Method for efficiently determining constant load fracture toughness of hydrogen transmission pipeline material in high-pressure hydrogen environment

Abstract

The present application relates to hydrogen energy transportation and material mechanical property testing technical field, specifically to a kind of high-pressure hydrogen environment hydrogen transportation pipeline material constant load fracture toughness efficient determination method, by precasting the crack depth corresponding to different stress intensity factor level in two compact tension specimens respectively, and using orifice plate to mechanically connect the two, make two specimens simultaneously bear the same constant tensile load in high-pressure hydrogen environment, and after the fracture of any specimen, load can still be stably transmitted to another specimen, so that the crack propagation response data under two different crack depths in single constant load test is simultaneously obtained.The present application effectively utilizes the test time resources, and makes the test efficiency more than doubled.

Description

Technical Field

[0001] This application relates to the field of hydrogen energy transportation and material mechanical property testing technology, specifically to an efficient method for determining the fracture toughness of hydrogen pipeline materials under constant load in a high-pressure hydrogen environment. Background Technology

[0002] Long-distance pipeline hydrogen transportation is a crucial pathway for achieving large-scale, efficient hydrogen energy delivery, helping to reduce storage and transportation costs and promoting the healthy development of the hydrogen energy industry. However, under high pressure, hydrogen is easily adsorbed and dissociated into hydrogen atoms on the surface of pipeline materials, which diffuse into the metal lattice, leading to hydrogen embrittlement and significantly reducing its fracture toughness, thus threatening the service safety of hydrogen pipelines. Therefore, accurately determining the constant-load fracture toughness of pipeline materials under high-pressure hydrogen conditions is a key step in evaluating the hydrogen environment compatibility of materials. Currently, the constant-load fracture toughness test is the most accurate method for simulating the long-term service stress state of hydrogen pipelines. Its typical procedure involves: sampling and machining a compact tensile specimen from the pipeline material, pre-fabricating an initial crack (usually 0.5W), applying a constant load in a high-pressure hydrogen environment, maintaining it for several hours to over a thousand hours, and determining the fracture toughness threshold value of the material by monitoring crack propagation behavior. The test typically requires multiple load levels (e.g., 0.6K). Q 0.7K Q 0.8K Q 0.9K Q The tests were conducted separately at different load levels, with each load level corresponding to an independent specimen, and each test cycle lasting no less than 1000 hours, in order to fully expose the hydrogen-induced crack initiation and propagation process.

[0003] In the aforementioned traditional techniques, each load level requires a separate specimen and independent constant load testing lasting over a thousand hours, resulting in enormous resource consumption, lengthy cycles, and inconsistent environmental conditions (such as hydrogen purity, temperature fluctuations, and loading stability) across different test batches, leading to poor data comparability. Furthermore, obtaining an accurate fracture toughness threshold often necessitates trial-and-error testing at multiple load levels to gradually approach the critical value, further extending the overall testing cycle and failing to meet the urgent needs of basic research for rapid material screening and engineering applications for efficient evaluation. Especially when evaluating multiple materials or different heat treatment states, the inefficiency of traditional methods becomes a bottleneck restricting progress in hydrogen environment compatibility research. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of huge resource consumption and long cycle of conventional methods by providing an efficient method for determining the fracture toughness of hydrogen pipeline materials under constant load in a high-pressure hydrogen environment.

[0005] The specific technical solution of the present invention is as follows:

[0006] An efficient method for determining the constant load fracture toughness of hydrogen transport pipeline materials in a high-pressure hydrogen environment includes:

[0007] Step S10: Take a test block from the test steel pipe and process two compact tensile specimens. The thickness of the specimens is not less than 85% of the wall thickness of the steel pipe, and the initial crack depth is a0 = 0.5W.

[0008] Step S20: Conduct fracture toughness tests in a high-pressure hydrogen environment using a quasi-static loading method to obtain the material's fracture toughness K. Q ;

[0009] Step S30: Keeping the pre-crack depth a0 of the specimen constant, calculate the load F applied to the specimen according to formula (1). app This results in a stress intensity factor level of 0.6K. Q ;

[0010] (1)

[0011] In the formula, K is the stress intensity factor of the steel pipe, F is the test load, B is the specimen thickness, and B N The net thickness of the specimen after removing the side groove is given, where W is the specimen width and a0 is the initial crack depth.

