Prediction method and model of fatigue crack growth rate of pipeline steel in hydrogen-doped environment

Abstract

The present application belongs to the field of metal material testing and specifically discloses a method and model for predicting the fatigue crack growth rate of pipeline steel in a hydrogen-doped environment. The prediction method comprises the following steps: processing multiple compact tensile specimens of the pipeline steel to be tested, and then conducting fatigue crack growth tests on the compact tensile specimens in a nitrogen environment and at different hydrogen-doping ratios to obtain the fatigue crack growth rate and the corresponding stress intensity factor range and fitting the constant term. ， This method establishes a fatigue crack growth prediction model for pipeline steel under a hydrogen-doped environment. Ultimately, given the hydrogen doping ratio, the fatigue crack growth rate of the pipeline steel can be predicted based on the fatigue crack growth prediction model. This application only requires conducting fatigue crack growth tests in a nitrogen environment and a few environments with different hydrogen doping ratios to establish a fatigue crack growth prediction model for pipeline steel under a hydrogen-doped environment, thereby achieving predictions. This effectively shortens the prediction test cycle and ensures the safety of test personnel and equipment.

Description

Technical Field

[0001] The present application belongs to the field of metal material testing, and more specifically, relates to a method and model for predicting the fatigue crack growth rate of pipeline steel in a hydrogen-doped environment. Background Art

[0002] With increasing environmental pollution, hydrogen energy has attracted widespread attention as a clean and efficient energy source. Mixing produced hydrogen into existing natural gas pipelines for transportation is considered an ideal method for hydrogen transportation. When hydrogen is transported in natural gas pipelines, hydrogen molecules undergo adsorption and dissociation, entering the pipeline steel as atomic hydrogen. These atoms diffuse and accumulate in defects and stress concentrations, causing hydrogen embrittlement. Furthermore, pipelines are susceptible to fatigue failure due to fluctuations in internal pressure and changes in external loads. Furthermore, the optimal hydrogen blending ratio remains undetermined. Therefore, fatigue testing of pipelines under different hydrogen blending ratios is necessary to determine the appropriate hydrogen blending ratio and ensure the safety and reliability of hydrogen blending in natural gas pipelines. However, testing the fatigue crack growth rate of pipeline steel under various hydrogen blending environments is costly and time-consuming. Being able to predict fatigue performance under other hydrogen blending environments based solely on fatigue crack growth test results in nitrogen and low-level hydrogen blending would have significant engineering implications for promoting the operation of hydrogen blending in natural gas pipelines.

[0003] CN103308381A discloses a fatigue crack growth rate normalization prediction method, which uses the fatigue crack growth rate curve under R=i to realize the normalization prediction of the data under different stress ratios R≠i of the metal material to be tested, and combines different types of stress intensity factors with energy as the control parameter. It has the characteristics of simple method and wide application range. CN110411833A discloses a method for predicting crack growth rates at different frequencies in seawater corrosion environment. The method calculates the fatigue crack growth rate at different frequencies f i Under different stress intensity factor ranges Δ K The corresponding acceleration ratio A is obtained, and the average value of the acceleration ratio is obtained, and then the frequency f is obtained by quadratic polynomial fitting. i The relationship between the stress ratio and the average value of the acceleration ratio is used to predict the crack growth rate of other frequencies in the seawater corrosion environment. The above two methods are only for air medium and liquid corrosion environment. For gas corrosion environment, the model needs to be modified according to some parameters of the gas environment. In addition, the above methods are aimed at the change of stress ratio R and loading frequency f i The prediction of fatigue crack growth rate based on the change of cannot guide the prediction of the change of fatigue crack growth rate caused by the change of test environment. Therefore, it is urgent to develop a prediction method for the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments. Summary of the Invention

[0004] In response to the defects of the existing technology, this application provides a prediction method and prediction model for the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments, aiming to solve the problem that the existing prediction methods cannot be applied to gas corrosion environments.

