Simulation method for optimizing stress corrosion cracking of underground oil pipeline steel

Abstract

The invention discloses a simulation method for optimizing stress corrosion cracking of underground oil pipeline steel, and relates to the technical field of simulation of stress corrosion cracking of underground oil pipelines. According to the method, the surface and internal structures of a base material are optimized through a specific geometric optimization method, so that the actual stress corrosion cracking state under high temperature and high pressure is clearly simulated. The method comprises the following steps: firstly, constructing an initial configuration of a stress corrosion test sample through Solidworks software, secondly, optimizing and improving a model by using python between a solving core and a graphical user interface by utilizing ABAQUS software, namely adding a FeCO3 corrosion product layer and improving a matrix to construct a matrix cohesive force unit, then adding a cohesive force unit to a pipeline matrix, and finally, constructing a stress corrosion test model by using python between the solving core and the graphical user interface. And calculating to obtain the stress corrosion cracking extension under the high-temperature and high-pressure conditions. The simulation method provided by the invention ensures the accuracy and reliability of simulation.

Description

Technical Field

[0001] The invention relates to the technical field of simulation of stress corrosion cracking of underground oil pipelines, and in particular to a simulation method of stress corrosion cracking of underground oil pipelines. Background Art

[0002] With the increasing demand for oil and natural gas, as the most economical and effective way to transport oil and natural gas over long distances, pipeline steel is developing towards high strength and large diameter. X80 grade pipeline steel is the highest strength grade pipeline steel used in China so far, and has been widely used in the "West-East Gas Transmission" project. However, as the environment in which pipeline steel is located becomes more and more diverse, the corrosion problem of pipelines is becoming more and more prominent.

[0003] In order to study the corrosion products, researchers used experimental methods and high-temperature and high-pressure reaction devices to determine that the corrosion product layer film produced by pipeline steel under high temperature and high pressure is a uniform and dense FeCO3 film. For example, application No. 202211124458.9 discloses a method for preparing a corrosion-inhibiting corrosion product film that reduces hydrogen damage to pipeline steel, which includes the following steps:

[0004] The pretreatment of X70 pipeline steel includes grinding the surface with metallographic water-abrasive sandpaper, from 150# to 2000# in sequence, and cleaning and drying with deionized water and acetone; immersing the pretreated material in a conversion solution containing a corrosion inhibitor and stabilizing it for 10-30 minutes; loading a cyclic potential on the surface of the material to promote the formation and homogenization of the corrosion product film, and after rinsing and drying, a corrosion product conversion film layer with the effect of reducing hydrogen damage to the material is obtained.

[0005] The corrosion-inhibiting corrosion product film disclosed in the above prior art can reduce the activity of hydrogen evolution reaction of materials and reduce the hydrogen damage effect of materials. However, the microscopic behavior of crack propagation and fracture of materials under such conditions cannot be accurately studied. Therefore, it is very important to accurately study the corrosion cracking behavior of pipeline steel in extreme environments through simulation. Summary of the invention

[0006] The purpose of the present invention is to provide a simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, thereby solving the simulated failure of pipelines under specific environments.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A simulation method for optimizing stress corrosion cracking of steel in an underground oil pipeline comprises the following steps in sequence:

[0009] Step 1: Build the initial model of the pipeline matrix

[0010] Use the Sketch tool in Solidworks software to construct the initial configuration of the pipeline matrix to be calculated; and import it into ABAQUS / CAE through CAD import for processing;

[0011] Step 2: Optimize the initial model

[0012] Using ABAQUS software, python is used between the solving core and the graphical user interface to process the initial model. A FeCO3 corrosion product layer is added to the outer surface of the initial model. A zero-thickness cohesion unit is added between the pipeline matrix and the FeCO3 corrosion product layer using the UMAT user subroutine. The cohesive unit stiffness is set, the corresponding stiffness is output, and the initial damage criterion is set for layered simulation of composite materials.

[0013] Step 3: Simulation calculation of pipeline materials

[0014] Set the convergence criterion for the fracture degree of the pipeline material, set the stress distribution state based on the actual environment, fix the clamping and pressure distribution, set the linear large displacement calculation step and calculation time of the pipeline material in the step, and finally perform the simulation calculation of the pipeline material;

[0015] Step 4: Determine whether the calculation has converged

[0016] After the simulation calculation is completed, check whether these convergence criteria are met and observe the convergence status of the iterative process. Observe the iterative process of the initial model on the Job-monitor interface. If the residual changes very little when the initial model is calculated to a certain step number, and the changes in the stress and strain physical quantities are not obvious, check the convergence information in the output file and check whether the convergence criteria are met. When both are met, the calculation is considered to have converged; if not, repeat step 2.

