 2℃~20℃, matching the temperature environment of different areas in the deep sea. Three temperature sensors (24a, 24b, 24c) are evenly distributed along the axial direction of the detachable experimental pipe (12) to comprehensively monitor the axial temperature gradient of the pipe. The gas-liquid mixing control system (20) includes a flow distribution valve, a flow pattern monitoring module and a control unit, which can realize the switching and stable control of slug flow, annular flow and laminar flow. The flow pattern regulation response time does not exceed 5s, which meets the needs of rapid switching of working conditions in the experiment. Atomizer assembly (21) It is a high-pressure atomizer that combines media atomization and gas-liquid ratio regulation. The gas-liquid ratio regulation range is 1:1 to 10:1, and the atomization particle size range is 5 to 50 μm. It can effectively improve the mixing uniformity of natural gas and various agents. The pressure regulation range of the pressurization and stabilization system is 0.1 MPa to 30 MPa, and the pressure stability accuracy is ±0.05 MPa. It can accurately simulate the pressure conditions at different deep sea depths. The eccentric hammer impact component (22) has an impact frequency regulation range of 0.2 Hz to 3 Hz. The impact force can be steplessly adjusted by the power of the drive motor to match the impact of unidirectional ocean currents of different intensities.

[0031] The control system cabinet (18) integrates control modules for pressure sensor (6), flow sensor (5), corrosion sensor (9), temperature sensors (24a, 24b, 24c), drive motor, gas-liquid mixing control system (20), and atomizer assembly (21). Pressure sensor (6) and flow sensor (5) are embedded in the wall of the main pipe (3) to ensure accurate monitoring. The control system cabinet (18) panel is equipped with pressure gauge, flow meter, flow pattern display, gas-liquid ratio adjustment knob, temperature display panel, tap parameter adjustment key, start / stop switch, emergency stop switch, and experimental operation display panel, which facilitates intuitive operation and monitoring by experimental personnel.

[0032] Example 1: Under a single operating condition (deep-sea high pressure + temperature gradient + gas-liquid mixed transport single flow pattern + homogeneous mixing of media, without simulating ocean current impact), the experimental steps are as follows: Experimental section preparation and installation: Select X65 grade pipeline steel experimental section (DN100, length 500mm), grind the inner wall to Ra=0.8μm, install electrochemical probe (9a) and ultrasonic probe (9b); connect the experimental section to the system through positioning pin (29) and quick-release flange (27), and perform pressure test after sealing connection (pressure 12MPa, pressure holding for 30 minutes without leakage).

[0033] Medium preparation and pretreatment: According to the experimental requirements, natural gas (95%), carbon dioxide (5%), high-mineralized water (mineralization 35000mg / L, pH=6) and corrosion inhibitor (concentration 100mg / L) were injected into the natural gas mixing tank (1) in proportion. The mixture was then atomized by the atomizer assembly (21) in the tank. The gas-liquid ratio was adjusted to 5:1 and the atomized particle size was controlled in the range of 10~20μm to ensure uniform mixing of the medium.

[0034] Pressure and flow rate setting: The circulating pump (2) is operated through the control system cabinet (18) to set the experimental pressure to 10MPa (pressure stability accuracy ±0.05MPa) and the liquid flow rate to 1m / s. The flow rate of the medium in the main pipeline (3) is assisted by the valves (4a, 4d). The flow sensor (5) and the pressure sensor (6) monitor and provide feedback on the changes in pressure and flow rate in the pipeline in real time to ensure the stability of parameters.

[0035] Flow pattern control: The laminar flow mode is selected by the gas-liquid mixing control system (20). The flow pattern monitoring module provides real-time feedback on the stable state of the flow pattern (liquid holdup 30%). After the flow pattern stabilizes, the next experiment is carried out.

[0036] Temperature regulation: The circulating water pump drives the fluid circulation in the circulating water pipe (23), and the outer heating belt sets the axial temperature gradient (2℃~18℃) of the detachable experimental pipe (12). Three temperature sensors (24a, 24b, 24c) monitor the temperature at both ends and the middle of the pipe (2℃, 10℃, 18℃) respectively. The data is transmitted to the control system cabinet (18) in real time. If there is a deviation, the heating belt power and circulating water flow rate are automatically adjusted.