[0005] This application provides a method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments, specifically including:

[0006] S1 processes multiple compact tensile specimens of pipeline steel to be tested, and then performs fatigue crack growth tests on some of the compact tensile specimens in a nitrogen environment to obtain the fatigue crack growth rate in a nitrogen environment. and the corresponding stress intensity factor range Δ K , and use formula (1) to fit to obtain the constant term C 1 and m 1:

[0007] (1)

[0008] Where, a is the crack length, N is the number of stress cycles, C 1 and m 1 is the fitting parameter in nitrogen environment;

[0009] S2 conducted fatigue crack growth tests on the remaining compact tensile specimens under different hydrogen doping ratios to obtain the fatigue crack growth rates under different hydrogen doping ratios. and the corresponding stress intensity factor range Δ K， And use formula (2) to fit to obtain the constant term C 2, C 3. m 2, m 3 and n :

[0010] (2)

[0011] Where, P H is the hydrogen partial pressure;

[0012] S3 substitutes the constant terms obtained in step S1 and step S2 into formula (2) to establish a fatigue crack growth prediction model for the pipeline steel to be tested in a hydrogen-doped environment. According to the fatigue crack growth prediction model, the fatigue crack growth rate of the pipeline steel can be predicted given the hydrogen doping ratio.

[0013] Through the above technical solution conceived in the present application, compared with the existing technology, since the present application only needs to carry out fatigue crack growth tests in a nitrogen environment and a few environments with different hydrogen doping ratios, a fatigue crack growth prediction model for the pipeline steel to be tested can be established, thereby realizing the prediction of the fatigue crack growth rate of the pipeline steel under different hydrogen doping ratios.

[0014] As a further preferred embodiment, in step S1, before performing the fatigue crack growth test, multiple tensile specimens of the pipeline steel to be tested are processed, and the mechanical property parameters of the pipeline steel to be tested are obtained through the tensile test, and the average value of each mechanical property parameter is used as the input parameter of the fatigue crack growth test.

[0015] As a further preference, the number of tensile specimens is 3 to 5.

[0016] As a further preferred embodiment, in step S1, a crack with a length of 2 mm to 3 mm is prefabricated on the compact tensile specimen.

[0017] As a further preferred embodiment, in step S1, a fatigue crack growth test is performed on at least one compact tensile specimen in a nitrogen environment.

[0018] As a further preferred embodiment, in step S2, fatigue crack growth tests are performed on different compact tensile specimens under at least three hydrogen doping ratio environments.

[0019] As a further preferred step, in step S2, the hydrogen partial pressure P H Greater than 0.02MPa.

[0020] As a further preferred embodiment, in steps S1 and S2, the stress intensity factor range Δ K Use the following formula to calculate:

[0021] (3)

[0022] Where, is the maximum load during the test, B 、 W are the thickness and width of the compact tensile specimen, R is the stress ratio, a is the crack length.

[0023] According to another aspect of the present application, a fatigue crack growth prediction model obtained by using the above prediction method is provided.

[0024] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technologies:

[0025] 1. This application provides a method for predicting the fatigue crack growth rate of pipeline steel in corrosive environments. This method only requires conducting fatigue crack growth tests in a nitrogen environment and a few environments with different hydrogen doping ratios. A fatigue crack growth prediction model for the pipeline steel under hydrogen doping can be established. This enables prediction of the fatigue crack growth rate of pipeline steel under different hydrogen doping ratios, effectively shortening the prediction test cycle and ensuring the safety of test personnel and equipment.

[0026] 2. In particular, this application optimizes the number of tests in nitrogen and hydrogen-doped environments, ensuring prediction accuracy while avoiding a decrease in safety due to excessive testing.

[0027] 3. In addition, this application optimizes the range of hydrogen blending ratio to avoid a decrease in test safety caused by an excessively high hydrogen blending ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments provided in the embodiments of the present application;

[0029] Figure 2 is a schematic structural diagram of a compact tensile specimen provided in an embodiment of the present application;

[0030] Figure 3 is a schematic structural diagram of a tensile specimen provided in an embodiment of the present application;

[0031] Figure 4 This is a surface diagram of a pipeline steel crack growth prediction model obtained in an embodiment of the present application;

[0032] Figure 5 This is a comparison chart of measured data and predicted data under an environment with a hydrogen doping ratio of 15% provided in an embodiment of the present application, wherein (a) is a comparison chart of measured data and a prediction model, and (b) is a comparison chart of measured data and a prediction curve. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0034] like Figure 1 As shown, according to one aspect of the present application, a method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments is provided, specifically comprising:

