Device and method for measuring slow tensile test elongation under high-pressure hydrogen environment

Abstract

The invention belongs to the technical field of pipeline steel testing, and discloses a device and a method for measuring the elongation of a slow tensile test in a high-pressure hydrogen environment. The method comprises the following steps: mounting a to-be-tested sample in a hydrogen environment box with a transparent kettle cover on the side wall; charging hydrogen into the hydrogen environment box; and after hydrogen charging, carrying out a slow tensile test on the sample to be tested, and at the same time, carrying out video capture and recording on the gauge length section of the sample in the hydrogen environment box through the transparent kettle cover by using a 3D video extensometer arranged outside the hydrogen environment box. The transparent kettle cover is adopted, the 3D video extensometer is combined, and the tensile displacement of the gauge length section of the sample can be accurately measured through the transparent kettle cover, so that the accurate elongation of the slow tensile test sample is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline steel testing, and more specifically, relates to a device and method for determining elongation of a slow tensile test under a high-pressure hydrogen environment. Background Art

[0002] Hydrogen energy is a green, clean and renewable energy. At present, hydrogen energy storage and transportation mainly uses long-tube trailers to transport high-pressure gaseous hydrogen, supplemented by low-temperature liquid hydrogen and pipeline transportation, and develops in a coordinated manner. According to relevant data, the demand for hydrogen will increase in the future. In particular, for regions and countries where supply and demand are inversely distributed, it will give rise to large-scale hydrogen transportation needs. In the long run, the construction of hydrogen pipelines has been accelerating to achieve coordinated development of different market segments and regions.

[0003] In a hydrogen environment, hydrogen will be adsorbed on the metal surface, dissolved, diffused in the metal, and enriched in specific parts. Some of the adsorbed hydrogen molecules dissociate into atomic hydrogen under the action of activation energy and produce chemical adsorption on the metal surface. Due to the affinity, the dissociated hydrogen atoms enter the vacancies of the metal lattice or the gaps between metal atoms from the metal surface to form a substitutional or interstitial solid solution. With the continuous entry of hydrogen atoms, due to the effect of concentration gradient, hydrogen atoms diffuse in the gaps between metal atoms, so that the hydrogen in the metal matrix reaches a certain concentration, causing hydrogen embrittlement, causing the metal plasticity to decrease, inducing cracks or producing delayed fractures. When pipeline steel is transporting hydrogen-containing media, hydrogen damage to the pipeline is often caused by hydrogen embrittlement. The higher the hydrogen pressure and the higher the strength of the material, the more obvious the hydrogen damage phenomenon is. It is extremely urgent to study the matching hydrogen damage detection and control technology.

[0004] The slow strain rate test is to slowly and uniformly stretch the sample (the sample is in the test solution or gas environment) on a constant strain rate machine until it breaks. After the test, the fracture morphology is analyzed by scanning electron microscopy. During the test, the load-elongation curve is measured, and many parameters reflecting stress corrosion or hydrogen embrittlement sensitivity can be analyzed from the curve. During the slow tensile test, it is necessary to obtain the tensile displacement of the sample gauge section to calculate the elongation of the sample. The tensile displacement recorded by the slow tensile instrument includes the displacement of the tensile machine loading shaft and the clamps at both ends of the sample. Therefore, using the tensile displacement of the tensile machine to calculate the elongation of the sample gauge section will cause a large error.

[0005] At present, there are generally two methods for determining the elongation in slow tensile tests. One is to manually mark the two ends of the gauge section of the specimen in advance, align the fracture surface after the test, and then measure the actual displacement of the gauge section; the other is to use an extensometer to observe the tensile displacement of the gauge section in real time and record the actual tensile displacement. The disadvantage of using the manual marking method to calculate the actual displacement of the gauge section is that manual marking and measurement will cause large errors, and aligning the fracture surface will damage the fracture morphology, affecting the microscopic analysis of the fracture surface. Using an extensometer to record the actual tensile displacement of the gauge section has high measurement accuracy and avoids the influence of the alignment fracture surface step on the fracture morphology. Therefore, using an extensometer to accurately measure the tensile displacement of the gauge section is expected to gradually become the mainstream elongation measurement method for slow tensile tests.

