CN108572134B - Method and system for testing residual life of pipe - Google Patents

Abstract

The invention provides a test method and a test system for the remaining life of a pipe. The test method for the remaining life of a pipe includes: obtaining the strain hardening modulus values G _P of at least three polyethylene materials with a known design service life T, so that the The at least three polyethylene materials are polyethylene materials of different types; according to the strain hardening modulus value G _P and the design service life value T, the construction function: T=a ₀ +a ₁ ×<G _p >+ a ₂ ×<G _p > ² +...+a _n ×<G _p > ⁿ , where a ₀ , a ₁ , a ₂ ...... a _n are preset coefficients, and n is the preset maximum degree of the function , take a positive integer; obtain the test sample from the in-service pipe; measure the strain hardening modulus value _GP ' of the test sample; according to the function and the strain hardening modulus value _GP ' of the test sample , to estimate the remaining life of the test sample. The present invention can obtain the remaining life of the test sample as a reference value of the remaining life of the in-service pipe due to slow crack propagation, so as to timely discover the risk of the in-service pipe failure due to slow crack propagation.

Description

Test method and test system for remaining life of pipes

technical field

The present invention relates to material testing technology, in particular to a testing method and testing system for the remaining life of pipes.

Background technique

Polyethylene (PE) gas pipelines have gradually replaced steel pipes due to their advantages of strong corrosion resistance, good mechanical properties, long service life and environmental protection. As a common means of natural gas transportation, they are widely used in urban gas pipeline networks. At present, the in-service polyethylene gas pipes laid in my country are mainly the third-generation PE100 grade pipes, which have a design life of 58 years and have been put into use for about 20 years. Affected by various external factors such as oxygen aging, point load and corrosion, with the increase of service time, the pipe itself is prone to local stress concentration, which eventually leads to the failure of slow cracks in the pipe, which directly affects the remaining life of the PE gas pipe in service. In-service PE gas pipes are pressure-bearing special equipment, which transports all flammable and explosive materials. Once gas leakage occurs, the consequences will be fatal; therefore, whether the remaining life of in-service PE gas pipes can reach the pre-designed life will directly affect The normal operation of the urban gas pipeline network and the safety of people's lives and properties is an extremely important technical indicator. But so far, there is a lack of fast and effective evaluation methods for the remaining life of PE gas pipes in service at home and abroad. Due to the lack of accurate and effective methods for predicting the remaining life of gas pipeline networks in many cities, the failed pipes cannot be replaced in a timely and effective manner. Gas leakage accidents and quality and safety accidents have occurred from time to time, and even explosion accidents have been caused, which has caused serious hidden dangers to urban public safety.

Therefore, accurate and effective analysis of the remaining life of in-service PE pipes and timely replacement of failed pipes can effectively reduce accidents such as gas leakage. Moreover, an in-service PE gas pipe with short test period, simple test conditions and low cost is proposed. The accelerated evaluation method of life prediction can provide a strong safety guarantee for the quality and cost control of PE gas pipes, shorten the development cycle of special resins for new gas pipes, and ensure the safe operation of existing gas pipeline systems.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve at least one of the above technical deficiencies, especially the problem of difficulty in estimating the remaining life of the piping system.

The invention provides a method for testing the remaining life of a pipe, comprising:

obtaining the strain hardening modulus values <G _p > of at least three polyethylene materials with known design service life T, the at least three polyethylene materials being polyethylene materials of different types;

According to the strain hardening modulus value <G _p > and the design service life T, a function is constructed:

T=a ₀ +a ₁ ×<G _p >+a ₂ ×<G _p > ² +……+a _n ×<G _p > ⁿ , where a ₀ , a ₁ , a ₂ …… a _n are pre- Let the coefficient, n be the preset maximum number of the function, which is a positive integer;

Obtain test specimens from in-service polyethylene pipe;

measuring the strain hardening modulus value <G _P '> of the test specimen;

According to the function and the strain hardening modulus value <G _P '> of the test sample, the remaining life of the test sample is calculated.

Preferably, after estimating the remaining life of the test sample, the method further includes:

According to the remaining life, it is judged whether to replace the in-service polyethylene pipe.

Preferably, the judging whether to replace the in-service polyethylene pipe includes:

When the remaining life is not greater than the first preset value, replace the in-service polyethylene pipe;

When the remaining life is greater than the first preset value and less than the second preset value, monitoring the in-service polyethylene pipe material.

Preferably, obtaining the strain hardening modulus values <G _P > of at least three polyethylene materials with known design service life T, including:

respectively making at least five standard samples of each polyethylene material in the at least three polyethylene materials;

Through the high temperature tensile test, the strain hardening modulus value <G _Pi > of each standard sample is obtained, where i is the serial number of the standard sample;

According to the strain hardening modulus value <G _Pi > of each standard sample, calculate the root mean square average value of the strain hardening modulus value of each polyethylene material, and use the root mean square average value as the strain Hardening modulus value <G _P >.

Preferably, the at least five standard samples of each polyethylene material in the at least three polyethylene materials are respectively made, including:

The at least five standard samples of each polyethylene material are prepared in a compression molding apparatus, and the standard samples are dumbbell-shaped sheets including a middle test portion and two end clamping portions, and the thickness of the dumbbell-shaped sheet is 0.3mm-1mm;

After annealing the at least five standard samples in an environment of 115°C-125°C for one hour, the samples are cooled to room temperature at a cooling rate of less than 2°C/min.

