A method for evaluating the service life of fiber reinforced plastic composite pipes

Abstract

The present invention belongs to the technical field of pipelines in the oil and gas industry, and specifically relates to a method for evaluating the service life of a fiber reinforced plastic composite pipe, the steps of which include determining test parameters, making samples and adjusting the state, conducting an instantaneous burst test at an evaluation test temperature, establishing a nominal confidence curve and a fitting equation, selecting different test times according to the nominal confidence curve to calculate the corresponding test pressure, conducting a long-term hydrostatic test, verifying or correcting the nominal confidence curve, obtaining a test evaluation curve and a fitting equation of the composite pipe's internal pressure strength failure value and failure time through data regression, and calculating the expected life or design pressure value of the pipe. Then, the obtained value is judged to be reliable through verification. If it is unreliable, a retest is conducted.

Description

Technical Field

[0001] The invention relates to the technical field of pipelines in the petroleum and natural gas industry, and in particular to a method for evaluating the service life of a fiber reinforced plastic composite pipe. Background Art

[0002] With the rapid development of the petroleum and natural gas industry, a large number of pressure pipelines are needed in the fields of oil and gas extraction, oil and gas gathering and injection, and sewage treatment. The fluids extracted from oil and gas wells are generally corrosive, which often causes carbon steel pipelines to suffer severe corrosion. Non-metallic fiber reinforced plastic composite pipes are a kind of pipe that has been developed in the past decade.

[0003] The non-metallic pipes for oil and gas gathering and transportation have been widely used in the transportation of fluids with severe corrosiveness, such as crude oil, natural gas, highly mineralized brine or sewage.

[0004] Non-metallic fiber reinforced plastic composite pipes usually have a three-layer structure. The innermost layer is made of thermoplastic plastic pipes (such as high-density polyethylene, polypropylene, nylon and other resin materials). The thermoplastic plastic pipe is in direct contact with the conveying fluid and plays the role of fluid shielding and corrosion protection; the middle layer is made of reinforcing fibers (such as polyester fibers,

[0005] The pipe is composed of non-metallic fibers such as aramid fibers or carbon fibers. The reinforcing fibers bear the internal pressure and axial load of the pipe. The outermost layer is a protective layer, which is usually composed of polyethylene resin.

[0006] Although non-metallic fiber reinforced plastic composite pipes have good corrosion resistance, in the oil and gas field gathering and transportation environment containing corrosive media such as H2S, CO2, Cl-, the service life of the composite pipe is mainly determined by the service parameters such as pipe characteristics, transportation medium, temperature, pressure, etc. Accurately predicting the service life of non-metallic fiber reinforced plastic composite pipes has important theoretical significance and practical engineering value for eliminating potential accidents in pressure pipelines, formulating effective maintenance plans, and making full use of composite pipes.

[0007] GB / T 18252-2000 and SY / T6794 proposed the determination of the long-term hydrostatic strength of thermoplastic plastic pipes by extrapolation. This method takes more than one year, and is aimed at plastic plastic pipes, without considering the impact of the conveying medium on the pipes. Invention patent ZL201410721347.5 discloses a method for predicting the life of fiber reinforced plastic composite pipes by using hydrostatic residual strength method based on linear regression. Prior art GB / T 18252-2000 and SY / T6794 use clean water as the test medium. The clean water environment has very limited effects on the corrosion and structural damage of the composite pipe. The composite pipe often has a longer service life in a clean water environment. However, petroleum and natural gas fluids usually cause physical and chemical aging damage to plastics through penetration, swelling and erosion. Thermoplastic plastic pipes age, and their chemical structure and properties change, thereby reducing or losing their performance. The existing method uses test media that does not meet the actual working conditions in the field of oil and gas, and the test cycle of this method exceeds one year, which is relatively inefficient. Patent ZL201410721347.5 adopts the method of fitting and extrapolating the instantaneous burst strength of the pipe after the hydrostatic pressure test to predict the life of the composite pipe. The instantaneous burst strength of the pipe cannot reflect the effect of the long-term pressure creep of the plastic pipe on the performance degradation of the pipe. Moreover, the reliability of the prediction results of this invention cannot be self-verified, and the influence of the fluid medium on the pipe is not considered. The pipe life predicted by the existing method will be dangerous. Summary of the invention

[0008] The present invention proposes a method for evaluating the service life of a fiber reinforced plastic composite pipe to solve the problems that a corresponding quantitative relationship cannot be established between short-term test data in the prior art and the expected long-term performance of the pipe, the reliability of the life fitting curve cannot be self-verified, and the effect of the corrosiveness of the pipeline transportation medium on the pipe life is not considered.

[0009] To achieve the above object, the present invention proposes the following technical solutions:

[0010] A method for evaluating the service life of a fiber reinforced plastic composite pipe comprises the following steps:

[0011] Step 1: Determine the evaluation test temperature Ttest, the maximum design pressure MOP of the pipeline, and the nominal pressure NPR of the pipeline;

[0012] Evaluation test temperature T test Taking the pipeline maximum design temperature MAOT, the calculation formula for the pipeline maximum design pressure MOP is:

[0013] MOP=NPR·f t

[0014] In the formula, f tis the temperature reduction factor corresponding to the test temperature; the nominal pressure of the pipeline NPR is the nominal pressure of the composite pipe at room temperature

[0015] Step 2: Randomly sample from the composite pipe products and make composite pipe short section specimens. Fill the composite pipe specimens with sealed joints at both ends with liquid test medium, put the specimens into a constant temperature water tank or environmental test box with a temperature control device, the environment outside the specimen tube is air or water, and place it under the test temperature Ttest for no less than 4 hours for state adjustment to keep the temperature of the pipe body and the medium inside the pipe consistent;

[0016] Step 3: Take the sample after the state adjustment in the second step and conduct an instantaneous burst test. Connect the sample to the hydraulic pressurizing equipment and control the pressurizing speed of the pressurizing equipment so that the sample fails by bursting between 30 seconds and 60 seconds. Record the internal pressure strength value, the corresponding failure time value and the instantaneous burst test point M of each sample when it bursts.

[0017] The arithmetic mean of the internal pressure strength values ​​when explosion occurs in no less than 3 valid tests is recorded as P 0 burst , the arithmetic mean of the corresponding explosion failure time is recorded as t 0 burst ;

[0018] If the failure mode of the sample is cracking or bursting of the composite pipe body, it is recorded as a valid test; if the joints at both ends of the sample fail or the pipe body comes out of the joint, it is an invalid sample and the test data of the invalid sample is discarded;

[0019] Step 4: Calculate the short-term hydrostatic test pressure value based on the fitting curve of the instantaneous burst test point M and the pipe failure strength threshold under the design life, carry out the short-term hydrostatic test until the sample fails, record the failure time, and obtain the short-term hydrostatic test point N;

[0020] Step 5: In the plane rectangular coordinate system, connect the short-term hydrostatic test point N obtained in the fourth step with the design life point L to draw a curve NL, which is called the nominal confidence curve for composite pipe life prediction, and calculate the linear fitting equation:

[0021] lgP=G n lg(t)+C n

[0022] In the formula, G n and C n is a constant that characterizes the fitting characteristics and is directly given by the fitting equation; P is the failure pressure of the composite pipe; t is the failure time;

[0023] Step 6: Determine the test time t testTake three discrete values ​​between 100h and 5000h and calculate different t according to step 5. test The corresponding P is calculated as the evaluation test pressure value P test , at the evaluation test temperature T test Under each evaluation test pressure value P test Under the conditions, take one sample for hydrostatic test; the preparation and state conditions of the sample are carried out according to the second step, the internal medium and pressurization process of the tube sample are the same as the second step, and the pressure is increased to the test pressure P test Then start timing;

[0024] The hydrostatic test is carried out until the pipe sample fails, ruptures or leaks, and the failure time t of the sample is recorded. failure Each t failure Corresponding test pressure value P test Composed of a pair of data (t failure , P test ), for (t failure , P test ) takes the common logarithm in the coordinate system and is called the test point;

[0025] The regulations for effective testing are the same as those in step 3. Otherwise, re-sampling should be done under the same conditions.

[0026] Step 7: Compare t failure With t test , life span assessment is carried out according to different situations.

[0027] Preferably, in the second step, the specimens adopt non-constrained field joints, and the length of the pipe body of each specimen between two sealing joints is not less than three times the outer diameter of the specimen and must not be less than 500 mm.

[0028] Preferably, in the second step, the test medium is a simulated pipeline transmission fluid consisting of light crude oil, diesel and brine.

[0029] Preferably, the composite pipe products in the second step are composite pipe products of the same batch that meet the quality requirements of standard SY / T6662.2 or SY / T6794.

