An experimental device for arc-shaped crevice corrosion between metal pipeline fasteners and a test method thereof

Abstract

The application discloses an experimental device for arc-shaped gap corrosion between metal pipeline fasteners and a test method thereof, and aims to explore the influence of different arc-shaped gap widths, different ion concentrations and other factors on the arc-shaped gap corrosion through the arc-shaped gap corrosion experimental test device and the electrochemical experimental method. The application discloses a test device for arc-shaped gap corrosion between metal pipeline fasteners. The core of the device is a three-electrode test system: a working electrode (9) is clamped in two clamps, an arc-shaped gap is formed through a gasket (8), and the gap width is adjusted by replacing gaskets (8) with different thicknesses or rotating a nut for extrusion. An electrochemical reaction tank (5) contains a solution, a built-in Pt pair electrode (10), a reference electrode (6) is connected to a reference electrode hole of a top clamp through a salt bridge, and the three electrodes are connected to an electrochemical workstation. The test device provided by the application is suitable for testing corrosion tests in arc-shaped gaps.

Description

Technical Field

[0001] This invention relates to the field of material corrosion evaluation devices, and more specifically, to an experimental apparatus for corrosion of arc-shaped gaps between metal pipe fasteners and a method for simulating arc-shaped metal gap corrosion. Background Technology

[0002] Crevice corrosion in metallic materials is a type of corrosion that occurs within narrow crevices. These confined crevices restrict mass transfer between the surrounding medium and the metal surface, making it more difficult to detect than typical corrosion and often exhibiting a long latency period before corrosion begins. However, once corrosion starts, it rapidly accelerates the destruction of the metal within the crevice. Therefore, crevice corrosion is one of the most destructive and dangerous forms of localized corrosion. In metal pipe joints where fasteners have gaps, corrosion-induced perforation can significantly reduce the pipe's service life.

[0003] Currently, most crevice corrosion testing methods are designed for flat metal samples, limited to using gaskets to create planar crevice corrosion simulation. Chinese Patent 202211498551 discloses a metal crevice corrosion simulation device. The main structure includes a threaded screw and nut, and auxiliary gaskets and disc-shaped gaskets placed between the screw and nut. In use, a titanium alloy sample is placed between the nut and the disc-shaped gasket, forming a crevice between the titanium alloy sample and the disc-shaped gasket. Chinese Patent 202411078845 discloses a testing device and method for fretting crevice corrosion between metal fasteners. It includes an upper working electrode and a lower working electrode. The lower working electrode is fixed in an electrochemical reaction cell containing NaCl solution. The electrochemical reaction cell also contains a reference electrode and a Pt counter electrode. The upper working electrode, lower working electrode, reference electrode, and Pt counter electrode together form a three-electrode testing system electrically connected to an electrochemical workstation. The two patents mentioned above only apply to planar corrosion. Due to differences in crevice geometry, media diffusion paths, and stress distribution, planar crevice corrosion tends to be wider and shallower, expanding laterally and thinning uniformly. Curved crevice corrosion, on the other hand, is more likely to be narrower and deeper, penetrating longitudinally, with localized concentration and accelerated stress. Therefore, there is a certain difference between the environmental factors of planar crevice corrosion and those of curved crevice corrosion, making them less instructive for actual curved corrosion conditions. Chinese Patent 202010395363 discloses a simulation device and method for simulating metal crevice corrosion. The main structure includes a fixture with a cavity. The fixture includes a bottom support plate, a top cover plate, and a support member. At least one set of crevice pads is provided between the bottom support plate and the top cover plate. Each set of crevice pads is arranged in pairs opposite each other, and a cavity for placing the metal object to be tested is reserved between the two crevice pads. The support member is supported between the bottom support plate and the top cover plate. This patented device is suitable for immersion experiments in arc-shaped gaps, but it lacks electrochemical simulation testing capabilities, making it impossible to conduct precise electrochemical parameter testing and unable to flexibly adjust the gap width, thus failing to meet the systematic research needs for the corrosion characteristics of arc-shaped gaps under multiple factors. Summary of the Invention

[0004] To address the shortcomings of existing methods for simulating and testing arc-shaped crevice corrosion, this invention provides an experimental apparatus for arc-shaped crevice corrosion between metal fasteners. Another objective of this invention is to provide a method for simulating arc-shaped metal crevice corrosion using the aforementioned apparatus. This apparatus allows for control of the crevice width by adjusting the thickness of the shim 8 or by rotating the nut 3 to compress the shim. It is suitable for testing corrosion with different ion concentrations and arc-shaped crevice widths, thus solving the technical problems of existing devices being unable to accurately simulate arc-shaped crevices, having limited parameter control, and insufficient testing functions. This provides a reliable experimental means for the study of the mechanism of arc-shaped crevice corrosion and for protective design.

