An Aging Characterization Method for In-Service Pipelines Based on Ultrasonic Testing

Abstract

This invention discloses a method for characterizing the aging of in-service pipelines based on ultrasonic testing, belonging to the field of pipe aging evaluation technology. First, a thickness-sound velocity mathematical relationship is obtained using a planar calibration block, and then the calibration coefficient of the pipe sample is obtained. Next, the ultrasonic velocity and mechanical properties of the aged pipe sample are tested, and a mathematical model of the correspondence between sound velocity and mechanical property parameters is established. Finally, the sound velocity of the in-service pipeline under test is tested, and after calibration, the sound velocity-mechanical property parameter mathematical relationship is entered to obtain the mechanical property parameters of the in-service pipeline under test. This method is based on the actual technical level in the field of ultrasonic non-destructive testing and is easy to implement; it enables on-site testing and evaluation of the aging state of in-service pipelines in oil fields; during testing, buried pipelines only require excavation and backfilling operations, without sampling and analysis, without damaging the pipeline, without production shutdown, and has minimal impact on production operations. Furthermore, this testing method can be extended to other thermoplastic pipes, with a wide range of applications.

Description

Technical Field

[0001] This invention belongs to the field of pipe aging evaluation technology, specifically relating to an aging characterization method for in-service pipelines based on ultrasonic testing. Background Technology

[0002] Polyethylene (PE) is widely used in oilfield pipelines for transporting oil and water media due to its corrosion resistance, as a base material or lining for stand-alone pressure pipes, internal repair pipes, and composite pipes. However, its service environment is subject to various aging factors, including temperature, mechanical loads, and the physical and chemical effects of the media. Aging causes performance degradation in PE pipes, and in severe cases, can lead to pipeline failure.

[0003] Existing methods for evaluating the aging of polyethylene pipes are mostly designed for municipal water supply and gas pipelines. These methods are based on thermo-oxidative aging or ultraviolet (UV) aging principles, employing analytical techniques such as surface microstructure, oxidation induction time, gel permeation chromatography, and infrared spectroscopy to analyze the aging status of the pipes. However, polyethylene pipelines used in oil fields are buried underground and do not undergo UV aging. Furthermore, the operating conditions of oil field pipelines are complex, and actual aging may not be primarily driven by thermo-oxidative aging. For example, studies on polyethylene pipelines transporting high-temperature oil-containing media have shown that even if the mechanical properties of the pipes have significantly decreased, the test results for oxidation induction time may still meet product standard requirements.

[0004] For pressure pipelines, the most important performance parameter is mechanical property. GB / T 34903.1-2017 stipulates that the rate of change of mechanical properties such as tensile breaking strength, elongation, and elastic modulus should be used as evaluation indicators for the compatibility of thermoplastics with oilfield media. Therefore, testing the changes in mechanical properties is essential for understanding the aging state of polyethylene pipes. Conventional mechanical property testing uses tensile testing, which is a destructive test and not suitable for pipelines in field service. GB / T 38897-2020 specifies ultrasonic volume wave testing technology for elastic modulus, but it is only applicable to block specimens and has strict requirements on specimen thickness, parallelism of the test surface, and roughness, so it is not suitable for the arc-shaped pipe walls of polyethylene pipelines; polyethylene material has high acoustic attenuation, making it impossible to obtain the high-order echoes specified in the standard; in addition, calculating the elastic modulus requires measuring the density and thickness of the specimen, which cannot be done without damaging the polyethylene pipeline. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides an in-service pipeline aging characterization method based on ultrasonic testing. This method is simple to operate and easy to implement; it requires no sampling analysis, does not damage the pipeline, does not require production shutdown, has minimal impact on production operations, and has a wide range of applications.

[0006] This invention is achieved through the following technical solution:

[0007] This invention discloses a method for characterizing the aging of in-service pipelines based on ultrasonic testing, comprising:

[0008] S1: Prepare a planar calibration test block with several thicknesses using pipe fittings of the same material as the in-service pipeline to be tested, and use ultrasonic waves to detect the sound velocity at different thicknesses to establish the mathematical relationship between the thickness and sound velocity of the calibration test block.

