Method for evaluating fracture toughness of metal material in hydrogen environment

Abstract

The invention discloses a method and system for evaluating the influence of hydrogen content on the fracture performance of a metal material under the stress-strain synergistic effect, and the method comprises the following steps: (1) carrying out a hydrogen diffusion and mechanical property coupling experiment, and carrying out an in-situ tensile hydrogen permeation experiment and a compact tensile experiment, and respectively obtaining a rule of hydrogen diffusion parameter co-evolution along with stress-strain and fracture toughness data in different hydrogen-stress-strain coupling states. (2) establishing and verifying a multi-physics field coupling numerical model, constructing a hydrogen diffusion-mechanical coupling model based on a stress driven diffusion and strain proliferation trap theory, and establishing a quantitative correlation function of stress-strain-hydrogen concentration-hydrogen induced crack initiation J integral through experimental data calibration; and (3) carrying out safety assessment on the defective pipeline, establishing an actual pipeline defect model, calculating J integral at the defect and predicted crack initiation J integral of the metal material under the working condition, and carrying out quantitative risk grading by defining a safety margin coefficient, so as to realize early warning and management and control of the hydrogen induced cracking risk.

Description

Technical Field

[0001] This invention relates to the field of energy storage and transportation technology, and in particular to a method for evaluating the fracture toughness of metallic materials in hydrogen-containing environments. Background Technology

[0002] Pipeline transportation, as a primary mode of transporting energy sources such as oil, natural gas, hydrogen, ammonia, and alcohols, is crucial for safety and long-term service performance. However, metallic materials are highly susceptible to hydrogen embrittlement when operating in hydrogen-containing environments, leading to decreased material toughness, reduced resistance to crack initiation and propagation, and seriously threatening the structural integrity and operational safety of pipelines. In actual service environments exposed to hydrogen, pipelines are subjected to internal pressure and external loads, simultaneously generating complex stress and strain fields. When the stress field acts as the primary driving force, it significantly accelerates the diffusion of hydrogen atoms to defect regions; while the strain field, through crystal defects such as multiplying dislocations and micropores, acts as hydrogen traps, dominating the local capture and enrichment of hydrogen. These two stages are sequential, synergistic, and mutually coupled, jointly determining the final hydrogen distribution and the hydrogen embrittlement effect. However, most studies attribute hydrogen embrittlement to static hydrogen concentration, failing to delve into the staged and synergistic influence mechanisms of stress and strain fields on the hydrogen-induced cracking process under complex service loads. Specifically, it ignores the significant driving effect of the stress field on hydrogen diffusion during the elastic or small-scale yielding stages, and the behavior of strain-induced dislocations, micropores and other defects as hydrogen traps during the large plastic deformation stages, which capture and locally enrich hydrogen.

[0003] Existing assessment methods often rely on empirical formulas or single-factor correlations, lacking physical models that can quantitatively characterize the multi-field coupling relationship of "stress-strain-hydrogen-fracture toughness". This makes it difficult to accurately predict the crack initiation behavior of defective pipelines under the combined action of dynamic loads and hydrogen environment, bringing significant uncertainty to pipeline integrity management. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing hydrogen embrittlement research, which neglects the synergistic effect of stress and strain, and provides a systematic method integrating experimental characterization, multiphysics coupling simulation, and engineering risk assessment. Through in-situ hydrogen permeation and fracture experiments conducted in an experimental device under controllable loads, combined with numerical simulation, the invention systematically reveals how the synergistic mechanism of stress-driven hydrogen diffusion and strain-induced hydrogen trapping affects hydrogen distribution and embrittlement behavior. Furthermore, it establishes a quantitative relationship between stress, strain, hydrogen concentration, and fracture toughness, providing a precise theoretical basis for the safety assessment of hydrogen-containing pipelines.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for evaluating the fracture toughness of metallic materials in a hydrogen-exposed environment, comprising the following steps:

[0007] Step S1: Determine the hydrogen concentration distribution under the synergistic effect of stress and strain. Through in-situ tensile hydrogen permeation experiments on metallic materials, systematically study the diffusion and enrichment behavior of hydrogen in materials under different stress and strain states, clarify the synergistic mechanism of stress-driven diffusion and strain multiplication trap, and provide key input parameters for subsequent multi-field coupled simulation.

