CN117990785A - Evaluation method for ageing performance of pipeline - Google Patents
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Abstract
The invention discloses a method for evaluating ageing performance of a pipeline, and belongs to the field of pipeline ageing evaluation. According to the method for evaluating the ageing performance of the pipeline, provided by the invention, v l and v s of the pipeline to be evaluated and the reference sample are subjected to ultrasonic nondestructive testing, the Young's modulus E u of each pipeline to be evaluated and the reference sample are obtained through calculation, the tensile elastic modulus E t of each pipeline to be evaluated and the reference sample are obtained based on a function of the construction E t＝f(Eu), and the ageing coefficient eta is further obtained; based on the ultrasonic nondestructive testing technology, the aging state of the in-service concentrated pipeline can be tested on site, the buried pipeline only needs excavation and backfilling operation, sampling analysis is not needed, the pipeline is not damaged, production stopping is not needed, and the influence on production operation is small; meanwhile, the aging coefficient characterization parameter is a mechanical property index, has definite physical meaning and is closely related to the service capacity of the pipeline; the invention can be widely applied to the aging evaluation of various PE pipelines and can be popularized and applied to other thermoplastic plastic pipelines.
Description
Technical Field
The invention belongs to the field of pipeline aging evaluation, and particularly relates to an evaluation method of pipeline aging performance.
Background
Thermoplastic plastic pipelines have the advantage of corrosion resistance, are widely applied to municipal water and gas pipelines, and are already used as a matrix or lining in the field of oil-water medium conveying pipelines in oil fields in a large number; among the various thermoplastic pipes, polyethylene (PE) pipes are used in the largest amount. In the service environment, various ageing causes such as temperature, mechanical load, physical and chemical actions of a medium and the like exist, the ageing can cause the performance degradation of the plastic pipeline, and the pipeline can fail when serious.
The existing plastic pipeline aging evaluation method comprises the following steps: firstly, an aging model is established based on principles of thermal oxidation aging, ultraviolet light aging, mechanical aging and the like; then sampling test is carried out, and analysis tests such as surface microscopic morphology, oxidation induction time, gel chromatography, infrared spectrum, long-term hydrostatic pressure or mechanical property are carried out in a laboratory; and finally, representing the aging condition of the pipeline based on the change of the performance index. The aging model used in the method is simple and only aims at a specific aging effect, so that the evaluation result cannot reflect aging caused by other principles; the test period is long, the cost is high, and expensive precision test devices are required to be used for part of the test, such as SEM, AFM, high-temperature GPC and the like; moreover, sampling (even broken pipe sampling) can interfere with normal production of in-service pipelines, destroy the integrity of the pipelines, and possibly increase the potential safety hazard of the pipelines; therefore, the application field of the above method is limited.
For pressure pipes, the most important performance parameter is the mechanical properties. Therefore, testing for changes in mechanical properties is necessary to understand the aging status of plastic pipes. The conventional mechanical property test adopts a tensile test, belongs to a destructive test, and is not suitable for a pipeline in field service. GB/T38897-2020 prescribes elastic modulus ultrasonic body wave test technology, but is only applicable to block samples, and has strict requirements on the thickness of the samples, the parallelism and the roughness of the detection surface, so that the ultrasonic body wave test technology is not applicable to the arc tube wall of a plastic pipeline; in addition, the calculation of the modulus of elasticity requires the measurement of the density and thickness of the test specimen, which cannot be done without damaging the pipe for in-service plastic pipes.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an evaluation method for ageing performance of a pipeline.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme:
the method for evaluating the ageing performance of the pipeline comprises the following steps of:
(1) Acquiring information of a pipeline to be evaluated, wherein the information comprises the specification, the material, the density rho, the wall thickness e, the type of pipeline conveying medium, the working pressure and the temperature of the pipeline and the external environment of the pipeline;
(2) Based on the type of the pipeline conveying medium, the working pressure and the temperature of the pipeline and the external environment of the pipeline, designing an exposure test to simulate the service environment of the pipeline, and performing an accelerated aging test to obtain a series of aging samples;
Measuring the tensile elastic modulus E t and the Young modulus E u of the aged sample to obtain a series of corresponding data of the tensile elastic modulus E t and the Young modulus E u, and fitting to obtain a functional relation of E t＝f(Eu);
measuring Young modulus E u of the pipeline to be evaluated and the reference sample by adopting an ultrasonic body wave method, and respectively calculating to obtain respective tensile elastic modulus E t based on a functional relation of E t＝f(Eu);
the reference sample is a PE pipe which is the same as the pipeline to be evaluated in material and specification and is brand new;
(3) Calculating an aging coefficient eta based on the tensile elastic modulus E t of the pipeline to be evaluated and the reference sample, and evaluating the aging state of the pipeline to be evaluated based on the aging coefficient eta;
Wherein,
Further, the obtaining mode of the to-be-evaluated pipeline density ρ and the wall thickness e in the step (1) is as follows:
If the pipeline to be evaluated supports actual measurement, adopting actual measurement data; if the actual measurement is not supported, the following data are used: data in the original materials of the delivery inspection and the arrival inspection, test data of the reference sample or data in manuals and standards.