[0009] S2: Prepare a pipe sample using pipe fittings of the same specifications and materials as the in-service pipeline to be tested. Use ultrasonic waves to detect the sound velocity of the pipe sample to obtain the measured sound velocity of the pipe sample. Substitute the thickness of the pipe sample into the thickness-sound velocity mathematical relationship established in S1 to obtain the theoretical sound velocity of the pipe sample. Obtain the pipe sample calibration coefficient from the obtained measured sound velocity and theoretical sound velocity of the pipe sample.

[0010] S3: Prepare aged pipe samples using pipe fittings made of the same material as the in-service pipe to be tested. Measure the sound velocity of the aged pipe samples using ultrasound to obtain the measured sound velocity. Substitute the thickness of the aged pipe samples into the thickness-sound velocity mathematical relationship established in S1 to obtain the theoretical sound velocity. Obtain the calibration coefficient for the aged pipe samples from the measured and theoretical sound velocities. Conduct aging tests on the aged pipe samples for different aging cycles to obtain aged pipe samples with different aging cycles. Measure the sound velocity of the aged pipe samples with ultrasound for different aging cycles, and obtain the calibrated sound velocity after calibration using the calibrated coefficient. Perform mechanical property tests on the aged pipe samples with different aging cycles to obtain mechanical property parameters. Establish a mathematical relationship between sound velocity and mechanical property parameters based on the calibrated sound velocity and mechanical property parameters of the aged pipe samples.

[0011] S4: The sound velocity of the in-service pipeline under test is detected by ultrasonic waves, and the calibration coefficient of the pipe sample obtained in S2 is used for calibration. The calibrated sound velocity is substituted into the sound velocity-mechanical performance parameter mathematical relationship established in S3 to obtain the mechanical performance parameters of the in-service pipeline under test, and the aging degree of the in-service pipeline under test is evaluated.

[0012] Preferably, the calibration test block is a stepped test block with ≥4 steps.

[0013] More preferably, the thickness direction of the calibration test block is the wall thickness direction of the pipe fitting.

[0014] Preferably, a transverse wave coupling agent is used when using ultrasonic waves to detect sound velocity, and the transverse wave coupling agent does not react physically or chemically with the material of the in-service pipeline being tested.

[0015] Preferably, when using ultrasound to detect sound velocity, a single-crystal transverse wave straight probe with a frequency of 0.5 to 2.5 MHz is used.

[0016] Preferably, the thickness-sound velocity mathematical relationship established in S1 and the sound velocity-mechanical performance parameter mathematical relationship established in S3 are both linear relationships.

[0017] Preferably, the sound velocity is calculated using the thickness calibration method.

[0018] More preferably, the thickness calibration method is as follows:

[0019] Based on the material of the object being tested, a hypothetical sound velocity is set in the ultrasonic testing instrument; ultrasonic testing is performed on the object to obtain its thickness; based on the actual thickness of the object, the measured sound velocity is obtained using the following formula:

[0020]

[0021] More preferably, the thickness of the calibration block is the actual thickness value obtained by measuring instruments; the thickness of the pipe sample is the largest integer wall thickness value within the tolerance range specified in the pipe product standard.

[0022] Preferably, the mechanical property parameters include tensile strength and tensile modulus of elasticity.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] This invention discloses an ultrasonic testing-based method for characterizing the aging of in-service pipelines. First, a thickness-sound velocity mathematical relationship is obtained using a planar calibration block. Then, this mathematical relationship is used to obtain calibration coefficients for pipe samples. Aged pipe samples are obtained through accelerated testing, and their ultrasonic velocity and mechanical properties are measured to establish a mathematical model of the correspondence between sound velocity and mechanical performance parameters. Finally, the sound velocity of the in-service pipeline under test is measured, and after calibration using the pipe sample calibration coefficients, the sound velocity-mechanical performance parameter mathematical relationship is entered to obtain the mechanical performance parameters of the in-service pipeline under test, thereby evaluating the degree of aging of the pipeline. This method is based on the actual technical level in the field of ultrasonic non-destructive testing and is easy to implement. It uses directly measurable sound velocity values ​​to characterize mechanical performance parameter values ​​that cannot be directly measured, enabling on-site testing and evaluation of the aging state of in-service pipelines in oil fields. For buried pipelines, testing only requires excavation and backfilling, without sampling or analysis, does not damage the pipeline, does not require production shutdown, and has minimal impact on production operations. Furthermore, this testing method can be applied to other thermoplastic pipes, making it widely applicable. Attached Figure Description

[0025] Figure 1 The diagram shows the structure and principle of an ultrasonic testing device.

