Method for predicting service life of glass reinforced plastic pipe under stress action

Abstract

The invention relates to a method for predicting the service life of a glass reinforced plastic pipe under the stress action. The method comprises the following specific steps: performing a hydrostatic test on a to-be-tested glass reinforced plastic pipe under the stress action; performing a hydraulic bursting test on the glass fiber reinforced plastic pipe subjected to the hydrostatic test; fitting the data of the hydrostatic pressure time and the bursting strength value, taking the logarithm value of the hydrostatic pressure time as an abscissa and the logarithm value of the bursting strength as an ordinate, performing numerical fitting by utilizing a linear regression method to obtain a fitting equation lnP = a * lnt + b of the hydrostatic pressure time and the bursting strength value, and calculating the service life of the glass fiber reinforced plastic pipe. The invention provides a novel glass reinforced plastic pipe service life prediction method based on stress action, overcomes the defects of the existing service life prediction technology of a glass reinforced plastic pipe for gathering and transportation in an oil and gas field, and can predict the service life of the glass reinforced plastic pipe under the combined action of four influence factors, namely pipe characteristics, a conveying medium, environmental factors and a stress state. The method is short in test period, convenient to implement and high in prediction reliability.

Description

Technical Field

[0001] This invention relates to the field of life prediction technology for fiberglass pipes in oil and gas fields, and specifically to a method for predicting the life of fiberglass pipes under stress. Background Technology

[0002] Most existing oil and gas pipelines in oil and gas fields are made of carbon steel, which has poor corrosion resistance. Oil and natural gas are generally corrosive fluids, and carbon steel pipelines in oil fields frequently fail due to severe corrosion. Fiberglass pipes, on the other hand, have excellent corrosion resistance and are a commonly used non-metallic pipe material in oil and gas fields, widely applied in the transportation of highly corrosive fluids such as crude oil, natural gas, and wastewater.

[0003] The operating environment of oil and gas pipelines is becoming increasingly harsh, with H2S, CO2, and Cl being present in high concentrations of pollutants. - With the increasing content of corrosive media, coupled with the complex environment and undulating terrain of FRP pipelines in oil fields, FRP pipeline failures occur frequently, and the failure sites mostly occur at the pipe joints.

[0004] The main reasons for the failure of FRP (fiberglass reinforced plastic) pipes in oilfields are twofold. Firstly, the corrosive environment: under the combined influence of corrosive chemical media and heat in oilfields, the resin-fiber interface of FRP is damaged, the chemical structure of the resin changes, leading to a decrease in the material's mechanical properties and consequently, a decline in the pressure-bearing capacity of the FRP pipe, resulting in failure. Secondly, as rigid pipes, FRP pipes are susceptible to bending stress when laid on uneven terrain, making the joints and pipe body prone to shear failure. Therefore, predicting the lifespan of FRP pipes requires comprehensive consideration of multiple factors, including the characteristics of the pipe material itself, the corrosiveness of the transported medium, the service environment, and the bending stress experienced by the pipeline in the field. Only by taking all four factors into account can the lifespan of FRP pipes be predicted more accurately.

[0005] Accurate prediction of the service life of fiberglass pipes is of great theoretical significance and practical engineering value for eliminating potential safety hazards in oilfield pressure pipelines and developing effective maintenance plans.

[0006] GB / T 18252-2000 proposes an extrapolation method for determining the long-term hydrostatic strength of thermoplastic pipes. This method requires one year to complete, is time-consuming and labor-intensive, and uses clean water as the test medium, making it unable to effectively simulate the impact of corrosive fluids such as oil and natural gas in oilfields on pipe performance. Invention patent ZL202010177150.5 discloses a method for predicting the service life of fiberglass pipes. This method considers the impact of the corrosiveness of the transported medium on the pipe's lifespan, better simulating the field conditions of fiberglass pipes. However, this method does not consider the impact of the pipe's stress state on its service life.

