CN115356199B - Evaluation method for hydrogen sulfide stress corrosion resistance sensitivity of oil well pipe - Google Patents
Evaluation method for hydrogen sulfide stress corrosion resistance sensitivity of oil well pipe Download PDFInfo
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- 230000007797 corrosion Effects 0.000 title claims abstract description 73
- 238000005260 corrosion Methods 0.000 title claims abstract description 73
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 title claims abstract description 44
- 229910000037 hydrogen sulfide Inorganic materials 0.000 title claims abstract description 44
- 239000003129 oil well Substances 0.000 title claims abstract description 40
- 230000035945 sensitivity Effects 0.000 title claims abstract description 34
- 238000011156 evaluation Methods 0.000 title claims abstract description 11
- 238000012360 testing method Methods 0.000 claims abstract description 91
- 239000000463 material Substances 0.000 claims abstract description 33
- 238000012545 processing Methods 0.000 claims abstract description 14
- 239000012085 test solution Substances 0.000 claims abstract description 13
- 238000007789 sealing Methods 0.000 claims abstract description 4
- 230000006641 stabilisation Effects 0.000 claims abstract description 3
- 238000011105 stabilization Methods 0.000 claims abstract description 3
- 238000000034 method Methods 0.000 claims description 27
- 238000005259 measurement Methods 0.000 claims description 15
- 230000003321 amplification Effects 0.000 claims description 6
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 6
- 238000004364 calculation method Methods 0.000 claims description 5
- 238000007781 pre-processing Methods 0.000 claims description 3
- 230000000644 propagated effect Effects 0.000 claims description 3
- 238000009864 tensile test Methods 0.000 abstract description 14
- 238000001514 detection method Methods 0.000 abstract description 3
- 206010017076 Fracture Diseases 0.000 description 74
- 239000000243 solution Substances 0.000 description 15
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 10
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 238000004381 surface treatment Methods 0.000 description 10
- 238000005336 cracking Methods 0.000 description 9
- 229910052717 sulfur Inorganic materials 0.000 description 7
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 6
- 239000007789 gas Substances 0.000 description 6
- 239000011593 sulfur Substances 0.000 description 6
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 5
- 239000004519 grease Substances 0.000 description 5
- 239000002932 luster Substances 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 229910052979 sodium sulfide Inorganic materials 0.000 description 2
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 2
- 206010041541 Spinal compression fracture Diseases 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000033558 biomineral tissue development Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
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- 238000011160 research Methods 0.000 description 1
- 239000012086 standard solution Substances 0.000 description 1
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- G01N2203/02—Details not specific for a particular testing method
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Abstract
本发明提供一种油井管抗硫化氢应力腐蚀敏感性的评价方法，包括：将试样加工成设定的尺寸，对其表面进行预处理；将试样安装在反应釜中的拉伸设备上，向反应釜中加入适量的测试溶液，封闭反应釜；调整测试溶液中的硫化氢浓度，快速拉伸预加载到试样的50％～80％屈服强度值；稳定后开始以设定的应变速率进行慢拉伸加载试验，直至试样被拉断，记录试验结果；取出断裂的拉伸试样，通过断口形貌观察，选取断口上面积最大的台阶裂纹平面的面积来评价油井管材料的抗应力腐蚀性能。利用断口上的台阶裂纹参数对慢拉伸试验结果进行精确化的分析，达到定量分析油井管材料的抗应力腐蚀敏感性的目的，缩短试验周期，提高检测效率。
The present invention provides an evaluation method for the hydrogen sulfide stress corrosion sensitivity of oil well pipes, comprising: processing the sample into a set size and pre-treating the surface thereof; installing the sample on a stretching device in a reactor, adding an appropriate amount of test solution into the reactor, and sealing the reactor; adjusting the hydrogen sulfide concentration in the test solution, and rapidly stretching and pre-loading the sample to 50% to 80% of the yield strength value; starting a slow tensile loading test at a set strain rate after stabilization until the sample is broken, and recording the test results; taking out the broken tensile sample, observing the fracture morphology, and selecting the area of the step crack plane with the largest area on the fracture to evaluate the stress corrosion resistance of the oil well pipe material. The step crack parameters on the fracture are used to accurately analyze the slow tensile test results, so as to achieve the purpose of quantitatively analyzing the stress corrosion resistance sensitivity of the oil well pipe material, shorten the test cycle, and improve the detection efficiency.