Preferably, through the high temperature tensile test, the strain hardening modulus value <G _Pi > of each piece of the standard sample is obtained, including:

Place the dumbbell-shaped sheet in an incubator at 80°C for 30min-60min;

The clamping parts at both ends are clamped on a high temperature tensile testing machine, and a prestress of 0.4Mpa is applied at a strain rate of 5mm/min;

其中L₀为所述中部 测试部分的初始长度，所述L为所述中部测试部分拉伸后的长度；The dumbbell-shaped sheet was stretched at a constant moving speed of 20 mm/min, and the data values of the stretch ratio λ between 8 and 12 of the middle test section were collected, the stretch ratio

Wherein L ₀ is the initial length of the middle test portion, and L is the stretched length of the middle test portion;

其中,F为与所述拉伸比的数据值对应的拉伸力，A₀为所述 哑铃状薄片中部测试部分的初始横截面积；Record the correspondence between the stretching ratio λ and the true stress σ _true during the stretching process:

Wherein, F is the tensile force corresponding to the data value of the stretch ratio, and A ₀ is the initial cross-sectional area of the test portion in the middle of the dumbbell-shaped sheet;

According to the Neo-Hookean constitutive model and the slope K of the corresponding relationship when λ=12 and λ=8, the strain hardening modulus value <G _Pi > of each standard sample is determined as:

<G _Pi >=20K.

Preferably, the test sample obtained from the in-service polyethylene pipe includes:

Obtain test material from the in-service polyethylene pipe, and process the test material into the test sample in a prototype machine;

The test sample is a dumbbell-shaped sheet comprising a middle test portion and a clamping portion at both ends, and the thickness of the dumbbell-shaped sheet is 0.3mm-1mm

Preferably, the measuring the strain hardening modulus value G _P ' of the test sample includes:

Place the test sample in an incubator at 80°C for 30min-60min;

Clamp both ends of the test sample on a high-temperature tensile testing machine, and apply a prestress of 0.4Mpa at a strain rate of 5mm/min;

其中L₀’ 为所述测试试样中部测试部分的初始长度，所述L’为所述测试试样中部测试 部分拉伸后的长度；The test specimen is stretched at a constant moving speed of 20 mm/min, and the data values of the stretch ratio λ' between 8 and 12 of the test portion in the middle of the test specimen are collected. The stretch ratio

Wherein L ₀ ' is the initial length of the test portion in the middle of the test sample, and the L' is the length of the test portion in the middle of the test sample after stretching;

其中,F’为与所述拉伸比λ’的数据值对应的拉伸力，A₀’ 为所述测试试样中部测试部分的初始横截面积；Record the correspondence between the stretching ratio λ' and the true stress σ _true ' during the stretching process:

Wherein, F' is the tensile force corresponding to the data value of the tensile ratio λ', and A ₀ ' is the initial cross-sectional area of the test portion in the middle of the test sample;

According to the Neo-Hookean constitutive model and the slope K' of the corresponding relationship when λ'=12 and λ'=8, the strain hardening modulus value <G _P '> of the test specimen is determined as

<GP'> ₌ 20K'.

Preferably, the test sample is at least two pieces; the test sample is determined according to the Neo-Hookean constitutive model and the slope K' of the corresponding relationship when λ'=12 and λ'=8 The value of the strain hardening modulus <G _P '>, including:

Determine the strain hardening modulus value <G _Pi '> of each of the test specimens;

Calculate the root mean square average value of the strain hardening modulus value <G _Pi '>, and use the root mean square average value as the strain hardening modulus value <G _P '> of the test sample.

The present invention also provides a test system for the remaining life of the pipe, comprising:

Sample preparation device: used to obtain test samples from in-service polyethylene pipes;

Tensile testing device: used to measure the strain hardening modulus value <G _P '> of the test sample;

Central processing unit: used to obtain the strain hardening modulus values <G _P > of at least three polyethylene materials with known design service life T, the at least three polyethylene materials are polyethylene materials of different types; according to the The value of the strain hardening modulus <G _P > and the design service life T, the construction function:

T=a ₀ +a ₁ ×<G _p >+a ₂ ×<G _p > ² +...+a _n ×<G _p > ⁿ , where a ₀ , a ₁ , a ₂ ...... a _n are pre- Set the coefficient, n is the preset maximum order of the function, which is a positive integer; according to the function and the strain hardening modulus value <G _P '> of the test sample, the remaining life of the test sample is calculated.

The beneficial effects of the present invention are as follows:

1. The present invention can first analyze the polyethylene material with known design service life T to construct the function of strain hardening modulus value <G _P > and the design service life T; and then obtain it from the in-service polyethylene pipe material Test the sample, measure the strain hardening modulus value <G _P '> of the in-service polyethylene pipe, and finally combine the function to obtain the remaining life of the test sample, which is used as the in-service polyethylene pipe due to The residual life reference value of the failure caused by slow crack propagation can timely find the risk of failure of the in-service polyethylene pipe due to slow crack propagation; the present invention can effectively evaluate the remaining life of different in-service polyethylene pipes. For the remaining life, different treatment measures are taken for the in-service polyethylene pipes.

2. The present invention can correct the strain hardening modulus values of polyethylene materials known in the prior art by measuring the strain hardening modulus values of a plurality of the standard samples and taking the root mean square average value; The production parameters and measurement parameters of the standard sample are used as the measurement parameters of the subsequent test sample, which can further improve the estimation result of the remaining life; the invention is especially suitable for the analysis of the remaining life of the gas pipeline.

Additional aspects and advantages of the present invention will be set forth in part in the following description, which will become apparent from the following description, or may be learned by practice of the present invention.

Description of drawings

The above-described and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic flowchart of the first embodiment of the testing method according to the present invention.

2 is a schematic structural diagram of an embodiment of a tensile testing device in the present invention;

3 is a schematic structural diagram of another embodiment of the tensile testing device in the present invention;

FIG. 4 is a schematic structural diagram of another embodiment of the tensile testing device in the present invention.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, but not to be construed as a limitation of the present invention.

