Method and model for predicting fatigue crack growth rate of pipeline steel in hydrogen-mixed environment

Abstract

The present invention relates to the field of metallic material measurement, and specifically to a method and model for predicting the fatigue crack growth rate of pipeline steel in a hydrogen-mixed environment. In this prediction method, multiple compact tension test specimens of the pipeline steel to be measured are prepared, and fatigue crack growth tests are then performed on the compact tension test specimens in a nitrogen environment and in environments with different hydrogen mixing ratios. The fatigue crack growth rates and corresponding stress intensity factor ranges are then obtained and fitted to obtain constant terms, and a fatigue crack growth prediction model for the pipeline steel to be measured in a hydrogen-mixed environment is constructed. Finally, the fatigue crack growth rate of the pipeline steel can be predicted based on the fatigue crack growth prediction model and the hydrogen mixing ratio. The present invention allows for the construction of a fatigue crack growth prediction model for the pipeline steel to be measured in a hydrogen-mixed environment by simply performing fatigue crack growth tests in a nitrogen environment and in environments with a few different hydrogen mixing ratios, thereby enabling predictions to be made, effectively shortening the prediction test period and ensuring the safety of testers and equipment.

Description

[Technical Field]

[0001] The present invention relates to the field of measurement of metallic materials, and more particularly to a method and model for predicting fatigue crack growth rate of pipeline steel in a hydrogen-mixed environment. [Background technology]

[0002] As environmental pollution worsens, hydrogen energy has attracted widespread attention as a clean and efficient energy source. Blending produced hydrogen gas into existing natural gas pipelines for transport is considered the primary method of hydrogen transport. During hydrogen blending through natural gas pipelines, hydrogen molecules adsorb and dissociate to form hydrogen atoms, which then enter the pipeline steel. The atoms then diffuse and accumulate at defects and stress concentrations, causing hydrogen embrittlement of the pipeline steel. Meanwhile, pipelines are susceptible to fatigue failure due to internal pressure fluctuations and external load changes. Furthermore, the selection of the hydrogen blend ratio remains unresolved. Therefore, to determine the appropriate hydrogen blend ratio and ensure the safety and reliability of hydrogen blending through natural gas pipelines, fatigue performance tests of pipelines under different hydrogen blend ratios are necessary. However, fatigue crack growth rate tests of pipeline steel under multiple hydrogen blending environments are costly and require long test cycles. Predicting fatigue performance under other hydrogen blending environments based solely on fatigue crack growth test results in nitrogen and low-level hydrogen blending environments would be of great significance for promoting hydrogen blending through natural gas pipelines.

[0003] CN103308381A discloses a fatigue crack growth rate normalization prediction method that uses the fatigue crack growth rate curve at R=i to realize normalized predictions for data at different stress ratios R≠i for the metal material under test, and combines different types of stress intensity factors using energy as a control parameter, resulting in a simple method and a wide range of applications. CN110411833A also discloses a fatigue crack growth rate normalization prediction method that uses the fatigue crack growth rate curve at R=i to realize normalized predictions for data at different stress ratios R≠i for the metal material under test, resulting in a simple method and a wide range of applications. iThe acceleration ratio A corresponding to the different stress intensity factor ranges ΔK at the frequency f is calculated, and the average value of the acceleration ratio is calculated. i This paper discloses a method for predicting crack growth rates at different frequencies in a seawater corrosive environment by obtaining the relationship between the stress ratio R and the average acceleration ratio. The above two methods are only applicable to air and liquid corrosive environments, and for gaseous corrosive environments, the model must be modified based on some parameters of the gaseous environment. In addition, the above methods do not predict crack growth rates at different frequencies in a seawater corrosive environment by obtaining the relationship between the stress ratio R and the average acceleration ratio f. i Therefore, it is not possible to predict changes in fatigue crack growth rate due to changes in the test environment. Therefore, there is an urgent need to develop a method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen mixing ratios. Summary of the Invention

[0004] In response to the deficiencies of the prior art, the present invention provides a method and model for predicting the fatigue crack growth rate of pipeline steel under different hydrogen mixing ratio environments, in order to solve the problem that the conventional prediction methods cannot be applied to gas corrosion environments.

[0005] According to the present invention, there is provided a method for predicting the fatigue crack growth rate of a pipeline steel under different hydrogen mixing ratio environments, comprising the following steps S1 to S3: S1: Prepare multiple compact tension test pieces of the pipeline steel to be measured, then perform fatigue crack growth tests on some of the compact tension test pieces in a nitrogen environment, and measure the fatigue crack growth rate in a nitrogen environment.