[0008] Step S2: Fracture performance test under hydrogen environment. Through a compact tensile test on metallic materials, the J-integral and hydrogen-induced crack initiation J-integral values ​​(J0.05) of the materials under different stress-strain-hydrogen environment coupling conditions are measured. IH ).

[0009] Step S3: Based on the multiphysics coupling theory, establish a numerical model that includes stress field, strain field, hydrogen diffusion field and damage field, simulate the behavior of compact tensile specimens under different loads and hydrogen concentrations, verify the accuracy of experimental results, and construct a quantitative correlation function of "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J integral".

[0010] Step S4: Apply the established quantitative correlation function to the engineering safety assessment of pipelines with defects. By comparing the J integral value at the actual defect with the predicted hydrogen-induced cracking J integral value of the material under the same working condition, the risk of hydrogen-induced cracking is quantitatively determined, providing a basis for pipeline maintenance decisions.

[0011] Furthermore, the method for the electrochemical experiment in step S1 is as follows:

[0012] Step S11: Select a suitable metallic material sample.

[0013] Step S12: Before the electrochemical experiment, the sample is polished, cleaned, dehydrated and dried.

[0014] Step S13: The sample is installed in an experimental apparatus with independently controllable load and displacement, and placed in a dual-electrolysis cell electrochemical hydrogen charging system. Hydrogen permeation current density-time curves under different stress-strain states are simultaneously measured through in-situ tensile testing and hydrogen charging.

[0015] Step S14: Process the hydrogen permeation current density-time curve using a constant concentration model, and calculate the surface hydrogen concentration C0 and the effective hydrogen diffusion coefficient D. eff Reversible hydrogen trap density N T Hydrogen permeation parameters were established. By analyzing the differences in permeation behavior between the elastic and plastic stages, the relationship between stress and hydrogen diffusion coefficient and the evolution relationship between plastic strain and reversible hydrogen trap density were established, thus providing staged physical parameter inputs for subsequent coupled models.

[0016] The hydrogen concentration distribution in a defective pipeline is calculated based on the above theoretical formula.

[0017] Furthermore, the method for the compact tensile test in step S2 is as follows:

[0018] Step S21: Select a suitable metallic material sample.

[0019] Step S22: Before the uniaxial tensile test, the specimen is polished, cleaned, dehydrated and dried, and then installed in the stress ring.

[0020] Step S23: A compact tensile test is conducted in a controlled hydrogen environment experimental setup. A load is applied to the metallic steel specimen at a constant displacement rate, and the precise load-displacement curve is recorded simultaneously. During the experiment, a constant hydrogen concentration environment is maintained through an electrochemical hydrogen charging system, and strain gauges monitor the dynamic behavior of the crack tip in real time. After the experiment is completed, according to the ASTM E1820 standard, the area energy under the load-displacement curve is calculated, and combined with the specimen geometry, the J-integral resistance curve of the material under the corresponding stress-strain-hydrogen coupling state is obtained to characterize its fracture toughness behavior in the corresponding hydrogen environment.

[0021] Step S24: The system changes the hydrogen concentration, load level, and pre-strain level, and conducts multiple sets of compact tensile tests to obtain J-integral data under different stress-strain-hydrogen coupling conditions. By analyzing the trend of the JR curve, the hydrogen-induced crack initiation J-integral value (JR) of the material under different working conditions is determined. IH ).

[0022] Furthermore, in step S3, numerical simulation is performed according to the following method:

[0023] Step S31: Establish a compact tensile specimen (CT) model using the finite element method and set an appropriate mesh density to ensure the calculation accuracy of the crack tip region.

[0024] Step S32: Based on the stress-driven diffusion theory, considering the influence of hydrostatic stress and concentration gradient on hydrogen diffusion, establish the hydrogen transport control equation:

[0025]

[0026] In the formula, D L ρ is the lattice diffusion coefficient of hydrogen atoms; R is the ideal gas constant, 8.314 J / (mol∙K); T is the temperature; The chemical potential gradient of hydrogen atoms between crystals, H The partial molar volume of hydrogen atoms in steel is 2 × 10⁻⁶. -6 m 3 / mol; σ h It is hydrostatic stress.

