Service life prediction method applicable to natural gas hydrogen blending pipelines

Abstract

The present invention relates to the field of pipeline testing, and specifically provides a service life prediction method applicable to natural gas hydrogen - blended pipelines. The service life prediction method applicable to natural gas hydrogen - blended pipelines includes establishing a failure assessment diagram, and drawing a load ratio cut - off line and a toughness ratio cut - off line in the failure assessment diagram to form a reference line and a safety zone. Based on the calculated depth a of i cracks, the load ratio #imgabs0# and the toughness ratio #imgabs1# are respectively calculated and the corresponding coordinate points (#imgabs2#, #imgabs3#) are formed to obtain the critical crack depth #imgabs4#. When the circumferential stress direction applied to the pipeline is the principal stress direction of the crack, the service life of the pipeline is calculated according to #imgabs5#, and when the axial stress direction applied to the pipeline is the principal stress direction of the crack, the service life of the pipeline is calculated according to #imgabs6#. The service life prediction method applicable to natural gas hydrogen - blended pipelines of the present invention has high accuracy.

Description

Technical Field

[0001] The present invention relates to the field of pipeline testing, and particularly relates to a service life prediction method applicable to natural gas hydrogen - blended pipelines. Background Art

[0002] Cracks will occur in pipelines during the manufacturing, construction, and operation processes. For example, weld cracks are generated during manufacturing, cracks caused by mechanical damage are generated during transportation and construction, and cracks caused by corrosion are generated during operation. When pipelines are used to transport fuels, cracks are important factors affecting the service life of pipelines. Therefore, life prediction methods for pipelines transporting oil and gas have been proposed in related technologies. However, after hydrogen is blended into natural gas pipelines, hydrogen embrittlement will occur in the pipelines under the influence of hydrogen, and cracks will further expand due to hydrogen embrittlement, resulting in brittle cracking failure of the pipelines. Therefore, natural gas hydrogen - blended pipelines are more likely to cause safety accidents such as leakage compared to oil and gas pipelines. Moreover, the life prediction methods for oil and gas pipelines in related technologies are not applicable to natural gas hydrogen - blended pipelines and cannot accurately predict the service life of natural gas hydrogen - blended pipelines. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related technologies to some extent.

[0004] To this end, the present invention proposes a service life prediction method applicable to natural gas hydrogen - blended pipelines.

[0005] The service life prediction method applicable to natural gas hydrogen - blended pipelines of the present invention includes:

[0006] Establish a failure assessment diagram, and draw a load ratio cut - off line and a toughness ratio cut - off line in the failure assessment diagram. The load ratio cut - off line is where is the maximum load ratio of the pipe material, is the tensile strength of the pipe material in the natural gas hydrogen - blended environment, is the tensile strength of the pipe material in the inert environment. The toughness ratio cut - off line is where is the fracture toughness of the pipe material in the natural gas hydrogen - blended environment, is the fracture toughness of the pipe material in the inert environment. In the failure assessment diagram, the load ratio cut - off line, the toughness ratio cut - off line, and the partial failure assessment curve connecting between the load ratio cut - off line and the toughness ratio cut - off line are used as the reference line, and the area formed by the surrounding of the reference line and the coordinate system of the failure assessment diagram is the safety area;

[0007] Based on the calculated depth a of i cracks, calculate the load ratio and the toughness ratio respectively. The values of the calculated depth a of i cracks are successively , +k, +2k...... + (i - 1)k, where k is a constant, is the initial crack depth, and the load ratio corresponding to each calculated crack depth a is used as the abscissa of the failure assessment diagram, and the corresponding toughness ratio is used as the ordinate of the failure assessment diagram, so that each calculated crack depth a has a corresponding coordinate point ( , ) in the failure assessment diagram. Among the i coordinate points, the coordinate point located in the safe area and having the smallest distance from the reference line is used as the critical coordinate point, and the calculated crack depth a corresponding to the critical coordinate point is the critical crack depth ;

[0008] When the circumferential stress direction of the pipeline is the principal stress direction of the crack, the service life of the pipeline is calculated according to , and when the axial stress direction of the pipeline is the principal stress direction of the crack, the service life of the pipeline is calculated according to , where and m are both Paris parameters, is the load fluctuation frequency, is the internal pressure load fluctuation of the pipeline, D is the diameter of the pipeline, and t is the thickness of the pipeline.

[0009] Furthermore, the service life prediction method for the hydrogen - blended natural gas pipeline further includes:

[0010] Characterize the defects of the pipeline and regularize the cracks of the pipeline to obtain the characterization depth of the regularized cracks , is multiplied by the safety factor of the defect characterization size.

[0011] Furthermore, when characterizing the defects of the pipeline,

[0012] At , the pipeline is unqualified;

[0013] At , if , regularize the crack into and semi - elliptical surface crack, if , regularize the crack into semicircular surface crack;

[0014] where is the actual depth of the crack, is the actual length of the crack, is the wall thickness of the pipeline, is the characteristic depth of the regularized crack, is 1 / 2 of the characteristic length of the regularized crack.

