CN117907198A - Corrosion resistance testing method for nonmetallic oil pipe - Google Patents
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Abstract
The invention belongs to the field of nonmetallic material performance test, and provides a nonmetallic oil pipe corrosion resistance test method, aiming at the technical problem of judging whether nonmetallic pipes can adapt to the oil-gas well corrosion working condition; testing the mechanical strength of the control group; the test group is placed in a simulation working condition of corrosion and load coupling to carry out corrosion test, and after the corrosion test is finished, the mechanical strength of the test group is tested; and calculating a proportion coefficient as a damage index according to the mechanical strength of the test group and the mechanical strength of the control group, and judging the damage degree according to the damage index, wherein the lower the damage degree is, the stronger the corrosion resistance is. According to the invention, the different performances of the samples before and after corrosion are tested, the anti-stretch ratio coefficient, the anti-bending ratio coefficient, the loss ratio and the moisture absorption rate are calculated, the damage degree is reflected more comprehensively from multiple angles, the damage degree evaluation range is divided, and the corrosion resistance grade evaluation is realized.
Description
Technical Field
The invention belongs to the field of nonmetallic material performance test, and particularly relates to a method for testing the corrosion resistance of a nonmetallic oil pipe.
Background
The nonmetallic materials are natural and inert, so that more and more novel nonmetallic underground oil pipes are developed at present, and more carbon fiber oil pipes are used for solving the corrosion problem of active metal oil pipes. The wellbore oil pipe is subjected to the coupling effect of corrosion and load, corrosive media and environmental parameters in the life cycle of the oil and gas field are complex and changeable, and in order to ensure that the oil pipe can safely run, the corrosion aging and the strength performance damage of the carbon fiber nonmetallic oil pipe are required to be evaluated before field application.
Most of the current evaluation methods are strength performance tests of metals, but lack of evaluation of performance damage of fiber composite materials, influence of different corrosion conditions on the materials is not clear, and lack of a systematic evaluation index.
① Invention patent CN201910381772.7: a glass fiber composite material bending damage evaluation method based on HHT adopts a Hilbert-Huang transformation method to process acoustic emission detection signals, and a processed time-frequency analysis chart is used for quantitatively evaluating different damage stages of the material. The purposes of quantitative evaluation and damage early warning of the whole life of the glass fiber composite material are realized. The method is simultaneously suitable for health monitoring of other reinforced fiber composite materials, has important practical application value, but the detection signal is easy to interfere, and the accuracy of the result is affected.
② Invention patent cn201910252801.X: according to the characterization method of the acoustic emission characteristic parameters of the bending damage of the glass fiber composite material, the energy of the acoustic emission signal is found out, and the internal relation between each characteristic parameter and different damage stages of the material is counted, so that the corresponding damage characterization is carried out, and the purposes of quantitative evaluation and damage early warning of the whole life of the glass fiber composite material are achieved. The method is suitable for health monitoring of other reinforced fiber composite materials, has important practical application value in engineering detection, but the damage evaluation reference index is not combined with corrosion and load coupling action, detection signals are easy to interfere, and accuracy of results is affected.
③ Li Wei, zhang Luying, huang Yuanhang, zhang Hongyuan, jiang Peng. Nondestructive testing 2019,41 (08): 1-5.): according to the nonlinear ultrasonic evaluation method for the fatigue damage of the carbon fiber composite material, fatigue damage tests under the action of different stress ratios are carried out on the carbon fiber composite material, nonlinear coefficients in the fatigue damage process of the composite material under different working conditions are obtained by utilizing a nonlinear ultrasonic detection technology, the safety of the composite material under the action of fatigue load is effectively monitored through the relative nonlinear coefficients, the service life of the composite material can be timely early warned, and a basis is provided for evaluating the fatigue damage of the material. However, the relative linear coefficient has a large influence on the material properties only at 50% of the fatigue life, and has a certain limitation.
