Method for controlling local hydrogen enrichment of girth welding joint of hydrogen conveying pipeline

Abstract

The invention belongs to the field of safe service of hydrogen conveying pipelines, and provides a method for controlling local hydrogen enrichment of a hydrogen conveying pipeline girth welding joint, which provides support for hydrogen embrittlement failure risk management and control of a related hydrogen conveying pipeline girth welding joint area, and comprises the following steps of: establishing a three-dimensional finite element model of the hydrogen conveying pipeline girth welding joint in a ratio of 1: 1 by utilizing ABAQUS simulation software; sequentially calculating a temperature field and a stress field of the ring welding joint; hydrogen permeation parameters of the pipeline base metal and the ring welding joint are obtained through a gas phase hydrogen permeation test; by taking the obtained hydrogen permeation parameters as initial conditions and a stress field as boundary conditions, calculating a full-size hydrogen distribution cloud chart of the ring welding joint of the hydrogen conveying pipeline; local heat treatment is conducted on the ring welding joint, the influence of heat treatment on hydrogen distribution of the full-size pipeline ring welding joint is simulated and calculated, and an optimization strategy for controlling local hydrogen enrichment of the ring welding joint is provided. According to the method, the stress distribution of the ring welding joint is uniform, so that the local hydrogen enrichment degree of the ring welding joint of the hydrogen conveying pipeline is effectively controlled, and the risk of hydrogen induced cracking of the ring welding joint is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of safe service of hydrogen transmission pipelines and provides a method for effectively controlling local hydrogen enrichment in girth weld joints of hydrogen transmission pipelines. Background Art

[0002] Hydrogen, with its high energy efficiency, zero pollution, renewable nature, and abundant resources, is hailed as the most promising green energy source of the 21st century. Hydrogen transportation is an essential component of its development and utilization, and pipeline transportation is the most cost-effective and efficient method for large-scale, long-distance hydrogen transportation. However, hydrogen atoms can penetrate the interior of the pipe and diffuse under the combined effects of concentration and stress gradients, leading to localized hydrogen enrichment. This can lead to localized reductions in the material's plasticity, accelerated crack propagation, and decreased durability. Therefore, localized hydrogen enrichment is a critical issue in the design, construction, and safe operation of hydrogen pipelines.

[0003] Welding is a standard installation process for long-distance pipelines. The use of filler metal and localized heat exposure lead to nonuniform stress fields in girth weld joints. Hydrogen diffusion caused by stress gradients can lead to localized hydrogen enrichment in girth weld joints, increasing the risk of hydrogen-induced cracking when the actual hydrogen concentration exceeds the critical embrittlement hydrogen concentration of the material. This makes the girth weld joint region a vulnerable location for failure in hydrogen-prone pipelines. To control localized hydrogen enrichment in girth weld joints, it is necessary to reduce the stress gradient within the girth weld joint. Adjusting the welding process can influence the weld residual stress field, but its optimization capability is limited. Existing research has shown that heat treatment of girth weld joints can effectively reduce weld residual stress, and the weld residual stress distribution in girth weld joints becomes more uniform with increasing heat treatment temperature. However, the hydrogen distribution in girth weld joints of hydrogen pipelines is the result of the coupled effects of hydrogen concentration gradients and stress gradients, and the degree of hydrogen distribution homogenization does not improve unidirectionally with increasing heat treatment temperature. Therefore, it is necessary to propose an appropriate heat treatment method to control localized hydrogen enrichment in girth weld joints of hydrogen pipelines, thereby providing technical support for the management of hydrogen embrittlement failure risks in girth weld joints of hydrogen pipelines. Summary of the Invention

[0004] The specific design of the present invention is as follows:

[0005] A three-dimensional finite element model was used to simulate the effect of uneven stress fields on hydrogen distribution in girth weld joints, and localized hydrogen enrichment in girth weld joints was controlled through localized heat treatment. To achieve these objectives, the following problems needed to be solved: (a) accurately calculate the temperature and stress fields in the girth weld joint; (b) obtain hydrogen permeation parameters for the pipe base material and the girth weld joint; (c) simulate and calculate the hydrogen distribution in the girth weld joint of a hydrogen transmission pipeline under the combined influence of uneven stress fields and concentration gradients; and (d) propose an optimal post-weld localized heat treatment temperature based on controlling localized hydrogen enrichment in the girth weld joint.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] A method for controlling local hydrogen enrichment in a girth weld joint of a hydrogen transmission pipeline comprises the following steps:

