Method for testing the lifetime of plastic pipes and device therefor

Abstract

The application provides a plastic pipe life test method and device thereof. The plastic pipe life test method comprises: filling test solution into a low-position water tank and a circulating test pipeline in communication with the low-position water tank, injecting test solution into a high-position water tank in communication with the low-position water tank, and making the high-position water tank have a preset initial volume of test solution; wherein the high-position water tank is higher than the low-position water tank by a preset height, and a gas phase space is formed at the top of the high-position water tank; filling compressed gas into the gas phase space, making the gas phase space of the high-position water tank have a preset pressure, and applying back pressure to the test solution in the low-position water tank; under the back pressure condition, heating the test solution in the low-position water tank to a target test temperature; and maintaining the back pressure condition and the target test temperature, and performing life test on a plastic pipe sample in the circulating test pipeline. Through the integrated structure and process design, the system is in a stable high-temperature and high-pressure test state, the energy utilization efficiency is improved, the operation cost is reduced, and the test efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of plastic pipe testing technology, and in particular to a method and apparatus for testing the lifespan of plastic pipes. Background Technology

[0002] When evaluating the long-term performance of plastic pipes, international standards require accelerated life testing. This involves placing the pipe sample in a constant-temperature air or water tank, with a continuously flowing aqueous solution at the same temperature inside the pipe. The temperature fluctuation of the aqueous solution should not exceed ±1°C, and the pressure fluctuation should not exceed ±0.02 MPa. The time from the start of loading to rupture failure is recorded. Typical test temperatures include 95°C, 105°C, and 115°C to enable rapid testing and prediction of pipe lifespan. When the test temperature is below 100°C, the circulating water can be directly heated and maintained at a stable temperature in an atmospheric pressure system. However, when the target temperature exceeds the atmospheric boiling point of water (e.g., 105°C or 115°C), sufficient pressure must be applied to the aqueous solution to suppress boiling and maintain stable circulation of the liquid water.

[0003] During the life test of plastic pipes, pressure needs to be applied to the system to suppress boiling in order to make the test solution temperature exceed 100℃. However, if it is attempted to directly pressurize and heat to the target temperature in a large-capacity water tank that serves as the main liquid storage unit, if a small amount of air remains or local vaporization occurs during heating, the gas expansion at high temperature combined with water vapor will cause the pressure to rise rapidly and uncontrollably, posing a serious risk of overpressure or even container failure. At the same time, under the coupled effect of dynamic circulation and thermal expansion, the large-capacity water tank is also difficult to achieve the ±0.02 MPa pressure stability required by international standards, and is prone to pressure oscillations due to thermal expansion and contraction.

[0004] Therefore, existing technologies generally adopt an indirect heat management strategy: first, preheat at atmospheric pressure, then pressurize, then locally heat up, and finally cool and reflux after the test. As shown in the patent text of CN223122818U, entitled "A System for Testing the Chlorine Oxidation Resistance of Plastic Pipes in High-Temperature Internal Pressure Fluids," the test solution is first preheated to below 95°C in an atmospheric pressure water tank (to avoid vaporization), then pressurized to the target pressure by a pressurizing pump, and then further heated to 105°C or 115°C in a separate small-volume heating device (such as a spiral coil heat exchanger). After the test, the fluid must be cooled to below 100°C by a cooling device before it can be refluxed to the atmospheric pressure water tank to prevent vaporization during the reflux process.

[0005] However, this multi-stage process requires repeated pressure heat exchange during both heating and cooling, which results in a large amount of heat energy being consumed and high operating costs. Summary of the Invention

[0006] The purpose of this application is to provide a method and apparatus for testing the life of plastic pipes, so as to achieve direct heating of the test solution to the target high temperature and continuous operation, thereby reducing energy consumption and operating costs.

[0007] To address the aforementioned technical problems, this application provides the following technical solutions:

[0008] The first aspect of this application provides a method for testing the lifespan of plastic pipes, including:

[0009] S1 fills the low-level water tank and the circulating test pipeline connected to the low-level water tank with test solution, and injects test solution into the high-level water tank connected to the low-level water tank, so that the high-level water tank has a preset initial volume of test solution; wherein, the high-level water tank is higher than the low-level water tank by a preset height, and a gas phase space is formed at the top;

[0010] S2 introduces compressed gas into the gas phase space to give the gas phase space of the high-level water tank a preset pressure, so as to apply back pressure to the test solution in the low-level water tank.

[0011] S3 heats the test solution in the low-level water tank to the target test temperature under the back pressure condition;

[0012] S4 maintains the back pressure conditions and the target test temperature to perform a life test on the plastic tube sample in the test system.

[0013] In some modified embodiments of the first aspect of this application, the method of step S1 includes:

[0014] S101 injects test solution into the test system through the water inlet. When the test solution overflows from the first predetermined overflow point, the test system is started under normal temperature and pressure conditions, so that the test solution circulates in it until the first predetermined overflow point overflows and the circulation stops, so that the low-level water tank and the circulating test pipeline are filled with test solution.

[0015] S102 continues to inject the test solution until the test solution overflows from the second predetermined overflow point, so that the high-level water tank has a preset initial volume of test solution.

[0016] In some modified embodiments of the first aspect of this application, step S4 further includes:

[0017] During the life test, dynamic data on the deformation parameters of the plastic tube sample as a function of time are collected.

[0018] Based on the dynamic data, the target test temperature, the preset pressure, and the failure time measured by the life test, a life prediction model is established.

[0019] The service status of similar plastic pipes under the same or equivalent working conditions is evaluated using the aforementioned life prediction model.

