Numerical analysis method for hydrogen damage assessment of pipelines with defects based on plastic damage model

Abstract

The present application proposes a numerical analysis method for evaluating hydrogen damage of a pipeline containing defects based on a plastic damage model, comprising the following steps: step S1: performing an electrochemical hydrogen charging experiment and hydrogen permeation simulation on a sample to determine the hydrogen concentration distribution inside the pipeline; step S2: performing a uniaxial tensile experiment under electrochemical hydrogen charging to obtain a stress-strain curve of the pipeline steel affected by hydrogen embrittlement; step S3: establishing a uniaxial tensile numerical model and calibrating plastic damage parameters under different hydrogen concentrations; step S4: fitting the plastic damage parameters to obtain a correlation function between the hydrogen concentration and the plastic damage parameters; and step S5: hydrogen damage evaluation, obtaining a dangerous point with the highest hydrogen concentration inside the pipeline, substituting the hydrogen concentration of the point into the correlation function, calculating the plastic damage parameters of the dangerous point of the pipeline, and obtaining the stress-strain curve at this time; the present application can analyze the plastic damage of the pipeline steel affected by hydrogen by using the finite element method, and provides a theoretical basis for pipeline design, material selection and protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the oil and gas storage and transportation technical field, and particularly to a numerical analysis method for evaluating hydrogen damage of a pipeline with defects based on a plastic damage model. BACKGROUND

[0002] Pipeline transportation is a high-efficiency and economical oil and gas transportation mode widely used in the world. After the pipeline material is in contact with hydrogen, hydrogen damage occurs, which leads to material embrittlement and affects the mechanical properties of the material. Meanwhile, the existence of pipeline defects forms local stress concentration at the defects, which further promotes the occurrence of hydrogen damage. Hydrogen damage makes the pipeline steel face the risk of premature fracture during service, thereby endangering the safe operation of the pipeline.

[0003] The prior art has carried out researches in many aspects around pipeline hydrogen damage, and designed hydrogen damage experimental devices under various research conditions, but lacks numerical research on plastic damage of a pipeline with defects under the influence of hydrogen embrittlement. Therefore, a numerical simulation method for evaluating hydrogen damage of a pipeline with defects is established based on a plastic damage model and hydrogen damage experimental research, so as to reduce the operation risk of the pipeline. SUMMARY

[0004] The present application proposes a numerical analysis method for evaluating hydrogen damage of a pipeline with defects based on a plastic damage model, which can analyze the plastic damage of pipeline steel under the influence of hydrogen by using a finite element method, and provides a theoretical basis for pipeline design, material selection and protection.

[0005] The present application adopts the following technical solutions.

[0006] The numerical analysis method for evaluating hydrogen damage of a pipeline with defects based on a plastic damage model comprises the following steps.

[0007] Step S1: hydrogen concentration determination, an electrochemical hydrogen charging experiment and hydrogen permeation simulation are performed on a pipeline steel sample to determine the hydrogen concentration distribution inside the pipeline;

[0008] Step S2: uniaxial tension experiment, a uniaxial tension experiment under electrochemical hydrogen charging is performed on the pipeline steel experiment to obtain a stress-strain curve of the pipeline steel subjected to hydrogen embrittlement and plastic damage;

[0009] Step S3: plastic damage parameter calibration, a uniaxial tension numerical model is established based on the plastic damage theory, and plastic damage parameters under different hydrogen concentrations are calibrated;

[0010] Step S4: function fitting, the plastic damage parameters under different hydrogen concentrations are fitted to obtain a correlation function between the hydrogen concentration and the plastic damage parameters;

[0011] Step S5: hydrogen damage assessment, the highest risk point of hydrogen concentration in the pipeline is obtained by hydrogen permeation numerical simulation, the hydrogen concentration of the point is substituted into the correlation function, the plastic damage parameter of the pipeline risk point is calculated, and the stress-strain curve at this time is obtained by uniaxial tension numerical simulation.