[0027] The expressions for dislocation hydrogen concentration and hydrogen trap captured hydrogen concentration are as follows:

[0028]

[0029]

[0030] In the formula, θ L θ T These represent the occupancy rates of lattice sites and hydrogen trap sites, respectively; N L N T These represent the site densities of lattice sites and hydrogen trap sites, respectively, where N... L N T The expression is:

[0031]

[0032]

[0033] The reversible hydrogen trap density is a function of the equivalent plastic strain, characterizing the multiplication effect of plastic strain on hydrogen traps. The equilibrium formula for lattice sites and hydrogen trap sites is then:

[0034]

[0035] In the formula, K T W is the balance coefficient. B Let be the binding energy of the metallic material. After simplification, the concentration relationship between dislocation hydrogen concentration and hydrogen trapped hydrogen concentration is expressed as:

[0036]

[0037] Therefore, the total hydrogen conservation equation driven by the concentration gradient, hydrostatic stress gradient, and equivalent plastic strain can be obtained as follows:

[0038]

[0039] The hydrogen atom diffusion equation is expressed as:

[0040]

[0041] The effective hydrogen diffusion coefficient is expressed as:

[0042]

[0043] Step S33: In the finite element simulation software, couple the "Solid Mechanics" and "Rare Material Transport" interfaces. In the coupled model, substitute the stress-driven diffusion coefficient function and the strain-increasing trap density function obtained in S1 into the corresponding control terms, thereby numerically simulating the staged and synergistic action mechanism of stress and strain. By adjusting the correlation coefficients in the coupled equations, ensure that the simulated hydrogen concentration distribution and effective hydrogen diffusion coefficient are consistent with the experimental trends in S1, thus completing the calibration of the hydrogen diffusion model.

[0044] Step S34: Using the validated multiphysics coupling model, calculate the corresponding J based on J-integral theory. IH Points:

[0045]

[0046]

[0047] Where w is the strain energy density, T i The stress component acting on the integration path, u i Let Γ be the corresponding displacement component, ds be the unit length on the loop, and Γ be any counterclockwise loop around the crack tip, starting at the lower surface of the crack and ending at the upper surface of the crack.

[0048] Meanwhile, considering the hydrogen-induced cracking mechanism: the increased concentration of external hydrogen intensifies stress and strain concentration at the crack tip, which, through stress-driven diffusion and plastic strain multiplication trapping, promotes an increase in internal hydrogen concentration, leading to an increase in hydrogen coverage θ and a decrease in the critical energy release rate. This ultimately manifests as a decrease in the crack initiation J integral value, as shown in the following equation:

[0049]

[0050]

[0051] In the formula, χ represents the hydrogen damage coefficient, and θ represents the hydrogen coverage. This represents the Gibbs free energy of the material. An increase in hydrogen coverage leads to G... c The decrease in the crack initiation J integral value reduces the material's ability to resist crack propagation.

[0052] The simulated crack initiation J integral value was compared with the experimental test results to verify the accuracy of the model in describing hydrogen-induced cracking behavior.

[0053] Step S35: Parametric analysis and correlation function establishment. The simulation results above clearly reveal the differential and synergistic effects of stress and strain fields on hydrogen concentration distribution, with typical characteristics as follows: Figure 2Based on the validated model, the system changes the load and hydrogen environment to study the coupled effects of stress state, plastic strain, and local hydrogen concentration on damage evolution, and finally establishes a quantitative correlation function of "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J integral".

[0054] Furthermore, the safety assessment of the actual engineering structure in step S4 is carried out according to the following steps:

[0055] Step S41: Establish a finite element model of the pipeline section containing the actual defects. Calculate the load and strain field based on actual operating pressure, soil constraints, and other conditions. Using the hydrogen diffusion coupling model calibrated in S32, simulate the local strain field and steady-state hydrogen concentration field of the pipeline defect area under a specified service hydrogen partial pressure environment, focusing on obtaining multi-field coupling data at the most dangerous points.