④ Guo Dewei, ma Jihua. Smart computers and applications, 2020,10 (03): 294-298.): the method comprises the steps of performing heat-map sampling on a CFRP thin-wall tube sample, obtaining the surface damage area of the sample by taking frames, enhancing images and the like, performing detection analysis on the damage of the sample by using a CT technology, comparing with an infrared detection method, and providing a certain reference for the subsequent quantitative evaluation research on the damage of the tubular carbon fiber composite material. However, the CT detection method cannot perform online measurement, the rays are harmful to human bodies, the application is limited to a certain extent, and the surface damage condition cannot be intuitively obtained due to the characteristics of tomography.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a method for testing the corrosion resistance of a non-metal oil pipe, which solves the technical problems of judging whether the non-metal pipe can adapt to the corrosion working condition of an oil gas well, such as a carbon fiber non-metal oil pipe and a glass fiber non-metal oil pipe.
The invention is realized by the following technical scheme: the corrosion resistance test method of the nonmetallic oil pipe comprises the steps of cutting a sample from the nonmetallic oil pipe to be tested, and dividing the sample into a control group and a test group; testing the mechanical strength of the control group; the test group is placed in a simulation working condition of corrosion and load coupling to carry out corrosion test, and after the corrosion test is finished, the mechanical strength of the test group is tested; and calculating a proportion coefficient as a damage index according to the mechanical strength of the test group and the mechanical strength of the control group, and judging the damage degree according to the damage index, wherein the lower the damage degree is, the stronger the corrosion resistance is.
Furthermore, corrosive gas and/or corrosive liquid are/is introduced into the high-temperature high-pressure kettle to simulate the corrosion working condition, and inert gas or nitrogen is introduced to boost pressure to simulate the load working condition.
Further, the mechanical strength comprises tensile strength, the damage index comprises a tensile ratio coefficient, and the ratio of the tensile strength of the test group to the tensile strength of the control group is the tensile ratio coefficient;
If the tensile ratio is 0.90 or more, the specimen is judged to be slightly damaged, if it is more than 0.80 and less than 0.90, the specimen is judged to be moderately damaged, and if it is 0.80 or less, the specimen is judged to be severely damaged.
Further, the mechanical strength comprises bending strength, the damage index comprises bending resistance coefficient, and the ratio of the bending strength of the test group to the bending strength of the control group is the bending resistance coefficient;
If the bending modulus is 0.90 or more, the test specimen is judged to be slightly damaged, if it is more than 0.80 and less than 0.90, the test specimen is judged to be moderately damaged, and if it is 0.80 or less, the test specimen is judged to be severely damaged.
Further, respectively drawing stress-strain curves of the control group and the test group in the tensile strength test process, and carrying out nonlinear fitting according to the respective stress-strain curves to obtain corresponding load-strain fitting functions;
Calculating work required to be done by the breaking test sample as tensile energy according to the load-strain fitting function, calculating the ratio of the tensile energy of the test group to the tensile energy of the control group to obtain a loss ratio, and adopting the loss ratio as a damage index;
If the loss ratio is 90% or more, the damage is judged to be mild, more than 75% and less than 90% are judged to be moderate, and 75% or less are judged to be severe.
Further, the tensile energy is calculated as follows:
Where ε k represents the strain corresponding to the maximum load and F (ε) represents the load-strain fit function.
Furthermore, the moisture absorption rate is used as a damage index, and the moisture absorption rate is calculated as follows:
wherein R represents the moisture absorption rate, M 0 represents the weight of the test group before corrosion test, and M t represents the weight of the test group after corrosion test;
If the moisture absorption rate is within 2.5%, it is judged that no obvious damage is found, and if it exceeds 2.5%, it is judged that more obvious damage is found.
Further, the judgment results obtained by the respective damage indexes are compared, and the judgment result with the most serious damage degree is used as the final standard for judging the corrosion resistance.
Further, a dumbbell-sized specimen was used for the tensile strength test, and a rectangular-sized specimen was used for the flexural strength test.