[0015] Furthermore, the service life prediction method of the natural gas hydrogen - blended pipeline further includes:

[0016] Conduct slow strain rate tensile tests on the pipeline in an inert environment to obtain the tensile strength of the pipe material in the inert environment ;

[0017] Conduct slow strain rate tensile tests on the pipeline in a natural gas hydrogen - blended environment to obtain the tensile strength of the pipe material in the natural gas hydrogen - blended environment .

[0018] Furthermore, the service life prediction method of the natural gas hydrogen - blended pipeline further includes:

[0019] Conduct fracture toughness tests on the pipeline in an inert environment to obtain the fracture toughness of the pipe material in the inert environment ;

[0020] Conduct fracture toughness tests on the pipeline in a natural gas hydrogen - blended environment to obtain the fracture toughness of the pipe material in the natural gas hydrogen - blended environment .

[0021] Furthermore, conduct fracture toughness tests on the pipeline in an inert environment to obtain the J - integral fracture toughness of the pipe material in the inert environment , and calculate the fracture toughness of the pipe material in the inert environment according to , conduct fracture toughness tests on the pipeline in a natural gas hydrogen - blended environment to obtain the J - integral fracture toughness of the pipe material in the natural gas hydrogen - blended environment , and calculate the fracture toughness of the pipe material in the natural gas hydrogen - blended environment according to , ; or

[0022] Conduct fracture toughness tests on the pipeline in an inert environment to obtain the CTOD fracture toughness of the pipe material in the inert environment , and calculate the fracture toughness of the pipe material in the inert environment according to , conduct fracture toughness tests on the pipeline in a natural gas hydrogen - blended environment to obtain the CTOD fracture toughness of the pipe material in the natural gas hydrogen - blended environment , and calculate the fracture toughness of the pipe material in the natural gas hydrogen - blended environment according to , ;

[0023] ​​where E is the elastic modulus of the pipe material, is the yield strength of the pipe material, is the Poisson's ratio of the pipe material.

[0024] Further, the failure assessment curve is .

[0025] Further, when the crack is an axial crack of the pipeline, the load ratio , , and are used together to calculate the load ratio ;

[0026] When the crack is a circumferential crack of the pipeline, the load ratio and are used together to calculate the load ratio ;

[0027] where is the membrane stress component of the primary stress, is the bending stress component of the primary stress, is the yield strength of the pipe material, c is multiplied by the safety factor of the defect characterization size, and R is the radius of the pipe material.

[0028] Further, the toughness ratio is calculated according to , where is multiplied by the safety factor of the material fracture toughness, is the plastic correction factor, is the stress intensity factor caused by the primary stress, is the stress intensity factor caused by the secondary stress.

[0029] Further, the stress intensity factor caused by the primary stress is calculated according to ,

[0030] The stress intensity factor caused by the secondary stress is calculated according to ,

[0031] where is the membrane stress component of the primary stress, is the bending stress component of the primary stress, is the membrane stress component of the secondary stress, is the bending stress component of the secondary stress,

[0032] ,

[0033] , c is multiply the defect characterization size by the safety factor.

[0034] Further, at the load ratio obtained corresponding to the ductility ratio and when < 0.8, calculate and obtain the plasticity correction factor according to ; ;

[0035] At the load ratio obtained corresponding to the ductility ratio and when 0.8 < < 1.1, calculate and obtain the plasticity correction factor according to ; ;

[0036] At the load ratio obtained corresponding to the ductility ratio and when > 1.1, ; ;

[0037] wherein the value of is obtained from the coordinate graph curve of and .

[0038] Further, the safety factor of the material fracture toughness is 1.15 - 1.25, and the safety factor of the defect characterization size is 1.05 - 1.15.

[0039] Further, the service life prediction method for the natural gas hydrogen - blended pipeline further includes:

[0040] Conduct fatigue crack growth tests on the pipeline in an inert environment and a natural gas hydrogen - blended environment to obtain the Paris parameter and the Paris parameter m in the Paris formula.

[0041] The service life prediction method for the natural gas hydrogen - blended pipeline according to the present invention calculates the load ratio and the ductility ratio respectively based on the i calculated crack depths a to form i coordinate points in the failure assessment diagram, and obtain the critical crack depth , and then select the corresponding service life formula according to the principal stress direction of the crack and calculate the predicted service life of the pipeline. Among them, both the load ratio cut-off line and the toughness ratio cut-off line in the failure assessment diagram are obtained based on the inert environment and the natural gas hydrogen-doped environment, making the accuracy of the reference line and the safety area higher, so as to obtain the critical crack depth more accurate. At the same time, the service life formula is based on the Paris parameter, which also makes the accuracy of the service life formula higher. In addition, based on the calculated depths a of i cracks, i coordinate points are obtained, and the coordinate point located in the safety area and having the smallest distance from the reference line is selected from the i coordinate points to obtain the critical crack depth , so as to obtain an accurate critical crack depth , thereby making the accuracy of the service life formula higher. Therefore, the service life prediction method for natural gas hydrogen-doped pipelines of the present invention has high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram of defect characterization in the service life prediction method for natural gas hydrogen-doped pipelines according to an embodiment of the present invention Figure 1 ;

[0043] Figure 2 is a schematic diagram of defect characterization in the service life prediction method for natural gas hydrogen-doped pipelines according to an embodiment of the present invention Figure 2 ;

[0044] Figure 3 is a schematic diagram of defect characterization in the service life prediction method for natural gas hydrogen-doped pipelines according to an embodiment of the present invention Figure 3 ;

[0045] Figure 4 is an example diagram of the failure assessment diagram in the service life prediction method for natural gas hydrogen-doped pipelines according to an embodiment of the present invention;

[0046] Figure 5 is in the service life prediction method for natural gas hydrogen-doped pipelines according to an embodiment of the present invention and coordinate diagram. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0048] The following will refer to Figures 1 - 5 to describe the service life prediction method for natural gas hydrogen-doped pipelines according to an embodiment of the present invention.