[0012] The electrochemical hydrogen charging experiment in step S1 specifically includes the following steps.

[0013] Step S11: selecting a suitable pipeline steel sample;

[0014] Step S12: treating the sample before the electrochemical experiment;

[0015] Step S13: measuring the hydrogen permeation current density-time curve of the pipeline steel by the electrochemical hydrogen charging method;

[0016] Step S14: processing the hydrogen permeation current density-time curve with the constant concentration model to calculate the hydrogen permeation parameter;

[0017] Step S15: establishing a pipeline model containing defects, considering the influence factors such as hydrostatic stress and temperature based on Fick's second law, ignoring the relationship between the diffusion coefficient and the concentration, and obtaining the constitutive equation of hydrogen diffusion under the influence of hydrostatic stress as follows:

[0018]

[0019] In the formula, J represents the hydrogen concentration flux, D represents the hydrogen diffusion coefficient, s represents the solubility of hydrogen in the medium, φ represents the hydrogen activity, σ represents the hydrostatic stress, k σ represents the stress-assisted diffusion factor, k s represents the influence of temperature gradient on diffusion.

[0020] The expression of the stress-assisted diffusion factor k σ is as follows:

[0021]

[0022] In the formula, R represents the gas constant, R=8.31432 J·mol -1 ·k -1 ; V H represents the partial molar volume of hydrogen in steel; θ represents the temperature; θ z represents absolute zero; and φ is the hydrogen activity.

[0023] Based on the above theoretical formula, the hydrogen concentration distribution in the pipeline containing defects is calculated.

[0024] In step S12, the treatment method of the sample includes polishing, cleaning, dehydration and drying.

[0025] The hydrogen permeation parameters calculated in step S14 include the surface hydrogen concentration C0, the effective hydrogen diffusion coefficient D eff .

[0026] The method of the uniaxial tensile test in step S2 includes the following steps:

[0027] Step S21: Selecting a suitable pipeline steel sample;

[0028] Step S22: treating the sample before the uniaxial tensile test;

[0029] Step S23: while the sample is electrochemically charged with hydrogen, a slow and constant loading rate is applied to the sample to cause strain in the sample until the sample breaks, thereby obtaining a stress-strain curve indicating plastic damage caused by hydrogen embrittlement of the pipeline steel;

[0030] Step S24: Processing the stress-strain curve to obtain the mechanical property parameters of the sample.

[0031] In step S22, the sample is processed by grinding, cleaning, dehydrating and drying;

[0032] The mechanical performance parameters of the sample obtained in step S23 include elastic modulus E and Poisson's ratio μ.

[0033] Step S3 includes the following data simulation steps:

[0034] Step S31: establishing a uniaxial tensile specimen model, and using the stress-strain curve obtained from the uniaxial tensile test as the mechanical parameters of the material;

[0035] Step S32: Use the Gurson-Tvergaard-Needleman (GTN) damage model to describe the plastic damage of the material; the undetermined parameters of the GTN damage model are: yield function correction coefficients q1, q2, q3, initial pore volume fraction f0 of the material, critical pore volume fraction f c , the volume fraction of the material fracture pores f F , volume fraction of nucleable binomial particles f N , average strain of hole nucleation ε N , standard deviation of the hole nucleation strain s N ; The yield function expression of the material based on the GTN damage model is:

[0036]

[0037] Where, f * is a function of the current porosity of the material; f c is the critical pore volume fraction when pores begin to aggregate; f Fis the volume fraction of voids at the moment of complete loss of load carrying capacity of the material; f = f F when, complete failure of the material; is the limiting value of f * ; f = f

[0038] is a function of the current void fraction of the material f * ; f = f

[0039]

[0040] is the limiting value of f* is expressed as:

[0041]

[0042] The rate of change of f is decomposed into two parts: the void growth rate and the void nucleation rate :

[0043]

[0044] The void growth rate is expressed as:

[0045]

[0046] where, is the plastic strain tensor; I is the second order unit tensor.