[0008] Step 1: Establish a 1:1 three-dimensional finite element model of the girth weld joint of the hydrogen pipeline, sequentially couple the temperature field and stress field of the girth weld joint, and verify the reliability of the temperature field and stress field calculation results;

[0009] Step 2: Obtain hydrogen permeation parameters of the pipe base material and the girth weld joint using a gas phase hydrogen permeation test;

[0010] Step 3: Using the hydrogen permeation parameters obtained from the gas phase hydrogen permeation test as initial conditions and the stress field as boundary conditions, calculate the full-scale hydrogen distribution cloud map of the girth weld joint;

[0011] Step 4: Perform local heat treatment on the girth weld joint of the hydrogen transmission pipeline, simulate and calculate the effect of local heat treatment on the hydrogen distribution of the girth weld joint, and propose an optimization strategy for controlling local hydrogen enrichment in the girth weld joint of the hydrogen transmission pipeline.

[0012] Preferably, step 1 specifically includes:

[0013] The three-dimensional finite element model was established using ABAQUS simulation software. The mesh was divided according to the morphology of the girth weld joint. The welding process was simulated using the birth-death unit technique and the heat source subroutine. Half of the simulated weld was compared with half of the actual weld to ensure that the shape and size of the simulated weld were consistent with the actual weld.

[0014] The method for reliability verification of the temperature field and stress field calculation results is: using the temperature field as a predefined field and applying corresponding boundary conditions to obtain the stress distribution cloud map of the girth weld joint, and at the same time using the blind hole method to test the stress distribution of the girth weld joint to ensure the accuracy of the temperature field and stress field calculation results.

[0015] Preferably, the specific steps of simulating the welding process by the life and death unit technology are as follows: when the first weld is about to be welded, the first weld unit set is activated, and the first weld unit set is calculated for thermal convection and thermal radiation during the welding process, and the remaining weld unit sets do not participate in the calculation; when the calculation of the first weld unit set is completed, the second weld unit set is activated, and the second weld unit set and the previously activated first weld unit set participate in the calculation of thermal convection and thermal radiation; each weld unit set is gradually activated according to the welding sequence, and the activated weld unit sets are calculated for thermal convection and thermal radiation during the welding process, and the girth weld joint is cooled to room temperature when the last weld is completed, and finally the evolution process of the temperature field during the pipeline welding process is obtained.

[0016] Preferably, step 2 specifically includes: performing a gas-phase hydrogen permeation test on the specimen under the working pressure of the pipeline to obtain the hydrogen permeation curves of the pipeline base metal and the girth weld joint, linearly fitting the hydrogen permeation curves with the aid of the function plotting software Origin to obtain the slope k of the hydrogen permeation curve; calculating the hydrogen permeation parameters by the Fourier method, and calculating the hydrogen diffusion coefficient, the adsorbed hydrogen concentration and the hydrogen solubility from the steady-state current density and the slope k of the hydrogen permeation curve.

[0017] Preferably, step 3 specifically includes: taking the hydrogen permeation parameters as the initial conditions and the stress field as the boundary conditions, and calculating the full-size hydrogen distribution nephogram of the girth weld joint under the action of the non-uniform stress field.

[0018] Preferably, step 4 specifically includes: determining the width HB of the heating band and the width GCB of the heat insulation band according to the wall thickness δ of the hydrogen transmission pipeline and the maximum width h of the weld, where HB = 7nh k (1 < n < 3), GCB = HB + 2a (a = 200 - 350 mm), and the weld is located at the middle position of the heating band; the local heat treatment temperature is controlled between 400 and 700 °C, the heating rate and the cooling rate are controlled at 120 °C / h, and the heat preservation time is 4 h. The local heat treatment temperature with the weakest hydrogen enrichment degree is used as the optimized temperature for controlling the local hydrogen enrichment of the girth weld joint of the hydrogen transmission pipeline.