[0049] As Figures 1 - 5As shown in the figure, the service life prediction method for a natural gas hydrogen - blended pipeline according to an embodiment of the present invention includes:

[0050] Establish a failure assessment diagram. Specifically, as Figure 4 shown, the horizontal axis of the failure assessment diagram is the load ratio , and the vertical axis is the toughness ratio . And draw a load ratio cut - off line (such as the line L1 shown in Figure 4 ) and a toughness ratio cut - off line (such as the line L2 shown in Figure 4 ) in the failure assessment diagram. The load ratio cut - off line is , where is the maximum load ratio of the pipe material, is the tensile strength of the pipe material in the natural gas hydrogen - blended environment, is the tensile strength of the pipe material in the inert environment. The toughness ratio cut - off line is , where is the fracture toughness of the pipe material in the natural gas hydrogen - blended environment, is the fracture toughness of the pipe material in the inert environment.

[0051] In the failure assessment diagram, the load ratio cut - off line (such as the line L1 shown in Figure 4 ), the toughness ratio cut - off line (such as the line L2 shown in Figure 4 ), and the partial failure assessment curve connecting the load ratio cut - off line and the toughness ratio cut - off line (the failure assessment curve is the line L3 shown in Figure 4 ) are used as the reference lines. The area formed by the reference lines and the coordinate system of the failure assessment diagram is the safe area. In other words, the area between the reference lines and the horizontal and vertical axes of the failure assessment diagram is the safe area, and the other areas of the failure assessment diagram are non - safe areas.

[0052] Based on the i calculated crack depths a, calculate the load ratio and the toughness ratio respectively. The values of the i calculated crack depths a are successively , +k, +2k...... + (i - 1)k. In other words, the value of the first crack depth a is , the value of the second crack depth a is +k, the value of the third crack depth a is +2k...... The value of the i - th crack depth a is + (i - 1)k, where k is a constant, is the initial crack depth.

[0053] For each crack depth a, the corresponding load ratio As the abscissa of the failure assessment diagram, and the corresponding toughness ratio As the ordinate of the failure assessment diagram, so that each crack calculation depth a has a corresponding coordinate point in the failure assessment diagram ( , ). Among the i coordinate points, the coordinate point located in the safe area and with the smallest distance from the reference line is used as the critical coordinate point, and the crack calculation depth a corresponding to the critical coordinate point is the critical crack depth .

[0054] When the circumferential stress direction of the pipeline is the principal stress direction of the crack, according to Calculate the service life of the pipeline.

[0055] When the axial stress direction of the pipeline is the principal stress direction of the crack, according to Calculate the service life of the pipeline.

[0056] Among them And m are both Paris parameters, Is the load fluctuation frequency, Is the internal pressure load fluctuation of the pipeline, D is the diameter of the pipeline, and t is the thickness of the pipeline.

[0057] It should be noted that the inert environment includes the air environment and the inert gas environment.

[0058] The service life prediction method for hydrogen-doped natural gas pipelines according to the embodiments of the present invention calculates the load ratio And toughness ratio Based on i crack calculation depths a respectively to form i coordinate points in the failure assessment diagram, and obtain the critical crack depth according to the reference line and the safe area in the failure assessment diagram , and then select the corresponding service life formula according to the principal stress direction of the crack and calculate the predicted service life of the pipeline.

[0059] Among them, the load ratio cut-off line and the toughness ratio cut-off line in the failure assessment diagram are both obtained based on the inert environment and the hydrogen-doped natural gas environment, making the accuracy of the reference line and the safe area higher, so that the obtained critical crack depth Is more accurate.

[0060] At the same time, the service life formula is based on the Paris parameters, which also makes the accuracy of the service life formula higher.

[0061] In addition, i coordinate points are obtained based on i crack calculation depths a, and the coordinate point located in the safe area and with the smallest distance from the reference line is selected among the i coordinate points to obtain the critical crack depth , in order to obtain an accurate critical crack depth , thereby making the accuracy of the service life formula higher.

[0062] Therefore, the service life prediction method for natural gas hydrogen - blended pipelines in the embodiments of the present invention has a high accuracy.

[0063] In some embodiments, the service life prediction method for natural gas hydrogen - blended pipelines in the embodiments of the present invention further includes characterizing the defects of the pipeline and regularizing the cracks of the pipeline to obtain the characterization depth of the regularized cracks , multiplying the defect characterization size by the safety factor.

[0064] Obtain the characterization depth of the regularized cracks through defect characterization , so as to obtain the initial crack depth , which is used to calculate the load ratio and the toughness ratio respectively based on the calculated depth a of the i - th crack.