[0037] Data acquisition: The experiment lasted for 72 hours. The electrochemical probe (9a) collected the LPR signal every minute, the resistance plate (9b) recorded the resistance change every 12 hours, and the ultrasonic probe (9b) scanned the pipe wall thickness every 24 hours. All experimental data (pressure, flow rate, temperature, flow pattern parameters, corrosion rate, etc.) were synchronously transmitted to the computer (19) background software interface to realize real-time display, storage and preliminary analysis.

[0038] Experimental conclusion and data processing: After depressurization, the experimental section and the hanging plate were removed. The hanging plate was weighed after film removal (using pickling passivation solution, temperature 25℃, time 5 minutes). The average corrosion rate was calculated to be 0.12 mm / a. Combining electrochemical signals and ultrasonic data, the corrosion type was confirmed to be uniform corrosion, and the main component of the corrosion product film was FeCO3.

[0039] Example 2: Under multiple operating conditions (deep-sea high pressure + temperature gradient + unidirectional ocean current impact + gas-liquid mixed transport with multiple flow patterns + homogeneous mixing of media), the experimental steps are as follows: Test section preparation and installation: Select an X70 grade pipeline steel test section (DN100, length 500mm), complete the sensor installation and system connection according to the method in Example 1, and test the pressure at 22MPa (hold pressure for 30 minutes without leakage).

[0040] Medium configuration: According to the experimental scheme, a mixed medium containing natural gas (90%), carbon dioxide (8%), hydrogen sulfide (2%), and high-mineralized water (mineralization 50000mg / L, pH=4) was prepared. The gas-liquid ratio was adjusted to 3:1 by the atomizer assembly (21) to control the atomized particle size to 5~15μm and improve the uniformity of medium mixing.

[0041] High pressure and flow rate control: The circulating pump (2) is controlled by the control system cabinet (18), the experimental pressure is set to 20MPa, the flow rate of the medium in the main pipeline (3) is finely adjusted to 2m / s by the valve (4), and the pressure sensor (6) monitors the pressure change in real time to ensure that the pressure is stable at the set value.

[0042] Multi-flow pattern switching: The gas-liquid mixed transport control system (20) sequentially switches between three flow patterns: slug flow (liquid holdup 50%), annular flow (liquid holdup 20%), and laminar flow (liquid holdup 40%). Each flow pattern runs stably for 2 hours, and the flow pattern control response time is controlled within 5 seconds. During the switching process, the flow pattern status is observed in real time through the flow pattern display instrument.

[0043] Ocean current simulation: The impact frequency of the eccentric hammer impact component (22) is set to 1.5Hz by the background program of the computer (19). The impact force is set to medium intensity by adjusting the power of the drive motor according to the experimental requirements, to simulate the impact of the deep-sea unidirectional ocean current on the pipeline.

[0044] Temperature gradient maintenance: The axial temperature gradient of the pipeline (5℃~20℃) is set and maintained by the circulation water pipe (23) in conjunction with the heating belt. Three temperature sensors (24a, 24b, 24c) monitor the temperature distribution in real time. After the data is fed back to the control system, the operating parameters of the heating belt and the circulation water pump are automatically adjusted to ensure the temperature gradient is stable.

[0045] Comprehensive data acquisition: The experiment lasted for 168 hours. The flow sensor (5) and pressure sensor (6) continuously monitored the changes in pressure and flow rate in the pipeline. The corrosion sensor (9) collected corrosion data from the detachable experimental pipeline (12) in real time. All experimental parameters (pressure, flow rate, temperature, impact parameters, flow pattern parameters, gas-liquid ratio, corrosion rate, etc.) were synchronously transmitted to the computer (19) to realize real-time display, storage, curve plotting and data analysis of the data.

[0046] Experimental results: The corrosion rate was highest under slug flow conditions (0.25 mm / a), which was 2.1 times higher than that under laminar flow conditions; ocean current impact increased the local corrosion rate by 35%, and the maximum pitting depth reached 0.3 mm; the synergistic effect of CO2 and H2S made the corrosion rate 1.6 times higher than that under CO2 alone, and the corrosion product film was a mixed film of FeCO3 and FeS.

