Corrosion test device and method for simulating dry-wet alternating corrosion of buried pipeline under thermal insulation layer

Abstract

The present application belongs to the technical field of material corrosion science and protection engineering, and discloses a kind of simulation of buried pipeline under thermal insulation layer dry-wet alternating corrosion experimental device and method, solve the technical problems of sample position variation, electrochemical monitoring distortion in existing dry-wet alternating simulation, cannot consider anaerobic microbial environment, thermal insulation layer interface effect multi-factor coupling simulation.The core of the device adopts the design of periodic tilting of box around stationary main shaft, realizes dynamic dry-wet alternating by liquid surface relative to fixed sample lifting, can stably maintain anaerobic environment in the box, and reduce the interface effect of thermal insulation layer.The present application realizes high-fidelity simulation of dry-wet alternating, adapts to microbial synergistic corrosion simulation, provides reliable experimental platform for pipeline corrosion mechanism research and protection technology evaluation, and has wide applicability.

Description

Technical Field

[0001] This invention belongs to the field of experimental technology of materials corrosion science and protective engineering. More specifically, it relates to an experimental apparatus and method for simulating the alternating dry and wet corrosion of buried pipelines under insulation layers. It is particularly suitable for the corrosion simulation experiment of buried insulated pipelines coupled with alternating dry and wet conditions and the interface effect of insulation layers. It can also be extended to the simulation of alternating dry and wet corrosion of pipelines under the action of other microorganisms such as iron bacteria and sulfur oxidizing bacteria or pure chemical action. Background Technology

[0002] Buried insulated pipelines are critical infrastructure for oil and gas transportation and urban heating systems, and their operational reliability is crucial to public safety and environmental protection. These pipelines typically use rigid polyurethane foam or similar materials as the external insulation layer. In complex soil environments, this insulation layer is prone to damage or aging, leading to water seepage. Moisture accumulates in the sealed gap between the pipeline's outer wall and the insulation layer, undergoing periodic evaporation and condensation due to temperature fluctuations, creating a localized environment of alternating wet and dry conditions. This process not only directly accelerates electrochemical corrosion but also causes Cl... - SO4² - The local concentration of corrosive ions creates an extremely harsh chemical microenvironment.

[0003] Numerous studies have shown that in this environment, there is a strong synergistic and positive feedback effect between the physical alternation of wet and dry conditions, the aging and degradation of insulation materials, and the microbial corrosion activity represented by sulfate-reducing bacteria (SRB). SRB are typical anaerobic corrosive microorganisms whose metabolism can reduce sulfates to highly corrosive sulfides, significantly accelerating localized corrosion. Crucially, the hygrothermal stress generated by the alternating wet and dry cycles promotes the hydrolysis of insulation materials such as polyurethane, releasing small organic molecules such as polyols and amines. These substances can directly provide carbon and nitrogen sources for SRB, forming a vicious cycle of "material degradation → nutrient release → microbial proliferation → intensified corrosion → further material damage." This multi-layered coupling of physical, chemical, material, and biological factors is the core mechanism leading to localized perforation and early failure of pipelines under insulation layers, posing a significant challenge to pipeline integrity management.

[0004] Current laboratory simulation methods for alternating wet and dry corrosion of buried pipelines all employ traditional designs involving active sample lifting or media extraction / filling to achieve the switching between wet and dry states. This type of design suffers from core technical defects, which are also the core technical problems this invention aims to solve: When using sample lifting, the spatial position of the sample and electrode changes with the wet-dry transition, making it impossible to guarantee the stability of the spatial reference for electrochemical monitoring, leading to distorted monitoring data and poor repeatability. When using media extraction / filling, it easily causes disturbance to the experimental liquid within the chamber, not only failing to replicate the natural rise and fall of the liquid level during actual operation but also disrupting the growth environment of microorganisms, making it difficult to achieve coupled simulation of dynamic wet-dry alternation and microbial corrosion. Furthermore, existing technologies conduct wet-dry alternation electrochemical experiments and microbial anaerobic corrosion experiments separately. Wet-dry alternation experimental devices for electrochemical corrosion cannot provide the strictly anaerobic environment necessary for SRB survival; static anaerobic bottle experiments for microbial corrosion cannot simulate the real dynamic wet-dry alternation process and its regulatory effect on SRB activity and electrochemical behavior, and generally lack the ability to monitor the microenvironment of the corrosion interface in situ in real time.

[0005] In summary, existing technologies cannot solve the core problem of fixed sample position in dynamic wet-dry alternation simulation, nor can they achieve multi-factor coupled simulation of dynamic wet-dry alternation, strict anaerobic microbial environment, and insulation layer interface effects, making it difficult to reflect the true laws of multi-factor synergistic effects under actual working conditions. Therefore, a novel wet-dry alternation simulation design is urgently needed to overcome the technical shortcomings of sample position variation, while integrating functions such as anaerobic environment maintenance, insulation layer interface simulation, and real-time electrochemical monitoring to achieve high-fidelity coupled simulation of multiple factors. This would provide a reliable basis for in-depth understanding of pipeline failure mechanisms under insulation layers and for the development of protection technologies. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a highly integrated corrosion experimental device and method for realistically simulating the alternating wet and dry processes of buried pipelines under insulation layers. It fundamentally solves the core technical problems of sample position variation and electrochemical monitoring distortion caused by traditional wet-dry alternation simulation methods. Furthermore, through structural optimization, it achieves the maintenance of an anaerobic microbial environment and the simulation of insulation layer interface effects, adapting to the coupled simulation requirements of wet-dry alternation and microbial synergistic corrosion. This provides a reliable experimental platform for in-depth research on the multi-factor synergistic corrosion mechanism of pipelines under insulation layers, as well as for evaluating materials and protection technologies.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a corrosion test apparatus for simulating alternating wet and dry conditions of buried pipelines under insulation layers, comprising: Main spindle, which is stationary; A housing, which is movably fitted onto the main shaft, contains an experimental liquid and a sample to be simulated for corrosion, and the sample is fixed relative to the main shaft. A driving mechanism is connected to the housing. The driving mechanism is used to drive the housing to periodically reciprocate around the main shaft, so that the liquid level of the experimental liquid in the housing rises and falls relative to the sample, thereby realizing a dry-wet alternation cycle.