[0019] In summary, the beneficial effects of the above technical solutions of the present invention are as follows:

[0020] The present invention uses a method combining gas-phase hydrogen permeation and finite element model simulation calculation to predict the hydrogen distribution of the girth weld joint of the hydrogen transmission pipeline, and solves the problem that it is currently impossible to test the hydrogen distribution of the in-service hydrogen transmission pipeline by experimental methods;

[0021] The present invention uses local heat treatment to control the local hydrogen enrichment of the girth weld joint, so that the hydrogen embrittlement index of the girth weld joint is significantly reduced, greatly reducing the risk of hydrogen-induced cracking of the girth weld joint of the hydrogen transmission pipeline, and providing technical support for the risk control of hydrogen embrittlement failure in the girth weld joint area of the relevant hydrogen transmission pipeline. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the girth weld joint of the embodiment of the present invention. 1a is a three-dimensional finite element model, and 1b is a cross-section of the girth weld joint;

[0023] Figure 2 It is a comparison diagram of the simulated weld pool and the actual weld appearance. 2a is a comparison diagram of the physical object and the simulation of the root pass welding, and 2b is a comparison diagram of the physical object and the simulation of the cap pass welding;

[0024] Figure 3 It is a comparison diagram of the simulated value and the measured value of the welding residual stress. 3a is a comparison diagram of the circumferential stress, and 3b is a comparison diagram of the axial stress; ​​

[0025] Figure 4 4a is the graph of hydrogen permeation curve and 4b is the Fourier fitting curve.

[0026] Figure 5 Schematic diagram of the stress-strain curve of X52 pipeline steel in application example. DETAILED DESCRIPTION

[0027] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with examples, but the content of the present invention is not limited to the following examples. Unless otherwise defined, all technical and scientific terms used in the following examples are identical with the meaning generally understood by those skilled in the art of the technical field of the present invention. The terms used in the following examples in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the following examples includes any and all combinations of one or more related listed items.

[0028] An embodiment of the present invention provides a method for controlling local hydrogen enrichment in a girth weld joint of a hydrogen pipeline, the specific steps of which are as follows:

[0029] Step 1: Using ABAQUS simulation software, a 1:1 three-dimensional finite element model of a hydrogen pipeline made of X52 pipeline steel was constructed in the axial and two perpendicular directions, based on the actual diameter and wall thickness of the hydrogen pipeline, the number of layers in the girth weld joint, and its morphology. The temperature and stress fields of the girth weld joint were sequentially coupled and calculated, and the results were verified.

[0030] Meshing was performed using the "mesh" module within ABAQUS simulation software. Since the simulation primarily focused on residual stress and hydrogen concentration distribution in the girth weld joint, the weld, heat-affected zone, and nearby pipe base material were meshed densely, while areas further from the girth weld joint were meshed coarser. This reduced the total number of meshes, ensuring calculation accuracy while effectively reducing computation time.

[0031] In order to accurately simulate the welding process, the welds are divided according to the shape and size of each layer of the actual weld of the girth weld joint and each layer of the weld. The unit type used for meshing the three-dimensional finite element model when calculating the temperature field is DC3D8. The heat source subroutine DFLUX is developed to apply a moving heat source load to the weld area during welding simulation. The heat source model uses a double ellipsoid heat source model. This heat source can consider the uneven distribution of heat flux in the front and rear areas of the weld and the distribution characteristics of heat flux along the longitudinal direction of the weld during welding. The double ellipsoid heat source model is composed of two different 1 / 4 ellipsoids, which are divided into two parts. Let the semi-axes of the double ellipsoid be a1, a2, b, c, and the heat input distribution ratio of the front and rear half ellipsoids be f1 and f2. Then the heat flux distribution function of the front and rear half ellipsoids is:

[0032]

[0033] The welding heat source acts on the pipe joint to form a temperature field. The temperature region above the pipe melting point (1500°C) is considered the weld pool. The weld pool condenses to form a weld bead after the welding heat source leaves. By continuously adjusting the welding heat source shape (a, b, and c) and welding process parameters (voltage U, current I) of the double ellipsoid heat source, the shape and size of the weld pool obtained by simulation gradually approach the weld bead in the actual pipe girth weld joint. Finally, the weld width and depth of each weld bead of the actual and simulated welds were calculated, and the relative error did not exceed 5%. This confirms that each calibrated heat source can accurately and reliably simulate the heat source used in actual welding.

