CN107367432A - The ageing test apparatus and life-span prediction method of PE pipelines under a kind of surge pressure - Google Patents

Abstract

The invention relates to an aging test device for PE pipelines under fluctuating pressure. The gas load of the entire pipeline is provided by a pressure supply device, and the air pressure in the pipeline is adjusted through the joint action of a pressure sensor, an electric control valve and a central controller. During the pressure injection and pressure relief process, a fatigue cyclic load is formed, and the test pipe section is aged through an aging device. This device has changed the previous single-factor aging research, and combined various environmental stresses to form a simulated urban natural gas pipeline. working laboratory environment. The present invention also relates to a method for predicting the aging life of PE pipes under fluctuating pressures. The aging pipe samples are taken out after a specific period, and the mechanical properties and physical and chemical properties are tested to obtain relevant data, which are used to measure the temperature of any environment and any pipeline. Compared with the previous method, the aging performance change has the advantages of simplicity, high efficiency and low cost.

Description

An aging test device and life prediction method for PE pipes under fluctuating pressure

technical field

The invention relates to the technical field of PE pipeline detection, in particular to an aging test device and a service life prediction method for PE pipelines under fluctuating pressure.

Background technique

Polyethylene (PE) is a high-molecular polymer widely used in the fields of gas transmission and water supply. It has good mechanical properties and excellent corrosion resistance. It has been put into production application in large quantities. However, in the installation and use of polyethylene (PE) pipes, it is inevitable that there will be damage caused by corrosion, microbial decomposition, thermo-oxidative aging and third-party construction reasons. The aging failure problem is particularly noteworthy. However, in recent years, aging research Among them, the fatigue effect caused by the fluctuating gas load on the pipeline during gas transmission under actual working conditions is often ignored, resulting in a large deviation between the research results and the actual situation. Therefore, it is necessary to develop a pipeline aging test device and life prediction method that are more in line with actual working conditions.

Contents of the invention

Based on this, the object of the present invention is to provide an aging test device for PE pipes under fluctuating pressure, which combines various environmental factors and is more in line with actual working conditions.

Another object of the present invention is to provide a method for predicting the aging life of PE pipes under fluctuating pressure, by which the life of PE pipes can be predicted, and a theoretical reference can be provided for engineering use.

The object of the present invention is achieved through the following technical solutions: an aging test device for PE pipelines under fluctuating pressure, comprising a pressure supply device, a first pipeline, a second pipeline, an aging device and a pressure regulating device, the pressure supply The device and the aging device are connected through the first pipeline and the second pipeline to form a circulation loop, and the test pipe section is placed in the aging device; the pressure regulating device includes a first pressure sensor, a first electric control valve, a second pressure sensor , the second electric control valve and the central controller, the first pressure sensor and the first electric control valve are arranged on the first pipeline, the second pressure sensor and the second electric control valve are arranged on the second pipeline, so The central controller is electrically connected to the first pressure sensor, the first electric control valve, the second pressure sensor, and the second electric control valve, and the central controller receives the signal of the first pressure sensor to control the first electric control valve. Opening and closing, the central controller receives the signal of the second pressure sensor to control the opening and closing of the second electric control valve.

Compared with the prior art, the present invention provides the gas load of the entire pipeline through the pressure supply device, adjusts the air pressure in the pipeline through the joint action of the pressure sensor, the electric control valve and the central controller, and repeats the pressure injection and pressure relief process to form Fatigue cyclic load, and aging of the test pipe section through the aging device, thus providing a pipeline aging test device under fluctuating pressure, this device has changed the previous single-factor aging research, and combined multiple environmental stresses to form a A laboratory environment that simulates the actual working conditions of urban natural gas pipelines is more applicable to actual situations.

Further, a decompression valve is also provided on the first pipeline, and the decompression valve is connected with the aging device. As a safety device, the pressure reducing valve plays the role of controlling the pressure in the pipeline not to exceed the preset value, preventing the safety hazard caused by the surge of internal air pressure.

Further, a clamp is also provided in the aging device, and the clamp includes a clamp hoop and a clamp head; a sealing collar is provided in the clamp hoop; the clamp head is provided with an opening . The hoop of the fixture is used to closely fit and connect with the test pipe section, and the head of the fixture is provided with openings to meet the needs of gas transmission and pressure relief of the connecting pipeline.

Further, a sealing ring is provided between the first pipeline, the second pipeline and the aging device. The sealing ring is used to ensure the sealing performance between the pipeline and the aging device and the constant environment in the aging device.

Further, the aging device is an oven. The oven plays the role of heating, providing high-temperature environmental stress, and aging the test pipe section.