It will be understood by those skilled in the art that the singular forms "a", "an", "said" and "the" as used herein can also include the plural forms unless expressly stated otherwise. It should be further understood that the word "comprising" used in the description of the present invention refers to the presence of stated features, integers, steps, operations, elements and/or components, but does not exclude the presence or addition of one or more other features, Integers, steps, operations, elements, components and/or groups thereof. It will be understood that when we refer to an element as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. Also, "connection" as used herein may include wireless connections. As used herein, the term "and/or" includes all or any element and all combinations of one or more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should also be understood that terms, such as those defined in a general dictionary, should be understood to have meanings consistent with their meanings in the context of the prior art and, unless specifically defined as herein, should not be interpreted in idealistic or overly formal meaning to explain.

As shown in the flow chart in Figure 1, the present invention proposes a first embodiment of a method for testing the remaining life of a pipe, comprising the following steps:

Step S10: obtaining strain hardening modulus values <G _P > of at least three polyethylene materials with known design service life T, the at least three polyethylene materials being polyethylene materials of different types;

The performance parameters of various materials have been disclosed in the prior art, such as elastic modulus, Poisson's ratio, density, thermal expansion coefficient, yield strength, tensile strength, elongation, strain hardening modulus value, etc. of the material. In the process of material testing, through correlation analysis, it can be found that the strain hardening modulus value in the performance parameters is highly correlated with the slow crack propagation of the material, so the slow crack growth of the material can be estimated by the strain hardening modulus value of the tested material. Crack propagation failure service life. Correlation analysis is performed on the strain hardening modulus values <G _P > of different types of polyethylene materials with known design service life T, and the strain hardening modulus value < G _P > and the design service life T can be obtained. functional relationship between. The different types of polyethylene materials include pipes made of polyethylene materials of different grades named by various polyethylene manufacturers, for example: pipes made of grade 100 high-density polyethylene with a design life T of 58 years, or Pipes made of crack-resistant polyethylene PE100-RC have a design life T of 100 years.

The strain hardening modulus value <G _P > and the corresponding design service life T can be the nominal values of various manufacturers, or can be tested by themselves to obtain more accurate values.

Step S20: According to the strain hardening modulus value <G _P > and the design service life T, construct a function:

T=a ₀ +a ₁ ×<G _p >+a ₂ ×<G _p > ² +……+a _n ×<G _p > ⁿ , where a ₀ , a ₁ , a ₂ …… a _n are pre- Let the coefficient, n be the preset maximum number of the function, which is a positive integer;

In the present invention, the designed service life T and the strain hardening modulus value <G _P > of at least three different types of polyethylene materials are known, and the equation can be solved by analytical methods such as Newton iteration method to obtain the value of each preset coefficient, Thus, the functional relationship between the strain hardening modulus value <G _P > and the design service life T is obtained. Taking the strain hardening modulus value <G _P > of a type of polyethylene material with known design service life and the design service life T as an array, when there are two groups of arrays, a straight line equation with zero error function can be obtained, However, its error is relatively large; in order to improve the iterative precision, the present invention can take more of the arrays to obtain a one-variable n-th degree fitting equation and improve the accuracy of constructing the function. The number of the array can exceed the positive integer n, and then a function that minimizes the error is fitted by the Newton iteration method, so as to further reduce the error of the fitted function; a part of the values in the array may be located in the fitting On the function curve, the other part is evenly distributed on both sides of the function curve. The greater the number of said arrays, the lower the error rate of the constructed function.

Step S30: obtaining test samples from in-service polyethylene pipes;

The in-service polyethylene pipes are pipes in use, such as gas pipes buried in the ground. After fitting the function of the strain hardening modulus value <G _P > and the design service life T in the previous step, it is only necessary to obtain the strain hardening modulus value of the in-service polyethylene pipe to directly obtain the service life of polyethylene pipes. Said to obtain the test sample from the in-service polyethylene pipe material, part of the pipe material sample can be directly cut from the in-service polyethylene pipe material, and the sample can be processed into a suitable test sample shape.

Step S40: measure the strain hardening modulus value < _GP '> of the test sample;

The measurement of the strain hardening modulus value <G _P ″ of the test sample can be measured by using existing tensile test equipment, or a suitable tensile test can be designed or assembled according to the specific conditions of the test sample. equipment. The parameters for measuring the strain hardening modulus values <G _P ″> of the test specimens are preferably consistent with the parameters for measuring the strain hardening modulus values <G _P > of the at least three polyethylene materials of the known design service life ; The parameters include the size of the test sample, the heating temperature and time of the test sample, the stretching force and the stretching time in the stretching process, and the like.

Step S50: Calculate the remaining life of the test sample according to the function and the strain hardening modulus value <G _P '> of the test sample.

After the strain hardening modulus value <G _P ″> of the test sample is obtained, it can be substituted into the function constructed in step S20 to obtain the remaining life of the test sample. Since the material of the test sample is taken from the in-service polyethylene pipe, its material has changed in the use environment, and the change is the same as that of the in-service polyethylene pipe still in use, so the remaining parts of the test sample can pass the test. Life estimates the remaining life of in-service polyethylene pipes. The remaining life of the in-service polyethylene pipe may be the same as the remaining life of the test sample, or there may be a certain proportional relationship.

Defects that may be caused by existing polyethylene pipes in the process of production, transportation and construction, and in subsequent use, affected by external factors such as temperature, pressure and point load, there may be creep, stress relaxation, and rapid crack propagation. , slow crack growth and material aging and other failure modes; among them, slow crack growth is the most important failure mode. Although the design service life of the existing polyethylene pipe has been estimated at the time of design, due to the influence of factors such as different actual use parameters and different use environments, the actual service life of the pipe may not be consistent with the design service life. As mentioned above, slow crack propagation is the main failure mode of pipes, and the service life of slow crack propagation failure is highly related to the strain hardening modulus value, so the present invention can first analyze and construct the strain hardening modulus value The functional relationship with the service life, and then obtain the test sample from the in-service polyethylene pipe, in order to calculate the remaining life of the test sample according to the strain hardening modulus value <G _P '> of the test sample; The residual life of the in-service polyethylene pipe due to slow crack propagation can be calculated based on the remaining life of the test sample.

