A microbial corrosion electrochemical testing device under stress coupling

Abstract

The present invention discloses an electrochemical testing device for microbial corrosion under stress coupling. The device includes an electrochemical workstation, a bending loading fixture, a corrosion reaction cell and a constant temperature box; the corrosion reaction cell is in the shape of a "concave" character, and a hole is opened on the end face of the inverted "concave" opening, a gasket is installed at the opening, and a hole is opened in the middle of the gasket; the bending loading fixture is fixed on the upper end face of the opening; the bending loading fixture includes a loading bracket, a loading rod and a loading module located inside the loading bracket and movable up and down; at least one pair of rollers is fixed on the inner side of the upper support foot of the loading bracket, and one or more grooves and rollers that can be accommodated in the grooves are arranged on the upper end face of the loading module. The testing device of the present invention can ensure the accuracy of the test data, and has the advantages of easy disassembly, simple design and small size.

Description

Technical Field

[0001] The invention relates to an electrochemical testing device for microbial corrosion of metal materials, and in particular to a device capable of testing the corrosion resistance of a sample under the combined effects of bending stress and a microbial corrosion environment. Background Art

[0002] Acidic oil and gas fields contain a large amount of corrosive media such as H2S and CO2, which leads to serious corrosion problems in the ground gathering and transportation pipeline system. In addition, the gathering and transportation pipelines of many domestic oil and gas fields are also facing serious microbiologically influenced corrosion (MIC) hazards. Accidents such as leakage and even explosions caused by failure of gathering and transportation pipelines due to corrosion perforation often occur. Among the various microbial communities existing in the oil and gas gathering and transportation system, the largest and most harmful one is sulfate reducing bacteria (SRB). In the production of oil wells in the United States, the corrosion caused by sulfate reducing bacteria reaches more than 77%. Under the synergistic effect of sulfate reducing bacteria, the corrosion rate of steel can increase by about 15 times.

[0003] In the process of service, pipelines are not only harmed by corrosive media and microorganisms, but also have an important impact on the safe operation of pipelines due to stress. Especially when the pipeline is locally bent and deformed, it becomes a weak link in its safe operation and is prone to corrosion damage. Therefore, it is very important to study the influence of stress and microorganisms in corrosive media on the corrosion behavior of metals. However, the existing electrochemical corrosion test devices are rarely able to measure the corrosion resistance of samples under the combined action of stress and microorganisms in corrosive media.

[0004] For example, the publication number CN107727564-"Electrochemical Test Device for Metal Microbial Corrosion in Flow System" makes microorganisms gather and grow on the metal surface, and performs real-time electrochemical measurement of microbial corrosion of metal materials in the flow system; CN109507263-"Microbial Corrosion Test System for Grounded Metal Materials" discloses a test system for microbial corrosion test of grounded metal materials; CN104458559-"Stress-Electrochemical Corrosion Test Device" uses a heavy object to provide a constant tensile force to study the stress corrosion of anaerobic bacteria at different temperatures; CN102590298-"Method for Testing the Microbial Corrosion Resistance of Antibacterial Stainless Steel by Electrochemical Means" specifically introduces a method for testing the microbial corrosion resistance of antibacterial stainless steel by electrochemical means. In addition, the existing test device method still has many limitations: it is not easy to disassemble and measure multiple times; the sample working area is manually sealed, the working area is not accurate, and the parallelism is poor; the design of the device is complex, the volume is large, and it is not easy to carry. Summary of the invention

[0005] In order to overcome the shortcomings of the existing microbial corrosion test device that cannot simultaneously couple the bending stress under the corrosive medium, the device design is complex, the sample working area is not accurate, and it is not easy to disassemble, the present invention provides a microbial corrosion electrochemical test device under the action of corrosive medium and bending stress. The device can realize the test of the microbial corrosion performance of the sample under the action of bending stress, and has a simple structure, a certain sample working area, and is easy to carry and disassemble.