[0008] Optionally, the box body is an integrally sealed structure, and a sealing structure is provided at the joint between the main shaft and the box body to ensure the sealing performance during the tilting process of the box body around the main shaft; the box body is provided with an air inlet, through which protective gas is introduced into the box body to realize and maintain the anaerobic environment inside the box body.

[0009] Optionally, an insulating mounting base is fixed to the main shaft, the sample is fixed to the insulating mounting base, and a counter electrode and a reference electrode adapted to the electrochemical monitoring equipment are also installed on the insulating mounting base. The counter electrode, the reference electrode and the sample are used in conjunction for electrochemical monitoring of corrosion state.

[0010] Optionally, the insulating mounting base is an L-shaped component made of polytetrafluoroethylene, and its vertical connecting arm can be locked to any position in the axial direction of the main shaft by a split locking sleeve. The horizontal mounting plate is used to fix the sample, the counter electrode and the reference electrode. The reference electrode has a capillary, and the tip of the capillary maintains a preset distance from the working surface of the sample.

[0011] Optionally, the drive mechanism includes an electric push rod, a metal back plate is fixed to the back of the housing, a hinge seat is provided on the metal back plate, the tail of the electric push rod is hinged to an external fixed base, and the end is hinged to the hinge seat through a universal joint. The housing is driven to tilt around the main shaft by the extension and retraction of the electric push rod. The electric push rod is a DC electric push rod with a built-in limit switch. It adopts worm gear transmission and has a self-locking characteristic. The electric push rod is connected to a time relay, which is used to set the duration of the wet period and the dry period to realize the automatic cyclic control of the box tilting.

[0012] Optionally, the chamber is a cavity structure made of high-strength, corrosion-resistant transparent material. The air inlet is located at the top of the chamber, which also has a liquid operation port, a gas outlet, and a spare interface. An operating door is located on the front of the chamber. The operating door is equipped with a quick-lock mechanism and a silicone rubber sealing gasket, and each interface is equipped with an integrated seal to achieve overall sealing of the chamber. The liquid operation port is used for injecting and sampling experimental liquids, the gas outlet is used for headspace gas collection, and the operating door is used for sample loading and unloading and device debugging.

[0013] Optionally, the experimental apparatus further includes a thermal insulation material used to cover the working surface of the sample. The thermal insulation material has a groove that matches the sample, and the working surface of the sample is embedded in the groove. The gaps between the edge of the sample, the lead-out part of the wire and the thermal insulation material are sealed with sealant.

[0014] Secondly, the present invention provides a method for simulating corrosion testing of buried pipelines under insulation layers during alternating wet and dry conditions, using the experimental apparatus described in the first aspect, and comprising the following steps: S1. Sample fixing: Fix the sample relative to the main shaft, inject the experimental liquid into the chamber, and when the chamber is horizontal, the experimental liquid completely submerges the sample. Seal all operating ports and interfaces of the chamber to form an overall sealed structure. S2. Establishment of anaerobic environment: Protective gas is introduced into the chamber through the air inlet on the chamber to replace the air in the chamber and maintain a slight positive pressure, thereby establishing and maintaining an anaerobic environment in the chamber. S3. Microbial inoculation: Inoculate the experimental liquid inside the chamber with corrosive microbial solution to bring the solution to the preset initial concentration. S4. Alternating wet and dry cycle operation: Start the drive mechanism to drive the chamber to rotate back and forth around the main shaft at a preset cycle, so that the liquid level of the experimental liquid in the chamber rises and falls periodically relative to the sample, thus realizing the alternating wet and dry cycle. S5. Corrosion Monitoring and Analysis: The corrosion status of the samples is monitored during the alternating wet and dry cycle. After the experiment, the samples are characterized and comprehensively analyzed to obtain the law of alternating wet and dry cycle and microbial synergistic corrosion of buried pipelines.

[0015] Optionally, in step S1, before the sample is fixed, it is ultrasonically cleaned and dried with acetone and anhydrous ethanol, and the initial size and weight are recorded; the experimental liquid is sterilized by high temperature and high pressure and deoxygenated by nitrogen for at least 1 hour, and then aseptically injected through the liquid operation port of the chamber. In step S2, the protective gas is high-purity nitrogen, and nitrogen is continuously introduced into the chamber for 2-4 hours to completely replace the air inside the chamber.

[0016] Optionally, in step S3, the corrosive microorganism is sulfate-reducing bacteria, the inoculated bacterial solution is a concentrated solution of sulfate-reducing bacteria in the logarithmic growth phase, and the initial concentration of sulfate-reducing bacteria in the experimental liquid inside the chamber after inoculation is 10. 5 cells / mL, before inoculation, the chamber was placed in a constant temperature environment and stabilized to the target temperature of 35.0±1℃; In step S4, the preset cycle for tilting the chamber is 2 hours for the wet period and 10 hours for the dry period, or the duration of the wet and dry periods can be adjusted according to experimental requirements. In step S5, after the chamber has stabilized for 30 minutes in the humid period, the open circuit potential and electrochemical impedance spectroscopy are monitored using an external electrochemical monitoring device. Depending on the experimental requirements, the pH, redox potential, ion concentration, and microbial count of the experimental liquid are aseptically sampled through the liquid operation port, or the headspace gas is collected through the gas outlet for component analysis. After the experiment, the corrosion products are removed according to GB / T16545, the corrosion rate is calculated, and the synergistic corrosion law is obtained by combining the correlation data of sample micromorphology and corrosion product component analysis.

[0017] The beneficial effects of this invention are as follows: The experimental apparatus of this invention is designed with the core feature of the box reciprocating around a stationary main axis. Dynamic wet-dry alternation is achieved by raising and lowering the sample with the liquid surface relatively fixed. This fundamentally avoids the defects of sample position change and electrochemical monitoring distortion caused by traditional sample raising and lowering and medium pumping methods. It ensures that the spatial position of the sample and electrode is absolutely fixed during the experiment, laying a solid foundation for obtaining reliable and repeatable real-time electrochemical monitoring data and realizing a technological breakthrough in the wet-dry alternation simulation method.