[0047] The void nucleation rate is expressed as:

[0048]

[0049] where, is the equivalent plastic strain of the matrix; A is defined as:

[0050]

[0051] where, ε N is the average strain of void nucleation; s N is the standard deviation of the strain of void nucleation, f N is the volume fraction of binomial particles that can be nucleated;

[0052] Step S33: calibrate the plastic damage parameter of the pipeline steel without hydrogen damage,

[0053] The initial void volume fraction f0 is determined by the element composition of the material, and is expressed as:

[0054]

[0055] S is the percentage of sulfur element in the material; Mn is the percentage of manganese element in the material;

[0056] f c 、f F 、f N , and the stress-strain curves under different f N , s N , f0 are calculated through trial and error method on the basis of fixed q1, q2, q3, ε c , f F , f N , and the calculation results are compared with the experimental results to determine the material plastic damage parameters consistent with the experimental results;

[0057] Step S34: It is assumed that hydrogen embrittlement produces plastic damage to the material, which affects the post-break elongation rate parameter, and is manifested as a decrease in the strain of the fracture point on the stress-strain curve; then, combined with the GTN model, the plastic damage produced by hydrogen embrittlement to the material is reflected in the GTN model as changes in each GTN parameter; the plastic damage parameters of the material under different hydrogen concentrations are calibrated by the inverse finite element method; wherein q1, q2, q3, and s N do not change with the influence of hydrogen concentration; the change trends of f0, f c , f F , ε N , and f N are determined according to theoretical analysis;

[0058] It is assumed that hydrogen diffusion significantly increases the initial porosity of the material under unloaded conditions, resulting in an increase in f0, and that for the expansion and aggregation of pores, the aggregation of hydrogen atoms promotes the formation of pores and cracks, and as the influence of hydrogen intensifies, f c and f F will decrease; from the perspective of pore nucleation, according to the hydrogen-induced weak bond theory, the effect of hydrogen in the region where hydrogen atoms are aggregated will weaken the bonding force between matrix atoms, making it easier for micro-pores in the material to nucleate, that is, ε N decreases and f N increases; as described above, as the hydrogen concentration increases, the plastic damage parameters f0 and f N increase, while f c , f F , and ε N decrease; the plastic damage parameters under different experimental conditions are determined by combining the above formula algorithm, thereby analyzing the influence of hydrogen concentration on material plastic damage.

[0059] In step S33, the yield function correction coefficient of the GTN damage model is q1=1.5, q2=1.0, and q3=2.25; it is assumed that there is no significant difference in the average strain of pore nucleation and the standard deviation of pore nucleation strain in different materials; when not affected by hydrogen embrittlement, ε N= 0.3, s N = 0.1.

[0060] The function fitting in the step S4 is carried out according to the following steps:

[0061] Step S41: assuming that there is a function relationship between hydrogen concentration and plastic damage parameters, fitting the plastic damage parameters under different hydrogen concentrations to determine the function relationship between each plastic damage parameter and hydrogen concentration; the function relationship is the function relationship formula reflecting the influence of hydrogen embrittlement on plastic damage;

[0062] Step S42: changing the electrochemical hydrogen charging condition, carrying out a group of uniaxial tension experiments, calculating each plastic damage parameter at the hydrogen concentration of the experiment according to the assumed function relationship, and calculating the stress-strain curve according to the calculated plastic damage parameters, and comparing with the experimental results to verify the accuracy of the assumed function relationship.

[0063] The hydrogen damage evaluation in the step S5 is carried out according to the following method:

[0064] Step S51: analyzing the hydrogen concentration distribution result obtained by hydrogen permeation simulation, and selecting the point with the highest hydrogen concentration as the dangerous point;

[0065] Step S52: substituting the hydrogen concentration of the dangerous point into the function relationship formula reflecting the influence of hydrogen embrittlement on plastic damage to obtain each plastic damage parameter under the hydrogen concentration of the dangerous point.