[0007] Failure data from FRP (fiberglass reinforced plastic) pipes in oilfields show that the service life of FRP pipes is determined by four factors: pipe material characteristics, type of transported medium, environmental parameters, and stress state. However, current methods for predicting the service life of FRP pipes do not fully consider the influence of these four factors, resulting in inaccurate predictions and an inability to accurately guide the application of FRP pipes in oilfields. Summary of the Invention

[0008] This invention provides a method for predicting the lifespan of fiberglass pipes under stress, aiming to solve the problems in the prior art.

[0009] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0010] A method for predicting the lifespan of fiberglass pipes under stress includes the following specific steps:

[0011] S1: Perform a hydrostatic test on the FRP pipe under stress;

[0012] S2: Conduct a water pressure burst test on the fiberglass pipes that have undergone hydrostatic testing;

[0013] S3: Fit the data of hydrostatic pressure time and blasting strength value, with the logarithm of hydrostatic pressure time as the abscissa and the logarithm of blasting strength as the ordinate, and use the linear regression method to perform numerical fitting to obtain the fitting equation of hydrostatic pressure time and blasting strength value: lnP=a*lnt+b, where b is a constant.

[0014] S4: The lifespan of the fiberglass pipe is calculated based on the above fitting equation.

[0015] The beneficial effects of this invention are: This invention provides a novel method for predicting the service life of FRP pipes based on stress, which overcomes the shortcomings of existing life prediction technologies for FRP pipelines used in oil and gas field gathering and transportation. It can predict the service life of FRP pipes under the combined influence of four factors: pipe material characteristics, transport medium, environmental factors, and stress state. The test cycle is short, it is easy to implement, and the prediction reliability is high.

[0016] Based on the above technical solution, the present invention can be further improved as follows.

[0017] Furthermore, S1 specifically includes: randomly selecting multiple pre-prepared test samples, dividing them into multiple groups, and performing hydrostatic tests under stress on the test samples in each group.

[0018] The advantage of adopting the above-mentioned further scheme is that it allows for the proper preparation and grouping of test samples for hydrostatic testing.

[0019] Furthermore, step S1 includes the following specific steps:

[0020] S11: Install the test sample on the bending test device according to the minimum bending radius, and apply bending stress to the fiberglass pipe through the bending test device;

[0021] S12: Connect the pressure-pressurizing adapter equipped with an inlet valve, a pressure relief valve, and a pressure gauge to the plug, and connect it to one end of the test sample. Pour the test medium obtained on-site or simulated from the other end of the test sample, and seal it with the connected plug in the same way.

[0022] S13: Place the sealed and assembled test sample on the support base, push it into the environmental test chamber, and control the environmental test chamber to heat up to the test temperature; connect the gas cylinder in the pressurization device to the pressurization transfer joint, close the pressure relief valve, open the air inlet valve, and slowly fill in the corresponding gas in sequence to keep its total pressure at the test pressure.

[0023] The advantages of adopting the above-mentioned further scheme are that the method is simple, the test is convenient, and the pressure resistance of the fiberglass pipe is tested.

[0024] Furthermore, S13 is followed by S14:

[0025] Once the set test time for the corresponding test sample is reached, the motor connected to the sample is stopped, and the pressure relief valve and exhaust gas treatment system are opened to release and treat the internal gas of the test sample.

[0026] The advantages of adopting the above-mentioned further scheme are that the method is simple, the design is reasonable, and the gas in the test sample is released after the hydrostatic test is completed.

[0027] Furthermore, S11 is preceded by S10:

[0028] Test medium configuration: The test medium is configured to simulate field service conditions.

[0029] The advantages of adopting the above-mentioned further scheme are that the method is simple, the design is reasonable, the test medium is configured, and the test medium is configured to simulate the on-site service conditions, thereby better predicting the service life of FRP pipes.

[0030] Furthermore, in the 12 mentioned above:

[0031] The test medium was a simulated oilfield transport medium. The hydrostatic pressure was 1.5 times the nominal pressure of the batch of FRP samples. The hydrostatic time was between 1 hour and 2000 hours, with at least 6 discrete points selected. The test temperature was the service temperature of the FRP pipe. The bending radius of the test sample was the minimum bending radius of the FRP pipe for field laying.