[0018] The experimental apparatus of this invention, through its supporting structures such as sealing structures, air inlets, and insulation materials, flexibly achieves the maintenance of a strictly anaerobic environment and the simulation of the interface effect of the insulation layer. It is suitable for simulating the synergistic corrosion of microorganisms such as sulfate-reducing bacteria with alternating wet and dry conditions, and can also be directly used for simulating the alternating wet and dry corrosion of buried pipelines under purely chemical action, demonstrating strong adaptability.

[0019] With the addition of a subordinate structure, this invention can simultaneously realize real dynamic wet-dry alternation, strict anaerobic microbial environment control, insulation material interface simulation, and active corrosion electrochemical environment within a single device. It breaks the existing research paradigm that artificially separates physical, chemical, and biological processes, and truly restores the actual corrosion conditions of buried insulation pipelines, accurately reflecting the laws of multi-factor synergistic effects.

[0020] This invention provides standardized experimental procedures from sample preparation to comprehensive analysis. It allows for flexible selection of whether to conduct anaerobic environment creation, microbial inoculation, and insulation layer interface simulation according to research needs. The experimental results can be quantitatively analyzed from multiple dimensions, such as corrosion rate, electrochemical parameters, microbial biomass, and the composition and morphology of corrosion products. It also has good repeatability and comparability, providing a reliable experimental basis for in-depth research on pipeline corrosion mechanisms under insulation layers, evaluation of materials and protection technologies. It has important engineering application value for pipeline integrity management in the oil and gas and heating industries.

[0021] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0022] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0023] Figure 1 A schematic structural diagram of a corrosion test apparatus for simulating alternating wet and dry conditions of buried pipelines under insulation layers according to Embodiment 1 of the present invention is shown.

[0024] Figure 2 A partial schematic structural diagram of the experimental apparatus for simulating the alternating wet and dry corrosion of buried pipelines under the insulation layer according to Embodiment 1 of the present invention is shown.

[0025] Figure 3 A schematic structural diagram of an insulating mounting base, a sample, a counter electrode, and a reference electrode according to Embodiment 1 of the present invention is shown.

[0026] Figure 4 A schematic diagram showing the positional relationship between the tank and the liquid surface under wet conditions according to Embodiment 1 of the present invention is shown.

[0027] Figure 5 A schematic diagram showing the positional relationship between the tank and the liquid surface under the dry state according to Embodiment 1 of the present invention is shown.

[0028] Figure 6 A flowchart of Embodiment 2 of the present invention is shown.

[0029] Figure 7 The macroscopic morphology of the insulation layer after 14 days of X70 corrosion test under the insulation layer according to Embodiment 3 of the present invention is shown.

[0030] Figure 8 The macroscopic morphology of the sample after 14 days of X70 corrosion test under the insulation layer according to Example 3 of the present invention is shown.

[0031] Figure 9 The SEM image of the sample surface after 14 days of X70 corrosion test under the insulation layer according to Embodiment 3 of the present invention is shown.

[0032] Figure 10 The SEM image of the surface of the X70 corrosion test sample under the insulation layer after 14 days of rust removal is shown in Embodiment 3 of the present invention.

[0033] Explanation of reference numerals in the attached figures: Main spindle 1; housing 2; air inlet 3; liquid operation port 4; gas outlet 5; spare interface 6; operation door 7; experimental liquid 8; sample 9; counter electrode 10; reference electrode 11; drive mechanism 13; insulating mounting base 14; electrochemical monitoring equipment 15; support frame 16; high-purity nitrogen source 17; constant temperature water bath 18. Detailed Implementation

[0034] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0035] Example 1

[0036] like Figures 1-5 As shown, this embodiment provides a corrosion test device for simulating the alternating dry and wet conditions of buried pipelines under insulation layers. The core design is that the box 2 reciprocates periodically around the stationary main axis 1. The dynamic alternation of dry and wet conditions is achieved by changing the relative position of the liquid surface and the sample 9. This fundamentally avoids the technical defects of traditional sample 9 lifting and media extraction methods. At the same time, it can be equipped with a sealing structure, electrode fixing unit, environmental control unit, monitoring and sampling unit, insulation materials, etc., to realize multi-factor coupled simulation and real-time monitoring.

[0037] As the core static spatial reference axis of the entire device, the main shaft 1 is made of high-strength stainless steel solid optical axis and is stationary on the external fixed base. It remains absolutely stationary throughout the experiment and serves as the fixed carrier for sample 9 and the electrode, ensuring that the position of sample 9 does not change, thus laying the foundation for real-time stable electrochemical monitoring.

[0038] The housing 2, which is mounted on the main shaft 1, is the core environmental carrier for corrosion simulation. Its main body is made of high-strength, corrosion-resistant transparent material, preferably polymethyl methacrylate (PMMA), also known as acrylic glass. It has a rectangular cavity structure with a top wall thickness of at least 20mm and other wall thicknesses of at least 15mm to ensure overall strength. The housing 2 can be designed as a completely sealed structure, with a rectangular operating door 7 on the front as a dedicated channel for loading and unloading samples 9. The top can integrate all necessary sealing interfaces, such as an air inlet 3, a liquid operating port 4, a gas outlet 5, and a spare interface 6. Each interface can be fitted with an integrated seal. The operating door 7 can use a quick-lock mechanism in conjunction with a silicone rubber sealing gasket, preferably a toggle-type clamp, to achieve complete sealing of the housing 2. The back of chamber 2 is fixedly connected to an integral metal backplate made of 5mm-6mm thick 304 stainless steel. The backplate is bonded to the outer surface of chamber 2 with epoxy resin structural adhesive and secured with countersunk screws along the perimeter. The screws do not penetrate the chamber wall, forming a high-strength rigid connection. A hinge seat is located in the center of the metal backplate for connecting with the drive mechanism 13 to transmit driving force. Chamber 2 can hold the experimental liquid 8 and the sample 9 to be simulated for corrosion. It can freely tilt around the main shaft 1 to achieve alternating wet and dry cycles. The transparent chamber 2 allows for direct observation of the wet and dry state of the sample 9, liquid level changes, and the experimental process, facilitating monitoring and troubleshooting. The integrated design of the front operating door 7 and the multiple interfaces on the top ensures convenience for all experimental operations, including sample 9 loading and unloading, medium filling, gas replacement, liquid sampling, and headspace gas collection. Multiple sealing structures work together to achieve complete airtightness of chamber 2, ensuring the stability of the anaerobic environment during long-term experiments, eliminating leakage and the risk of external bacterial contamination.