[0056] Step S42: Extract the strain and hydrogen concentration data at the most dangerous point of the defect, substitute them into the established "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J integral" correlation function, and calculate the predicted hydrogen-induced crack initiation J integral of the pipeline under this working condition.

[0057] Step S43: Based on the stress field at the defect obtained in step S41, the J integral value of the defect under the current load is calculated using fracture mechanics methods. This value is then directly compared with the J integral value of hydrogen-induced cracking of the material under the current operating conditions, which is predicted by the correlation function. If the former is less than the latter, the pipeline is deemed safe, and operation can be maintained or the inspection and maintenance plan can be optimized. If the former is greater than or equal to the latter, the risk of hydrogen-induced cracking is determined, and an immediate warning should be issued, and risk control measures such as pressure reduction, repair and replacement, or enhanced online monitoring should be taken.

[0058] The beneficial effects of this invention are as follows: By fitting the crack initiation J-integral data under different hydrogen concentrations, stress, and strain coupling conditions, this invention obtains a quantitative correlation function of "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J-integral". Assuming that stress, strain, and hydrogen concentration jointly affect the crack initiation J-integral, regression analysis is performed on experimental and simulated data under multiple coupled conditions to determine the functional relationship between them. This function mathematically describes the entire process from "stress-driven diffusion" to "strain multiplication trap," ultimately leading to "hydrogen enrichment and embrittlement," providing a direct quantitative analysis tool for engineering safety assessment. This invention achieves a quantitative assessment of the synergistic effect of stress and strain in the hydrogen-induced cracking process, providing a theoretical basis and practical method for defect safety assessment, remaining service life prediction, and maintenance decisions for hydrogen-containing pipelines. Attached Figure Description

[0059] Figure 1 This is a technical roadmap for the present invention;

[0060] Figure 2A comparison of simulation results for local hydrogen concentration enrichment at the crack tip under different stress and strain coupling conditions.

[0061] Figure 3 This is a schematic diagram comparing the J-integral of the crack tip with and without strain influence under the same load and hydrogen environment in an embodiment of the present invention.

[0062] Figure 4 In this embodiment of the invention, the critical energy release rate distribution cloud maps of the samples under different hydrogen environments are as follows: (a)-(d) without considering the hydrogen trapping effect (hydrogen concentration: 0.05, 0.1, 0.2, 0.4 wt.ppm); (e)-(h) with considering the hydrogen trapping effect (hydrogen concentration: 0.05, 0.1, 0.2, 0.4 wt.ppm). Detailed Implementation

[0063] The specific embodiments of the present invention will be further described below.

[0064] A method for evaluating the effect of stress-strain coupling on the fracture toughness of metallic materials in a hydrogen-containing environment, such as... Figure 1 As shown, the overall technical route includes the following steps. The core mechanism of this invention—the synergistic effect of stress and strain on hydrogen enrichment—can be found in [reference needed]. Figure 2 A visually intuitive display.

[0065] Electrochemical experiments were conducted on metallic material samples. Before the electrochemical experiments, the samples were polished, cleaned, dehydrated, and dried. They were installed in an experimental apparatus capable of independent and precise control of load and displacement, and placed within a dual-electrolysis cell electrochemical hydrogen charging system. In-situ stretching and hydrogen charging were performed under different preset stress-strain paths, and the corresponding hydrogen permeation current density-time curves were simultaneously measured. A constant concentration model was used to process the permeation curves, extracting parameters such as surface hydrogen concentration and effective hydrogen diffusion coefficient. By analyzing the experimental data, the different effects of the elastic stress-dominated stage and the plastic strain-dominated stage were distinguished, and a functional relationship between the reversible hydrogen trap density and the equivalent plastic strain was established as shown in the following equation to quantify the effect of strain field-induced hydrogen trap proliferation.

[0066]

[0067] The staged hydrogen transport parameters obtained from the above experiments provide key input parameters for the subsequent construction of a multiphysics coupled numerical model.