Further, the tensile elastic modulus E t of the aged sample in step (2) is measured by:
a tensile specimen was prepared from the aged sample and tested for E t in the axial direction of the aged sample.
Further, the young's modulus E u of the aged sample measured in step (2) is:
based on the bulk wave method in GB/T38897-2020 "nondestructive test elastic modulus and Poisson ratio ultrasonic measurement method", the longitudinal wave sound velocity v l and the transverse wave sound velocity v s of the aged sample are measured, and based on the longitudinal wave sound velocity v l, the transverse wave sound velocity v s and the density ρ, young modulus E u of the aged sample in the wall thickness direction is calculated according to formula (1):
Wherein E u -Young's modulus, MPa; ρ -density, kg/m 3;vl -longitudinal wave sound velocity, m/s; v s -transverse wave speed of sound, m/s.
Further, the density ρ of the aged sample was measured by the dipping method.
Further, the measurement was performed using a 2.5MHz longitudinal wave transducer and a 1.0MHz transverse wave transducer.
Further, a wall thickness micrometer or vernier caliper is used to measure the wall thickness e of the aged sample.
Further, in the step (3), the aging state of the evaluation object is further processed based on the aging coefficient η, specifically:
when the eta is less than or equal to 5 percent, the treatment is not needed;
when 5% <|eta| is less than or equal to 10%, performing ultrasonic examination for 1 time/3 years;
when the ratio of 10% <|eta| is less than or equal to 15%, performing ultrasonic examination for 1 time/2 years;
when 15% <|eta| is less than or equal to 20%, performing ultrasonic examination for 1 time/1 year, and sampling and checking;
When 20% <|eta| is less than or equal to 25%, stopping use, and sampling and checking;
When 25% < |eta| the process is disabled.
Further, the pipe is a thermoplastic pipe.
Compared with the prior art, the invention has the following beneficial effects:
According to the method for evaluating the ageing performance of the pipeline, provided by the invention, v l and v s of the pipeline to be evaluated and the reference sample are subjected to ultrasonic nondestructive testing, the Young's modulus E u of each pipeline to be evaluated and the reference sample are obtained through calculation, the tensile elastic modulus E t of each pipeline to be evaluated and the reference sample are obtained based on a function of the construction E t＝f(Eu), and the ageing coefficient eta is further obtained; based on the ultrasonic nondestructive testing technology, the aging state of the in-service concentrated pipeline can be tested on site, the buried pipeline only needs excavation and backfilling operation, sampling analysis is not needed, the pipeline is not damaged, production stopping is not needed, and the influence on production operation is small; meanwhile, the characteristic parameter aging coefficient is the change rate of the mechanical property index, has definite physical meaning and is closely related to the service capacity of the pipeline; the invention can be widely applied to the aging evaluation of various PE pipelines and can be popularized and applied to other thermoplastic plastic pipelines.