[0039] The drive mechanism 13 preferably uses a direct drive scheme with an electric actuator, but other drive methods such as linear drive with rocker arm structure, crank-rocker mechanism, and lead screw-nut mechanism can also be used. The electric actuator is a DC electric actuator with a built-in limit switch. Its tail is mounted on the crossbeam of the external fixed foundation through a hinge support, and the end of the actuator is connected to the hinge seat of the metal back plate through a universal joint. The electric actuator uses worm gear transmission and has a self-locking characteristic. After power failure, the actuator position remains unchanged, thus reliably locking the housing 2 in the current position. With the built-in limit switch of the actuator, the power supply can be automatically cut off when the horizontal wet period or the preset tilt angle dry period position is reached, achieving precise positioning and locking. The electric actuator is connected to a time relay, which can set the duration of the wet period and dry period. It automatically switches the power supply direction according to the set time to achieve unattended automatic cycle, and can also be manually controlled by a button. The electric push rod can directly drive the chamber 2 to tilt around the main shaft 1 by extending and retracting. When the push rod extends, the chamber 2 tilts forward, and the sample 9 rises relative to the liquid surface to enter the dry phase. When the push rod retracts, the chamber 2 returns to the horizontal position, and the sample 9 is re-immersed to enter the wet phase. This drive structure has a short transmission path and fast response. With the built-in limit switch, the position of the chamber 2 can be accurately positioned. The self-locking characteristic of the worm gear drive can stably lock the chamber 2 in the target position, avoiding liquid surface fluctuations caused by the shaking of the chamber 2 during tilting, and ensuring the stability of the dry and wet state switching. The time relay can flexibly set the duration of the wet and dry phases to realize fully automatic cyclic control of the tilting of the chamber 2, supporting unattended long-cycle corrosion experiments and greatly reducing the intensity of experimental operations.

[0040] The aforementioned core structure fundamentally overturns the traditional dry-wet alternation simulation method of sample 9 lifting and media extraction, and completely solves the core technical defects of electrochemical monitoring spatial reference instability, data distortion and poor repeatability caused by sample 9 position changes; sample 9 remains absolutely stationary throughout the process, ensuring that the spatial position of sample 9 and corrosion interface is constant during the dry-wet alternation process, and truly restores the dry-wet alternation process of pipeline fixed and liquid surface fluctuating in the actual working conditions of buried pipeline, realizing high-fidelity simulation of dry-wet alternation, and providing a stable and reliable core platform for corrosion experiments.

[0041] A sealing structure is provided at the mating point between the main shaft 1 and the housing 2. The sealing structure includes a deep groove ball bearing and rotating shaft lip seals located on both sides of the bearing, forming a reliable rotary dynamic seal assembly. The inner ring of the bearing is fixed to the main shaft 1, and the outer ring of the bearing is fixed to the housing 2, thereby allowing the housing 2 to rotate freely around the stationary main shaft 1, while ensuring the sealing performance of the housing 2 during the tilting process around the main shaft 1. Combined with the overall sealed structure of the housing 2, an anaerobic environment can be maintained. This rotary dynamic seal, in conjunction with the overall sealed structure of the housing 2, can ensure the sealing performance of the housing 2 throughout the tilting process, eliminating the risk of gas leakage. Combined with the air inlet 3 on the housing 2, a strictly anaerobic environment can be established and maintained stably for a long time within the housing 2, fully meeting the survival requirements of anaerobic corrosive microorganisms such as sulfate-reducing bacteria. This solves the industry pain point that traditional wet-dry alternation devices cannot be compatible with anaerobic microbial corrosion experiments, realizing the coupled simulation of wet-dry alternation and microbial corrosion.

[0042] An insulating mounting base 14 is fixedly connected to the main shaft 1. The sample 9 is fixed to the insulating mounting base 14. The insulating mounting base 14 is also equipped with a counter electrode 10 and a reference electrode 11 adapted to the electrochemical monitoring equipment 15. The sample 9, counter electrode 10, and reference electrode 11 are all relatively stationary with respect to the main shaft 1. The wires of all electrodes can be led out from the interface at the top of the housing 2 without leakage and connected to the external electrochemical monitoring equipment 15 to ensure the stability of electrochemical monitoring. The insulating mounting base 14 is an L-shaped component made of polytetrafluoroethylene. Its vertical connecting arm can be locked to any axial position of the main shaft 1 by a split locking sleeve. The horizontal mounting plate is used to fix the sample 9, counter electrode 10, and reference electrode 11. The reference electrode 11 is a reference electrode with a capillary tube. Its capillary tip maintains a preset distance from the working surface of the sample 9. A standard thickness shim can be used to assist in positioning. A 1.5mm shim is preferred. After locking, the shim can be removed. The integrated fixing of the working electrode (sample 9), counter electrode 10, and reference electrode 11 is achieved through the insulating mounting base 14. The three electrodes remain relatively stationary with respect to the main shaft 1 throughout the entire process, completely eliminating interference from changes in the relative positions of the electrodes during wet-dry switching. This ensures a constant spatial reference for electrochemical testing and significantly improves the accuracy, stability, and repeatability of monitoring data such as open-circuit potential and electrochemical impedance spectroscopy, providing precise in-situ monitoring data support for corrosion mechanism research. The polytetrafluoroethylene (PTFE) material possesses excellent insulation and corrosion resistance, avoiding interference from the device itself in corrosion experiments. The L-shaped structure and segmented locking sleeve design allow the mounting base to be locked at any position along the main shaft 1 axis, flexibly adapting to different liquid level heights and the experimental requirements of multiple parallel samples 9, facilitating installation and debugging. The reference electrode 11 with a capillary tube allows for precise control of the distance to the working surface of sample 9, effectively reducing the ohmic voltage drop of the solution during electrochemical testing and further improving the accuracy of electrochemical monitoring data.