[0065] In some embodiments, when characterizing the defects of the pipeline, when Figure 1 as shown in , after crack regularization, it is and a through - crack that penetrates the wall of the pipeline along the thickness direction of the pipeline. Since the regularized through - crack penetrates the wall of the pipeline, the pipeline is unqualified. In other words, the service life of the pipeline is zero. There is no need to continue predicting the service life of this pipeline.

[0066] At , if , regularize the crack into and a semi - elliptical surface crack as shown in Figure 2 . If , in other words, if , regularize the crack into a semi - circular surface crack as shown in Figure 3 .

[0067] Where is the actual depth of the crack, is the actual length of the crack, is the wall thickness of the pipeline, is the characterization depth of the regularized crack, is 1 / 2 of the characterization length of the regularized crack. In other words, 2 is the characterization length of the regularized crack.

[0068] Thus, obtain the characterization depth of the regularized crack, so as to obtain the initial crack depth 。

[0069] In some embodiments, the safety factor of the defect characterization size is 1.05 - 1.15, preferably 1.1. Therefore, = 1.1 。

[0070] In some embodiments, the service life prediction method for the natural gas hydrogen - blended pipeline according to the embodiments of the present invention further includes obtaining the pipe material information and crack defect information of the pipeline. The pipe material information includes the wall thickness of the pipeline and so on. The crack defect information includes the location of the crack, the actual length of the crack , the actual depth of the crack and so on. Thus, the defect characterization of the pipeline can be carried out.

[0071] Specifically, the crack defect information can be obtained by internal inspection methods such as ultrasonic testing, magnetic flux leakage testing, eddy current testing, etc., and can also be obtained by external inspection methods such as girth weld non - destructive testing.

[0072] In some embodiments, the service life prediction method for the natural gas hydrogen - blended pipeline according to the embodiments of the present invention further includes performing a slow strain rate tensile test on the pipeline in an inert environment to obtain the tensile strength of the pipe material in the inert environment . Performing a slow strain rate tensile test on the pipeline in a natural gas hydrogen - blended environment to obtain the tensile strength of the pipe material in the natural gas hydrogen - blended environment .

[0073] Specifically, the slow strain rate tensile test preferably but not limited to uses a smooth tensile specimen. The smooth tensile specimen preferably but not limited to uses a base metal specimen or a weld specimen. The length direction of the base metal specimen of the smooth tensile specimen is the circumferential direction of the pipeline. In other words, the length direction of the base metal specimen of the smooth tensile specimen is the circumferential direction of the pipeline. The length direction of the weld specimen of the smooth tensile specimen is perpendicular to the extension direction of the pipeline weld, and the center position of the gauge section of the weld specimen is located at the weld center. If the wall thickness and diameter of the pipeline cannot meet the sampling size requirements of the base metal specimen and the weld specimen, then a smooth tensile specimen is obtained along the axial direction of the pipeline, and the length direction of the obtained smooth tensile specimen is the axial direction of the pipeline.

[0074] The smooth tensile specimen is in a round bar shape, the surface machining roughness Ra of the gauge section of the smooth tensile specimen ≤ 0.8μm, and the tensile rate of the smooth tensile specimen is less than or equal to 2x10 -5 s -1 。

[0075] Slow strain rate tensile tests were respectively carried out on the pipeline in an inert environment and a natural gas with hydrogen admixture environment. For each environment, multiple sampling positions were set along the circumferential direction of the pipeline during the slow strain rate tensile test, and multiple smooth tensile specimens were obtained at each sampling position. Preferably, 3 sampling positions were set along the circumferential direction of the pipeline, and 3 smooth tensile specimens were obtained at each sampling position.

[0076] When carrying out the slow strain rate tensile test on the pipeline in the natural gas with hydrogen admixture environment, it is necessary to pre-fill hydrogen into the slow strain rate tensile test equipment to simulate the natural gas with hydrogen admixture environment during the pipeline operation. The pre-filling time of hydrogen is more than 24 hours. After the pre-filling of hydrogen is completed, in-situ slow tensile test is carried out to complete the slow strain rate tensile test on the pipeline in the natural gas with hydrogen admixture environment.

[0077] After carrying out the slow strain rate tensile tests on the pipeline in the inert environment and the natural gas with hydrogen admixture environment respectively, the displacement-stress curve of the pipe material is obtained, so as to obtain the tensile strength of the pipe material in the inert environment and the tensile strength in the natural gas with hydrogen admixture environment .

[0078] By carrying out the slow strain rate tensile tests on the pipeline in the inert environment and the natural gas with hydrogen admixture environment respectively, the tensile strength of the pipe material in the inert environment and the tensile strength in the natural gas with hydrogen admixture environment are obtained for obtaining the load ratio cut-off line in the failure assessment diagram.