[0030] Preferably, in the fourth step, the specific steps are:

[0031] Under the condition of maximum design temperature MAOT, the design life of the composite pipe is t life and its corresponding pipe failure strength threshold P threshold Composition number pairs (t life , P threshold ), take the common logarithmic value as the design life point L in the plane rectangular coordinate system;

[0032] Pipe failure strength threshold P threshold Calculate according to the following formula:

[0033]

[0034] Where, the pipe failure strength threshold P threshold The unit is MPa, F p is the pipeline pressure safety factor, which is determined based on the frequency and amplitude of fluid fluctuations;

[0035] Strong fluctuation Fp is not greater than 0.65; moderate fluctuation Fp p Greater than 0.65 and less than 0.85; Slight fluctuation F p Greater than 0.85 and not greater than 1.0;

[0036] F f is the pipeline fluid coefficient, which is determined according to Appendix C of SY / T6794;

[0037] When the transported fluid is water, F f Not more than 1.0; the conveying fluid is oil-water two-phase or multi-phase medium, F f Not more than 0.8; when the conveying fluid is gas, F f Not more than 0.67;

[0038] In the plane rectangular coordinate system, the instantaneous burst test data point M obtained in the third step is connected with the design life point L to draw a curve as the pressure calculation curve of the short-term hydrostatic test, and the fitting equation of the curve ML is calculated:

[0039] lgP=G m lg(t)+C m

[0040] In the formula, G m and C m is a constant that characterizes the fitting characteristics;

[0041] The time t is between 10h and 100h, and the pressure value P of the short-term hydrostatic test of the pipe corresponding to t is calculated by the formula N ;

[0042] In MAOT, P N Under the conditions, at least 5 effective hydrostatic tests are carried out. The sample is made according to the second step. The sample is filled with the same light crude oil or diesel, brine and other test media as in the second step. The liquid phase of crude oil or diesel and brine accounts for 50% to 100% of the sample volume. Then, the sample is placed in an environment at a temperature of T test The state is adjusted in a constant temperature water bath or environmental test chamber for no less than 4 hours. Then, according to the oil and gas composition ratio of the pipeline on-site transmission fluid, carbon dioxide, methane, nitrogen or a mixture of the above gases is slowly added to the sample using carbon dioxide, methane or nitrogen gas cylinders to the test pressure value PN If the cylinder pressure is too low to be pressurized to P N , connect the sample to the hydraulic pressure equipment, and slowly increase the internal pressure of the sample to the test pressure value P N The test operation is carried out according to GB / T 6111-2018, and the external environment is air or water bath with controllable temperature; pressurized to P N Then start timing; the test is carried out until the sample fails, and the time value of each sample failure is recorded;

[0043] Take the 97.5% confidence lower limit of the failure time of 5 valid hydrostatic tests and record it as t N , the calculation method of the confidence lower limit refers to Appendix B of standard SY / T6794-2018; t N and P N Composition number pairs (t N , P N ), logarithmic pair (t N , P N ) Take the common logarithm and record it as point N in the coordinate system;

[0044] The provisions for valid tests are the same as in step 3.

[0045] Preferably, in the sixth step, each t test The interval is not less than 500h; the external environment of the sample is air or a water bath with controllable temperature.

[0046] Preferably, the seventh step includes:

[0047] Case 1: All test points [lg(t failure ), lg(P test )] all fall on or above the nominal confidence curve NL, and the t failure Not less than the evaluation test time t test , one or two specimens have t failure More than 1.5t test , but not all samples have t failure More than 1.5t test , determine that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is not less than the design life t life ;

[0048] Case 2: All test points [lg(t failure ), lg(P test )] all fall in the area above the nominal confidence curve NL, and the t failure More than 1.5t test The assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is not less than the design life t life ; Conduct retest;

[0049] Case 3: t of all samples failure Less than t test ; Determine that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is less than the design life t life ;

[0050] Case 4: t with only one sample failure Not less than t test , t of the remaining samples failure Both are less than t test ; Determine that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is less than the design life t life ;

[0051] Case 5: t with only one sample failure Less than t test , t of the remaining samples failure Not less than t test ; Unable to judge, re-test.

[0052] Preferably, in case 2, two retest methods are included:

[0053] A) Return to the first step and evaluate the test temperature T test or if the MOP increases, repeat the test;

[0054] B) Re-evaluate the life or MOP calculation based on the test data completed in steps 1 to 6 as follows:

[0055] The t of three test points failure All over 1.5t test , connect the test point closest to the nominal confidence curve NL in step 6 with the base point N to form the test evaluation curve;

[0056] The fitting equation of the evaluation curve is as follows:

[0057] lgP=G f lg(t)+C f

[0058] Evaluation curve extension and P = P threshold The intersection point K, the time t value corresponding to point K is P threshold ;

[0059] Re-evaluated lifespan value t under unchanged conditions k life , t k life Calculate according to the following formula:

[0060] t klife =10^[Lg(P threshold )-C f ] / G f

[0061] Evaluation curve and t=t life The intersection point J, the pressure P value corresponding to point J is the design life t life The critical pressure value P re-evaluated under unchanged conditions J threshold , P J threshold Calculate according to the following formula:

[0062] P J threshold =10^[G f· lg(t life )+C f ]

[0063] Calculate the re-evaluated maximum design pressure MOP of the pipeline:

[0064] MOP=P J threshold ·F p ·F f .

[0065] Preferably, the life expectancy and MOP calculation method in Case 3 and Case 4 are the same as B) in Case 2.

[0066] Preferably, the retest results of situation 5 are processed as follows:

[0067] If the two retest results test points [lg(t failure ), lg(P test )] all fall on or above the nominal confidence curve and are handled as in Case 1;

[0068] If there are 2 or 1 retest result test point [lg(t failure ), lg(P test )] falls in the area below the nominal confidence curve, the test point that falls in the area below the nominal confidence curve and is farthest from the nominal confidence curve in the two tests is connected with the base point N as the test evaluation curve, and the life re-evaluation or MOP accounting is processed according to the method of case 3. The benefits of the present invention are:

[0069] The nominal confidence curve and fitting equation of the failure pressure and failure time of the composite pipe are calculated by using the confidence lower limit value of the instantaneous burst strength of the pipe and the short-term hydrostatic test data, combined with the nominal pressure and working coefficient data of the pipe. Then, a longer hydrostatic failure test is used to verify or correct the nominal regression confidence curve. The test evaluation curve and fitting equation of the failure value and failure time of the internal pressure strength of the composite pipe are obtained through data regression, and the expected life or design pressure value of the pipe is calculated, and the quantitative relationship between the short-term test data and the expected long-term performance of the pipe is established.

[0070] During the experiment, the pipe was filled with simulated conveying medium to determine the impact of the corrosiveness of the pipeline conveying medium on the life of the pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0072] Figure 1 This is a pressure calculation curve of a short-term hydrostatic test of a composite pipe provided in the second embodiment of the present invention.

[0073] Figure 2 This is the nominal confidence curve for predicting the life of the composite pipe provided in the second embodiment of the present invention.

[0074] Figure 3 This is the nominal confidence curve for predicting the life of the composite pipe provided in the third embodiment of the present invention.

[0075] Figure 4 This is a pressure calculation curve of a short-term hydrostatic test of a composite pipe provided in the fourth embodiment of the present invention.

[0076] Figure 5 This is a test evaluation curve of the composite pipe provided in Example 4 of the present invention.

[0077] Figure 6 This is a pressure calculation curve of a short-term hydrostatic test of a composite pipe provided in Example 5 of the present invention.

[0078] Figure 7 This is a test evaluation curve of the composite pipe provided in Example 5 of the present invention.

[0079] Figure 8 The present invention is a flow chart of a service life assessment method for fiber reinforced plastic composite pipes. DETAILED DESCRIPTION

[0080] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0081] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0082] Embodiment 1:

[0083] The theoretical basis of the present invention is that the pressure bearing performance of the non-metallic fiber reinforced plastic composite pipe has a significant regression characteristic, that is, lgP and lg(t) satisfy a linear relationship:

[0084] lgP=Glg(t)+C

[0085] Among them, G and C are constants that characterize the regression characteristics and are related to the composite pipe material and structure as well as the test conditions; P is the failure pressure of the composite pipe, and t is the failure time.

[0086] The specific steps are as follows:

[0087] Step 1: Determine the experimental parameters

[0088] Evaluation test temperature: Evaluation test temperature T test Take the maximum design temperature MAOT of the pipeline.

[0089] Pipeline maximum design pressure MOP: The pipeline maximum design pressure MOP is the maximum working pressure of the pipeline during normal operation under the conditions of maximum design temperature MAOT, conveying fluid medium and design life.

[0090] MOP=NPR·f t ,

[0091] f t is the temperature reduction factor corresponding to the test temperature, f t Selected according to SY / T6662.2 Table C.1 or provided by the composite pipe manufacturer.