Therefore, the present invention can timely find the risk of failure of the in-service polyethylene pipe due to slow crack propagation, and avoid the danger caused by the failure of the in-service pipeline before the designed service life. For example, the polyethylene gas pipeline causes gas leakage due to slow crack propagation. accidents, etc.; through the present invention, the remaining life of different polyethylene pipes in service can be effectively evaluated, so as to perform different treatments on the polyethylene pipes in service according to the remaining life.

Based on the remaining life of the test sample in the previous embodiment, the present invention proposes another embodiment: after estimating the remaining life of the test sample, the method further includes:

According to the remaining life, it is judged whether to replace the in-service polyethylene pipe.

Although the test sample is taken from the in-service polyethylene pipe, the test sample may be subsequently processed into a shape suitable for testing and other processes, so the remaining life of the test sample is the same as the actual in-service polyethylene pipe. There may be a gap in the remaining life of the ethylene pipe. You can refer to the use environment, safety factor, processing technology of the test sample and other specific conditions of the polyethylene pipe in service, and judge whether it is necessary to replace the Service polyethylene pipe. For example, due to the harsh use environment, the service life of the in-service pipe is still 20 years away from the original design, but the remaining service life calculated by the test method of the present invention is only 3 years, and the in-service polyethylene pipe involves environmental pollutants The user can comprehensively judge whether the in-service polyethylene pipe needs to be replaced immediately, or when to replace the in-service polyethylene pipe at the latest, or replace the in-service polyethylene pipe with other material.

Based on the previous embodiment, the present invention proposes another embodiment: the judging whether to replace the in-service polyethylene pipe material includes:

When the remaining life is not greater than the first preset value, replace the in-service polyethylene pipe;

When the remaining life is greater than the first preset value and less than the second preset value, monitoring the in-service polyethylene pipe material.

In practical applications, corresponding measures can be taken according to the value of the remaining life, such as immediately replacing the in-service polyethylene pipe, or regularly inspecting the in-service polyethylene pipe, so as to provide a reference for the user's decision-making. Different parameters can also be set according to the use conditions of the in-service polyethylene pipes. For example: for the water supply pipeline, if the remaining life is more than 5 years, it will continue to be used normally; if the remaining life is more than 2 years and less than 5 years, it should be checked regularly every year to monitor the polyethylene pipe in service and prevent the water pipe from bursting ; For gas pipelines, if the remaining service life is greater than 5 years and less than 8 years, regular inspections should be conducted once a year to monitor the in-service polyethylene pipes and prevent gas leakage.

Based on the first embodiment, the present invention also proposes a second embodiment: obtaining the strain hardening modulus values <G _P > of at least three polyethylene materials with known design service life T, including:

respectively making at least five standard samples of each of the at least three polyethylene materials;

Through the high temperature tensile test, the strain hardening modulus value <G _Pi > of each standard sample is obtained, where i is the serial number of the standard sample;

According to the strain hardening modulus value <G _Pi > of each standard sample, calculate the root mean square average value of the strain hardening modulus value of each polyethylene material, and use the root mean square average value as the strain Hardening modulus value <G _P >.

Although the strain hardening modulus <GP> and design service life _T of various polyethylene materials are known in the prior art, due to the improvement of the material itself, the improvement of the processing technology, the test environment, the test equipment, etc., in order to increase the calculation of the residual The accuracy of the life can be re-measured for the value of the known strain hardening modulus value <G _P >. In this embodiment, at least five standard samples of each polyethylene material are remade to obtain the strain hardening modulus value <G _Pi > of each standard sample, and then the strain hardening of each polyethylene material is calculated. The RMS average of the moduli as <G _P > can further improve the accuracy of the strain hardening modulus value <G _P >.

Based on the second embodiment, the present invention also proposes another embodiment: the at least five standard samples of each polyethylene material in the at least three polyethylene materials are respectively made, including:

The at least five standard samples of each polyethylene material are prepared in a compression molding apparatus, and the standard samples are dumbbell-shaped sheets including a middle test portion and two end clamping portions, and the thickness of the dumbbell-shaped sheet is 0.3mm-1mm;

After annealing the at least five standard samples in an environment of 115°C-125°C for one hour, the samples are cooled to room temperature at a cooling rate of less than 2°C/min.

When making the standard samples, the preset number of the standard samples can be twice or three times the actual target number, so as to avoid the standard samples from being defective or becoming defective products during the production process. and reserve a sufficient number of tests for subsequent tensile tests to prevent excessive tensile test failures and the need for more of the standard specimens. The shape of the standard sample can refer to the shape of the existing tensile test, and its thickness can be determined according to the thickness of the polyethylene pipe in service.

Based on the previous embodiment, the present invention further proposes the following embodiment: the strain hardening modulus value <G _Pi > of each standard sample is obtained through the high temperature tensile test, including:

Place the dumbbell-shaped sheet in an incubator at 80°C for 30min-60min;

The clamping parts at both ends are clamped on a high temperature tensile testing machine, and a prestress of 0.4Mpa is applied at a strain rate of 5mm/min;

其中L₀为所述中部 测试部分的初始长度，所述L为所述中部测试部分拉伸后的长度；The dumbbell-shaped sheet was stretched at a constant moving speed of 20 mm/min, and the data values of the stretch ratio λ between 8 and 12 of the middle test section were collected, the stretch ratio

Wherein L ₀ is the initial length of the middle test portion, and L is the stretched length of the middle test portion;

其中,F为与所述拉伸比的数据值对应的拉伸力，A₀为所述 哑铃状薄片中部测试部分的初始横截面积；Record the correspondence between the stretching ratio λ and the true stress σ _true during the stretching process:

Wherein, F is the tensile force corresponding to the data value of the stretch ratio, and A ₀ is the initial cross-sectional area of the test portion in the middle of the dumbbell-shaped sheet;

According to the Neo-Hookean constitutive model and the slope K of the corresponding relationship when λ=12 and λ=8, the strain hardening modulus value <G _Pi > of each standard sample is determined as:

<G _Pi >=20K.