[0066] Step S53: calculating the stress-strain curve of the material under the hydrogen concentration of the dangerous point from each plastic damage parameter, and analyzing the plastic damage parameters and the stress-strain curve to determine the plastic damage of the pipeline caused by hydrogen embrittlement under the condition of the pipeline.

[0067] The present application realizes the numerical analysis method of hydrogen damage of the pipeline with defects based on the plastic damage model, and provides theoretical basis support for pipeline design, material selection and protection. BRIEF DESCRIPTION OF DRAWINGS

[0068] The present application will be further described in detail below in combination with the drawings and specific embodiments:

[0069] Figure 1 is a schematic diagram of the technical scheme of the present application; Figure 1 Figure 2 is a schematic diagram of the modeling of the pipeline with defects of the present application;

[0070] Figure 3 is a schematic diagram of the uniaxial tension sample modeling of the present application. Figure 2

[0071] Figure 4 is a schematic diagram of the uniaxial tension sample modeling of the present application. Figure 3 DETAILED DESCRIPTION As

[0072] As Figure 1 ​As shown, the numerical analysis method for evaluating hydrogen damage of the defective pipeline based on the plastic damage model comprises the following steps;

[0073] Step S1: hydrogen concentration determination, electrochemical hydrogen charging experiment and hydrogen permeation simulation are performed on the pipeline steel sample to determine the hydrogen concentration distribution inside the pipeline;

[0074] Step S2: uniaxial tension experiment, uniaxial tension experiment under electrochemical hydrogen charging is performed on the pipeline steel experiment to obtain the stress-strain curve of the pipeline steel affected by hydrogen embrittlement plastic damage;

[0075] Step S3: plastic damage parameter calibration, a uniaxial tension numerical model is established based on the plastic damage theory, and the plastic damage parameters under different hydrogen concentrations are calibrated;

[0076] Step S4: function fitting, the plastic damage parameters under different hydrogen concentrations are fitted to obtain the correlation function between the hydrogen concentration and the plastic damage parameters;

[0077] Step S5: hydrogen damage evaluation, the most dangerous point of the hydrogen concentration inside the pipeline is obtained by hydrogen permeation numerical simulation, the hydrogen concentration of the point is substituted into the correlation function, the plastic damage parameters of the dangerous point of the pipeline are calculated, and the stress-strain curve at this time is obtained by uniaxial tension numerical simulation.

[0078] The electrochemical hydrogen charging experiment in step S1 specifically comprises the following steps;

[0079] Step S11: selecting a suitable pipeline steel sample;

[0080] Step S12: treating the sample before the electrochemical experiment;

[0081] Step S13: measuring the hydrogen permeation current density-time curve of the pipeline steel by the electrochemical hydrogen charging method;

[0082] Step S14: processing the hydrogen permeation current density-time curve by the constant concentration model to calculate the hydrogen permeation parameters;

[0083] Step S15: establishing a suitable defective pipeline model, such as Figure 2 According to the constitutive equation of hydrogen diffusion under the influence of hydrostatic stress, the hydrogen concentration distribution inside the defective pipeline is calculated, specifically: a defective pipeline model is established, based on Fick's second law, the influence factors such as hydrostatic stress and temperature are considered, the relationship between the diffusion coefficient and the concentration is ignored, and the constitutive equation of hydrogen diffusion under the influence of hydrostatic stress is obtained as follows:

[0084]

[0085] In the formula, J represents the hydrogen concentration flux, D represents the hydrogen diffusion coefficient, s represents the solubility of hydrogen in the medium, φ represents the hydrogen activity, σ represents the hydrostatic stress, and kσ k represents stress-assisted diffusion factor; k s k represents the effect of temperature gradient on diffusion;

[0086] Stress-assisted diffusion factor k σ The expression is:

[0087]

[0088] In the formula, R represents gas constant, R = 8.31432 J·mol -1 ·k -1 ; V H represents the partial molar volume of hydrogen in steel; θ represents temperature; θ z represents absolute zero; φ is hydrogen activity.