Description
Technical Field
The invention relates to the technical field of corrosion tests, in particular to an evaluation method for hydrogen sulfide stress corrosion resistance sensitivity of an oil well pipe.
Background
In recent years, with the exploration and development of oil and gas wells in ultra-deep, ultra-high temperature and ultra-high corrosion harsh environments, the working conditions of the oil and gas wells generally have the characteristics of high temperature, high pressure, high CO2, high H2S and high Cl-, and high mineralization, and the oil well pipes are subjected to stress corrosion cracking failure due to the complex harsh working conditions and the special working process, so that the normal production operation of the oil and gas fields is seriously influenced. In particular to an oil well pipe used in the exploration and exploitation process of sulfur-containing oil and gas resources, which is easy to generate hydrogen sulfide stress corrosion cracking, is a low-stress brittle fracture, has high crack propagation speed, has burst fracture and highest danger coefficient, and is easy to cause major accidents and casualties.
Aiming at the situation, relevant standards are established at home and abroad to reduce the risk brought by hydrogen Sulfide Stress Corrosion Cracking (SSCC), and strict detection and evaluation are carried out on SSCC resistance of the oil well pipe. The standard tensile test (method A) is regulated in NACE STANDARD TM0177-2005 "indoor test of sulfide stress corrosion cracking resistance and stress corrosion cracking resistance of metal in H2S environment" and GB/T4157-2006 "laboratory test of special form environment cracking resistance of metal in hydrogen sulfide environment", the hydrogen sulfide stress corrosion resistance performance is determined according to the breaking time in the experimental period, products which are not broken in more than 720H are qualified, products which are broken in 720H are unqualified, and the test result only can give out failure and non-failure information. Similarly, the four-point bending loading test in the ASTM G39-99 standard is also a common method for evaluating the stress corrosion resistance of an oil well pipe, an A method standard solution is adopted, a product which is not broken in 720h is qualified, a product which is broken in 720h is unqualified, a 10-time magnifying glass is used for observing whether cracks exist on the surface of a non-broken sample, and the test result can only give out failure and non-failure information. The methods have the advantages that the test conditions are harsh, the test period is long, the test results can only give out failure and non-failure information, the hydrogen sulfide stress corrosion resistance grade of a non-failure sample cannot be evaluated, other test means are combined for comprehensive evaluation, the test period is prolonged, and the test cost is increased.
Therefore, a new method is needed to be found, the hydrogen sulfide stress corrosion resistance of the oil well pipe material can be rapidly and accurately evaluated, the test period is shortened, and the test cost is reduced. The slow-rate tensile test is one of the current mature and advanced methods for researching stress corrosion standards because of the rapidness, accuracy and high reproducibility, and the obtained parameter information is more, which is widely used by the researchers. When evaluating the hydrogen sulfide stress corrosion resistance of an oil well pipe by a slow tensile test, the oil well pipe is generally evaluated by adopting fracture morphology and stress corrosion cracking sensitivity index, and if the fracture morphology is characterized by brittle fracture or the stress corrosion cracking sensitivity index is greater than a certain value (generally 25%), the oil well pipe material is generally considered to have stress corrosion cracking sensitivity in a corresponding research system.
However, in the practical test process, fracture morphology is often found to be a ductile fracture or a mixed fracture mechanism, and the stress corrosion sensitivity index calculated by using the elongation after fracture, the shrinkage after fracture and the yield strength loss ratio is lower than 25%, so that the material is often considered to have no stress corrosion sensitivity, but a stepped crack platform appears near the circumference of the fracture, which indicates that the material has obvious stress corrosion sensitivity in practice, which is not consistent with the test result of the test. In addition, even if two materials with the same stress corrosion sensitivity index have larger actual stress corrosion resistance difference, especially step cracks perpendicular to the stretching direction in fracture morphology are distributed along the circumferential direction, the sizes and the numbers of the step cracks are obviously different, and the stress corrosion resistance of the material is not favorable for accurate evaluation.
Based on the above, the present invention has been made in order to accurately and rapidly evaluate the hydrogen sulfide stress corrosion resistance of an oil well pipe material.