Further, the tensile strength is calculated as follows:
Wherein σ t is the tensile strength; h is the thickness of the sample; h is the width of the sample; p t is the maximum load of the sample when the tensile failure occurs;
the flexural strength is calculated as follows:
Wherein σ f is the bending strength; l is the sample span; b is the sample width; p f is the maximum load at which the specimen fails to bend.
Further, before the tensile strength test, epoxy glue is used to paste reinforcing aluminum sheets at two ends of the dumbbell-shaped test sample, and screws are drilled into the reinforcing sheets to fix the reinforcing aluminum sheets with the dumbbell-shaped test sample.
Further, the moisture absorption rate was calculated from the weights of the rectangular samples in the test group before and after the corrosion test.
Further, the step of performing the corrosion test includes: the petroleum ether and alcohol are adopted to clean the sample, the oilfield on-site produced liquid is injected into the high-temperature high-pressure kettle, the cleaned sample is put into the high-temperature high-pressure kettle to be sealed and deoxidized, corrosive gas and nitrogen are introduced to be boosted to the actual working condition pressure, and the corrosion test is carried out for 7 days.
Compared with the prior art, the invention has the beneficial effects that:
1. According to the invention, the corrosion test is carried out under the simulated working condition, so that the corrosion process under the coupling of corrosion and load is simulated, and the guarantee of more truly reflecting corrosion resistance is provided.
2. The corrosion resistance test device tests different performances of the corroded test sample, including the tensile ratio coefficient, the bending ratio coefficient, the loss ratio and the moisture absorption rate, so that the damage degree can be reflected more comprehensively from multiple angles, the damage degree evaluation range is divided, and the corrosion resistance grade evaluation is realized.
3. The invention introduces tensile energy and loss ratio for the first time to obtain the change of the elastic-plastic property inside the material, and the damage of the material is shown more specifically and clearly.
Drawings
FIG. 1 is a flow chart of a method of testing corrosion resistance of a nonmetallic oil pipe;
FIG. 2 is a schematic illustration of a dumbbell gauge specimen;
fig. 3 is a stress-strain curve for different sets of samples.
Reference numerals illustrate: 1-reinforcing aluminum sheet, 2-screw
Detailed Description
The invention is described in further detail below with reference to the attached drawing figures:
referring to FIG. 1, a method for testing corrosion resistance of a nonmetallic oil pipe is disclosed, wherein a sample is cut from the nonmetallic oil pipe to be tested, and the sample is divided into a control group and a test group; testing the mechanical strength of the control group; the test group is placed in a simulation working condition of corrosion and load coupling to carry out corrosion test, and after the corrosion test is finished, the mechanical strength of the test group is tested; and calculating a proportion coefficient as a damage index according to the mechanical strength of the test group and the mechanical strength of the control group, and judging the damage degree according to the damage index, wherein the lower the damage degree is, the stronger the corrosion resistance is.
The working condition environment of the nonmetallic oil pipe to be tested, including corrosion working condition, temperature and pressure, is determined, the simulated corrosion working condition environment in the high-temperature high-pressure kettle comprises CO 2、O2、H2 S and other gases and/or corrosive liquid, and inert gas or nitrogen is introduced to boost pressure so as to simulate the load working condition. This embodiment will provide two examples to illustrate corrosion performance testing under the production and O 2 corrosion conditions, respectively.
The mechanical strength tested in this embodiment includes tensile strength and bending strength, the damage index includes tensile ratio coefficient and bending resistance ratio coefficient, the ratio of tensile strength of the test group to tensile strength of the control group is the tensile ratio coefficient, and the ratio of bending strength of the test group to bending strength of the control group is the bending resistance ratio coefficient.
In this embodiment, the damage index includes a loss ratio and a moisture absorption rate in addition to a tensile ratio coefficient and a bending resistance coefficient, and is described below.