[0032] The advantage of adopting the above-mentioned further scheme is that it uses test media to simulate the transportation media in the oil field, thereby better predicting the life of FRP pipes with higher accuracy.

[0033] Furthermore, step S2 includes the following specific steps:

[0034] According to relevant standards, burst tests were conducted on the glass pipes after the hydrostatic pressure test to measure their burst strength value and calculate the average value of each group of tests in order to obtain the remaining strength of the fiberglass pipes after the hydrostatic pressure test.

[0035] The data is analyzed, and the relative deviation is used to determine the relative deviation: relative deviation = [(single measurement value - average value) / average value] × 100%;

[0036] When the relative deviation of each set of test data is within the range of -15% to 15%, it is considered qualified data, and the final fitted data is taken as the average value; otherwise, repeat S1.

[0037] The advantages of adopting the above-mentioned further scheme are that the method is simple, realizes the burst test of FRP pipes, and tests the burst strength value of FRP pipes.

[0038] Furthermore, step S4 includes the following specific steps:

[0039] The expected life of fiberglass pipes is defined as the period when the long-term strength of the fiberglass pipe is lower than the safety critical pressure P. limit The time corresponding to P limit Substitute into equation lnP limit =a*t limit +b, to get the time value t limit ;

[0040] Finally, the corresponding time value is obtained by using the known life pressure value in the equation. This value is the life time of this batch of composite pipes.

[0041] Among them, the safety critical pressure P limit =f*PN, where f is the safety factor, and f takes values ​​from 1.0 to 2.0.

[0042] The advantages of adopting the above-mentioned further solutions are that the method is simple, the design is reasonable, and the lifespan of FRP pipes can be accurately predicted.

[0043] Furthermore, S0 is included before S1:

[0044] Randomly select fiberglass pipes from the same batch, connect two fiberglass pipes with a joint to form a test sample, and at the same time process and manufacture corresponding plugs.

[0045] The advantages of adopting the above-mentioned further scheme are that the method is simple, the design is reasonable, and the test samples are prepared in advance for subsequent hydrostatic tests.

[0046] Furthermore, curve correction is also included between S3 and S4:

[0047] If a test point with a large deviation is observed, it should be discarded and a new experiment should be conducted. Repeat steps S1 and S2 to determine the final fitting equation lnP = a * lnt + b. If the distribution of each point meets the requirements of linear regression, this step can be skipped.

[0048] The advantages of adopting the above-mentioned further scheme are that the method is simple and the curve can be further corrected to ensure the accuracy of the life prediction of FRP pipes. Attached Figure Description

[0049] Figure 1 This is a flowchart of the prediction method of the present invention;

[0050] Figure 2 This is a schematic diagram of the structure by which the stress is applied by the stress-applying device in this invention. Detailed Implementation

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0052] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0053] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0054] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0055] Example 1

[0056] like Figure 1 and Figure 2 As shown, this embodiment provides a method for predicting the lifespan of fiberglass pipes under stress, including the following specific steps:

[0057] S1: Perform a hydrostatic test on the FRP pipe under stress;

[0058] S2: Conduct a water pressure burst test on the fiberglass pipes that have undergone hydrostatic testing;

[0059] S3: Fit the data of hydrostatic pressure time and blasting strength value, with the logarithm of hydrostatic pressure time as the abscissa and the logarithm of blasting strength as the ordinate, and use the linear regression method to perform numerical fitting to obtain the fitting equation of hydrostatic pressure time and blasting strength value: lnP=a*lnt+b, where b is a constant.

[0060] S4: The lifespan of the fiberglass pipe is calculated based on the above fitting equation.

[0061] This embodiment provides a novel method for predicting the service life of FRP pipes based on stress, which overcomes the shortcomings of existing life prediction technologies for FRP pipelines used in oil and gas field gathering and transportation. It can predict the service life of FRP pipes under the combined influence of four factors: pipe material characteristics, transport medium, environmental factors, and stress state. The test cycle is short, it is easy to implement, and the prediction reliability is high.

