Device and method for testing the corrosion performance of materials under stress and crevice
By designing a test device including stress corrosion specimens, stress loading fixtures and test pieces, the problem of difficult testing of corrosion performance under the synergistic effect of material stress and gaps in oil field environment is solved, and the gap corrosion sensitivity in high temperature and high pressure environment is achieved The quality evaluation meets the needs of oilfield pipe material selection and failure mechanism research, and has simple structure and corrosion resistance.
Patent Information
- Application Number
- CN202010463086.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2020-05-27
- Publication Date
- 2024-12-27
- Estimated Expiration
- 2040-05-27
AI Technical Summary
The prior art is difficult to test the corrosion performance of materials under the synergistic effect of stress and gaps, especially under the high temperature and high pressure conditions of pipes in oil field environments, resulting in frequent corrosion failure.
A test device including stress corrosion specimens, stress loading fixtures and test pieces is designed. The specimen is kept bent through stress loading fixtures, the fixing clip maintains the gap between the specimen, and the gap is adjusted by rotating screws, combining with high temperature and high pressure. Immersion method and electrochemical testing method to evaluate the sensitivity of the gap corrosion of the pipe.
The corrosion performance test of the synergistic effect of material stress and gaps in high temperature and high pressure environment can be achieved, and the impact of different gap sizes on material cracking sensitivity can be evaluated, and the needs of oilfield pipe material selection and failure mechanism research are met. The device structure is simple and corrosion-resistant , use less materials.
Smart Images
Figure CN111579471B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of testing devices, and in particular relates to a device and method for testing the corrosion performance of a material under the action of stress and crevice. Background Art
[0002] When the oil casing is in service under the complex working conditions of the oil field, it is subjected to certain tensile stress due to the deadweight of the pipe string. At the same time, the swing or vibration of the oil pipe string causes the pipe body to tilt, sometimes contacting with the casing or forming certain gaps. Another more frequent phenomenon is that there are more gaps between the pipe string structure and between the pipe body and the accessories. When this pipe body is under tensile stress and the gap structure exists, under the action of corrosive media in the process of high temperature and high pressure oil and gas mixed transportation and oil and gas production, there is a greater corrosion risk of stress and gap synergy. It is well known that stress corrosion cracking is one of the most harmful corrosion forms in the oil field environment. Coupled with the promotion of crevice corrosion between the pipe body, the corrosion failure of the pipe body is more frequent. Therefore, in terms of material selection and anti-corrosion control measures for oil field pipe strings, mastering the crevice corrosion sensitivity of materials under stress state is one of the key technologies to prevent pipe string failure.
[0003] At present, in the research on stress and crevice corrosion of pipes, the common stress corrosion methods are: three-point loading bending method; four-point loading bending method and round bar stretching method. There is no unified loading method for crevice corrosion. The most common method is to process a certain gap on the fixture and install it on the specimen. Therefore, stress and crevice corrosion are tested separately, and there are few test devices that can achieve the synergistic effect of stress and crevice corrosion at the same time. Combined with the large number of corrosion failure analyses currently existing in oil fields, it can be seen that pipes are under stress and there are crevice corrosion phenomena everywhere. Therefore, it is of great significance to design a test device that realizes the synergistic effect of metal materials under stress and crevice corrosion to meet the selection of oil field pipes and the study of failure mechanisms. Summary of the invention
[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings and provide a device and method for testing the corrosion performance of materials under stress and crevice action, so as to meet the needs of evaluating the crevice corrosion sensitivity of pipes by high temperature and high pressure environment immersion method and high temperature electrochemical testing method.
[0005] In order to achieve the above-mentioned purpose, a corrosion performance testing device for materials under the action of stress and crevice is provided, which includes a stress corrosion specimen, a stress loading fixture and a test piece. The stress loading fixture is used to fix the stress corrosion specimen and keep the stress corrosion specimen bent at all times. The test piece and the stress corrosion specimen are fixed by a fixing clamp so that a gap is maintained between the test piece and the stress corrosion specimen. A screw is provided on the test piece, and the gap distance between the test piece and the stress corrosion specimen can be adjusted by rotating the screw.