[0043] This device is equipped with an environmental control unit, enabling precise control of temperature and atmosphere. For temperature control, the entire chamber 2 can be placed in a constant-temperature environment, accurately setting and stabilizing the experimental temperature to simulate actual working conditions. For atmosphere control, the air inlet 3 at the top of chamber 2 can be connected to a high-purity nitrogen source 17, continuously supplying high-purity nitrogen into the completely sealed chamber 2 through inlet 3. This maintains a slight positive pressure within chamber 2, completely replacing the air and achieving and strictly maintaining an anaerobic environment that meets the survival requirements of anaerobic microorganisms such as sulfate-reducing bacteria. All external pipelines connected to the top interface of chamber 2 have buffer sections provided near the connection point using stainless steel corrugated pipes or spiral protective sleeves to accommodate changes in the tilt of chamber 2.

[0044] This device is equipped with a monitoring and sampling unit, which can realize multi-dimensional data acquisition of the corrosion process. In terms of electrochemical monitoring, the working electrode, counter electrode 10, and reference electrode 11 are pre-installed in a fixed spatial relationship through the electrode fixing unit. After the wires are sealed and led out, they are connected to the external electrochemical monitoring equipment 15. The electrochemical monitoring equipment 15 is preferably an electrochemical workstation, which only performs open circuit potential and electrochemical impedance spectroscopy measurements during the wet period. If necessary, the potentiodynamic polarization curve is also measured to achieve real-time and stable monitoring of corrosion electrochemical signals. In terms of physicochemical and biological sampling, the liquid operation port 4 at the top of the chamber 2 can be used with a sterile syringe to periodically sample according to experimental needs to analyze pH, redox potential, ion concentration, and sulfate-reducing bacteria count, or the headspace gas can be collected through the gas outlet 5 for component analysis.

[0045] This device is also equipped with insulation material, which uses rigid polyurethane foam or other specified insulation materials consistent with actual engineering projects. A groove matching the sample 9 is machined into the insulation material, and the working surface of the sample 9 is embedded in the groove. Gaps between the edge of the sample 9, the lead-out part of the wire, and the insulation material are sealed with sealant. Through insulation material and encapsulation structure consistent with actual engineering projects, the contact interface between the outer wall of the buried insulated pipe and the insulation layer is replicated 1:1. This allows for realistic simulation of actual working conditions such as insulation layer hydrolysis, local concentration of corrosive ions, and release of organic nutrients. It overcomes the shortcomings of traditional experimental devices that cannot reproduce the influence of insulation layer interface effects on the corrosion process, making the corrosion simulation results more consistent with engineering practice and significantly improving the engineering application value of the experimental results.

[0046] This device is also equipped with a support frame 16, welded from steel plates, providing a stable mounting reference for the main body. Its core structure includes: a left and right side plate arranged parallel to each other, three top crossbeams connecting the tops of the left and right side plates, and a back crossbeam connecting the backs of the left and right side plates. The interior of the support frame 16 is an open space to accommodate the housing 2. A hinge support is provided on the back crossbeam for mounting the tail of the electric push rod. The electric push rod is located in the dry area behind the frame. The position of the hinge support must ensure that the extension and retraction direction of the push rod matches the movement trajectory of the hinge seat on the back of the housing 2. The main shaft 1 is fixedly mounted at both ends to the upper part of the left and right side plates. The top crossbeam and the back crossbeam together ensure the overall rigidity of the frame, ensuring that the supports at both ends of the main shaft 1 remain precisely coaxial under long-term cyclic loading, thereby ensuring the smooth rotation of the housing 2 and the absolute stability of the sample 9's position.

[0047] This device is also equipped with a constant temperature water bath 18. The lower part of the box 2 is placed in the constant temperature water bath 18, which provides a constant temperature environment for the box 2.

[0048] Example 2

[0049] Based on the apparatus of Example 1, this example provides a method for simulating the corrosion of buried pipelines under insulation layers under alternating wet and dry conditions. The method involves a complete process including sample preparation (9), system assembly, addition of experimental liquid (8), establishment of an anaerobic environment, microbial inoculation, alternating wet and dry cycle operation, and comprehensive testing and analysis. The simulation of corrosion under insulation layers under alternating wet and dry conditions can be performed selectively according to experimental requirements, and specifically includes the following steps: S1. Specimen 9 Fixation: The pipe steel is processed into standard specimen 9. After ultrasonic cleaning and drying with acetone and anhydrous ethanol, the initial dimensions and weight are accurately measured and recorded. The working electrode wires are bonded to the pre-reserved positions on the non-working surface of specimen 9 using conductive silver paste, or micro-spot welding can be used. If it is necessary to simulate the interface effect of the insulation layer, the working surface of specimen 9 is embedded in the pre-formed groove of the insulation material, ensuring tight coverage. Silicone sealant is evenly applied to seal all edges of specimen 9 and gaps between the wire lead-out parts and the insulation material, and cured at room temperature for more than 24 hours. Specimen 9 is installed on the working electrode fixture of the insulating mounting base 14. The counter electrode 10 and reference electrode 11 can be installed according to experimental requirements. The assembled specimen 9 assembly can be surface sterilized by irradiation with ultraviolet light for 30-60 minutes. Fix the sample 9 assembly relative to the main shaft 1, inject the experimental liquid 8 into the chamber 2, and make the experimental liquid 8 completely submerge the sample 9 when the chamber 2 is horizontal. If it is necessary to create an anaerobic environment, seal all operating ports and interfaces of the chamber 2 to achieve overall sealing.

[0050] S2. Establishment of anaerobic environment: Protective gas is introduced into the completely sealed box 2 through the air inlet 3 on the box 2 to replace the air in the box 2 and maintain a slight positive pressure, thereby establishing and maintaining a strict anaerobic environment in the box 2.

[0051] S3. Microbial inoculation: Place chamber 2 in a constant temperature environment, set and stabilize to the target temperature of 35.0±1℃, and inoculate the experimental liquid 8 in chamber 2 with a concentrated bacterial solution of corrosive microorganisms such as sulfate-reducing bacteria in the logarithmic growth phase, so that the initial concentration of microorganisms in the experimental liquid 8 in chamber 2 reaches 10 after inoculation. 5 cells / mL.