[0062] Example 2

[0063] Based on Example 1, in this example, S1 specifically includes: randomly selecting multiple pre-prepared test samples and dividing them into multiple groups, and performing hydrostatic tests under stress on the test samples in each group.

[0064] Prepare test samples appropriately and group them for hydrostatic testing.

[0065] Example 3

[0066] Based on Example 2, in this example, S1 includes the following specific steps:

[0067] S11: Install the test sample on the bending test device according to the minimum bending radius, and apply bending stress to the fiberglass pipe through the bending test device;

[0068] S12: Connect the pressure-pressurizing adapter equipped with an inlet valve, a pressure relief valve, and a pressure gauge to the plug, and connect it to one end of the test sample. Pour the test medium obtained on-site or simulated from the other end of the test sample, and seal it with the connected plug in the same way.

[0069] S13: Place the sealed and assembled test sample on the support base, push it into the environmental test chamber, and control the environmental test chamber to heat up to the test temperature; connect the gas cylinder in the pressurization device to the pressurization transfer joint, close the pressure relief valve, open the air inlet valve, and according to the test gas components (such as CO2, H2S, CH4, N2) and partial pressure requirements, slowly fill the corresponding gas in sequence to keep the total pressure at the test pressure.

[0070] This method is simple and convenient to test, and it is used to test the pressure resistance of fiberglass pipes.

[0071] Example 4

[0072] Based on Example 3, in this example, S13 is followed by S14:

[0073] Once the set test time for the corresponding test sample is reached, the motor connected to the sample is stopped, and the pressure relief valve and exhaust gas treatment system are opened to release and treat the internal gas of the test sample.

[0074] This method is simple and well-designed, and the gas inside the test sample is released after the hydrostatic test is completed.

[0075] Preferably, in this embodiment, the hydrostatic pressure is 1.5 times the nominal pressure PN of the fiberglass pipe, and the test pressure is provided by pressurizing the test medium using a pressurizing device.

[0076] Preferably, in this embodiment, at least 6 discrete points are selected between 1 hour and 2000 hours for the hydrostatic time, including at least 1 time point below 100 hours, at least 3 time points below 1000 hours, and at least 2 time points between 1500 hours and 2000 hours.

[0077] Preferably, in this embodiment, the test temperature is the service temperature of the fiberglass pipe. The temperature is provided by the test chamber, and the maximum test temperature should be at least 15°C lower than the glass transition temperature of the pipe resin.

[0078] Preferably, in this embodiment, the stress is provided by a bending stress application device (using existing technology), which can apply a bending moment to the pipe. The minimum bending radius of different specifications of FRP pipes is shown in Table 1 below.

[0079] Table 1 Minimum Bending Radius (SY / T 6769.1-2010)

[0080]

[0081] Example 5

[0082] Based on any one of Embodiments 3 to 4, in this embodiment, S10 is included before S11:

[0083] Test medium configuration: The test medium is configured to simulate field service conditions.

[0084] This method is simple, reasonably designed, and involves configuring the test medium to simulate on-site service conditions, thereby better predicting the lifespan of fiberglass pipes.

[0085] Different types of fiberglass pipes require different test media, as detailed below:

[0086] (1) If the FRP pipe is a water-containing crude oil pipeline, the test medium is a mixture of crude oil and brine. The concentration of brine is consistent with the formation water in the FRP pipe's gathering and transporting fluid. The oil-water mixture used in the oilfield can be used directly as the test liquid medium, or the oil-water medium can be simulated based on the composition analysis of the transported medium: use kerosene or diesel to simulate the transported oil medium; use NaCl, CaCO3, distilled water, etc. to simulate the transported aqueous solution, and adjust its pH value so that the solution composition and pH value are as consistent as possible with the on-site aqueous solution.

[0087] If the medium is an oil-water mixture from the oilfield, it can be directly introduced into the sample.

[0088] If it is a simulated medium, first weigh a certain amount of distilled water or deionized water (20%–70% by volume), then add NaCl (2%–10% by mass), CaCO3 (3%–30% by mass), and HCl (0.5%–5% by mass) to the deionized water, stir and mix evenly, and then pour it into the sample.