[0017] In the above-mentioned simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, the thickness of the FeCO3 corrosion product layer is 25 mm, which is characterized by a homogeneous solid with linear thermoelasticity and transverse isotropy.

[0018] In the above-mentioned simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, the pipeline substrate is X80 steel, and the initial model of the pipeline substrate is a type I crack specimen based on the pipeline material.

[0019] The above-mentioned simulation method for optimizing stress corrosion cracking of underground oil pipeline steel is as follows: The empirical formula for calculating the CO2 corrosion rate in a high temperature and high pressure environment is as follows:

[0020] lgV=5.8-1710 / T+0.67lgPc (1)

[0021] In formula (1), T is 250°C, and Pc is the carbon dioxide partial pressure of 1 MPa.

[0022] In the above-mentioned simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, in step 2, a dynamic analysis step is adopted in ABAQUS, and the initial model unit is C3D8R, which is isotropic; the calculation step in the calculation of the initial model adopts the static criterion.

[0023] The above-mentioned simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, after simulating and calculating the pipeline material, uses the field output request provided by ABAQUS to output the hierarchical set value, pound level and failure state of the crack fracture, compares the continuity of the crack, and compares it with the structure of crack propagation in actual situations to judge the rationality of the crack.

[0024] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0025] The present invention proposes a simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines. The method first constructs the initial configuration of a stress corrosion test specimen by using Solidworks software; secondly, the model is optimized and improved by using python between the solver core (Solver / Kernel) and the graphical user interface (GUI) by using ABAQUS software, including adding a FeCO3 corrosion product layer (defining contact properties) and improving the internal structure of the matrix (constructing matrix cohesion units), and then adding cohesion units to the pipeline matrix. Finally, the stress corrosion cracking extension under the high temperature and high pressure conditions is obtained by calculation.

[0026] Specifically, this method uses ABAQUS to calculate stress corrosion cracking in high temperature and high pressure environments such as underground oil pipelines. It uses the empirical formula for calculating CO2 corrosion rate, the high temperature and high pressure performance parameters of the material, the cohesive unit and the composite layering area of ​​the material corrosion product layer to realize the simulation calculation method of the fracture and crack propagation of the composite layer of the corrosion product of the underground oil pipeline, and solves the simulated failure of the pipeline under specific conditions.

[0027] The simulation method of the present invention provides an accurate, stable and practically similar simulation process for finite element simulation of stress corrosion cracking of steel in underground oil pipelines, thereby ensuring the accuracy and reliability of the simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The prefabricated crack model and mesh division diagram of the steel surface corrosion layer structure constructed by the present invention.

[0029] Figure 2 This is the stress distribution after the crack extends to the interface.

[0030] Figure 3 is the loading stress distribution.

[0031] Figure 4 is the normalized distance distribution of the type I stress intensity factor along the leading edge.

[0032] Figure 5 is the distance distribution of type I stress intensity factor along the path.

[0033] Figure 6 is the normalized distance distribution of the type I stress intensity factor along the leading edge. DETAILED DESCRIPTION

[0034] The present invention proposes a simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0035] The underground oil pipeline steel mentioned in the present invention mainly refers to steel plates for oil and gas transmission pipelines, which can be X80 steel, X60 steel, X70 steel, etc. This application mainly takes X80 steel as an example for detailed description.

[0036] A simulation method for optimizing stress corrosion cracking of steel in an underground oil pipeline comprises the following steps in sequence:

[0037] Step 1: Build the initial model of the pipeline matrix

[0038] The Sketch tool in Solidworks software is used to construct the initial configuration of the pipeline matrix to be calculated; and then it is imported into ABAQUS / CAE for processing through CAD import; the initial model of the pipeline matrix is ​​a type I crack specimen based on the pipeline material.

[0039] Step 2: Optimize the initial model

[0040] ABAQUS software is used to process the initial model using python between the solution core and the graphical user interface. A FeCO3 corrosion product layer is added to the outer surface of the initial model. The thickness of the FeCO3 corrosion product layer is 25 mm, which is characterized by a linear thermoelastic, transversely isotropic homogeneous solid. A zero-thickness cohesion unit is added between the pipeline matrix and the FeCO3 corrosion product layer using the UMAT user subroutine, and the cohesive unit stiffness is set, the corresponding stiffness is output, and the initial damage criterion is set for layered simulation of composite materials;

[0041] Step 3: Simulation calculation of pipeline materials

[0042] Set the convergence criterion of the fracture degree of the pipeline material, set the stress distribution state based on the actual environment, fix the clamping and pressure distribution, set the linear large displacement calculation step and calculation time of the pipeline material in step, and finally perform the simulation calculation of the pipeline material; the empirical formula for calculating the CO2 corrosion rate in a high temperature and high pressure environment is as follows:

[0043] lgV=5.8-1710 / T+0.67lgPc (1)

[0044] In formula (1), T is 250°C, and Pc is the carbon dioxide partial pressure of 1 MPa.