Furthermore, the two quantities of wall thickness and density have small change degree along with aging, and have opposite trend, if the wall thickness and density of the pipeline to be evaluated cannot be measured, when sound velocity measurement and E u calculation are carried out, the data from three sources are used for replacing the actually measured data, so that the error is small, and the invention is also a precondition for realizing on-site sampling and nondestructive detection.
Furthermore, the ultrasonic nondestructive testing method is carried out according to the existing standard, and the result is reliable.
Drawings
FIG. 1 is a flow chart of the aging performance evaluation of PE pipeline of the invention;
fig. 2 is a schematic diagram of v measurement mode.
Wherein, 1-ultrasonic transducer; 2-couplant; 3-ultrasonic test sample.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention is described in further detail below with reference to the attached drawing figures:
the invention provides an evaluation method for ageing performance of a plastic pipeline, in particular to an in-service PE pipeline, which comprises the following steps: on the premise of no pipeline stop and no on-site sampling test, the quick evaluation of the ageing performance of the plastic pipeline is realized based on the ultrasonic nondestructive testing result.
Referring to fig. 1, fig. 1 is a flowchart of the evaluation of the aging performance of a PE pipe according to the present invention, and a method for evaluating the aging performance of a pipe includes the following steps:
(1) Acquiring pipeline information to be evaluated;
specifically, information related to the pipeline to be evaluated and the service conditions thereof is collected for designing exposure tests, determining reference samples, measuring Young's modulus E u and the like.
The relevant information should include: pipe specification and material; pipe manufacturing information; pipe stock conditions; a tubing media type; pipeline working pressure and temperature; the external environment of the pipe.
The information sources include: actual measurement; pipeline design, purchase and delivery files; pipeline construction files, operation, maintenance and other operations and record files; product standards and technical manuals.
(2) Obtaining a functional relation of E t＝f(Eu), measuring Young modulus E u of the pipeline to be evaluated and the reference sample by adopting an ultrasonic body wave method, and respectively calculating and obtaining a corresponding tensile elastic modulus E t based on the functional relation of E t＝f(Eu).
Judging based on the material, specification and service environment of the pipeline to be evaluated, and directly applying if the existing E t＝f(Eu) function relation meets the requirement; if the existing E t＝f(Eu) functional relationship does not meet the requirement, a corresponding E t＝f(Eu) functional relationship should be established through a test, and the steps of establishing E t＝f(Eu) functional relationship are as follows:
(201) Exposure test
And simulating the service environment of the PE pipeline, and performing an accelerated aging test (namely, an exposure test) on the PE pipeline to obtain an aging sample with a series of aging performances.
A tube segment of suitable length (or sheet of suitable size having a full wall thickness) was cut from an unaged PE tube as a sample for exposure testing. The PE pipe for preparing the exposure test sample and the pipeline to be evaluated are identical in material, specification and manufacturing process.
At least 4 different exposure periods were chosen: (1) the exposure period for the blank sample was considered to be 0 days; (2) Other exposure periods are selected according to actual conditions, and are recommended to be positive integer multiples of 7 days (or 10 days); (3) The time difference between exposure periods is chosen according to the actual situation, and is recommended to be a positive integer multiple of 7 days (or 10 days).
The test conditions should be such as to simulate the actual ageing history of the pipe to be evaluated: (1) The test conditions should include a dominant factor that causes aging of the pipe under evaluation, but not introduce an aging factor that the pipe under evaluation has not experienced; (2) The difference of aging factors of the inner wall and the outer wall of the pipeline to be evaluated should be fully considered; (3) If the increase in test temperature only promotes the ageing factor used in the test, while not causing unexpected ageing or other effects that would deteriorate the material properties, the test temperature is preferably higher than the maximum allowable use temperature of the tubing.
