Pre-tensile stress corrosion wear test system and test method

Abstract

The invention discloses a tensile stress preloading corrosion wear test system and a tensile stress preloading corrosion wear test method. The tensile stress preloading corrosion wear test system comprises a test pool, an electrode fixing seat, a sample loading device and a load monitoring unit, the test pool is made of 316L stainless steel, a sample is processed into a specified size and is mounted in the test pool through a sample clamp and a fixing pin, and a polytetrafluoroethylene insulating tube is arranged at the contact part of the sample and the sample clamp, so that the influence of a pool body and the sample clamp on an electrochemical signal in the test process is avoided; an electrode fixing seat is mounted at the top of the test pool; a reference electrode and an auxiliary electrode are mounted in corresponding electrode grooves; the sample loading device comprises a sample clamp, a loading shaft, a loading spring and a pushing nut, and provides tensile stress vertical to the friction direction for the sample through mechanical action; the load monitoring unit is composed of a load measuring sensor and a monitoring device and can monitor and record the change of tensile stress borne by the sample in real time in the testing process and output the change to a computer in the form of data.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of friction equipment, and particularly relates to a pre-tension stress corrosion wear test system and a test method. BACKGROUND

[0002] Components in petrochemical, marine and nuclear power engineering equipment are often served in corrosive media, facing material loss caused by corrosion wear phenomenon. Corrosion wear is a phenomenon of material loss caused by mechanical action (i.e. friction shear stress) in the friction process and electrochemical (or chemical) reaction of the friction surface material and the surrounding medium. Unlike the simple superposition of pure electrochemical corrosion and mechanical wear, the essence of corrosion wear lies in the interaction of corrosion and wear, that is, electrochemical corrosion will promote the progress of mechanical wear, while mechanical wear will accelerate the occurrence of electrochemical corrosion, and the two will greatly increase the material loss, exceeding the sum of the material loss caused by the two independently.

[0003] In heat exchangers (especially tubular) and other equipment, in order to accommodate longer heat transfer area in limited shell space, the internal heat exchanger pipes usually need to be bent into a specific shape. When the pipe is bent, the material on the outside of the pipe is stretched and is in a tensile stress state; the material on the inside is compressed and is in a compressive stress state. After plastic deformation, these stresses will not completely disappear even after unloading. The external material is more prone to plastic flow and micro-crack initiation under the action of tensile stress, and the crack propagation is accelerated under the action of corrosive medium and mechanical friction, forming transgranular cracks, resulting in increased material loss and causing stress corrosion cracking. Therefore, it is necessary to study the corrosion wear law and mechanism under tensile stress.

[0004] At present, there are some corrosion wear test systems, but the design flexibility of these systems is insufficient and the functions are relatively single, which is difficult to meet the needs of corrosion wear scene simulation under specific working conditions. The existing systems can usually only process the corresponding materials into disc, ring and other friction samples and fix them in a semi-closed liquid tank for wear test, cannot measure the electrochemical signals in real time in situ during the wear process to study the corrosion related information, and cannot meet the corrosion wear environment simulation of materials in tensile stress state due to plastic deformation, so that the corrosion wear phenomenon of materials under specific working conditions cannot be comprehensively tested and evaluated, and the mechanism cannot be comprehensively studied. At the same time, the working condition parameters provided by the existing equipment cannot be measured and recorded in real time, affecting the accuracy and repeatability of the corrosion wear test. SUMMARY

[0005] In response to the shortcomings of existing corrosion and wear testing equipment, and in order to study the corrosion and wear characteristics of materials bearing tensile stress, the present invention provides a pre-tensile stress corrosion and wear testing system. This system can apply precise and controllable tensile stress to the sample in a corrosive medium. At the same time, it has a three-electrode system for real-time in-situ electrochemical measurement, which can more comprehensively measure and evaluate the corrosion and wear behavior of different metal materials when subjected to external tensile stress.