[0006] One end of the stress corrosion test specimen is connected to an electrochemical test lead.
[0007] The width of the test piece is the same as that of the stress corrosion test specimen.
[0008] The test piece is provided with a threaded hole, into which the screw is screwed.
[0009] The fixing clips are fixed on both ends of the test piece.
[0010] The gap size between the test piece and the stress corrosion specimen can be adjusted in the range of 0.01 mm to 1 mm.
[0011] A method for using a device for testing the corrosion performance of a material under stress and crevice, comprising the following steps:
[0012] Step 1, fixing the stress corrosion specimen on a stress loading fixture to load tensile stress on the surface of the corrosion specimen;
[0013] Step 2, fixing the test piece on the stress corrosion specimen by a fixing clamp so that a gap is maintained between the test piece and the stress corrosion specimen;
[0014] Step 3, adjusting the gap distance between the test piece and the stress corrosion specimen by rotating the screw;
[0015] Step 4: Conduct corrosion performance test.
[0016] Compared with the prior art, the stress corrosion specimen is always kept bent by a stress loading fixture, a gap is maintained between the test piece and the stress corrosion specimen by a fixing clamp, and the gap distance between the test piece and the stress corrosion specimen is adjusted by rotating a screw, so that it is suitable for corrosion performance testing under different gap effects. The present invention aims at the actual needs of the oil and gas field, chemical, marine and other industries for stress and crevice corrosion evaluation of materials, and at the service conditions of pipes in harsh environments under high temperature and high pressure conditions. In addition, the test device has a simple structure, is corrosion-resistant, and uses less materials. At the same time, a high temperature and high pressure immersion method and an electrochemical test method can be realized.
[0017] This method first fixes the stress corrosion specimen on the stress loading fixture to keep the stress corrosion specimen bent; then fixes the test piece on the stress corrosion specimen by fixing the clamp to keep the gap between the test piece and the stress corrosion specimen; adjusts the gap distance between the test piece and the stress corrosion specimen by rotating the screw; and finally performs a corrosion performance test. This method can meet the needs of evaluating the crevice corrosion sensitivity of pipes by high temperature and high pressure environment immersion method and high temperature electrochemical test method, and can also realize the influence of the change of the crevice size under different stress states on the cracking sensitivity of the material. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is a structural diagram of the present invention;
[0019] Among them, 1. stress corrosion specimen, 2. fixing clamp, 3. test piece, 4. screw, 5. electrochemical test wire, 6. stress loading fixture. DETAILED DESCRIPTION
[0020] The present invention will be further described below in conjunction with the accompanying drawings.
[0021] See also Figure 1 , a corrosion performance test device for materials under stress and crevice action is provided, comprising a stress corrosion specimen 1, a stress loading fixture 6 and a test piece 3, wherein the stress loading fixture 6 is used to fix the stress corrosion specimen 1 and keep the stress corrosion specimen 1 bent all the time, the test piece 3 is fixed to the stress corrosion specimen 1 by a fixing clamp 2, the fixing clamp 2 is fixed at both ends of the test piece 3, so that a gap is maintained between the test piece 3 and the stress corrosion specimen 1, the width of the test piece 3 is the same as that of the stress corrosion specimen 1, a screw 4 is provided on the test piece 3, a threaded hole is provided on the test piece 3, the screw 4 is screwed into the threaded hole, and the gap distance between the test piece 3 and the stress corrosion specimen 1 can be adjusted by rotating the screw 4. The gap between the test piece 3 and the stress corrosion specimen 1 can be adjusted in a range of 0.01 mm to 1 mm, and one end of the stress corrosion specimen 1 is connected to an electrochemical test lead 5, so that the electrochemical corrosion characteristics of the coordinated crevice corrosion action under stress state can be tested. The welding part is sealed with epoxy coating to avoid the influence of welding materials on the test results.
