Numerical simulation method for different precrack propagation of pressure steel pipe welding joint

Abstract

The invention discloses a numerical simulation method for different pre-crack propagation of a pressure steel pipe welding joint. The numerical simulation method comprises the following steps: S1, calculating the change rule of the mechanical property and the thermal physical property of steel along with the temperature through JmatPro; by analyzing change characteristics of crack stress under multiple working conditions such as different initial crack angles, positions and welding residual stress, a basis is provided for preventing crack propagation and identifying dangerous working conditions, so that safe and stable operation of a vertical shaft structure is guaranteed, the problem of pipeline crack propagation caused by the welding residual stress can be effectively prevented, and the working efficiency is improved. Therefore, safety accidents such as pipeline breakage and leakage are avoided, and scientific basis can be provided for structural design and welding process optimization of the pipeline by determining the relation between the welding residual stress and the initial crack, so that the design precision and reliability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of penstock welding, and particularly to a numerical simulation method for different pre-crack propagations of a penstock welding joint. Background Art

[0002] As a key structure of a hydropower station, the structural integrity and operational reliability of a shaft directly affect the safety and stability of the entire power station. During long-term operation, the shaft structure not only has to bear huge water pressure loads but also must effectively resist potential risks such as hydraulic fracturing. To ensure the structural performance of the shaft, steel pipes are commonly used as the inner lining material of the shaft in engineering practice, and welding technology is used to connect pipe segments. However, due to factors such as complex welding operation environments, variable process parameters, and high operation technical requirements, residual stress concentration inevitably occurs in the welding joint area. This stress concentration effect easily leads to microcracks in the weld area, thereby changing the original distribution state of the structural stress field, affecting the crack propagation behavior and rate, and ultimately forming a significant stress concentration area. Therefore, the welding joint area often becomes the weakest part of the structure where cracks are most likely to initiate and propagate.

[0003] The existence of cracks will not only significantly reduce the bearing capacity of the pipeline but also increase the risk of pipeline failure and may even trigger serious safety accidents. At present, research on the influence of welding residual stress on crack propagation mainly focuses on conventional working conditions, and there is still a lack of research on the crack propagation behavior of different initial angle cracks in steel pipe welds with welding residual stress. Especially under the action of hydraulic pressure, the interaction mechanism between welding residual stress and crack propagation behavior has not been fully revealed. Therefore, conducting research on the influence of welding residual stress on the crack propagation behavior of different initial angle cracks in steel pipe welds under fluid penetration pressure has important theoretical significance and engineering value for improving the reliability of steel pipe welds and ensuring the safe operation of high-pressure fluid pipelines. For this reason, the present application proposes a numerical simulation method for different pre-crack propagations of a penstock welding joint. Summary of the Invention

[0004] Based on the technical problems existing in the background art, the present invention proposes a numerical simulation method for different pre-crack propagations of a penstock welding joint.

[0005] A numerical simulation method for different pre-crack propagations of a penstock welding joint proposed by the present invention includes the following steps:

[0006] S1: Calculate the laws of the mechanical properties and thermophysical properties of the steel varying with temperature through JmatPro;

[0007] S2: Use the finite element software ABAQUS to calculate the welding residual stress in combination with the laws of the mechanical properties and thermophysical properties of the steel varying with temperature;

[0008] S3: Establish a model of the pipeline welded joint, divide the mesh, set the boundary conditions and the applied loads;

[0009] S4: Combine the model in S3 and use FORTRAN language to write a DFLUX subroutine to implement the movement of the welding heat source, and simulate it through the built-in birth and death element technology during the welding process;

[0010] S5: Calculate the welding residual stress in the weld area;

[0011] S6: Define the initial crack direction and position in the welded part, and use the extended finite element to calculate the crack propagation;

[0012] S7: Analyze the calculation results of steps S5 and S6, and perform data processing to obtain the stress values at the tips and tip regions of pre-cracks with different initial angles in the simulation.