[0092] The nominal pressure NPR of the pipeline is the nominal pressure under normal temperature conditions provided by the composite pipe manufacturer.

[0093] Step 2: Sample preparation and state adjustment

[0094] Randomly sample the composite pipe products from the same batch that meet the quality requirements of standard SY / T6662.2 or SY / T6794, and make composite pipe short section specimens. The pipe length of each specimen between two sealing joints should be no less than three times the outer diameter of the specimen, and no less than 500mm. The specimen should use non-constrained field joints.

[0095] Fill the composite pipe sample with sealed joints at both ends with liquid test medium, the test medium is a simulated pipeline transmission fluid composed of light crude oil or diesel, brine, etc., put the sample into a constant temperature water tank or environmental test box with a temperature control device, and the environment outside the sample tube is air or water. Place it under the test temperature Ttest for no less than 4 hours for state adjustment to keep the temperature of the pipe body and the medium in the pipe consistent.

[0096] Step 3: Evaluate the test temperature T test Instantaneous burst test

[0097] Take the sample after the state adjustment in step 2 for instantaneous burst test, connect the sample to the hydraulic pressurizing equipment, control the pressurizing speed of the pressurizing equipment, make the sample burst and fail between 30 seconds and 60 seconds, and record the internal pressure strength value and the corresponding failure time value each time the sample bursts.

[0098] The arithmetic mean of the instantaneous burst strength values ​​of no less than 3 valid tests is recorded as P 0 burst , the arithmetic mean of the corresponding explosion failure time is recorded as t 0 burst ;

[0099] Step 4: Evaluate the test temperature T test Short-term hydrostatic test

[0100] The short-term hydrostatic test pressure value is calculated based on the fitting curve of the instantaneous burst test point M and the pipe failure strength threshold under the design life. The short-term hydrostatic test is carried out until the sample fails, and the failure time is recorded to obtain the base point N. The specific method is as follows:

[0101] Under the condition of maximum design temperature MAOT, the design life of the composite pipe is t life and its corresponding pipe failure strength threshold P threshold Composition number pairs (t life , P threshold ), take the common logarithmic value as the design life point L in the plane rectangular coordinate system.

[0102] Design life of pipe life It is defined as the time when the predicted failure internal pressure strength value of the pipe is equal to the failure internal pressure strength threshold of the pipe.

[0103] Pipe failure strength threshold P threshold Calculate according to the following formula:

[0104]

[0105] Pipe failure strength threshold P threshold The unit is MPa, Fp It is the pipeline pressure safety factor, providing an additional protection against pipeline damage caused by pressure fluctuations of the transported fluid. The value is determined according to the frequency and amplitude of fluid fluctuations. For strong fluctuations, Fp is not greater than 0.65; for medium fluctuations, F p No more than 0.85; slight fluctuation F p Not greater than 1.0;

[0106] F f It is the pipeline fluid coefficient, providing an additional protection for pipeline operation safety due to the risk of fluid leakage. The value is based on Appendix C of SY / T6794. When the transported fluid is water, F f Not more than 1.0; the conveying fluid is oil-water two-phase or multi-phase medium, F f Not more than 0.8; when the conveying fluid is gas, F f Not more than 0.67.

[0107] In the plane rectangular coordinate system, connect the instantaneous burst test data point M obtained in step 3 with the design life point L obtained in this step to draw a curve. The curve ML is used as the pressure of the short-term hydrostatic test.

[0108] Calculate the curve and calculate the fitting equation of the curve ML:

[0109] lgP=G m lg(t)+C m

[0110] In the formula, G m and C m is a constant that characterizes the fitting characteristics.

[0111] The time t is between 10h and 100h, preferably 10h or 100h. The pressure value P of the short-term hydrostatic test of the pipe corresponding to t is calculated by the formula N .

[0112] In MAOT, P N The test sample is prepared according to step 2, and the test medium such as light crude oil or diesel, brine, etc. is filled into the sample, and the liquid phase of crude oil or diesel or brine accounts for 50% to 100% of the sample volume. Then, the sample is placed in an environment at a temperature of T test The state is adjusted in a constant temperature water bath or environmental test chamber for no less than 4 hours. Then, according to the oil and gas composition ratio of the pipeline on-site transmission fluid, carbon dioxide, methane, nitrogen or a mixture of the above gases can be slowly added to the sample using carbon dioxide, methane, nitrogen gas cylinders to the test pressure value P N If the cylinder pressure is too low to be pressurized to P N, the sample can be connected to the hydraulic pressure equipment, and the internal pressure of the sample can be slowly increased to the test pressure value P N , the test operation can be carried out according to GB / T 6111-2018, and the external environment is air or water bath with controllable temperature. Pressurize to P N The test is continued until the specimen fails, and the time value of each specimen failure is recorded.

[0113] Take the 97.5% confidence lower limit of the failure time of 5 valid hydrostatic tests and record it as t N The calculation method of the lower confidence limit is in accordance with Appendix B of SY / T6794-2018. N and P N Composition number pairs (t N , P N ), take the common logarithm and record it as point N in the coordinate system. The provisions for the effective test are the same as those in step 3.

[0114] Step 5: Create nominal confidence curve and fitting equation

[0115] In the plane rectangular coordinate system, the short-term hydrostatic test point N obtained in step 4 is connected with the design life point L to draw a curve. The curve NL is called the nominal confidence curve for composite pipe life prediction, and the linear fitting equation is calculated:

[0116] lgP=G n lg(t)+C n

[0117] In the formula, G n and C n is a constant that characterizes the fitting characteristics.

[0118] Step 6: Select different test times according to the nominal confidence curve to calculate the corresponding test pressure, conduct a longer hydrostatic test, and verify or correct the nominal confidence curve.

[0119] Evaluation test time t test Take 3 discrete values ​​between 100h and 5000h, each t test The interval should be no less than 500h. Calculate the different t test Corresponding evaluation test pressure value P test .

[0120] At the test temperature T test Under each evaluation test pressure value P test Take a sample under the conditions for hydrostatic test. The sample preparation and state conditions are carried out according to step 2. The internal medium of the tube sample is

[0121] The process is the same as step 4, pressurizing to the test pressure Ptest The external environment should be air or a water bath with controllable temperature.

[0122] The hydrostatic test should be carried out until the pipe sample fails, ruptures or leaks, and the failure time t of the sample should be recorded. failure Each t failure Corresponding test pressure value P test Composed of a pair of data (t failure , P test ), take the common logarithm of it in the coordinate system and it is called the test point. The provisions for valid test are the same as step 3, otherwise re-sampling should be done under the same conditions.

[0123] Step 7: Lifespan Assessment

[0124] The results of the long-term hydrostatic test described in step 6 may show one of the following five situations. For different situations, life assessment is performed according to the following methods.

[0125] Case 1:

[0126] All samples t failure Not less than the evaluation test time t test , some samples have t failure More than 1.5t test , but not all samples have t failure More than 1.5t test .

[0127] That is to say, all test points [lg(t failure ), lg(P test )] all fall on or above the nominal confidence curve NL, it is determined that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is not less than the design life t life .

[0128] Case 2:

[0129] All samples t failure More than 1.5t test .

[0130] All test points [lg(t failure ), lg(P test )] are all above the nominal confidence curve NL, but far from the nominal confidence curve, it is determined that the composite pipe is not good under the conditions of MAOT, MOP and conveying fluid.

[0131] Estimated life is not less than the design life t life However, the composite pipe has a design life of t life, MAOT, MOP and conveying fluid conditions are too safe and cannot effectively exert the performance potential of the pipe. If necessary, one of the following two situations can be selected to continue the test:

[0132] A) Return to step 1 and evaluate the test temperature T test Or after the MOP is appropriately increased, the test is repeated;

[0133] B) Re-evaluate the life or MOP calculation based on the test data completed in steps 1 to 6 as follows:

[0134] The t of three test points failure All over 1.5t test , take the test point closest to the nominal confidence curve in step 6 and connect it with the base point N to form the test evaluation curve. The fitting equation of the evaluation curve is as follows:

[0135] lgP=G f lg(t)+C f

[0136] Evaluation curve extension and P = P threshold The intersection point K, the time t value corresponding to point K is P threshold

[0137] Re-evaluated lifespan value t under unchanged conditions k life , t k life Calculate according to the following formula:

[0138] t k life＝ 10^[Lg(P threshold )-C f ] / G f

[0139] Evaluation curve and t=t life The intersection point J, the pressure P value corresponding to point J is the design life t life The critical pressure value P re-evaluated under unchanged conditions J threshold , P J threshold Calculate according to the following formula:

[0140] P J threshold =10^[G f· lg(t life )+C f ]

[0141] The re-evaluated maximum design pressure (MOP) of the pipeline can be obtained:

[0142] MOP=P J threshold ·F p ·F f

[0143] Case 3:

[0144] All samples t failure Less than t test .