[0068] Standard compact tensile specimens were selected and pretreated similarly before being mounted on the experimental setup. Under controlled hydrogen conditions, a constant displacement rate was applied, and load-displacement curves were recorded simultaneously. Strain gauges were used to monitor the local strain field at the crack tip. According to ASTM E1820, the data were processed to obtain the J-integral resistance curve of the material under specific stress-strain-hydrogen concentration coupled conditions. Multiple sets of experiments were conducted by systematically varying the hydrogen concentration, load level, and pre-strain level to construct a fracture toughness database under different coupled conditions. By analyzing the JR curves, the hydrogen-induced crack initiation toughness values ​​of the material under each condition were extracted as benchmark data for establishing a quantitative correlation function.

[0069] Based on the physical mechanisms revealed by the aforementioned experiments, a multiphysics coupling numerical model was established and verified.

[0070] A fine finite element model of a CT specimen with pre-existing cracks was established, and the mesh was refined in the crack tip region to ensure calculation accuracy.

[0071] Constructing the coupled control equations. Based on stress-driven diffusion theory, considering the effects of hydrostatic stress and concentration gradient on hydrogen diffusion, the hydrogen transport control equations are established:

[0072]

[0073] In the formula, D L ρ is the lattice diffusion coefficient of hydrogen atoms; R is the ideal gas constant, 8.314 J / (mol∙K); T is the temperature; The chemical potential gradient of hydrogen atoms between crystals, H The partial molar volume of hydrogen atoms in steel is 2 × 10⁻⁶. -6 m 3 / mol; σ h It is hydrostatic stress.

[0074] The expressions for dislocation hydrogen concentration and hydrogen trap captured hydrogen concentration are as follows:

[0075]

[0076]

[0077] In the formula, θ L θ T These represent the occupancy rates of lattice sites and hydrogen trap sites, respectively; N L N T These represent the site densities of lattice sites and hydrogen trap sites, respectively, where N... L N T The expression is:

[0078]

[0079]

[0080] The reversible hydrogen trap density is a function of the equivalent plastic strain, characterizing the multiplication effect of plastic strain on hydrogen traps. The equilibrium formula for lattice sites and hydrogen trap sites is then:

[0081]

[0082] In the formula, K T W is the balance coefficient. B Let be the binding energy of the metallic material. After simplification, the concentration relationship between dislocation hydrogen concentration and hydrogen trapped hydrogen concentration is expressed as:

[0083]

[0084] Therefore, the total hydrogen conservation equation driven by the concentration gradient, hydrostatic stress gradient, and equivalent plastic strain can be obtained as follows:

[0085]

[0086] The hydrogen atom diffusion equation is expressed as:

[0087]

[0088] The effective hydrogen diffusion coefficient is expressed as:

[0089]

[0090] In finite element simulation software, the "solid mechanics" and "rare mass transport" interfaces are coupled to obtain staged parameters, such as the effective hydrogen diffusion coefficient D measured under different hydrostatic stress levels. eff The reversible hydrogen trap density measured at different plastic strain levels and its functional relationship with equivalent plastic strain are input into the model. By adjusting the correlation coefficients in the coupling equations, the simulated hydrogen concentration distribution and effective hydrogen diffusion coefficient are made consistent with the trends of hydrogen permeation experiments, thus completing the calibration of the hydrogen diffusion model.

[0091] Using the validated multiphysics coupling model, and based on J-integral theory, the corresponding J is calculated. IH Points

[0092]

[0093]

[0094] Where w is the strain energy density, T i The stress component acting on the integration path, u iLet Γ be the corresponding displacement component, ds be the unit length on the loop, and Γ be any counterclockwise loop around the crack tip, starting at the lower surface of the crack and ending at the upper surface of the crack.

[0095] To visually verify the crucial role of the strain field in the hydrogen-induced cracking process, this embodiment compares the J-integral calculations under the same load and hydrogen environment, considering and not considering the effect of strain. The results are as follows... Figure 3 As shown, the J-integral value considering the effect of strain is significantly higher than that without considering it. This directly proves that strain increases the driving force for crack propagation by multiplying hydrogen traps and promoting local hydrogen enrichment, thus quantitatively demonstrating the contribution of strain to the synergistic embrittlement mechanism.