[0045] like Figure 2 The figure shows the stress distribution after the crack extends to the interface. Figure 3 is the loading stress distribution.

[0046] Step 4: Determine whether the calculation has converged

[0047] After the simulation is completed, check whether these convergence criteria are met and observe the convergence status of the iteration process. Observe the iteration process of the initial model on the Job-monitor interface. If the residual changes very little when the initial model is calculated to a certain number of steps, and the changes in the stress and strain physical quantities are not obvious, check the convergence information in the output file and check whether the convergence criteria are met. When both are met, the calculation is considered to have converged; if not, repeat step 2. Figure 4 is the normalized distance distribution of the type I stress intensity factor along the leading edge, Figure 5 is the distance distribution of type I stress intensity factor along the path, Figure 6 is the normalized distance distribution of the type I stress intensity factor along the leading edge.

[0048] The above-mentioned simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, after simulating and calculating the pipeline material, uses the field output request provided by ABAQUS to output the hierarchical set value, pound level and failure state of the crack fracture, compares the continuity of the crack, and compares it with the structure of crack propagation in actual situations to judge the rationality of the crack.

[0049] Embodiment 1:

[0050] The following takes the optimization of the corrosion cracking simulation process of X80 steel under underground oil pipeline conditions as an example to further understand the technical solutions and advantages of the present invention.

[0051] The specific steps include:

[0052] Step 1: Construct the initial model of the stress corrosion test specimen to be calculated

[0053] The Sketch tool in Solidworks software was used to construct the initial model of the stress corrosion test specimen to be calculated; and then it was imported into ABAQUS / CAE for processing through CAD import. Figure 1 The prefabricated crack model and mesh division diagram of the steel surface corrosion layer structure constructed by the present invention.

[0054] Step 2: Optimize the stress corrosion test specimen

[0055] The experiments in step 1 were processed using python between the solver / kernel and the graphical user interface (GUI) using ABAQUS software. Cohesion units with zero thickness were inserted into the matrix. The FeCO3 layer was remodeled to a thickness of 25 mm, which was characterized as a linear thermoelastic, transversely isotropic homogeneous solid. The damage and fracture micromechanisms that control the onset of fracture (i.e., plastic deformation of the matrix, brittle fiber fracture, and frictional sliding between the fiber / matrix) are included in the behavior of different phases and interfaces, and the corresponding micromechanical parameters that control their behavior are measured independently. The contact properties between the corrosion product layer and the matrix material are defined as cohesive units with surface-to-surface contact.

[0056] In the above method, the X80 steel parameters and FeCO3 corrosion product layer parameters are described as follows:

[0057] In high temperature and high pressure environment, the elastic modulus of X80 steel material is 2.06*10^5Mpa, the average compressive strength is 726MPa, the poise ratio is 0.3, and the material density is 7.86g / cm 3 , yield limit is 490MPa, elongation is 0.0267, fracture toughness is 226.981kJ / m 2， The stress intensity factor is 40 and the crack growth rate is 0.005 m / s.

[0058] In the above method, the model parameters are set as follows

[0059] The FeCO3 corrosion product layer is the FeCO3 corrosion product layer with the corresponding thickness under experimental conditions. The thickness of the X80 steel layer is 50 mm, the thickness of the corrosion layer is 25 mm, and the elastic modulus of the thickness is obtained from the experiment. Its elastic modulus is 1*10^4 Gpa, the poisson ratio is 0.19, and the density is 3.8 g / cm 3 , yield limit is 180MPa, elongation is 0.028, fracture toughness is 20kJ / m 2 Stress intensity factor 5, crack growth rate 0.002m / s

[0060] The empirical formula for calculating the CO2 corrosion rate in a high temperature and high pressure environment is:

[0061] lgV=5.8-1710 / T+0.67lgPc (1)

[0062] Where T is 250°C and Pc is the carbon dioxide partial pressure 1Mpa=1000kpa.

[0063] A hole with a diameter of 0.1 mm was prefabricated in the center of the model, a normal constraint was applied to the bottom of the model, and the upper surface was compressed using displacement-controlled loading. The maximum loading displacement was 0.5 mm, and the loading rate was controlled to be 0.005 mm / s.

[0064] The dynamic analysis step is adopted in the ABAQUS analysis platform, the model unit is C3D8R, isotropic; the calculation model calculation step adopts the static criterion.

[0065] In the above method, the maximum tensile stress criterion of the model unit is f = |σ1|-σt = 0. The maximum compressive stress criterion of the model is f = |σ3|-σc = 0, where σ1 is the first principal stress of the model unit, σ3 is the third principal stress of the model unit, σt is the tensile stress, and σc is the compressive stress.