[0006] The essence of extensometer measurement is to measure the deformation of two points. The development of its measurement technology from manual to automatic, and from contact to non-contact has become a trend. Manual electronic extensometers have many disadvantages, such as one gauge length must correspond to one specification, the extensometer measurement device must be installed on the specimen gauge length section before the test, the contact type is prone to slipping and falling off or the flexible material is difficult to clamp, the instrument needs to be removed before measuring the fracture, and the extensometer is large in size.

[0007] The schematic diagram of the mainstream high-pressure hydrogen environment chamber device currently used for slow tensile testing is as follows Figure 1 As shown, this environmental chamber is generally made of austenitic stainless steel. If an existing conventional extensometer is used to measure the tensile displacement of the gauge section, the extensometer must be installed inside the environmental chamber, such as Figure 2 However, the conventional specimen gauge length is generally 30mm, and the maximum elongation can reach 40%, so the maximum tensile displacement that needs to be measured is more than 12mm. At present, the lateral width of the extensometer for measuring the tensile displacement of 12mm is 110mm, and the size cannot be reduced due to the limitation of measurement technology. Figure 2 As shown, if the conventional extensometer is introduced into the environmental chamber, the internal diameter of the environmental chamber will be at least 250 mm, which makes the environmental chamber too large. The volume of hydrogen required for the high-pressure hydrogen test is large, which greatly increases the risk of the test.

[0008] Therefore, in view of the above problems, it is urgent to propose a new device and method for measuring the elongation of a slow tensile test under a high-pressure hydrogen environment. Summary of the invention

[0009] The purpose of the present invention is to address the deficiencies of the prior art and to propose a device and method for determining the elongation of a slow tensile test under a high-pressure hydrogen environment. The present invention uses a transparent kettle cover and combines it with a 3D video extensometer to accurately measure the tensile displacement of the sample gauge section through the transparent kettle cover, thereby obtaining an accurate elongation of the slow tensile test sample.

[0010] In order to achieve the above object, the present invention provides a method for determining the elongation of a slow tensile test under a high-pressure hydrogen environment, the method comprising the following steps:

[0011] S1: Install the sample to be tested into a hydrogen environment box with a transparent kettle cover on the side wall;

[0012] S2: filling the hydrogen environment box with hydrogen;

[0013] S3: After hydrogen filling, a slow tensile test is performed on the test sample. At the same time, a 3D video extensometer arranged outside the hydrogen environment box is used to capture and record the gauge length section of the sample inside the hydrogen environment box through the transparent kettle cover.

[0014] According to the present invention, preferably, the sample to be tested is pipeline steel for transporting hydrogen-containing media.

[0015] According to the present invention, preferably, in step S1, the installation process of the sample to be tested includes:

[0016] Step S11: Open the transparent lid of the hydrogen environment box and put the sample to be tested into it;

[0017] Step S12: Pass one end of the sample to be tested through the top of the hydrogen environment box, and the other end through the bottom of the box, and seal the sample to be tested and the box with a sealing device;

[0018] Step S13: Close the transparent kettle cover.

[0019] In the present invention, as a preferred embodiment, Figure 3 As shown, the sealing device includes a first sealing ring and a second sealing ring, which are respectively installed on the top and bottom of the box body by screw fastening. The middle through hole of the first sealing ring is in sealing contact with the pipeline steel, and the bottom surface of the first sealing ring is in sealing contact with the upper surface of the top of the box body, so as to achieve sealing between the pipeline steel and the top of the box body. The middle through hole of the second sealing ring is in sealing contact with the pipeline steel, and the upper surface of the second sealing ring is in sealing contact with the surface of the bottom of the box body, so as to achieve sealing between the pipeline steel and the bottom of the box body.