[0145] All test points [lg(t failure ), lg(P test )] all fall below the nominal confidence curve, it is determined that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is less than the design life t life .

[0146] Failure time t of three test points failure Both are less than the evaluation test time t test , connect the test point farthest from the nominal confidence curve with the base point N to form the test evaluation curve. The expected life and MOP calculation method are the same as in case 2B).

[0147] Case 4:

[0148] Only one sample t failure Not less than t test , t of the remaining samples failure Both are less than t test .

[0149] That is to say, there is only one test point [lg(t failure ), lg(P test )] falls on or above the nominal confidence curve NL, and the remaining test points [lg(t failure ), lg(P test )] falls below the nominal confidence curve NL, it is determined that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is less than the design life t life .

[0150] Take the test point that falls below the nominal confidence curve NL and is farthest from the nominal confidence curve NL and connect it with the base point N as the test evaluation curve. The life re-evaluation or MOP calculation method is handled according to Case 3.

[0151] Case 5:

[0152] Only one sample t failure Less than t test , t of the remaining samples failure Not less than t test That is to say, there is only one test point [lg(tfailure ), lg(P test )] falls below the nominal confidence curve NL, and the remaining test points [lg(t failure ), lg(P test )] falls on or above the nominal confidence curve NL, in which case retesting is required.

[0153] For the test points that fall below the nominal confidence curve NL, take two pipe samples for retesting under the same test conditions. The retest results are processed as follows: If the two retest results test points [lg(t failure ), lg(P test )] all fall on or above the nominal confidence curve, handle as in Case 1; if there are two or one retest result test point [lg(t failure ), lg(P test )] falls below the nominal confidence curve. The test point that falls below the nominal confidence curve in the two tests and is farthest from the nominal confidence curve is connected with the base point N as the test evaluation curve. The life reassessment or MOP accounting is handled in accordance with Case 3.

[0154] The samples used in the present invention are composite pipes with the same manufacturing process, the same raw materials, the same nominal pressure, the same nominal diameter, the same wall thickness and the same manufacturing batch;

[0155] In the process described in the present invention, the effective test described in the third to seventh steps means that the failure mode of the sample should be cracking or explosion of the composite pipe body. Failure of the joints at both ends of the sample or the detachment of the pipe body from the joints are invalid samples, and the test data of the invalid sample should be discarded and re-done.

[0156] The simulated pipeline transport fluid used in the fourth, sixth and seventh steps can be oil phase, water phase, or two phases of oil and water, oil and gas, water and gas, or three phases of oil, gas and water. The liquid phase composed of crude oil, diesel and / or brine accounts for 50% to 100% of the sample volume, and the rest is the gas phase.

[0157] The concentration of brine is consistent with the formation water in the transported fluid, and the volume ratio of crude oil to brine is consistent with the formation water in the pipe transported fluid. The gas phase is carbon dioxide, methane, nitrogen or a mixture of the above gases.

[0158] Embodiment 2:

[0159] The service life of a polyester industrial filament reinforced high-density polyethylene composite pipe (hereinafter referred to as composite pipe) with a nominal diameter of DN = 100 mm and a nominal pressure of NPR = 4.0 MPa at room temperature is predicted. The conditions for conveying fluids are shown in Table 1.

[0160] Table 1

[0161]

[0162] The specific steps are as follows:

[0163] first step:

[0164] Determine experimental parameters

[0165] Evaluation test temperature: Evaluation test temperature T test Take the maximum design temperature of pipeline MAOT, T test =60℃; nominal pressure: NPR = 4.0Mpa; maximum design pressure of pipeline MOP: MOP = NPR·f t . Temperature reduction factor f t f is the corresponding temperature of the test t , polyester industrial filament reinforced high-density polyethylene flexible composite pipe belongs to type I pipe, f t According to SY / T6662.2 Table C.1, at 60℃, f t =0.81. Therefore, MOP = NPR·f t =3.24MPa.

[0166] Pipeline design life: Pipeline design life t life Take 20 years, which is 175200 hours.

[0167] Step 2: Make the sample

[0168] 11 composite pipes were randomly selected from the same batch of composite pipes that met the quality requirements of product standard SY / T6662.2 as spare parts, and were made into short sections with a free length of 1000mm between the sealed joints at both ends. One end of the specimen was sealed, and the other end was a metal connection hole with a threaded structure, which could be injected with the test medium and could be sealed and connected to the pressure testing machine through the joint.

[0169] Step 3: After the pipe is filled with the test medium, the state is adjusted

[0170] Take the three samples prepared in the second step and fill the flexible composite pipe samples with sealed joints at both ends with the test medium listed in Table 1. Put the samples into a constant temperature water tank with temperature control. The temperature in the water tank has been adjusted to 60℃±2℃ before the samples are put into the constant temperature water tank. The samples are placed in the constant temperature water tank for 4h±0.1h to adjust the temperature state so that the temperature of the pipe body and the medium in the pipe are maintained at 60℃±2℃.

[0171] Step 4: Instantaneous burst test of pipes

[0172] Take the three samples that have been adjusted in the third step and connect them to the pressurizing equipment one after another to carry out the burst test. Control the pressurizing speed of the pressurizing equipment so that the samples fail by bursting between 30 seconds and 60 seconds. Record the single burst strength value and the corresponding failure time. The test results are shown in Table 2. It can be seen from Table 2 that the test results of the three samples are all valid. 0 burst =18.6MPa,t 0 burst =52s=0.0144h.

[0173] Table 2

[0174] Sample No. Single burst strength value, MPa Failure time, s Failure morphology 3-1# 28.6 60 The middle of the tube bursts 3-2# 27.1 56 The middle of the tube bursts 3-3# 29.4 52 The middle of the tube bursts average value 28.4 56

[0175] The instantaneous explosion test data (t 0 burst , P 0 burst ) Take the common logarithm value as Figure 1 Flat right angle seat

[0176] Point M(-1.84, 1.27) in the coordinate system.

[0177] Step 5: Calculate the expected life coordinate point L of the pipe

[0178] The design life of the pipe is defined as the predicted failure strength value of the pipe equal to the failure strength threshold value of the pipe P threshold The time corresponding to Life Take 20 years (175200h).

[0179] Pipe failure strength threshold P threshold Calculate according to the following formula:

[0180] P threshold =MOP / (F p ·F f )=6.04MPa

[0181] In the formula, F p is the pipeline pressure safety factor. According to Table 1, the pipeline pressure safety factor belongs to moderate fluctuation. p =0.67.

[0182] F f is the pipeline fluid coefficient. The transported liquid is oil-water two-phase medium. According to Appendix C of SY / T6794, take F f =0.8.

[0183] Under the condition of the maximum design temperature of the composite pipe (MAOT = 60 ° C), the design life of the composite pipe is 20 years (t life =175200h) and its corresponding pipe failure strength threshold Pthreshold =6.04MPa forms the number pair (175200, 6.04), and takes the common logarithm value as Figure 1 The expected life point L(5.24,0.78) in the rectangular coordinate system.

[0184] Step 6: Short-term hydrostatic test of pipes at test temperature

[0185] In the plane rectangular coordinate system, connect the instantaneous burst test data M (-1.84, 1.27) obtained in the fourth step with the expected life point L (5.24, 0.78) obtained in the fifth step to draw a curve, such as Figure 1 The curve ML shown is the pressure calculation curve of the short-term hydrostatic test, and the linear fitting equation is calculated as follows:

[0186] lgP=-0.0685lg(t)+1.1433

[0187] Take time t = 10h, and calculate the corresponding pipe predicted failure pressure value P by the formula N =11.9MPa.

[0188] In T test =60℃、P N = 11.9MPa, carry out 5 effective hydrostatic tests, each test is carried out until the specimen fails, and record the time of failure of each specimen.

[0189] The specific process of the test is as follows: according to the second step, 5 samples are processed, and the composite pipe samples with sealed joints at both ends are filled with the test medium listed in Table 1. Then, according to the third step, the sample is placed in a constant temperature water bath at 60℃±2℃ for 4h±0.1h to adjust the temperature state. Then, the test pressure is evenly and steadily applied to the sample within 6min~10min to PN=11.9±0.1MPa. After reaching the set pressure, the timing starts until the sample fails, and the failure time is recorded. The relevant parameters and results of the test process are shown in Table 3.

[0190] Table 3

[0191] Sample No. <![CDATA[Actual loading pressure value P1MP a > <![CDATA[Test failure time t r h]]> Failure morphology 3-4# 17.2±0.1 11.3 The middle of the tube bursts 3-5# 17.2±0.1 9.8 The middle of the tube bursts 3-6# 17.2±0.1 8.2 The middle of the tube bursts 3-7# 17.2±0.1 10.5 The middle of the tube bursts 3-8# 17.2±0.1 9.6 The middle of the tube bursts average value 9.9

[0192] Referring to the method provided in Appendix B of standard SY / T6794-2018, the 97.5% confidence lower limit value of the failure time of the hydrostatic test of five pipes 4# to 8# is taken, and the confidence lower limit value tN = 16.9h.