[0089] Based on the above theoretical formula, the hydrogen concentration distribution in the pipeline containing defects is calculated.

[0090] In step S12, the treatment method of the sample includes polishing, cleaning, dehydration and drying.

[0091] The hydrogen permeation parameters calculated in step S14 include surface hydrogen concentration C0, effective hydrogen diffusion coefficient D eff .

[0092] The method of uniaxial tensile test in step S2 includes the following steps:

[0093] Step S21: selecting a suitable pipeline steel sample;

[0094] Step S22: treating the sample before the uniaxial tensile test;

[0095] Step S23: while the sample is electrochemically charged with hydrogen, a slow and constant loading speed is applied to the sample to cause strain until the sample is broken, and the stress-strain curve of the pipeline steel affected by hydrogen embrittlement is tested to obtain the plastic damage of the sample;

[0096] Step S24: processing the stress-strain curve to obtain the mechanical property parameters of the sample.

[0097] In step S22, the treatment method of the sample includes polishing, cleaning, dehydration and drying;

[0098] The mechanical property parameters of the sample obtained in step S23 include elastic modulus E and Poisson's ratio μ.

[0099] Step S3 includes the following data simulation steps:

[0100] Step S31: establishing a uniaxial tensile sample model, as shown in Figure 3 , taking the stress-strain curve obtained by the uniaxial tensile test as the mechanical parameters of the material;

[0101] Step S32: use the Gurson-Tvergaard-Needleman (GTN) damage model to describe the plastic damage of the material; the GTN damage model contains undetermined parameters: yield function correction coefficients q1, q2, q3, material initial void volume fraction f0, material critical void volume fraction f c , material fracture void volume fraction f F , nucleated binomial particle volume fraction f N , average strain of void nucleation ε N , standard deviation of void nucleation strain s N ; the yield function expression of the material based on the GTN damage model is:

[0102]

[0103] In the formula, f * is a function of the current void ratio of the material; f c is the critical void volume fraction when the void begins to aggregate; f F is the fracture void volume fraction when the material completely loses the carrying capacity; when f = f F , the material completely fails; f * is the limit value;

[0104] The function f * of the current void ratio of the material is:

[0105]

[0106] The limit value of f* is: The expression is:

[0107]

[0108] The change rate of f is decomposed into void expansion rate and void nucleation rate :

[0109]

[0110] The void expansion rate is expressed as:

[0111]

[0112] In the formula, is the plastic strain tensor; I is a 2-order unit tensor.

[0113] The void nucleation rate is expressed as:

[0114]

[0115] wherein, is the equivalent plastic strain of the matrix; A is defined as follows:

[0116]

[0117] wherein, ε N is the average strain of the void nucleation; s N is the standard deviation of the void nucleation strain, f N is the volume fraction of the nucleable binary particles;

[0118] Step S33: calibrating the plastic damage parameters of the pipeline steel without hydrogen damage,

[0119] The initial void volume fraction f0 is determined by the element composition of the material, and the expression is:

[0120]

[0121] wherein, S is the percentage content of sulfur element of the material; Mn is the percentage content of manganese element of the material;

[0122] f c , f F , f N Calibrated by the inverse finite element method, by trial method, on the basis of fixed q1, q2, q3, ε N , s N , f0, the stress-strain curves under different f c , f F , f N are calculated, and the calculation results are compared with the experimental results to determine the material plastic damage parameters consistent with the experimental results;

[0123] Step S34: assuming that hydrogen embrittlement produces plastic damage to the material, which affects the elongation at break parameter, which is manifested as the reduction of the strain of the fracture point on the stress-strain curve; then, combining the GTN model, the plastic damage produced by hydrogen embrittlement to the material is reflected in the GTN model as the change of each GTN parameter; the plastic damage parameters of the material under different hydrogen concentrations are calibrated by the inverse finite element method; wherein q1, q2, q3 and s N do not change with the influence of hydrogen concentration; the change trends of f0, f c , f F , ε N , f N are determined according to theoretical analysis;