[0020] According to the present invention, preferably, in step S2, the hydrogen charging process of the test sample includes:

[0021] Step S21: replacing the internal gas of the box with high-purity nitrogen;

[0022] Step S22: Fill the box with hydrogen and reach a predetermined pressure.

[0023] According to the present invention, preferably, step S21 is repeated 3-5 times to ensure that the oxygen content in the box is lower than the explosion range of hydrogen.

[0024] According to the present invention, preferably, the high-purity nitrogen replacement process is: injecting nitrogen into the box through the inlet pipe of the hydrogen environment box, and at the same time opening the outlet pipe of the hydrogen environment box to discharge the gas inside the box.

[0025] According to the present invention, preferably, the volume of nitrogen injected into the box during the high-purity nitrogen replacement process is n times the volume of the box, where n is a natural number greater than 2.

[0026] According to the present invention, preferably, in step S3, after the test sample is pre-filled with hydrogen in a hydrogen environment box for 3-5 days, a slow tensile tester is connected to both ends of the test sample through threads to perform a slow tensile test.

[0027] In the present invention, the hydrogen environment box is used to simulate the hydrogen pressure environment; the slow tensile test specimen is placed, that is, the pipeline steel is placed in the hydrogen environment box; the slow tensile tester is used to stretch the metal specimen, that is, the pipeline steel is stretched by the slow tensile tester. The slow tensile tester is an instrument for performing the slow tensile test, which is an existing product and will not be described in detail in the present invention.

[0028] Another aspect of the present invention provides a device for measuring the elongation of a slow tensile test under a high-pressure hydrogen environment. The above method is performed in the following measuring device, which includes a 3D video extensometer, a slow tensile tester, and a hydrogen environment box;

[0029] The 3D video extensometer is arranged outside the hydrogen environment box;

[0030] The hydrogen environment box comprises a box body and a transparent kettle cover;

[0031] The box is used to accommodate the sample to be tested; the top and bottom of the box are both provided with openings, which are used for the two ends of the sample to be tested to extend out of the box.

[0032] The transparent kettle cover is arranged on the side of the box body, and is used to enable the 3D video extensometer to capture and record the video of the gauge length section of the sample to be tested inside the hydrogen environment box;

[0033] The box body is provided with an air intake / exhaust pipe.

[0034] According to the present invention, preferably, the shape and structure of the hydrogen environment box is a rectangular parallelepiped structure, and the gas volume is 95-105 ml.

[0035] Since the hydrogen environment box of the present invention is used to store high-pressure hydrogen, the box body and the transparent kettle cover are required to have good structural strength. Therefore, the thickness of the box body and the thickness of the transparent kettle cover are designed according to the maximum hydrogen pressure of the hydrogen environment box. According to the present invention, preferably, the thickness of the box body and the thickness of the transparent kettle cover enable the hydrogen environment box to withstand a pressure of 12-15MPa.

[0036] According to the present invention, preferably, the material of the box body is austenitic stainless steel, and it is strictly forbidden to use ferritic stainless steel and high-strength low-alloy steel that are sensitive to hydrogen embrittlement; the material of the transparent kettle cover is Pam board and / or acrylic transparent plexiglass board.

[0037] According to the present invention, preferably, the 3D video extensometer comprises an imaging device, a light source, a mechanical support adjustment platform, a tripod, and a computer;

[0038] The imaging device is used to enable the 3D video extensometer to capture the video of the gauge length section of the sample inside the hydrogen environment box, and transmit the captured image to the computer in real time;

[0039] The mechanical support adjustment platform is used to support the imaging device; the tripod support is used to support the mechanical support adjustment platform and adjust the height of the imaging device;

[0040] The computer is used to process the image data captured by the imaging device, record the tensile displacement of the gauge length section in real time and calculate the elongation.

[0041] In the present invention, the 3D video extensometer is a new generation of non-contact measurement method based on visual technology. It captures continuous images of the sample during the loading process, tracks the marked object in real time, solves various types of data such as the target's coordinates, displacement, strain, etc., and outputs the measurement results and generates a work report. The 3D video extensometer can communicate data with the testing machine equipment. The measured value is transmitted from the 3D video extensometer to the testing machine through a digital or analog interface, and then the testing machine can record and post-process each measured value like other strain sensors or strain gauges. The 3D video extensometer uses digital image tracking, high precision, arbitrary gauge length measurement, and extremely high reliability.