[0012] Step S40: While holding the F app Under the premise of not changing, calculate the value corresponding to 0.9K according to formula (1). Q The pre-existing crack depth a0;

[0013] Step S50: Pre-introduce two different depths of cracks in the two compact tensile specimens respectively: one corresponding to 0.6K. Q The crack depth is one, and the other corresponds to 0.9K. Q The depth of the crack;

[0014] Step S60: Mechanically connect the two pre-fabricated compact tensile specimens with different crack depths through a perforated plate, so that both are subjected to the same axial tensile load F. app Furthermore, when one of the specimens breaks, the load can still be transferred to the other specimen;

[0015] Step S70: Install the connected dual-sample system in a high-pressure hydrogen environment test chamber and apply the F simultaneously. app Load the load and start timing. The test time is m hours, where m ≥ 1000. During the test, two fracture extensometers are used simultaneously to monitor the notch opening displacement of the two specimens.

[0016] Step S80: After the test, the crack propagation size of the two specimens is measured respectively, and the maximum pre-crack depth t of the specimen that did not show significant propagation is determined.N The pre-existing crack depth t of the specimen with the minimum measurable propagation (≥0.254 mm). C ;

[0017] Step S90: If the minimum crack propagation is less than 0.254 mm, the constant load fracture toughness of the material is directly calculated according to formula (2), where a = t C ;

[0018] (2)

[0019] In the formula, K is the threshold value of the stress intensity factor of the steel pipe, and F app Where B is the test load, and B is the specimen thickness. N The net thickness of the sample after removing the side groove is given, f is a dimensionless shape factor, a is the crack depth, and t is taken as... C

[0020] If 0.6K Q If the sample expands by more than 0.254 mm, one of the following two treatment methods shall be adopted:

[0021] Method 1): Take t N With t C The average value of a is substituted into formula (2) to calculate the constant load fracture toughness of the material;

[0022] Method 2): Add a new experiment and recalculate the corresponding 0.7K. Q and 0.8K Q To determine the pre-existing crack depth, repeat steps S60–S80 to obtain a more precise t. C The value is then substituted into formula (2) for calculation.

[0023] Furthermore, in step S70, the high-pressure hydrogen environment test chamber is equipped with at least one pressure sensor with an accuracy of not less than 0.5, and includes a temperature sensor with a resolution of not less than 0.1℃, and is also equipped with an extensometer for fatigue and fracture testing.

[0024] Furthermore, prior to step S70, the hydrogen environment test chamber and pipelines are replaced with nitrogen, and then replaced with hydrogen to create a pure hydrogen environment.

[0025] Furthermore, in step S70, the gas in the test chamber is pressurized to a specified pressure, with pressure fluctuation not exceeding 5%. After the pressure reaches the set value, it is left to stand for at least 1 hour until the load value of the test machine stabilizes. This standing process ensures that hydrogen atoms fully diffuse into the interior of the material, so that the material reaches a hydrogen saturation state.

[0026] Furthermore, if both extensometer readings show significant changes after step S80, the test pressure is increased to 1.1F. appAnd repeat steps S60–S80.

[0027] Furthermore, after step S80 is completed, the test is stopped, and the pre-cracked sample is removed after depressurization and replacement.

[0028] The beneficial effects of this invention are as follows:

[0029] By applying the technical solution of this application, by pre-fabricating materials corresponding to 0.6K in two compact tensile specimens respectively Q and 0.9K Q The crack depth was determined at the stress intensity factor level, and the two specimens were mechanically connected using a perforated plate, allowing them to simultaneously withstand the same constant tensile load F in a high-pressure hydrogen environment. app Furthermore, the load can be stably transferred to the other specimen after either specimen fractures, thus enabling the simultaneous acquisition of crack propagation response data at two different crack depths in a single constant load test. During the test, two fracture extensometers were used simultaneously to accurately monitor the notch opening displacement of the two specimens. After the test, based on whether the crack propagation reached the measurable threshold of 0.254 mm, the maximum pre-crack depth t of the specimen that did not show significant propagation was determined. N The pre-existing crack depth t of the smallest measurable propagation specimen C Then, through logical judgment, a processing strategy is selected to directly calculate, estimate the average value, or add intermediate load level tests to accurately derive the constant load fracture toughness of the material. This scheme breaks through the limitations of traditional methods that require multiple constant load tests one by one, which is time-consuming. The fracture toughness assessment process, which originally required more than two independent tests, is condensed into a single constant load test of more than 1,000 hours. This effectively utilizes test time resources and improves test efficiency by more than double. At the same time, through the dual-sample synchronous monitoring and load sharing mechanism, the impact of environmental fluctuations and loading deviations on the results is significantly reduced, improving the accuracy and reliability of the fracture toughness assessment of materials under high-pressure hydrogen environment. Attached Figure Description

[0030] Figure 1 Figure (a) shows the connection structure of the constant load fracture toughness specimen, and Figure (b) shows the state diagram during the connection process.