[0005] The technical solution of this invention is as follows: an experimental apparatus for detecting arc-shaped gap corrosion between fasteners of metal pipes, characterized in that it comprises a top clamp 1, a bottom clamp 2, a nut 3, a screw 4, an electrochemical reaction cell 5, a reference electrode 6, a salt bridge 7, a gasket 8, a working electrode 9, and a Pt counter electrode 10. The inner surfaces of the top clamp 1 and the bottom clamp 2 are arc-shaped with consistent curvature. The working electrode 9 is fixed within the top clamp 1 and the bottom clamp 2. The gasket 8, cut into a U-shape, is placed on the upper surface of the working electrode 9 to form an arc-shaped gap. The gap width can be changed by replacing gaskets of different thicknesses or by rotating the nut 3 to compress the gasket. A reference electrode hole is provided at the center of the top clamp 1. The reference electrode 6, along with the salt bridge 7, is fixed to the exposed surface of the working electrode 9 through the reference electrode hole channel within the top clamp 1, without contacting the working electrode. The Pt counter electrode 10 is placed in the electrochemical reaction cell 5, directly opposite the cavity formed by the two clamps 1 and 2. The top clamp 1 and bottom clamp 2 are respectively provided with screw holes, and are fixed and clamped by screws 4 and nuts 3 and placed in the electrochemical reaction cell 5. The electrochemical reaction cell 5 is filled with electrolyte solution, and the lower ends of all electrodes are immersed in the solution in the electrochemical reaction cell 5. The arc-shaped working electrode 9, the reference electrode 6, and the Pt counter electrode 10 together form a three-electrode test system and are connected to the electrochemical workstation by wires.

[0006] Preferably, the top clamp 1 and the bottom clamp 2 each have 2 or 4 screw holes. These holes are used to clamp the screw 4 and nut 3. The screw holes are located on both sides of the clamp and are evenly distributed to ensure uniform force during clamping. The bottom clamp 2 is located below the top clamp 1 and forms a "clamping cavity" with the top clamp 1 to clamp the working electrode 9 and the gasket 8 together.

[0007] Preferably, the spacer 8 and the working electrode 9 are the same size. A groove with an area of ​​1 cm² is formed in the center of the spacer 8. 2 -2cm 2 A square.

[0008] Preferably, the reference electrode 6, together with the salt bridge 7, is fixed 2mm-8mm above the exposed surface of the working electrode 9 through the reference electrode hole channel, and does not contact the working electrode.

[0009] The present invention also provides a method for simulating arc-shaped metal crevice corrosion using the above-mentioned experimental testing device, the specific steps of which are as follows:

[0010] Step 1: Installation and Fixing. Place the arc-shaped working electrode 9 on the inner surface of the bottom clamp 2, and cover the working electrode 9 with the grooved pad 8 in the middle. Adjust the force of the screw 4 and nut 3 to clamp the working electrode 9 and pad 8 between the top clamp 1 and the bottom clamp 2, creating a gap between the pad 8 and the working electrode 9. Then place the fixed device into the electrochemical reaction cell 5.

[0011] Step 2: Prepare a sodium chloride electrolyte solution and pour it into the electrochemical reaction cell 5 to cover the gasket 8.

[0012] Step 3: Place the Pt counter electrode 10, salt bridge 7, and reference electrode 6, and connect them to the electrochemical workstation. The lower ends of the electrodes are immersed in the electrolyte solution within the electrochemical reaction cell 5.

[0013] Step 4: Perform electrochemical measurements using an electrochemical workstation. During polarization testing, set the voltage and scan rate to obtain the polarization curve of the arc-shaped working electrode. Replace the working electrode to perform impedance testing. First, perform electrochemical pretreatment, setting the sampling interval, potential range, and measurement duration. After the open circuit potential stabilizes, set the scan frequency and AC disturbance voltage to obtain the impedance curve of the arc-shaped working electrode.