[0020] In some modified embodiments of the first aspect of this application, the method for collecting dynamic data on the deformation parameters of the plastic tube sample over time includes:

[0021] The circumferential geometric data of the plastic tube sample at multiple axial positions are obtained through non-contact motion detection.

[0022] Based on the changes in the circumferential geometric data over time, the dynamic data of the deformation parameters over time are calculated.

[0023] The deformation parameters include at least one of circumferential strain and ellipticity.

[0024] In some modified embodiments of the first aspect of this application, the assessment includes at least one of predicting remaining life expectancy and health status level.

[0025] In some modified embodiments of the first aspect of this application, the total volume of the elevated water tank does not exceed 20 L; and / or,

[0026] The initial volume of the test solution is equal to the initial volume of the compressed gas in the gas phase space; and / or,

[0027] The target test temperature is 95℃, 105℃, or 115℃; and / or,

[0028] The preset height is ≥20 cm; and / or,

[0029] The high-level water tank and the low-level water tank are connected by a connecting pipe with a nominal diameter of not less than DN50.

[0030] A second aspect of this application provides a plastic pipe life testing system for performing the plastic pipe life testing method as described in the first aspect, comprising:

[0031] The elevated water tank is equipped with a first safety valve and a solution level detection device.

[0032] The compressor is connected to the high-level water tank via a pressure reducing valve;

[0033] A low-level water tank is connected to a high-level water tank via a connecting pipe; the high-level water tank is at a predetermined height higher than the low-level water tank; a gas phase space is formed at the top;

[0034] A heating element is installed in the low-level water tank;

[0035] The circulating test pipeline is connected in series with the centrifugal pump and the low-level water tank to form a closed loop. The circulating test pipeline is used to install plastic tube samples.

[0036] Some modified embodiments of the second aspect of this application also include:

[0037] A position detection device is used to detect the position and height of the liquid in the liquid phase space of the high-level water tank and output a first signal;

[0038] The controller is communicatively connected to the position detection device and is used to acquire the first signal and determine the current volume of the liquid phase space based on the first signal. The position detection device and the controller together form the solution storage detection element.

[0039] Some modified embodiments of the second aspect of this application also include:

[0040] A constant temperature environment chamber has a containment space, and the constant temperature environment chamber is equipped with an optical window, with the plastic tube sample located within the containment space;

[0041] The driving component is connected to the constant temperature environment chamber;

[0042] A base is connected to the driving component, which drives the base to move along the length of the plastic tube sample.

[0043] A detection component is disposed on the base. The detection component is annular. The constant temperature environment chamber passes at least partially through the central through-hole of the detection component so that the detection end of the detection component is opposite to the optical window. The detection component detects the circumferential geometric data of the plastic tube sample non-contactly through the optical window and generates a second signal.

[0044] The control unit is communicatively connected to the detection component and is used to acquire the second signal and determine dynamic data of deformation parameters changing over time based on the second signal.

[0045] In some modified embodiments of the second aspect of this application, the connecting pipeline is equipped with a first overflow valve, and the position of the first overflow valve is higher than the position of the inlet valve;

[0046] The elevated water tank is equipped with a first pressure sensor and a second overflow valve, with the second overflow valve located in the middle area of ​​the elevated water tank.

[0047] The low-level water tank is equipped with a second pressure sensor, a second safety valve, a dosing device, and a circulation pump. The two ends of the circulation pump are connected to the low-level water tank for internal circulation of the test solution in the low-level water tank.

[0048] The circulating test pipeline includes a main pipeline and multiple parallel branch pipelines. One end of the main pipeline is connected to the low-level water tank, and the other end of the main pipeline is connected to the first end of the multiple branch pipelines. The second end of each branch pipeline is connected to the low-level water tank.

[0049] The main pipeline is equipped with the centrifugal pump, temperature sensor, and third pressure sensor;

[0050] Each of the branch pipes is sequentially equipped with a pressure regulating valve, a fourth pressure sensor, a first electric valve, the plastic pipe sample, a second electric valve, and a flow regulating valve from its inlet to its outlet.

[0051] The constant temperature environment chamber is equipped with a water leakage detector, which is communicatively connected to the first electric valve and the second electric valve, respectively, and is used to control the first electric valve and the second electric valve to close when a leak is detected.

[0052] Compared to existing technologies, the plastic pipe life testing method provided in this application effectively eliminates air inside the system by filling the low-level water tank and the circulating test pipeline connected to it with test solution, thus avoiding pressure fluctuations or local dry burning caused by air bubbles. At the same time, the initial volume of the test solution is preset, so that after the system is filled with liquid, only the gas phase space at the top of the high-level water tank contains gas, and the initial volume of the gas phase space is uniquely determined, thereby laying the foundation for high-precision temperature and pressure control under high-temperature conditions.

[0053] By filling the gas phase space of the high-level water tank with compressed gas, a controllable preset back pressure is established, so that the entire water tank system (including the low-level water tank and the high-level water tank) is in a stable pressure state. Then, under this back pressure condition, the test solution in the low-level water tank is directly heated to the target test temperature (e.g., 115℃) in one go and continuously. Finally, under the established constant high temperature and high pressure environment, the plastic tube sample is subjected to continuous life test until it fails naturally, thereby obtaining real, repeatable, and high-confidence life data that meets international standards.

[0054] The plastic pipe life testing method of this application, through integrated structure and process design, keeps the system in a stable high temperature and high pressure testing state at all times. It eliminates the intermediate cooling link required in traditional methods to achieve the return of the test solution to the atmospheric pressure water tank, which can significantly reduce energy consumption, improve energy utilization efficiency, and reduce operating costs. Attached Figure Description

[0055] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein:

[0056] Figure 1 The plastic pipe life testing system of this application is illustrated schematically;

[0057] Figure 2 A schematic diagram of the high-level water tank structure of the plastic pipe life testing system of this application is shown.