In this embodiment, the specific calculation process of the <G _Pi >=20K is as follows:

其中j为拉伸测试中λ的取值编号，σ_j为 λ取第j个值时，对应的的真应力σ_true的值，σ_j+1为λ取第j+1个值时，对 应的真应力σ_true的值，m为λ取值个数的数量上限；将

代入 上述公式，根据Neo-Hookean本构模型，可推导出：

Where j is the value number of λ in the tensile test, σ _j is the value of the corresponding true stress σ _true when λ takes the j-th value, and σ _j+1 is when λ takes the j+1-th value, the corresponding The value of the true stress σ _true , m is the upper limit of the number of λ values;

Substituting into the above formula, according to the Neo-Hookean constitutive model, it can be deduced:

则有：Wherein, K is the slope of the corresponding relationship when λ∈(λ ₁ ,λ ₂ ), and C is a constant; when λ ₁ =8 and λ ₂ =12,

Then there are:

After obtaining the strain hardening modulus value <G _Pi > of each standard sample, the strain hardening modulus of each polyethylene material is calculated according to the strain hardening modulus value <G _Pi > of each standard sample. The root-mean-square average value of the amount is taken as the strain hardening modulus value <G _P >, that is:

其中，N为测量的所述标准试样的总数量。

Wherein, N is the total number of the standard samples measured.

Based on the second embodiment, the present invention also proposes another embodiment: the test sample obtained from the in-service polyethylene pipe includes:

Obtain the test material from the in-service polyethylene pipe, and process the test material into the test sample in a prototype machine; the test sample is a dumbbell-shaped sheet including a middle test part and two end clamping parts , the thickness of the dumbbell-shaped sheet is 0.3mm-1mm.

The test sample in this embodiment can obtain material from the in-service polyethylene pipe, and then place the material in a sample making machine for cutting, so as to be processed into a dumbbell-shaped shape consistent with the standard sample. flakes.

Further, the parameters for measuring the strain hardening modulus value G _P ′ of the test sample can also be the same as the parameters for measuring the standard sample, so the measuring the strain hardening modulus value of the test sample <G _P '>, including:

Place the test sample in an incubator at 80°C for 30min-60min;

Clamp both ends of the test sample on a high-temperature tensile testing machine, and apply a prestress of 0.4Mpa at a strain rate of 5mm/min;

其中L₀’ 为所述测试试样中部测试部分的初始长度，所述L’为所述测试试样中部测试 部分拉伸后的长度；The test specimen is stretched at a constant moving speed of 20 mm/min, and the data values of the stretch ratio λ' between 8 and 12 of the test portion in the middle of the test specimen are collected. The stretch ratio

Wherein L ₀ ' is the initial length of the test portion in the middle of the test sample, and the L' is the length of the test portion in the middle of the test sample after stretching;

其中,F’为与所述拉伸比λ’的数据值对应的拉伸力，A₀’ 为所述测试试样中部测试部分的初始横截面积；Record the correspondence between the stretching ratio λ' and the true stress σ _true ' during the stretching process:

Wherein, F' is the tensile force corresponding to the data value of the tensile ratio λ', and A ₀ ' is the initial cross-sectional area of the test portion in the middle of the test sample;

According to the Neo-Hookean constitutive model and the slope K' of the corresponding relationship when λ'=12 and λ'=8, the strain hardening modulus value G _P ' of the test sample is determined as:

<GP'> ₌ 20K'.

The calculation process of the <GP '> ₌ 20K' is the same as the calculation process in the standard sample, and will not be repeated here.

In order to improve the accuracy of the test, the test sample is at least two pieces; according to the Neo-Hookean constitutive model, and when λ'=12 and λ'=8, the slope K' of the corresponding relationship is determined. The strain hardening modulus value <G _P '> of the test specimen, including:

Determine the strain hardening modulus value <G _Pi '> of each of the test specimens;

Calculate the root mean square average value of the strain hardening modulus value <G _Pi '>, and use the root mean square average value as the strain hardening modulus value <G _P '> of the test sample.

In this embodiment, the root-mean-square average value of the strain hardening modulus values <G _Pi '> of a plurality of the test samples can be taken, which can further improve the reliability of the strain hardening modulus values <G _P '>.

Further, the test samples can be taken from different positions of the in-service polyethylene pipe, so as to obtain the remaining life of the test samples at different positions, so that the user can understand the difference of the remaining life of the in-service polyethylene pipe in different positions. , in order to carry out different treatments; or take the root mean square average value of the strain hardening modulus values <G _Pi '> of the test specimens at different positions, as the overall strain hardening modulus value <G _P at the location of the test specimens '>, in order to reduce the accidental error caused by a single test sample. Of course, it is also possible to take materials from the same position of the in-service polyethylene pipe to make multiple test samples as a set of test samples; and also take materials from another location to make multiple test samples to As another set of test specimens to further improve the accuracy of the test.

According to the test method, the present invention also provides a test system for the remaining life of the pipe, including:

Sample preparation device: used to obtain test samples from in-service polyethylene pipes;

Tensile testing device: used to measure the strain hardening modulus value <G _P '> of the test sample;

Central processing unit: used to obtain the strain hardening modulus values <G _P > of at least three polyethylene materials with known design service life T, the at least three polyethylene materials are polyethylene materials of different types; according to the The value of the strain hardening modulus <G _P > and the design service life T, the construction function:

T=a ₀ +a ₁ ×<G _p >+a ₂ ×<G _p > ² +……+a _n ×<G _p > ⁿ , where a ₀ , ax, a ₂ …… a _n are preset coefficient, n is the preset maximum order of the function, which is a positive integer; according to the function and the strain hardening modulus value <G _P '> of the test sample, the remaining life of the test sample is calculated.