[0193] tN and test pressure PN form a pair (16.9h, 11.9MPa), and the common logarithm is taken in Figure 1 The coordinate system shown is recorded as the base point N (1.23, 1.07) for the composite pipe life evaluation.

[0194] Step 7: Establish nominal confidence curve and fitting equation

[0195] In the plane rectangular coordinate system, the short-term hydrostatic test data N obtained in the sixth step is compared with the design life point L(t life , P threshold ) are connected to form a curve, such as Figure 2 As shown, the curve NL is called the nominal confidence curve for pipe life prediction, and the linear fitting equation is calculated:

[0196] lgP=-0.07321g(t)+1.1646

[0197] Step 8: Select different test times based on the nominal confidence curve to calculate the corresponding test pressure and conduct a longer hydrostatic test

[0198] Select 3 evaluation test times to conduct a longer hydrostatic test. Evaluation test time t test Select 3 values: 100h, 1000h and 2000h.

[0199] According to the formula, different t test Corresponding evaluation test pressure value P test , respectively:

[0200] t test =100h, P test =10.4MPa;

[0201] t test =1000h, P test =8.8MPa;

[0202] t test =2000h, P test =8.4MPa.

[0203] Take a tube sample and test it at the test temperature (T test =60℃), at each evaluation test pressure value P test The static hydraulic test is carried out under the conditions. The sample is made according to the second step, and the test is carried out according to GB / T 6111. The medium inside the tube sample is filled with the oil-water two-phase medium described in Table 1. After the state is adjusted for 4 hours at the test temperature, the pressure is slowly increased to the test pressure P test The test should be carried out until the tube sample fails (breaks or leaks), and the failure time t is recorded. faflure .

[0204] Step 9: Lifespan Assessment

[0205] It can be seen from Table 4 that the failure time of all pipe samples is t failure All exceed t test , and the failure time of all samples is t failure Not exceeding 1.5t test All pipe sample evaluation test points [lg(t failure ), lg(P test )] all fall in the area above the nominal confidence curve NL, such as points A, B, and C in Table 4.

[0206] Table 4

[0207]

[0208] Therefore, the result of the life assessment is: at MAOT = 60°C, MOP = 3.24 MPa, and under the oil-water two-phase medium transportation conditions described in Table 1, the expected life of this type of polyester industrial filament reinforced high-density polyethylene composite pipe is not less than 20 years.

[0209] Embodiment three:

[0210] The service life of polyester industrial filament reinforced high-density polyethylene composite pipe with a nominal diameter of DN = 100 mm and a nominal pressure of NPR = 4.0 MPa at room temperature is predicted. The conditions for conveying fluids are shown in Table 1.

[0211] The first step to the seventh step are the same as those in the second embodiment.

[0212] Step 8: Select different test times based on the nominal confidence curve to calculate the corresponding test pressure and conduct a longer hydrostatic test

[0213] Select 3 evaluation test times t test Conduct a long-term hydrostatic test. Evaluation test time t test Select 3 values: 100h, 800h and 3000h.

[0214] Calculate different t test Corresponding evaluation test pressure value P test , respectively:

[0215] t test =100h, P test =10.4MPa;

[0216] t test =800h, P test =9.0MPa;

[0217] t test＝ At 3000h, P test =8.1MPa.

[0218] Take a tube sample and test it at the test temperature T test =60℃, at each evaluation test pressure value P test The sample was prepared according to the second step of Example 2, and the test was carried out according to GB / T 6111. The medium inside the tube sample was filled with the oil-water two-phase medium described in Table 1. The sample was placed in an environmental test box with a constant temperature control function, and the external environment of the sample was air with controllable temperature. After the state was adjusted for 4 hours at the test temperature, the pressure was slowly increased to the test pressure P test The test should be continued until the tube sample fails (breaks or leaks), and the failure time t is recorded. failure .

[0219] Step 9: Lifespan Assessment

[0220] It can be seen from Table 5 that in the first test, there are two tube samples with failure times t failure All exceed t test , 2-3# pipe sample failure time t failure Not exceeding t test .like Figure 3 As shown, test points A and B both fall in the area above the nominal confidence curve NL, and test point C falls in the area below the nominal confidence curve NL.

[0221] Table 5

[0222]

[0223] Since only one test point (point C) falls below the nominal confidence curve, a pipe sample is taken for retesting the hydrostatic test under the same test conditions (60°C, 8.1MPa). The retest result is: the sample fails at 3260.5h, and the retest point D falls above the nominal confidence curve.

[0224] Therefore, the result of the life assessment is: at MAOT = 60°C, MOP = 3.24 MPa, under the conditions of transporting oil-water two-phase media as described in Table 1, the expected life of this type of polyester reinforced high-density polyethylene flexible composite pipe is not less than 20 years (175200 h).

[0225] Embodiment 4:

[0226] The service life of the aramid filament reinforced poly(vinylidene fluoride) (PVDF) flexible composite pipe with a nominal diameter of DN = 100 mm and a nominal pressure of NPR = 4.0 MPa is predicted. The conditions for conveying fluids are shown in Table 6.

[0227] Table 6

[0228]

[0229] The specific steps are as follows:

[0230] Step 1: Determination of test parameters

[0231] Evaluation test temperature: Test temperature T test The maximum design temperature MAOT of the pipeline is 95°C. Nominal pressure: NPR = 4.0 MPa; Maximum design pressure MOP of the pipeline: MOP = NPR·ft.

[0232] The temperature reduction factor ft is the f corresponding to the evaluation test temperature. t , f t Selected according to SY / T6662.2 Table C.1 or provided by the composite pipe manufacturer, at 95℃ t =0.90.

[0233] MOP=NPR·f t =3.6MPa.

[0234] Pipeline design life: Pipeline design life t life Take 20 years, which is 175200 hours.

[0235] Step 2: Make the sample

[0236] 11 flexible composite pipes were randomly selected from the same batch that met the quality requirements of product standard SY / T6662.2, and made into short sections with a free length of 1000mm between the sealed joints at both ends. One end of the specimen was sealed, and the other end was a metal connection hole with a threaded structure, which could be injected with the test medium and could be sealed and connected to the pressure testing machine through the joint.

[0237] Step 3: After the pipe is filled with the test medium, the state is adjusted

[0238] Take the three samples prepared in the second step and fill the composite pipe samples with sealed joints at both ends with the liquid test medium listed in Table 6. Put the samples into a constant temperature water tank with temperature control. The temperature in the water tank has been adjusted to 95℃±2℃ before the samples are put into the water tank. The samples are placed in the constant temperature water tank for 4h±0.1h for state adjustment.

[0239] Step 4: Instantaneous burst test of pipes

[0240] The three samples after the third step of state adjustment were connected to the pressurizing equipment one after another for bursting test. The pressurizing speed of the pressurizing equipment was controlled so that the samples failed due to bursting between 30 seconds and 60 seconds. The single bursting strength value and the corresponding failure time were recorded. The test results are shown in Table 4. It can be seen from Table 7 that the test results of the three samples are all valid. 0 burst =28.4MPa,t 0 burst=56s=0.0156h.

[0241] Table 7

[0242] Sample No. Single burst strength value, MPa Failure time, s Failure morphology 3-1# 28.6 60 The middle of the tube bursts 3-2# 27.1 56 The middle of the tube bursts 3-3# 29.4 52 The middle of the tube bursts average value 28.4 56

[0243] The instantaneous explosion test data (t 0 burst , P 0 burst ) Take the common logarithmic value as the midpoint M (-1.84, 1.27) of the plane rectangular coordinate system, such as Figure 4 shown.

[0244] Step 5: Calculate the expected life coordinate point L of the pipe

[0245] The design life of the pipe is defined as the time when the predicted failure strength value of the pipe is equal to the failure strength threshold of the pipe, t life Take 20 years, which is 175200 hours.

[0246] Pipe bursting strength threshold P threshold Calculate as follows:

[0247] P threshold =MOP / (F p ·F f )=3.6 / (0.67·0.67)=8.02MPa

[0248] F p is the pipeline pressure safety factor. According to the fluid fluctuations given in Table 6, the pipeline pressure fluctuation is moderate, so F p =0.67;

[0249] F p is the pipeline fluid coefficient. The transported fluid is oil-water two-phase fluid. According to Appendix C of SY / T6794, take F f =0.67.

[0250] Under the condition of the maximum design temperature of the composite pipe (MAOT = 95 ° C), the design life of the composite pipe is 20 years (t life =175200h) and its corresponding pipe failure strength threshold P threshold =8.02MPa forms a number pair (175200, 8.02), and the common logarithmic value is taken as the expected life point L (5.24, 0.90) in the plane rectangular coordinate system, such as Figure 4 shown.