[0096] Meanwhile, considering the hydrogen-induced cracking mechanism: the increased concentration of external hydrogen environment exacerbates the stress and strain concentration at the crack tip. Through stress-driven diffusion and plastic strain multiplication trapping, it promotes the increase of internal hydrogen concentration, increases hydrogen coverage θ, and thus leads to a decrease in critical energy release rate, which is ultimately manifested as a decrease in the crack initiation J integral value, as shown in the following formula.

[0097]

[0098]

[0099] In the formula, χ represents the hydrogen damage coefficient, and θ represents the hydrogen coverage. This represents the Gibbs free energy of the material. Figure 4 By comparing the critical energy release rate distribution cloud maps at the crack tip under the same working conditions, the influence of the strain field on the fracture resistance of the material is visually demonstrated. The results show that, considering the effect of strain, the fracture resistance at the crack tip is significantly reduced due to the promotion of local hydrogen enrichment. This directly confirms the mechanism by which strain exacerbates material embrittlement through the "hydrogen trap" effect. The increase in hydrogen coverage leads to G... c The decrease in the crack initiation J integral value reduces the material's ability to resist crack propagation.

[0100] The simulated hydrogen-induced cracking J integral value was compared with the experimental test results to verify the accuracy of the model in describing hydrogen-induced cracking behavior.

[0101] By fitting crack initiation J-integral data under different hydrogen concentrations, stress, and strain coupling conditions, a quantitative correlation function of "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J-integral" was obtained. Assuming that stress, strain, and hydrogen concentration jointly influence the crack initiation J-integral, regression analysis was performed on experimental and simulated data under multiple coupled conditions to determine the functional relationship between them. This function mathematically describes the entire process from "stress-driven diffusion" to "strain multiplication trap," ultimately leading to "hydrogen enrichment and embrittlement," providing a direct quantitative analysis tool for engineering safety assessment.

[0102] By changing the load conditions and hydrogen environment, a set of compact tensile verification experiments were conducted. Under the working conditions of this experiment, the predicted crack initiation J integral was calculated from the assumed functional relationship and compared with the experimentally measured crack initiation J integral value to verify the accuracy of the functional relationship.

[0103] A safety assessment of hydrogen-induced cracking was conducted on a defective pipeline. The stress, strain, and hydrogen concentration distribution in the defect area, obtained from multiphysics coupled simulation, were analyzed, and the point with the most severe mechanical and chemical conditions was selected as the hazard point. The stress, strain, and hydrogen concentration data of the hazard point were substituted into the aforementioned correlation function to calculate the predicted crack initiation J-integral value for the pipeline under this operating condition. Simultaneously, based on the actual stress field at the defect location, the driving J-integral value under the current service load was calculated using fracture mechanics methods. By comparing the driving J-integral value with the predicted crack initiation J-integral value, the safety margin was quantitatively assessed, thereby determining whether the pipeline faces a risk of hydrogen-induced cracking under the current operating condition and the risk level, providing a basis for operation and maintenance decisions.

[0104] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the scope of the present invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for evaluating the fracture toughness of metallic materials in a hydrogen-exposed environment, characterized in that, Includes the following steps: Step S1: Determine the hydrogen concentration distribution under the synergistic effect of stress and strain. Through in-situ tensile hydrogen permeation experiments on metallic materials, the diffusion and enrichment behavior of hydrogen in materials under different stress and strain states is systematically studied. The synergistic mechanism of stress-driven diffusion and strain multiplication trap is clarified, providing key input parameters for subsequent multi-field coupling simulation. Step S2: Fracture performance test under hydrogen environment. Through a compact tensile test on metallic materials, the J-integral and hydrogen-induced crack initiation J-integral values ​​of the materials under different stress-strain-hydrogen environment coupling conditions are measured. IH ; Step S3: Based on the multiphysics coupling theory, establish a numerical model including stress field, strain field, hydrogen diffusion field and damage field, simulate the behavior of compact tensile specimens under different loads and hydrogen concentrations, verify the accuracy of experimental results, and construct a quantitative correlation function of "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J integral". Step S4: Apply the established quantitative correlation function to the engineering safety assessment of pipelines with defects. By comparing the J integral value at the actual defect with the predicted hydrogen-induced cracking J integral value of the material under the same working condition, the risk of hydrogen-induced cracking is quantitatively determined, providing a basis for pipeline maintenance decisions.