Disclosure of Invention
In order to overcome the defects in the background art, the invention provides the evaluation method for the hydrogen sulfide stress corrosion resistance sensitivity of the oil well pipe, which can rapidly and accurately evaluate the hydrogen sulfide stress corrosion resistance of the oil well pipe material, and accurately analyze the slow tensile test result by using the step crack plane parameters on the fracture, so that the aim of quantitatively evaluating the stress corrosion resistance sensitivity of the oil well pipe material is fulfilled, the test period is shortened, and the detection efficiency is improved.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
An evaluation method for hydrogen sulfide stress corrosion resistance sensitivity of an oil well pipe comprises the following steps:
step 1, processing a sample into a set size, and preprocessing the surface of the sample;
Step 2, mounting a sample on stretching equipment in a reaction kettle, adding a proper amount of test solution into the reaction kettle, and sealing the reaction kettle;
Step3, adjusting the concentration of hydrogen sulfide in the test solution, and rapidly stretching and preloading the test solution to 50% -80% yield strength value of the test sample;
Step 4, after stabilization, starting to perform a slow tensile loading test at a set strain rate until the sample is broken, and recording a test result;
And 5, finally taking out the broken tensile sample, removing corrosion products on the surface of the sample and the fracture, and selecting the area of the step crack plane with the largest area on the fracture to evaluate the stress corrosion resistance of the oil well pipe material through observing the fracture morphology.
Further, the strain rate of the slow tensile loading test was 1X 10 -7～5×10-5 mm/s.
Further, the strain rate of the rapid stretching is 1×10 -4 mm/s or more.
Further, the evaluating the stress corrosion resistance of the oil well pipe material in the step 5 specifically comprises the following steps:
1) The crack propagation direction is along the step crack plane where the crack propagation direction is, and the crack propagation direction is respectively and simultaneously propagated from the outer surface of the sample to the center along the radius and along the circumferential direction;
2) The fracture morphology observation adopts a laser confocal microscope, the amplification factor is 20-100, the fracture surface is rugged, step cracks are formed in the circumferential direction, meanwhile, the distance between a workbench and a lens is adjusted, the fracture morphology of a sample is ensured to be clear, and the step crack area measurement is accurate;
3) The step crack plane is used for measuring the step crack area with the largest area on the fracture;
4) Step crack area selection vertical projection area calculation;
5) The plane shape of the step crack is elliptical, the stress corrosion resistance is related to the largest vertical projection area S of the step crack, the formula of stress corrosion sensitivity R is simplified to R=K R/b S, b is the short axis length of the ellipse, namely the radial crack expansion depth, R is the radius of a slow tensile sample testing area, and K is a constant.
Further, the slow tensile loading test loads along the length direction of the sample, and the tensile direction is parallel to the length direction of the sample.
Further, the stretching direction of the slow stretching loading test is perpendicular to the crack plane of the step, and the stretching direction is perpendicular to the crack propagation direction and is different from 90 degrees.
Further, the test solution is Nace standard A solution, and the concentration of hydrogen sulfide is 0-3500 ppm.
Compared with the prior art, the invention has the beneficial effects that:
According to the invention, the stress corrosion resistance performance of the oil well pipe material in a service environment or a simulated actual environment is tested, the stress corrosion resistance sensitivity of the oil well pipe material is evaluated through fracture morphology observation and the area of a step crack plane, and further the practicability of the oil well pipe material in a specific working condition environment is evaluated, so that the material selection and equipment maintenance are guided.
Drawings
FIG. 1 is a vertical projection of a fracture sample when the concentration of hydrogen sulfide is zero in an embodiment of the present invention
FIG. 2 is a macroscopic perspective morphology of a fracture sample when the concentration of hydrogen sulfide is zero in an embodiment of the present invention;
FIG. 3 is a vertical projection of a fracture sample at a hydrogen sulfide concentration of 1000ppm in accordance with an embodiment of the present invention;
FIG. 4 is a graph of macroscopic perspective morphology of a fracture sample at a hydrogen sulfide concentration of 1000ppm in an embodiment of the present invention;
FIG. 5 is a vertical projection of a fracture sample at a concentration of 3500ppm of hydrogen sulfide in accordance with an embodiment of the present invention;
FIG. 6 is a graph of macroscopic perspective morphology of a fracture sample at a concentration of 3500ppm of hydrogen sulfide in an embodiment of the present invention;
fig. 7 is a graph of the radial width b of the step crack plane and the elliptic vertical projection area S of the embodiment of the present invention.