[0042] According to the present invention, preferably, a high-pressure ball valve is installed on the intake / exhaust pipe, and the high-pressure ball valve is used to control the opening and closing of the intake / exhaust pipe.

[0043] According to the present invention, preferably, a pressure gauge is installed on the hydrogen environment box to monitor the gas pressure in the box in real time.

[0044] The beneficial effects of the technical solution of the present invention are as follows:

[0045] The device of the present invention can realize the compact design of the hydrogen environment box by arranging a transparent kettle cover and a 3D video extensometer. The gas volume inside the hydrogen environment box is 95-105ml, which greatly reduces the release energy of hydrogen in the event of leakage and other accidents, and greatly improves the safety of the test process.

[0046] The device of the present invention can meet the test requirements of the elongation of the slow tensile test in a conventional high-pressure hydrogen environment below 12 MPa.

[0047] The camera of the 3D video extensometer of the present invention can capture and record the gauge length section of the sample through a transparent kettle cover, accurately measure the tensile displacement of the test gauge length section, and obtain accurate elongation of the slow tensile test sample.

[0048] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0050] Figure 1 A schematic diagram showing a high-pressure hydrogen environment chamber apparatus currently used in a slow tensile test.

[0051] Figure 2 A schematic diagram showing an existing conventional extensometer installed inside a high-pressure hydrogen environment box.

[0052] Figure 3 A schematic diagram of a device for measuring elongation of a slow tensile test in a high-pressure hydrogen environment provided in Example 1 of the present invention is shown.

[0053] Figure 4 A left view of a device for measuring the elongation of a slow tensile test in a high-pressure hydrogen environment provided in Example 1 of the present invention is shown.

[0054] Figure 5 A schematic diagram of a 3D video extensometer and related settings of a device for measuring elongation in a slow tensile test under a high-pressure hydrogen environment provided in Example 1 of the present invention is shown.

[0055] The following are the descriptions of the reference numerals:

[0056] 1-box; 2-intake / exhaust pipe; 3-first sealing ring; 4-second sealing ring; 5-support pad; 7-pipeline steel; 8-pressure gauge;

[0057] 301-transparent kettle cover; 302-conventional extensometer; 303-slow tensile tester loading piece; 304-slow tensile tester; 305-imaging device; 306-light source; 307-mechanical support adjustment platform; 308-triangular bracket; 309-computer. DETAILED DESCRIPTION

[0058] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0059] Example 1

[0060] This embodiment provides a method for determining the elongation of a slow tensile test under a high-pressure hydrogen environment, comprising the following steps:

[0061] S1: The sample to be tested is a pipeline steel 7 for transporting hydrogen-containing medium. The sample to be tested is installed in a hydrogen environment box with a transparent kettle cover on the side wall; specifically, the installation process of the sample to be tested includes:

[0062] Step S11: Open the transparent lid of the hydrogen environment box and put the sample to be tested into it;

[0063] Step S12: Pass one end of the sample to be tested through the top of the hydrogen environment box, and the other end through the bottom of the box, and seal the sample to be tested and the box with a sealing device;

[0064] Step S13: Close the transparent kettle cover.

[0065] S2: filling the hydrogen environment box with hydrogen; specifically, the hydrogen filling process of the test sample includes:

[0066] Step S21: high-purity nitrogen is used to replace the internal gas of the box; the high-purity nitrogen replacement process is: nitrogen is injected into the box through the inlet pipe of the hydrogen environment box, and the outlet pipe of the hydrogen environment box is opened to discharge the gas inside the box. Repeat the high-purity nitrogen replacement 3-5 times to ensure that the oxygen content in the box is lower than the explosion range of hydrogen; the volume of nitrogen injected into the box during the high-purity nitrogen replacement process is n times the volume of the box, where n is a natural number greater than 2.