First) tensile ratio coefficient and flexural ratio coefficient
According to the test standards of the tensile test and the bending test, corresponding test samples are prepared, and in the specific embodiment, 3 groups of test samples, one control group and two test groups are prepared, wherein the two test groups are respectively used for testing the corrosion resistance under the working conditions of extraction and O 2 corrosion. All samples were taken from the same carbon fiber nonmetallic tubing, each group of samples consisted of two regular tests, including dumbbell-sized samples: 180×20×2mm (length×width×thickness) and rectangular specification sample: 80×15×2mm, and span l=16×h (span represents the distance between two support points of the test specimen on the bending test apparatus), each of the test specimens has 3 test specimens of each specification, that is, each test specimen includes 3 test specimens of dumbbell type specification, 3 test specimens of rectangular specification, a test specimen of dumbbell type specification (hereinafter abbreviated as a specification) is used for tensile strength test, and a test specimen of rectangular specification (hereinafter abbreviated as B specification) is used for bending strength test.
Referring to fig. 2, before the tensile strength test, reinforcing aluminum sheets were adhered to both ends of the dumbbell-sized test pieces using epoxy glue, and screws were drilled into the reinforcing sheets to fix the dumbbell-sized test pieces. If the sample is directly clamped, damage to the clamping part of the pattern can be caused; the adhesion and the screw ensure that the reinforcing sheet and the sample are not separated, and prevent the clamping part of the stretcher and the sample from falling off due to overlarge stretching force in the stretching process.
The tensile strength test is performed on the samples with the A specification in the control group, the bending strength test is performed on the samples with the B specification in the control group, and the tensile strength and the bending strength are calculated according to the formulas (1) and (2) respectively:
wherein: sigma t is tensile strength, MPa; h is the thickness of the sample, and mm; b is the width of the sample, mm; p t is the maximum load and N when the sample fails in tension;
Wherein: sigma f is bending strength, MPa; l is the sample span, mm; b is the width of the sample, mm; p f is the maximum load when the sample is bent and fails, N;
The tensile strength of the three samples of A specification in the control group was measured and calculated to be 1069MPa on average, and the bending strength of the three samples of B specification was measured to be 615MPa on average.
Two) loss ratio
Respectively drawing stress-strain curves of a control group and a test group in the tensile strength test process, and carrying out nonlinear fitting according to the respective stress-strain curves to obtain corresponding load-strain fitting functions;
Calculating work required to be done by the breaking test sample as tensile energy according to the load-strain fitting function, calculating the ratio of the tensile energy of the test group to the tensile energy of the control group to obtain a loss ratio, and adopting the loss ratio as a damage index;
If the loss ratio is 90% or more, the damage is judged to be mild, more than 75% and less than 90% are judged to be moderate, and 75% or less are judged to be severe.
First, stress-strain curves of the control group during the tensile strength test (stress-strain data of three samples of a specification are averaged for the first time, where the stress-strain curve refers to an average stress-strain curve of three samples of a specification), and the non-corroded curves are shown with reference to fig. 3.
And then carrying out nonlinear fitting according to the stress-strain curve of the control group to obtain a corresponding load-strain fitting function: f (epsilon) = -2× 9x4+6×106x3-21891x2 +87430x-74.531, wherein the strain interval is 0-1.46%, and the tensile energy of the control group is 8.01X10 6 J according to the formula (3);
The tensile energy is calculated as follows:
Where ε k represents the strain corresponding to the maximum load and F (ε) represents the load-strain fit function.
Three) moisture absorption Rate
In this embodiment, the moisture absorption rate is calculated by using the weight of the sample of the specification B in the test group before and after the corrosion test, and the moisture absorption rate is calculated as follows:
wherein R represents the moisture absorption rate, M 0 represents the weight of the test group before corrosion test, and M t represents the weight of the test group after corrosion test;
If the moisture absorption rate is within 2.5%, it is judged that no obvious damage is found, and if it exceeds 2.5%, it is judged that more obvious damage is found.
In order to ensure the weighing accuracy, the samples are required to be cleaned before and after the corrosion test, and the samples are cleaned by petroleum ether and alcohol, so that the weighing accuracy is 0.01g.
Two examples are provided below for more specific illustration.
Example 1
The present embodiment simulates the corrosion process under the production conditions.