[0079] In some embodiments, the service life prediction method of the natural gas with hydrogen admixture pipeline in the embodiments of the present invention further includes obtaining the pipe material information and pipeline service information of the pipeline. The pipe material information includes the type of the pipe material, the wall thickness of the pipeline , the diameter D of the pipeline, the thickness t of the pipeline, as well as the welding process, chemical composition, mechanical tensile properties, elastic modulus, Poisson's ratio, etc. of the weld. The pipeline service information includes the design pressure, operating pressure, design temperature, operating temperature of the pipeline, as well as the maximum hydrogen admixture ratio, load, stress generated during the operation period of the pipeline, etc. Thus, the slow strain rate tensile tests can be respectively carried out on the pipeline in the inert environment and the natural gas with hydrogen admixture environment.

[0080] In some embodiments, the service life prediction method of the natural gas with hydrogen admixture pipeline in the embodiments of the present invention further includes carrying out a fracture toughness test on the pipeline in the inert environment to obtain the fracture toughness of the pipe material in the inert environment . Carrying out a fracture toughness test on the pipeline in the natural gas with hydrogen admixture environment to obtain the fracture toughness of the pipe material in the natural gas with hydrogen admixture environment .

[0081] Specifically, the fracture toughness test preferably but not limited to using a compact tension specimen. In the fracture toughness test, the compact tension specimen preferably but not limited to using a base metal specimen or a weld specimen. The crack propagation direction on the base metal specimen of the compact tension specimen is the axial direction of the pipeline, and the crack propagation direction on the weld specimen of the compact tension specimen is the extension direction of the weld of the pipeline.

[0082] In the fracture toughness test, the thickness of the compact tension specimen is greater than 85% of the designed thickness of the pipeline, preferably but not limited to greater than 85% of the wall thickness of the pipeline. The tensile rate of the compact tension specimen is 0.1 MPa·m / min to 1 MPa·m 1 / 2 / min. 1 / 2

[0083] The fracture toughness tests of the pipeline are respectively carried out in an inert environment and a natural gas hydrogen-doped environment. For each environment, a plurality of sampling positions are set along the circumferential direction of the pipeline, and a plurality of compact tension specimens are obtained at each sampling position. Preferably, 3 sampling positions are set along the circumferential direction of the pipeline, and 3 compact tension specimens are obtained at each sampling position.

[0084] When carrying out the fracture toughness test of the pipeline in the natural gas hydrogen-doped environment, it is necessary to pre-fill hydrogen into the fracture toughness test equipment to simulate the natural gas hydrogen-doped environment during the operation of the pipeline. The pre-filling time of hydrogen is greater than 24 hours. After the pre-filling of hydrogen is completed, an in-situ fracture toughness test is carried out to complete the fracture toughness test of the pipeline in the natural gas hydrogen-doped environment.

[0085] By carrying out the fracture toughness tests of the pipeline in an inert environment and a natural gas hydrogen-doped environment respectively, the fracture toughness of the pipe material in the inert environment and the fracture toughness in the natural gas hydrogen-doped environment are obtained, so as to be used to obtain the toughness ratio cut-off line in the failure assessment diagram.

[0086] In some embodiments, the fracture toughness test of the pipeline is carried out in an inert environment to obtain the J-integral fracture toughness of the pipe material in the inert environment , and according to calculate the fracture toughness of the pipe material in the inert environment , the fracture toughness test of the pipeline is carried out in the natural gas hydrogen-doped environment to obtain the J-integral fracture toughness of the pipe material in the natural gas hydrogen-doped environment , and according to calculate the fracture toughness of the pipe material in the natural gas hydrogen-doped environment , where E is the elastic modulus of the pipe material, is the yield strength of the pipe material, is the Poisson's ratio of the pipe material.

[0087] ​In some embodiments, the fracture toughness test of the pipeline is carried out in an inert environment to obtain the CTOD fracture toughness of the pipe material in the inert environment , according to calculate the fracture toughness of the pipe material in the inert environment , carry out the fracture toughness test on the pipeline in the natural gas hydrogen-doped environment to obtain the CTOD fracture toughness of the pipe material in the natural gas hydrogen-doped environment , according to calculate the fracture toughness of the pipe material in the natural gas hydrogen-doped environment , where E is the elastic modulus of the pipe material, is the yield strength of the pipe material, is the Poisson's ratio of the pipe material.

[0088] Therefore, by carrying out the fracture toughness test on the pipeline in the inert environment and the natural gas hydrogen-doped environment respectively, the J-integral fracture toughness of the pipe material in the inert environment and the J-integral fracture toughness in the natural gas hydrogen-doped environment can be obtained to calculate the fracture toughness of the pipe material in the inert environment and the fracture toughness in the natural gas hydrogen-doped environment , and the CTOD fracture toughness of the pipe material in the inert environment and the CTOD fracture toughness in the natural gas hydrogen-doped environment can also be obtained to calculate the fracture toughness of the pipe material in the inert environment and the fracture toughness in the natural gas hydrogen-doped environment . Thus, the toughness ratio cut-off line in the failure assessment diagram is obtained.

[0089] In some embodiments, the service life prediction method of the natural gas hydrogen-doped pipeline according to the embodiments of the present invention further includes obtaining the pipe material information, crack defect information and pipeline service information of the pipeline. The pipe material information includes the type of the pipe material, the wall thickness of the pipeline , the diameter D of the pipeline, the thickness t of the pipeline, as well as the welding process, chemical composition, mechanical tensile properties, elastic modulus, Poisson's ratio, etc. of the weld. The crack defect information includes the position of the crack, the actual length of the crack , the actual depth of the crack , etc. The pipeline service information includes the design pressure, operating pressure, design temperature, operating temperature of the pipeline, as well as the maximum hydrogen doping ratio, load, stress generated during the operation period of the pipeline, etc. Thus, the fracture toughness test can be carried out on the pipeline in the inert environment and the natural gas hydrogen-doped environment respectively.