The sample preparation device can be an existing sample preparation machine, and the tensile testing device can be a high temperature tensile testing machine. The high temperature tensile testing machine can adopt the tensile structure shown in Figure 2-Figure 4, including:

rack 1;

A pair of clamps 2, namely clamps 2A and clamps 2B in the figure, clamps 2A and clamps 2B are fixed on the frame 1, clamps 2A and clamps 2B are provided with a clamping groove for clamping one end of the sample 9, clamps 2A and 2B are provided with a clamping groove. The opening directions of the clamping grooves of the clamp 2B are opposite to respectively clamp the two ends of the sample 9 and fix the sample 9;

Moving device 3, at least one fixture 2 is fixed on the frame 1 through the moving device 3, so that the fixture 2 moves in a direction away from or close to another fixture 2; in FIG. 1, the fixture 2A is fixed by the moving device 3, and the The device 3 can drive the fixture 2A to move upward or downward in the figure, so as to increase or decrease the distance between the fixture 2A and the fixture 2B, so as to achieve the purpose of stretching the sample 9 between the fixture 2A and the fixture 2B;

The auxiliary locking device is fixed on the fixture 2. The auxiliary locking device includes a locking station and an avoidance station. When the auxiliary locking device is located at the locking station, the clamping groove is applied Auxiliary clamping force to increase the clamping force of the sample 9, so that the sample 9 is not easy to slide or shift during the stretching process, and increase the accuracy of the tensile test;

The force measuring device 4 is connected with at least one of the fixtures 2 and is used to measure the tensile force generated when the moving device 3 moves; taking FIG. 1 as an example, since the sample 9 is clamped between the fixture 2A and the fixture 2B When the moving device 3 drives the clamp 2A to move upward, the sample 9 will generate a certain resistance; when the tensile force exceeds the resistance, the distance between the clamp 2A and the clamp 2B increases, and the sample 9 is elongated ; The force measuring device 4 is used to measure the tensile force when the sample 9 is elongated;

The length measuring device, fixed on the frame 1, includes a measuring head, and the measuring range of the measuring head is larger than the moving range of the fixture 2 to measure the real-time length of the sample 9 being elongated during the movement of the fixture 2.

When in use, the auxiliary locking device is located in the avoidance station in advance, so that the two ends of the sample 9 are respectively inserted into the clamping groove of the clamp 2A and the clamping groove of the clamp 2B and clamped; The auxiliary locking device is adjusted to the locking station to increase the clamping force on the sample 9; the moving device 3 is activated again, so that the moving device 3 drives the clamp 2A to move in a direction away from the clamp 2B, for example, to FIG. 1 During the stretching process, the force measuring device 4 measures the tensile force of the tensile sample 9, and the length measuring device measures the real-time tensile length of the sample 9; The aforementioned strain hardening modulus can be calculated from the tensile force and the applied tensile length. The auxiliary locking device in the present invention can strengthen the friction force between the sample 9 and the fixture 2, so that the sample 9 is not easy to slide during the stretching process, thereby improving the accuracy of the tensile test and reducing the tension of the sample. probability of failure.

Referring to FIGS. 2 and 3 , each of the clamps includes a pair of clamping panels 21 and a fixing base 22 with a positioning groove in the middle, and the pair of clamping panels 21 are fixed on opposite sides of the positioning grooves. ; One side of each of the clamping panels 21 is a fixed surface provided with anti-skid lines, and the other side is an adjustment surface connected with a screw; the clamping grooves are formed between the fixed surfaces of the pair of clamping panels 21, One end of the screw rod is rotatably fixed to the adjustment surface, and the other end penetrates the fixing seat and is connected with an adjustment knob 23. The rotation axis of the screw rod is perpendicular to the adjustment surface, so as to convert the rotation of the adjustment knob 23 into The clamping panel 21 moves linearly along the direction of the screw rotation axis to adjust the distance between a pair of clamping panels 21 so as to clamp samples 9 with different thicknesses; after the test is completed, the clamping panel 21 is increased by adjusting the knob 23 The distance between them is also convenient for taking out the sample 9.

The adjustment knobs 23 on the two clamps can be set on the same side to adjust the clamping panels 21 on the same side of the two clamps 2 to avoid the dislocation of the clamping grooves and to ensure that the clamped sample 9 remains vertical or The horizontal position improves the test accuracy; moreover, it is also convenient to reserve adjustment space on one side of the test equipment.

3, the auxiliary locking device includes a first locking mechanism and a second locking mechanism;

The two sides of each clamping panel 21 are respectively provided with card slots 211 , the first locking mechanism and the second locking mechanism respectively include two protruding edges, and the two protruding edges are respectively connected with the pair of clips. When the auxiliary locking device is located at the locking station, the two protruding edges are inserted into the card slots 211 on the same side of the pair of clamping panels respectively. .

When the slot 211 in this embodiment cooperates with the protruding edge, it can maintain the clamping force between the two clamping panels 21; especially when the first locking mechanism and the second locking mechanism are locked When it is a mechanism that can apply auxiliary clamping force, the distance between the two raised edges of each locking mechanism can be adjusted. By reducing the distance between the two raised edges, the distance between the two clamping panels 21 can be increased. The clamping force between the two clamping panels 21 can prevent the sample 9 from slipping.

The same effect can also be achieved when the positions of the card slot and the raised rib are exchanged; that is, the auxiliary locking device includes a first locking mechanism and a second locking mechanism; each of the clamping panels The two sides of 21 are respectively provided with protruding edges, and the first locking mechanism and the second locking mechanism of the lock respectively include two card slots, and the two card slots are respectively the same as the pair of clamping panels 21 on the same side. The protruding edges match; when the auxiliary locking device is located at the locking station, the protruding edges on the same side of the pair of clamping panels 21 are inserted into the two card slots respectively. When the first locking mechanism and the second locking mechanism are mechanisms that can apply auxiliary clamping force, the distance between the two card grooves of each locking mechanism can be adjusted. The distance between the grooves can increase the clamping force between the two clamping panels 21 .