[0067] Step S22: Fill the box with hydrogen and reach a predetermined pressure.

[0068] S3: After the test sample is pre-filled with hydrogen in a hydrogen environment box for 3-5 days, a slow tensile tester is connected to both ends of the test sample through threads, and a slow tensile test is performed on the test sample. At the same time, a 3D video extensometer arranged outside the hydrogen environment box is used to capture and record the sample gauge section inside the hydrogen environment box through the transparent kettle cover.

[0069] The above method is performed in the following measuring device, such as Figure 3-5 As shown, the measuring device includes a 3D video extensometer, a slow stretching instrument 304, and a hydrogen environment box;

[0070] The 3D video extensometer is arranged outside the hydrogen environment box; Figure 4 As shown, the 3D video extensometer includes an imaging device 305, a light source 306, a mechanical support adjustment platform 307, a tripod bracket 308, and a computer 309;

[0071] The imaging device 305 is used to realize the video capture of the gauge length section of the sample inside the hydrogen environment box by the 3D video extensometer, and transmit the captured image to the computer 309 in real time;

[0072] The mechanical support adjustment platform 307 is used to support the imaging device 305;

[0073] The tripod support 308 is used to support the mechanical support adjustment platform 307 and adjust the height of the imaging device 305;

[0074] The computer 309 is used to process the image data captured by the imaging device 305, record the tensile displacement of the gauge length section in real time and calculate the elongation.

[0075] like Figure 3-4 As shown, the hydrogen environment box includes a box body 1 and a transparent kettle cover 301;

[0076] The box 1 is used to accommodate the sample to be tested; the top and bottom of the box 1 are both provided with openings, which are used for the two ends of the sample to be tested to extend out of the box 1 respectively; Figure 3 As shown, the sealing device includes a first sealing ring 3 and a second sealing ring 4, which are respectively installed on the top and bottom of the box body 1 by screw fastening. The middle through hole of the first sealing ring 3 is in sealing contact with the pipeline steel 7, and the bottom surface of the first sealing ring 3 is in sealing contact with the upper surface of the top of the box body 1, so as to achieve sealing between the pipeline steel 7 and the top of the box body 1. The middle through hole of the second sealing ring 4 is in sealing contact with the pipeline steel 7, and the upper surface of the second sealing ring 4 is in sealing contact with the surface of the bottom of the box body 1, so as to achieve sealing between the pipeline steel 7 and the bottom of the box body 1.

[0077] The box 1 is a rectangular parallelepiped structure with a gas volume of 100 ml. The thickness of the box 1 and the thickness of the transparent kettle cover 301 enable the hydrogen environment box to withstand a pressure of 12-15 MPa; the box 1 is made of austenitic stainless steel; and the transparent kettle cover 301 is made of Pam board.

[0078] The transparent kettle cover 301 is arranged on the side of the box body 1, and is used to enable the 3D video extensometer to capture and record the video of the gauge section of the to-be-tested sample inside the hydrogen environment box;

[0079] The box body 1 is provided with an air intake / exhaust pipe 2 .

[0080] A high-pressure ball valve is installed on the intake / exhaust pipe 2 , and the high-pressure ball valve is used to control the opening and closing of the intake / exhaust pipe 2 .

[0081] The hydrogen environment box is provided with a pressure gauge 8 for real-time monitoring of the gas pressure in the box body 1 .

[0082] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for determining the elongation of a slow tensile test under a high-pressure hydrogen environment, characterized in that: The method comprises the following steps: S1: Install the sample to be tested into a hydrogen environment box with a transparent kettle cover on the side wall; S2: filling the hydrogen environment box with hydrogen; S3: After hydrogen filling, a slow tensile test is performed on the test sample. At the same time, a 3D video extensometer arranged outside the hydrogen environment box is used to capture and record the gauge length section of the sample inside the hydrogen environment box through the transparent kettle cover.