[0089] (2) If the FRP pipe is an oil, gas and water mixed transport FRP pipeline, the test medium is divided into liquid phase and gas phase. The liquid phase is a mixture of crude oil and brine. The concentration of brine is consistent with the formation water in the FRP pipe collection and transport fluid. The gas phase is simulated by using a certain composition of H2S, CO2 and CH4 gas based on the gas phase composition on site.

[0090] Liquid phase composition configuration:

[0091] If the medium is an oil-water mixture from the oilfield, it can be directly introduced into the sample.

[0092] If it is a simulated medium, first weigh a certain amount of distilled water or deionized water (20%–70% by volume), then add NaCl (2%–10% by mass), CaCO3 (3%–30% by mass), and HCl (0.5%–5% by mass) to the deionized water, stir and mix evenly, and then pour it into the sample.

[0093] Gas phase composition configuration:

[0094] To simulate the composition of the gas medium in the field, a certain amount of CO2 (0%–30% volume fraction), H2S (0–50% volume fraction), CH4 or N2 (50%–95% volume fraction) is injected into the sample using a gas pump.

[0095] (3) If the fiberglass pipe is a gas transmission pipeline, a certain composition of H2S, CO2 and CH4 gas will be used to simulate the gas phase composition on site.

[0096] Gas phase composition configuration:

[0097] To simulate the composition of the gas medium in the field, a certain amount of CO2 (0%–30% volume fraction), H2S (0–50% volume fraction), CH4 or N2 (50%–95% volume fraction) is injected into the sample using a gas pump.

[0098] (4) If the FRP pipe is a gas transmission pipeline, the oilfield water medium can be used directly as the test liquid medium, or the aqueous solution to be transported can be simulated by NaCl, CaCO3, distilled water, etc., based on the analysis of the water medium composition at the site, and the pH value can be adjusted to make the solution composition and pH value as consistent as possible with the aqueous solution at the site.

[0099] If the medium is water used in the oilfield, it can be directly introduced into the sample;

[0100] If it is a simulated medium, first weigh a certain amount of distilled water or deionized water (20%–70% by volume), then add NaCl (2%–10% by mass), CaCO3 (3%–30% by mass), and HCl (0.5%–5% by mass) to the deionized water, stir and mix evenly, and then pour it into the sample.

[0101] Example 6

[0102] Based on any one of Embodiments 3 to 5, in this embodiment, in 12:

[0103] The test medium was a simulated oilfield transport medium. The hydrostatic pressure was 1.5 times the nominal pressure of the batch of FRP samples. The hydrostatic time was between 1 hour and 2000 hours, with at least 6 discrete points selected. The test temperature was the service temperature of the FRP pipe. The bending radius of the test sample was the minimum bending radius of the FRP pipe for field laying.

[0104] By using test media to simulate the transport media in the oil field, the lifespan of FRP pipes can be better predicted with higher accuracy.

[0105] Example 7

[0106] Based on the above embodiments, in this embodiment, step S2 includes the following specific steps:

[0107] According to standard GB5351 "Test Method for Short-Time Hydrostatic Failure of Fiber Reinforced Thermosetting Plastic Pipes", burst tests were conducted on the glass pipes after hydrostatic pressure tests to test their burst strength values ​​and calculate the average value of each group of tests to obtain the remaining strength of the fiberglass pipes after hydrostatic pressure tests.

[0108] The data is analyzed, and the relative deviation is used to determine the relative deviation: relative deviation = [(single measurement value - average value) / average value] × 100%;

[0109] When the relative deviation of each set of test data is within the range of -15% to 15%, it is considered qualified data, and the final fitted data is taken as the average value; otherwise, repeat S1.

[0110] This method is simple and enables burst testing of fiberglass pipes to measure their burst strength.

[0111] Example 8

[0112] Based on the above embodiments, in this embodiment, step S4 includes the following specific steps:

[0113] The expected life of fiberglass pipes is defined as the period when the long-term strength of the fiberglass pipe is lower than the safety critical pressure P. limit The time corresponding to P limit Substitute into equation lnP limit =a*t limit +b, to get the time value t limit ;

[0114] Finally, the corresponding time value is obtained by using the known life pressure value in the equation. This value is the life time of this batch of composite pipes.