[0058] Figure 3 A schematic diagram of the base structure of one embodiment of the plastic pipe life testing system of this application is shown.

[0059] Figure 4 A schematic diagram of the base structure of another embodiment of the plastic tube life testing system of this application is shown.

[0060] Explanation of icon numbers:

[0061] 1. High-level water tank; 11. First safety valve; 12. Solution level detection device; 13. First pressure sensor; 14. Second overflow valve; 2. Compressor; 21. Pressure reducing valve; 3. Low-level water tank; 31. Connecting pipeline; 32. Inlet valve; 33. First overflow valve; 34. Second pressure sensor; 35. Second safety valve; 36. Dosing device; 37. Circulation pump; 4. Heating assembly; 5. Circulation test pipeline; 51. Centrifugal pump; 52. Constant temperature environment chamber; 53. Drive component; 54. Base; 55. Detection assembly; 56. Temperature sensor; 57. Third pressure sensor; 58. Pressure regulating valve; 59. Fourth pressure sensor; 510. First electric valve; 511. Second electric valve; 512. Flow regulating valve; 513. Leakage detector; 6. Plastic tube sample. Detailed Implementation

[0062] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0063] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application pertains.

[0064] To address the technical challenges mentioned in the background section, the inventors, through in-depth research, have provided a method and apparatus for testing the lifespan of plastic pipes. This solution utilizes a coordinated structure of a high-level water tank and a low-level heating water tank. After system injection and venting, a gas phase space of a defined volume is formed only at the top of the high-level water tank, providing a stable back pressure. Based on this, the test solution in the low-level water tank is directly heated to the target temperature, ensuring the system remains under constant high temperature and high pressure throughout the process. This completely eliminates the intermediate cooling step required in traditional methods to return the test solution to the atmospheric pressure storage tank. While ensuring safe and controllable pressure with fluctuations less than or equal to ±0.02 MPa, it significantly reduces energy loss during non-testing phases, shortens the test cycle, and improves data comparability and system reliability.

[0065] The first aspect of this application provides a method for testing the lifespan of plastic pipes, including:

[0066] S1 fills the low-level water tank and the circulating test pipeline connected to the low-level water tank with test solution, and injects test solution into the high-level water tank connected to the low-level water tank; wherein, the high-level water tank is higher than the low-level water tank by a preset height, and a gas phase space is formed at the top.

[0067] Specifically, the test solution can be prepared according to international standards or actual application scenarios. For example, the test solution can be deionized water or distilled water, or sodium hypochlorite can be added to simulate the chlorination effect of disinfectants in drinking water on plastic pipes; or pH adjustment can be added to control the pH within the range of 6.0–7.5 to meet the actual water supply quality, and so on.

[0068] The test solution can be pumped into the low-level water tank and the circulating test pipeline to fill it. A manual venting valve can be installed at the highest bend of the circulating test pipeline, which should be closed after continuous liquid flow to enhance the venting effect.

[0069] After the low-level tank is full, a preset volume of test solution can be injected into the high-level tank using a metering pump or a filling funnel with level markings. The liquid level in the high-level tank can be monitored in real time using a magnetic level gauge or an ultrasonic level sensor to ensure the volume of the gas phase space.

[0070] The total volume of the elevated water tank can be determined based on the total liquid volume of the system and the thermal expansion compensation requirements. The initial volume of the test solution inside is set to form a gas phase space of appropriate volume at the top. This gas phase space can effectively absorb the liquid expansion caused by the temperature rise during the test, while ensuring that the system pressure fluctuation meets the accuracy requirements of international standards.

[0071] Furthermore, the total volume of the elevated water tank should not exceed 20 L to avoid reducing pressure response sensitivity and to prevent pressure exceeding limits due to thermal expansion. The volume and operating pressure of the elevated water tank are optimized so that it can be treated as a standard pressure-bearing component, simplifying system installation and operation management. The volume of the lower water tank needs to ensure stable operation of the test solution during circulation. For example, it can be at least 1.5 times the total volume of the circulation test pipeline to prevent the centrifugal pump from cavitating, maintain stable flow, and provide sufficient thermal buffering capacity for the heating process.

[0072] The volumes of the gas phase space and liquid phase space of the elevated water tank can be adjusted according to system requirements: when the volume of the gas phase space is greater than that of the liquid phase space, it is suitable for scenarios with extremely high pressure stability requirements and high test temperatures (such as 115℃); when the volume of the liquid phase space is greater than that of the gas phase space, it is suitable for tests with slower temperature rise or slightly higher tolerance for pressure fluctuations. Alternatively, the initial volume of the test solution is equal to the initial volume of the compressed gas in the gas phase space. That is, when the volumes of the gas phase space and liquid phase space of the elevated water tank are equal, taking a total volume of 20 L of elevated water tank as an example, the initial volume of the test solution is 10 L, and the volume of the compressed gas in the gas phase space before the test begins after inflation is 10 L. At this point, the elevated water tank achieves the best balance between pressure response sensitivity and thermal expansion buffering capacity, which is suitable for plastic pipe life testing that requires long-term stable operation and meets the accuracy requirement of ±0.02 MPa.

[0073] The preset height is ≥20 cm. This height difference ensures that the higher water tank is always higher than the lower water tank, while providing sufficient static pressure head. This facilitates the natural migration of gas to the higher water tank during circulation and prevents negative pressure or cavitation at the centrifugal pump inlet. The preset height can be selected as 20 cm, 30 cm, 40 cm, 45 cm, 50 cm, 55 cm, or 60 cm, with 45-55 cm being the preferred setting. The higher and lower water tanks are connected by a pipe with a nominal diameter of not less than DN50. For example, DN50 or DN65 stainless steel or high-temperature resistant engineering plastic pipes can be used. A larger pipe diameter can significantly reduce liquid flow resistance, ensuring that the fluid can flow quickly and smoothly between the higher and lower water tanks during liquid injection, thermal expansion compensation, and pressure balancing, thereby improving the system's pressure response speed and stability, and helping to maintain continuous and controllable back pressure.