[0124] The hydrogen diffusion can significantly increase the initial porosity of the material under no load, resulting in the increase of f0, and the hydrogen atom aggregation promotes the formation of holes and cracks for the expansion and aggregation of the holes. With the increasing influence of hydrogen, f c and f F will decrease; from the perspective of hole nucleation, according to the hydrogen-weak bond theory, the hydrogen effect in the hydrogen atom aggregation area will weaken the binding force between the matrix atoms, so that the material micropores are more likely to nucleate, that is, ε N decreases, and f N increases; as described above, with the increase of hydrogen concentration, the plastic damage parameters f0and f N increase, and f c , f F and ε N decrease; the plastic damage parameters under different experimental conditions are determined by combining the above formula algorithm, so as to analyze the influence of hydrogen concentration on the material plastic damage.

[0125] In step S33, the yield function correction coefficients of the GTN damage model are q1=1.5, q2=1.0, and q3=2.25; it is assumed that there is no significant difference in the average strain of hole nucleation and the standard deviation of hole nucleation strain in different materials; ε N =0.3 and s N =0.1 are directly taken when there is no hydrogen embrittlement effect.

[0126] In the step S4, the function fitting is performed as follows:

[0127] Step S41: it is assumed that there is a function relationship between the hydrogen concentration and the plastic damage parameters, the plastic damage parameters under different hydrogen concentrations are fitted, and the function relationship between each plastic damage parameter and the hydrogen concentration is determined; the function relationship is the function relationship formula reflecting the influence of hydrogen embrittlement on plastic damage;

[0128] Step S42: the electrochemical hydrogen charging condition is changed, a group of uniaxial tension experiments are performed, the plastic damage parameters are calculated under the hydrogen concentration of this experiment according to the assumed function relationship, and the stress-strain curve is calculated according to the calculated plastic damage parameters, which is compared with the experimental results to verify the accuracy of the assumed function relationship.

[0129] In the step S5, the hydrogen damage evaluation is performed as follows:

[0130] Step S51: the hydrogen concentration distribution result obtained by hydrogen permeation simulation is analyzed, and the point with the highest hydrogen concentration is selected as the dangerous point;

[0131] Step S52: the hydrogen concentration of the dangerous point is substituted into the function relationship formula reflecting the influence of hydrogen embrittlement on plastic damage, to obtain the plastic damage parameters under the hydrogen concentration of the dangerous point.

[0132] Step S53: Calculate the stress-strain curve of the material under the dangerous point hydrogen concentration from the plastic damage parameters, analyze the plastic damage parameters and the stress-strain curve, and determine the plastic damage of the pipeline caused by hydrogen embrittlement under the pipeline condition.