[0115] Among them, the safety critical pressure P limit =f*PN, where f is the safety factor, and f takes values ​​from 1.0 to 2.0.

[0116] This method is simple, reasonably designed, and requires the pre-preparation of test samples for subsequent hydrostatic tests.

[0117] Example 9

[0118] Based on the above embodiments, in this embodiment, S0 is included before S1:

[0119] Randomly select fiberglass pipes from the same batch, connect two fiberglass pipes with a joint to form a test sample, and at the same time process and manufacture corresponding plugs.

[0120] This method is simple, reasonably designed, and requires the pre-preparation of test samples for subsequent hydrostatic tests.

[0121] Example 10

[0122] Based on the above embodiments, this embodiment further includes curve correction between S3 and S4:

[0123] If a test point with a large deviation is observed, it should be discarded and a new experiment should be conducted. Repeat steps S1 and S2 to determine the final fitting equation lnP = a * lnt + b. If the distribution of each point meets the requirements of linear regression, this step can be skipped.

[0124] This method is simple, and the curve is further corrected to ensure the accuracy of the life prediction of FRP pipes.

[0125] The specific steps of the fiberglass pipe life prediction method under stress provided by this invention are as follows:

[0126] Step 1: Randomly select fiberglass pipes from the same batch, connect every two fiberglass pipes with a connector to form a test sample, then refer to the product external thread manufacturing method to make external threads at both ends of the test sample, and at the same time process and manufacture plugs accordingly.

[0127] Furthermore, in step one, each sample consists of two fiberglass tubes connected in the middle by a connector.

[0128] Step 2: Conduct a hydrostatic test on the fiberglass pipe under stress.

[0129] Randomly select at least 18 test samples prepared in step one and connected with intermediate connectors (18 is the lower limit for testing; if significant deviations in test data occur, the number of pipes needs to be increased), divide them into at least 6 groups, and each group should contain at least 3 samples. Perform a hydrostatic test on each group of samples under stress. The test medium is a simulated oilfield transport medium. The hydrostatic pressure is 1.5 times the nominal pressure of the batch of FRP samples. The hydrostatic time is between 1 hour and 2000 hours, with at least 6 discrete points selected. The test temperature is the service temperature of the FRP pipe, and the bending radius of the test sample is the minimum bending radius for field laying of the FRP pipe.

[0130] Specifically, the operating procedure for the hydrostatic test in step two is as follows:

[0131] (1) Test medium configuration: The test medium is configured to simulate the field service conditions.

[0132] (2) Install the sample on the bending test device according to the minimum bending radius, and apply bending stress to the pipe through the bending test device.

[0133] (3) System connection: Connect the pressure transfer connector equipped with an air inlet valve, a pressure relief valve and a pressure gauge to the plug, and connect it to one end of the test sample. Pour the oil-water medium obtained on site or simulated from the other end, and use the connected plug to seal the connection.

[0134] (4) Place the sealed and assembled test sample on the support base, push it into the environmental test chamber, and control the environmental test chamber to heat up to the test temperature.

[0135] (5) Connect the gas cylinder in the pressurization device to the pressurization transfer joint, close the pressure relief valve, open the air inlet valve, and according to the test gas composition (such as CO2, H2S, CH4, N2) and partial pressure requirements, slowly fill the corresponding gas in sequence to keep the total pressure at the test pressure; start the hydrostatic test timing of the environmental simulation field working conditions.

[0136] (6) After the test time set for the corresponding sample is reached, stop the motor connected to the sample, and open the pressure relief valve and the exhaust gas treatment system to release and treat the internal gas of the test sample.