[0074] Furthermore, the method in step S1 includes:

[0075] S101 injects test solution into the test system through the water inlet. After the test solution overflows from the first predetermined overflow point, the test system is started under normal temperature and pressure conditions, so that the test solution circulates in it until it overflows from the first predetermined overflow point and then stops circulating, so that the low-level water tank and the circulating test pipeline are filled with test solution.

[0076] Specifically, both the water inlet and the first predetermined overflow point can be located on the connecting pipeline, with the first predetermined overflow point positioned higher than the water inlet. The test solution is injected from the water inlet, and when the liquid level rises to the first predetermined overflow point and begins to overflow, it indicates that the low-level water tank is initially full. At this point, the centrifugal pump on the circulating test pipeline is activated to circulate the test solution within the system, thereby expelling any residual gas from the pipeline.

[0077] During the circulation process, the liquid level in the low-level tank may temporarily drop due to gas discharge and liquid filling. Therefore, it is necessary to continue replenishing the test solution until the test solution rises back to the first predetermined overflow point and overflows continuously and stably, indicating that the low-level tank and the entire circulation test pipeline are completely filled with liquid and the internal air has been basically expelled. At this time, maintain stable operation of the system for more than half an hour to ensure that the gas is fully released.

[0078] S102 continues to inject the test solution until the test solution overflows from the second predetermined overflow point, so that the high-level water tank has a preset initial volume of test solution.

[0079] Specifically, the second predetermined overflow point is set in the elevated water tank. Taking a cylindrical elevated water tank as an example, its height can be 1 meter and its diameter can be 0.1 meters. The second predetermined overflow point can be set at its height of 0.5 meters. Water continues to be injected through the inlet point. When the test solution rises to the second predetermined overflow point and begins to overflow continuously, it indicates that the test solution in the elevated water tank has reached the initial volume and preset height.

[0080] Through two-stage overflow control, not only is it ensured that there is no residual air in the circulation loop, but it also achieves highly repeatable setting of the liquid level in the high-level water tank, providing a reliable foundation for establishing accurate and stable back pressure in the future.

[0081] S2 introduces compressed gas into the gas phase space, giving the gas phase space of the high-level water tank a preset pressure, so as to apply back pressure to the test solution in the low-level water tank.

[0082] Specifically, the compressed gas can be nitrogen, argon, or air. Compressed gas can be introduced into the gas phase space using a compressor and a pressure reducing valve. The preset pressure can be 0.12 MPa, and closed-loop feedback control can stabilize the pressure at the preset value with a control accuracy of ±0.005 MPa.

[0083] S3 heats the test solution in the low-level water tank to the target test temperature under the back pressure condition.

[0084] Specifically, the target test temperature can be set below 100°C, such as 85°C or 95°C, for routine heat resistance assessments; or the target test temperature can be set above 100°C, such as 105°C, 115°C, or 120°C, for accelerated aging life testing. Furthermore, the target test temperature of 95°C, 105°C, or 115°C covers the requirements for both routine and high-speed accelerated aging tests.

[0085] S4 maintains the back pressure conditions and the target test temperature to perform a life test on the plastic tube sample in the test system.

[0086] Specifically, the system operates continuously without human intervention until the plastic tube sample leaks or bursts, recording the failure time. Throughout the test, the elevated water tank automatically compensates for thermal expansion through the gas phase space, keeping system pressure fluctuations within ±0.02 MPa and maintaining constant test conditions, thereby obtaining high-confidence life data that meets international standards.

[0087] Furthermore, step S4 also includes:

[0088] During the life test, dynamic data on the deformation parameters of the plastic tube sample as a function of time are collected.

[0089] Based on the dynamic data, the target test temperature, the preset pressure, and the failure time measured by the life test, a life prediction model is established.

[0090] The service status of similar plastic pipes under the same or equivalent working conditions is evaluated using the aforementioned life prediction model.

[0091] Specifically, during life testing, deformation parameters such as radial expansion or local bulging can be acquired in real time using laser sensors or vision sensors, and dynamic data on deformation changes over time can be recorded. This dynamic data, along with the target test temperature, preset back pressure, and the final measured failure time, is input into a data analysis module (e.g., a processing platform built using MATLAB, Python, or dedicated engineering analysis software). Then, a life prediction model can be established using the Arrhenius accelerated aging model, the Larson-Miller parametric method, or machine learning algorithms (such as support vector regression or random forest).

[0092] Furthermore, the assessment includes at least one of predicting remaining service life and health status level. The service life prediction model can be used to predict the remaining service life of similar plastic pipes under actual service conditions, or to assess their health status level. The equivalent service condition refers to the equivalent damage time under standard reference conditions, converted from actual service time to such conditions using an accelerated aging model (such as the Arrhenius equation or the Larson-Miller parameter method) under different temperature and pressure combinations. Based on this equivalence, the model can be extrapolated to non-test conditions to achieve the assessment of the service life and health status of pipelines in operation in the field.

[0093] Health status levels can be divided into:

[0094] Level I (Good): Deformation rate is stable and below the threshold, with no abnormal fluctuations;

[0095] Level II (Warning): Deformation rate accelerates, approaching the inflection point of historical failure samples;

[0096] Level III (Hazardous): Localized abrupt changes or accelerated creep occur, and failure is expected in the short term. This model provides a scientific basis for engineering maintenance decisions and supports the shift from periodic replacement to condition-based maintenance.