[0031] Reference numerals: 1-Compact tensile specimen; 2-Initial crack; 3-Mounting hole; 4-Connecting plate; 5-Connecting hole; 6-Intermediate connector. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] An efficient method for determining the constant load fracture toughness of hydrogen transport pipeline materials in a high-pressure hydrogen environment includes:

[0034] Step S10: Take a test block from the test steel pipe and process two compact tensile specimens. The thickness of the specimens is not less than 85% of the wall thickness of the steel pipe, and the initial crack depth is a0 = 0.5W.

[0035] Step S20: Conduct fracture toughness tests in a high-pressure hydrogen environment using a quasi-static loading method to obtain the material's fracture toughness K. Q ;

[0036] Step S30: Keeping the pre-crack depth a0 of the specimen constant, calculate the load F applied to the specimen according to formula (1). app This results in a stress intensity factor level of 0.6K. Q ;

[0037] (1)

[0038] Step S40: While holding the F app Under the premise of not changing, calculate the value corresponding to 0.9K according to formula (1). Q The pre-existing crack depth a0;

[0039] Step S50: Pre-introduce two different depths of cracks in the two compact tensile specimens respectively: one corresponding to 0.6K. Q The crack depth is one, and the other corresponds to 0.9K. Q The depth of the crack;

[0040] Step S60: Mechanically connect the two pre-fabricated compact tensile specimens with different crack depths through a perforated plate, so that both are subjected to the same axial tensile load F. app Furthermore, when one of the specimens breaks, the load can still be transferred to the other specimen, such as... Figure 1 As shown, symmetrical mounting holes 3 are formed on both sides of the initial crack 2 of the compact tensile specimen 1. Four mounting holes 3 on two compact tensile specimens 1 are aligned in a line. A connecting plate 4 is placed on each compact tensile specimen 1. The connecting plate 4 has connecting holes 5 corresponding to the positions of the mounting holes 3 on the compact tensile specimen 1. An intermediate connector 6 is also provided between the compact tensile specimen 1 and the connecting plate 4. The intermediate connector 6 is a long strip-shaped plate, with its two ends hinged to the two connecting plates 4 by pins. The middle area is used to connect the loading device. The compact tensile specimen 1 and the connecting plate 4 are also fastened together by pins, forming a symmetrical loading system. The connecting plate 4 is made of microalloyed steel or high-temperature alloy with a yield strength not lower than that of the test material.

[0041] Step S70: Install the connected dual-sample system in a high-pressure hydrogen environment test chamber and apply the F simultaneously. app Load the load and start timing. The test time is m hours, where m ≥ 1000. During the test, two fracture extensometers are used simultaneously to monitor the notch opening displacement of the two specimens.

[0042] Step S80: After the test, the crack propagation size of the two specimens is measured respectively, and the maximum pre-crack depth t of the specimen that did not show significant propagation is determined. N The pre-existing crack depth t of the specimen with the minimum measurable propagation (≥0.254 mm). C ;

[0043] Step S90: If the minimum crack propagation is less than 0.254 mm, the constant load fracture toughness of the material is directly calculated according to formula (2), where a = t C ;

[0044] (2)

[0045] In the formula, K is the threshold value of the stress intensity factor of the steel pipe, and F app B is the test pressure, and B is the sample thickness. N The net thickness of the sample after removing the side groove is given, f is a dimensionless shape factor, a is the crack depth, and t is taken as... C

[0046] If 0.6K Q If the sample expands by more than 0.254 mm, one of the following two treatment methods shall be adopted:

[0047] Method 1): Take t N With t C The average value of a is substituted into formula (2) to calculate the constant load fracture toughness of the material;

[0048] Method 2): Add a new experiment and recalculate the corresponding 0.7K. Q and 0.8K Q To determine the pre-existing crack depth, repeat steps S60–S80 to obtain a more precise t. C The value is then substituted into formula (2) for calculation.