Further, the pressure supply device is a compressor. As a gas generating device, the compressor provides gas load for the pipeline, and also acts as an air extraction device to ensure that the gas load in the pipeline fluctuates within a certain range.

Further, the central controller is a PLC controller. Each parameter value is set through PLC programming, and the pressure change in the pipeline is controlled according to the feedback signal of the pressure sensor.

The present invention also provides a method for predicting the aging life of PE pipes under fluctuating pressures. The method is based on the aging test device described in the present invention and includes the following steps:

S1: Under the conditions of fluctuating pressure and temperature T _i , carry out aging test on the sample;

S2: After the aging test is over, measure the elongation at break δ _i of the sample at T _i temperature;

S3: Taking 50% of the elongation at break δ _i of the sample as the end of life of the sample material, calculate the life t _{i of the sample at the temperature T i ;}

S4: Perform data processing to obtain the functional relationship between life t _i and temperature T _i , so as to predict the life of the sample material at any temperature;

Among them, the value of i is 1, 2, 3, ..., N, and N is the number of test points.

Compared with the prior art, the present invention predicts the aging life of the pipeline under fluctuating pressure. Since the fluctuating gas will cause fatigue to the pipeline during gas transmission, the present invention performs aging under the condition that the fluctuating pressure forms a fatigue load on the pipeline The test is more in line with actual working conditions; moreover, the functional relationship between life and temperature obtained through the aging life prediction method of the present invention can predict the life of materials at any temperature, and has the advantages of simplicity, high efficiency and low cost.

Further, in step S1, the fluctuating pressure changes in a pressurized-unpressurized cycle, or changes in a sine wave, or changes in a rectangular wave.

Further, the time ratio of the pressurized-unpressurized cycle change is 1:1˜1:3.

Further, in step S4, use the Arrhenius equation lnt _i =A+B/T _i to process the data, set lnt _i =y _i , 1/T _i = _xi , and the calculation formula of the slope B is: The formula for calculating the intercept A is: Thus, the functional relationship between life and temperature is obtained.

For better understanding and implementation, the present invention will be described in detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is a structural schematic diagram of an aging test device for PE pipes under fluctuating pressure according to an embodiment.

Fig. 2 is a schematic structural diagram of the jig of the embodiment.

Fig. 3 is an aging diagram of material properties in the case of a pressurized-unpressurized time ratio of 1:1 in the embodiment.

Fig. 4 is an aging diagram of material properties under the condition that the pressurized-unpressurized time ratio of the embodiment is 1:3.

detailed description

Please refer to FIG. 1 , which is a structural schematic diagram of an aging test device for PE pipes under fluctuating pressure in this embodiment. The aging test device includes a compressor 1, a pipeline 2, an oven 6, a first pressure sensor 4, a first electric control valve 3, a second pressure sensor 8, a second electric control valve 9, a central controller 10 and a pressure reducing valve 5.

The compressor 1 and the oven 6 are connected through a pipeline 2 to form a circulation loop, and the test pipe section 7 is placed in the oven 6 .

Specifically, the compressor 1 serves as a gas generating device to provide a gas load for the pipeline, and also serves as an air extraction device to ensure that the gas load in the pipeline fluctuates within a certain range. The oven 6 plays the role of heating, providing high-temperature environmental stress to age the test pipe section 7 . A sealing ring is tightly fitted between the pipeline 2 and the oven 6 to ensure the sealing performance and to ensure a constant temperature environment in the oven 6 .

Further, a fixture 11 is also provided in the oven 6 for clamping the test pipe section 7 . The fixture 11 is resistant to high temperature, ensuring that under high temperature, the deformation stress generated between the fixture 11 and the test pipe section will not affect the smooth progress of the experiment. In this embodiment, the jig 11 has nine branches and is used to clamp multiple parallel samples to ensure the scientificity of the experimental data. Please refer to FIG. 2 , which is a schematic structural diagram of the fixture 11 . Specifically, the fixture 11 includes a fixture hoop 13 and a fixture head 12, the fixture hoop 13 is used to closely fit and connect with the test pipe section 7, and a sealing collar is provided inside to ensure good sealing performance; the fixture seal The head 12 is provided with openings, in order to cooperate with the needs of the gas transmission and pressure relief of the connecting pipeline.

The pipeline 2 includes a first pipeline and a second pipeline. The first pressure sensor 4 and the first electric control valve 3 are arranged on the first pipeline, and the second pressure sensor 8 and the second electric control valve 9 are arranged on the second pipe. On the road, the central controller 10 is electrically connected to the first pressure sensor 4 , the first electric control valve 3 , the second pressure sensor 8 , and the second electric control valve 9 respectively.