[0006] The technical solution adopted by the present invention is:

[0007] A microbial corrosion electrochemical testing device under stress coupling, the device comprising an electrochemical workstation, a bending loading fixture, a corrosion reaction cell and a constant temperature box;

[0008] The corrosion reaction pool is in the shape of an inverted "concave" character, and a bending loading fixture is fixedly installed on the surface (end surface) of the inverted "concave"-shaped opening; at the same time, a hole is opened on the upper surface of the inverted concave-shaped opening; a sealing insulating soft gasket is installed at the opening, and the middle opening of the sealing insulating soft gasket has a shape and size that matches the opening area of ​​the corrosion reaction pool;

[0009] The bending loading fixture comprises a loading bracket, a loading rod and a loading module located inside the loading bracket and movable up and down; wherein,

[0010] The loading bracket is hollow inside and open at the top; the two opposite sides of the upper opening are provided with supporting feet protruding inwards, and the inner end surfaces of the supporting feet (i.e., the end surfaces away from the reaction tank opening) are fixed with at least one pair of symmetrically arranged rollers;

[0011] The end surface of the loading module opposite to the opening is provided with at least one or more symmetrically arranged grooves, and the grooves include rollers that can be accommodated therein;

[0012] ——The loading module is connected to the loading rod, and the loading module can only move up and down (without horizontal displacement) with the movement of the loading rod.

[0013] Furthermore, when the loading rod rotates, it can drive the loading module to move upward or downward.

[0014] Furthermore, the loading bracket is fixed on the plane of the inverted concave opening of the reaction tank by at least one pair of fastening bolts and fastening nuts.

[0015] Furthermore, the loading rod is threadedly connected to the loading module, and the loading rod is arranged through the loading bracket (lower end surface). In this case, the loading rod can only rotate without generating relative (up and down) displacement relative to the loading bracket. Alternatively, the lower end (lower part) of the loading rod is threadedly connected to the loading bracket, and the upper end of the loading rod is fixedly connected to the loading module, and the loading rod can rotate in the loading module without generating relative up and down displacement relative to the loading module. Among them, the threaded connection is a conventional structure in the art.

[0016] Furthermore, the loading module may adopt an internal hollow structure.

[0017] Furthermore, the opening of the sealing insulating soft gasket matches the opening of the recessed plane area, which means that the opening areas of the two openings are not much different.

[0018] Furthermore, the length of the rollers provided on the legs of the loading bracket should be greater than or equal to the width of the sample to be tested, and the spacing between the rollers on the legs should be less than the length of the sample to be tested. The legs on one side of the loading bracket can be an integral continuous structure or a hollow structure in the middle.

[0019] Furthermore, the number of rollers (grooves) provided on the loading module is more than one, preferably more than two. For more than two rollers (grooves), the spacing between the outermost pair of rollers (grooves) should be smaller than the spacing between the grooves (rollers) on the legs of the loading bracket. Through the rollers provided on the legs of the loading bracket, and the grooves and rollers on the loading module, the loading fixture can realize different forms of bending deformation and stress loading such as four-point bending, three-point bending, and U-shaped bending on the specimen.

[0020] Furthermore, the loading module and the rollers on the loading bracket legs are used to place the sample to be tested. After the sample to be tested is placed, one or a pair of rollers are inserted into the appropriate grooves on the loading module as needed.

[0021] Furthermore, the roller can be made of a material such as glass or ceramics that has a certain rigidity and is not easily deformed. The roller is preferably a cylindrical structure.

[0022] Furthermore, the upper end surface of the corrosion reaction pool is provided with at least four openings, and the four or more openings are preferably arranged at intervals on the upper end surface. Two of the openings are respectively provided with a salt bridge and a platinum sheet, and a reference electrode is connected in the salt bridge. The salt bridge and the platinum sheet should be immersed in the reaction solution of the reaction pool. The salt bridge, the platinum sheet and the upper end surface of the reaction pool are sealed and fixed. Another group of openings can be an air inlet and an air outlet, a dosing hole and a sampling port, respectively. The air inlet (dosing port) is used to introduce nitrogen, hydrogen sulfide, carbon dioxide and other gases or add liquid medicine into the corrosion reaction pool, and the air outlet (sampling port) is used to discharge gas or take samples.