[0006] To this end, the present invention adopts the following technical solutions: A pre-tension stress corrosion wear test system includes a test cell, an electrode fixing seat, a sample loading device and a load monitoring unit; The test cell is a trough-shaped structure with an open top. The sample is machined to the required test size and installed in the test cell using a sample fixture and a fixing pin. The contact portion between the sample and the sample fixture is insulated to prevent the cell body and the sample fixture from affecting the electrochemical signal during the test. The sample fixture includes a left sample fixture and a right sample fixture, which respectively clamp the left and right ends of the sample. The grinding head is located above the test cell, with the lower end of the grinding head resting against the upper surface of the sample for friction testing. The electrode holder is fixed on the top of the test cell. A vertical reference electrode and an auxiliary electrode are installed on the electrode holder. The lower ends of the reference electrode and the auxiliary electrode extend into the test cell. The specimen loading device is connected to the left and right ends of the test cell. The head end of the test loading device extends into the test cell and is connected to the left specimen clamp and the right specimen clamp respectively. The tensile stress is applied to the specimen by pulling the left specimen clamp and the right specimen clamp. The load monitoring unit includes a load measuring sensor, which is used to measure the value of the tensile stress.

[0007] Furthermore, the test cell is provided with an electrode fixture made of resin material, and the electrode fixture is provided with two electrode slots. The reference electrode and the auxiliary electrode are installed in the electrode slots and are tightly fixed by screws. Loosening the screws is used to adjust the vertical distance between the electrode and the sample.

[0008] Furthermore, the sample is plugged into the sample fixture via a polyetheretherketone fixing pin, and a polytetrafluoroethylene insulating tube is installed between the sample fixture and the sample to prevent the metal sample fixture from directly contacting the sample.

[0009] Furthermore, a sample fixture guide block is provided in the test pool to limit the freedom of the sample friction direction; a sample support is provided below the sample friction position, and the upper surface of the sample support contacts the bottom surface of the sample to prevent the sample from bending under the action of the friction load.

[0010] Further, the sample loading device connected to the left sample clamp comprises a loading shaft, a sealing ring, a flat pad and a sample clamp fixing screw; the loading shaft is horizontally arranged, the head end of the loading shaft is threadedly connected to the left sample clamp, the tail end of the loading shaft is led out from the left side of the test tank, and the sealing ring is used for sealing the gap between the test tank and the loading shaft; the flat pad and the sample clamp fixing screw are connected to the tail end of the loading shaft, and the load measuring sensor is located between the flat pad and the outer wall of the test tank, and the flat pad applies pressure to the load measuring sensor when the load is applied.

[0011] Further, the sample loading device connected to the right sample clamp comprises a loading shaft, a sealing ring, a loading spring, a hard gasket, a super nut and a super nut pushing screw; the loading shaft is horizontally arranged, the head end of the loading shaft is threadedly connected to the right sample clamp, the tail end of the loading shaft is led out from the right side of the test tank, and the sealing ring is used for sealing the gap between the test tank and the loading shaft; the hard gasket and the super nut are connected to the tail end of the loading shaft, the loading spring is located between the hard gasket and the outer wall of the test tank, and the flat pad extrudes the loading spring when the load is applied, the super nut is connected with the super nut pushing screw, and pressure is applied by adjusting the super nut pushing screw.

[0012] Further, the signal of the load measuring sensor is transmitted to a computer, and the monitored tensile stress value is displayed in real time.

[0013] Further, the test tank is made of 316L stainless steel.

[0014] A test method of a pre-tensile stress corrosion and wear test system comprises the following steps: S1. Sample and electrode installation The sample to be tested is placed in the sample clamp, and the sample is fixed; the reference electrode and the auxiliary electrode are respectively inserted into the electrode fixing seat, and the horizontal position of the electrode fixing seat and the vertical distance between the two electrodes and the sample are adjusted; the wire is spot-welded on the sample and led out as a working electrode, after the test medium is injected into the test tank, the three electrodes are connected to the corresponding electrode ports of the electrochemical workstation; S2. Pre-tensile stress operation The super nut is adjusted to apply a tensile stress load to the sample, and the change of the tensile stress value displayed on the computer is paid attention to during the process, and the load is stopped and maintained after the set value is reached; S3. Test preparation and start After the pre-tensile stress operation is completed, the parameters of the friction and wear equipment are set, the equipment is started after the setting is completed to start the friction and wear test, and the electrochemical software is started for corrosion and electrochemical test after the friction and wear is stable.

[0015] The beneficial effects of the present application are: 1. The system is equipped with detachable electrode clamps made of resin material, on which reference electrodes and auxiliary electrodes required for electrochemical tests can be installed, and the placement position of the electrodes and the vertical distance from the sample can be adjusted in real time, so that the test system can not only meet the pure friction and wear test, but also can be used in corrosion and wear test in corrosive medium, and the electrochemical three-electrode system can be set synchronously to perform real-time in-situ electrochemical test.