[0013] Preferably, in S4, the heat source welding formula used for the welding heat source is:

[0014]

[0015] where f1 and f2 are the energy distribution coefficients of the front and rear parts of the heat source, Q is the power of the welding heat source, Q = current I × arc voltage U × arc E efficiency, a1, a2, b, and c are the double ellipsoid heat source shape parameters, which are related to the characteristics of the welding heat source, and the parameters of the heat source can be adjusted according to the welding conditions to generate the required melting zone.

[0016] Preferably, in S6, the formula used for calculating the crack propagation using the extended finite element is:

[0017]

[0018] where u(x) is the displacement vector; N I (x) is the finite element nodal shape function; u I is the displacement vector of the continuous part in the finite element solution; α I is the improved degree of freedom of the nodes of the element penetrated by the crack; F α (x) is the crack tip asymptotic displacement function; b I j is the improved degree of freedom of the nodes of the element where the crack tip is located, H(x) is the Heaviside step function, which is used to represent the jump effect of the crack, and its value is taken as 1 or -1 according to different crack surfaces of the crack;

[0019] The mathematical expression of the Heaviside step function H(x) is:

[0020]

[0021] Preferably, the α expression of the asymptotic displacement function at the crack tip of F

[0022]

[0023] is: where r and θ are the local polar coordinate system at the crack tip; A and B are coefficients related to the crack propagation mode, usually related to the stress intensity factor.

[0024] Preferably, in S4, during the simulation of the welding process, according to the welding simulation results, a stress field nephogram is obtained (as Figure 7 shown). In S5, after calculating the welding residual stress, the longitudinal residual stress and the transverse residual stress of the welding residual stress are extracted along the center line direction of the weld. The longitudinal residual stress shows a distribution of compressive stress - tensile stress - compressive stress, and the stress in the middle area of the welded part is tensile stress, up to 38.26 MPa at most, and the two end areas are compressive stress. The transverse residual stress also shows tensile stress in the middle area of the welded part. During the welding process, the longitudinal residual stress and the transverse residual stress are the main influencing factors, and the welding residual tensile stress is considered to have a greater impact on crack propagation.

[0025] Preferably, in S6, when calculating the crack propagation, the calculated residual stress is used as the initial condition for crack propagation analysis and input into the welding model. At the same time, it is necessary to combine the transverse residual stress corresponding to different initial directions under the condition of not considering the welding residual stress and the transverse residual stress corresponding to different initial directions under the condition of considering the welding residual stress.

[0026] Compared with the existing technology, the beneficial effects of the present invention are:

[0027] By analyzing the variation characteristics of crack stress under multiple working conditions such as different initial crack angles, positions, and welding residual stresses, the present invention provides a basis for preventing crack propagation and identifying dangerous working conditions, thereby ensuring the safe and stable operation of the shaft structure, effectively preventing the problem of crack propagation in the pipeline caused by welding residual stress, and avoiding safety accidents such as pipeline rupture and leakage. By clarifying the relationship between welding residual stress and the initial crack, it can provide a scientific basis for the structural design and welding process optimization of the pipeline, thereby improving the accuracy and reliability of the design. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a diagram showing the variation of thermophysical properties with temperature in a numerical simulation method for different pre-crack propagations of a welded joint of a penstock proposed by the present invention;

[0029] Figure 2Schematic diagram of welding residual stress in a numerical simulation method for different pre-crack propagations of a penstock welded joint proposed by the present invention;

[0030] Figure 3 Schematic diagram of the corresponding transverse residual stress at different initial directions under the condition of considering welding residual stress in a numerical simulation method for different pre-crack propagations of a penstock welded joint proposed by the present invention;

[0031] Figure 4 Schematic diagram of the corresponding transverse residual stress at different initial directions under the condition of not considering welding residual stress in a numerical simulation method for different pre-crack propagations of a penstock welded joint proposed by the present invention;

[0032] Figure 5 Schematic diagram of the stress corresponding to the crack tip at different initial directions in a numerical simulation method for different pre-crack propagations of a penstock welded joint proposed by the present invention;

[0033] Figure 6 Schematic diagram of the stress amplitude at different initial crack angles at the welded joint in a numerical simulation method for different pre-crack propagations of a penstock welded joint proposed by the present invention;

[0034] Figure 7 Schematic diagram of the stress field contour after cooling in a numerical simulation method for different pre-crack propagations of a penstock welded joint proposed by the present invention. Detailed implementation manners

[0035] The present invention will be further explained below with reference to specific embodiments.