Claims

1. A numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model, characterized by: The following steps are included: Step S1: Determine the hydrogen concentration by conducting an electrochemical hydrogen charging experiment and a hydrogen permeation simulation on the pipeline steel sample to determine the hydrogen concentration distribution inside the pipeline; Step S2: a uniaxial tensile test is performed on the pipeline steel under electrochemical hydrogen charging to obtain a stress-strain curve of the pipeline steel that is affected by hydrogen embrittlement and produces plastic damage; Step S3: Plastic damage parameter calibration: a uniaxial tensile numerical model is established based on the plastic damage theory to calibrate the plastic damage parameters under different hydrogen concentrations; Step S4: Function fitting, fitting the plastic damage parameters under different hydrogen concentrations to obtain the correlation function between hydrogen concentration and plastic damage parameters; Step S5: Hydrogen damage assessment: The dangerous point with the highest hydrogen concentration in the pipeline is obtained by hydrogen permeation numerical simulation. The hydrogen concentration of this dangerous point is substituted into the correlation function to calculate the plastic damage parameter of the dangerous point of the pipeline and obtain the stress-strain curve at this time through uniaxial tension numerical simulation. Step S3 includes the following data simulation steps: Step S31: establishing a uniaxial tensile specimen model, and using the stress-strain curve obtained from the uniaxial tensile test as the mechanical parameters of the material; Step S32: Use the GTN damage model to describe the plastic damage of the material; the undetermined parameters of the GTN damage model are: yield function correction coefficients q1, q2, q3, initial pore volume fraction f0 of the material, critical pore volume fraction f c , the volume fraction of the material fracture pores f F , volume fraction of nucleable binomial particles f N , average strain of hole nucleation ε N , standard deviation of the hole nucleation strain s N ; The yield function expression of the material based on the GTN damage model is: Where, f * is a function of the current porosity of the material; f c is the critical pore volume fraction when pores begin to aggregate; f F is the volume fraction of fracture pores when the material completely loses its bearing capacity; when f = f F hour, Complete failure of the material; f * The limit value of Function f of the material's current porosity * for: Limiting value of f* The expression is: The rate of change of f is decomposed into the hole expansion rate and pore nucleation rate Two parts: Hole expansion rate Expressed as: Where, is the plastic strain tensor; I is the 2nd-order unit tensor; Pore ​​nucleation rate Expressed as: Where, is the equivalent plastic strain of the matrix; A is defined as follows: Where, ε N is the average strain of hole nucleation; s N is the standard deviation of the hole nucleation strain, f N is the volume fraction of nucleable binomial particles; Step S33: calibrate the plastic damage parameters of the pipeline steel when it is not damaged by hydrogen. The initial void volume fraction f0 is determined by the elemental composition of the material and is expressed as: Where, S is the percentage of sulfur in the material; Mn is the percentage of manganese in the material; f c 、f F 、f N The inverse finite element method is used for calibration. The trial algorithm is used to fix q1, q2, q3, ε N 、s N , f0, different f c 、f F 、f N The stress-strain curve under the condition of α is compared with the experimental results to determine the material plastic damage parameters that are consistent with the experimental results; Step S34: Assume that hydrogen embrittlement affects the elongation parameter when it causes plastic damage to the material, which is manifested as a decrease in strain at the fracture point on the stress-strain curve; then, combined with the GTN model, the plastic damage caused by hydrogen embrittlement to the material is reflected in the GTN model as changes in various GTN parameters; the plastic damage parameters of the material under different hydrogen concentrations are calibrated using the inverse finite element method; where q1, q2, q3 and s N Does not change with the influence of hydrogen concentration; f0 and f are determined based on theoretical analysis c 、f F , ε N 、f N the changing trend of Assuming that hydrogen diffusion will significantly increase the initial porosity of the material under unloaded conditions, resulting in an increase in f0, and for the expansion and aggregation of pores, hydrogen atoms gather to promote the formation of pores and cracks. As the influence of hydrogen intensifies, f c With f F From the perspective of pore nucleation, according to the hydrogen-induced weakening bond theory, the effect of hydrogen in the area where hydrogen atoms gather will weaken the binding force between the matrix atoms, making it easier for the micropores in the material to nucleate, that is, ε N Lower, f N Increase; In summary, as the hydrogen concentration increases, the plastic damage parameters f0 and f N increases, and f c 、f F With ε N Reduce; Combined with the above formula algorithm, the plastic damage parameters under different experimental conditions are determined to analyze the effect of hydrogen concentration on the plastic damage of the material.

2. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 1, characterized in that: The electrochemical hydrogen charging experiment in step S1 specifically includes the following steps: Step S11: selecting a suitable pipeline steel sample; Step S12: treating the sample before the electrochemical experiment; Step S13: measuring the hydrogen permeation current density-time curve of the pipeline steel by an electrochemical hydrogen charging method; Step S14: Processing the hydrogen permeation current density-time curve using a constant concentration model to calculate hydrogen permeation parameters; Step S15: Establish a defective pipeline model. Based on Fick's second law, consider the influence of hydrostatic stress and temperature, ignore the relationship between diffusion coefficient and concentration, and obtain the constitutive equation of hydrogen diffusion under the influence of hydrostatic stress: Where: J represents the hydrogen concentration flux; D represents the hydrogen diffusion coefficient; s represents the solubility of hydrogen in the medium; φ represents the hydrogen activity; σ represents the hydrostatic stress; k σ represents the stress-assisted diffusion factor; k s Represents the effect of temperature gradient on diffusion; Stress-assisted diffusion factor k σ The expression is: Where: R represents the gas constant, R = 8.31432 J·mol -1 ·k -1 ; V H represents the partial molar volume of hydrogen in steel; θ represents temperature; θ z represents absolute zero; φ is the hydrogen activity; The hydrogen concentration distribution in the defective pipeline is calculated based on the above theoretical formula.

3. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 2, characterized in that: In step S12, the sample processing method includes polishing, cleaning, dehydration and drying.

4. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 2, characterized in that: The hydrogen permeation parameters calculated in step S14 include the surface hydrogen concentration C0, the effective hydrogen diffusion coefficient D eff .

5. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 1, characterized in that: The method of the uniaxial tensile test in step S2 includes the following steps: Step S21: Selecting a suitable pipeline steel sample; Step S22: treating the sample before the uniaxial tensile test; Step S23: while the sample is electrochemically charged with hydrogen, a slow and constant loading rate is applied to the sample to cause strain in the sample until the sample breaks, thereby obtaining a stress-strain curve indicating plastic damage caused by hydrogen embrittlement of the pipeline steel; Step S24: Processing the stress-strain curve to obtain the mechanical property parameters of the sample.

6. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 5, characterized in that: In step S22, the sample is processed by grinding, cleaning, dehydrating and drying; The mechanical performance parameters of the sample obtained in step S23 include elastic modulus E and Poisson's ratio μ.

7. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 1, characterized in that: In step S33, the yield function correction coefficients of the GTN damage model are q1 = 1.5, q2 = 1.0, and q3 = 2.25; it is assumed that there is no significant difference in the average strain of void nucleation and the standard deviation of void nucleation strain in different materials; when not affected by hydrogen embrittlement, ε is directly taken. N =0.3,s N =0.

1.

8. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 1, characterized in that: In step S4, function fitting is performed according to the following steps: Step S41: Assuming that there is a functional relationship between hydrogen concentration and plastic damage parameters, fitting the plastic damage parameters at different hydrogen concentrations to determine the functional relationship between each plastic damage parameter and hydrogen concentration; this functional relationship is the functional relationship formula for the effect of reaction hydrogen embrittlement on plastic damage; Step S42: Change the electrochemical hydrogen charging conditions and conduct a set of uniaxial tensile tests. Under the hydrogen concentration of the experiment, various plastic damage parameters are calculated using the assumed functional relationship. The stress-strain curve is calculated based on the calculated plastic damage parameters and compared with the experimental results to verify the accuracy of the assumed functional relationship.

9. The numerical analysis method for evaluating hydrogen damage in defective pipelines based on a plastic damage model according to claim 1, characterized in that: In step S5, hydrogen damage assessment is performed according to the following method: Step S51: analyzing the hydrogen concentration distribution results obtained from the hydrogen permeation simulation, and selecting the point with the highest hydrogen concentration as the dangerous point; Step S52: Substituting the hydrogen concentration at the dangerous point into the functional relationship of the effect of hydrogen embrittlement on plastic damage, and obtaining various plastic damage parameters under the hydrogen concentration at the dangerous point; Step S53: Calculate the stress-strain curve of the material at the dangerous point hydrogen concentration based on various plastic damage parameters, analyze the plastic damage parameters and the stress-strain curve, and determine the plastic damage caused by hydrogen embrittlement to the pipeline under this pipeline condition.

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