[0035] S1 processes multiple compact tensile specimens of pipeline steel to be tested. The basic parameters of each compact tensile specimen, such as thickness, width, and machining notch length, are consistent. Then, some compact tensile specimens are placed on a metal material environmental compatibility testing machine and fatigue crack growth tests are carried out in a nitrogen environment to obtain the fatigue crack growth rate in the nitrogen environment. and the corresponding stress intensity factor range Δ K , and use formula (1) to fit to obtain the constant term C 1 and m 1:

[0036] (1)

[0037] Where, a is the crack length, N is the number of stress cycles, C 1 and m 1 is the fitting parameter in nitrogen environment;

[0038] S2 performs fatigue crack growth tests on the remaining compact tensile specimens under different hydrogen doping ratio environments, where the total gas pressure, loading method, stress ratio, loading frequency, etc. are consistent with step S1, thereby obtaining the fatigue crack growth rate under different hydrogen doping ratio environments. and the corresponding stress intensity factor range Δ K， by is the Z axis, hydrogen partial pressure P H (converted by hydrogen doping ratio and total pressure) is the X-axis, the stress intensity factor range Δ K The Y axis is used, and the constant term is obtained by nonlinear least square fitting using formula (2) C 2, C 3. m 2, m 3 and n :

[0039] (2)

[0040] Where, P H is the hydrogen partial pressure;

[0041] S3 substitutes the constant terms obtained in step S1 and step S2 into formula (2) to establish a fatigue crack growth prediction model for the pipeline steel to be tested in a hydrogen-doped environment. According to the fatigue crack growth prediction model, the fatigue crack growth rate of the pipeline steel can be predicted given the hydrogen doping ratio.

[0042] Specifically, the fatigue crack growth rate of the compact tensile specimen in a hydrogen-doped environment is It consists of the following two aspects:

[0043] (4)

[0044] Where, is the fatigue crack growth rate in hydrogen-doped environment, is the effect of nitrogen environment on fatigue crack growth rate, calculated by formula (1), is the fatigue crack growth rate accelerated by hydrogen partial pressure, calculated by formula (4),

[0045] (5)

[0046] Where, is the transient hydrogen-promoted fatigue crack growth rate, For steady-state hydrogen to promote fatigue crack growth rate;

[0047] The first term in formula (4) Expressed as:

[0048] (6)

[0049] In the formula a 1 、m 2 、c 1 and d 1 is a constant, P H is the hydrogen partial pressure, Q is the activation energy, v is the partial molar volume of hydrogen in the metal, σ b is the stress at the critical distance from the crack tip, R is the gas constant, T is the thermodynamic temperature. When the temperature is the same, (-Q+V σ b ) / (RT) Simplified extraction into constant terms, so the first term Simplified to:

[0050] (7)

[0051] Where, C 2, m 2 and n is the fitting constant of transient hydrogen-promoted fatigue crack growth rate;

[0052] The second term in formula (4) Expressed as:

[0053] (8)

[0054] Where, a 2 、m 3、c 2 and d 2 is a constant, and the other parameters are consistent with the definitions of formula (5). The change of hydrogen pressure has almost no effect on the steady-state hydrogen-promoted fatigue crack growth rate, so the parameters are d 2 is set to 0, the second item Simplified to:

[0055] (9)

[0056] Where, C 3 and m 3 is the fitting constant of the steady-state hydrogen-promoted fatigue crack growth rate.

[0057] In summary, the fatigue crack growth rate in hydrogen-doped environment is expressed as:

[0058] (2).

[0059] The method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments provided in this application can predict the fatigue crack growth rate under other different hydrogen doping ratios by only conducting fatigue crack growth tests in nitrogen environment and a small amount of hydrogen doping environment, which greatly saves the test cost and improves efficiency. At the same time, considering that the fatigue crack growth test under hydrogen doping environment has cumbersome operating steps and a long test cycle, prediction through the prediction model saves a lot of time, and can accurately and quickly predict the fatigue crack growth rate under different hydrogen doping ratio environments, providing a basis for the selection of hydrogen doping ratio. In addition, the hydrogen doped gas environment is flammable and explosive, and poses a great safety hazard to test personnel and the environment. The prediction method provided in this application only needs to carry out a small number of tests to predict the fatigue crack growth rate under different hydrogen doping ratio environments, which can better ensure the safety of test personnel and equipment.