[0090] In some embodiments, the failure assessment curve is .

[0091] Specifically, as Figure 4 shown, with the load ratio As the horizontal axis and with the toughness ratio As the vertical axis, establish the coordinate system of the failure assessment diagram, and draw the failure assessment curve based on the coordinate system of the failure assessment diagram (such as Figure 4 The line L3 shown) , draw the original load ratio cut-off line based on the coordinate system of the failure assessment diagram (such as Figure 4 The line L4 shown) , so as to form the failure assessment diagram.

[0092] Then draw the load ratio cut-off line (such as Figure 4 The line L1 shown) and the toughness ratio cut-off line (such as Figure 4 The line L2 shown) in the failure assessment diagram, so as to determine the reference line and the safe area.

[0093] It can be understood that the failure assessment diagram is not limited to having the original load ratio cut-off line. In some other embodiments, with the load ratio As the horizontal axis and with the toughness ratio As the vertical axis, establish the coordinate system of the failure assessment diagram, and draw the failure assessment curve based on the coordinate system of the failure assessment diagram, so as to form the failure assessment diagram.

[0094] In some embodiments, the service life prediction method of the natural gas hydrogen blending pipeline in the embodiments of the present invention further includes obtaining the pipe material information of the pipeline. The pipe material information of the pipeline includes the maximum load ratio of the pipe material etc. Thus, the failure assessment diagram can be established.

[0095] In some embodiments, the crack is divided into a pipeline axial crack and a pipeline circumferential crack according to the extension direction. The pipeline axial crack extends along the axis of the pipeline, and the pipeline circumferential crack extends along the circumference of the pipeline. In other words, it extends along the circumferential direction of the pipeline.

[0096] When the crack is a pipeline axial crack, according to , , and Cooperate to calculate the load ratio .

[0097] When the crack is a pipeline circumferential crack, according to and Cooperate to calculate the load ratio .

[0098] Where Is the membrane stress component of the primary stress, Is the bending stress component of the primary stress, Is the yield strength of the pipe material, c is Multiply the safety factor of the defect characterization size, and R is the radius of the pipe material.

[0099] Thus, the load ratio corresponding to the calculated depth a of each crack is calculated. .

[0100] In some embodiments, according to the toughness ratio is calculated as , where is the product of the material fracture toughness divided by the safety factor, is the plastic correction factor, is the stress intensity factor caused by the primary stress, is the stress intensity factor caused by the secondary stress.

[0101] Thus, the toughness ratio corresponding to the calculated depth a of each crack is calculated. .

[0102] In some embodiments, the safety factor for the material fracture toughness is 1.15 - 1.25, preferably 1.2, and the safety factor for the defect characterization size is 1.05 - 1.15, preferably 1.1. Therefore, c = 1.1 , = 1.2 .

[0103] In some embodiments, according to ) the stress intensity factor caused by the primary stress is calculated as . According to ) the stress intensity factor caused by the secondary stress is calculated as . Where is the membrane stress component of the primary stress, is the bending stress component of the primary stress, is the membrane stress component of the secondary stress, is the bending stress component of the secondary stress,

[0104] ,

[0105] , c is the product of

[0106] multiplied by the safety factor for the defect characterization size. Based on the membrane stress component of the primary stress and the bending stress component of the primary stress, the stress intensity factor caused by the primary stress is calculated, and based on the membrane stress component of the secondary stress and the bending stress component of the secondary stress, the stress intensity factor .

[0107] In some embodiments, the present invention also includes obtaining service information of the pipeline, and the pipeline service information includes stresses generated by the pipeline during operation, including the pressure of the transport medium and the stress generated by it, the gravity load of the transport medium and the structure and the stress generated by it, external mechanical loads and the stress generated by them, loads such as vibration and wind loads and the stress generated by them, welding residual stresses caused by welding, stresses generated by structural geometric discontinuities such as misaligned edges, edges and corners, local thinning of walls, unequal thicknesses, etc. when loads act on them, thermal temperature difference stresses or thermal stresses generated by temperature differences, uncoordinated thermal expansion and contraction, etc.

[0108] The stress generated during the operation of the pipeline is divided into primary stress and secondary stress. The primary stress includes the stress caused at the connecting pipe due to the thermal expansion of the pipeline system. The secondary stress includes the residual stress caused by welding, the local stress caused by misalignment, edges and corners, and local thickness difference, and the thermal stress caused by the wall temperature difference or the different thermal expansion coefficients of the materials.

[0109] The film stress component of the primary stress is obtained according to the primary stress , the bending stress component of the primary stress , according to the secondary stress, the film stress component of the secondary stress is obtained and the bending stress component of the secondary stress , so that the load ratio can be calculated and toughness ratio .