[0014] The preferred voltage scan setting is to scan from a negative open-circuit potential of 0.6V to a positive open-circuit potential of 0.6V, with a scan rate of 0.01V / s. After replacing the working electrode, electrochemical pretreatment is performed first, with a sampling interval of 0.1s, a potential range of ±1V, and a measurement duration of 300s. Once the open-circuit potential stabilizes, the scan frequency is set to 100kHz-0.01Hz, and the AC perturbation voltage is 10mV. The polarization and impedance curves of the arc-shaped working electrode are then obtained.

[0015] The thickness of the preferred gasket (8) is 50~70μm. The concentration of the electrolyte solution is 50~500mg / L.

[0016] This invention provides a simulation device for arc-shaped crevice corrosion between metal pipe fasteners. The device includes a clamp with a cavity, the cavity itself, a gasket, and the sample, all of which are arc-shaped. This addresses the lack of an electrochemical simulation device with an adjustable crevice width for arc-shaped crevice corrosion. The clamp includes a top clamp 1 and a bottom clamp 2, with a grooved gasket 8 and a working electrode 9 positioned between them. Through this arc-shaped crevice corrosion experimental testing device and electrochemical experiments, various electrochemical parameters are obtained, and the effects of different crevice widths, different solution concentrations, and other factors on arc-shaped crevice corrosion are investigated.

[0017] The metal crevice corrosion simulation device provided by this invention can be used to assess the degree of crevice corrosion of the metal under test in the environment. The use of the metal crevice corrosion simulation device provided by this invention in the service environment is not considered an accelerated testing method, which has important guiding significance for the actual corrosion situation of metal pipes.

[0018] The metal crevice corrosion simulation device provided by this invention requires the metal object to be tested to be processed into experimental specimens during the crevice corrosion assessment process.

[0019] The metal crevice corrosion simulation device provided by this invention can be adapted to metal objects within a certain size range, is easy to disassemble, and can be reused.

[0020] The evaluation method provided by this invention simulates the metal gap state in a real industrial environment. Therefore, the corrosion results are consistent with the actual situation, which helps to guide the selection of metal pipe materials in industrial environments.

[0021] By applying pressure from the top clamp 1 and the bottom clamp 2 to the grooved pad 8 and the working electrode 9 respectively, and placing the working electrode 9 between the grooved pad 8 and the bottom clamp 2, the upper and lower clamps can clamp the working electrode 9 to be tested.

[0022] Furthermore, by adjusting the thickness of the gasket 8 or by rotating the nut 3 to compress the gasket, electrochemical experiments were conducted under different gap widths to investigate the effect of gap width on the gap corrosion of the working electrode 9.

[0023] The top clamp (1) and the bottom clamp (2) are each provided with 2 or 4 mounting holes for mounting screws, and the mounting holes of the top clamp (1) and the bottom clamp (2) correspond to each other in space. The screw passes through the top clamp (1) and the bottom clamp (2), and a nut is provided on the outside to lock the top clamp (1) and the bottom clamp (2).

[0024] The purpose of opening 2 or 4 symmetrical mounting holes on the top clamp 1 and the bottom clamp 2 is to make the force on the left and right sides more even during installation, and to ensure that the gap width is uniform.

[0025] In other embodiments, when conducting simulation tests using the natural gap between the grooved gasket 8 and the working electrode 9 under test, the gasket can be made of a non-metallic material or a metallic material similar to that used in actual working conditions.

[0026] Furthermore, specifically including:

[0027] Platinum sheet Pt counter electrode 10 is placed vertically, close to but not in contact with the sample working electrode 9. Reference electrode 6 is connected through salt bridge 7 and immersed in the gap solution, located 2mm-8mm from the exposed surface of working electrode 9 without contacting working electrode 9. Working electrode 9 to be tested is connected to electrochemical testing equipment to carry out a series of electrochemical experiments.

[0028] According to the simulation device provided by the present invention, a metal crevice corrosion device, a working electrode 9 to be tested, and a prefabricated crevice gasket are assembled, and the crevice width is controlled by changing the thickness of the gasket 8 or by rotating the nut 3 to squeeze the gasket.

[0029] Further crevice corrosion experiments were conducted: the assembled metal crevice corrosion device was placed in a corrosive environment, including but not limited to the actual field corrosion environment and the laboratory simulation test environment, according to the actual working conditions.