Specifically, the first pressure sensor 4 and the second pressure sensor 8 are used to monitor the air pressure inside the pipeline, convert the air pressure signal into an electrical signal, and then transmit it to the central controller 10 . When the central controller 10 receives the signal from the first pressure sensor 4, it adjusts the first electric control valve 3 to control the opening and closing of the first electric control valve 3; the central controller 10 receives the signal from the second pressure sensor 8 When the signal is received, the second electric control valve 9 is adjusted to control the opening and closing of the first electric control valve 9 . In this embodiment, the central controller 10 is implemented by PLC programming, and each parameter value is set. When the pressure change in the pipe reaches the threshold value, the central controller 10 receives the feedback signal from the pressure sensor and controls the opening and closing of the electric control valve. The pipeline section is charged and discharged to control the pressure in the pipeline to change within a certain range.

The pressure reducing valve 5 is arranged on the first pipeline and is connected with the oven 6 . Specifically, the pressure reducing valve 5 is sealed by high-temperature sealing rubber, which plays a role in controlling the pressure in the pipeline not to exceed a preset value, prevents potential safety hazards caused by a surge in internal air pressure, and at the same time ensures the safety of experimenters.

The working principle of this embodiment is: the compressor 1 is used as a power device to deliver the gas load to the aging test device of the entire PE pipeline through the pipeline 2, providing the gas load of the entire pipeline; the central controller 10 and the first pressure sensor 4 , the first electric control valve 3, the second pressure sensor 8, and the second electric control valve 9 together constitute a pressure regulation system, and when it is detected that the pressure change in the pipe reaches a threshold value, the first electric control valve 3 is controlled to open for pressure delivery, or , to control the opening of the second electric control valve 9 for pressure relief. Specifically, the second electric control valve 9 is closed in the initial state, and the gas in the test pipe section 7 is pressurized. When the calibration pressure is reached, the first electric control valve 3 and the compressor 1 are closed to form a stable load, which is maintained under the control of the central controller 10. A period of time; then by controlling the second electric control valve 9 to release pressure, the central controller 10 is provided with a cycle program to form a fatigue cycle load; heated by the aging oven 6 to form a high temperature environmental stress, and the test pipe section 7 is aged.

Compared with the prior art, the present invention provides the gas load of the entire pipeline through the pressure supply device, adjusts the air pressure in the pipeline through the joint action of the pressure sensor, the electric control valve and the central controller, and repeats the pressure injection and pressure relief process to form Fatigue cyclic load, and aging of the test pipe section through the aging device, thus providing a pipeline aging test device under fluctuating pressure, this device has changed the previous single-factor aging research, and combined multiple environmental stresses to form a A laboratory environment that simulates the actual working conditions of urban natural gas pipelines is more applicable to actual situations.

Based on the above-mentioned aging test device, this embodiment also provides a method for predicting the aging life of PE pipes under fluctuating pressures. Under fluctuating pressures and at different temperatures, three groups of parallel test pipe sections are taken out at three time points. To test its mechanical properties and physical and chemical properties, it specifically includes the following steps:

Step 1: Place three groups of samples at each temperature, corresponding to three sampling time points, and each group of samples includes three parallel samples;

Step 2: Take out the samples at three sampling time points, measure their elongation at break, and take the average among three parallel samples in each group to obtain δ ₁ , δ ₂ , δ ₃ , and other relevant physical and chemical properties ;

Step 3: Take 50% of the elongation at break of each group as the end of the life of the sample material, draw a regression curve between life and elongation at break, and predict the end of life t ₁ , t ₂ , t ₃ at each temperature ;

Step 4: The end of life corresponding to each temperature is shown in the table below:

temperature(°C) T ₁ T ₂ T ₃ lifespan (h) t ₁ t ₂ t ₃

Use the Arrhenius equation lnt=A+B/T to process the above data, let lnt=y, 1/T=x, the calculation formula of the slope B is: The formula for calculating the intercept A is: Thus, the functional relationship between life and temperature is obtained, and the life of the sample material at any temperature can be predicted according to the functional relationship.

Compared with the prior art, the present invention predicts the aging life of the pipeline under fluctuating pressure. Since the fluctuating gas will cause fatigue to the pipeline during gas transmission, the present invention performs aging under the condition that the fluctuating pressure forms a fatigue load on the pipeline The test is more in line with actual working conditions; moreover, the functional relationship between life and temperature obtained through the aging life prediction method of the present invention can predict the life of materials at any temperature, and has the advantages of simplicity, high efficiency and low cost.