[0251] Step 6: Short-term hydrostatic test of pipes at test temperature

[0252] like Figure 4As shown, in the plane rectangular coordinate system, the instantaneous burst test data M (-1.81, 1.45) obtained in the fourth step is connected with the expected life point L (5.24, 0.90) obtained in the fifth step to draw a curve ML, which is the pressure calculation curve of the short-term hydrostatic test, and the fitting equation of the curve ML is obtained:

[0253] lgP=-0.07791g(t)+1.3126

[0254] Take time t = 10h, and calculate the corresponding pipe predicted failure pressure value P by the formula N =17.2MPa. At 95℃, P N =17.2MPa, carry out effective hydrostatic tests for no less than 5 times. Each test shall be carried out until the specimen fails, and the time of failure of each specimen shall be recorded.

[0255] The specific process of the test is as follows: 5 samples are processed according to the second step of Example 2, and the liquid test medium listed in Table 6 is filled into the composite pipe sample, and then the state of the sample is adjusted at 95°C, and then the sample is connected to the pressurizing equipment and placed in a constant temperature water tank with temperature control. The temperature of the water tank has been adjusted to 95°C ± 2°C before the sample is placed. Then, the test pressure is evenly and steadily applied to the sample within 6min to 10min to P N =17.2±0.1MPa, start timing after reaching the set pressure until the sample fails, and record the failure time. The relevant parameters and results of the test process are shown in Table 8.

[0256] Table 8

[0257] Sample No. <![CDATA[Actual loading pressure value P1 MPa]]> Test failure time th Failure morphology 3-4# 17.2±0.1 11.3 The middle of the tube bursts 3-5# 17.2±0.1 9.8 The middle of the tube bursts 3-6# 17.2±0.1 8.2 The middle of the tube bursts 3-7# 17.2±0.1 10.5 The middle of the tube bursts 3-8# 17.2±0.1 9.6 The middle of the tube bursts average value 9.9

[0258] According to Appendix B of SY / T6794-2018, the 97.5% confidence lower limit of the failure time of the hydrostatic test of the five pipes is taken and recorded as t N =6.38h.

[0259] tN and its corresponding test pressure PN form a pair (6.38h, 17.2MPa), and the common logarithm is taken to record it in the coordinate system as the base point N (0.8, 1.24) for the composite pipe life assessment, such as Figure 4 shown.

[0260] Step 7: Establish nominal confidence curve and fitting equation

[0261] like Figure 5As shown in the plane rectangular coordinate system, the confidence lower limit value N (0.8, 1.24) of the short-term hydrostatic test data obtained in the sixth step is connected with the expected life point L (5.24, 0.90) to draw a curve. The curve NL is called the nominal confidence curve for pipe life prediction, and the linear fitting equation is calculated:

[0262] lgP=-0.0748lg(t)+1.2965

[0263] Step 8: Select different test times based on the nominal confidence curve to calculate the corresponding test pressure and conduct a longer hydrostatic test

[0264] Select 3 evaluation test times for hydrostatic test, evaluation test time t test Select 100h or 1000h

[0265] There are 3 values ​​in total: 1, 2, 3, and 2000h.

[0266] According to the formula, different t test The corresponding evaluation test pressure values ​​Ptest are:

[0267] t test =100h, P test =10.45MPa

[0268] t test =1000h, P test＝ 8.84MPa

[0269] t test =2000h, P test =8.41MPa

[0270] Take a tube sample and test it at the test temperature T test =95℃, at each evaluation test pressure value P Test The static hydraulic test is carried out under the conditions. The sample is made according to the second step, and the test is carried out according to GB / T 6111. The medium inside the tube sample is filled with the oil-water two-phase medium described in Table 6. After the state is adjusted for 4 hours at the test temperature, the pressure is slowly increased to the test pressure P test The test should be carried out until the tube sample fails, ruptures or leaks, and the failure time t is recorded. failure The test results are shown in Table 9.

[0271] Table 9

[0272]

[0273] Step 9: Lifespan Assessment

[0274] It can be seen from Table 9 that all tube samples tfailure Both are greater than the evaluation test time t test , and the failure time of all samples is t failure More than 1.5t test .like Figure 5 As shown in Table 6, the evaluation test points A, B and C all fall in the area above the nominal confidence curve NL. Therefore, it can be judged that this type of composite pipe is suitable for conveying fluids as described in Table 6, MAOT = 95 ° C,

[0275] The design life under the condition of MOP=3.6MPa is more than 20 years, and the values ​​of MAOT=95℃ and MOP=3.6MPa are on the safe side. Therefore, the expected life or MOP is recalculated based on the test data completed from the first step to the eighth step, as follows:

[0276] exist Figure 5 In the equation, point C is the point closest to the nominal confidence curve NL in this test. Connect NC to make a curve. The curve NC is called the evaluation curve. The equation of the evaluation curve is calculated as follows:

[0277] lgP=-0.0671lg(t)+1.2903

[0278] Evaluation curve NC and P = P threshold =8.02MPa, the intersection point K, the time t value corresponding to point K is P threshold The expected life span under the unchanged condition is t k life , we can find t by the formula k life :

[0279]

[0280] Test evaluation curve NC and t=t life =175200h, the intersection point J, the pressure P value corresponding to point J is the critical pressure value P when the expected life remains unchanged (20 years). J threshold At the same time, the approved MOP can be calculated.

[0281]

[0282] MOP=P J threshold ·F p ·F f =3.90

[0283] Therefore, the conclusion of the service life assessment of this type of aramid filament reinforced polyvinylidene fluoride (PVDF) flexible composite pipe is:

[0284] 1) The design life of this type of composite pipe exceeds 20 years under the conditions of conveying fluids as described in Table 6, MAOT = 95 ° C, MOP = 3.6 MPa, and the values ​​of MAOT = 95 ° C and / or MOP = 3.6 MPa are on the safe side;

[0285] 2) The recalculated expected life of this type of composite pipe under the conditions of conveying fluid, MAOT = 95 ° C, MOP = 3.6 MPa as described in Table 6 is 64.8 years;

[0286] 3) When the design life of this type of composite pipe is 20 years and the fluid is transported as described in Table 6, and MAOT = 95°C, the recalculated MOP = 3.9 MPa.

[0287] Embodiment five:

[0288] The service life of polyester fiber reinforced high-density polyethylene composite pipe with nominal diameter DN = 80mm and nominal pressure NPR = 4.0Mpa (value at room temperature) is predicted. The conditions for conveying fluid are shown in Table 10.

[0289] Table 10

[0290]

[0291] Step 1: Determination of test parameters

[0292] Evaluation test temperature: Evaluation test temperature T test The maximum design temperature MAOT of the pipeline is 70°C. The nominal pressure NPR at room temperature is 4.0 MPa.

[0293] Maximum design pressure of pipeline MOP: MOP = NPR f t , temperature reduction factor f t To evaluate the test temperature T test The corresponding ft, ft is selected according to Table C.1 of SY / T6662.2. The polyester fiber reinforced high-density polyethylene composite pipe belongs to Type I pipe. At 70℃, f t =0.7. Therefore, MOP = NPR·f t =2.8MPa.

[0294] Design life of pipe Life Take 30 years, which is 262800 hours.

[0295] Step 2: Make the sample

[0296] Random samples were taken from the polyester fiber reinforced high-density polyethylene composite pipes in the same batch that met the quality requirements of product standard SY / T6662.2, and 11 short sections with a free length of 1000mm between the sealed joints at both ends were made. One end of the sample was sealed, and the other end was a metal connecting hole with a threaded structure. The metal connecting hole can be injected with the test medium and can be sealed and connected to the pressure testing machine through a joint.

[0297] Step 3: After the pipe is filled with the test medium, the state is adjusted

[0298] Take the three samples prepared in the second step of this embodiment, and fill the composite pipe samples with sealed joints at both ends with the liquid test medium listed in Table 10. Put the samples into a constant temperature water tank with temperature control, and the temperature in the water tank has been adjusted to 70°C ± 2°C before the samples are put into the constant temperature water tank. The samples are placed in the constant temperature water tank for 4h ± 0.1h for state adjustment.

[0299] Step 4: Instantaneous burst test of pipes

[0300] The three samples after the state adjustment in the third step of this embodiment were connected to the pressurizing equipment one after another to carry out the bursting test. The pressurizing speed of the pressurizing equipment was controlled so that the sample would fail due to bursting between 30 seconds and 60 seconds, and the single bursting strength value and the corresponding failure time were recorded. The test results are shown in Table 11.