[0023] Furthermore, the salt bridge and platinum sheet should be arranged near the opening between the sample loading and the reaction tank, and the lower ends of the salt bridge and platinum sheet should be at the same height as the opening on the inverted concave opening plane of the reaction tank.

[0024] Furthermore, the sealing insulating gasket can be made of elastic and waterproof materials such as silicone rubber and polyolefins.

[0025] Furthermore, the openings of the corrosion reaction pool and the sealing insulating soft gasket are in square or circular shapes, so that the contact area between the sample and the reaction solution can be easily determined.

[0026] Furthermore, the electrochemical workstation includes an auxiliary electrode interface, a working electrode interface and a reference electrode interface, wherein the platinum sheet is connected to the auxiliary electrode interface of the workstation, the sample loaded in the fixture is connected to the working electrode interface of the workstation, and the reference electrode is connected to the reference electrode interface of the workstation.

[0027] Furthermore, the thermostat is used to accommodate the corrosion reaction pool, and is used to ensure that the temperature of the test environment is constant, so as to study the corrosion effect of microorganisms on the sample at different temperatures. The side wall of the thermostat is provided with a small hole, which is used to connect the pipeline required to be connected to the corrosion reaction pool during the test with the external equipment of the thermostat. The salt bridge is connected to the reference electrode, and the platinum sheet, the sample in the loading fixture and the reference electrode are respectively connected to the various electrode interfaces of the electrochemical workstation.

[0028] Furthermore, the corrosion reaction tank can contain various solution media such as potassium chloride and hydrochloric acid according to test requirements.

[0029] In the present invention, the sample is deformed by bending loading in the fixture, and the fixture is fixed on the plane of the inverted "concave" shaped opening at the bottom of the corrosion reaction tank by a fixture, so that the sample in the fixture is in close contact with the soft gasket of the corrosion reaction tank and the loading stress of the sample is guaranteed to be constant.

[0030] The corrosion reaction tank may be added with culture fluid inoculated with specific bacteria according to test requirements.

[0031] The air inlet can be fed with gases such as nitrogen, hydrogen sulfide, and carbon dioxide.

[0032] The bactericide for specific bacteria can be added into the drug adding hole.

[0033] The present invention also provides an electrochemical testing method for microbial corrosion under stress coupling, in which the above-mentioned testing device is applied.

[0034] Compared with the prior art, the testing device of the present invention has the following beneficial effects:

[0035] 1. The present invention introduces a bolt structure in the corrosion reaction tank and the loading fixture, so that the loading fixture can be fixed to the corresponding position of the corrosion reaction tank by fixing the fastening bolts, which is convenient for loading the loading fixture on the reaction tank and fixing the corrosion reaction tank, and can ensure that the force of the sample and the gasket after contact is constant and stable, and can more accurately determine the load value applied to the sample. The loading method can be selected as manual mechanical loading, or it can introduce motors and stress sensors for electric mechanical loading.

[0036] 2. The grooves provided on the lower legs of the loading bracket, the rollers provided in the grooves, the grooves on the lower end face of the loading module and the insertable rollers, and the fact that the rollers are made of insulating material, ensure that the loading module can apply bending stress to the specimen without directly contacting the specimen, thereby ensuring the accuracy of the test data.

[0037] 3. In view of the shortcomings of the prior art, the present invention provides an electrochemical evaluation device for microbial corrosion under bending stress, which makes up for the shortcomings of the prior art. At the same time, when the test device of the present invention is used, it is not necessary to do waterproof sealing treatment during the sample assembly process, and the sample working area does not need to be manually sealed each time. At the same time, the working area is accurate and the parallelism is high. In addition, the device of the present invention also has the advantages of easy disassembly, easy to carry, simple design and small size. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a front cross-sectional view of the microbial corrosion electrochemical testing device of the present invention.