Based on the above-mentioned aging test device, the change mode of the gas load during the test is changed, and the aging test results are studied, and the comparison is as follows:

Comparative experiment 1: Under constant temperature (80°C) and constant pressure amplitude (0.8MPa), the pressure change is controlled by PLC programming, so that the pressure changes according to the pressurized-no-pressurized cycle, and the time ratio is 1:1 and 1:3 respectively. Change, the aging time is 800h, and the aging results of the sample materials are obtained. Please refer to Figure 3 and Figure 4, which are the aging diagrams of material properties under the conditions of pressurized-unpressurized time ratios of 1:1 and 1:3, respectively. It can be seen from the figure that the force-time curves in the two cases are obviously different, the maximum load changes, and the material ages faster when the pressurized-unpressurized time ratio is 1:1.

Comparative experiment 2: Under constant temperature (80°C), constant pressure amplitude (0.8MPa), and constant change period (1200s), through PLC programming control, change the gas load loading form, load sine wave pressure and rectangular wave pressure respectively, and aging The time is 800h, record the maximum tensile strength. The results show that the maximum tensile strength is 1690N under the sine wave loading form, and 1860N under the rectangular wave loading form. It can be concluded that under the sine wave loading mode, the material ages faster.

The above-mentioned embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it should not be understood as limiting the patent scope of the invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims (10)

1. A kind of 1. ageing test apparatus of PE pipelines under surge pressure, it is characterised in that：Including pressure supply device, the first pipeline, Two pipelines, aging equipment and regulator, the pressure supply device and aging equipment connect shape by the first pipeline and the second pipeline Into circulation loop, test section is placed in the aging equipment；The regulator includes first pressure sensor, first electronic Control valve, second pressure sensor, the second motor-operated control valve and central controller, the first pressure sensor and first electronic Control valve is on the first pipeline, and the second pressure sensor and the second motor-operated control valve are on the second pipeline, in described Pivot controller is electrically connected with first pressure sensor, the first motor-operated control valve, second pressure sensor, the second motor-operated control valve respectively Connect, the central controller receives the signal of first pressure sensor to control the opening and closing of the first motor-operated control valve, the maincenter Controller receives the signal of second pressure sensor to control the opening and closing of the second motor-operated control valve.
2. 2. ageing test apparatus according to claim 1, it is characterised in that：Pressure-reducing valve is additionally provided with first pipeline, The pressure-reducing valve is connected with aging equipment.
3. 3. ageing test apparatus according to claim 1, it is characterised in that：Fixture, institute are additionally provided with the aging equipment Stating fixture includes fixture garter spring and fixture end socket；Sealing necklace is provided with the fixture garter spring；The fixture end socket is provided with perforate.
4. 4. ageing test apparatus according to claim 1, it is characterised in that：First pipeline, the second pipeline and aging Sealing ring is provided between device.
5. 5. ageing test apparatus according to claim 1, it is characterised in that：The aging equipment is baking oven；The voltage supply Device is compressor.
6. 6. ageing test apparatus according to claim 1, it is characterised in that：The central controller is PLC.
7. 7. the aging life-span Forecasting Methodology of PE pipelines under a kind of surge pressure, the aging life-span Forecasting Methodology are based on claim 1 Described ageing test apparatus, it is characterised in that：Comprise the following steps：

   S1：It is T in surge pressure and temperature_iUnder conditions of, degradation is carried out to sample；

   S2：After degradation terminates, T is measured_iAt a temperature of sample elongation at break δ_i；

   S3：With the elongation at break δ of sample_i50% end of life as sample material, calculate T_iAt a temperature of sample life-span t_i；

   S4：Data processing is carried out, obtains life-span t_iWith temperature T_iFunctional relation, to predict the sample material under arbitrary temp Life-span；

   Wherein, i value 1,2,3 ..., N, N for experiment count.
8. 8. aging life-span Forecasting Methodology according to claim 7, it is characterised in that：In step S1, the surge pressure is pressed Pressurization-without pressure mechanical periodicity, or sine wave change, or square wave change.
9. 9. aging life-span Forecasting Methodology according to claim 8, it is characterised in that：The pressurization-without pressure mechanical periodicity Time ratio is 1:1~1:3.
10. 10. aging life-span Forecasting Methodology according to claim 7, it is characterised in that：In step S4, A Leiniwusi is utilized Equation lnt_i=A+B/T_i, data are handled, make lnt_i=y_i, 1/T_i=x_i, slope B calculation formula is：Intercept A calculation formula is：So as to obtain life-span and temperature Functional relation.