[0030] After the experimental test, the metal crevice corrosion device was removed and disassembled. The macro / micro corrosion morphology of the crevice corrosion of the metal pipe fittings was observed according to the relevant standards for crevice corrosion evaluation to characterize the severity of crevice corrosion.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention provides a simulation device for arc-shaped metal crevice corrosion and a method for simulating metal crevice corrosion tests. The simulation device allows for adjustment of the crevice width to evaluate the corrosion degree of metal pipelines in a field environment under different arc-shaped crevice widths. During the crevice corrosion evaluation process, the metal sample to be tested needs to be fabricated into experimental specimens. The simulation device is easily disassembled and reusable. The method of this invention allows for the acquisition of various electrochemical parameters to explore the effects of different crevice widths, different ion solution concentrations, and other factors on arc-shaped crevice corrosion. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the main structure of the present invention; wherein 1-top clamp; 2-bottom clamp; 3-plastic nut; 4-plastic screw; 5-electrochemical reaction cell; 6-reference electrode; 7-salt bridge; 8-gasket; 9-working electrode; 10-Pt counter electrode;

[0034] Figure 2 Three views of the arc-shaped crevice corrosion test apparatus; where a-front view, b-side view, c-top view;

[0035] Figure 3 For the arc-shaped crevice corrosion test device along Figure 1 Dashed line cross-section;

[0036] Figure 4 for Figure 1 Mid-top clamp diagram;

[0037] Figure 5 for Figure 1 Diagram of the bottom clamp;

[0038] Figure 6 for Figure 1 Diagram of the middle gasket and working electrode;

[0039] Figure 7 This is a polarization curve diagram of the curved working electrode in Example 2 under different gap widths;

[0040] Figure 8 Impedance diagrams of the curved working electrode in Example 2 at different gap widths;

[0041] Figure 9 The graph shows the polarization curves of the curved working electrode in Example 3 at different Cl- concentrations.

[0042] Figure 10 The impedance diagrams of the curved working electrode in Example 3 at different Cl- concentrations are shown. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0045] Secondly, it should be noted that in the description of this application, the terms "upper", "lower", "left", "right", "front", "back", "inner", "outer", etc., which indicate the direction or positional relationship, are based on the direction or positional relationship shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

[0046] This invention utilizes a simulated metal and non-metal arc-shaped crevice corrosion test apparatus and electrochemical experimental methods to obtain various electrochemical parameters and investigate the effects of factors such as crevice width and calcium ion solution concentration on arc-shaped crevice corrosion of metals. This invention is not limited to a single metal; it is also applicable to the crevice corrosion characterization of other pipe metals. The main structure of the arc-shaped crevice corrosion test apparatus involved in this embodiment includes upper and lower clamps 1 and 2, a screw 4, a nut 3, a washer 8, and a working electrode 9. The upper and lower clamps 1 and 2 are fixed and tightened by the screw 4 and the nut 3. Different arc-shaped crevice widths are achieved by changing the thickness of different washer 8 or by rotating the nut 3 to compress the washer.

[0047] Example 1

[0048] This embodiment provides a device for simulating arc-shaped metal crevice corrosion, such as... Figure 1 As shown, an experimental apparatus for detecting arc-shaped gap corrosion between fasteners of metal pipes is characterized by comprising a top clamp 1, a bottom clamp 2, a nut 3, a screw 4, an electrochemical reaction cell 5, a reference electrode 6, a salt bridge 7, a gasket 8, a working electrode 9, and a Pt counter electrode 10. The inner surfaces of the top clamp 1 and the bottom clamp 2 are arc-shaped with consistent curvature. The working electrode 9 is fixed within the clamps 1 and 2. The gasket 8, cut into a U-shape, is placed on the upper surface of the working electrode 9 to form an arc-shaped gap. The gap width is adjusted by changing gaskets of different thicknesses and by rotating the nut 3 to compress the gasket. A reference electrode hole is located at the center of the top clamp 1. The reference electrode 6, along with the salt bridge 7, is fixed to the exposed surface of the working electrode 9 through the reference electrode hole in the top clamp 1, without contacting the working electrode. The Pt counter electrode 10 is placed in the electrochemical reaction cell 5, directly opposite the cavity formed by the two clamps 1 and 2. The top clamp 1 and bottom clamp 2 are respectively provided with screw holes, and are fixed and clamped in the electrochemical reaction cell 5 by screws 4 and nuts 3. The electrochemical reaction cell 5 is filled with electrolyte solution, and the lower ends of all electrodes are immersed in the solution in the electrochemical reaction cell 5 to provide a medium environment for the electrochemical reaction. The arc-shaped working electrode 9, the reference electrode 6, and the Pt counter electrode 10 together form a three-electrode test system and are connected to the electrochemical workstation by wires.