[0026] Figure 2 This is a schematic diagram of the stepped calibration test block of the present invention;

[0027] Figure 3 This is a schematic diagram of the testing method for the pipe sample of the present invention;

[0028] Figure 4 This is a graph showing the results of a single echo peak test for sound velocity in an embodiment of the present invention. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. These descriptions are intended to explain the invention and not to limit it.

[0030] The ultrasonic testing device used in the ultrasonic testing of this invention is as follows: Figure 1 As shown, the device consists of an ultrasonic testing instrument and a probe, used to test the velocity of ultrasonic waves. The ultrasonic testing instrument should have the functions of a pulse signal generator and an oscilloscope to control the probe to excite ultrasonic waves and to process and display the ultrasonic signals received by the probe. The probe is a single-crystal shear wave straight probe used to excite and receive ultrasonic signals of a specific frequency; the frequency selection range of the probe is 0.5MHz to 2.5MHz, preferably 1.0MHz.

[0031] Calibration test block such as Figure 2 As shown, stepped test blocks with a series of thicknesses are used to calibrate the ultrasonic test results of the pipeline; the calibration test blocks should be made of the same material as the polyethylene pipe; it is recommended to use polyethylene pipe of the same material, large diameter, and large wall thickness to process the calibration test blocks, and the thickness direction of the steps should be consistent with the wall thickness direction of the pipe.

[0032] Pipe samples, such as Figure 3 As shown, it can be a section or a whole polyethylene pipe, or any part of the polyethylene pipe.

[0033] Sound speed testing method

[0034] A specialized transverse wave coupling agent is used to directly couple the probe to the surface of the pipe sample. The coupling agent used should not be absorbed by the polyethylene material, nor should it cause changes in the properties of the polyethylene material, react with the polyethylene material, or damage the polyethylene sample. For pipe samples, the probe is positioned as follows... Figure 3 As shown, it is coupled to the outer surface of the pipe wall and receives the echo signal of the ultrasonic wave on the inner surface of the pipe wall.

[0035] Methods for calculating the speed of sound

[0036] Based on the maximum amplitude (peak value) of a single echo, the echo signal time is determined. The propagation path of the ultrasonic wave is determined by the thickness of the sample, and the speed of sound is calculated. For calibration blocks, the actual thickness of each step is obtained by actual measurement using measuring tools such as vernier calipers and micrometers. For polyethylene pipe samples, the maximum integer wall thickness value within the allowable tolerance range is selected as the thickness based on product standards.

[0037] The thickness calibration method is preferred for calculating sound velocity.

[0038] (a) Set the ultrasonic testing instrument to thickness measurement mode and input an assumed sound velocity, which is recommended to be 1000 m / s for polyethylene pipes;

[0039] (b) Test the sample to obtain the test thickness h′ (unit: mm). For example... Figure 4 As shown, in this example, based on the peak position of a single echo, h′=38.32mm;

[0040] (c) Substitute the actual thickness h (unit, mm) of the sample into the formula to calculate v = 1000h / h′, where v (unit, m / s) is the measured sound velocity of the sample.

[0041] Sound speed calibration method

[0042] The sound velocity measured from the calibration test block can be used directly.

[0043] The sound velocity measured from the pipe sample includes the influence of radians and must be calibrated before use. The calibration method is as follows:

[0044] (a) Test the sound velocity of steps with different thicknesses of the test block and fit the linear relationship between thickness and sound velocity y=ax+b, where y represents "sound velocity" (unit, m / s), x represents thickness (unit, mm), and a and b are constants.