[0034] The birth-and-death element technique is used to simulate the multi-layer and multi-pass welding process. The specific operation is as follows: the three-dimensional finite element model established based on the actual pipeline girth weld joint contains welds. Therefore, before welding the pipeline model, the element set in the weld area needs to be "killed", that is, it is assumed that it does not exist. When welding the first weld, the first weld element set is activated, making it in the "live" state, while the other weld element sets are still in the "killed" state. Thermal convection and thermal radiation calculations are performed on this weld element set during the welding process, while the other weld element sets do not participate in the calculation. After the calculation of the first weld is completed, the second weld element set is activated. At this time, the second weld element set is in the "live" state, while the previously activated first weld element set is still in the "live" state and can participate in the subsequent thermal convection and thermal radiation calculations, while the other weld element sets are still in the "killed" state. As described above, each weld pass is gradually activated and welded according to the welding sequence. When the last weld is completed, the girth weld joint is cooled to room temperature. Finally, the evolution of the temperature field during the hydrogen pipeline welding process can be obtained.

[0035] Based on the calculated results of the girth weld temperature field and the material's high-temperature mechanical properties, a sequential coupling method is used to calculate weld residual stresses, using the temperature field as a predefined field. The material's mechanical properties must be added, and the heat transfer analysis unit DC3D8, which calculates the temperature field, must be replaced with the stress field unit C3D8R.

[0036] After completing the stress field simulation calculation of the girth weld joint, it is necessary to verify the obtained results. It is recommended to use the industry-known technology "blind hole method" to measure the stress in the weld and its surrounding areas of the actual pipeline girth weld joint. The measured stress at the measuring point location is compared with the stress calculation result at the corresponding location in the pipeline model. The specific operation of the "blind hole method" test is as follows:

[0037] After the strain gauge is pasted on the surface-treated part to be measured, a hole of a certain depth is drilled, which causes the residual stress near the position to be partially released and redistributed, thereby forming a new strain field and stress field. These changes are captured by the resistance strain gauge, and the numerical value of the welding residual stress is calculated using formulas (3), (4) and (5).

[0038]

[0039] like Figure 1 The following are the three-dimensional finite element model and cross-sectional diagram of the girth weld joint. In view of the symmetry of the hydrogen pipeline structure, in order to shorten the calculation period, the embodiment of the present invention uses half of the actual circumference of the hydrogen pipeline for modeling.

[0040] like Figure 2 As shown in the figure, the simulated weld pool is compared with the actual weld morphology, and the color scale unit is ℃. Since the melting point of low carbon steel is 1500℃ and the phase transformation temperature AC1 is around 750℃, in the calculated girth weld joint temperature field cloud map, the area with a temperature above 1500℃ is regarded as the molten pool (forming a simulated weld after condensation), and the area with a temperature between 750 and 1500℃ is regarded as the heat affected zone. Figure 2 It can be seen that the simulated molten pool and the actual weld have a high degree of consistency in morphology, indicating that the constructed three-dimensional finite element model of the girth weld joint is reliable and the calculation results of the temperature field are relatively accurate.

[0041] like Figure 3 As shown in Figure 2, the simulated welding residual stress values ​​are compared with the tested values. Figure 3 It can be seen that although the test stress value and the simulated stress value are different in numerical value, the stress distribution law of the two is the same, which proves that the stress field calculation results are reliable.

[0042] Step 2: Obtain hydrogen permeation parameters of the pipe base material and the girth weld joint using a gas phase hydrogen permeation test;

[0043] The gas-phase hydrogen permeation test utilizes a high-pressure gas-phase hydrogen charging-electrochemical hydrogen measurement method: one side of the hydrogen pipeline sample is placed in a high-pressure hydrogen environment, while the other side is exposed to an alkaline electrolyte solution and subjected to constant potential polarization. On the hydrogen-charging side, hydrogen dissociates into hydrogen atoms through adsorption and then penetrates the material. The infiltrating hydrogen atoms diffuse toward the hydrogen-measuring side due to the concentration difference. Hydrogen atoms that reach the surface of the hydrogen-measuring side are oxidized into hydrogen ions, generating an oxidation current, the hydrogen permeation current. As the test progresses, the hydrogen permeation current density increases from zero to a steady state, then from small to large, before reaching a steady state. The resulting hydrogen permeation current density versus time is the hydrogen permeation curve, and the final stable value is the steady-state current density. The hydrogen permeation curve can be used to calculate the hydrogen diffusion coefficient of the material and the subsurface adsorbed hydrogen concentration at the test hydrogen pressure. Obtaining hydrogen permeation parameters using the gas-phase hydrogen permeation test has the advantage of simulating the actual service environment of a hydrogen pipeline and providing parameters for the subsurface adsorbed hydrogen concentration of the inner wall of the pipeline under service conditions.