At least one of the pair of clamping panels 21 may be provided with a concave portion, and the shape of the concave portion may be consistent with the shape of one end of the sample 9 to be clamped, or the size of the partial shape may be larger than the outline size of one end of the sample 9, as long as The concave portion can hold the sample 9 so that it is not easy to slip.

The concave portion may only be provided on one clamping panel 21; more preferably, the concave portion is provided on both the pair of clamping panels 21, and the depth of the concave portion is less than half of the thickness of the sample 9, that is: all the The thickness of the sample 9 is greater than the sum of the depths of the two concave portions, so as to balance the forces of the two clamping panels 21 , and improve the clamping reliability and the service life of the clamping panels 21 . When the recesses on the two clamping panels 21 are buckled and abut against the sample 9, there is still a partial gap between the two clamping panels 21, so as to exert a clamping force on the sample 9; and The concave portion can also play a role in positioning the sample 9, so that the sample 9 can be clamped in an optimal position. Depending on the thickness of the sample 9, the depth of the recesses may range from 0.1 mm to 3 mm.

In order to further improve the clamping effect, the surface of the concave portion is provided with anti-skid patterns, so as to increase the frictional force between the specimen 9 and the concave portion when the specimen 9 is stretched, thereby increasing the clamping force.

In order to facilitate holding the sample 9, each of the clamps 2 further includes a sample positioning device. As shown in FIG. 3, the sample positioning device includes a fixing component 51 and a positioning component 52. The fixing component 51 is fixed to a On the side of the clamping panel 21 , the positioning assembly 52 is perpendicular to the clamping panel 21 and faces the other clamping panel 21 . When clamping the sample 9, as shown in FIG. 2, one side of the sample 9 can abut on the positioning assembly 52, so that the positioning assembly 52 can be used as a reference for the positioning of the sample 9, so that the sample 9 can be clamped in a suitable position. s position. A chute can be provided on the fixing assembly 51, so that the sample positioning device can slide along the chute to adjust the position of the positioning assembly 52, thereby adjusting the positioning reference position of the sample 9.

In another embodiment, the measuring head of the length measuring device includes a first measuring rod 61 that can be aligned with one end of the length to be measured of the sample 9, and a second measuring rod 62 that is aligned with the other end of the length to be measured of the sample 9; The first measuring rod 61 moves synchronously with one of the fixtures 2, and the second measuring rod 62 moves synchronously with the other fixture, so as to ensure that the distance between the first measuring rod 61 and the second measuring rod 62 is the same as that of the sample 9. Length synchronization. Of course, one or both of the fixtures 2 can also be in a static state, and the corresponding first measuring rod 61 and/or the second measuring rod 62 are also in a static state. The two measuring rods in this embodiment can be installed on the frame 1 or on a slide rail 8, and can be separated with the stretching of the sample 9, so as to identify the stretching length of the sample 9 in real time .

More preferably, the measurement head includes a non-contact video optical measurement assembly. The non-contact video optical measurement component is an instrument that optically measures the deformation of the line between two points of the target member or object. It usually consists of an illumination field, a camera and a control chip. The deformation process is directly recorded by the camera, without the need for amplification and digital-to-analog conversion processing of the measured signal, which improves the measurement speed and accuracy, and the measurement accuracy is also higher than that of the existing extensometer; It can avoid any damage caused by the sample, thus avoiding the impact on the tensile test; during the test, there is no need to remove the measuring head, and the strain of the sample can be tracked throughout the whole process; it also avoids the existing tensile equipment when the sample is broken, resulting in stretching. Danger of falling and breaking the long gauge.

A pair of clamps 2 in the present invention, i.e. clamp 2A and clamp 2B shown in the figure, can be set up and down, also can be set up and down, in order to avoid the influence of gravity on testing, preferably clamp 2A and clamp 2B are set up and down. When the pair of clamps 2 is an upper clamp and a lower clamp arranged up and down, the moving device 3 is fixed above the upper clamp. As shown in FIG. 2 , the force measuring device 4 is fixed at the bottom of the lower clamp. The tensile force received by the lower clamp is detected, and the tensile force of the tensile sample 9 is obtained.

The tensile testing device in the present invention may further include a heating device 7 to heat the sample 9 to improve the activity of the polymer material, so as to obtain tensile testing results under different parameter conditions.

The above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (9)

1. A method for testing the residual life of a pipe is characterized by comprising the following steps:

obtaining strain hardening modulus values for at least three polyethylene materials of known design service life T<G_P>The at least three polyethylene materials are polyethylene materials with different types;

hardening modulus value according to the strain<G_P>And establishing a function with the design service life T:

T＝a₀+a₁×<G_p>+a₂×<G_p>²+……+a_n×<G_p>ⁿ，

wherein, a₀、a₁、a₂……a_nTaking a positive integer as a preset coefficient, wherein n is the preset maximum number of times of the function;

obtaining a test specimen from an in-service polyethylene pipe, comprising: intercepting part of the pipe from the in-service polyethylene pipe to be used as the test sample;

measuring the strain hardening modulus value of the test specimen<G_P'>；

According to the function and the testStrain hardening modulus value of test specimen<G_P'>Calculating the residual life of the test sample;

the strain hardening modulus values of at least three polyethylene materials of known design service life T are obtained<G_P>The method comprises the following steps:

respectively manufacturing at least five standard samples of each polyethylene material in the at least three polyethylene materials;

obtaining the strain hardening modulus value of each standard sample through a high-temperature tensile test<G_Pi>Wherein i is the number of the standard sample;

according to the strain hardening modulus value of each standard sample<G_Pi>Calculating the root mean square average value of the strain hardening modulus values of each polyethylene material, and taking the root mean square average value as the strain hardening modulus value<G_P>。

2. The method of claim 1, wherein after estimating the remaining life of the test specimen, further comprising:

and judging whether to replace the in-service polyethylene pipe or not according to the residual service life.