[0301] Table 11

[0302] Sample No. Single burst strength value, MPa Failure time, s Failure mode 1# 24.2 50 The middle of the tube bursts 2# 23.9 54 The middle of the tube bursts 3# 24.1 52 The middle of the tube bursts average value 24.1 52

[0303] From Table 11, we can see that:

[0304] P 0 burst =24.1MPa,t 0 burst =52s=0.0144h;

[0305] The instantaneous explosion test data (t 0 burst , P 0 burst )Take the common logarithmic value as the midpoint M (-1.84, 1.38) of the plane rectangular coordinate system.

[0306] Step 5: Calculate the expected life coordinate point L of the pipe

[0307] The design life of the pipe is defined as the time when the predicted failure strength value of the pipe is equal to the failure strength threshold of the pipe, t Life Take 30 years, which is 262800 hours.

[0308] P threshold =MOP / (F p ·Ff )=7.0MPa

[0309] F p is the pipeline pressure safety factor. According to the fluid fluctuations given in Table 1, the pipeline pressure fluctuation is a severe fluctuation. p =0.53;

[0310] F f is the pipeline fluid coefficient, the transported fluid is oil, gas and water three-phase medium, according to SY / T6794 Appendix C, F f Take 0.75.

[0311] Under the condition of the maximum design temperature MAOT of the composite pipe, the design life of the composite pipe is t life =262800h and its corresponding pipe failure strength threshold P threshold =7.0MPa to form a number pair (262800h, 7.0MPa), and take the common logarithm value of this number pair as Figure 6 The design life point L(5.42,0.85) in the plane rectangular coordinate system shown.

[0312] Step 6: Short-term hydrostatic test of pipes at test temperature

[0313] In the plane rectangular coordinate system, the instantaneous burst test data M (-1.84, 1.38) obtained in the fourth step is connected with the design life point L (5.42, 0.84) obtained in the fifth step to draw a curve ML, and the linear fitting equation formula is calculated.

[0314] lgP=-0.0739lg(t)+1.2458

[0315] Curve ML is the pressure calculation curve of the short-term hydrostatic test. Take the time t = 100h, and calculate the corresponding pipe predicted failure pressure value P by the formula N =12.5MPa.

[0316] Five effective hydrostatic tests were conducted at 70°C and PN = 12.5 MPa. Each test was conducted until the specimen failed, and the time of failure of each specimen was recorded.

[0317] The specific process of the hydrostatic test is as follows: 5 samples are processed according to the second step of this embodiment, and the liquid medium described in Table 10 is filled into the inside of the sample, and the liquid phase accounts for 70% of the total volume of the sample. Then, the state is adjusted in a constant temperature water bath with an ambient temperature of 70℃±2℃ for no less than 4h, and then carbon dioxide is slowly added to the sample using a carbon dioxide gas cylinder to a pressure value of 1.25MPa (accounting for 10% of the total volume of the gas phase according to the partial pressure conversion), and then nitrogen gas cylinders are used to pressurize to P NThen connect the sample to the hydraulic pressure equipment to maintain the internal pressure of the sample at a stable pressure value P N =12.5±0.1MPa, the test operation can be carried out according to GB / T6111-2018. Pressurize to P N Then start timing. The test is carried out until the sample fails, and the time value of each sample failure is recorded. The relevant parameters and results of the test process are shown in Table 12.

[0318] Table 12

[0319]

[0320] Take the 97.5% confidence lower limit value for the failure time value of the pipe hydrostatic test specimen. According to the calculation method provided in Appendix B of the standard SY / T6794-2018, the 97.5% confidence lower limit value t of the specimen failure time value can be calculated. N =58.4h.

[0321] t N and its corresponding test pressure P N The number pair (58.4h, 12.5MPa) is taken, and the common logarithm is recorded in the coordinate system as the base point N (1.77, 1.10) for the composite pipe life assessment, such as Figure 6 shown.

[0322] Step 7: Establish nominal confidence curve and fitting equation

[0323] In the plane rectangular coordinate system, the short-term hydrostatic test data N (1.77, 1.10) obtained in the sixth step is connected with the expected life point L (5.42, 0.85) to draw a curve NL, which is called the nominal confidence curve for pipe life prediction, and the linear fitting equation is calculated, such as Figure 7 shown.

[0324] lgP=-0.0692lg(t)+1.2202

[0325] Step 8: Select different test times based on the nominal confidence curve to calculate the corresponding test pressure and conduct a longer hydrostatic test

[0326] Select 3 evaluation test times to conduct the hydrostatic test. Evaluation test time t test Select 3 values: 500h, 1000h and 2000h.

[0327] According to the formula, different t test Corresponding evaluation test pressure value P test , respectively:

[0328] t test =500h, Ptest =10.8MPa;

[0329] t test =1000h, P test =10.3MPa;

[0330] t test =2000h, P test =9.8MPa.

[0331] At each test point, take one tube sample and test it at the test temperature (T test =70℃), at three different evaluation test pressure values ​​P test The hydrostatic test was carried out under the conditions, and the sample was prepared according to the second step of this embodiment.

[0332] The medium inside the tube sample is the same as that in step 6 of this embodiment, and the external environment is a water bath with controllable temperature. After the sample is injected with 70% of the total volume of the sample liquid medium, the state is adjusted at the test temperature for 4 hours and then slowly pressurized. After pressurization reaches the test pressure, the timing begins.

[0333] The hydrostatic test should be carried out until the pipe sample fails (ruptures or leaks). If failure occurs, record the failure time, which is called the sample failure time t failure .

[0334] Step 9: Lifespan Assessment

[0335] Failure time t of three tube samples failure Both are less than the evaluation test calculation time (t test ).like Figure 7 As shown, the test points A, B and C all fall in the area below the nominal confidence curve NL, which means that the design life of this type of composite pipe is less than 30 years under the conditions of MAOT = 70 ° C and MOP = 2.8 MPa for the fluid conveyed as described in Table 10; or, in other words, the values ​​of MAOT = 70 ° C and / or MOP = 2.8 MPa for this type of composite pipe are dangerous under the conditions of the fluid conveyed as described in Table 10 for a design life of 30 years.

[0336] Therefore, the expected life or MOP is selected based on the test data completed in steps 1 to 8.

[0337] Recalculate as follows:

[0338] exist Figure 7 In the equation, point A is the point closest to the nominal confidence curve of the test point. Connect NA to make a curve, which is called the evaluation curve. The equation of the evaluation curve is calculated as follows:

[0339] lgP=-0.0842lg(t)+1.2466

[0340] Evaluation curve NA and P = P threshold =7.0MPa, the intersection point K, the time t value corresponding to point K is P threshold The expected life span under k life .

[0341]

[0342] Evaluation curve NA vs. t=t life =30 years (262800 hours), the pressure P value corresponding to point J is the critical pressure value P under the condition of expected life of 30 years. J threshold , and the approved MOP can be calculated at the same time.

[0343]

[0344] It can be found that:

[0345] MOP=P J threshold ·F p ·F f =2.47MPa

[0346] If life expectancy is adjusted to t life = 20 years (175200 hours), evaluation curve NA and t = t life = 20 years (175200 hours) and the corresponding critical pressure and MOP are:

[0347]

[0348] MOP=P J threshold ·F p ·F f =2.56MPa

[0349] Therefore, the conclusion of the service life assessment of this type of polyester fiber reinforced high-density polyethylene composite pipe is:

[0350] 1) The design life of this type of composite pipe is less than 30 years under the conditions of MAOT = 70 ° C and MOP = 2.8 MPa when conveying the fluid as described in Table 10; or in other words, the values ​​of MAOT = 70 ° C and / or MOP = 2.8 MPa for this type of composite pipe are dangerous when conveying the fluid as described in Table 10 with a design life of 30 years;

[0351] 2) The recalculated MOP of this type of composite pipe is 2.47MPa when the fluid is transported as described in Table 10 with a design life of 30 years and MAOT = 70°C;

[0352] 3) When the composite pipe of this type is designed to have a service life of 20 years and is conveying the fluid as described in Table 10, and MAOT = 70°C, the recalculated MOP = 2.56 MPa.