[0110] In some embodiments, the plasticity correction factor Toughness ratio The corresponding load ratio <0.8, according to Calculate the plasticity correction factor . With the plasticity correction factor Toughness ratio The corresponding load ratio 0.8< <1.1, according to Calculate the plasticity correction factor . With the plasticity correction factor Toughness ratio The corresponding load ratio >1.1, .in The value of and The coordinate diagram (such as Figure 5 The curve shown is obtained.

[0111] According to the plasticity correction factor The ductility ratio can be calculated .

[0112] In some embodiments, the service life prediction method of the hydrogen-doped natural gas pipeline according to the embodiments of the present invention further includes performing fatigue crack growth tests on the pipeline in an inert environment and a hydrogen-doped natural gas environment to obtain the Paris parameter in the Paris formula and the Paris parameter m

[0113] Specifically, the fatigue crack growth test preferably but not limited to use a compact tension specimen. In the fatigue crack growth test, the compact tension specimen preferably but not limited to use a base metal specimen or a weld specimen. The crack extension direction on the base metal specimen of the compact tension specimen is the axial direction of the pipeline, and the crack extension direction on the weld specimen of the compact tension specimen is the extension direction of the weld of the pipeline, and the weld specimen is taken from the center of the weld

[0114] In the fatigue crack growth test, the thickness of the compact tension specimen is greater than 85% of the designed thickness of the pipeline, preferably but not limited to greater than 85% of the wall thickness of the pipeline of the pipeline

[0115] Perform fatigue crack growth tests on the pipeline in an inert environment and a hydrogen-doped natural gas environment respectively. For each environment, multiple sampling positions are set along the circumferential direction of the pipeline, and multiple compact tension specimens are obtained at each sampling position. Preferably, 3 sampling positions are set along the circumferential direction of the pipeline, and 3 compact tension specimens are obtained at each sampling position

[0116] When performing the fatigue crack growth test on the pipeline in the hydrogen-doped natural gas environment, it is necessary to pre-fill hydrogen into the fatigue crack growth test equipment to simulate the hydrogen-doped natural gas environment during pipeline operation, and the pre-filling time of hydrogen is greater than 24 hours

[0117] The test frequencies of performing fatigue crack growth tests on the pipeline in an inert environment and a hydrogen-doped natural gas environment are both 0.1Hz to 1Hz

[0118] By performing fatigue crack growth tests on the pipeline in an inert environment and a hydrogen-doped natural gas environment respectively, the Paris parameter in the Paris formula and the Paris parameter m can be obtained based on the Paris formula, so that the service life of the pipeline can be calculated

[0119] In some embodiments, the service life prediction method of the hydrogen-doped natural gas pipeline according to the embodiments of the present invention further includes obtaining the pipe material information and pipeline service information of the pipeline. The pipe material information includes the type of the pipe material and the wall thickness of the pipeline , the diameter D of the pipeline, the thickness t of the pipeline, as well as the welding process, chemical composition, mechanical tensile properties, elastic modulus, Poisson's ratio, etc. of the weld. The pipeline service information includes the design pressure, operating pressure, design temperature, operating temperature of the pipeline, as well as the maximum hydrogen blending ratio, load, and stress generated during the operation of the pipeline. Thus, fatigue crack growth tests can be carried out on the pipeline in an inert environment and a natural gas hydrogen blending environment respectively.

[0120] Preferably, the method for predicting the service life of the natural gas hydrogen blending pipeline according to the embodiment of the present invention first obtains the pipe material information, crack defect information, and pipeline service information of the pipeline, and then respectively conducts slow strain rate tensile tests, fracture toughness tests, and fatigue crack growth tests.

[0121] In the description of the present invention, it should be understood that the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0122] In the present invention, the terms "an embodiment", "some embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0123] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A service life prediction method applicable to natural gas hydrogen - blended pipelines, characterized in that, Including: Establish a failure assessment diagram, and draw a load ratio cut-off line and a toughness ratio cut-off line in the failure assessment diagram. The load ratio cut-off line is , where is the maximum load ratio of the pipe, is the tensile strength of the pipe in a natural gas blended with hydrogen environment, is the tensile strength of the pipe in an inert environment. The toughness ratio cut-off line is , where is the fracture toughness of the pipe in a natural gas blended with hydrogen environment, is the fracture toughness of the pipe in an inert environment. In the failure assessment diagram, the load ratio cut-off line, the toughness ratio cut-off line, and the partial failure assessment curve connecting the load ratio cut-off line and the toughness ratio cut-off line are used as reference lines. The area formed by the reference lines and the coordinate system of the failure assessment diagram is the safety zone; Calculate the load ratio respectively based on the calculated depths a of i cracks and the toughness ratio . The values of the calculated depths a of the i cracks are successively , +k, +2k...... + (i - 1)k, where k is a constant, is the initial crack depth. Take the load ratio corresponding to each calculated crack depth a as the abscissa of the failure assessment diagram, and take the corresponding toughness ratio as the ordinate of the failure assessment diagram, so that each calculated crack depth a has a corresponding coordinate point ( , ) in the failure assessment diagram. Among the i coordinate points, the coordinate point that is located within the safety zone and has the smallest distance from the reference line is used as the critical coordinate point, and the calculated crack depth a corresponding to the critical coordinate point is the critical crack depth ; When the circumferential stress direction of the pipeline is the principal stress direction of the crack, calculate the service life of the pipeline according to When the axial stress direction of the pipeline is the principal stress direction of the crack, calculate the service life of the pipeline according to where and m are both Paris parameters, is the load fluctuation frequency, is the internal pressure load fluctuation of the pipeline, D is the diameter of the pipeline, and t is the thickness of the pipeline.