[0049] The shape of the top clamp 1 is referenced. Figure 4 As shown, the shape of the bottom clamp 2 is referenced. Figure 5 As shown. In this embodiment, four mounting holes are provided on the top clamp 1 and the bottom clamp 2 respectively. The mounting holes are used to install the screw 4 and the nut 3. The screw 4 and the nut 3 fix and clamp the top clamp 1 and the bottom clamp 2.

[0050] Reference Figure 2 As shown in Figure c, the mounting holes are symmetrically arranged about the center of the top clamp 1 and the bottom clamp 2. The four mounting holes prevent uneven gap width caused by uneven force during clamping. The purpose of making the inner surfaces of the top clamp 1 and the bottom clamp 2 curved is to ensure better contact between the clamps, the gasket 8, and the working electrode 9, since the working electrode 9 is a curved sample. The radius of curvature of the inner surfaces of the clamps can be set according to the radius of curvature of the working electrode of the sample to be tested.

[0051] Because the position of the reference electrode 6 in solution can have different effects on electrochemical experiments, in order to make the device more accurate in electrochemical testing in low-concentration solutions, such as... Figure 1 As shown, a hole is made inside the top clamp 1 to facilitate the insertion of the salt bridge 7 and the reference electrode 6, so that the salt bridge 7 and the reference electrode 6 are inserted into the arc-shaped slit solution.

[0052] Figure 6 for Figure 1Diagram of the middle gasket and working electrode. Gasket 8 is cut into a U-shape, as shown. Figure 3 The pad 8 shown is placed above the working electrode 9. (As shown) Figure 1 The space between the middle empty part of the pad 8, the working electrode 9, and the top clamp 1 is formed.

[0053] In other embodiments, the shape of the gasket is not limited to a U-shape and can be other shapes.

[0054] The method for simulating arc-shaped crevice corrosion of metal using the arc-shaped metal corrosion simulation device provided in this embodiment includes the following steps:

[0055] Step 1: Based on the size of the actual metal sample, process each component of the simulation device for metal crevice corrosion, mainly quantifying the dimensions of each part of the simulation device for metal arc crevice corrosion, and then processing and shaping it.

[0056] Step 2, Installation and Fixing: According to the example image provided in Embodiment 1, the arc-shaped working electrode 9 is placed between the upper and lower clamps 1 and 2, and the pre-cut concave gasket 8 is placed on the inner surface of the working electrode 9. The working electrode 9 is connected by a wire, and the connection between the wire and the working electrode 9, as well as the working electrode 9 exposed outside the clamp, is sealed with epoxy resin.

[0057] Step 3: By adjusting the force of screw 4 and nut 3, clamp the arc-shaped working electrode 9 and the washer 8 to form a gap between the washer 8 and the arc-shaped working electrode 9.

[0058] Step 4: The reference electrode 6 is connected to the salt bridge 7 and placed 2mm-8mm away from the exposed surface of the working electrode 9 through the reference electrode hole without contacting the working electrode 9. The Pt counter electrode 10 is placed in the electrochemical reaction cell 5 so that it is directly opposite the cavity formed by the two clamps 1 and 2.

[0059] Step 5: Prepare the solution required for the experiment and simulate the corrosive environment. Add an appropriate amount of solution to the electrochemical reaction cell and place the device in the solution. The lower ends of all electrodes are immersed in the solution in the electrochemical reaction cell 5 to provide a medium environment for the electrochemical reaction.

[0060] Step 6: The working electrode 9, the reference electrode 6, and the Pt counter electrode 10 are connected to the electrochemical workstation via wires.

[0061] Example 2

[0062] In this embodiment, the gasket 8 is cut into a square U-shape. For example... Figure 1The gap is created between the empty space in the middle of the gasket, the working electrode 9, and the top clamp 1. The gap width can be adjusted in two ways. Method 1: Different arc-shaped gap widths are achieved by changing the thickness of different gaskets 8. Method 2: In this study, an M4 bolt (pitch 0.8 mm) is used. Therefore, the gap width can be calculated by adjusting the rotation angle of the nut. When the rotation angle of the gap former is x°, the gap width can be calculated as y = x° / 360° × 0.8 mm.