[0016] 2. The system has a sample clamp and a bearing platform that can restrict and fix the sample in multiple degrees of freedom, while making insulated contact with the sample to avoid affecting the electrochemical test signal, meet the diversified experimental needs, improve the accuracy and repeatability of the test, and ensure efficient testing under different samples and different corrosion environments.

[0017] 3. The system is equipped with a tensile stress loading system that can apply tensile stress in the vertical friction direction to the sample to simulate the corrosion and wear environment of special components in corrosive medium, and the applied tensile stress can be monitored and controlled in real time, accurately analyzing the influence of tensile stress change on corrosion and wear rate, and providing more detailed and comprehensive data support for corrosion and wear research under specific service environment.

[0018] 4. The system overcomes many shortcomings of existing corrosion and wear test equipment in design, has the function of applying tensile stress and monitoring and controlling it in real time, can comprehensively and accurately evaluate the corrosion and wear behavior of special service components with high applied stress in corrosive environment, meets the accurate and diversified needs of modern corrosion test, and provides a scientific basis for the selection of metal materials and process design under corresponding working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a structural schematic diagram of the test system of the present application; Figure 2 is a structural front view of the test system of the present application; Figure 3 is a structural top view of the test system of the present application; Figure 4 is a comparison chart of electrochemical test data of 316LN stainless steel using the test system of the present application and without applied tensile stress; Figure 5 is a comparison chart of wear test data of 316LN stainless steel using the test system of the present application and without applied tensile stress; In the figure: 1-test cell, 2-electrode fixing seat, 3-reference electrode, 4-auxiliary electrode, 5-sample fixture fixing screw, 6-flat washer, 7-load measuring sensor, 8-sample fixture, 9-grinding head, 10-sample, 11-loading spring, 12-hard gasket, 13-super nut, 14-super nut push screw, 15-sealing ring, 16-loading shaft, 17-insulating tube, 18-sample base, 19-insulating pin, 20-sample fixture guide block, 21-electrode fixing seat screw. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and specific examples: like Figure 1 As shown, a pre-tension stress corrosion wear test system includes a test cell 1, an electrode fixing seat 2, a sample fixture 8, a tensile stress loading unit and a load measurement sensor 7.

[0021] The test cell 1 is made of 316L stainless steel, with through-holes on the left and right sides of its outer wall. A loading shaft 16, also made of 316L stainless steel, passes through the through-holes. An EPDM rubber seal 15 is installed in the through-hole to prevent leakage of the test medium from the test cell. An adjustable resin electrode holder 2 is placed above the test cell 1 and secured with screws 21. Two electrode fixtures are mounted on the holders, each containing two electrode slots. A reference electrode 3 and an auxiliary electrode 4 are placed in the slots, enabling real-time, in-situ electrochemical testing during the corrosion and wear test.

[0022] like Figure 2 As shown, a sample 10 processed into a suitable size is placed in a sample holder 8 made of 316L stainless steel. The two are connected and fixed by a zirconia insulating pin 19. A polytetrafluoroethylene insulating tube 17 is provided between the sample holder 8 and the sample 10 to avoid the direct contact between the sample holder and the sample affecting the electrochemical signal and ensure the accuracy of the test. A wire is spot-welded on the sample 10 and led out to serve as a working electrode. The sample 10 is in direct contact with the grinding head 9 for friction and wear testing. A sample support 18 made of resin material is provided below to prevent the sample 10 from bearing plastic deformation during the friction and wear test, which affects the effect of the friction and wear test.

[0023] The sample clamp 8 is directly connected with the loading shaft 16, one side of which passes through the test cell 1 and is connected with the super nut 13 through thread connection, the super nut 13 is provided with six super nut pushing screws 14, the position of the super nut 13 is controlled by rotating the pushing screws to extrude the loading spring 11 to provide tensile stress for the sample 10; the other side of the loading shaft passes through the test cell 1 and is connected with the load measuring sensor 7 through the sample clamp fixing screw 5 and the flat washer 6, the load measuring sensor is connected with the tensile stress display and the computer, the real-time change of the tensile stress can be monitored and displayed in the form of data, and the accuracy and repeatability of the corrosion and wear test parameters are ensured.