2. The service life prediction method of the natural gas hydrogen-blended pipeline according to claim 1, characterized in that Also including: Characterize the defects of the pipeline and regularize the cracks of the pipeline to obtain the characterized depth of the regularized cracks , is multiply the defect characterization size by the safety factor.

3. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 2, wherein, When characterizing the defects of the pipeline, At time, the pipeline is unqualified; At When, if Regularize the crack into And Semi-elliptical surface crack of , Regularize the crack into Semicircular surface crack of wherein is the actual depth of the crack, is the actual length of the crack, is the wall thickness of the pipe, is the characteristic depth of the regularized crack, is 1 / 2 of the characteristic length of the regularized crack.

4. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 1, characterized in that Also including: Perform slow strain rate tensile tests on the pipeline in an inert environment to obtain the tensile strength of the pipe material in an inert environment ; Conduct a slow strain rate tensile test on the pipeline in a natural gas-hydrogen blended environment to obtain the tensile strength of the pipe material in a natural gas-hydrogen blended environment .

5. The service life prediction method of the natural gas hydrogen-blended pipeline according to claim 1, characterized in that, Also including: Conduct a fracture toughness test on the pipeline in an inert environment to obtain the fracture toughness of the pipe material in the inert environment ; Conduct a fracture toughness test on the pipeline in a natural gas blended with hydrogen environment to obtain the fracture toughness of the pipe material in a natural gas blended with hydrogen environment .

6. The service life prediction method of the natural gas hydrogen-doped pipeline according to claim 5, characterized in that, Conduct a fracture toughness test on the pipeline in an inert environment to obtain the J-integral fracture toughness of the pipe material in the inert environment , according to Calculate the fracture toughness of the pipe material in the inert environment , conduct a fracture toughness test on the pipeline in a hydrogen-enriched natural gas environment to obtain the J-integral fracture toughness of the pipe material in the hydrogen-enriched natural gas environment , according to Calculate the fracture toughness of the pipe material in the hydrogen-enriched natural gas environment ; Or Conduct a fracture toughness test on the pipeline in an inert environment to obtain the CTOD fracture toughness of the pipe material in the inert environment , according to Calculate the fracture toughness of the pipe material in the inert environment , conduct a fracture toughness test on the pipeline in a hydrogen-doped natural gas environment to obtain the CTOD fracture toughness of the pipe material in the hydrogen-doped natural gas environment , according to Calculate the fracture toughness of the pipe material in the hydrogen-doped natural gas environment ; where E is the elastic modulus of the pipe material, is the yield strength of the pipe material, is the Poisson's ratio of the pipe material.

7. The service life prediction method of the natural gas hydrogen-doped pipeline according to claim 1, wherein The failure assessment curve is .

8. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 3, characterized in that When the crack is an axial crack of the pipeline, according to , , and are used in combination to calculate the load ratio ; When the crack is a circumferential crack of the pipeline, according to and cooperate to calculate the load ratio ; wherein is the membrane stress component of the primary stress, is the bending stress component of the primary stress, is the yield strength of the pipe, and c is the safety factor multiplied by the defect characterization size, and R is the radius of the pipe.

9. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 3, characterized in that According to the toughness ratio is calculated as , where is the safety factor multiplied by the fracture toughness of the material, is the plastic correction factor, is the stress intensity factor caused by the primary stress, is the stress intensity factor caused by the secondary stress.

10. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 9, characterized in that According to ) Calculate the stress intensity factor caused by the primary stress , According to ) Calculate the stress intensity factor caused by secondary stress , wherein is the membrane stress component of the primary stress, is the bending stress component of the primary stress, is the membrane stress component of the secondary stress, is the bending stress component of the secondary stress, ， , c is the safety factor multiplied by the defect characterization size.

11. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 9, characterized in that At the plastic correction factor The toughness ratio obtained The corresponding load ratio <0.8, according to Calculate and obtain the plastic correction factor ; In relation to the plastic correction factor The ductility ratio obtained The corresponding load ratio Is 0.8 < < 1.

1. According to Calculate to obtain the plastic correction factor ; In relation to the plastic correction factor The ductility ratio obtained The corresponding load ratio > 1.1, ; Among them The value of is obtained from and the coordinate graph curve of 12. The service life prediction method of the natural gas hydrogen blending pipeline according to claim 9, characterized in that, The safety factor of the material fracture toughness is 1.15 - 1.25, and the safety factor of the defect characterization size is 1.05 - 1.

15.

13. The service life prediction method of the natural gas hydrogen-doped pipeline according to claim 1, characterized in that, Also including: The fatigue crack growth test is carried out on the pipeline in an inert environment and a natural gas hydrogen-doped environment respectively to obtain the Paris parameter C and the Paris parameter m in the Paris formula. and the Paris parameter m.

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