[0137] Step 3: Conduct a water pressure burst test on the FRP pipes that have undergone hydrostatic testing to test the burst strength value of the FRP pipes;

[0138] According to standard GB5351 "Pressure Test Method for Short-Time Hydrostatic Failure of Fiber Reinforced Thermosetting Plastic Pipes", burst tests were conducted on the pipes after hydrostatic pressure testing to measure their burst strength (evaluation parameter). The average value of each test group was calculated to obtain the residual strength of the pipe after hydrostatic pressure testing. The data were analyzed, and the relative deviation was used for judgment. Relative deviation = [(single measurement value - average value) / average value] × 100%. When the relative deviation range of each test data group is -15% to 15%, it is considered qualified data. The final fitted data is the average value. Otherwise, steps one and two are repeated.

[0139] Step 4: Fit the data of hydrostatic pressure time and blasting strength value. With the logarithm of hydrostatic pressure time as the abscissa and the logarithm of blasting strength as the ordinate, use the linear regression method to perform numerical fitting and obtain the fitting equation of hydrostatic pressure time and blasting strength value: lnP=a*lnt+b.

[0140] Step 5: Curve Correction. Observe the obtained regression line and test points. If there are test points with large deviations, discard them and conduct additional experiments. Repeat steps one through three to determine the final fitted equation lnP = a * lnt + b. If the distribution of each point meets the requirements of linear regression, this step can be skipped.

[0141] Step Six: Pipe Life Calculation. The expected life of FRP pipes is defined as the lifespan of the FRP pipes when their long-term strength value is below the safe critical pressure P. limit The time corresponding to P limit Substitute into equation lnP limit =a*t limit +b, to get the time value t limit ;

[0142] Finally, the corresponding time value is obtained by using the known life pressure value in the equation. This value is the life time of this batch of composite pipes.

[0143] Among them, the safety critical pressure P limit =f*PN, where f is the safety factor, and f takes values ​​from 1.0 to 2.0.

[0144] The purpose of this invention is to overcome the shortcomings of existing life prediction technologies for FRP (fiberglass reinforced plastic) pipes used in oil and gas field gathering and transportation, and to provide a novel FRP pipe life prediction method based on stress. This method can predict the service life of FRP pipes under the combined influence of four factors: pipe material characteristics, transport medium, environmental factors, and stress state. It features a shorter testing cycle, ease of implementation, and high predictive reliability. Specific advantages are as follows:

[0145] Advantage 1: The sample used is a full-size fiberglass pipe sample, not a small sample or a pipe ring sample cut from the pipe. In addition, the sample has a joint in the middle as a connection, which can better simulate the performance changes of the pipe in the joint connection state.

[0146] Advantage 2: Regarding the test medium, instead of using the commonly used clean water in current tests, the test medium is the oilfield transport medium or the oil, water and gas media simulated based on the composition analysis of the transport medium. All media act inside the pipeline, which can better simulate the corrosion and aging of the fiberglass pipeline under the action of the field medium.

[0147] Advantage 3: In terms of environmental factors, the test chamber provides a temperature environment, and the pressurization device provides a pressure environment, which can completely simulate the service environment of the pipeline.

[0148] Advantage 4: In terms of stress, the use of a bending stress application device can simulate the bending radius of FRP pipes when they are laid in the oil field, and can completely simulate the bending stress state of the pipes when they are in service in the field.

[0149] Advantage 5: The entire test can be completed within 2000 hours, with a short test cycle.

[0150] Advantage 6: The entire experiment can be simulated in an indoor laboratory, which is convenient for implementation.

[0151] Advantage 7: The life prediction method provided by this invention comprehensively considers all factors that will affect the performance of FRP pipes during field service, can completely simulate field service conditions, and the prediction results are highly reliable.

[0152] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0153] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0154] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for predicting the lifespan of fiberglass pipes under stress, characterized in that, The specific steps include the following: S1: Perform a hydrostatic test on the FRP pipe under stress; S2: Conduct a water pressure burst test on the fiberglass pipes that have undergone hydrostatic testing; S3: Fit the data of hydrostatic pressure time and blasting strength value, with the logarithm of hydrostatic pressure time as the abscissa and the logarithm of blasting strength as the ordinate, and use the linear regression method to perform numerical fitting to obtain the fitting equation of hydrostatic pressure time and blasting strength value: lnP=a*lnt+b, where b is a constant. S4: The lifespan of the fiberglass pipe is calculated based on the above fitting equation.