[0036] Embodiment

[0037] Referring to Figure 1-7 , this embodiment proposes a numerical simulation method for different pre-crack propagations of a penstock welded joint, including the following steps:

[0038] S1: Calculate the laws of the mechanical properties and thermophysical properties of the steel varying with temperature through JmatPro;

[0039] S2: Use the finite element software ABAQUS to calculate the welding residual stress in combination with the laws of the mechanical properties and thermophysical properties of the steel varying with temperature;

[0040] S3: Establish a model of the pipeline welded joint, divide the mesh, set the boundary conditions and the loads applied;

[0041] S4: Combine the model in S3 and use FORTRAN language to write a DFLUX subroutine to realize the movement of the welding heat source, and perform the simulation through the built-in birth and death element technology during the welding process;

[0042] The heat source welding formula used for the welding heat source is as follows:

[0043]

[0044] Among them, f1 and f2 are the energy distribution coefficients of the first half and the second half of the heat source, Q is the power of the welding heat source, Q = current I × arc voltage U × arc E efficiency, a1, a2, b, and c are the double ellipsoid heat source shape parameters, which are related to the characteristics of the welding heat source. The parameters of the heat source can be adjusted according to the welding conditions to generate the required melting zone;

[0045] In addition, during the simulation of the welding process, according to the welding simulation results, a stress field nephogram is obtained (as Figure 7 shown);

[0046] S5: Calculate the welding residual stress in the weld area. After calculating the welding residual stress, extract the longitudinal residual stress and the transverse residual stress of the welding residual stress along the weld center line direction. The longitudinal residual stress shows a compressive stress - tensile stress - compressive stress distribution, and the stress in the middle area of the welded part is tensile stress, reaching a maximum of 38.26 MPa. The two end areas are compressive stress. The transverse residual stress also shows tensile stress in the middle area of the welded part. During the welding process, the longitudinal residual stress and the transverse residual stress are the main influencing factors, and the welding residual tensile stress is considered to have a greater impact on crack propagation;

[0047] S6: Define the initial crack direction and position in the welded part, and use the extended finite element method to calculate the crack propagation;

[0048] When calculating the crack propagation, the calculated residual stress is used as the initial condition for crack propagation analysis and input into the welding model. At the same time, it is necessary to combine the transverse residual stress corresponding to different initial directions under the condition of not considering the welding residual stress and the transverse residual stress corresponding to different initial directions under the condition of considering the welding residual stress;

[0049] The formula used when calculating the crack propagation by the extended finite element method is as follows:

[0050]

[0051] Among them, u(x) is the displacement vector; N I (x) is the finite element node shape function; u I is the displacement vector of the continuous part in the finite element solution; α I is the improved degree of freedom of the nodes of the element penetrated by the crack; F α (x) is the crack tip asymptotic displacement function; b I jTo improve the degrees of freedom of the unit node where the crack tip is located, H(x) is the Heaviside step function, which is used to represent the jump effect of the crack, and its value is taken as 1 or -1 respectively according to different crack surfaces of the crack;

[0052] The mathematical expression of H(x) as the Heaviside step function is:

[0053]

[0054] F α (x) The expression of the crack tip asymptotic displacement function is:

[0055]

[0056] where r and θ are the local polar coordinates at the crack tip; A and B are coefficients related to the crack propagation mode, usually related to the stress intensity factor;

[0057] S7: Analyze the calculation results of steps S5 and S6, and perform data processing to obtain the stress values at the pre-crack tips and tip regions with different initial angles in the simulation;

[0058] This embodiment analyzes the variation characteristics of crack stress under multiple working conditions such as different initial crack angles, positions, and welding residual stresses, provides a basis for preventing crack propagation and identifying dangerous working conditions, thereby ensuring the safe and stable operation of the shaft structure, effectively preventing the problem of pipeline crack propagation caused by welding residual stresses, and avoiding safety accidents such as pipeline rupture and leakage. By clarifying the relationship between welding residual stresses and initial cracks, it can provide a scientific basis for the structural design and welding process optimization of pipelines, thereby improving the accuracy and reliability of the design.