[0052] S4. Start the alternating wet and dry cycle: Start the drive mechanism 13, and set the preset cycle of the tilting of the chamber 2 to 2 hours for the wet period and 10 hours for the dry period through the time relay. The duration of the wet and dry periods can be adjusted according to the experimental requirements. Drive the chamber 2 to tilt back and forth around the main shaft 1 according to the preset cycle. When the chamber 2 is horizontal, the sample 9 is completely immersed in the experimental liquid 8, which is the wet period. When the chamber 2 is tilted to the preset angle, the sample 9 rises relative to the liquid surface, which is the dry period. This makes the liquid surface of the experimental liquid 8 in the chamber 2 rise and fall periodically relative to the sample 9, so as to realize the alternating wet and dry cycle.

[0053] S5. Corrosion Monitoring and Analysis: During the alternating wet and dry cycle, if an electrochemical monitoring electrode is installed, connect the electrode to the external electrochemical monitoring device 15. After the wet chamber 2 stabilizes for 30 minutes, monitor the open circuit potential and electrochemical impedance spectroscopy. Depending on the experimental requirements, aseptic sampling and analysis of the experimental liquid 8 can be performed through the liquid operation port 4, including pH, redox potential, ion concentration, and microbial count. Alternatively, headspace gas can be collected through the gas outlet 5 for component analysis. After the preset experimental cycle is reached, the wet-dry cycle is stopped. If it is an anaerobic environment, sample 9 is taken out under nitrogen protection. The corrosion products on the surface of sample 9 are removed in accordance with the national standard GB / T16545. After cleaning and drying, the sample is weighed and the average corrosion rate is calculated. The corrosion morphology of sample 9 is observed using a scanning electron microscope. The micro-area composition of the corrosion products is analyzed using an energy dispersive spectroscopy (EDS) instrument. The phase composition of the corrosion products is determined by an X-ray diffractometer. The dynamically acquired electrochemical parameters, the chemical evolution data of the experimental liquid 8, and the final corrosion morphology, product type, and corrosion rate are systematically correlated and comprehensively analyzed to elucidate the dynamic interaction between wet-dry alternation, the interface of the insulation material, and microbial activity. The corrosion law of buried pipeline wet-dry alternation is obtained. The microbial activity correlation analysis can be selected and performed according to experimental requirements.

[0054] The above method forms a complete and standardized experimental procedure for simulating the alternating wet and dry corrosion of buried pipelines under insulation layers. The procedure is closed-loop and standardized, and can fully reproduce the corrosion process involving multiple coupled factors such as alternating wet and dry conditions, anaerobic microbial environment, and insulation layer interface effects. The method is fully compatible with the experimental apparatus of this invention, fully leveraging the structural advantages of the apparatus to ensure the stability of the experimental process and the repeatability of the experimental results. It provides a standardized operating procedure for simulating pipeline corrosion under different working conditions and with different materials. Through standardized pretreatment steps including sample 9 cleaning and drying, sterilization and deoxygenation of the experimental medium, and long-term replacement with high-purity nitrogen, interference from irrelevant factors such as surface impurities, dissolved oxygen, and bacteria in the medium is completely eliminated, ensuring the strictness of the anaerobic environment and the purity of the experimental system. This significantly improves the accuracy and reliability of the microbial corrosion experimental results and eliminates the influence of irrelevant variables. The method clarifies the key experimental parameters for simulating the synergistic corrosion of sulfate-reducing bacteria, ensuring the stability and activity of the microbial growth environment. The duration of the wet and dry periods can be flexibly adjusted to adapt to the simulation requirements of different actual working conditions for wet-dry alternation frequencies. Through full-chain data acquisition and correlation analysis, including electrochemical in-situ monitoring, detection of physicochemical and biological indicators of the medium, and multi-dimensional characterization of corrosion products, the interaction law between wet-dry alternation and microbial synergistic corrosion can be systematically revealed, providing comprehensive and accurate experimental data support for pipeline corrosion mechanism research and protection technology evaluation.

[0055] Example 3

[0056] This embodiment uses the experimental apparatus from Embodiment 1 and the experimental method from Embodiment 2. X70 pipeline steel is used as the simulated sample 9, and water from the pit is used as the experimental liquid 8. Anaerobic environment maintenance and insulation materials are provided. A 14-day simulation experiment of alternating wet and dry conditions and SRB synergistic corrosion of the buried pipeline under the insulation layer is conducted to verify the effectiveness and reliability of the apparatus and method. The specific steps are as follows: X70 pipeline steel was processed into standard specimen 9, measuring 50mm × 25mm × 3mm. After ultrasonic cleaning with acetone and anhydrous ethanol for 15 minutes each, and drying with cold air, the specimen was accurately weighed using an electronic balance, and the initial weight was recorded. Conductive silver paste was used to bond the working electrode wire to a pre-reserved position on the non-working surface of specimen 9, and the wire connection was completed after curing at room temperature. Pre-formed rigid polyurethane foam was machined with grooves matching specimen 9. Specimen 9 was inserted into the grooves with its working surface facing inwards. Silicone sealant was evenly applied to all gaps between the edges of specimen 9, the wire lead-out area, and the rigid polyurethane foam. The insulation material was encapsulated after curing at room temperature for 24 hours, realistically simulating the interface between the pipeline and the insulation layer. The encapsulated sample 9 is installed on the working electrode fixture of the PTFE insulated mounting base 14 on the main shaft 1. Simultaneously, the graphite counter electrode 10 and the saturated calomel reference electrode 11 with a capillary tube are installed. A 1.5mm thick PTFE gasket is used to precisely set the distance between the capillary tip and the working surface of the sample 9. After locking, the gasket is removed to ensure the three electrodes are in a fixed spatial position. A 30W ultraviolet lamp is used to irradiate the sample 9 assembly at a distance of 25cm for 45 minutes to complete surface sterilization. The sterilized sample 9 assembly is then fixed relative to the main shaft 1. Water from the field pit, sterilized by 121℃ high-pressure steam for 20 minutes and deoxygenated by nitrogen for 1 hour, is injected into the chamber 2. When the chamber 2 is horizontal, the experimental liquid 8 completely submerges the upper edge of the sample 9 by approximately 5mm. The operating door 7 of the chamber 2 is closed, and the operating door 7 is sealed by a quick-lock mechanism and a silicone rubber sealing gasket, sealing all interfaces to achieve overall airtightness of the chamber 2.