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[0006] Compared to the prior art, the above-mentioned technical means of the present invention make it possible to construct a prediction model for fatigue crack growth of the pipeline steel being measured simply by conducting fatigue crack growth tests in a nitrogen environment and in environments with a small number of different hydrogen mixing ratios, and to realize the prediction of the fatigue crack growth rate of pipeline steel with different hydrogen mixing ratios.

[0007] More preferably, before conducting the fatigue crack growth test, multiple tension test pieces of the pipeline steel to be measured are prepared, and mechanical property parameters of the pipeline steel to be measured are obtained by a tensile test, and the average value of each mechanical property parameter is used as the input parameter for the fatigue crack growth test.

[0008] More preferably, the number of tension test pieces is three to five.

[0009] More preferably, in step S1, a pre-crack having a length of 2 mm to 3 mm is introduced into the compact tension test piece.

[0010] More preferably, in step S1, a fatigue crack growth test is performed on at least one compact tension test piece in a nitrogen environment.

[0011] More preferably, in step S2, fatigue crack growth tests are performed on different compact tension test pieces under at least three different hydrogen mixing ratio environments.

[0012] More preferably, in step S2, the hydrogen partial pressure P H is greater than 0.02 MPa.

[0013] More preferably, in steps S1 and S2, the stress intensity factor range ΔK is determined by the following formula:

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[0014] In another aspect of the present invention, there is provided a fatigue crack growth prediction model obtained by the above prediction method.

[0015] As a result, the above technical means of the present invention has the following technical advantages over the prior art. 1. This invention provides a method for predicting the fatigue crack growth rate of pipeline steel in a corrosive environment. By simply conducting fatigue crack growth tests in a nitrogen environment and a few different hydrogen mixing ratio environments, a fatigue crack growth prediction model for the pipeline steel being tested in a hydrogen mixing environment can be constructed, enabling prediction of the fatigue crack growth rate of pipeline steel under different hydrogen mixing ratios, effectively shortening the prediction test cycle and ensuring the safety of test personnel and equipment. 2. In particular, the present invention optimizes the number of tests in a nitrogen environment and a hydrogen mixed environment, thereby ensuring prediction accuracy and avoiding a decrease in safety due to an excessive number of tests. 3. Furthermore, the present invention optimizes the range of the hydrogen mixing ratio, thereby avoiding a decrease in test safety due to an excessively high hydrogen mixing ratio. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen mixing ratio environments provided in an embodiment of the present invention. [Figure 2] 1 is a structural schematic diagram of a compact tension test specimen provided in an embodiment of the present invention. [Figure 3] 1 is a structural schematic diagram of a tension test piece provided in an embodiment of the present invention. [Figure 4] FIG. 1 is a surface diagram of a crack propagation prediction model for a pipeline steel obtained in an example of the present invention. [Figure 5] 5(a) and 5(b) are graphs comparing actual measurement data and predicted data in an environment with a hydrogen mixing ratio of 15% provided in an embodiment of the present invention. Fig. 5(a) is a graph comparing the actual measurement data and the prediction model, and Fig. 5(b) is a graph comparing the actual measurement data and the prediction curve. DETAILED DESCRIPTION OF THE INVENTION

[0017] In order to clarify the objectives, technical solutions and advantages of the present invention, the present invention will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only for the purpose of illustrating the present invention and are not intended to limit the present invention.

[0018] As shown in Figure 1, one aspect of the present invention provides a method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen mixing ratio environments. The method specifically includes the following steps S1 to S3.

[0019] S1: Prepare multiple compact tension test pieces of the pipeline steel to be measured. The basic parameters of each compact tension test piece, such as thickness, width, and length of the machined notch, are consistent. Next, some of the compact tension test pieces are placed in a metallic material environmental compatibility testing machine and subjected to a fatigue crack growth test in a nitrogen environment to measure the fatigue crack growth rate in the nitrogen environment.

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[0020] S2: Conduct fatigue crack growth tests on the remaining compact tension specimens under different hydrogen mixing ratios. Here, the gas total pressure, loading method, stress ratio, loading frequency, etc. are the same as in step S1. This allows us to determine the fatigue crack growth rate under different hydrogen mixing ratios.

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[0021] S3: The constant terms obtained in steps S1 and S2 are substituted into equation (2) to construct a fatigue crack growth prediction model for the pipeline steel to be measured in a hydrogen-mixed environment, and the fatigue crack growth rate of the pipeline steel can be predicted based on the fatigue crack growth prediction model by providing the hydrogen mixing ratio.