[0063] The method for simulating crevice corrosion of metal using the simulation device for corrosion of arc-shaped metal with different crevice widths provided in this embodiment includes the following steps:

[0064] Step 1: Installation and Fixing. Based on the example image provided in Example 1, place the arc-shaped working electrode 9 between the upper and lower clamps 1 and 2, and place the gasket 8. To investigate the effect of different gap widths on corrosion, a 50μm gasket was selected. The arc-shaped working electrode 9 and the gasket 8 are clamped by adjusting the force of the plastic screw 4 and the plastic nut 3, forming a gap between the gasket 8 and the arc-shaped working electrode 9. Then, the fixed device is placed into the electrochemical reaction cell 5.

[0065] Step 2: Connect the wires to the working electrode 9, place the Pt counter electrode 10, the salt bridge 7, and the reference electrode 6, and connect to the electrochemical workstation.

[0066] Step 3: Prepare a NaCl solution with a Cl- concentration of 100 mg / L to simulate a corrosive environment. Add an appropriate amount of the solution to the electrochemical reaction cell, and immerse the lower ends of all electrodes in the solution in the electrochemical reaction cell 5.

[0067] Step 4: During testing, a voltage scan is set, scanning from a negative open-circuit potential of 0.6V to a positive open-circuit potential of 0.6V, with a scan rate of 0.01V / s. The working electrode is replaced, and electrochemical pretreatment is performed first. The sampling interval is set to 0.1s, the potential range to ±1V, and the measurement duration to 300s. After the open-circuit potential stabilizes, the scan frequency is set to 100kHz-0.01Hz, and the AC perturbation voltage is 10mV. The polarization and impedance curves of the arc-shaped working electrode with a slit width of 50μm are obtained.

[0068] Step 5: Replace the shim thickness with 400 μm and repeat steps 1-4 to obtain the polarization curve of the arc-shaped working electrode with an arc-shaped gap width of 400 μm. Replace the shim thickness with 700 μm and repeat steps 1-4 to obtain the polarization curve of the arc-shaped working electrode with an arc-shaped gap width of 700 μm. The polarization curves for arc-shaped gap widths of 50 μm, 400 μm, and 700 μm are shown below. Figure 7 The impedance data shown are as follows Figure 8 As shown. Figure 7 and Figure 8As shown: Based on the polarization curves and impedance curves under different gaps, the corrosion current density and impedance value under different gaps can be obtained, and then the influence of different gap widths on the arc-shaped gaps can be determined.

[0069] This application can also study the effect of different ion concentrations on the arc-shaped metal gap. By preparing solutions with different ion concentrations and fixing the gap width, the influence of a single variable, ion concentration, on the arc-shaped metal gap can be explored.

[0070] Example 3

[0071] This embodiment provides a simulation device and method for simulating the effect of different ion concentrations on the corrosion of arc-shaped metal crevices. The simulation is performed using the arc-shaped metal simulation device described in Example 1, and includes the following steps.

[0072] Step 1: Installation and Fixing. Based on the example image provided in Example 1, place the arc-shaped working electrode 9 between the upper and lower clamps and place the shim 8. Select a shim 8 with a thickness of 300 μm. Clamp the arc-shaped working electrode 9 and the shim 8 by adjusting the force of the screw 4 and nut 3, forming a 300 μm gap between the shim 8 and the arc-shaped working electrode 9. Then, place the fixed device into the electrochemical reaction cell 5.

[0073] Step 2: Connect the wires to the working electrode 9, place the Pt counter electrode 10, the salt bridge 7, and the reference electrode 6, and connect to the electrochemical workstation.

[0074] Step 3: Prepare a NaCl solution with a Cl- concentration of 50 mg / L to simulate a corrosive environment. Add an appropriate amount of the solution to the electrochemical reaction cell, and immerse the lower ends of all electrodes in the solution in the electrochemical reaction cell 5.

[0075] Step 4: During testing, a voltage scan is set, scanning from a negative open-circuit potential of 0.6V to a positive open-circuit potential of 0.6V, with a scan rate of 0.01V / s. The working electrode is replaced, and electrochemical pretreatment is performed first. The sampling interval is set to 0.1s, the potential range to ±1V, and the measurement duration to 300s. After the open-circuit potential stabilizes, the scan frequency is set to 100kHz-0.01Hz, and the AC perturbation voltage is 10mV. The polarization and impedance curves of the arc-shaped working electrode at a Cl- concentration of 50mg / L are obtained.