[0060] Furthermore, in step S1, before the fatigue crack growth test is performed, a plurality of tensile specimens of pipeline steel to be tested are processed. The tensile specimens are Figure 3 The tensile test is carried out on the tensile specimen to obtain the basic mechanical properties of the pipeline steel, such as elastic modulus, tensile strength, yield strength and elongation. The average value of each mechanical property parameter is used as the input parameter of the fatigue crack growth test to calculate and output the crack length. a .

[0061] Furthermore, the number of tensile specimens is 3 to 5, thereby ensuring the accuracy of the test of basic mechanical property parameters of the pipeline steel to be tested.

[0062] Further, in step S1, if Figure 2As shown, the length of the prefabricated crack is related to the size of the compact tensile specimen. In this application, a crack with a length L of 2 mm to 3 mm is prefabricated on the compact tensile specimen, thereby eliminating the influence of the machining notch on the subsequent crack propagation.

[0063] Furthermore, in step S1, a fatigue crack growth test is performed on at least one compact tensile specimen in a nitrogen environment. In step S2, fatigue crack growth tests are performed on different compact tensile specimens in at least three hydrogen doping ratio environments. Therefore, the number of compact tensile specimens is at least four.

[0064] Furthermore, in step S2, the hydrogen blending ratio is within the range of 5% to 30%, and several appropriate hydrogen blending ratios can be selected within this range to avoid an increase in the risk factor of the test due to excessively high hydrogen content.

[0065] Furthermore, in steps S1 and S2, the stress intensity factor range Δ K Use the following formula to calculate:

[0066] (3)

[0067] Where, is the maximum load during the test, B 、 W are the thickness and width of the compact tensile specimen, R is the stress ratio, a is the crack length.

[0068] According to another aspect of the present application, a fatigue crack growth prediction model obtained by using the above prediction method is provided, and the fatigue crack growth rate of pipeline steel can be predicted given the hydrogen doping ratio.

[0069] The technical solution provided in this application is further described below based on specific embodiments.

[0070] X65 pipeline steel commonly used in natural gas transportation was selected as the verification object. The prediction method for the fatigue crack growth rate of pipeline steel in a hydrogen-doped environment provided by the present invention was adopted. The prediction method includes the following steps:

[0071] S1 processed three dog-bone tensile specimens on the X65 pipeline steel used in the test for tensile performance testing. The final tensile performance parameters are shown in Table 1. The average value of each parameter was taken as the input parameter for the fatigue crack growth test.

[0072] Table 1 Tensile properties of X65 pipeline steel

[0073]

[0074] S2 processed 5 compact tensile specimens, namely specimens 1#, 2#, 3#, 4# and 5#, and measured the basic parameters of the specimens such as thickness, width, and machining notch length. In an air environment, the specimens were placed on a high-frequency fatigue testing machine to prefabricate a crack of about 2 mm. According to the national standard GB / T 34542.2-2018 "Hydrogen Storage and Transportation System Part 2: Test Method for Compatibility of Metallic Materials with Hydrogen Environment", the fatigue crack growth rate test of specimen 1# in a nitrogen environment was carried out. The total test pressure was 10 MPa, sinusoidal wave loading was used, the stress ratio was 0.1, the test frequency was 1 Hz, and the fatigue crack growth rate was obtained. da / dN and stress intensity factor range Δ K The relationship is fitted by the Paris formula as follows:

[0075] (10)

[0076] Right now C 1=2.511×10 -9 , m 1=3.030.

[0077] S3 conducted fatigue crack growth rate tests on samples 2#-4# under hydrogen-doped environment. The total test pressure was 10 MPa, and the hydrogen doping ratios were 5%, 10%, and 20%, respectively. Other test parameters were consistent with those of sample 1#. Finally, the fatigue crack growth rate was obtained. da / dN , hydrogen partial pressure P H (0.5, 1 and 2 MPa, respectively) and the stress intensity factor range Δ K The fatigue crack growth rate is the z-axis, hydrogen partial pressure P H is the x-axis, the stress intensity factor range Δ K For the y-axis, nonlinear least squares fitting is performed according to the following formula:

[0078] (11)

[0079] Finally, the fitting parameters are obtained C 2=1.128×10 -8 , C 3=1.494×10 -6 , m 2=3.486, m 3=2.176 and n =0.183, the final fitting model is:

[0080] (12)

[0081] Figure 4is a surface plot of the fitted model.