[0044] The Fourier method is often used to calculate the hydrogen permeation kinetic parameters in gas phase hydrogen permeation tests. The expression for calculating the hydrogen diffusion coefficient D using the Fourier method is:

[0045]

[0046] Where i ∞ is the steady-state current density, μA · cm -2 ; t is time, s; L is the sample thickness, mm; From formula (6), we can see that the curve ln(1-i t / i ∞ )~t has a slope of -π 2 Dt / L 2 ; Select two time detection points t1 and t2 in the hydrogen permeation transient process and substitute them into formula (6) to obtain formulas (7) and (8):

[0047]

[0048] By subtracting formulas (7) and (8) and simplifying them, the hydrogen diffusion coefficient D can be calculated as shown in formula (9):

[0049]

[0050] From formula (9), we can see that the hydrogen diffusion coefficient D is only affected by L, i ∞ 、i t1 and i t2 The influence of the difference between t1 and t2 is independent of the specific values ​​of t1 and t2, and the hydrogen diffusion coefficient D is not affected by the start time of hydrogen permeation current. Therefore, the Fourier method can accurately calculate the hydrogen diffusion coefficient D, and the calculation formula is shown in (10):

[0051]

[0052] Where k = ln(1-i t / i ∞ ). Based on the known hydrogen diffusion coefficient D, the adsorbed hydrogen concentration c can be calculated using the formula (11):

[0053]

[0054] Where F is the Faraday constant, which is 96500 C·mol -1 Therefore, the subsurface adsorbed hydrogen concentration of the hydrogen pipeline sample can be calculated by the diffusion coefficient D and the steady-state current density i ∞ Calculated.

[0055] After obtaining the hydrogen permeation curve, we used Origin to perform a linear fit on the test data to obtain the curve slope k. The hydrogen diffusion coefficient and adsorbed hydrogen concentration can be calculated using the above formula using the steady-state current density and the curve slope k.

[0056] Step 3: Using the parameters obtained from the hydrogen permeation test as initial conditions and the stress field as boundary conditions, calculate the full-scale hydrogen distribution cloud map of the girth weld joint;

[0057] Step 3 uses the parameters obtained from the hydrogen permeation test as the initial conditions. In the hydrogen diffusion analysis, the parameter characterizing the boundary conditions is the hydrogen activity φ, φ = c / s, atm 1 / 2 , and then the residual stress field is used as a predefined field for hydrogen diffusion to perform sequential coupling calculations of stress-induced hydrogen diffusion, and the hydrogen distribution cloud map of the girth weld joint under the action of welding residual stress is obtained to determine the local enrichment peak concentration and area.

[0058] like Figure 4 Figure 2 shows the hydrogen permeation curves and Fourier fitting curves for the pipe base material and girth weld joint. Using a gas-phase hydrogen permeation test, hydrogen permeation curves for the pipe base material and girth weld joint at a hydrogen pressure of 6 MPa were obtained. The hydrogen diffusion coefficient, adsorbed hydrogen concentration, and hydrogen solubility of the materials were calculated using the Fourier method.

[0059] Step 4: Perform local heat treatment on the girth weld joint after welding, simulate and calculate the impact of local heat treatment on the hydrogen distribution of the girth weld joint of the pipeline in the hydrogen transmission state, and propose an optimization strategy for controlling local hydrogen enrichment.

[0060] Post-weld heat treatment mainly includes overall heat treatment and local heat treatment. In practical applications, local heat treatment is usually selected due to the large size of the pipeline. The process parameters mainly include heating width, heating rate, holding time and cooling rate. In order to explore the effect of heat treatment temperature on the stress distribution and hydrogen distribution of the girth weld joint, step 4 simulates the post-weld local heat treatment of the three-dimensional finite element model of step 1, adopts the heating belt heating mode, and controls the heat treatment temperature at 400℃~700℃. The specific local heat treatment steps are as follows:

[0061] The girth weld joint within the heating zone is heated from 20°C to the preset holding temperature, the holding time is set to 4 hours, and then cooled to 20°C at the same speed. During the heating and cooling process, the heating rate and cooling rate are controlled at 120°C·h -1 .