[0039] Figure 2 It is a left view of the corrosion reaction pool in the device of the present invention.

[0040] Figure 3 It is a top view of the corrosion reaction pool in the device of the present invention.

[0041] The device in the figure is composed of: 1-electrochemical workstation, 2-constant temperature box, 3-corrosion reaction cell, 4-groove, 5-loading rod, 6-loading bracket, 7-loading module, 8-roller, 9-sample, 10-opening gasket, 11-fastening nut, 12-fastening bolt, 13-reference electrode, 14-salt bridge, 15-platinum sheet, 16-(loading bracket) support foot, 17-reference electrode interface, 18-auxiliary electrode interface, 19-air inlet (dosing hole), 20-air outlet, 21-opening at the bottom of the corrosion reaction cell. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and features of the present invention more clear, the present invention is further described in detail in conjunction with the accompanying drawings and implementation methods. It should be noted that the described embodiments are only some embodiments of the present invention. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without making creative work are all within the scope of protection of the present invention.

[0043] like Figure 1 , 2 As shown in Figure 3, the test device of the present invention includes an electrochemical workstation 1, a thermostat 2, a corrosion reaction cell 3, and a loading fixture. The corrosion reaction cell 3 is in the shape of an inverted "concave" character, and the end surface of the inverted "concave" character opening is fixedly installed with a bending loading fixture, and the upper surface of the inverted concave character opening has an opening 21. A sealed insulating opening gasket 10 is installed at the opening, and the middle opening of the sealed insulating soft gasket, and the shape and size match the opening of the corrosion reaction cell.

[0044] The fastening nut 11 is passed through the corresponding opening at the bottom of the corrosion reaction tank 3 , and the bending loading fixture (loading bracket 6 ) is fixed to the middle bottom of the corrosion reaction tank 3 by the fastening bolt 12 .

[0045] The bending loading fixture includes a loading bracket 6, a loading rod 5, and a loading module 7 located inside the loading bracket and movable up and down. The loading bracket 6 is hollow inside and open at the top; the two opposite sides of the upper opening have 16 legs protruding inwardly toward each other, and the inner end faces of the legs 16 (i.e., the end faces away from the opening of the reaction tank) are fixed with at least one pair of symmetrically arranged rollers 8. The end face of the loading module opposite to the opening is provided with at least one or several symmetrically arranged grooves 4, and the grooves include rollers 8 that can be accommodated therein. The loading module and the loading rod can be connected by threads, and the loading module can only move up and down (without horizontal displacement) with the movement of the loading rod. Preferably, when the loading rod 5 rotates, the loading module 7 can be driven to move upward or downward.

[0046] The sample 9 is fixed in the loading bracket 6 by the cylindrical roller 8 placed in the groove. An opening gasket 10 is provided between the sample 9 and the corrosion reaction tank 3. An opening is provided in the middle of the opening gasket 10. The middle force-bearing part of the sample 9 contacts the corrosion solution in the corrosion reaction tank 3 through the opening. The loading module 7 of the fixture is moved toward the opening direction of the corrosion reaction tank 3 by rotating the loading rod 5 to load the sample 9.

[0047] A plurality of holes are provided on the upper part of the corrosion reaction pool 3, including an air inlet (drug adding port) 19 for introducing corrosive gases such as hydrogen sulfide and carbon dioxide (adding specific bactericides); an air outlet 20 is used for discharging the gas introduced into the solution, a reference electrode socket 17 is used to place a salt bridge 14 and a reference electrode 13, an auxiliary electrode socket 18 is used to place a platinum sheet 15, the salt bridge 14 and the platinum sheet 15 are placed close to the loaded sample 9, and the reference electrode 13, the platinum sheet 15 and the loaded sample 9 are respectively connected to the reference electrode interface, the auxiliary electrode interface and the working electrode interface in the electrochemical workstation 1.