Step one: the specific corrosion conditions are determined to be 180 ℃ at the temperature of H 2 S partial pressure of 1.0MPa and CO 2 partial pressure of 1.2MPa, and the working conditions are simulated in a high-temperature high-pressure kettle.
Step two: preparing experimental gas and liquid, wherein the experimental gas comprises CO 2、N2、O2、H2 S, and the experimental liquid comprises oilfield on-site produced liquid and on-site injected water;
step three: preparing a test group (b) sample, and preparing the test group sample from the same carbon fiber nonmetal oil pipe with the control group (a) sample;
Step four: pretreating test group samples, cleaning the samples by using petroleum ether and alcohol, measuring and recording the average weight of each group of samples, and weighing to be accurate to 0.01g;
Step five: adopting clear water and N 2 to test the sealing performance of the high-temperature high-pressure kettle, and carrying out subsequent steps after the test performance passes;
Step six: pouring experimental liquid into the high-temperature high-pressure kettle according to the corrosion working condition, putting the group b samples with two specifications of A, B into the high-temperature high-pressure kettle, sealing the high-temperature high-pressure kettle after confirming that the samples are put well, deoxidizing for 3 hours, introducing experimental gas into the high-temperature high-pressure kettle, introducing nitrogen to boost the pressure to the corrosion working condition, and performing the experiment for 7 days;
step seven: unloading the kettle pressure after the test is finished, cooling to room temperature, taking out the samples in the group b, discharging the solution in the kettle, and cleaning the kettle;
Step eight: the group b samples of two specifications of A, B are cleaned by petroleum ether and alcohol, the average weight of each group of samples is measured and recorded, the weight is accurate to 0.01g, and the average moisture absorption rate of each group of samples is calculated according to the formula (4):
Wherein: r is the moisture absorption rate,%; m t is the total weight of the B specification sample after the experiment, g; m 0 is the total weight of the B specification sample before the experiment, g;
Step nine: judging the performance of the sample by the moisture absorption rate, if the moisture absorption rate is within 2.5%, judging that the performance of the sample is not obviously damaged, and if the moisture absorption rate exceeds 2.5%, judging that the performance of the sample is obviously damaged;
The moisture absorption rate of the B-specification B-group sample is 0.38% after test and calculation, no obvious damage is seen, and the B-specification B-group sample has higher corrosion resistance.
Step ten: respectively carrying out tensile strength test and bending strength test on the corroded group b samples with A, B specifications, drawing stress-strain curves in the tensile strength test process of the different groups of samples, and calculating the tensile strength and the bending strength according to the formula (1) and the formula (2) in the fourth step;
Step eleven: the tensile strength and bending strength calculation results of the samples with two specifications of A, B are used for introducing a stretch ratio coefficient L and a bending ratio coefficient W, and the tensile strength and bending ratio coefficient L and the bending ratio coefficient W are calculated according to formulas (5) and (6) respectively:
Wherein: sigma t is the average value of the tensile strength of the three samples of A specification in the test group, MPa; sigma t0 is the average value of the tensile strength of the A specification three samples in the control group, and MPa;
wherein: sigma f is the average value of the bending strength of three samples of the B specification in the test group, MPa; sigma f0 is the average value of bending strength of three samples of B specification in the control group, MPa;
If the tensile ratio coefficient and the bending resistance ratio coefficient are larger than 0.90, judging that the sample is slightly damaged, if the tensile ratio coefficient and the bending resistance ratio coefficient are larger than 0.80 and smaller than 0.90, judging that the sample is moderately damaged, and if the tensile ratio coefficient and the bending resistance coefficient are smaller than 0.80, judging that the sample is severely damaged;
The tensile strength and the bending strength are 1023MPa and 594MPa respectively, the tensile ratio coefficient L is calculated to be 0.96 according to the formula (5), the bending ratio coefficient W is calculated to be 0.97 according to the formula (6), and the test sample is judged to be slightly damaged and has stronger corrosion resistance.