[0062] The effects of local heat treatment on hydrogen distribution in girth weld joints were analyzed. Post-weld heat treatment significantly reduced the Mises equivalent stress peak in girth weld joints, while also making the stress distribution more uniform. The effect of eliminating weld residual stress became increasingly significant with increasing heat treatment temperature. When the heat treatment temperature exceeded 600°C, the effect of eliminating weld residual stress remained essentially stable. Changes in stress gradient inevitably affect hydrogen distribution. After heat treatment, the distribution contours show a significant decrease in hydrogen concentration within the entire girth weld joint, both in the enriched region and in the local peak concentration. This decrease became more pronounced with increasing treatment temperature. In particular, at a heat treatment temperature of 600°C, the local hydrogen enrichment in the girth weld joint decreased significantly, with the peak hydrogen concentration located near the inner surface of the pipe. When the heat treatment temperature reached 700°C, the peak hydrogen concentration increased slightly, primarily due to the combined influence of stress and concentration gradients on the actual hydrogen concentration distribution. Therefore, post-weld heat treatment is beneficial for reducing local hydrogen enrichment in girth weld joints, and a heat treatment temperature of 600°C is particularly effective in reducing the risk of hydrogen-induced cracking in girth weld joints.

[0063] like Figure 5The figure shows the stress-strain curves of the girth weld joint under nitrogen environment, when the pipeline transports 6MPa hydrogen, and when the girth weld joint is under an equivalent hydrogen pressure of 18MPa, and after post-weld heat treatment, when the girth weld joint is under an equivalent hydrogen pressure of 8.3MPa. Through the above operations, the equivalent hydrogen pressure of 18MPa in the actual service process of the girth weld joint and the equivalent hydrogen pressure of 8.3MPa in the service process after 600℃ heat treatment are obtained. Through the environmental slow tensile test, the plasticity index - cross-sectional shrinkage rate of the X52 steel girth weld joint under nitrogen, 18MPa and 8.3MPa hydrogen pressure can be obtained. The hydrogen-induced plasticity loss rate obtained in the hydrogen environment relative to the nitrogen environment is calculated using formula (13). The hydrogen embrittlement index under 18MPa and 8.3MPa hydrogen pressures is 14.44% and 6.90%, respectively. After the girth weld joint is heat treated at 600℃, the hydrogen embrittlement index decreases by 52.22%, significantly reducing the risk of hydrogen-induced cracking of the girth weld joint.

[0064] This paper simulates the hydrogen concentration distribution of girth welded joints in hydrogen pipelines using a finite element model. To evaluate the effect of localized hydrogen enrichment on hydrogen-induced cracking, the concept of equivalent hydrogen charging pressure is proposed. Pre-charging the specimen at the equivalent hydrogen charging pressure yields the corresponding maximum hydrogen enrichment concentration. The results of slow strain rate tensile (SSRT) tests at this hydrogen enrichment concentration comprehensively reflect the material's sensitivity to hydrogen-induced embrittlement under the synergistic effects of microstructure and residual stress. Based on Sievert's law, the equivalent hydrogen charging pressure is calculated using the following formula:

[0065]

[0066] Where, P eq is the equivalent hydrogen filling pressure, in MPa; c max is the maximum hydrogen concentration in the area, in ppm; S is the solubility of hydrogen in the area, in ppm atm -1 / 2 .

[0067] The mechanical properties of girth weld joints under different hydrogen pressures were tested using slow strain rate tensile tests. The material's hydrogen embrittlement sensitivity was quantitatively evaluated by the change in plasticity index caused by the hydrogen environment. Pipeline steel's cross-sectional shrinkage is more sensitive to changes in the hydrogen environment than its elongation. This paper uses cross-sectional shrinkage to measure the loss of material plasticity and uses this to calculate the hydrogen embrittlement index. The calculation formula is as follows:

[0068]

[0069] Where, EI is the hydrogen embrittlement index of the sample, R N is the cross-sectional shrinkage of the sample in nitrogen, R H is the cross-sectional shrinkage of the sample in hydrogen.

[0070] Through simulation calculations, it can be seen that according to the above technical solution, the peak hydrogen concentration of the girth weld joint can be significantly reduced, resulting in a significant decrease in the hydrogen embrittlement index.

[0071] The above embodiment is one of the specific implementation methods selected by the present invention. Common changes and substitutions made by those skilled in the art within the scope of this technical solution should be included in the protection scope of the present invention.