2. The evaluation method according to claim 1, characterized in that, Step S1, the in-situ tensile hydrogen permeation experiment of the metallic material, specifically includes the following steps: Step S11: Select a suitable metallic material sample; Step S12: Before the electrochemical experiment, the sample is polished, cleaned, dehydrated and dried. Step S13: Install the sample in an experimental device in which the load and displacement can be controlled independently, and place it in a dual-electrolysis cell electrochemical hydrogen charging system; through in-situ stretching and hydrogen charging, simultaneously measure the hydrogen permeation current density-time curves under different stress-strain states. Step S14: Process the hydrogen permeation current density-time curve using a constant concentration model, and calculate the surface hydrogen concentration C0 and the effective hydrogen diffusion coefficient D. eff Reversible hydrogen trap density N T Hydrogen permeation parameters were established. By analyzing the differences in permeation behavior between the elastic and plastic stages, the relationship between stress and hydrogen diffusion coefficient, as well as the evolution relationship between plastic strain and reversible hydrogen trap density, were established, thus providing staged physical parameter inputs for the subsequent coupled model. The functional relationship of reversible hydrogen trap density with equivalent plastic strain is shown in the following equation: 。 3. The evaluation method according to claim 1, characterized in that, The method for the compact tensile test described in step S2 includes the following steps: Step S21: Select a suitable metallic material sample; Step S22: Before the uniaxial tensile test, the specimen is polished, cleaned, dehydrated and dried, and then installed in the stress ring; Step S23: A compact tensile test is conducted in a controlled hydrogen environment experimental setup. A load is applied to the steel specimen at a constant displacement rate, and the precise load-displacement curve is recorded simultaneously. During the experiment, a constant hydrogen concentration environment is maintained through an electrochemical hydrogen charging system, and the dynamic behavior of the crack tip is monitored in real time by strain gauges. After the experiment is completed, according to the ASTM E1820 standard, the area energy under the load-displacement curve is calculated, and combined with the specimen geometry, the J integral resistance curve of the material under the corresponding stress-strain-hydrogen coupling state is obtained to characterize its fracture toughness behavior in the corresponding hydrogen environment. Step S24: The system changes the hydrogen concentration, load level, and pre-strain level to conduct multiple sets of compact tensile tests, obtaining J-integral data under different stress-strain-hydrogen coupling conditions; by analyzing the trend of the JR curve, the hydrogen-induced crack initiation J-integral value J under different working conditions is determined. IH .