[0097] Furthermore, the method for collecting dynamic data on the deformation parameters of the plastic tube sample over time includes:

[0098] The circumferential geometric data of the plastic tube sample at multiple axial positions are obtained through non-contact motion detection.

[0099] Based on the changes in the circumferential geometric data over time, the dynamic data of the deformation parameters over time are calculated.

[0100] The deformation parameters include at least one of circumferential strain and ellipticity.

[0101] Specifically, a non-contact mobile detection device can be used to move at a constant speed along the axial direction of the plastic tube sample to acquire circumferential cross-sectional profile point cloud data at multiple axial positions. This detection process can continuously and in real-time record the geometric morphology of the outer surface of the tube wall without interfering with the flow of the test fluid or the stress state of the tube. Subsequently, based on the circumferential geometric data collected over time at each axial position, a cross-sectional ellipse model at each moment is fitted using a data processing algorithm, and then the key deformation parameters are calculated.

[0102] Among them, the circumferential strain is determined by the rate of change of the current cross-sectional perimeter relative to the initial perimeter; ellipticity is defined as the ratio of the difference between the maximum and minimum diameters of the cross-section to the nominal diameter, used to characterize the degree of cross-sectional out-of-roundness. The above dynamic data are stored synchronously with timestamps to form a high-temporal-resolution deformation evolution curve, providing refined input features for subsequent lifetime prediction models.

[0103] By capturing the local deformation evolution process of plastic tube samples along the axial direction without interfering with high-temperature and high-pressure fluid cycling tests, early failure precursors such as bulging and out-of-roundness can be effectively identified; this provides more sensitive and discriminative input features for lifetime prediction models, thereby improving the accuracy of remaining lifetime prediction and the timeliness of health status assessment.

[0104] Compared to existing technologies, the plastic pipe life testing method provided in this application effectively eliminates air inside the system by filling the low-level water tank and the circulating test pipeline connected to it with test solution, thus avoiding pressure fluctuations or local dry burning caused by air bubbles. At the same time, the initial volume of the test solution is preset, so that after the system is filled with liquid, only the gas phase space at the top of the high-level water tank contains gas, and the initial volume of the gas phase space is uniquely determined, thereby laying the foundation for high-precision temperature and pressure control under high-temperature conditions.

[0105] By filling the gas phase space of the high-level water tank with compressed gas, a controllable preset back pressure is established, so that the entire water tank system (including the low-level water tank and the high-level water tank) is in a stable pressure state. Then, under this back pressure condition, the test solution in the low-level water tank is directly heated to the target test temperature (e.g., 115℃) in one go and continuously. Finally, under the established constant high temperature and high pressure environment, the plastic tube sample is subjected to continuous life test until it fails naturally, thereby obtaining real, repeatable, and high-confidence life data that meets international standards.

[0106] The plastic pipe life testing method of this application, through integrated structure and process design, keeps the system in a stable high temperature and high pressure testing state at all times. It eliminates the intermediate cooling link required in traditional methods to achieve the return of the test solution to the atmospheric pressure water tank, which can significantly reduce energy consumption, improve energy utilization efficiency, and reduce operating costs.

[0107] like Figure 1 As shown, the second aspect of this application provides a plastic pipe life testing system for performing the plastic pipe life testing method as described in the first aspect, comprising:

[0108] The high-level water tank 1 is equipped with a first safety valve 11 and a solution level detection device 12;

[0109] Compressor 2 is connected to the high-level water tank 1 via pressure reducing valve 21;

[0110] The low-level water tank 3 is connected to the high-level water tank 1 via a connecting pipe 31; the high-level water tank is at a preset height higher than the low-level water tank; a gas phase space is formed at the top of the high-level water tank 1; and the connecting pipe 31 is equipped with a water inlet valve 32.

[0111] Heating component 4 is installed in the low-level water tank 3;

[0112] The circulating test pipeline 5 is connected in series with the centrifugal pump 51 and the low-level water tank 3 to form a closed loop. The circulating test pipeline 5 is used to install the plastic tube sample 6.

[0113] Specifically, the gas phase space at the top of the elevated water tank 1 is used to contain compressed gas to apply and stabilize back pressure. Simultaneously, it automatically compensates for the volume expansion or contraction of the test solution due to temperature changes through liquid level changes, ensuring the circulation system is full and free of air bubbles, and providing a constant high-temperature and high-pressure testing environment for the plastic tube sample 6. The elevated water tank 1 can also be equipped with an exhaust valve (or exhaust port) to open during the system's water filling phase to release residual gas from the pipelines and tank. It closes after the liquid is full to ensure system sealing. The first safety valve 11 can be a mechanical automatic pressure relief device, with its opening pressure set higher than the preset working pressure (e.g., set to 0.13 MPa). When the system pressure abnormally rises due to a malfunction and reaches this opening pressure, the first safety valve 11 automatically opens to relieve pressure and ensure system safety. For example, when the preset working pressure is 0.12 MPa, the pressure warning threshold can be set to 0.13 MPa. The solution level detection element 12 is used to monitor the amount of test solution in the elevated water tank 1; for example, it can be a level gauge 12.

[0114] Compressor 2 is used to provide compressed gas (such as air, nitrogen, or helium) at a certain pressure; pressure reducing valve 21 is used to adjust the pressure of the compressed gas to the preset back pressure value required for testing and maintain stable output pressure. An air inlet can be provided on the top of the high-level water tank 1, and pressure reducing valve 21 can be connected to the high-level water tank 1 through the air inlet.