[0059] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A numerical simulation method for different pre-crack propagations of a welded joint of a penstock, characterized in that It includes the following steps: S1: Calculate the laws of the mechanical properties and thermophysical properties of the steel varying with temperature by JmatPro; S2: Use the finite element software ABAQUS to calculate the welding residual stress by combining the laws of the mechanical properties and thermophysical properties of the steel varying with temperature; S3: Establish a pipeline welding joint model, divide the mesh, set the boundary conditions and the applied loads; S4: Combine the model in S3 and use FORTRAN language to write a DFLUX subroutine to realize the movement of the welding heat source, and simulate it through the built-in birth and death element technology during the welding process; S5: Calculate the welding residual stress in the weld area; S6: Define the initial crack direction and position in the welded part, and use the extended finite element to calculate the crack propagation; S7: Analyze the calculation results of steps S5 and S6, and perform data processing to obtain the stress values at the tips and tip regions of pre-cracks with different initial angles in the simulation.

2. A numerical simulation method for different pre-crack propagations of a penstock welded joint according to claim 1, characterized in that, In S4, the heat source welding formula used for the welding heat source is: Among them, f1 and f2 are the energy distribution coefficients of the first half and the second half of the heat source, Q is the power of the welding heat source, Q = current I × arc voltage U × arc E efficiency, a1, a2, b, and c are the double ellipsoid heat source shape parameters, which are related to the characteristics of the welding heat source, and the parameters of the heat source can be adjusted according to the welding conditions to generate the required melting zone.

3. A numerical simulation method for different pre-crack propagations of a welded joint of a penstock according to claim 1, characterized in that, In S6, the formula used for calculating the crack propagation by the extended finite element is: where \(u(x)\) is the displacement vector; \(N\) I (x) is the finite element nodal shape function; \(u\) I is the displacement vector of the continuous part in the finite element solution; \(\alpha\) I is the improved degree of freedom of the nodes of the element penetrated by the crack; \(F\) α (x) is the crack tip asymptotic displacement function; \(b\) I j is the improved degree of freedom of the nodes of the element where the crack tip is located, \(H(x)\) is the Heaviside step function, which is used to represent the jump effect of the crack, and its value is 1 or -1 according to different crack surfaces of the crack; The mathematical expression of H(x) as the Heaviside step function is:

4. A numerical simulation method for different pre-crack propagations of a penstock welded joint according to claim 3, characterized in that, The said F α (x) The expression of the crack tip progressive displacement function is as follows: Among them, r and θ are the local polar coordinate systems at the crack tip; A and B are the coefficients related to the crack propagation mode, usually related to the stress intensity factor.

5. A numerical simulation method for different pre-crack propagations of a penstock welded joint according to claim 1, characterized in that In S4, during the simulation of the welding process, a stress field contour map is obtained according to the welding simulation results; in S5, after calculating the welding residual stress, the longitudinal residual stress and the transverse residual stress are extracted from the direction along the weld center line. The longitudinal residual stress shows a distribution of compressive stress - tensile stress - compressive stress, and the stress in the middle area of the welded part shows tensile stress, up to 38.26 MPa at most, and the two end areas are compressive stress. The transverse residual stress also shows tensile stress in the middle area of the welded part. During the welding process, the longitudinal residual stress and the transverse residual stress are the main influencing factors, and the welding residual tensile stress is considered to have a greater impact on the crack propagation.

6. The numerical simulation method for different pre-crack propagations of a penstock welded joint according to claim 1, wherein In S6, when calculating the crack propagation, the calculated residual stress is used as the initial condition for the crack propagation analysis and input into the welding model. At the same time, it is necessary to combine the transverse residual stress corresponding to different initial directions under the condition of not considering the welding residual stress and the transverse residual stress corresponding to different initial directions under the condition of considering the welding residual stress.

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