Detailed Description
The following detailed description of the embodiments of the invention is provided with reference to the accompanying drawings.
An evaluation method for hydrogen sulfide stress corrosion resistance sensitivity of an oil well pipe comprises the following steps:
step 1, processing a sample into a set size, and preprocessing the surface of the sample;
And 2, installing a sample on stretching equipment in a reaction kettle, adding a proper amount of test solution into the reaction kettle, and sealing the reaction kettle, wherein the test solution is Nace standard A solution, and the concentration of hydrogen sulfide is 0-3500 ppm.
And 3, adjusting the concentration of hydrogen sulfide in the test solution, and rapidly stretching and preloading the test solution to a yield strength value of 50% -80%, wherein the strain rate of the rapid stretching is more than or equal to 1X 10 -4 mm/s.
And 4, after the test is stabilized, starting to perform a slow-stretching loading test at a set strain rate until the test sample is broken, and recording test results, wherein the strain rate of the slow-stretching loading test is 1X 10 -7～5×10-5 mm/s.
And 5, finally taking out the broken tensile sample, removing corrosion products on the surface of the sample and the fracture, and selecting the area of the step crack plane with the largest area on the fracture to evaluate the stress corrosion resistance of the oil well pipe material through observing the fracture morphology.
The method specifically comprises the following steps:
1) The crack propagation direction is along the step crack plane where the crack propagation direction is, and the crack propagation direction is respectively and simultaneously propagated from the outer surface of the sample to the center along the radius and along the circumferential direction;
2) The fracture morphology observation adopts a laser confocal microscope, the amplification factor is 20-100, the fracture surface is rugged, step cracks are formed in the circumferential direction, meanwhile, the distance between a workbench and a lens is adjusted, the fracture morphology of a sample is ensured to be clear, and the step crack area measurement is accurate;
3) The step crack plane is used for measuring the step crack area with the largest area on the fracture;
4) Step crack area selection vertical projection area calculation;
5) As shown in fig. 7, the planar shape of the step crack is elliptical, the stress corrosion resistance is related to the largest vertical projection area S of the step crack, the formula of stress corrosion sensitivity R is simplified as r=k×r/b×s, where b is the minor axis length of the ellipse, i.e. the radial crack propagation depth, R is the radius of the slow tensile test specimen test area, and K is a constant.
The appearance observation of the fracture adopts a microscope, the amplification factor is 20-100, when the step crack is smaller, the larger amplification factor is adopted, and when the step crack is larger, the smaller amplification factor is adopted, so that the appearance of the fracture of the sample is completely presented, and the area measurement of the step crack is accurate.
The slow tensile loading test loads along the length direction of the sample, and the tensile direction is parallel to the length direction of the sample. The stretching direction of the slow stretching loading test is perpendicular to the step crack plane, and the stretching direction is perpendicular to the crack propagation direction and is different from 90 degrees.
Example 1
The test material is 110-grade sulfur-resistant oil well pipe, the yield strength is 800Mpa, and the method comprises the steps of sample processing I, surface treatment II, slow-stretching loading test III, appearance observation of fracture IV and step crack area measurement.
The sample processing in the step I is to process the test material into a proper cylindrical tensile sample with the length of 72mm, the diameter of a test area of 6.40mm and the surface finish of 0.3 mu m;
the surface treatment in the step II is to clean the sample in the step I by ultrasonic wave, and clean the sample in acetone and absolute ethyl alcohol for one time respectively for removing residues and grease on the surface of the sample;
The slow tensile loading test in the step III is to adopt a slow strain rate tensile testing machine, the test temperature is room temperature, a Nace standard A solution is injected into a reaction kettle, the reaction kettle is closed, high-purity nitrogen is introduced to deoxidize for 2 hours, the concentration of hydrogen sulfide in the solution is 0, a sample is loaded to 600Mpa in advance, the sample is kept in an elastic stress deformation stage, then the slow tensile loading test is started according to the strain rate of 5 x 10 -6 mm/s, after the test is finished, the test result is recorded, the broken tensile sample is taken out, corrosion products on the surface and the fracture of the sample are removed, the surface of the sample is ensured to present metallic luster, and the fracture morphology is clear;
In the step IV, fracture morphology observation and step crack area measurement are carried out by adopting a laser confocal microscope, vertically placing a broken tensile sample on an objective table, enabling the tensile direction to be perpendicular to the plane of the objective table, properly adjusting the distance between the fracture sample and a lens, enabling the magnification to be 100 times, photographing the fracture morphology after focusing clearly, wherein the fracture is in a cup shape, belongs to ductile fracture, stress corrosion does not occur, the step crack area S is recorded as 0, and the stress corrosion sensitivity formula R=3r/b is brought into the table 1, and the test result is shown in the table 1.