[0045] (b) Measured sound velocity v of the test pipe sample 0测试 (Unit: m / s), and substitute its thickness as x0 into the above formula to calculate the theoretical sound velocity y0 of the corresponding flat tubular sample, and calculate the calibration coefficient α = y0 / v. 0测试 ;

[0046] (c) Measure the sound velocity v of aged pipe samples or in-service pipes under test at different aging cycles. 测试 (Unit: m / s), calculate its speed of sound v = αv 测试 .

[0047] (d) The pipe samples in (b) above and the in-service pipes to be tested in (c) must be of the same specifications and material.

[0048] The steps of the aging characterization method are as follows:

[0049] (a) Aging test. Based on the expected service environment, simulated aging test conditions are designed, and accelerated aging tests are conducted on the aged pipe samples to obtain aged pipe samples with different aging cycles;

[0050] (b) Performance testing. First, the "velocity of sound" of the aged specimens was tested; then, tensile specimens were prepared from the aged pipe specimens of different aging cycles, and the corresponding mechanical properties were tested.

[0051] (c) Establish a mathematical model. Establish a formula relating mechanical performance parameters to sound velocity. Depending on the actual situation, linear, exponential, logarithmic, or polynomial mathematical relationships can be selected. The linear relationship Y = AX + B is recommended, where Y represents mechanical performance parameters such as tensile strength (unit, MPa) and tensile modulus of elasticity (unit, MPa), X represents the sound velocity (unit, m / s), and A and B are constants.

[0052] (d) On-site testing. The sound velocity of the pipeline under test is tested, and the corresponding mechanical performance parameters are calculated using the above mathematical formula. The aging condition of the pipeline is analyzed according to the established judgment principles.

[0053] (e) If the relationship between “pipeline service life and mechanical properties” is obtained by combining the Arrhenius formula when designing aging tests, the remaining service life of the pipeline can be evaluated by the sound velocity of the pipeline under test.

[0054] (f) The specifications of the pipe samples for aging tests and mathematical modeling can be different from those of the in-service pipes to be tested, but the materials and manufacturing processes must be consistent.

[0055] The present invention will be further explained and illustrated below with a specific embodiment:

[0056] Test subjects and objectives

[0057] An aging assessment was conducted on an in-service buried polyethylene pipeline in an oil field. The pipeline specification is d. n 200SDR11, made of PE100 grade polyethylene, conforms to product standard GBT 13663.2-2018. It transports oily wastewater at atmospheric pressure, operates at 60℃, and has a service life of 5 years. According to the requirements in Table 7 of GBT 34903.1-2017, a 20% decrease in the axial tensile strength or tensile modulus of elasticity is used as a threshold to determine whether the pipeline has undergone severe aging. Relevant regulations regarding tensile strength and tensile modulus of elasticity are found in GB / T1040.1-2018.

[0058] Test device

[0059] The Olympus EPOCH 650 digital ultrasonic flaw detector was selected, along with the SN1P13 1MHz shear wave straight probe and 6JS0124 shear wave dedicated coupling agent from Guangzhou Duopule Electronic Technology Co., Ltd.

[0060] Calibration block preparation

[0061] The specification is d n The calibration test block is made from 500 SDR11 polyethylene pipe of grade PE100. The calibration test block has 4 steps with thicknesses of 20mm, 25mm, 30mm and 35mm respectively.

[0062] Establish the sound velocity-thickness relationship of the calibration block

[0063] The sound velocity corresponding to each step of the calibration block was tested, and the data were linearly fitted to establish the mathematical relationship between the thickness and sound velocity of the calibration block, as shown in Table 1.

[0064] Table 1

[0065]

[0066] Aging test

[0067] For ease of operation and subsequent analysis, the aging pipe sample was selected with a specification of d. n The polyethylene pipes used were 90 SDR11 grade, PE100 grade, and conformed to the product standard GBT 13663.2-2018. Each aged pipe sample was 1m long. An aging test was designed based on the service conditions of the in-service pipelines to be tested: the aged pipe samples were filled with 0# diesel oil, sealed at both ends, and placed in an 80℃ water bath. The aging cycles were 1 week, 2 weeks, 4 weeks, 6 weeks, and 8 weeks.