[0082] In order to verify the accuracy of the prediction model corresponding to formula (12), the fatigue crack growth rate of sample 5# was tested under a total pressure of 10 MPa and a hydrogen doping ratio of 15%. Other test conditions were kept consistent with those of samples 1#-4#, and the measured data points were obtained.

[0083] In an environment with a hydrogen doping ratio of 15%, the measured data distribution and the predicted model surface are as follows: Figure 5 As shown in (a), the predicted surface is highly consistent with the measured data points. According to formula (10), the stress intensity factor range Δ K The predicted values ​​of crack growth rate under the conditions are compared with the measured values, as shown in Table 2 and Figure 5 The comparison results show that the standard deviation of the predicted value relative to the measured value is within 10%, and the model can accurately and quickly predict the fatigue crack growth rate under different hydrogen doping ratio environments.

[0084] Table 2 Comparison and verification statistics of fatigue crack growth rate measured and predicted under 15% hydrogen doping ratio

[0085]

[0086] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for predicting the fatigue crack growth rate of pipeline steel under different hydrogen doping ratio environments, characterized in that: Specifically include: S1 processes multiple compact tensile specimens of pipeline steel to be tested, and then performs fatigue crack growth tests on some of the compact tensile specimens in a nitrogen environment to obtain the fatigue crack growth rate in a nitrogen environment. and the corresponding stress intensity factor range Δ K , and use formula (1) to fit to obtain the constant term C 1 and m 1: （1） Where, a is the crack length, N is the number of stress cycles, C 1 and m 1 is the fitting parameter in nitrogen environment; S2 Fatigue crack growth rate of compact tensile specimen in hydrogen-doped environment It consists of the following two aspects: （4） Where, is the fatigue crack growth rate in hydrogen-doped environment, is the effect of nitrogen environment on fatigue crack growth rate, calculated by formula (1), is the fatigue crack growth rate accelerated by hydrogen partial pressure, calculated by formula (5), （5） （7） （9） Where, is the transient hydrogen-promoted fatigue crack growth rate, For the steady-state hydrogen-promoted fatigue crack growth rate, C 2, m 2 and n is the fitting constant of transient hydrogen-promoted fatigue crack growth rate, C 3 and m 3 is the fitting constant of the steady-state hydrogen-promoted fatigue crack growth rate, In summary, the fatigue crack growth rate in hydrogen-doped environment is expressed as: (2) Fatigue crack growth tests were carried out on the remaining compact tensile specimens under different hydrogen doping ratios to obtain the fatigue crack growth rates under different hydrogen doping ratios. and the corresponding stress intensity factor range Δ K , and use formula (2) to fit to obtain the constant term C 2, C 3. m 2, m 3 and n : （2） Where, P H is the hydrogen partial pressure; S3 substitutes the constant terms obtained in step S1 and step S2 into formula (2) to establish a fatigue crack growth prediction model for the pipeline steel to be tested in a hydrogen-doped environment. According to the fatigue crack growth prediction model, the fatigue crack growth rate of the pipeline steel can be predicted given the hydrogen doping ratio.

2. The prediction method according to claim 1, wherein: In step S1, before performing the fatigue crack growth test, multiple tensile specimens of the pipeline steel to be tested are processed, and the mechanical property parameters of the pipeline steel to be tested are obtained through the tensile test, and the average value of each mechanical property parameter is used as the input parameter of the fatigue crack growth test.

3. The prediction method according to claim 2, wherein: The number of tensile specimens is 3 to 5.

4. The prediction method according to claim 1, wherein: In step S1, a crack with a length of 2 mm to 3 mm is prefabricated on the compact tensile specimen.

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

6. The prediction method according to claim 1, wherein: In step S2, fatigue crack growth tests are performed on different compact tensile specimens under at least three hydrogen doping ratio environments.

7. The prediction method according to claim 1, wherein: In step S2, the hydrogen partial pressure P H Greater than 0.02MPa.

8. The prediction method according to claim 1, wherein: In steps S1 and S2, the stress intensity factor range Δ K Use the following formula to calculate: （3） Where, is the maximum load during the test, B 、 W are the thickness and width of the compact tensile specimen, R is the stress ratio, a is the crack length.

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