Example 2
The test material is 110-grade sulfur-resistant oil well pipe, the yield strength is 800Mpa, and the method comprises the steps of sample processing I, surface treatment II, slow-stretching loading test III, appearance observation of fracture IV and step crack area measurement.
The sample processing in the step I is to process the test material into a proper cylindrical tensile sample with the length of 72mm, the diameter of a test area of 6.40mm and the surface finish of 0.3 mu m;
the surface treatment in the step II is to clean the sample in the step I by ultrasonic wave, and clean the sample in acetone and absolute ethyl alcohol for one time respectively for removing residues and grease on the surface of the sample;
The slow tensile loading test in the step III is to adopt a slow strain rate tensile testing machine, inject Nace standard A solution into a reaction kettle, introduce high-purity nitrogen to deoxidize for 2 hours, add a proper amount of analytically pure sodium sulfide, ensure the concentration of hydrogen sulfide in the solution to be 1000ppm after full reaction, seal the reaction kettle, load a sample to 600Mpa in advance, keep the sample in an elastic stress deformation stage, then start the slow tensile loading test according to the strain rate of 5 x 10 -6 mm/s, record the test result after the test is finished, take out the broken tensile sample, remove corrosion products on the surface and fracture of the sample, ensure the surface of the sample to present metallic luster, and the fracture morphology is clear;
The fracture morphology observation and step crack area measurement in the step IV are carried out by adopting a laser confocal microscope, vertically placing a broken tensile sample on an objective table, enabling the tensile direction to be perpendicular to the plane of the objective table, properly adjusting the distance between the fracture sample and a lens, enabling the magnification to be 100 times, photographing the fracture morphology after focusing clearly, selecting the largest step crack plane, calculating the radial width b and the elliptic vertical projection area S (mm 2) of the step crack plane through matched software, and carrying out a stress corrosion sensitivity formula R=3r/b×S, wherein the test result is shown in table 1.
Example 3
The test material is 110-grade sulfur-resistant oil well pipe, the yield strength is 800Mpa, and the method comprises the steps of sample processing I, surface treatment II, slow-stretching loading test III, appearance observation of fracture IV and step crack area measurement.
The sample processing in the step I is to process the test material into a proper cylindrical tensile sample with the length of 72mm, the diameter of a test area of 6.40mm and the surface finish of 0.3 mu m;
the surface treatment in the step II is to clean the sample in the step I by ultrasonic wave, and clean the sample in acetone and absolute ethyl alcohol for one time respectively for removing residues and grease on the surface of the sample;
The slow tensile loading test in the step III is to adopt a slow strain rate tensile testing machine, the test temperature is room temperature, a Nace standard A solution is injected into a reaction kettle, the reaction kettle is closed, high-purity nitrogen is firstly introduced to deoxidize for 2 hours, then high-purity hydrogen sulfide gas (99.99%) is introduced until the solution is saturated, the concentration of hydrogen sulfide in the solution is 3500ppm at room temperature and normal pressure, a sample is loaded to 600Mpa in advance, the sample is kept in an elastic stress deformation stage, then the slow tensile loading test is started according to the strain rate of 5mm & lt 10 & gt -6 mm/s, after the test is finished, the test result is recorded, the broken tensile sample is taken out, corrosion products on the surface and fracture of the sample are removed, the surface of the sample is ensured to present metallic luster, and the fracture morphology is clear;
The fracture morphology observation and step crack area measurement in the step IV are carried out by adopting a laser confocal microscope, vertically placing a broken tensile sample on an objective table, enabling the tensile direction to be perpendicular to the plane of the objective table, properly adjusting the distance between a fracture and a lens, enabling the magnification to be 100 times, photographing the fracture morphology after focusing clearly, selecting the largest step crack plane, calculating the radial width b and the elliptic vertical projection area S (mm 2) of the step crack plane through matched software, and bringing the radial width b and the elliptic vertical projection area S into a stress corrosion sensitivity formula R=3r/b, wherein the test result is shown in Table 1.