The test device is selected according to the type of the exposed sample and the test condition, risk factors possibly related to the test are fully expected, and the test device with corresponding protection capability is adopted. The following proposed scheme may be employed: (1) Using a tube section sample, sealing two ends of the tube section sample and injecting a test medium into the tube section sample, and then placing the tube section sample into a temperature control device (such as a constant temperature water tank, an air constant temperature box and the like) for testing; by means of the scheme, the hydraulic (or pneumatic) loading of the inside of the sample can be realized by matching with the end sealing device. (2) Using a sheet sample, fully immersing the sheet sample in a test medium, and placing an immersed container into a temperature control device (such as a constant temperature water tank, an air constant temperature box and the like) for test; the sample may also be placed in a high temperature autoclave and subsequently injected with a test medium and tested. (3) A sample of the tube section was used, which was bottom sealed and filled with a liquid medium inside, and then vertically placed into a high temperature autoclave for testing. Using this protocol, it can be seen that test conditions comprising high pressure gas and/or hazardous (or toxic) medium as in SY/T7369 and GB/T34903.1 are established.
(202) Ultrasonic testing
Referring to a bulk wave method in GB/T38897-2020 "nondestructive test elastic modulus and Poisson ratio ultrasonic measurement method", young modulus E u of a sample in the wall thickness direction of the exposed sample in each exposure period is calculated according to a longitudinal wave sound velocity v l, a transverse wave sound velocity v s and a density ρ of the sample, and a calculation formula is shown in a formula (1):
Wherein E u -Young's modulus in megapascals (MPa); ρ -density in kilograms per cubic meter (kg/m 3);vl -longitudinal sound velocity in meters per second (m/s)), v s -transverse sound velocity in meters per second (m/s).
The density ρ is determined by dipping samples in GB/T1033.1.
The testing device is selected according to the requirements of GB/T38897, and instruments with the same functions such as a flaw detector, a thickness gauge and the like can be adopted to replace oscilloscopes and pulse signal generators in standards. A longitudinal wave transducer of 2.5MHz and a transverse wave transducer of 1.0MHz are used. V l and v s of the aged samples were measured in the manner shown in fig. 2, in which an ultrasonic transducer 1 was placed on the outer wall of an ultrasonic specimen 3 with a couplant 2 applied between them. The wall thickness e of the sample is measured using a wall thickness micrometer or vernier caliper.
(203) Mechanical property test
Tensile specimens were prepared from the aged samples and the E t in the axial direction of the aged samples was tested for each exposure cycle. Sampling and tensile property testing were performed as specified in GB/T8804.1-3-2003.
(204) Data processing
Fitting the data of E t and E u of all exposure periods, and establishing a functional relation E t＝f(Eu of the two according to actual conditions.
Typically, a linear fit is used to obtain the functional relationship E t＝AEu +b (where A, B is a constant, a is dimensionless, and B is the same dimension as the modulus).
(3) And calculating an aging coefficient eta based on the tensile elastic modulus E t of the pipeline to be evaluated and the reference sample, and evaluating the aging state of the pipeline to be evaluated based on the aging coefficient eta.
And taking the PE pipe with the same material, the same specification and the brand new shape as a reference sample, namely the mechanical property of the PE pipe can represent the initial state of the pipeline to be evaluated before aging.
The aging coefficient eta is the change rate of the tensile elastic modulus of the PE pipeline caused by aging, and the calculation method comprises the following steps: measuring E u of the pipeline to be evaluated and the reference sample by adopting an ultrasonic body wave method, substituting the data of the pipeline to be evaluated and the reference sample into a functional formula E t＝f(Eu) respectively to obtain corresponding E t, and further calculating
When the pipe to be evaluated does not support the actual measured thickness e and density ρ, the data from the following sources are used: (1) Data in original materials such as factory inspection, arrival inspection and the like; (2) test data for a reference sample; (3) data in handbooks and standards.
Η is positive indicating that aging results in an increase in E t of the PE tubing; η is negative indicating that aging results in a decrease in E t of the PE pipe.
The larger the absolute value of eta is, the larger the ageing degree is, whereas the smaller the absolute value of eta is, the smaller the ageing degree is. PE pipes with different ageing environments or materials cannot be compared with the ageing degree according to the absolute value of eta.
Setting a series of thresholds, ageing states and treatment measures corresponding to each other according to application experience and research results, and when the absolute value of eta exceeds a certain threshold, judging that the PE pipe is in a corresponding ageing state and adopting corresponding treatment measures. For PE pipes, the following empirical decision basis may be used in general.