[0115] The lower-level water tank 3 is used to contain the test solution and serves as the liquid storage and heating unit for the circulation loop. Its position is lower than the upper-level water tank 1, facilitating a stable liquid level difference and enabling gas-liquid isolation and pressure transmission in conjunction with the upper-level water tank 1. The inlet valve 32 controls the injection of the test solution and the initial liquid filling process of the system, ensuring that the lower-level water tank 3 and the circulation test pipeline 5 are fully vented and filled with liquid. The inlet valve 32 forms the water inlet point. The connecting pipeline 31 can extend vertically.

[0116] The heating component 4 is used to heat the test solution in the low-level water tank 3 to the target test temperature. It is located inside the low-level water tank 3 and can be a heating rod, a thin film heater, etc., so as to heat up quickly and evenly and be easy to control.

[0117] The circulating test line 5 is used to install the plastic tube sample 6 and forms the flow path for the high-temperature and high-pressure test fluid. A centrifugal pump 51 is installed in the circulating test line 5 to drive the test solution to continuously circulate within the closed loop, ensuring uniform heating and stable pressure of the sample, and enabling dynamic life testing. The outlet of the low-level water tank 3 is sequentially connected to the centrifugal pump 51 and the circulating test line 5 (containing the plastic tube sample 6). The outlet of the circulating test line 5 returns to the inlet of the low-level water tank 3, thus forming a closed loop. The high-level water tank 1 is connected to the low-level water tank 3 via the connecting pipe 31, providing back pressure and compensating for volume changes, but does not participate in the main circulation flow.

[0118] Furthermore, such as Figure 1 and Figure 2 As shown, it also includes:

[0119] The position detection device is used to detect the position height of the liquid in the liquid phase space of the high-level water tank 1 and output a first signal;

[0120] The controller is communicatively connected to the position detection device and is used to acquire the first signal and determine the current volume of the liquid phase space based on the first signal. The position detection device and the controller together form the solution storage detection element 12.

[0121] The position detection device can be a contact type. Alternatively, the position detection device can be configured to non-contactly monitor whether the liquid level has changed and output a first signal indicating that it is full. After receiving this signal, the controller determines that the circulation system is full of liquid, thereby automatically closing the inlet valve 32 and entering the next stage. At this time, a high-temperature and high-pressure resistant transparent liquid level tube can be installed on the outside of the high-level water tank 1. The liquid level tube can be made of quartz glass or sapphire, and the position detection device can be installed on the outside of the high-level water tank 1. The position detection device can be a laser displacement sensor or a fiber optic displacement sensor, etc. The controller can be a programmable logic controller or an embedded microcontroller, etc., installed on the outside of the high-level water tank 1.

[0122] Furthermore, such as Figure 1 and Figure 3 , Figure 4 As shown, it also includes:

[0123] The constant temperature environment chamber 52 has a containment space, and the constant temperature environment chamber 52 is equipped with an optical window. The plastic tube sample 6 is located in the containment space.

[0124] The driving component 53 is connected to the constant temperature environment chamber 52;

[0125] The base 54 is connected to the driving member 53, which is used to drive the base 54 to move along the length direction of the plastic tube sample.

[0126] A detection component 55 is disposed on the base 54. The detection component 55 is annular. The constant temperature environment chamber 52 passes at least partially through the central through hole of the detection component 55 so that the detection end of the detection component 55 is opposite to the optical window. The detection component 55 detects the circumferential geometric data of the plastic tube sample 6 non-contactly through the optical window and generates a second signal.

[0127] The control unit is communicatively connected to the detection component 55 and is used to acquire the second signal and determine dynamic data of deformation parameters changing over time based on the second signal.

[0128] Specifically, the constant temperature environment chamber 52 is used to contain the plastic tube sample and provide it with a sealed high-temperature and high-pressure testing environment. Simultaneously, the constant temperature environment chamber 52 possesses sufficient mechanical strength and safety protection capabilities to effectively isolate the high-temperature and high-pressure medium in the event of sample rupture, ensuring operational safety. Its optical window supports non-contact in-situ monitoring of the sample by the external detection component 55. The window of the constant temperature environment chamber 52 can be made of quartz glass or sapphire.

[0129] The drive unit 53 is connected to the constant temperature environment chamber 52 via a bracket, and there can be one or more drive units 53. When multiple drive units 53 are used, each drive unit 53 is uniformly controlled by the control unit to achieve synchronous operation. The drive unit 53 can be a linear motor or a hydraulic cylinder.

[0130] In one embodiment, the base 54 is generally annular, with a central through-hole on its inner side for the plastic tube sample and the observation section of the constant temperature environment chamber 52 to pass through. In this case, the detection component 55 can be a ring laser profile scanner or a ring machine vision system, and is mounted on the annular base 54. Alternatively, the detection component 55 includes multiple laser displacement sensors or multiple vision sensors, evenly spaced along a circumferential trajectory on the base 54. The constant temperature environment chamber 52 has a continuous annular optical window along the circumference of the detection area, or is composed of multiple arc-shaped optical windows spliced ​​together to support 360° omnidirectional observation.

[0131] In another embodiment, the base 54 includes multiple mounting plates arranged in a ring around the circumference of the plastic tube sample. The number of mounting plates is equal to the number of driving components 53, and the driving end of each driving component 53 is connected to a mounting plate, thereby coordinating to drive the entire base 54 to move smoothly along the length of the tube. In this case, the detection assembly 55 includes multiple laser displacement sensors or multiple vision sensors, the number of which corresponds one-to-one with the number of mounting plates, and each sensor is fixed to its corresponding mounting plate. The constant temperature chamber 52 has multiple strip-shaped optical windows in the detection area, the number of which is equal to the number of sensors and their positions correspond one-to-one, ensuring that each sensor can perform non-contact detection of the plastic tube sample through its respective window.