[0022] Specifically, the fatigue crack growth rate of compact tension test specimens in a hydrogen-mixed environment

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[0023] In equation (4),

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[0024] In equation (4),

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[0025] From the above, the fatigue crack growth rate in a hydrogen-mixed environment is

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[0026] The method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen mixing ratios provided by the present invention can predict the fatigue crack growth rate under other different hydrogen mixing ratios simply by conducting fatigue crack growth tests in a nitrogen environment and a low-volume hydrogen mixing environment, thereby significantly reducing testing costs and improving efficiency. Furthermore, fatigue crack growth tests under hydrogen mixing environments require cumbersome procedures and long test cycles. Prediction using a predictive model not only saves a significant amount of time but also enables accurate and rapid prediction of fatigue crack growth rates under different hydrogen mixing ratios, providing a basis for selecting the hydrogen mixing ratio. Furthermore, hydrogen mixing environments are flammable and explosive, posing a significant safety hazard to test personnel and the environment. The prediction method provided by the present invention can predict the fatigue crack growth rate under different hydrogen mixing ratios simply by conducting a small number of tests, thereby more reliably protecting the safety of test personnel and equipment.

[0027] Furthermore, in step S1, before conducting the fatigue crack growth test, multiple tension test specimens of the pipeline steel to be measured are prepared. These tension test specimens have the shape shown in Figure 3. A tensile test is performed using these tension test specimens to obtain basic mechanical property parameters of the pipeline steel to be measured, such as elastic modulus, tensile strength, yield strength, and elongation rate. The average values ​​of each mechanical property parameter are used as input parameters for the fatigue crack growth test to calculate and output the crack length a.

[0028] Furthermore, the number of tension test specimens is 3 to 5. This ensures the accuracy of the measurement of the basic mechanical property parameters of the pipeline steel to be measured.

[0029] Furthermore, in step S1, the length of the pre-crack is related to the size of the compact tension test specimen, as shown in Figure 2. In the present invention, a pre-crack with a length L of 2 mm to 3 mm is introduced into the compact tension test specimen, thereby eliminating the effect of the machined notch on the subsequent crack propagation.

[0030] Furthermore, in step S1, a fatigue crack growth test is performed on at least one compact tension test specimen in a nitrogen environment. In step S2, fatigue crack growth tests are performed on different compact tension test specimens in at least three hydrogen mixing ratio environments. Therefore, the number of compact tension test specimens is at least four.

[0031] Furthermore, in step S2, the hydrogen mixing ratio is in the range of 5% to 30%, and several appropriate hydrogen mixing ratios can be selected within this range to avoid the hydrogen content being too high and causing an increase in test risk.

[0032] Furthermore, in steps S1 and S2, the stress intensity factor range ΔK is calculated by the following formula:

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[0033] According to another aspect of the present invention, there is provided a fatigue crack growth prediction model obtained by the above prediction method, which can measure the fatigue crack growth rate of pipeline steel by providing a hydrogen mixing ratio.

[0034] The technical solutions provided by the present invention are further illustrated below through specific examples.

[0035] The test object is X65 pipeline steel, which is commonly used in natural gas transmission, and the method for predicting the fatigue crack growth rate of pipeline steel in a hydrogen-mixed environment provided by the present invention is used. The prediction method includes the following steps S1 to S3.

[0036] S1: Three dog-bone type tension test specimens were fabricated using the X65 pipeline steel used in the test, and the tensile properties were measured. The final tensile property parameters are shown in Table 1. The average values ​​of each parameter were used as input parameters for the fatigue crack propagation test.

[0037] Table 1: Tensile properties of X65 pipeline steel [Table 1]

[0038] S2: Five compact tension specimens were fabricated and designated as specimens 1, 2, 3, 4, and 5. The specimens' basic parameters, such as thickness, width, and machined notch length, were measured. A precrack of approximately 2 mm was introduced into the specimens in an air environment by placing them in a high-frequency fatigue testing machine. A fatigue crack growth rate test was conducted on specimen 1 in a nitrogen environment in accordance with national standard GB / T 34542.2-2018, "Hydrogen Storage and Transport Systems, Part 2: Test Methods for Metallic Materials and Hydrogen Environment Compatibility." The test pressure was 10 MPa, sinusoidal loading was used, the stress ratio was 0.1, and the test frequency was 1 Hz. The relationship between the fatigue crack growth rate da / dN and the stress intensity factor range ΔK was obtained and fitted to the following equation using the Paris equation:

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[0039] S3: Fatigue crack growth rate tests were conducted on specimens 2#-4# in a hydrogen-mixed environment. The total test pressure was 10 MPa, and the hydrogen mixing ratios were 5%, 10%, and 20%, respectively. Other test parameters were the same as those of specimen 1#. Finally, the fatigue crack growth rate da / dN and hydrogen partial pressure P H (0.5, 1, and 2 MPa, respectively) and stress intensity factor range ΔK.

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[0040] FIG. 4 is a surface diagram of this fitting model.