[0049] Applying the technical solution of this embodiment, the efficient method for determining the constant load fracture toughness of hydrogen pipeline materials in a high-pressure hydrogen environment involves taking a test block from a test steel pipe and processing two compact tensile specimens. The specimen thickness is not less than 85% of the steel pipe wall thickness, and the initial crack depth is pre-fabricated as a0 = 0.5W. A quasi-static loading method is used to conduct fracture toughness tests in a high-pressure hydrogen environment to obtain the material's fracture toughness K. QKeeping the pre-crack depth a0 of the specimen constant, the load F applied to the specimen is calculated according to formula (1). app This results in a stress intensity factor level of 0.6K. Q ; while maintaining F app Assuming the values ​​remain unchanged, the value corresponding to 0.9K is calculated according to Formula 1. Q The pre-existing crack depth a0; two different crack depths were pre-existing in two compact tensile specimens: one corresponding to 0.6K. Q The crack depth is one, and the other corresponds to 0.9K. Q The crack depth; two pre-fabricated compact tensile specimens with different crack depths are mechanically connected by a perforated plate so that they bear the same axial tensile load F. app Furthermore, even after one specimen breaks, the load can still be transferred to the other specimen; the connected dual-specimen system is installed in a high-pressure hydrogen environment test chamber, and F is applied simultaneously. app Loading is applied and timing begins; the test duration is m hours, where m is greater than or equal to 1000. During the test, two fracture extensometers are used simultaneously to monitor the notch opening displacement of the two specimens. After the test, the crack propagation dimensions of the two specimens are measured separately to determine the maximum pre-existing crack depth t of the specimen that did not show significant propagation. N The pre-crack depth t of the specimen with a minimum measurable propagation of not less than 0.254 mm. C If the minimum crack propagation is less than 0.254 mm, the constant load fracture toughness of the material can be directly calculated according to formula (2), where a equals t. C ;If 0.6K Q If the sample spreads beyond 0.254 mm, one of two treatment methods should be adopted: Method 1: Take t N With t C The average value is used as 'a' and substituted into Formula 2 to calculate the material's constant load fracture toughness; Method 2: Add a new test and recalculate the corresponding 0.7K. Q and 0.8K Q To determine the pre-existing crack depth, repeat steps S60 to S90 to obtain a more accurate t. CThe value is then substituted into formula (2) for calculation. This scheme achieves synchronous transfer of load between two specimens through an orifice plate, enabling the crack propagation behavior under two different stress intensity factor levels to respond in parallel in a single test. The notch opening displacement data is collected in real time using a fracture extensometer, and the crack propagation state is judged in combination with the preset propagation threshold of 0.254 mm. Thus, without extending the test cycle, the fracture toughness assessment basis under multiple load levels can be obtained at one time, significantly reducing the number of independent tests to be carried out repeatedly under high-pressure hydrogen environment. This overcomes the defects of traditional methods that require sequential loading, multiple tests, and long cycles, achieving a test efficiency improvement of more than 100%, while ensuring the synchronization and comparability of data, providing an efficient and reliable test method for the service safety assessment of hydrogen pipeline materials.

[0050] Testing machine and sensors:

[0051] The testing machine should be an electro-hydraulic servo testing machine equipped with a high-pressure hydrogen environment test chamber; the hydrogen environment test chamber should be equipped with at least one pressure sensor that can accurately display the test pressure, with an accuracy of not less than 0.5 grade; the hydrogen environment test chamber should include a sensor that can accurately display the test temperature, with a resolution of not less than 0.1℃; the hydrogen environment test chamber should be able to house extensometers for fatigue and fracture tests.

[0052] Experimental preparation:

[0053] Sample installation and installation of extensometers for fatigue and fracture analysis;

[0054] The hydrogen environmental test chamber and pipelines were replaced with nitrogen, and then replaced with hydrogen.

[0055] The gas inside the test chamber is pressurized to the specified pressure, and the pressure fluctuation does not exceed 5%.