[0024] As shown in Figure 3 The sample clamp 8 is provided with four sample clamp guide blocks 20 made of resin around the sample clamp 8, the freedom degree of the parallel friction direction of the sample 10 is fixed, and the stability of the sample 10 in the friction and wear test is ensured.

[0025] The device is used in cooperation with the friction and wear equipment, the friction and wear equipment can accurately control the corrosion and wear working condition parameters such as load, frequency and displacement amplitude, and realize the pre-tension corrosion and wear test. The specific test operation process is as follows: 1. Sample and electrode installation The test sample is placed in the sample clamp 8, and the sample is fixed by using the insulating pin 19. Then, the reference electrode 3 and the auxiliary electrode 4 are respectively inserted into the corresponding electrode grooves in the electrode fixing seat 2, and the horizontal position of the electrode fixing seat and the vertical distance between the two electrodes and the sample are adjusted. The test sample is spot-welded with a lead wire and is led out as a working electrode. After the test medium is injected into the test cell 1, the three electrodes are connected to the corresponding electrode ports of the electrochemical workstation.

[0026] 2. Pre-tension operation The super nut pushing screw 14 is rotated to push the super nut 13 to move towards the test cell 1 to compress the loading spring 11, and the tensile stress value displayed on the computer is paid attention to during the process, and the process is stopped and kept when the set value is reached.

[0027] 3. Test preparation and start After the pre-tension operation is completed, the parameters of the friction and wear equipment are set, the equipment is started after the setting is completed to start the friction and wear test, and the electrochemical test is started after the friction and wear is stable.

[0028] The pre-tension corrosion and wear test system and the corrosion and wear electrochemical test data obtained by the ordinary friction and wear test are compared as shown in Figure 4 Figure 4 ​a shows that the open circuit potential of 316LN stainless steel in the corrosion wear process under 800N tensile stress is lower than that without external tensile stress, indicating that the corrosion sensitivity of the material is improved at this time; as Figure 4 b shows that the material impedance arc radius is smaller under 800N tensile stress, and the corrosion resistance of the material is reduced; the dynamic point potential polarization curve shows that the corrosion potential of the material under 800N tensile stress is reduced from-0.49V without tensile force to-0.71V, and the corrosion current density is increased by one order of magnitude, and the corrosion resistance is obviously reduced, as Figure 4 c and d show. The corrosion wear test system under pre-tensile stress is compared with the corrosion wear test data obtained by ordinary friction and wear test, as Figure 5 shown. Figure 5 a and b show that the wear scar size of 316LN stainless steel significantly increases under 800N tensile stress; without tensile force, the material wear rate is 1.38×10 -8 mm 3 / N·m, and under 800N tensile stress, the material wear rate increases by two orders of magnitude, reaching 4.67×10 -6 mm 3 / N·m. In summary, the corrosion and wear resistance of the material under tensile stress is significantly reduced, the test system of the application can more accurately simulate the actual service environment, greatly improve the accuracy of the test data, and has important significance for studying the corrosion and wear behavior under specific service environment.

Claims

1. A pre-tension stress corrosion wear test system, characterized in that: It includes a test cell (1), an electrode fixing seat (2), a sample loading device and a load monitoring unit; The test cell (1) is a trough-shaped structure with an open top; the sample (10) is processed into the required size for the test and is installed in the test cell (1) through a sample fixture (8) and a fixing pin, and the contact portion between the sample (10) and the sample fixture (8) is insulated to prevent the cell body and the sample fixture (8) from affecting the electrochemical signal during the test; the sample fixture (8) includes a left sample fixture and a right sample fixture, and the two sample fixtures (8) respectively clamp the left and right ends of the sample; the grinding head (9) is located above the test cell (1), and the lower end of the grinding head (9) is low against the upper surface of the sample to perform the friction test; The electrode fixing seat (2) is fixed to the top of the test cell (1), and a vertical reference electrode (3) and an auxiliary electrode (4) are mounted on the electrode fixing seat (2), and the lower ends of the reference electrode (3) and the auxiliary electrode (4) extend into the test cell (1); The sample loading device is connected to the left and right ends of the test pool (1), and the head end of the test loading device extends into the test pool (1) and is respectively connected to the left sample clamp and the right sample clamp, and applies tensile stress to the sample (10) by pulling the left sample clamp and the right sample clamp; The load monitoring unit comprises a load measuring sensor (7), which is used to measure the value of tensile stress.