[0132] The control unit can be a programmable logic controller or an embedded microcontroller, etc.

[0133] The driving component 53 moves the base 54 and the detection component 55 along the length of the plastic tube sample, enabling continuous scanning detection across the entire length of the sample. Combined with annular or circumferentially distributed non-contact sensors, the system can acquire circumferential geometric deformation data. This mobile detection structure significantly improves the spatial coverage density and failure warning sensitivity of the data, making it particularly suitable for capturing the progressive deformation of localized weak areas in plastic tubes under long-term high-temperature and high-pressure cycling. This provides high-dimensional dynamic input for life prediction models, greatly enhancing the scientific validity and engineering guidance value of the test results.

[0134] Furthermore, such as Figure 1 As shown, the connecting pipe 31 is equipped with a first overflow valve 33, and the position of the first overflow valve 33 is higher than the position of the inlet valve 32;

[0135] The elevated water tank 1 is equipped with a first pressure sensor 13 and a second overflow valve 14, with the second overflow valve 14 located in the middle area of ​​the elevated water tank 1.

[0136] The low-level water tank 3 is equipped with a second pressure sensor 34, a second safety valve 35, a dosing device 36, and a circulation pump 37. The two ends of the circulation pump 37 are connected to the low-level water tank 3 and are used to circulate the test solution in the low-level water tank 3 internally.

[0137] The circulating test pipeline 5 includes a main pipeline and multiple parallel branch pipelines. One end of the main pipeline is connected to the low-level water tank 3, and the other end of the main pipeline is connected to the first end of the multiple branch pipelines. The second end of each branch pipeline is connected to the low-level water tank 3.

[0138] The main pipeline is equipped with the centrifugal pump 51, the temperature sensor 56, and the third pressure sensor 57;

[0139] Each of the branch pipes is provided with a pressure regulating valve 58, a fourth pressure sensor 59, a first electric valve 510, the plastic pipe sample 6, a second electric valve 511 and a flow regulating valve 512 in sequence from its inlet end to its outlet end.

[0140] The constant temperature environment chamber 52 is equipped with a water leakage detector 513, which is communicatively connected to the first electric valve 510 and the second electric valve 511, respectively, and is used to control the first electric valve 510 and the second electric valve 511 to close when a leak is detected.

[0141] Specifically, the first overflow valve forms the first predetermined overflow point. The second overflow valve 14 forms the first predetermined overflow point. The first pressure sensor 13 can be installed in the gas phase space of the high-level water tank 1 to monitor the gas phase space pressure in real time and provide feedback signals for back pressure control. The second pressure sensor 34 is used to monitor the pressure of the test solution in the low-level water tank 3 for circulation system pressure regulation. The second safety valve 35 is used to automatically release pressure when the system is overpressured to ensure safety. The dosing device 36 is used to quantitatively add stabilizers, antioxidants, or chemical media simulating actual working conditions to the test solution. The two ends of the circulation pump 37 are connected to the inside of the low-level water tank 3 to internally circulate and stir the solution in the tank before testing to ensure uniform temperature and concentration.

[0142] The number of branches can be specifically designed according to requirements, for example, 6, 12 or even more. Pressure regulating valve 58 is used to adjust the initial pressure entering the corresponding branch; fourth pressure sensor 59 is used to monitor the inlet pressure of the plastic tube sample in the corresponding branch. The plastic tube sample is placed in a constant temperature environment chamber 52 for high-temperature and high-pressure testing. First electric valve 510 is used to control the upstream flow of the plastic tube sample, and second electric valve 511 is used to control the downstream flow. Flow regulating valve 512 is used to adjust the flow rate of the corresponding branch. Leakage detector 513 is installed at the bottom of the constant temperature environment chamber 52 or at key joints to monitor for test solution leakage in real time; once a leakage signal is detected, it immediately sends a shut-off command to the first electric valve 510 and the second electric valve 511, quickly cutting off the flow paths at both ends of the sample to prevent leakage from expanding and ensure safety.

[0143] The specific work process for this application is as follows:

[0144] Install all components and install the plastic tube samples in the constant temperature environment chamber 52 of each branch.

[0145] Open the inlet valve 32 to add water to the low-level water tank 3. When water overflows from the first overflow valve, start the centrifugal pump 51 to continue adding water to the low-level water tank 3. When the pressure of each branch reaches the set pressure value and the first overflow valve overflows water again, continue to run stably for more than half an hour.

[0146] Close the first overflow valve and continue filling with water until the second overflow valve overflows. Continue to run stably for more than half an hour, and then close the second overflow valve. At this time, the entire low-level water tank 3 and the circulation test pipeline 5 are filled with water, and the gas phase space volume of the high-level water tank 1 is 10 liters.

[0147] Set the pressure of pressure reducing valve 21 to 0.12 MPa, start compressor 2, and allow compressed air to enter high-level water tank 1; when the pressure of high-level water tank 1 stabilizes at 0.12 MPa, start heating component 4 to raise the water temperature to the required test temperature, such as 105℃ or 115℃; the water temperature is monitored by temperature sensor 56 of the main pipeline.

[0148] During the test, if the water level in the high-level water tank 1 drops, the heating component 4 and centrifugal pump 51 will be shut down. During the test, if the pressure in both the high-level water tank 1 and the low-level water tank 3 exceeds 0.12 MPa, the first safety valve 11 and the second safety valve 35 will automatically open to release pressure, shutting down the heating component 4 and centrifugal pump 51. When the leak detector 513 detects a leak in the plastic tube sample, the first electric valve 510 and the second electric valve 511 on the corresponding branch will close, ensuring that after the test sample fails, the corresponding branch no longer leaks, and other samples can be tested normally.