[0057] Connect the air inlet 3 at the top of the chamber 2 to the high-purity nitrogen source 17, and continuously introduce high-purity nitrogen into the chamber 2 at a flow rate of 0.2L / min for 3 hours to completely replace the residual air in the chamber 2. After the replacement is completed, maintain the nitrogen supply at a slightly positive pressure to maintain a strict anaerobic environment in the chamber 2 and meet the survival requirements of SRB.

[0058] The entire chamber 2 was placed in a constant temperature environment and set and stabilized to the target temperature of 35.0±1℃. Using a sterile syringe, concentrated SRB bacterial solution in the logarithmic growth phase was injected into the experimental liquid 8 inside the chamber 2 through the liquid operation port 4 at the top of the chamber 2, so that the initial concentration of SRB in the experimental liquid 8 inside the chamber 2 after inoculation reached 1×10⁻⁶. 5 cells / mL. Retract the electric push rod of the drive mechanism 13 to the lower limit to keep the chamber 2 in a horizontal position, which is defined as the start of the first "wet period"; connect the three electrode wires to the external electrochemical monitoring device 15. In this embodiment, an electrochemical workstation is used. Start the device to continuously monitor the open circuit potential of the sample 9.

[0059] The automatic cycle mode of the drive mechanism 13 is activated. The wet-dry alternation cycle is set to 2 hours for the wet period and 10 hours for the dry period via a time relay. The time relay automatically controls the extension and retraction of the electric push rod: during the wet period, the electric push rod remains retracted, the chamber 2 is horizontal, and the sample 9 is completely immersed in the experimental liquid 8; during the dry period, the electric push rod extends to its upper limit, the chamber 2 tilts around the main shaft 1 to a preset angle, and the sample 9 is raised relative to the liquid surface and exposed to the anaerobic atmosphere inside the chamber 2, realizing unattended automatic wet-dry alternation cycle. After the chamber 2 stabilizes for 30 minutes in each wet period, the electrochemical impedance spectroscopy of the sample 9 is measured using the electrochemical monitoring device 15, and the open circuit potential change is continuously recorded; every 24 hours, a small amount of the experimental liquid 8 is extracted through the liquid operation port 4 using a sterile syringe for pH measurement and SRB count, and the physicochemical and biological index changes during the corrosion process are monitored throughout; or, according to experimental needs, headspace gas is collected through the gas outlet 5 to analyze the changes in gas composition.

[0060] The experimental period was set to 14 days. After the preset period, the wet-dry alternation cycle was stopped, the electric push rod was retracted to return chamber 2 to a horizontal position, and high-purity nitrogen gas was introduced under slight positive pressure. The operating door 7 was opened, and sample 9 was quickly removed under nitrogen protection. According to the national standard GB / T16545, rust remover was used to remove corrosion products from the surface of sample 9. After ultrasonic cleaning with acetone and anhydrous ethanol, it was dried with cold air and accurately weighed using an electronic balance. The average corrosion rate of X70 steel under these experimental conditions was calculated to be 0.326 mm / a. The corrosion morphology of the sample 9 surface was observed using a scanning electron microscope. Figure 7 and 8 As shown, obvious adhesion marks are visible on the insulation layer. After removing the insulation layer, the surface of sample 9 is covered with a black microbial film and light brown iron oxide corrosion products. After rust removal, the surface exhibits typical microbial corrosion pits. Energy dispersive spectroscopy (EDS) analysis of the micro-area composition of the corrosion products reveals... Figure 9 As shown, the black film region is rich in Fe and S elements, confirming it to be the SRB metabolite FeS, while the light brown product region mainly contains Fe and O elements, indicating it to be an iron oxide. X-ray diffraction further confirmed the phase composition of the corrosion products, which was consistent with the EDS analysis results. Figure 10 As shown, the SEM morphology after rust removal reveals typical microbial corrosion characteristics on the sample surface, accompanied by localized pitting corrosion. Correlation analysis of dynamically acquired electrochemical data and microbial biomass data shows that the charge transfer resistance (Rct) gradually decreases with the alternating wet and dry cycles, reaching an inflection point between days 5 and 7; the SRB biomass rapidly reaches its peak value of approximately 1 × 10⁻⁶ on days 4 and 5. 8 The peak SRB count was measured in cells / mL, then entered a plateau phase and remained there for several days. After that, it gradually decreased as nutrients were consumed. The peak value and plateau phase of SRB count closely coincided with the time period of the inflection point of Rct decline.

[0061] Experimental conclusions: The alternating wet and dry process not only exacerbated the electrochemical corrosion of the pipeline steel through the concentration effect of the experimental liquid 8, but also created a suitable environment for the periodic metabolism of SRB. The insulation material interface not only strengthened the local corrosion microenvironment, but its material degradation products also continuously provided carbon and nitrogen sources for SRB, promoting the activity of the microbial community and the accumulation of corrosion product FeS, thus forming a significant synergistic corrosion acceleration mechanism of alternating wet and dry process, insulation material interface, and SRB. The device and method of this invention can truly reproduce this synergistic corrosion process, and the experimental results are highly consistent with the actual working conditions.

[0062] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A test apparatus for simulating the corrosion of buried pipelines under insulation layers under alternating wet and dry conditions, characterized in that, include: Main shaft (1), the main shaft (1) is set at rest; Box (2), the box (2) is movably sleeved on the main shaft (1), the box (2) contains experimental liquid (8) and sample (9) to be simulated corrosion, the sample (9) is fixed relative to the main shaft (1); The driving mechanism (13) is connected to the box (2). The driving mechanism (13) is used to drive the box (2) to periodically reciprocate around the main shaft (1), so that the liquid level of the experimental liquid (8) in the box (2) rises and falls relative to the sample (9), thereby realizing the alternating cycle of dry and wet.