2. The method for determining the elongation of a slow tensile test under a high pressure hydrogen environment according to claim 1, wherein: The sample to be tested is a pipeline steel for conveying a hydrogen-containing medium.

3. The method for determining the elongation of a slow tensile test under a high pressure hydrogen environment according to claim 1, wherein: In step S1, the installation process of the sample to be tested includes: Step S11: Open the transparent lid of the hydrogen environment box and put the sample to be tested into it; Step S12: Pass one end of the sample to be tested through the top of the hydrogen environment box, and the other end through the bottom of the box, and seal the sample to be tested and the box with a sealing device; Step S13: Close the transparent kettle cover.

4. The method for determining the elongation of a slow tensile test under a high pressure hydrogen environment according to claim 1, wherein: In step S2, the hydrogen charging process of the test sample includes: Step S21: replacing the internal gas of the box with high-purity nitrogen; Step S22: Fill the box with hydrogen and reach a predetermined pressure.

5. The method for determining the elongation of a slow tensile test under a high-pressure hydrogen environment according to claim 4, wherein: Step S21 is repeated 3-5 times to ensure that the oxygen content in the box is lower than the explosion range of hydrogen; The high-purity nitrogen replacement process is as follows: nitrogen is injected into the box through the inlet pipe of the hydrogen environment box, and at the same time, the outlet pipe of the hydrogen environment box is opened to discharge the gas inside the box.

6. The method for determining the elongation of a slow tensile test under a high-pressure hydrogen environment according to claim 5, wherein: The volume of nitrogen injected into the box during the high-purity nitrogen replacement process is n times the volume of the box, where n is a natural number greater than 2.

7. The method for determining the elongation of a slow tensile test under a high pressure hydrogen environment according to claim 1, wherein: In step S3, after the sample to be tested is pre-filled with hydrogen in a hydrogen environment box for 3-5 days, a slow tensile tester is connected to both ends of the sample to be tested through threads to perform a slow tensile test.

8. A device for measuring elongation of a slow tensile test under a high-pressure hydrogen environment, wherein the method described in any one of claims 1 to 7 is performed in the following measuring device, characterized in that: The measuring device includes a 3D video extensometer, a slow stretching instrument, and a hydrogen environment chamber; The 3D video extensometer is arranged outside the hydrogen environment box; The hydrogen environment box comprises a box body and a transparent kettle cover; The box is used to accommodate the sample to be tested; the top and bottom of the box are both provided with openings, which are used for the two ends of the sample to be tested to extend out of the box. The transparent kettle cover is arranged on the side of the box body, and is used to enable the 3D video extensometer to capture and record the video of the gauge length section of the sample to be tested inside the hydrogen environment box; The box body is provided with an air intake / exhaust pipe.

9. The device for measuring elongation of slow tensile test under high pressure hydrogen environment according to claim 8, wherein: The shape and structure of the hydrogen environment box is a rectangular parallelepiped structure, and the gas volume is 95-105ml; The thickness of the box body and the thickness of the transparent kettle cover are such that the hydrogen environment box can withstand a pressure of 12-15 MPa; The material of the box body is austenitic stainless steel; the material of the transparent kettle cover is Pam board and / or acrylic transparent organic glass board; The 3D video extensometer includes an imaging device, a light source, a mechanical support adjustment platform, a tripod, and a computer; The imaging device is used to enable the 3D video extensometer to capture the video of the gauge length section of the sample inside the hydrogen environment box, and transmit the captured image to the computer in real time; The mechanical support adjustment platform is used to support the imaging device; the tripod support is used to support the mechanical support adjustment platform and adjust the height of the imaging device; The computer is used to process the image data captured by the imaging device, record the tensile displacement of the gauge length section in real time and calculate the elongation.

10. The device for measuring elongation of slow tensile test under high pressure hydrogen environment according to claim 8, wherein: A high-pressure ball valve is installed on the intake / exhaust pipe, and the high-pressure ball valve is used to control the opening and closing of the intake / exhaust pipe; The hydrogen environment box is equipped with a pressure gauge for real-time monitoring of the gas pressure in the box.

Images