[0041] To verify the accuracy of the prediction model corresponding to Equation (12), the fatigue crack growth rate was measured for specimen 5# under a total pressure of 10 MPa and a hydrogen mixing ratio of 15%. The other test conditions were consistent with those of specimens 1#-4#, and actual measurement data points were obtained.

[0042] The distribution of measured data and the prediction model surface for a 15% hydrogen mixture are shown in Figure 5(a). The predicted surface closely matches the measured data points. The predicted crack growth rates for different stress intensity factor ranges, ΔK, were measured using Equation (10) and compared with the measured values ​​(Table 2 and Figure 5(b)). As can be seen from the comparison results, the standard deviation of the predicted values ​​was within 10% of the measured values, demonstrating that this model can accurately and quickly predict fatigue crack growth rates under different hydrogen mixture environments.

[0043] Table 2: Comparison of measured and predicted fatigue crack growth rates in a 15% hydrogen mixture environment [Table 2]

[0044] Those skilled in the art will recognize that these are merely preferred embodiments of the present invention, and do not limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for predicting the fatigue crack growth rate of a pipeline steel under different hydrogen mixing ratio environments, comprising the following steps S1 to S3: S1: Prepare a plurality of compact tension test pieces of the pipeline steel to be measured, and then perform a fatigue crack growth test on some of the compact tension test pieces in a nitrogen environment to determine the fatigue crack growth rate in a nitrogen environment. [Equation 1] and the corresponding stress intensity factor range ΔK is obtained, and the constant term C is obtained by fitting using Equation (1). １ and m １ Get [Equation 2] where a is the crack length, N is the number of stress cycles, and C １ and m １ is the fitting parameter in the nitrogen environment, S2: Fatigue crack growth rate of compact tension test specimens in a hydrogen-mixed environment [Equation 3] It consists of the following two elements: [Equation 4] During the ceremony, [Equation 5] is the fatigue crack growth rate in a hydrogen-mixed environment, [Equation 6] is the effect of the nitrogen environment on the fatigue crack growth rate, calculated by Equation (1), [Equation 7] is the fatigue crack growth rate accelerated by hydrogen partial pressure, calculated by equation (5), [Equation 8] During the ceremony, [Equation 9] is the transient-state hydrogen enhanced fatigue crack growth rate, [Equation 10] is the steady-state hydrogen enhanced fatigue crack growth rate, and C ２ , m ２ and n are fitting constants for the transient hydrogen-accelerated fatigue crack growth rate, and C ３ and m ３ is a fitting constant for the steady-state hydrogen-accelerated fatigue crack growth rate, From the above, the fatigue crack growth rate in a hydrogen-mixed environment is [0011] is expressed as Fatigue crack growth tests were conducted on the remaining compact tension test specimens under different hydrogen mixing ratios to determine the fatigue crack growth rate under different hydrogen mixing ratios. [0012] and the corresponding stress intensity factor range ΔK is obtained, and the constant term C is obtained by fitting using Equation (2). ２ , C ３ , m ２ , m ３ and n are obtained, [0013] In the formula, P Ｈ is the hydrogen partial pressure, S3: A prediction method characterized by constructing a fatigue crack growth prediction model for the pipeline steel to be measured in a hydrogen-mixed environment by substituting the constant terms obtained in steps S1 and S2 into equation (2), and being able to predict the fatigue crack growth rate of the pipeline steel by providing the hydrogen mixing ratio based on the fatigue crack growth prediction model.

2. 2. The prediction method according to claim 1, characterized in that in step S1, before conducting a fatigue crack growth test, a plurality of tension test pieces of the pipeline steel to be measured are prepared, mechanical property parameters of the pipeline steel to be measured are obtained by a tensile test, and the average value of each mechanical property parameter is used as an input parameter for the fatigue crack growth test.

3. The prediction method according to claim 2, wherein the number of tension test pieces is 3 to 5.

4. The prediction method according to claim 1, characterized in that in step S1, a pre-crack having a length of 2 mm to 3 mm is introduced into the compact tension test piece.

5. 2. The prediction method according to claim 1, wherein in step S1, a fatigue crack growth test is performed on at least one compact tension test piece in a nitrogen environment.

6. 2. The prediction method according to claim 1, wherein in step S2, fatigue crack growth tests are conducted on different compact tension test pieces under at least three different hydrogen mixing ratio environments.

7. In step S2, the hydrogen partial pressure P Ｈ The prediction method of claim 1 , wherein is greater than 0.02 MPa.

8. In steps S1 and S2, the stress intensity factor range ΔK is calculated using the following formula: [0014] is calculated by In the formula, P ｍａｘ 2. The prediction method of claim 1, characterized in that: σ is the maximum load during measurement; B and W are the thickness and width of the compact tension test specimen, respectively; R is the stress ratio; and a is the crack length.

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