[0068] Performance testing

[0069] After the aging test, 20cm was cut off from both ends of the aged pipe specimen, and the remaining 40cm length was used for tensile property testing. Type I tensile specimens were prepared according to GB / T 8804.3-2003 "Determination of Tensile Properties of Thermoplastic Pipes - Part 3: Polyolefin Pipes". Tensile properties of the Type I specimens were tested according to GB / T 1040.2-2006 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics". The remaining 20cm length of the aged pipe specimen was used for sound velocity testing.

[0070] Following the above steps, select specification d. n 200 SDR11, pipe samples were made from PE100 grade polyethylene pipes.

[0071] The tensile properties of the aged pipe samples after different aging cycles are shown in Table 2. The data are rounded to the nearest integer.

[0072] Table 2

[0073]

[0074] When performing sound velocity testing, refer to product standard GB / T 13663.2-2018: Table 3 Nominal Wall Thickness, d n The nominal wall thickness corresponding to 90SDR11 and PE100 grades is 8.2 mm; the maximum tolerance corresponding to the nominal wall thickness of 8.2 mm in "Table 4 Wall Thickness Tolerance at Any Point" is 1.0 mm. Therefore, the thickness of the aged pipe sample is taken as 9.0 mm, i.e., x0 = 9.0. Substituting x0 = 9.0 into the linear equation in Table 1, we have y0 = 986. The measured sound velocity v of the aged pipe sample... 0测试 =1050m / s, therefore the calibration coefficient α for the aged pipe sample is... 90 =986 / 1050=0.94.

[0075] Similarly, for the in-service pipeline d to be tested... n The thickness of the pipe sample corresponding to 200 SDR11 is 20.0 mm, and the measured sound velocity v is... 0测试 =991m / s, and therefore the pipe sample calibration coefficient α 200 =993 / 991=1.003.

[0076] The sound velocity test results of aged pipe samples with different aging cycles are shown in Table 3. The data are rounded to the nearest integer.

[0077] Table 3

[0078]

[0079] Establishing mathematical relationships

[0080] Based on the data in Tables 2 and 3, establish the linear relationships between sound velocity and tensile strength, and between sound velocity and tensile modulus of elasticity:

[0081] The linear relationship between sound velocity and tensile strength is: Y = 0.0186X + 6.0913, R 2 =0.9466, where Y represents tensile strength (unit, MPa) and X represents the speed of sound (unit, m / s);

[0082] The linear relationship between sound velocity and tensile modulus of elasticity is: Y = 1.2854X - 456.15, R 2 =0.9373, where Y represents tensile strength (unit, MPa) and X represents the speed of sound (unit, m / s).

[0083] Field test

[0084] The sound velocity was measured on the in-service pipeline under test at the site, and the measured sound velocity was 910 m / s. The calibration coefficient α was then used. 200The calibration was performed using a value of 1.003, yielding a calibrated sound velocity of 911 m / s. Substituting this calibrated sound velocity value into the linear relationships between sound velocity and tensile strength and between sound velocity and tensile modulus of elasticity, respectively, the mechanical performance parameters of the in-service pipeline under test were obtained. The results were rounded to integers.

[0085] The tensile strength is 23 MPa, which is 4% lower than the 24 MPa data for the non-in-service pipes in Table 2; the tensile modulus of elasticity is 715 MPa, which is 16% lower than the 855 MPa data for the non-in-service pipes in Table 2.

[0086] Aging assessment

[0087] Based on the decrease of less than 20% in tensile strength and tensile modulus of elasticity calculated from sound velocity, it is determined that the polyethylene pipes in service have not undergone significant aging and do not require sampling and testing, and can continue to be used. However, since the decrease in tensile modulus of elasticity is close to the threshold, it is recommended to conduct ultrasonic testing during excavation next year.

[0088] It should be noted that the present invention is not limited to the above embodiments, and any obvious improvements or modifications made by those skilled in the art to the above embodiments will not exceed the scope of the concept of the present invention and the protection scope of the appended claims.