[0048] In the present invention, the reaction solution may also include a microbial culture solution. For example, the selected microorganism may be sulfate-reducing bacteria (SRB), and the culture of the strain adopts the liquid culture medium and experimental conditions recommended by API. Since the pH value of the most suitable growth environment for SRB is 7.0-7.5, the culture medium uses a sodium hydroxide solution to adjust the pH value to 7.2. Before use, the SRB culture medium is deoxygenated with nitrogen for 1 hour, and the culture medium is sealed and placed in a high-temperature and high-pressure sterilizer for sterilization at high temperature of 121°C + 15psi for 20 minutes. In an anaerobic glove box, the bacteria are inoculated into the culture solution and placed in a 38°C biochemical incubator for enrichment culture. The culture solution is added to the corrosion reaction tank 3, and the corrosion reaction tank 3 is placed in a 38°C constant temperature box 2 during the experiment. The data results such as open circuit potential, polarization curve and alternating current impedance (EIS) can be measured separately according to the test needs. After the test, the sample 9 is promptly processed, including fixed corrosion products for macroscopic photo observation, gold spraying treatment for scanning electron microscope observation, surface bacterial concentration measurement and sample 9 pitting and depth measurement.

Claims

1. A microbial corrosion electrochemical testing device under stress coupling, the device comprising an electrochemical workstation, a bending loading fixture, a corrosion reaction cell and a constant temperature box; The corrosion reaction pool is in the shape of an inverted "concave" character, and a hole is opened on the end surface of the inverted "concave" opening, and a sealing insulating soft gasket is installed at the opening, and a hole is opened in the middle of the gasket; the shape and size of the opening on the gasket match the opening on the end surface; The bending loading fixture is fixed on the end surface and covers the end surface opening; The bending loading fixture comprises a loading bracket, a loading rod and a loading module located inside the loading bracket and movable up and down; the loading bracket is fixed on the end surface of the inverted concave opening of the reaction pool by at least one pair of fastening bolts and fastening nuts; wherein, The loading bracket is hollow inside and open at the top; two opposite sides of the upper opening are provided with supporting feet protruding inwards, and at least one pair of symmetrically arranged rollers are fixed to the inner end surfaces of the supporting feet; The end surface of the loading module opposite to the opening is provided with at least one or more symmetrically arranged grooves, and the grooves include rollers that can be accommodated therein; ——The loading module is connected to the loading rod, and the loading module can only move up and down with the movement of the loading rod; The loading rod is connected to the loading module by a threaded connection, and the loading rod is arranged through the lower end surface of the loading bracket; The lower part of the loading rod is connected to the loading bracket by a thread, and the upper end of the loading rod is movably connected to the loading module, so that the loading rod can rotate in the loading module without generating an up-and-down displacement relative to the loading module; The upper end surface of the corrosion reaction pool is provided with at least four openings, two of which are respectively provided with a salt bridge and a platinum sheet, and the salt bridge is connected to a reference electrode; the other group of openings are respectively an air inlet, an air outlet, a dosing hole and a sampling port.

2. The testing device according to claim 1, characterized in that The loading module adopts a hollow structure.

3. The testing device according to claim 1, characterized in that The length of the rollers arranged on the legs of the loading bracket is greater than or equal to the width of the sample to be tested, and the spacing between the rollers on the legs should be less than the length of the sample to be tested.

4. The testing device according to claim 1, characterized in that The number of rollers arranged on the loading module is two or more.

5. The testing device according to claim 4, characterized in that For more than two rollers, the spacing between the outermost pair of rollers should be smaller than the spacing between the rollers on the loading bracket legs.

6. The testing device according to claim 1, characterized in that The lower ends of the salt bridge and the platinum sheet are at the same height as the opening on the inverted concave opening plane of the reaction tank.

7. The testing device according to claim 1, characterized in that: The constant temperature box is used to accommodate the corrosion reaction pool and to ensure that the temperature of the test environment is constant.

8. The testing device according to claim 1, characterized in that A culture solution inoculated with specific bacteria is added into the corrosion reaction tank.

9. An electrochemical testing method for microbial corrosion under stress coupling, wherein the testing device described in any one of claims 1 to 8 is used.

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