[0056] After the pressure reaches the set value, let it stand for no less than 1 hour until the load value of the testing machine stabilizes.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly efficient method for determining the constant load fracture toughness of hydrogen transport pipeline materials in a high-pressure hydrogen environment, characterized in that, include: Step S10: Take a test block from the test steel pipe and process two compact tensile specimens. The thickness of the specimens is not less than 85% of the wall thickness of the steel pipe, and the initial crack depth is a0 = 0.5W. Step S20: Conduct fracture toughness tests in a high-pressure hydrogen environment using a quasi-static loading method to obtain the material's fracture toughness K. Q ; Step S30: Keeping the pre-crack depth a0 of the specimen constant, calculate the load F applied to the specimen according to formula (1). app This results in a stress intensity factor level of 0.6K. Q ; （1） In the formula, K is the stress intensity factor of the steel pipe, F is the test load, B is the specimen thickness, and B N The net thickness of the specimen after removing the side groove is given, W is the specimen width, and a0 is the initial crack depth. Step S40: While holding the F app Under the premise of not changing, calculate the value corresponding to 0.9K according to formula (1). Q The pre-existing crack depth a0; Step S50: Pre-introduce two different depths of cracks in the two compact tensile specimens respectively: one corresponding to 0.6K. Q The crack depth is one, and the other corresponds to 0.9K. Q The depth of the crack; Step S60: Mechanically connect the two pre-fabricated compact tensile specimens with different crack depths through a perforated plate, so that both are subjected to the same axial tensile load F. app Furthermore, when one of the specimens breaks, the load can still be transferred to the other specimen; Step S70: Install the connected dual-sample system in a high-pressure hydrogen environment test chamber and apply the F simultaneously. app Load the load and start timing. The test time is m hours, where m ≥ 1000. During the test, two fracture extensometers are used simultaneously to monitor the notch opening displacement of the two specimens. Step S80: After the test, the crack propagation size of the two specimens is measured respectively, and the maximum pre-crack depth t of the specimen that did not show significant propagation is determined. N The pre-existing crack depth t of the specimen with the minimum measurable propagation (≥0.254 mm). C ; Step S90: If the minimum crack propagation is less than 0.254 mm, the constant load fracture toughness of the material is directly calculated according to formula (2), where a = t C ; （2） In the formula, K is the threshold value of the stress intensity factor of the steel pipe, and F app Where B is the test load, and B is the specimen thickness. N The net thickness of the sample after removing the side groove is given, f is a dimensionless shape factor, a is the crack depth, and t is taken as... C If 0.6K Q If the sample expands by more than 0.254 mm, one of the following two treatment methods shall be adopted: Method 1): Take t N With t C The average value of a is substituted into formula (2) to calculate the constant load fracture toughness of the material; Method 2): Add a new experiment and recalculate the corresponding 0.7K. Q and 0.8K Q To determine the pre-existing crack depth, repeat steps S60–S80 to obtain a more precise t. C The value is then substituted into formula (2) for calculation.

2. The efficient method for determining the fracture toughness of hydrogen transport pipeline materials under constant load in a high-pressure hydrogen environment according to claim 1, characterized in that, In step S70, the high-pressure hydrogen environment test chamber is equipped with at least one pressure sensor with an accuracy of not less than 0.5, and includes a temperature sensor with a resolution of not less than 0.1℃, and an extensometer for fatigue and fracture testing is placed there.

3. The efficient method for determining the fracture toughness of hydrogen transport pipeline materials under constant load in a high-pressure hydrogen environment according to claim 1, characterized in that, Before step S70, the hydrogen environment test chamber and pipelines are replaced with nitrogen, and then replaced with hydrogen to form a pure hydrogen environment.

4. The efficient method for determining the constant load fracture toughness of hydrogen transport pipeline materials in a high-pressure hydrogen environment according to claim 1, characterized in that, In step S70, the gas in the test chamber is pressurized to the specified pressure, with pressure fluctuation not exceeding 5%. After the pressure reaches the set value, it is left to stand for no less than 1 hour until the load value of the test machine stabilizes. This standing process ensures that hydrogen atoms diffuse fully into the interior of the material, so that the material reaches a hydrogen saturation state.

5. The efficient method for determining the fracture toughness of hydrogen transport pipeline materials under constant load in a high-pressure hydrogen environment according to claim 1, characterized in that, If both fracture extensometer data show significant changes after step S80, the test pressure is increased to 1.1F. app And repeat steps S60–S80.

6. The efficient method for determining the fracture toughness of hydrogen pipeline materials under constant load in a high-pressure hydrogen environment according to claim 1, characterized in that, After step S80 is completed, the test is stopped, and the pre-cracked sample is removed after depressurization and replacement.

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