Claims

1. An in-service pipeline aging characterization method based on ultrasonic detection, characterized in that, The method comprises the following steps: S1: a flat calibration block with several thickness parts is prepared by using a pipe fitting with the same material as the in-service pipeline to be detected, the sound velocity at different thicknesses is detected by using ultrasonic waves, a thickness-sound velocity mathematical relationship of the calibration block is established, and the thickness direction of the calibration block is the wall thickness direction of the pipe fitting; S2: a pipe sample is prepared by using a pipe fitting with the same specification and material as the in-service pipeline to be detected, the sound velocity of the pipe sample is detected by using ultrasonic waves, the actual measured sound velocity of the pipe sample is obtained, the thickness of the pipe sample is substituted into the thickness-sound velocity mathematical relationship established in S1 to obtain the theoretical sound velocity of the pipe sample, and the calibration coefficient of the pipe sample is obtained from the actual measured sound velocity and the theoretical sound velocity of the pipe sample; S3: an aging pipe sample is prepared by using a pipe fitting with the same material as the in-service pipeline to be detected, the sound velocity of the aging pipe sample is detected by using ultrasonic waves, the actual measured sound velocity of the aging pipe sample is obtained, the thickness of the aging pipe sample is substituted into the thickness-sound velocity mathematical relationship established in S1 to obtain the theoretical sound velocity of the aging pipe sample, the calibration coefficient of the aging pipe sample is obtained from the actual measured sound velocity and the theoretical sound velocity of the aging pipe sample, aging tests are performed on the aging pipe sample in different aging periods to obtain aging pipe samples in different aging periods, the sound velocities of the aging pipe samples in different aging periods are detected by using ultrasonic waves, the calibrated sound velocities of the aging pipe samples are obtained after calibration by using the calibration coefficient of the aging pipe sample, the mechanical performance parameters of the aging pipe samples in different aging periods are obtained by performing mechanical performance tests on the aging pipes in different aging periods, and a sound velocity-mechanical performance parameter mathematical relationship is established according to the calibrated sound velocities of the aging pipe samples and the mechanical performance parameters; S4: the sound velocity of the in-service pipeline to be detected is detected by using ultrasonic waves, the calibration coefficient of the pipe sample obtained in S2 is used for calibration, the calibrated sound velocity is substituted into the sound velocity-mechanical performance parameter mathematical relationship established in S3 to obtain the mechanical performance parameters of the in-service pipeline to be detected, and the aging degree of the in-service pipeline to be detected is evaluated.

2. The ultrasonic detection based in-service pipeline aging characterization method of claim 1, wherein, The calibration block is a stepped block, and the number of steps is greater than or equal to 4.

3. The ultrasonic detection based in-service pipeline aging characterization method of claim 1, wherein, When the sound velocity is detected by using ultrasonic waves, a transverse wave coupling agent is used, and the transverse wave coupling agent does not have physical or chemical reactions with the material of the in-service pipeline to be detected.

4. The ultrasonic detection based in-service pipeline aging characterization method of claim 1, wherein, When the sound velocity is detected by using ultrasonic waves, a single-crystal transverse wave straight probe with a frequency of 0.5-2.5 MHz is used.

5. The ultrasonic detection based in-service pipeline aging characterization method of claim 1, wherein, The thickness-sound velocity mathematical relationship established in S1 and the sound velocity-mechanical performance parameter mathematical relationship established in S3 are linear relationships.

6. The ultrasonic detection based in-service pipeline aging characterization method of claim 1, wherein, The sound velocity is calculated by using the thickness calibration method.

7. The ultrasonic detection based in-service pipeline aging characterization method of claim 6, wherein, The thickness calibration method specifically comprises the following steps: The assumed sound velocity is set in the ultrasonic detector according to the material of the detection object, the detection object is detected by using ultrasonic waves to obtain the detection thickness of the detection object, and the actual measured sound velocity of the detection object is obtained by using the following formula according to the actual thickness of the detection object: 。 8. The ultrasonic detection-based in-service pipeline aging characterization method of claim 7, wherein, The thickness of the calibration block is the actual thickness value detected by using a measuring tool, and the thickness of the pipe sample is the maximum integer wall thickness value in the tolerance range specified in the pipe product standard.

9. The ultrasonic detection based in-service pipeline aging characterization method of claim 1, wherein, The mechanical performance parameters include tensile strength and tensile elastic modulus.

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