Claims

1. A method for controlling local hydrogen enrichment in a girth weld joint of a hydrogen pipeline, characterized in that: The steps include: Step 1: Establish a 1:1 three-dimensional finite element model of the girth weld joint of the hydrogen pipeline, sequentially couple and calculate the temperature field and stress field of the girth weld joint, and verify the reliability of the calculation results of the temperature field and stress field; Step 2: using a gas phase hydrogen permeation test to obtain hydrogen permeation parameters of the pipe base material and the girth weld joint; Step 3, using the hydrogen permeation parameters obtained from the gas phase hydrogen permeation test as initial conditions and the stress field as boundary conditions, calculate the full-size hydrogen distribution cloud map of the girth weld joint; Step 4: Perform local heat treatment on the girth weld joint of the hydrogen pipeline, simulate and calculate the effect of local heat treatment on the hydrogen distribution of the girth weld joint, and propose an optimization strategy for controlling local hydrogen enrichment in the girth weld joint of the hydrogen pipeline.

2. A method for controlling local hydrogen enrichment of a girth weld joint of a hydrogen pipeline according to claim 1, characterized in that: Step 1 specifically includes: The three-dimensional finite element model is established by using ABAQUS simulation software, the mesh is divided according to the morphology of the girth weld joint, the welding process is simulated by using the birth-death unit technology and the heat source subroutine, and half of the simulated weld is compared with the actual weld to ensure that the shape and size of the simulated weld are consistent with the actual weld; The method for reliability verification of the calculation results of temperature field and stress field is: taking the temperature field as the predefined field and applying the corresponding boundary conditions to obtain the stress distribution cloud map of the girth weld joint, and at the same time using the blind hole method to test the stress distribution of the girth weld joint to ensure the accuracy of the calculation results of the temperature field and stress field.

3. A method for controlling local hydrogen enrichment of a girth weld joint of a hydrogen pipeline according to claim 2, characterized in that: The specific steps of simulating the welding process by the birth and death unit technology are as follows: when the first weld is about to be welded, the first weld unit set is activated, and the first weld unit set is calculated for thermal convection and thermal radiation during the welding process, and the remaining weld unit sets do not participate in the calculation; when the calculation of the first weld unit set is completed, the second weld unit set is activated, and the second weld unit set and the previously activated first weld unit set participate in the calculation of thermal convection and thermal radiation; each weld unit set is gradually activated according to the welding sequence, and the thermal convection and thermal radiation of the activated weld unit set are calculated during the welding process, and when the last weld is completed, the girth weld joint is cooled to room temperature, and finally the evolution process of the temperature field during the pipeline welding process is obtained.

4. A method for controlling local hydrogen enrichment of a girth weld joint of a hydrogen pipeline according to claim 1, characterized in that: Step 2 specifically includes: subjecting the sample to a gas phase hydrogen permeation test under the pipeline working pressure to obtain the hydrogen permeation curves of the pipeline base material and the girth weld joint, performing linear fitting on the hydrogen permeation curve with the aid of the function drawing software Origin to obtain the slope k of the hydrogen permeation curve; calculating the hydrogen permeation parameters using the Fourier method, and calculating the hydrogen diffusion coefficient, adsorbed hydrogen concentration and hydrogen solubility from the steady-state current density and the slope k of the hydrogen permeation curve.

5. A method for controlling local hydrogen enrichment of a girth weld joint of a hydrogen pipeline according to claim 1, characterized in that: Step 3 specifically includes: taking the hydrogen permeation parameter as the initial condition and the stress field as the boundary condition, calculating the full-size hydrogen distribution cloud map of the girth weld joint under the action of the non-uniform stress field.

6. A method for controlling local hydrogen enrichment of a girth weld joint of a hydrogen pipeline according to claim 1, characterized in that: Step 4 specifically includes: according to the wall thickness δ of the hydrogen transmission pipeline and the maximum width h of the weld k determine the width HB of the heating tape and the width GCB of the heat insulation tape, where HB = 7nh k (1 < n < 3), GCB = HB + 2a (a = 200 - 350 mm), and the weld is located at the middle position of the heating tape; the local heat treatment temperature is controlled between 400 and 700 °C, the heating rate and the cooling rate are controlled at 120 °C / h, and the heat preservation time is 4 h. The local heat treatment temperature with the weakest hydrogen enrichment degree is used as the optimized temperature for controlling the local hydrogen enrichment of the circumferential weld joint of the hydrogen transmission pipeline.

Images