2. The method for predicting the lifespan of fiberglass pipes under stress according to claim 1, characterized in that, S1 specifically includes: randomly selecting multiple pre-prepared test samples, dividing them into multiple groups, and performing hydrostatic tests under stress on the test samples in each group.

3. The method for predicting the lifespan of fiberglass pipes under stress according to claim 2, characterized in that, S1 includes the following specific steps: S11: Install the test sample on the bending test device according to the minimum bending radius, and apply bending stress to the fiberglass pipe through the bending test device; S12: Connect the pressure-pressurizing adapter equipped with an inlet valve, a pressure relief valve, and a pressure gauge to the plug, and connect it to one end of the test sample. Pour the test medium obtained on-site or simulated from the other end of the test sample, and seal it with the connected plug in the same way. S13: Place the sealed and assembled test sample on the support base, push it into the environmental test chamber, and control the environmental test chamber to heat up to the test temperature; connect the gas cylinder in the pressurization device to the pressurization transfer joint, close the pressure relief valve, open the air inlet valve, and slowly fill in the corresponding gas in sequence to keep its total pressure at the test pressure.

4. The method for predicting the lifespan of fiberglass pipes under stress according to claim 3, characterized in that, S13 is followed by S14: Once the set test time for the corresponding test sample is reached, the motor connected to the sample is stopped, and the pressure relief valve and exhaust gas treatment system are opened to release and treat the internal gas of the test sample.

5. The method for predicting the lifespan of fiberglass pipes under stress according to claim 3, characterized in that, S10 precedes S11: Test medium configuration: The test medium is configured to simulate field service conditions.

6. The method for predicting the lifespan of fiberglass pipes under stress according to claim 3, characterized in that, Of the 12 mentioned above: The test medium was a simulated oilfield transport medium. The hydrostatic pressure was 1.5 times the nominal pressure of the batch of FRP samples. The hydrostatic time was between 1 hour and 2000 hours, with at least 6 discrete points selected. The test temperature was the service temperature of the FRP pipe. The bending radius of the test sample was the minimum bending radius of the FRP pipe for field laying.

7. The method for predicting the lifespan of fiberglass pipes under stress according to any one of claims 1-6, characterized in that, S2 includes the following specific steps: According to relevant standards, burst tests were conducted on the glass pipes after the hydrostatic pressure test to measure their burst strength value and calculate the average value of each group of tests in order to obtain the remaining strength of the fiberglass pipes after the hydrostatic pressure test. The data is analyzed, and the relative deviation is used to determine the relative deviation: relative deviation = [(single measurement value - average value) / average value] × 100%; When the relative deviation of each set of test data is within the range of -15% to 15%, it is considered qualified data, and the final fitted data is taken as the average value; otherwise, repeat S1.

8. The method for predicting the lifespan of fiberglass pipes under stress according to any one of claims 1-6, characterized in that, S4 includes the following specific steps: The expected life of fiberglass pipes is defined as the period when the long-term strength of the fiberglass pipe is lower than the safety critical pressure P. limit The time corresponding to P limit Substitute into equation lnP limit =a*t limit +b, to get the time value t limit ; Finally, the corresponding time value is obtained by using the known life pressure value in the equation. This value is the life time of this batch of composite pipes. Among them, the safety critical pressure P limit =f*PN, where f is the safety factor, and f takes values ​​from 1.0 to 2.

0.

9. The method for predicting the lifespan of a fiberglass pipe under stress according to any one of claims 1-6, characterized in that, S0 is preceding S1: Randomly select fiberglass pipes from the same batch, connect two fiberglass pipes with a joint to form a test sample, and at the same time process and manufacture corresponding plugs.

10. The method for predicting the lifespan of a fiberglass pipe under stress according to any one of claims 1-6, characterized in that, Curve correction is also included between S3 and S4: If a test point with a large deviation is observed, it should be discarded and a new experiment should be conducted. Repeat steps S1 and S2 to determine the final fitting equation lnP = a * lnt + b. If the distribution of each point meets the requirements of linear regression, this step can be skipped.

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