Step twelve: according to the stress-strain curve of the sheet tensile strength test in the step ten, referring to the working condition curve obtained in fig. 3, carrying out nonlinear fitting on the curve to obtain a fitting function F (epsilon), taking a strain infinitesimal d epsilon, carrying out nonlinear fitting to obtain F (epsilon) = -1× 8ε3+3×106ε2 +63279 epsilon-42.175, wherein the strain interval is 0-1.42%,
Calculating the area of the fitting function in the corresponding strain zone under the maximum load (namely, carrying out integral in the range), wherein the area is the stretching resistance of the plate, S is used for representing the work required to be done by the breaking test sample, the unit J is calculated as 7.63 multiplied by 10 6 J according to the formula (3)
Step thirteen: the tensile energy of the corroded test group is compared with the tensile energy of the non-corroded control group to obtain a loss ratio H, and the loss ratio H is calculated according to the formula (7):
Wherein: h is loss ratio,%; s' is the tensile energy and J of the corroded test group; s 0 is the tensile energy, J, of the non-corroded control group;
And if the loss ratio is more than 90%, judging that the carbon fiber nonmetallic oil pipe plate is slightly damaged, wherein more than 75% and less than 90% are judged to be medium damage, and less than 75% are judged to be heavy damage. The loss ratio was calculated to be 95.26% according to the formula (7), and the test piece was judged to be slightly damaged.
And the test sample is judged to be slightly damaged by combining the moisture absorption rate, the tensile ratio coefficient, the bending resistance coefficient and the loss ratio, so that the nonmetallic oil pipe to be tested has high-strength corrosion resistance under the extraction working condition.
Example 2
In the embodiment, the A, B-specification B group sample is corroded according to the O 2 corrosion condition, the specific corrosion condition is that the temperature is 160 ℃, the O 2 content is 0.7-0.9%, the field produced liquid is injected into the field, after 7 days of corrosion, the moisture absorption rate of the B-specification B group sample is 0.66%, the tensile strength and the bending strength are 983MPa and 579MPa respectively, the anti-tensile coefficient L is 0.92 according to the formula (5), the anti-bending coefficient W is 0.94 according to the formula (6), and the light damage of the sample is judged.
Referring to the curve of the corrosion condition of O 2 in fig. 3, the curve is subjected to nonlinear fitting to obtain F (epsilon) = 621654 epsilon 2 +59958epsilon+ 31.842, the strain interval is 0-1.37%, the tensile resistance is 6.61×10 6 J according to the formula (3), the loss ratio is 82.52% according to the formula (7), and the sample is determined to be moderately damaged.
And judging that the sample is moderately damaged from the viewpoints of comprehensive moisture absorption, tensile ratio coefficient, bending resistance coefficient and loss ratio, so that the nonmetallic oil pipe to be tested has moderate-strength corrosion resistance under the O 2 corrosion working condition.
In the description of the present invention, unless otherwise indicated, the terms "upper," "lower," "left," "right," "inner," "outer," and the like are used for convenience in describing the present invention and simplifying the description based on the orientation or positional relationship shown in the drawings, and do not denote or imply that the devices or elements in question must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
The foregoing technical solution is only one embodiment of the present invention, and various modifications and variations can be easily made by those skilled in the art based on the principles disclosed in the present invention, and are not limited to the technical solutions described in the foregoing specific examples of the present invention, therefore, the foregoing description is only preferred and not in any limiting sense.
Claims (13)
1. The corrosion resistance testing method for the nonmetallic oil pipe is characterized in that a sample is cut from the nonmetallic oil pipe to be tested, and the sample is divided into a control group and a test group; testing the mechanical strength of the control group; the test group is placed in a simulation working condition of corrosion and load coupling to carry out corrosion test, and after the corrosion test is finished, the mechanical strength of the test group is tested; and calculating a proportion coefficient as a damage index according to the mechanical strength of the test group and the mechanical strength of the control group, and judging the damage degree according to the damage index, wherein the lower the damage degree is, the stronger the corrosion resistance is.
2. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 1, wherein corrosive gas and/or corrosive liquid is introduced into the high-temperature high-pressure kettle to simulate a corrosion working condition, and inert gas or nitrogen is introduced into the high-temperature high-pressure kettle to boost pressure to simulate a load working condition.
3. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 1, wherein the mechanical strength comprises tensile strength, the damage index comprises a tensile ratio coefficient, and the ratio of the tensile strength of the test group to the tensile strength of the control group is the tensile ratio coefficient;
If the tensile ratio is 0.90 or more, the specimen is judged to be slightly damaged, if it is more than 0.80 and less than 0.90, the specimen is judged to be moderately damaged, and if it is 0.80 or less, the specimen is judged to be severely damaged.
4. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 1 or 3, wherein the mechanical strength comprises bending strength, the damage index comprises bending resistance coefficient, and the ratio of the bending strength of the test group to the bending strength of the control group is the bending resistance coefficient;
If the bending modulus is 0.90 or more, the test specimen is judged to be slightly damaged, if it is more than 0.80 and less than 0.90, the test specimen is judged to be moderately damaged, and if it is 0.80 or less, the test specimen is judged to be severely damaged.
5. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 4, wherein stress-strain curves of a control group and a test group in the tensile strength testing process are respectively drawn, and nonlinear fitting is performed according to the stress-strain curves to obtain corresponding load-strain fitting functions;
Calculating work required to be done by the breaking test sample as tensile energy according to the load-strain fitting function, calculating the ratio of the tensile energy of the test group to the tensile energy of the control group to obtain a loss ratio, and adopting the loss ratio as a damage index;
If the loss ratio is 90% or more, the damage is judged to be mild, more than 75% and less than 90% are judged to be moderate, and 75% or less are judged to be severe.
6. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 5, wherein the tensile energy is calculated as follows:
Where ε k represents the strain corresponding to the maximum load and F (ε) represents the load-strain fit function.
7. The method for testing corrosion resistance of a non-metallic oil pipe according to claim 5, further comprising the step of using a moisture absorption rate as an index of damage, wherein the moisture absorption rate is calculated according to the following formula:
wherein R represents the moisture absorption rate, M 0 represents the weight of the test group before corrosion test, and M t represents the weight of the test group after corrosion test;
If the moisture absorption rate is within 2.5%, it is judged that no obvious damage is found, and if it exceeds 2.5%, it is judged that more obvious damage is found.
8. The method for testing the corrosion resistance of a nonmetallic oil pipe according to claim 7, wherein the judgment results obtained by the respective damage indexes are compared, and the judgment result with the most serious damage degree is used as the final standard for judging the corrosion resistance.
9. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 7, wherein a dumbbell-shaped test piece is used for the tensile strength test, and a rectangular test piece is used for the bending strength test.
10. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 8, wherein the tensile strength is calculated as follows:
Wherein σ t is the tensile strength; h is the thickness of the sample; h is the width of the sample; p t is the maximum load of the sample when the tensile failure occurs;
the flexural strength is calculated as follows:
Wherein σ f is the bending strength; l is the sample span; b is the sample width; p f is the maximum load at which the specimen fails to bend.
11. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 9, wherein the reinforcing aluminum sheets are adhered to two ends of the test piece with the dumbbell type specification by using epoxy glue before the tensile strength test is performed, and screws are drilled into the reinforcing sheets to fix the reinforcing aluminum sheets with the test piece with the dumbbell type specification.
12. The method for testing the corrosion resistance of the nonmetallic oil pipe according to claim 11, wherein the moisture absorption rate is calculated according to the weights of the samples with rectangular specifications in the test group before and after the corrosion test.
13. The method of claim 2, wherein the step of performing the corrosion test comprises: the petroleum ether and alcohol are adopted to clean the sample, the oilfield on-site produced liquid is injected into the high-temperature high-pressure kettle, the cleaned sample is put into the high-temperature high-pressure kettle to be sealed and deoxidized, corrosive gas and nitrogen are introduced to be boosted to the actual working condition pressure, and the corrosion test is carried out for 7 days.
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