TABLE 1 PE pipeline aging evaluation basis
Examples
And (5) performing aging evaluation on one in-service PE buried pipeline of the oil field.
(1) Pipeline information
The pipeline specification is d n SDR11, the material is PE100 grade polyethylene, the product standard is GBT 13663.2-2018, the conveying medium is oily sewage, the conveying pressure is normal pressure conveying, the working temperature is 60 ℃, and the service time is 2 years.
The field allows for excavation testing, and does not allow sampling or other operations that disrupt the integrity of the pipeline. I.e. the wall thickness e and the density p of the pipe to be evaluated cannot be measured practically.
And searching PE pipeline field archive files, and failing to find the pipeline wall thickness e and the density rho.
(2) Acquisition E t＝f(Eu) functional relationship
By taking PE100 grade materials and oil media as search conditions, searching to find one corresponding exposure test case:
a) The sample is PE pipe (polyethylene pipe with specification of d n to 90 SDR11, PE100 grade, GBT 13663.2-2018);
b) Exposing the test conditions to a hydrocarbon high-temperature environment (sealing two ends of a pipe sample and filling the inside of the pipe sample with 0# diesel oil, and placing the pipe sample in a water bath at 80 ℃ for 0 week, 1 week, 2 weeks, 4 weeks, 6 weeks and 8 weeks of aging period);
c) The tensile test and the tensile property test are carried out according to GB/T8804.1-3-2003;
d) The E t and E u data are shown in table 2, with the linear correlation coefficient r=0.97 for both sets of data (calculated using the CORREL function of Excel software);
e) Equation E t＝f(Eu) was E t＝0.27Eu +21.7MPa (linear fitting using Origin software).
TABLE 2E t and E of exposed samples after exposure test u
| Aging cycle/week | Et/MPa | Eu/MPa |
| 0 | 855 | 2930 |
| 1 | 659 | 2512 |
| 2 | 582 | 2064 |
| 4 | 523 | 1648 |
| 6 | 359 | 1430 |
| 8 | 391 | 1265 |
According to the judgment, the case can simulate the service environment of the pipeline to be evaluated, so that the E t＝f(Eu) function relation of the case can be directly used.
(3) Determining a reference sample
The on-site warehouse is searched, and the sample reservation of the same batch is not found.
Connecting pipe processing factories, finding PE pipes which are made of the same material, have the same specification and are not used, and taking 0.5m as a reference sample. The actual measurement shows that the thickness of the reference sample is e=19 mm, and the sampling measurement shows that the density is ρ=0.963 km/m 3.
Test
(1) Ultrasonic testing instrument
An Olympus EPOCH 650 digital ultrasonic flaw detector is selected. The longitudinal wave transducer is a 2.5Z20N MHz longitudinal wave straight probe of Shanzhi ultrasonic instrument research institute Co, inc., and is matched with Hongda CG-98 type ultrasonic flaw detection couplant. The transverse wave transducer is selected from SN1P13 type 1MHz transverse wave straight probe of Guangzhou Duozu Pule electronic technology, inc., and is matched with Guangzhou Duozu 6JS0124 type transverse wave special coupling agent.
(2) Ultrasonic testing
Performing excavation ultrasonic detection on the PE pipeline, and calculating to obtain E u of the pipeline to be evaluated by using thickness and density data of the reference sample; performing ultrasonic detection on a reference sample, and calculating to obtain a reference sample object E u; substituting the data into "E t＝0.27Eu +21.7mpa" calculates E t for the pipe under evaluation and the reference sample. The results are shown in Table 3.