TABLE 1 results of Slow tensile test of oil country tubular goods at different Hydrogen sulfide concentrations
According to the test results, in Nace standard A solution, when the concentration of hydrogen sulfide is zero, the oil well pipe material does not generate stress corrosion, the fracture is cup-shaped, the fracture belongs to ductile fracture, the sensitivity index of stress corrosion is 0, along with the increase of the concentration of hydrogen sulfide, the sensitivity index of stress corrosion of the oil well pipe material is increased from 56.75 to 86.37, the fracture morphology shows step cracks, and the fracture morphology has obvious stress corrosion characteristics, which are similar to the conventional stress corrosion sensitivity calculation results, such as elongation loss ratio and fracture time loss ratio. The method realizes the measurement of the hydrogen sulfide stress corrosion resistance sensitivity index of the oil well pipe, and the stress corrosion resistance performance of the oil well pipe material is more accurately and comprehensively evaluated through fracture morphology observation and step crack area calculation.
Example 4
The test specimens used were A, B kinds of sulfur-resistant oil country tubular goods, which were two different kinds of oil country tubular goods (for example, oil country tubular goods having different materials or different processes such as rolling and heat treatment, and the explanation of the following examples is the same here). The method comprises the steps of sample processing I, surface treatment II, slow-stretching loading test III, fracture morphology observation IV and step crack area measurement.
The sample processing in the step I is to process the test material into a proper cylindrical tensile sample with the length of 72mm, the diameter of a test area of 6.40mm and the surface finish of 0.3 mu m;
the surface treatment in the step II is to clean the sample in the step I by ultrasonic wave, and clean the sample in acetone and absolute ethyl alcohol for one time respectively for removing residues and grease on the surface of the sample;
The slow tensile loading test in the step III is to adopt a slow strain rate tensile testing machine, the test temperature is room temperature, the Nace standard A solution is injected into a reaction kettle, the reaction kettle is closed, high-purity nitrogen is firstly introduced to deoxidize for 2 hours, then high-purity hydrogen sulfide gas (99.99%) is introduced until the solution is saturated, the concentration of hydrogen sulfide in the solution is 3500ppm at room temperature and normal pressure, then the slow tensile loading test is started according to the strain rate of 1 x 10 -7 mm/s, after the test is finished, the test result is recorded, a broken tensile sample is taken out, corrosion products on the surface and a fracture of the sample are removed, the surface of the sample is ensured to present metallic luster, and the fracture morphology is clear;
The fracture morphology observation and step crack area measurement in the step IV are carried out by adopting a laser confocal microscope, vertically placing a broken tensile sample on an objective table, enabling the tensile direction to be perpendicular to the plane of the objective table, properly adjusting the distance between a fracture and a lens, enabling the magnification to be 80 times, shooting the fracture morphology after focusing clearly, selecting the largest step crack plane, calculating the radial width B and the elliptic vertical projection area S (mm 2) of the step crack plane through matched software, and carrying out a stress corrosion sensitivity formula R=3r/b×S, wherein the test result is shown in Table 2, and analysis shows that the stress corrosion sensitivity is in the order of from high to low, and B > A.
TABLE 2 results of Slow tensile test for oil well pipes
Example 5
The test specimens used were A, B kinds of sulfur-resistant oil country tubular goods, which were two different kinds of oil country tubular goods (for example, oil country tubular goods having different materials or different processes such as rolling and heat treatment, and the explanation of the following examples is the same here). The method comprises the steps of sample processing I, surface treatment II, slow-stretching loading test III, fracture morphology observation IV and step crack area measurement.