[0076] Step 5: Replace the NaCl solution with a Cl- concentration of 500 mg / L, and repeat steps 1-4 to obtain the polarization and impedance curves of the arc-shaped working electrode at a Cl- concentration of 500 mg / L. The polarization curves of the arc-shaped working electrode at Cl- concentrations of 50 mg / L and 500 mg / L are shown below. Figure 9 The impedance data shown are as follows Figure 10 As shown. Figure 9 and Figure 10 As shown: Based on the polarization curves and impedance curves at different Cl- concentrations, the corrosion current density and impedance values ​​at different Cl- concentrations can be obtained, and the influence of different Cl- concentrations on the arc-shaped gap can be determined.

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

Claims

1. An experimental apparatus for detecting corrosion in arc-shaped gaps between fasteners of metal pipes, characterized in that, It consists of a top clamp (1), a bottom clamp (2), a nut (3), a screw (4), an electrochemical reaction cell (5), a reference electrode (6), a salt bridge (7), a gasket (8), a working electrode (9), and a Pt counter electrode (10); the inner surfaces of the top clamp (1) and the bottom clamp (2) are arc-shaped and have the same curvature; the working electrode (9) is fixed inside the top clamp (1) and the bottom clamp (2); the gasket (8) is cut into a U-shape and placed on the upper surface of the working electrode (9) to form an arc-shaped gap; the top clamp (1) has a reference electrode hole at its center, and the reference electrode (6) and the salt bridge (7) pass through the reference electrode hole in the top clamp (1). The electrode is fixed on the exposed surface of the working electrode (9); the Pt counter electrode (10) is placed in the electrochemical reaction cell (5) so that it is directly opposite the clamping cavity formed by the top clamp (1) and the bottom clamp (2); the top clamp (1) and the bottom clamp (2) are respectively opened with screw holes, and are fixed and clamped by screws (4) and nuts (3) and placed in the electrochemical reaction cell (5); the electrochemical reaction cell (5) is filled with electrolyte solution, and the lower ends of all electrodes are immersed in the solution in the electrochemical reaction cell (5); the arc-shaped working electrode (9), the reference electrode (6) and the Pt counter electrode (10) together form a three-electrode test system and are connected to the electrochemical workstation through wires.

2. The experimental apparatus according to claim 1, characterized in that, The top clamp (1) and the bottom clamp (2) each have 2 or 4 screw holes.

3. The experimental apparatus according to claim 1, characterized in that, The pad (8) is the same size as the working electrode (9); the groove in the middle of the pad (8) has an area of ​​1 cm². 2 -2cm 2 A square.

4. The experimental apparatus according to claim 1, characterized in that, The reference electrode (6) is paired with a salt bridge (7) and fixed 2mm-8mm above the exposed surface of the working electrode (9) through the reference electrode hole channel, without contacting the working electrode.

5. A method for simulating arc-shaped metal crevice corrosion using the experimental testing apparatus as described in claim 1, comprising the following specific steps: Step 1: Installation and Fixing. Place the arc-shaped working electrode (9) on the inner surface of the bottom clamp (2) and cover the working electrode (9) with the grooved pad (8) in the middle. Clamp the working electrode (9) and the pad (8) between the top clamp (1) and the bottom clamp (2) by adjusting the screw (4) and nut (3) to form a gap between the pad (8) and the working electrode (9). Then place the fixed device into the electrochemical reaction cell (5). Step 2: Prepare sodium chloride electrolyte solution and pour the electrolyte solution into the electrochemical reaction cell (5) to cover the gasket (8). Step 3: Place the Pt counter electrode (10), salt bridge (7), and reference electrode (6) and connect them to the electrochemical workstation; the lower ends of the electrodes are all immersed in the electrolyte solution in the electrochemical reaction cell (5); Step 4: Perform electrochemical measurements using an electrochemical workstation. During polarization testing, set the voltage and scan rate to obtain the polarization curve of the arc-shaped working electrode. Replace the working electrode to perform impedance testing. First, perform electrochemical pretreatment, setting the sampling interval, potential range, and measurement duration. After the open circuit potential stabilizes, set the scan frequency and AC disturbance voltage to obtain the impedance curve of the arc-shaped working electrode.

6. The method according to claim 5, characterized in that... The thickness of the gasket (8) is 50~70μm.

7. The method according to claim 5, characterized in that... The concentration of the electrolyte solution is 50~500 mg / L.

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