[0066] When the stress of any model unit of the model meets the maximum tensile stress standard or the maximum compressive stress standard under load, the model unit is regarded as fracture deformation. The UMAT user subroutine is used to add zero-thickness cohesive units in the X80 steel matrix and FeCO3 corrosion product layer to simulate the adhesion between materials and optimize the interaction.

[0067] The interaction properties of the materials are set as follows:

[0068] The interaction properties of the material are surface-to-surface contact, the contact properties of the material are defined as tangential behavior, normal behavior, fracture criterion and viscous behavior, and the crack growth direction is defined as the normal direction along the cohesive unit section.

[0069] Step 3: Determine the rationality of the crack.

[0070] The field output request provided by ABAQUS is used to output the hierarchical set value, pound level and failure state of the crack fracture, and the coherence of the crack is compared with the structure of the crack extension in the actual situation to judge the rationality of the crack.

[0071] In summary, in a simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines proposed by the present invention, the unit stress is determined by the failure criterion, and in the underground oil pipeline environment, the empirical formula for calculating the CO2 corrosion rate, the high temperature and high pressure performance parameters of the material, the underground oil pipeline corrosion product layer and other concepts are included, which solves the simulated failure of the pipeline in a specific environment and uses various forms and methods of research on the fracture and crack propagation of composite materials in this specific environment.

[0072] The X80 steel matrix described in the present invention can also be expanded to other types of X60 steel, X70 steel or others known to those skilled in the art.

[0073] It should be noted that those skilled in the art should recognize that the above implementation modes are only used to illustrate the present application and are not used as limitations on the present application. As long as they are within the essential spirit of the present application, appropriate changes and modifications made to the above embodiments are within the scope of protection required by the present application.

Claims

1. A simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines, characterized in that: The following steps are included in sequence: Step 1: Build the initial model of the pipeline matrix Use the Sketch tool in Solidworks software to construct the initial configuration of the pipeline matrix to be calculated; and import it into ABAQUS / CAE through CAD import for processing; Step 2: Optimize the initial model Using ABAQUS software, python is used between the solving core and the graphical user interface to process the initial model. A FeCO3 corrosion product layer is added to the outer surface of the initial model. A zero-thickness cohesion unit is added between the pipeline matrix and the FeCO3 corrosion product layer using the UMAT user subroutine. The cohesive unit stiffness is set, the corresponding stiffness is output, and the initial damage criterion is set for layered simulation of composite materials. Step 3: Simulation calculation of pipeline materials Set the convergence criterion for the fracture degree of the pipeline material, set the stress distribution state based on the actual environment, fix the clamping and pressure distribution, set the linear large displacement calculation step and calculation time of the pipeline material in the step, and finally perform the simulation calculation of the pipeline material; Step 4: Determine whether the calculation has converged After the simulation calculation is completed, check whether these convergence criteria are met and observe the convergence status of the iterative process. Observe the iterative process of the initial model on the Job-monitor interface. If the residual changes very little when the initial model is calculated to a certain step number, and the changes in the stress and strain physical quantities are not obvious, check the convergence information in the output file and check whether the convergence criteria are met. When both are met, the calculation is considered to have converged; if not, repeat step 2.

2. A simulation method for optimizing stress corrosion cracking of steel in underground oil pipelines according to claim 1, characterized in that: The thickness of the FeCO3 corrosion product layer is 25 mm and it is characterized by a linear thermoelastic, transversely isotropic homogeneous solid.

3. The method for simulating optimization of stress corrosion cracking of steel in underground oil pipelines according to claim 1, characterized in that: The initial model of the pipeline matrix is ​​a mode I crack specimen based on the pipeline material.

4. The method for simulating optimization of stress corrosion cracking of steel in underground oil pipelines according to claim 1, characterized in that: The empirical formula for calculating the CO2 corrosion rate in a high temperature and high pressure environment is as follows: lgV=5.8-1710 / T+0.67lgPc (1) In formula (1), T is 250°C, and Pc is the carbon dioxide partial pressure of 1 MPa.

5. The method for simulating optimization of stress corrosion cracking of steel in underground oil pipelines according to claim 1, characterized in that: In step 2, a dynamic analysis step is used in ABAQUS, and the initial model unit is C3D8R, which is isotropic; the calculation step in the initial model adopts the static criterion.

6. The method for simulating optimization of stress corrosion cracking of steel in underground oil pipelines according to claim 1, characterized in that: After simulating and calculating the pipeline material, the field output request provided by ABAQUS is used to output the hierarchical set value, pound level and failure state of the crack fracture, and the continuity of the crack is compared with the structure of crack propagation in actual situations to judge the rationality of the crack.

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