The sample processing in the step I is to process the test material into a proper cylindrical tensile sample with the length of 72mm, the diameter of a test area of 6.40mm and the surface finish of 0.3 mu m;
the surface treatment in the step II is to clean the sample in the step I by ultrasonic wave, and clean the sample in acetone and absolute ethyl alcohol for one time respectively for removing residues and grease on the surface of the sample;
The slow tensile loading test in the step III is to adopt a slow strain rate tensile testing machine, inject Nace standard A solution into a reaction kettle, introduce high-purity nitrogen to deoxidize for 2 hours, add a proper amount of analytically pure sodium sulfide, ensure the concentration of hydrogen sulfide in the solution to be 1000ppm after full reaction, seal the reaction kettle, then start the slow tensile loading test according to the strain rate of 5 x 10 -5 mm/s, record the test result after the test is finished, take out the broken tensile sample, remove corrosion products on the surface and fracture of the sample, ensure that the surface of the sample presents metallic luster, the fracture morphology is clear;
The fracture morphology observation and step crack area measurement in the step IV are carried out by adopting a laser confocal microscope, vertically placing a broken tensile sample on an objective table, enabling the tensile direction to be perpendicular to the plane of the objective table, properly adjusting the distance between a fracture and a lens, enabling the magnification to be 80 times, shooting the fracture morphology after focusing clearly, selecting the largest step crack plane, calculating the radial width B and the elliptic vertical projection area S (mm 2) of the step crack plane through matched software, and carrying out a stress corrosion sensitivity formula R=3r/b×S, wherein the test result is shown in Table 3, and analysis shows that the stress corrosion sensitivity is in the order of from high to low, and B > A.
TABLE 3 results of Slow tensile test for oil well pipes
The above examples are implemented on the premise of the technical scheme of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the above examples. The methods used in the above examples are conventional methods unless otherwise specified.
Claims (3)
1. The evaluation method of the hydrogen sulfide stress corrosion resistance sensitivity of the oil well pipe is characterized by comprising the following steps:
step 1, processing a sample into a set size, and preprocessing the surface of the sample;
step 2, mounting a sample on stretching equipment in a reaction kettle, adding a test solution into the reaction kettle, and sealing the reaction kettle;
Step3, adjusting the concentration of hydrogen sulfide in the test solution, and rapidly stretching and preloading the test solution to 50% -80% yield strength value of the test sample;
Step 4, after stabilization, starting to perform a slow tensile loading test at a set strain rate until the sample is broken, and recording a test result;
Step 5, finally taking out a broken tensile sample, removing corrosion products on the surface of the sample and the fracture, and selecting a step crack plane with the largest area on the fracture to evaluate the stress corrosion resistance of the oil well pipe material through the observation of fracture morphology;
the step 5 of evaluating the stress corrosion resistance of the oil well pipe material specifically comprises the following steps:
1) The crack propagation direction is along the step crack plane where the crack propagation direction is, and the crack propagation direction is respectively and simultaneously propagated from the outer surface of the sample to the center along the radius and along the circumferential direction;
2) The fracture morphology observation adopts a laser confocal microscope, the amplification factor is 20-100, the fracture surface is rugged, a step crack plane is presented in the circumferential direction, and meanwhile, the distance between a workbench and a lens is adjusted, so that the fracture morphology of a sample is clear, and the step crack area measurement is accurate;
3) The step crack plane is used for measuring the step crack with the largest area on the fracture;
4) Step crack area selection vertical projection area calculation;
5) The plane shape of the step crack is elliptical, the stress corrosion resistance is related to the largest vertical projection area S of the step crack, the formula of stress corrosion sensitivity R is simplified to R=K R/b S, wherein b is the short axis length of the ellipse, namely radial crack expansion depth, the unit is mm, R is the radius of a slow tensile sample testing area, the unit is mm, and the unit of K is 3;S is mm 2;
the slow tensile loading test loads along the length direction of the sample, and the tensile direction is parallel to the length direction of the sample;
The stretching direction of the slow stretching loading test is perpendicular to the crack plane of the step, and the stretching direction is perpendicular to the crack propagation direction and is different from 90 degrees.
2. The method for evaluating the hydrogen sulfide stress corrosion resistance sensitivity of an oil well pipe according to claim 1, wherein the strain rate of the slow tensile loading test is 1 x 10 -7 ~ 5×10-5 mm/s.
3. The method for evaluating the hydrogen sulfide stress corrosion resistance sensitivity of an oil well pipe according to claim 1, wherein the strain rate of the rapid stretching is 1 x 10 -4 mm/s or more.
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