[0353] The experimental results of Example 5 can be seen in Table 13:

[0354] Table 13

[0355]

[0356] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

Claims

1. A method for evaluating the service life of a fiber reinforced plastic composite pipe, characterized in that: The steps include: Step 1: Determine the evaluation test temperature Ttest, the maximum design pressure MOP of the pipeline, and the nominal pressure NPR of the pipeline; Evaluation test temperature T test Taking the pipeline maximum design temperature MAOT, the calculation formula for the pipeline maximum design pressure MOP is: MOP=NPR·f t In the formula, f t is the temperature reduction factor corresponding to the test temperature; the pipeline nominal pressure NPR is the nominal pressure of the composite pipe at room temperature; Step 2: Randomly sample from the composite pipe products and make composite pipe short section specimens. Fill the composite pipe specimens with sealed joints at both ends with liquid test medium, put the specimens into a constant temperature water tank or environmental test box with a temperature control device, the environment outside the specimen tube is air or water, and place it under the test temperature Ttest for no less than 4 hours for state adjustment to keep the temperature of the pipe body and the medium inside the pipe consistent; Step 3: Take the sample after the state adjustment in the second step and conduct an instantaneous burst test. Connect the sample to the hydraulic pressurizing equipment and control the pressurizing speed of the pressurizing equipment so that the sample fails by bursting between 30 seconds and 60 seconds. Record the internal pressure strength value, the corresponding failure time value and the instantaneous burst test point M of each sample when it bursts. The arithmetic mean of the internal pressure strength values ​​when explosion occurs in no less than 3 valid tests is recorded as P 0 burst , the arithmetic mean of the corresponding explosion failure time is recorded as t 0 burst ; If the failure mode of the sample is cracking or bursting of the composite pipe body, it is recorded as a valid test; if the joints at both ends of the sample fail or the pipe body comes out of the joint, it is an invalid sample and the test data of the invalid sample is discarded; Step 4: Calculate the short-term hydrostatic test pressure value based on the fitting curve of the instantaneous burst test point M and the pipe failure strength threshold under the design life, carry out the short-term hydrostatic test until the sample fails, record the failure time, and obtain the short-term hydrostatic test point N; Step 5: In the plane rectangular coordinate system, connect the short-term hydrostatic test point N obtained in the fourth step with the design life point L to draw a curve NL, which is called the nominal confidence curve for composite pipe life prediction, and calculate the linear fitting equation: lgP=G n log(t)+C n In the formula, G n and C n is a constant that characterizes the fitting characteristics and is directly given by the fitting equation; P is the failure pressure of the composite pipe; t is the failure time; Step 6: Determine the test time t test Take three discrete values ​​between 100h and 5000h and calculate different t according to step 5. test The corresponding P is calculated as the evaluation test pressure value P test , at the evaluation test temperature T test Under each evaluation test pressure value P test Under the conditions, take one sample for hydrostatic test; the preparation and state conditions of the sample are carried out according to the second step, the internal medium and pressurization process of the tube sample are the same as the second step, and the pressure is increased to the test pressure P test Then start timing; The hydrostatic test is carried out until the pipe sample fails, ruptures or leaks, and the failure time t of the sample is recorded. failure Each t failure Corresponding test pressure value P test Composed of a pair of data (t failure , P test ), for (t failure , P test ) takes the common logarithm in the coordinate system and is called the test point; If the test cannot be recorded as valid, re-sampling should be done under the same conditions; Step 7: Compare t failure With t test , life span assessment is carried out according to different situations.

2. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 1, characterized in that: In the second step, the specimens adopt non-constrained field joints, and the pipe length of each specimen between two sealing joints shall not be less than three times the outer diameter of the specimen and shall not be less than 500mm.

3. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 1, characterized in that: In the second step, the test medium is a simulated pipeline fluid consisting of light crude oil, diesel and brine.

4. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 1, characterized in that: The composite pipe products in the second step are composite pipe products that meet standard quality requirements in the same batch.

5. The method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 1, characterized in that: In the fourth step, the specific steps are: Under the condition of maximum design temperature MAOT, the design life of the composite pipe is t life and its corresponding pipe failure strength threshold P threshold Composition number pairs (t life , P threshold ), take the common logarithmic value as the design life point L in the plane rectangular coordinate system; Pipe failure strength threshold P threshold Calculate according to the following formula: P threshold =MOP / F p ·F f Where, the pipe failure strength threshold P threshold The unit is MPa, F p is the pipeline pressure safety factor, which is determined based on the frequency and amplitude of fluid fluctuations; Strong fluctuation Fp is not greater than 0.65; moderate fluctuation Fp p Greater than 0.65 and less than 0.85; Slight fluctuation F p Greater than 0.85 and not greater than 1.0; F f is the pipeline fluid coefficient; When the transported fluid is water, F f Not more than 1.0; the conveying fluid is oil-water two-phase or multi-phase medium, F f Not more than 0.8; when the conveying fluid is gas, F f Not more than 0.67; In the plane rectangular coordinate system, the instantaneous burst test data point M obtained in the third step is connected with the design life point L to draw a curve as the pressure calculation curve of the short-term hydrostatic test, and the fitting equation of the curve ML is calculated: lgP=G m log(t)+C m In the formula, G m and C m is a constant that characterizes the fitting characteristics; The time t is between 10h and 100h, and the pressure value P of the short-term hydrostatic test of the pipe corresponding to t is calculated by the formula N ; In MAOT, P N Under the conditions, at least 5 effective hydrostatic tests are carried out. The sample is made according to the second step. The sample is filled with the same light crude oil or diesel and salt water test medium as in the second step. The liquid phase of crude oil or diesel and salt water accounts for 50% to 100% of the sample volume. Then, the sample is placed in an environment at a temperature of T test The state is adjusted in a constant temperature water bath or environmental test chamber for no less than 4 hours. Then, according to the oil and gas composition ratio of the pipeline on-site transmission fluid, carbon dioxide, methane, nitrogen or a mixture of the above gases is slowly added to the sample using carbon dioxide, methane or nitrogen gas cylinders to the test pressure value P N If the cylinder pressure is too low to be pressurized to P N , connect the sample to the hydraulic pressure equipment, and slowly increase the internal pressure of the sample to the test pressure value P N , the external environment is air or water bath with controlled temperature; pressurized to P N Then start timing; the test is carried out until the sample fails, and the time value of each sample failure is recorded; Take the 97.5% confidence lower limit of the failure time of 5 valid hydrostatic tests and record it as t N , the calculation method of the confidence lower limit refers to Appendix B of standard SY / T6794-2018; t N and P N Composition number pairs (t N , P N ), logarithmic pair (t N , P N ) Take the common logarithm and record it as point N in the coordinate system; If the failure mode of the specimen is cracking or bursting of the composite pipe body, it is recorded as a valid test.

6. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 1, characterized in that: In the sixth step, each t test The interval is not less than 500h; the external environment of the sample is air or a water bath with controllable temperature.

7. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 1, characterized in that: The seventh step includes: Case 1: All test points [lg(t failure ), lg(P test )] all fall on or above the nominal confidence curve NL, and the t failure Not less than the evaluation test time t test , one or two specimens have t failure More than 1.5t test , but not all samples have t failure More than 1.5t test , determine that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is not less than the design life t life ; Case 2: All test points [lg(t failure ), lg(P test )] all fall in the area above the nominal confidence curve NL, and the t failure More than 1.5t test The assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is not less than the design life t life ; Conduct retest; Case 3: t of all samples failure Less than t test ; Determine that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is less than the design life t life ; Case 4: t with only one sample failure Not less than t test , t of the remaining samples failure Both are less than t test ; Determine that the assessed life of the composite pipe under MAOT, MOP and conveying fluid conditions is less than the design life t life ; Case 5: t with only one sample failure Less than t test , t of the remaining samples failure Not less than t test ; Unable to judge, re-test.

8. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 7, characterized in that: In case 2, there are two retesting methods: A) Return to the first step and evaluate the test temperature T test or if the MOP increases, repeat the test; B) Re-evaluate the life or MOP calculation based on the test data completed in steps 1 to 6 as follows: The t of three test points failure All over 1.5t test , connect the test point closest to the nominal confidence curve NL in the sixth step with the base point N to form the test evaluation curve; The fitting equation formula of the evaluation curve is as follows: lgP=G f log(t)+C f Evaluation curve extension and P = P threshold The intersection point K, the time t value corresponding to point K is P threshold ; Re-evaluated lifespan value t under unchanged conditions k life , t k life Calculate according to the following formula: t k life =10^[Lg(P threshold )-C f ] / G f Evaluation curve and t=t life The intersection point J, the pressure P value corresponding to point J is the design life t life The critical pressure value P re-evaluated under unchanged conditions J threshold , P J threshold Calculate according to the following formula: P J threshold =10^[G f ·lg(t life )+C f ] Calculate the re-evaluated maximum design pressure MOP of the pipeline: MOP=P J threshold ·F p ·F f 。 9. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 8, characterized in that: The life expectancy and MOP calculation methods in Cases 3 and 4 are the same as those in Case 2 (B).

10. A method for evaluating the service life of a fiber reinforced plastic composite pipe according to claim 8, characterized in that: The retest results of situation 5 are handled as follows: If the two retest results test points [lg(t failure ), lg(P test )] all fall on or above the nominal confidence curve and are handled as in Case 1; If there are 2 or 1 retest result test point [lg(t failure ), lg(P test )] falls below the nominal confidence curve. The test point that falls below the nominal confidence curve in the two tests and is farthest from the nominal confidence curve is connected with the base point N as the test evaluation curve. The life reassessment or MOP accounting is handled in accordance with Case 3.

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