2. The experimental apparatus according to claim 1, characterized in that, The box (2) is an integral sealed structure. The main shaft (1) and the box (2) are fitted with a sealing structure to ensure the sealing performance of the box (2) during the tilting process around the main shaft (1). The box (2) is provided with an air inlet (3). Protective gas is introduced into the box (2) through the air inlet (3) to realize and maintain the anaerobic environment inside the box (2).

3. The experimental apparatus according to claim 1, characterized in that, An insulating mounting base (14) is fixedly connected to the main shaft (1), and the sample (9) is fixed to the insulating mounting base (14). The insulating mounting base (14) is also equipped with a counter electrode (10) and a reference electrode (11) adapted to the electrochemical monitoring device (15). The counter electrode (10), the reference electrode (11) and the sample (9) are used together for electrochemical monitoring of corrosion status.

4. The experimental apparatus according to claim 3, characterized in that, The insulating mounting base (14) is an L-shaped component made of polytetrafluoroethylene. Its vertical connecting arm can be locked to any position in the axial direction of the main shaft (1) by a split locking sleeve. The horizontal mounting plate is used to fix the sample (9), the counter electrode (10) and the reference electrode (11). The reference electrode (11) has a capillary, and its capillary tip maintains a preset distance from the working surface of the sample (9).

5. The experimental apparatus according to claim 1, characterized in that, The drive mechanism (13) includes an electric push rod. A metal back plate is fixed to the back of the housing (2). A hinge seat is provided on the metal back plate. The tail of the electric push rod is hinged to an external fixed base, and the end is hinged to the hinge seat through a universal joint. The extension and retraction of the electric push rod drives the housing (2) to tilt around the main shaft (1). The electric push rod is a DC electric push rod with a built-in limit switch. It adopts worm gear transmission and has self-locking characteristics. The electric push rod is connected to a time relay. The time relay is used to set the duration of the wet period and the dry period in order to realize the automatic cyclic control of the tilting of the box (2).

6. The experimental apparatus according to claim 2, characterized in that, The chamber (2) is a cavity structure made of high-strength, corrosion-resistant transparent material. The air inlet (3) is located on the top of the chamber (2). The top of the chamber (2) is also provided with a liquid operation port (4), a gas outlet (5) and a spare interface (6). The front of the chamber (2) is provided with an operation door (7). The operation door (7) of the chamber (2) is provided with a quick-lock mechanism and a silicone rubber sealing gasket. Each interface is provided with an integrated sealing element to achieve overall sealing of the chamber (2). The liquid operation port (4) is used for the injection and sampling of experimental liquid (8). The gas outlet (5) is used for headspace gas collection. The operation door (7) is used for the placement and removal of samples (9) and device debugging.

7. The experimental apparatus according to claim 3, characterized in that, It also includes thermal insulation material, which is used to cover the working surface of the sample (9). The thermal insulation material has a groove that matches the sample (9). The working surface of the sample (9) is embedded in the groove. The gap between the edge of the sample (9), the lead-out part of the wire and the thermal insulation material is sealed with sealant.

8. A method for simulating corrosion of buried pipelines under insulation layers under alternating wet and dry conditions, using the experimental apparatus described in claims 2 and 6, characterized in that, Includes the following steps: S1. Fixing the sample (9): Fix the sample (9) relative to the main shaft (1), inject the experimental liquid (8) into the box (2), so that the experimental liquid (8) completely submerges the sample (9) when the box (2) is horizontal, seal all operating ports and interfaces of the box (2), so that the box (2) forms an overall sealed structure. S2. Establishment of anaerobic environment: Protective gas is introduced into the box (2) through the air inlet (3) on the box (2) to replace the air in the box (2) and maintain a slight positive pressure, thereby establishing and maintaining the anaerobic environment in the box (2); S3. Microbial inoculation: Inoculate corrosive microbial solution into the experimental liquid (8) inside the box (2) to make the solution reach the preset initial concentration; S4. Alternating dry and wet cycle operation: Start the drive mechanism (13) to drive the box (2) to rotate around the main shaft (1) according to the preset cycle, so that the liquid level of the experimental liquid (8) in the box (2) rises and falls periodically relative to the sample (9) to achieve alternating dry and wet cycle. S5. Corrosion monitoring and analysis: The corrosion state of the sample (9) was monitored during the alternating wet and dry cycle. After the experiment, the corrosion characterization and comprehensive analysis of the sample (9) were carried out to obtain the law of alternating wet and dry and microbial synergistic corrosion of buried pipelines.

9. The experimental method according to claim 8, characterized in that, In step S1, the sample (9) was ultrasonically cleaned and dried with acetone and anhydrous ethanol before fixation, and the initial size and weight were recorded; the experimental liquid (8) was sterilized by high temperature and high pressure and deoxygenated by nitrogen for at least 1 hour, and then aseptically injected through the liquid operation port (4) of the chamber (2). In step S2, the protective gas is high-purity nitrogen, and nitrogen is continuously introduced into the box (2) for 2 to 4 hours to completely replace the air inside the box (2).

10. The experimental method according to claim 8, characterized in that, In step S3, the corrosive microorganism is sulfate-reducing bacteria, and the inoculated bacterial solution is a concentrated solution of sulfate-reducing bacteria in the logarithmic growth phase. After inoculation, the initial concentration of sulfate-reducing bacteria in the experimental liquid (8) inside the chamber (2) is 10. 5 cells / mL, before inoculation, the chamber (2) was placed in a constant temperature environment and stabilized to the target temperature of 35.0±1℃; In step S4, the preset cycle for tilting the box (2) is 2 hours for the wet period and 10 hours for the dry period, or the duration of the wet and dry periods can be adjusted according to experimental requirements; In step S5, the open circuit potential and electrochemical impedance spectrum are monitored by an external electrochemical monitoring device (15) after the wet chamber (2) has been stabilized for 30 minutes. According to the experimental requirements, the pH, redox potential, ion concentration and microbial count of the experimental liquid (8) are aseptically sampled and analyzed through the liquid operation port (4), or the headspace gas is collected through the gas outlet (5) for component analysis. After the experiment, the corrosion products are removed according to GB / T16545 and the corrosion rate is calculated. The synergistic corrosion law is obtained by combining the correlation data of the micromorphology of the sample (9) and the component analysis of the corrosion products.

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