2. The pre-tension stress corrosion wear test system according to claim 1, characterized in that: The test cell (1) is provided with an electrode fixture made of resin material. The electrode fixture is provided with two electrode slots. The reference electrode (3) and the auxiliary electrode (4) are installed in the electrode slots and are tightly fixed by screws. The screws are loosened to adjust the vertical distance between the electrode and the sample (10).

3. The pre-tension stress corrosion wear test system according to claim 1, characterized in that: The sample (10) is plugged into the sample fixture (8) via a polyetheretherketone fixing pin, and a polytetrafluoroethylene insulating tube (17) is installed between the sample fixture (8) and the sample to prevent the metal sample fixture (8) from directly contacting the sample (10).

4. The pre-tension stress corrosion wear test system according to claim 1, characterized in that: The test pool (1) is provided with a guide block of a sample fixture (8) to limit the degree of freedom of the sample friction direction; a sample support (18) is provided below the friction position of the sample (10), and the upper surface of the sample support (18) contacts the bottom surface of the sample to prevent the sample (10) from bending under the action of the friction load.

5. The pre-tension stress corrosion wear test system according to claim 1, characterized in that: The sample loading device connected to the left sample fixture comprises a loading shaft (16), a sealing ring (15), a flat washer (6) and a fixing screw of the sample fixture (8); the loading shaft (16) is arranged horizontally, the head end of the loading shaft (16) is threadedly connected to the left sample fixture (8), the tail end of the loading shaft (16) passes through the left side of the test pool (1), and the sealing ring (15) is used to seal the gap between the test pool (1) and the loading shaft (16); the flat washer (6) and the fixing screw of the sample fixture (8) are connected to the tail end of the loading shaft (16), and the load measurement sensor (7) is located between the flat washer (6) and the outer wall of the test pool (1), and when a load is applied, the flat washer (6) applies pressure to the load measurement sensor (7).

6. The pre-tension stress corrosion wear testing system according to claim 5, characterized in that: The sample loading device connected to the right sample fixture includes a loading shaft (16), a sealing ring (15), a loading spring (11), a hard gasket (12), a super nut (13) and a super nut (13) push screw; the loading shaft (16) is arranged horizontally, the head end of the loading shaft (16) is threadedly connected to the right sample fixture (8), the tail end of the loading shaft (16) passes through the right side of the test pool (1), and the sealing ring (15) is used to seal the gap between the test pool (1) and the loading shaft (16); the hard gasket (12) and the super nut (13) are connected to the tail end of the loading shaft (16), the loading spring (11) is located between the hard gasket (12) and the outer wall of the test pool (1), and when a load is applied, the flat gasket (6) squeezes the loading spring (11), and the super nut (13) push screw is connected to the super nut (13), and pressure is applied by adjusting the super nut (13) push screw.

7. The pre-tension stress corrosion wear testing system according to claim 5, characterized in that: The signal of the load measuring sensor (7) is transmitted to the computer, which displays the monitored tensile stress value in real time.

8. The pre-tension stress corrosion wear testing system according to claim 1, characterized in that: The test pool (1) is made of 316L stainless steel.

9. A test method for a pre-tension stress corrosion wear test system according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Sample and electrode installation The sample (10) to be tested is placed in the sample fixture (8) and the sample (10) is fixed; the reference electrode (3) and the auxiliary electrode (4) are respectively inserted into the electrode holder (2), and the horizontal position of the electrode holder (2) and the vertical distance between the two electrodes and the sample (10) are adjusted; a wire is spot-welded on the sample (10) and led out to serve as a working electrode, and after the test medium is injected into the test cell (1), the three electrodes are externally connected to the corresponding electrode ports of the electrochemical workstation; S2. Prestressing operation Adjust the super nut (13) to apply tensile stress to the specimen (10), pay attention to the change of tensile stress value displayed on the computer during the process, and stop and maintain the load after reaching the set value; S3. Test preparation and start After the pre-stressing operation is completed, the parameters of the friction and wear equipment are set. After the settings are completed, the equipment is started to start the friction and wear test. After the friction and wear are stable, the electrochemical software is started to perform the corrosion electrochemical test.

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