4. The evaluation method according to claim 1, characterized in that, Step S3, which simulates the behavior of a compact tensile specimen under different loads and hydrogen concentrations, includes the following steps: Step S31: Establish a compact tensile specimen model using the finite element method, and set an appropriate mesh density to ensure the calculation accuracy of the crack tip region; Step S32: Based on the stress-driven diffusion theory, considering the influence of hydrostatic stress and concentration gradient on hydrogen diffusion, establish the hydrogen transport control equation: In the formula, D L ρ is the lattice diffusion coefficient of hydrogen atoms; R is the ideal gas constant, 8.314 J / (mol∙K); T is the temperature; The chemical potential gradient of hydrogen atoms between crystals, H The partial molar volume of hydrogen atoms in steel is 2 × 10⁻⁶. -6 m 3 / mol; σ h For hydrostatic stress; Step S33: In the finite element simulation software, couple the "Solid Mechanics" and "Dilute Mass Transport" interfaces. In the coupled model, substitute the stress-driven diffusion coefficient function and the strain-increasing trap density function obtained in S1 into the corresponding control terms, thereby numerically simulating the staged and synergistic action mechanism of stress and strain. By adjusting the correlation coefficients in the coupled equations, make the simulated hydrogen concentration distribution and effective hydrogen diffusion coefficient consistent with the experimental trend in S1, thus completing the calibration of the hydrogen diffusion model. Step S34: Using the validated multiphysics coupling model, calculate the corresponding J based on J-integral theory. IH Points Where w is the strain energy density, T i The stress component acting on the integration path, u i Let Γ be the corresponding displacement component, ds be the unit length on the loop, and Γ be any counterclockwise loop around the crack tip, starting at the lower surface of the crack and ending at the upper surface of the crack. Meanwhile, considering the hydrogen-induced cracking mechanism: the increased concentration of external hydrogen intensifies stress and strain concentration at the crack tip, which, through stress-driven diffusion and plastic strain multiplication trapping, promotes an increase in internal hydrogen concentration, leading to an increase in hydrogen coverage θ and a decrease in the critical energy release rate. This ultimately manifests as a decrease in the crack initiation J integral value, as shown in the following equation: In the formula, χ represents the hydrogen damage coefficient, and θ represents the hydrogen coverage. This represents the Gibbs free energy of the material; an increase in hydrogen coverage leads to G... c The decrease in the crack initiation J integral value reduces the material's ability to resist crack propagation. The simulated crack initiation J integral value was compared with the experimental test results to verify the accuracy of the model in describing hydrogen-induced cracking behavior. Step S35: Parametric analysis and correlation function establishment; the load and hydrogen environment are changed systematically to study the coupled effects of stress state, plastic strain, and local hydrogen concentration on damage evolution, and finally a quantitative correlation function of "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J integral" is established.

5. The evaluation method according to claim 4, characterized in that, In the hydrogen transport control equation, the expressions for dislocation hydrogen concentration and hydrogen trap captured hydrogen concentration are as follows: In the formula, θ L θ T These represent the occupancy rates of lattice sites and hydrogen trap sites, respectively; N L N T These represent the site densities of lattice sites and hydrogen trap sites, respectively, where N... L N T The expression is: The reversible hydrogen trap density is a function of the equivalent plastic strain, characterizing the multiplication effect of plastic strain on hydrogen traps; the equilibrium formula for lattice sites and hydrogen trap sites is then: In the formula, K T W is the balance coefficient. B The binding energy of the metallic material; after simplification, the concentration relationship between dislocation hydrogen concentration and hydrogen trap trapped hydrogen concentration is expressed as: Therefore, the total hydrogen conservation equation driven by the concentration gradient, hydrostatic stress gradient, and equivalent plastic strain can be obtained as follows: The hydrogen atom diffusion equation is expressed as: The effective hydrogen diffusion coefficient is expressed as: 。 6. The evaluation method according to claim 1, characterized in that, The engineering safety assessment of the defective pipeline described in step S4 specifically includes the following steps: Step S41: Establish a finite element model of the pipeline section containing real defects; calculate its load and strain field based on actual operating pressure, soil constraints and other conditions; use the hydrogen diffusion coupling model calibrated in S32 to simulate the local strain field and steady-state hydrogen concentration field of the pipeline defect area under a specified service hydrogen partial pressure environment, focusing on obtaining multi-field coupling data at the most dangerous point. Step S42: Extract the strain and hydrogen concentration data at the most dangerous point of the defect, substitute them into the established "stress-strain-hydrogen concentration-hydrogen-induced crack initiation J integral" correlation function, and calculate the predicted hydrogen-induced crack initiation J integral of the pipeline under this working condition. Step S43: Based on the stress field at the defect obtained in step S41, the J integral value of the defect under the current load is calculated using fracture mechanics methods. This value is then directly compared with the J integral value of hydrogen-induced cracking of the material under the current operating conditions, which is predicted by the correlation function. If the former is less than the latter, the pipeline is deemed safe, and operation can be maintained or the inspection and maintenance plan can be optimized. If the former is greater than or equal to the latter, the risk of hydrogen-induced cracking is determined, and an immediate warning should be issued, and risk control measures such as pressure reduction, repair and replacement, or enhanced online monitoring should be taken.

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