[0047] In summary, this annular experimental setup for simulating corrosion within a natural gas pipeline in a deep-sea environment is rationally designed and easy to operate. It comprehensively considers the core complex factors of actual deep-sea pipeline operation: a wide range of high-pressure environments, axial temperature gradients, unidirectional ocean current impacts, multi-flow patterns in gas-liquid mixing, and the need for uniform mixing of complex media. The atomizer assembly enables precise control of media atomization and gas-liquid ratio, improving mixing uniformity. The gas-liquid mixing control system achieves multi-flow pattern switching and stable control, closely mirroring actual transport conditions. The combination of a spiral circulating water pipe and heating belt, along with three temperature sensors, accurately reproduces the temperature gradient distribution. An eccentric hammer impact assembly simulates unidirectional ocean current impacts, allowing for flexible control. A pressurization and stabilization system enables wide-range pressure regulation, adapting to different deep-sea depths. A standardized quick-release structure facilitates easy replacement of experimental sections made of different materials, improving experimental efficiency. A triple corrosion signal acquisition system and dedicated interpretation software enable comprehensive acquisition and precise analysis of corrosion data. A specialized sensitivity experiment design quantifies the influence of various parameters on corrosion. This experimental device has a simple structure and wide applicability. The experimental data obtained are accurate and reliable. It can be used for real-time monitoring and mechanism research of corrosion in pipelines in the laboratory, providing a precise reference for the research and development of corrosion protection technology for deep-sea natural gas pipelines.

Claims

1. A loop experimental device for simulating the corrosion in a natural gas pipeline in a deep sea environment, characterized in that: The utility model relates to a natural gas corrosion test device, which comprises a natural gas mixing box (1), a main pipeline (3), a corrosion test box (10), a detachable experimental pipeline (12), a control system cabinet (18), a computer (19), a gas-liquid mixed transportation control system (20), an atomizer assembly (21) and an eccentric hammer knocking assembly (22), the natural gas mixing box (1) is connected with the corrosion test box (10) through the main pipeline (3) and forms a circulating loop, the main pipeline (3) is sequentially provided with a circulating pump (2), a valve (4), a flow sensor (5), a pressure sensor (6), and the gas-liquid mixed transportation control system (20) is arranged near the inlet of the corrosion test box (10).

2. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The detachable experimental pipeline (12) is connected with the main pipeline (3) or adjacent experimental pipelines through a sealing connection assembly (7) and can adapt to the replacement requirements of experimental sections made of different materials such as X65, X70, X80 pipeline steel and 316L stainless steel.

3. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The sealing connection assembly (7) comprises a nut (13), an inner rear sealing gasket (14), an inner front sealing gasket (15) and a connecting bolt (16), the nut (13) and the inner rear sealing gasket (14) are sequentially sleeved into the detachable experimental pipeline (12), the small-diameter end of the inner front sealing gasket (15) is embedded into the detachable experimental pipeline (12), and the connecting bolt (16) is threadedly connected with the nut (13) under extrusion, thereby realizing the quick sealing and dismounting of the experimental section.

4. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The detachable experimental pipeline (12) is made of X65 pipeline steel, and can be replaced by X70 pipeline steel, 316L stainless steel and other materials according to experimental requirements. The inner wall of the pipeline is provided with a sensor mounting groove for fixing a corrosion monitoring probe.

5. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The circulating water pipe (23) is made of high-pressure corrosion-resistant material, spirally wound from the upper end along an S-shaped transmission, and returns from the lower end in the same way. The temperature regulation range of the heating belt is 20-60 DEG C, which can jointly regulate the temperature with the circulating water pipe. Three temperature sensors (24a, 24b, 24c) are uniformly distributed along the axis of the detachable experimental pipeline (12).

6. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The gas-liquid mixed transportation control system (20) includes a flow distribution valve, a flow pattern monitoring module (including a flow sensor and a pressure sensor), and a control unit, which can realize the switching and stable control of slug flow, annular flow and stratified flow. The flow pattern regulation response time is not more than 5s.

7. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The atomizer assembly (21) is a high-pressure atomizer with medium atomization and gas-liquid ratio control functions. The gas-liquid ratio control range is 1:1-10:1, and the atomized particle size range is 5-50μm.

8. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The pressure regulation range of the pressurizing and stabilizing system is 0.1-30MPa.

9. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The frequency regulation range of the eccentric hammer knocking assembly (22) is 0.2-3Hz, and the knocking force can be steplessly adjusted by the power of the driving motor.

10. The loop experimental device for simulating the internal corrosion of a natural gas pipeline in a deep sea environment according to claim 1, characterized in that: The corrosion sensor (9) includes an embedded electrochemical probe in the pipeline inner wall and an ultrasonic corrosion monitoring probe, which can synchronously collect electrochemical signals and physical corrosion signals.

Images