[0149] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method of testing the lifetime of a plastic pipe, characterized in that The method comprises the following steps: S1, filling the low-position water tank and the circulating test pipeline connected with the low-position water tank with test solution, and injecting test solution into the high-position water tank connected with the low-position water tank, so that the high-position water tank has a preset initial volume of test solution; wherein the high-position water tank is higher than the low-position water tank by a preset height, and a gas phase space is formed at the top of the high-position water tank; S2, filling the gas phase space with compressed gas, so that the gas phase space of the high-position water tank has a preset pressure, to apply back pressure to the test solution in the low-position water tank; S3, heating the test solution in the low-position water tank to a target test temperature under the back pressure condition; S4, maintaining the back pressure condition and the target test temperature, and performing life test on the plastic pipe sample in the test system; The method of step S1 comprises: S101, injecting test solution into the test system through a water inlet, starting the test system under normal temperature and pressure conditions after test solution overflows from a first predetermined overflow point, and circulating the test solution until the circulation stops after the test solution overflows from the first predetermined overflow point, so that the low-position water tank and the circulating test pipeline are filled with test solution; S102, continuing to inject test solution until test solution overflows from a second predetermined overflow point, so that the high-position water tank has a preset initial volume of test solution; The step S4 further comprises: During the life test, dynamic data of a deformation parameter of the plastic pipe sample changing with time is collected; Based on the dynamic data, the target test temperature, the preset pressure and the failure time measured in the life test, a life prediction model is established; The life prediction model is used to evaluate the service state of the same type of plastic pipe under the same or equivalent working conditions; The method of collecting dynamic data of a deformation parameter of the plastic pipe sample changing with time comprises: Obtaining hoop geometry data of the plastic pipe sample at multiple axial positions through non-contact mobile detection; Based on the change of the hoop geometry data with time, dynamic data of the deformation parameter changing with time is calculated; Wherein, the deformation parameter includes at least one of hoop strain and ovality.

2. The plastic pipe life test method according to claim 1, wherein The evaluation content includes at least one of predicted remaining life and health state grade.

3. The plastic pipe life test method according to claim 1, wherein The total volume of the high-position water tank is not more than 20 L; and / or The initial volume of the test solution is equal to the initial volume of the compressed gas in the gas phase space; and / or The target test temperature is 95℃, 105℃ or 115℃; and / or The preset height is greater than or equal to 20 cm; and / or The high-position water tank and the low-position water tank are connected through a connecting pipeline with a nominal diameter not less than DN50.

4. A plastic pipe life test system for performing the plastic pipe life test method according to any one of claims 1 to 3, characterized in that The method comprises the following steps: A high-position water tank is provided with a first safety valve and a solution inventory detection element; A compressor is connected with the high-position water tank through a pressure reducing valve; A low water tank is communicated with the high water tank through a connecting pipeline; the high water tank is higher than the low water tank by a preset height; the top of the high water tank forms a gas phase space; the connecting pipeline is provided with a water inlet valve; A heating assembly is arranged in the low water tank; A circulating test pipeline is connected with the centrifugal pump and the low water tank in series to form a closed circulation loop, and the circulating test pipeline is used for mounting a plastic pipe sample.

5. The plastic pipe service life testing system according to claim 4, wherein Further comprising: A position detection device is used for detecting the position height of the liquid in the liquid phase space of the high water tank and outputting a first signal; A controller is communicated with the position detection device, used for acquiring the first signal and determining the current volume of the liquid phase space according to the first signal; the position detection device and the controller jointly form the solution inventory detection member.

6. The plastic pipe service life testing system of claim 4, wherein, Further comprising: A constant temperature environment box has a containing space, the constant temperature environment box is provided with an optical window, and the plastic pipe sample is located in the containing space; A driving member is connected with the constant temperature environment box; A base is connected with the driving member, and the driving member is used for driving the base to move along the length direction of the plastic pipe sample; A detection assembly is arranged in the base, the detection assembly is annular, the constant temperature environment box at least partially passes through the central through hole of the detection assembly, so that the detection end of the detection assembly is opposite to the optical window; the detection assembly detects the annular geometric data of the plastic pipe sample through the optical window in a non-contact manner and generates a second signal; A control unit is communicated with the detection assembly, used for acquiring the second signal and determining dynamic data of the deformation parameter changing with time according to the second signal.

7. The plastic pipe service life test system according to claim 6, wherein The connecting pipeline is provided with a first overflow valve, and the position of the first overflow valve is higher than that of the water inlet valve; The high water tank is provided with a first pressure sensor and a second overflow valve, and the second overflow valve is arranged in the middle region of the high water tank; The low water tank is provided with a second pressure sensor, a second safety valve, a dosing device and a circulating pump, two ends of the circulating pump are communicated with the low water tank, and the circulating pump is used for internally circulating the test solution in the low water tank; The circulating test pipeline comprises a main pipeline and a plurality of parallel branch pipelines, one end of the main pipeline is communicated with the low water tank, the other end of the main pipeline is communicated with the first ends of the plurality of branch pipelines, and the second ends of the branch pipelines are all communicated with the low water tank; The main pipeline is provided with the centrifugal pump, a temperature sensor and a third pressure sensor; From the water inlet end to the water outlet end of each branch pipeline, a pressure regulating valve, a fourth pressure sensor, a first electric valve, the plastic pipe sample, a second electric valve and a flow regulating valve are arranged in sequence; A water leakage detector is arranged in the constant temperature environment box, the water leakage detector is communicated with the first electric valve and the second electric valve respectively, and is used for controlling the first electric valve and the second electric valve to be closed when leakage is detected.

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