TABLE 3 ultrasonic test results of pipes to be evaluated and reference samples
| Sample of | Eu/MPa | Et/MPa |
| Pipeline to be evaluated | 2319 | 648 |
| Reference sample | 2623 | 730 |
Evaluation of aging
(1) Calculating eta
Based on the data in table 3,
(2) Evaluation of aging
The length of service of the pipe to be evaluated is 2 years, and eta= -11.2% of the pipe indicates that the elastic modulus of the pipe is reduced, and the pipe is judged to be obviously aged according to table 1, but normal use is not affected, and then regular ultrasonic inspection is carried out according to 1 time/2 years.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (9)
1. The method for evaluating the ageing performance of the pipeline is characterized by comprising the following steps of:
(1) Acquiring information of a pipeline to be evaluated, wherein the information comprises the specification, the material, the density rho, the wall thickness e, the type of pipeline conveying medium, the working pressure and the temperature of the pipeline and the external environment of the pipeline;
(2) Based on the type of the pipeline conveying medium, the working pressure and the temperature of the pipeline and the external environment of the pipeline, designing an exposure test to simulate the service environment of the pipeline, and performing an accelerated aging test to obtain a series of aging samples;
Measuring the tensile elastic modulus E t and the Young modulus E u of the aged sample to obtain a series of corresponding data of the tensile elastic modulus E t and the Young modulus E u, and fitting to obtain a functional relation of E t＝f(Eu);
measuring Young modulus E u of the pipeline to be evaluated and the reference sample by adopting an ultrasonic body wave method, and respectively calculating to obtain respective tensile elastic modulus E t based on a functional relation of E t＝f(Eu);
the reference sample is a PE pipe which is the same as the pipeline to be evaluated in material and specification and is brand new;
(3) Calculating an aging coefficient eta based on the tensile elastic modulus E t of the pipeline to be evaluated and the reference sample, and evaluating the aging state of the pipeline to be evaluated based on the aging coefficient eta;
Wherein,
2. The method for evaluating the aging performance of a pipeline according to claim 1, wherein the obtaining manner of the density ρ and the wall thickness e of the pipeline to be evaluated in the step (1) is as follows:
If the pipeline to be evaluated supports actual measurement, adopting actual measurement data; if the actual measurement is not supported, the following data are used: data in the original materials of the delivery inspection and the arrival inspection, test data of the reference sample or data in manuals and standards.
3. The method for evaluating the aging performance of a pipe according to claim 1, wherein the tensile elastic modulus E t of the aged sample is measured in the step (2) by:
a tensile specimen was prepared from the aged sample and tested for E t in the axial direction of the aged sample.
4. The method for evaluating the aging performance of a pipe according to claim 1, wherein the young's modulus E u of the aged sample measured in step (2) is:
based on the bulk wave method in GB/T38897-2020 "nondestructive test elastic modulus and Poisson ratio ultrasonic measurement method", the longitudinal wave sound velocity v l and the transverse wave sound velocity v s of the aged sample are measured, and based on the longitudinal wave sound velocity v l, the transverse wave sound velocity v s and the density ρ, young modulus E u of the aged sample in the wall thickness direction is calculated according to formula (1):
Wherein E u -Young's modulus, MPa; ρ -density, kg/m 3;vl -longitudinal wave sound velocity, m/s; v s -transverse wave speed of sound, m/s.
5. The method for evaluating the aging performance of a pipe according to claim 4, wherein the density ρ of the aged sample is measured by a dipping method.
6. The method for evaluating the aging performance of a pipe according to claim 1, wherein in the step (2), the measurement is performed using a longitudinal wave transducer of 2.5MHz and a transverse wave transducer of 1.0 MHz.
7. The method for evaluating the aging performance of a pipe according to claim 1, wherein in the step (2), the wall thickness e of the aged sample is measured by using a wall thickness micrometer or a vernier caliper.
8. The method for evaluating the aging performance of a pipe according to claim 1, wherein in the step (2), in the step (3), the aging state of the evaluation object is further processed based on the aging coefficient η, specifically:
when the eta is less than or equal to 5 percent, the treatment is not needed;
when 5% <|eta| is less than or equal to 10%, performing ultrasonic examination for 1 time/3 years;
when the ratio of 10% <|eta| is less than or equal to 15%, performing ultrasonic examination for 1 time/2 years;
when 15% <|eta| is less than or equal to 20%, performing ultrasonic examination for 1 time/1 year, and sampling and checking;
When 20% <|eta| is less than or equal to 25%, stopping use, and sampling and checking;
When 25% < |eta| the process is disabled.
9. The method for evaluating the aging performance of a pipe according to any one of claims 1 to 8, wherein the pipe is a thermoplastic pipe.
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