[0022] A method for using a device for testing the corrosion performance of a material under stress and crevice, comprising the following steps:
[0023] Step 1, fixing the stress corrosion specimen 1 on the stress loading fixture 6, so that the stress corrosion specimen 1 remains bent;
[0024] Step 2: fix the test piece 3 on the stress corrosion specimen 1 by means of the fixing clamp 2, so that a gap is maintained between the test piece 3 and the stress corrosion specimen 1;
[0025] Step 3, adjusting the gap distance between the test piece 3 and the stress corrosion test piece 1 by rotating the screw 4;
[0026] Step 4: Conduct corrosion performance test.
[0027] The present invention is used for corrosion evaluation test of stress and crevice synergistic effect under high temperature and high pressure conditions and in a harsh environment where CO2 and / or H2S coexist. It can realize electrochemical performance test and weight loss method corrosion rate test. Through experiments, the critical crevice size that plays a leading role in the stress corrosion cracking sensitivity of the material can be grasped.
[0028] After stress corrosion specimen 1 is loaded with different tensile stress values, the size of the gap set on the surface of the stress concentration area of stress corrosion specimen 1 is adjusted to test and evaluate the corrosion cracking sensitivity or corrosion degree of the specimen under stress state and the action of gaps of different sizes. The size of stress corrosion specimen 1 is 120mm×15mm×3mm, and the stress loading range of stress corrosion specimen 1 is 60% to 90% of the nominal yield strength of the specimen material. The gap on the surface of the stress concentration area is formed by a test piece 3 with the same width as the specimen fixed on the top of stress corrosion specimen 1. Test piece 3 is a polytetrafluoroethylene sheet. After test piece 3 is installed, it can be adjusted to form a gap of 0.01mm to 1mm with the surface of stress corrosion specimen 1.
[0029] The stress and gap synergistic testing device designed in the present invention can be applied to a certain temperature and pressure range (≥25°C, room temperature and ≤70MPa), meet the requirements of immersion method and electrochemical testing method, and realize the screening and corrosion performance evaluation of oil well pipes in an oil field environment containing CO2 / H2S medium.
Claims
1. A device for testing the corrosion performance of materials under stress and crevice, characterized in that: The invention comprises a stress corrosion specimen (1), a stress loading fixture (6) and a test piece (3); the stress loading fixture (6) is used to fix the stress corrosion specimen (1) and keep the stress corrosion specimen (1) bent at all times; the test piece (3) and the stress corrosion specimen (1) are fixed by a fixing clamp (2) so that a gap is maintained between the test piece (3) and the stress corrosion specimen (1); a screw (4) is provided on the test piece (3); and the gap distance between the test piece (3) and the stress corrosion specimen (1) can be adjusted by rotating the screw (4); One end of the stress corrosion test specimen (1) is connected to an electrochemical test wire (5); The test piece (3) is provided with a threaded hole, and the screw (4) is screwed into the threaded hole.
2. A device for testing the corrosion performance of materials under stress and crevice according to claim 1, characterized in that: The width of the test piece (3) is the same as that of the stress corrosion test piece (1).
3. The device for testing the corrosion performance of materials under stress and crevice according to claim 1, characterized in that: The fixing clips (2) are fixed on both ends of the test piece (3).
4. The device for testing the corrosion performance of materials under stress and crevice according to claim 1, characterized in that: The gap size between the test piece (3) and the stress corrosion test specimen (1) can be adjusted in the range of 0.01 mm to 1 mm.
5. The method for using the device for testing the corrosion performance of materials under stress and crevice as claimed in claim 1, characterized in that: The following steps are involved: Step 1, fixing the stress corrosion specimen (1) on a stress loading fixture (6) so that tensile stress is loaded on the surface of the stress corrosion specimen (1) and the specimen is kept bent; Step 2: fix the test piece (3) on the stress corrosion test piece (1) by means of a fixing clamp (2) so that a gap is maintained between the test piece (3) and the stress corrosion test piece (1); Step 3, adjusting the gap distance between the test piece (3) and the stress corrosion test specimen (1) by rotating the screw (4); Step 4: Conduct corrosion performance test.