3. The method of claim 2, wherein the determining whether to replace in-service polyethylene pipe comprises:

when the residual life is not more than a first preset value, replacing the in-service polyethylene pipe;

and when the residual life is greater than the first preset value and less than a second preset value, monitoring the in-service polyethylene pipe.

4. The test method according to claim 1, wherein said separately making at least five standard specimens of each of said at least three polyethylene materials comprises:

preparing the at least five standard test samples of each polyethylene material in a die-pressing device, wherein the standard test samples are dumbbell-shaped sheets, each dumbbell-shaped sheet comprises a middle testing part and two end clamping parts, and the thickness of each dumbbell-shaped sheet is 0.3mm-1 mm;

and annealing the at least five standard samples at 115-125 ℃ for one hour, and cooling the samples to room temperature at a cooling speed of less than 2 ℃/min.

5. The method according to claim 4, wherein the strain hardening modulus value of each of the standard samples is obtained by a high temperature tensile test<G_Pi>The method comprises the following steps:

placing the dumbbell-shaped sheet in a thermostat at 80 ℃ for 30-60 min;

clamping the two end clamping parts on a high-temperature tensile testing machine, and applying 0.4Mpa prestress at a strain rate of 5 mm/min;

stretching the dumbbell sheet at a constant moving speed of 20mm/min, and collecting data values of the middle test portion having a stretch ratio lambda of 8 to 12, the stretch ratio lambda being

Wherein L is₀Is the initial length of the middle test portion, and the L is the stretched length of the middle test portion;

recording the draw ratio λ and the true stress σ during the draw_trueThe corresponding relation of (1):

wherein F is a tensile force corresponding to the data value of the tensile ratio, and A is₀The initial cross-sectional area of the middle test part of the dumbbell-shaped sheet is shown;

determining the strain hardening modulus value of each standard sample according to the Neo-Hookean constitutive model and the slope K of the corresponding relation when the lambda is 12 and the lambda is 8<G_Pi>Comprises the following steps:

<G_Pi>＝20K。

6. the method of claim 4, wherein the obtaining of test specimens from in-service polyethylene pipe comprises:

obtaining a test material from the in-service polyethylene pipe, and processing the test material into the test sample in a sampling machine;

the test sample is a dumbbell-shaped sheet, the dumbbell-shaped sheet comprises a middle test part and two end clamping parts, and the thickness of the dumbbell-shaped sheet is 0.3mm-1 mm.

7. The method of claim 6, wherein the measuring the strain hardening modulus value of the test specimen<G_P'>The method comprises the following steps:

placing the test sample in a thermostat at 80 ℃ for 30-60 min;

clamping the clamping parts at the two ends of the test sample on a high-temperature tensile testing machine, and applying 0.4Mpa prestress at a strain rate of 5 mm/min;

stretching the test specimen at a constant moving speed of 20mm/min, and collecting data values of a stretching ratio lambda 'between 8 and 12 at a middle test part of the test specimen, wherein the stretching ratio lambda' is

Wherein L is₀'is the initial length of the middle test portion of the test specimen, and L' is the stretched length of the middle test portion of the test specimen;

recording the draw ratio λ' and the true stress σ during the draw_true' the correspondence relationship:

wherein F 'is a stretching force corresponding to the data value of the stretching ratio lambda', and A₀' is the initial cross-sectional area of the middle test portion of the test specimen;

determining the strain hardening of the test sample according to the Neo-Hookean constitutive model and the slope K ' of the corresponding relation when the lambda ' is 12 and the lambda ' is 8Modulus value<G_P'>Is composed of

<G_P'>＝20K’。

8. The test method of claim 7, wherein the test sample is in at least two pieces; determining the strain hardening modulus value of the test sample according to the Neo-Hookean constitutive model and the slope K ' of the corresponding relation when the lambda ' is 12 and the lambda ' is 8<G_P'>The method comprises the following steps:

determining the strain hardening modulus value of each of the test specimens<G_Pi'>；

Calculating the strain hardening modulus value<G_Pi'>The root mean square average value is taken as the strain hardening modulus value of the test sample<G_P'>。

9. A system for testing the remaining life of a pipe, comprising:

a sample preparation device: for obtaining test specimens from in-service polyethylene pipe, comprising: intercepting part of the pipe from the in-service polyethylene pipe to be used as the test sample;

a tensile test device: for measuring the strain hardening modulus value of the test specimen<G_P'>；

A central processing unit: strain hardening modulus values for at least three polyethylene materials for obtaining a known design service life T<G_P>The at least three polyethylene materials are polyethylene materials with different types; hardening modulus value according to the strain<G_P>And establishing a function with the design service life T:

T＝a₀+a₁×<G_p>+a₂×<G_p>²+……+a_n×<G_p>ⁿwherein a is₀、a₁、a₂……a_nTaking a positive integer as a preset coefficient, wherein n is the preset function highest frequency; according to the function and the strain hardening modulus value of the test sample<G_P'>Push awayCalculating the residual life of the test sample;

the strain hardening modulus values of at least three polyethylene materials of known design service life T are obtained<G_P>The method comprises the following steps:

respectively manufacturing at least five standard samples of each polyethylene material in the at least three polyethylene materials;

obtaining the strain hardening modulus value of each standard sample through a high-temperature tensile test<G_Pi>Wherein i is the number of the standard sample;

according to the strain hardening modulus value of each standard sample<G_Pi>Calculating the root mean square average value of the strain hardening modulus values of each polyethylene material, and taking the root mean square average value as the strain hardening modulus value<G_P>。

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